JP2017069996A - Non-Isolated Power Conversion Device and Non-Isolated Power Conversion System - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive non-isolated power conversion device capable of effectively suppressing a leakage current even in a system power source of any ground system such as a three-phase four-wire type O(N) phase ground system.SOLUTION: A power conversion device comprises: a three-phase inverter 3; a plurality of input-side capacitors connected in series between DC input terminals of the three-phase inverter; an LC filter 4 consisting of a reactor and capacitors connected to AC output terminals of the three-phase inverter; and a control part 30 for controlling the three-phase inverter. A node between the input-side capacitors and a node of some of a plurality of capacitors constituting the LC filter are connected as a virtual ground point so as to match with a ground phase of a system power source at an interconnection destination. A common mode filter is further connected on a post-stage of the LC filter, and the control part 30 controls the three-phase inverter so as to match with the ground phase of the system power source at the interconnection destination with the virtual ground point defined as a reference.SELECTED DRAWING: Figure 1

Description

  The present invention is an LC composed of a three-phase inverter, a plurality of input-side capacitors connected in series between the DC input terminals of the three-phase inverter, and a reactor and a capacitor connected to the AC output terminal of the three-phase inverter. The present invention relates to a non-insulated power conversion device and a non-insulated power conversion system including a filter and a control unit that controls the three-phase inverter.

  A distributed power source such as a solar cell or a fuel cell includes a power conditioner that converts a frequency and a voltage into AC power so as to be compatible with the power system in order to be used in conjunction with system power.

  For example, in a distributed power source using a solar cell, the zero-phase is generated through a floating capacitance formed between the solar cell structure and the ground when the surface of the solar cell gets wet due to rain or condensation. Current, that is, leakage current flows.

  If the value of the zero-phase current exceeds the sensitivity current of the earth leakage breaker connected to the AC side of the grid interconnection inverter, there will be a loss of opportunity to reverse the flow of power generated by the earth leakage breaker unnecessary operation. There was a risk of inviting.

  For this reason, the grid connection regulations (JEAC 9701-2012 (2014 supplement (Part 1))) indicate that “when a power conditioner that does not conform to the grounding system of the grid system is linked, the commercial voltage is connected to the DC side. As a result, leakage current may be generated due to the ground capacitance in the DC circuit, and this leakage current may cause a safety problem. Therefore, the power conditioner should be adapted to the grounding system of the interconnected system in principle. It shall be ".

  FIGS. 16A, 16B, and 16C show schematic circuit blocks of a typical conventional power conditioner of a three-phase type having an output of 10 kW. 16 (a) is a power conditioner with a built-in high-frequency transformer, FIG. 16 (b) is a transformerless power conditioner with V (S) phase grounding, and FIG. 16 (c) is ungrounded. This is a transformerless power conditioner.

  When connecting to a high-voltage system power supply exceeding AC600V and AC7000V or less, the grounding method of the transformer for boosting the voltage of 210 / 6600V is used as the power conditioner for any type of power conditioner described above. By selecting it together, it will be possible to connect to the grid without any problems.

  However, when the pole transformer is connected to a grounded low-voltage system power supply, three-phase three-wire V (S) phase grounding and three-phase four-wire O (N) Since there are a plurality of grounding systems such as phase grounding, as described below, there are cases where direct connection is possible and cases where connection is required via an isolation transformer of commercial frequency.

  The power conditioner with a built-in high-frequency transformer shown in FIG. 16A is either a three-phase three-wire V (S) phase grounding system or a three-phase four-wire O (N) phase grounding system. Can also be connected directly.

  The transformerless type power conditioner of the V (S) phase grounding shown in FIG. 16B can be directly connected to the three-phase three-wire [V (S) phase grounding] system. When connecting to a 4-wire [O (N) phase ground] system, a commercial frequency isolation transformer is required.

  The non-grounded transformerless power conditioner shown in FIG. 16 (c) includes a three-phase three-wire [V (S) phase ground] system and a three-phase four-wire [O (N) phase ground] system. Any of these cannot be directly connected, and it is necessary to use a commercial frequency isolation transformer.

  In particular, when a three-phase transformer-less power conditioner is to be connected to a three-phase four-wire lighting combined system [O (N) phase grounding], the following measures are required. There was a problem that the plan also needed to be changed and the cost increased.

  Insert the isolation transformer on the AC side as the first correspondence to make V (S) phase grounding, change the power conditioner to single phase output as the second correspondence, built-in transformer type as the third correspondence The fourth countermeasure is to add a three-phase V (S) -phase grounded pole transformer for a fee after consulting with the power company.

  In Patent Document 1, it is possible to prevent the occurrence of a leakage current in any system power source such as a three-phase three-wire system, a single-phase three-wire system, a single-phase two-wire system, etc., and the grounding system is also medium. It is not limited to gender point grounding, it can easily cope with the V (S) phase grounding system that is common in Japan, and its versatility is enhanced, and the circuit system is not only half-bridge circuit configuration but also full bridge circuit configuration For the purpose of providing a power conversion device for photovoltaic power generation that can be easily handled, a plurality of capacitors are connected in series between DC input sections, and a switch is connected between the connection section of these capacitors and the output line of the inverter circuit. And a switch for controlling the inverter circuit by switching the switch according to a system power supply so as to be able to be switched.

  Patent document 2 discloses a transformerless power conversion apparatus for photovoltaic power generation in which the ground-to-ground potential of the DC portion of the inverter does not fluctuate even when connected to a three-phase three-wire V (S) phase grounding system. For solar power generation, which converts DC power from solar cells into AC power with three-phase output, and sends AC power to the system connected to a three-phase system with one phase grounded The power converter includes an inverter circuit having two sets of series circuits of two switching elements, a plurality of capacitors for dividing a DC voltage are connected in series between the DC input portions of the inverter circuit, and the three-phase output 1 One output line is drawn out from the connection portion of the capacitor, and two output lines are drawn out from the midpoints of the switching elements of each set as the other two of the three-phase outputs. Configuration and then, solar photovoltaic power converter according to claim output line drawn from the connection portion that is connected to a phase and the ground of the capacitor is disclosed.

JP 2000-102265 A JP 2001-103768 A

  However, the power conversion device disclosed in Patent Document 1 is provided with a switch between a connection part of a capacitor connected in series between DC input parts, that is, a DC side neutral point, and an output line of an inverter circuit. The inverter circuit can be switched according to the system power supply to switch the control of the inverter circuit, but leakage current is not suppressed due to the capacitor connected to the output side of the inverter for three-phase system interconnection. It is sufficient, and when connecting to a three-phase four-wire O (N) phase grounding system, the DC neutral point is not connected to the output line of the inverter circuit. It was difficult.

  Moreover, although the power converter device disclosed by patent document 2 is disclosed about the structure of the two-phase inverter connected with the system | strain of a three-phase three-wire system V (S) phase grounding system, it targets three-phase inverter There is no disclosure regarding the relationship with the capacitor connected to the output side of the three-phase inverter, for example, the connection mode in the case of a delta-connected capacitor, and the three-phase four-wire O ( N) Since there was no disclosure about how to suppress the leakage current when interconnecting with the phase grounding system, it was necessary to deal with these problems.

  In other words, the techniques disclosed in Patent Documents 1 and 2 have insufficient consideration of leakage current, and there is a problem that the risk of unnecessary operation of the leakage breaker due to leakage current cannot be reduced.

  In view of the above-described problems, the object of the present invention is to use any of the three-phase three-wire V (S) phase grounding system and the three-phase four-wire O (N) phase grounding system power supply. An object of the present invention is to provide an inexpensive non-insulated power conversion device and non-insulated power conversion system that can effectively suppress leakage current.

  In order to achieve the above-mentioned object, a first characteristic configuration of the non-insulated power converter according to the present invention includes a three-phase inverter and a direct current of the three-phase inverter as described in claim 1 of the claims. A plurality of input-side capacitors connected in series between the input terminals, an LC filter composed of a reactor and a capacitor connected to the AC output terminal of the three-phase inverter, and a control unit for controlling the three-phase inverter, A non-insulated power conversion apparatus comprising: a connection point between the input-side capacitors and any one of a plurality of capacitors constituting the LC filter so as to match a ground phase of a system power source of a connection destination Is connected as a virtual ground point, and a common mode filter is further connected after the LC filter, and the control unit uses the virtual ground point as a reference. It lies in controlling the three-phase inverter to match the ground phase of the system destination of the system power source.

  A common mode current, which is an asymmetrical portion of the current flowing through the reactor of each phase of U, V, W generated by switching of the three-phase inverter, is connected to the input side capacitor via the LC filter capacitor. By bypassing to the sex point, the high-frequency leakage current flowing out to the system can be reduced. In addition, by providing a common mode filter downstream of the LC filter and reducing the impedance on the three-phase inverter side, leakage of leakage current to the system is effectively suppressed. Moreover, since the three-phase inverter is controlled by the control unit so as to match the ground phase of the system power source of the connection destination with reference to the virtual ground point, the potential fluctuation of the commercial frequency is suppressed on the DC side, and the commercial frequency Leakage current can also be reduced.

  As described in claim 2, the second characteristic configuration is a three-phase four-wire system power supply in which the system power supply is O (N) phase grounding in addition to the first characteristic configuration described above. The capacitor constituting the LC filter is constituted by a plurality of divided capacitors connected in delta, at least one of which is connected in series, and the virtual ground point is constituted by a connection point between the divided capacitors.

  When the system power supply is a three-phase four-wire system power supply with O (N) phase grounding and the capacitors constituting the LC filter are delta-connected, at least one is configured with a plurality of divided capacitors connected in series Thus, the connection point between the divided capacitors can be set as a virtual ground point.

  The third characteristic configuration is the three-phase three-wire system power supply of V (S) phase grounding in addition to the first characteristic configuration described above, as described in claim 3. The capacitors constituting the LC filter are delta-connected, and the virtual ground point is formed by a connection point between the delta-connected capacitors.

  When the system power supply is a three-phase three-wire system power supply with V (S) phase grounding and the capacitors constituting the LC filter are delta-connected, the connection point between the delta-connected capacitors is the virtual grounding point. be able to.

  In the fourth feature configuration, in addition to the first feature configuration described above, the system power supply is a three-phase four-wire system power supply with O (N) phase grounding. The capacitor constituting the LC filter is star-connected, and the virtual ground point is formed by a neutral point of the star-connected capacitor.

  When the system power supply is a three-phase four-wire system power supply with O (N) phase grounding and the capacitors constituting the LC filter are star-connected, the neutral point of the star-connected capacitor is set as a virtual grounding point. be able to.

  In the fifth feature configuration, as described in claim 5, in addition to the first feature configuration described above, the system power supply is a V (S) phase grounded three-phase three-wire system power supply, The capacitor constituting the LC filter is star-connected, and the virtual ground point is formed by a neutral point of the star-connected capacitor.

  Similarly, when the system power supply is a three-phase three-wire system power supply with V (S) phase grounding and the capacitors constituting the LC filter are star-connected, the neutral point of the star-connected capacitor is defined as the virtual grounding point. can do.

  In addition to any one of the first to fifth feature configurations described above, the sixth feature configuration is a system power supply based on the ground phase of the housing. The ground phase of the system power source of the connection destination is determined based on the phase voltage or the line voltage of the power source, and the three-phase inverter is adjusted to match the ground phase of the system power source of the connection destination based on the virtual ground point. In that it is configured to control.

  Focusing on the fact that the grounding phase of the chassis and the grounding phase of the system power supply are substantially the same voltage, if the phase voltage or line voltage of the system power supply is measured based on the grounding phase of the chassis, It is possible to grasp the ground phase of the system power supply. Based on the result, the three-phase inverter is controlled so as to match the ground phase of the system power source of the interconnection destination with reference to the virtual ground point. The frequency leakage current can also be reduced.

  In the seventh feature configuration, in addition to any one of the first to sixth feature configurations described above, the control unit includes a system power supply based on the ground phase of the housing. The grounding phase of the system power source of the connection destination is determined based on the phase voltage or the line voltage of the power source, and the connection point of the input side capacitors is set so that the virtual grounding point matches the ground phase of the system power source of the connection destination And a connection point of a plurality of capacitors constituting the LC filter are automatically connected.

  Focusing on the fact that the grounding phase of the chassis and the grounding phase of the system power supply are substantially the same voltage, if the phase voltage or line voltage of the system power supply is measured based on the grounding phase of the chassis, It is possible to grasp the ground phase of the system power supply. Based on the result, the connection point between the input capacitors, that is, the neutral point on the DC side, and the connection points of the capacitors that make up the LC filter are automatically connected, so that complicated connection work can be simplified. Become. For example, a mechanical switch or semiconductor switch such as an electromagnetic relay is provided between the neutral point on the DC side and the connection point of a plurality of capacitors constituting the LC filter, and the target mechanical switch or semiconductor is controlled by the control unit. The switch may be turned on.

  In the eighth feature, as described in claim 8, in addition to any of the first to seventh features described above, the three-phase inverter is a two-level inverter controlled by sinusoidal PWM control. It is in the point.

  If a three-phase inverter is constituted by a two-level inverter controlled by sine wave PWM, it can be realized at low cost.

  In the ninth feature configuration, as described in claim 9, in addition to any of the first to seventh feature configurations described above, the three-phase inverter is configured by a three-level inverter controlled by sinusoidal PWM control. It is in the point.

  If a three-phase inverter is constituted by a three-level inverter controlled by sinusoidal PWM, high-frequency leakage current can be effectively suppressed, and the current ripple of the reactor can be reduced, so that the loss is improved.

  According to the tenth feature configuration, as described in claim 10, in addition to the ninth feature configuration described above, the control unit is configured to perform the three-dimensional measurement using a PWM signal obtained by comparing a reference sine wave and a triangular wave. A PWM control unit for driving the phase inverter is provided, and the triangular wave is composed of a vertically symmetric waveform with respect to the zero point.

  When a PWM signal is generated by preparing a triangular wave as a carrier on both the positive and negative sides so that it is line symmetric with respect to the zero point of the sine wave, the symmetry of the output voltage waveform from the DC neutral point improves. Since the symmetry of the current flowing through the reactor of each phase is improved when the inverter is switched, the common mode current generated in the reactor is effectively suppressed.

  The characteristic configuration of the non-insulated power conversion system according to the present invention includes a non-insulated power conversion device having any one of the first to tenth characteristic configurations described above, and the power conversion device as described in claim 11. It is in the point provided with any one or those combination of the solar cell which supplies direct-current power to the provided inverter, a storage battery, and a fuel cell.

  Since the leakage current is effectively reduced, it is possible to realize a non-insulated power conversion system that does not cause the leakage circuit breaker to operate unnecessarily during grid connection.

  As described above, according to the present invention, any system power supply of the three-phase three-wire V (S) phase grounding method and the three-phase four-wire O (N) phase grounding method is effective. In addition, it is possible to provide an inexpensive non-insulated power conversion device and non-insulated power conversion system that can suppress leakage current.

Circuit diagram of a non-insulated power converter connected to a three-phase four-wire system power supply with O (N) -phase grounding and delta-connected to an LC filter capacitor Circuit diagram of a non-insulated power converter connected to a V (S) -phase grounded three-phase three-wire system power supply and delta-connected to the LC filter capacitor Circuit diagram of a non-insulated power converter connected to an O (N) -phase grounded three-phase, four-wire system power supply and with an LC filter capacitor star connected Comparison of voltage vector diagram controlled by control unit of conventional three-phase inverter and voltage vector diagram controlled by control unit of three-phase inverter according to the present invention Circuit diagram of 2-level inverter Circuit diagram of 3-level inverter Circuit diagram of a three-level inverter showing another embodiment (A), (b) is explanatory drawing of the PWM signal with respect to a 3 level inverter (A), (b) is explanatory drawing of the PWM signal by another embodiment with respect to a 3 level inverter Explanatory drawing of solar cell to be simulated Circuit diagram of the system power supply linked to the non-insulated power converter shown in FIG. Circuit diagram of the system power supply linked to the non-insulated power converter shown in FIG. 2 to be simulated Illustration of simulation conditions Explanatory diagram of the schnulation constant Illustration of simulation results (A), (b), (c) is a circuit diagram of a conventional power converter.

Hereinafter, a non-insulated power conversion device and a non-insulated power conversion system according to the present invention will be described with reference to the drawings.
FIG. 1 shows a non-insulated power conversion system 1 (hereinafter also referred to as a “solar cell power generation device”) according to the present invention as an example of a distributed power source.

  The solar cell power generation device 1 is configured to include the non-insulated power conversion device 2 of the present invention (hereinafter also referred to as “power conditioner 2”) to which the solar cell panel PV and the solar cell panel PV are connected, and the leakage leakage is interrupted. It is connected to a three-phase four-wire system power supply Eg with O (N) phase grounding via a device Sg.

  The power conditioner 2 includes a three-phase inverter 3 that converts a DC voltage generated by the solar battery panel PV into a three-phase AC voltage having a predetermined frequency and voltage value so as to be linked to a three-phase commercial system, and a three-phase inverter. 3 includes a control unit 30 that performs PWM control on the motor 3, and is configured without a transformer. The control unit 30 includes a microcomputer, a memory, an input / output circuit, and the like.

A plurality of input-side capacitors C _d1 and C _d2 connected in series are connected between the DC input terminals of the three-phase inverter 3, and a DC neutral point NP is configured at these connection points. The number of capacitors on the input side and the capacitance value of each capacitor are not particularly limited if the point at which the voltage that is approximately half of the input voltage to the three-phase inverter 3 becomes the DC neutral point NP. Absent.

An LC filter 4 including a reactor L _id and a capacitor C _i for removing harmonic components from the output of the three-phase inverter 3 is connected to the subsequent stage of the three-phase inverter 3. Each reactor constituting the LC filter 4 is connected in series to each output terminal of the three-phase inverter 3, and a capacitor constituting the LC filter 4 is delta-connected between the U, V and W three-phase phases after each reactor. ing. The capacitors between the phases constituting the LC filter 4 are configured to include at least two capacitors connected in series.

  Further, a switch circuit 7 including a semiconductor switch for connecting any one of the series-connected capacitors and the above-described DC neutral point NP is provided, and the control circuit 30 controls the switch circuit 7. It is configured.

  Connection points of a plurality of capacitors arranged between the U, V, and W phases constituting the LC filter 4 so as to match the ground phase of the three-phase four-wire system power supply Eg with O (N) phase grounding. One is selected, and the switch circuit 7 is controlled so that the selected connection point and the DC neutral point NP are connected as a virtual ground point. In addition, the switch circuit should just be comprised by the element which can be controlled by the control part 30, and may be comprised by the relay circuit etc. provided with the mechanical contact other than the semiconductor switch.

  Note that at least one of the capacitors connected between the phases constituting the LC filter is composed of at least two capacitors connected in series, and the neutral point and the DC neutral point NP can be connected. Good. In this case, the switch circuit 7 is unnecessary, and the U, V, and W phases may be connected so that the midpoint corresponds to the ground phase of the system power supply Eg.

Further, a common mode filter 5 having a reactor L _ic is connected to the downstream side of the LC filter 4, and the casing 8 of the power conditioner 2 is grounded via a grounding resistor.

That is, the power conditioner 2 according to the present invention has a plurality of capacitors C constituting the LC filter 4 and a connection point between the input side capacitors C _d1 and C _d2 so as to match with the ground phase of the system power source Eg of the connection destination. A connection point of _i is connected as a virtual ground point, and a common mode filter 5 is further connected to the subsequent stage of the LC filter 4. Then, the three-phase inverter 3 is controlled by the control unit 30 so as to be matched with the ground phase of the system power source of the interconnection destination on the basis of the virtual ground point.

A common mode current, which is an asymmetrical amount of current flowing through the reactor of each phase of U, V, W generated by switching of the three-phase inverter 3, is connected to the input side capacitors via the capacitor C _i of the LC filter 4. By being bypassed to the DC neutral point NP, the high-frequency leakage current flowing out to the system power supply is reduced.

  Further, by providing the common mode filter 5 at the subsequent stage of the LC filter 4, the impedance on the three-phase inverter 3 side is lowered from the system side, and the outflow of leakage current to the system is effectively suppressed.

  In addition, since the three-phase inverter 3 is controlled by the control unit 30 so as to match the ground phase of the system power source of the interconnection destination with reference to the virtual ground point, the potential fluctuation of the commercial frequency is suppressed on the DC side, The frequency leakage current can also be reduced.

  The control unit 30 discriminates the ground phase of the system power supply Eg of the connection destination based on the phase voltage or the line voltage of the system power supply Eg with the ground phase of the housing 8 as a reference, and connects to the virtual ground point as a reference. The three-phase inverter 3 is configured to be matched with the ground phase of the system power supply Eg at the system destination.

With reference to the voltage vector diagram shown in FIG. 4, the control of the three-phase inverter 3 executed by the conventional control unit and the control unit of the present invention will be described.
In the conventional high-frequency isolation transformer built-in power conditioner shown in FIG. 16A and the conventional non-grounded transformerless power conditioner shown in FIG. As shown in the voltage vector diagram, PWM control waveforms of U, V, and W phases are generated by shifting the phase by 120 ° from the neutral point of the star connection by the control unit of the inverter.

  In this method, control is performed so that the phase voltage is 115 V AC and the line voltage is 200 V AC. For this purpose, the input DC voltage required is as low as DC326 (= 115 × √2 × 2) V, and there is an advantage that it is easy to reduce the switching loss of the inverter alone.

  As already explained, if this method is simply applied, the potential of the DC neutral point NP, which is the base point of control, and the ground point of the low-voltage system are different. Therefore, in order to prevent the occurrence of leakage current, It is necessary to provide high-frequency insulation on the direct current side or to interpose a commercial frequency insulation transformer on the output side of the power conditioner. As a result, it is difficult to achieve high efficiency in the entire system during low voltage interconnection.

  In the transformerless type power conditioner of V (S) phase grounding shown in FIG. 16B, as shown in the voltage vector diagram of the second stage from the top of FIG. The U (R) phase and W (T) phase PWM control waveforms are generated by shifting by 60 °.

  This method has the advantage of reducing the number of switching elements because only two-phase control is required, but the required DC voltage is as high as DC566 (= 200 × √2 × 2) V, and the switching loss of the inverter element alone is increased. There is a drawback that it is easy. As for the phase current of the V (S) phase, since the commercial frequency current flows directly from the DC capacitor, it is necessary to increase the capacitance of the capacitor as compared with other methods so that the commercial frequency ripple current can flow.

  Assuming that there is a ground point between U (R) and V (S), the control unit 30 of the power conditioner 2 shown in FIG. 1 controls the PWM as shown in the voltage vector diagram shown on the right side of the lowermost stage in FIG. Generate a waveform. More specifically, an AC 100V voltage is output to the U (R) phase with the O (N) phase as a base point, and an AC 100V is output to the V (S) phase with a 180 ° shift. The W (T) phase is shifted from the U (R) phase by 90 ° to output AC173V.

  The DC voltage required at this time is DC490 (= 173 × √2 × 2) V, which is larger than the above-described star connection method, but can be lower than the V (S) phase grounding method.

  The control unit 30 pays attention to the fact that the grounding phase E of the housing and the grounding phase of the system power supply Eg are substantially the same voltage, and the phase voltage or line voltage of the system power supply Eg with reference to the grounding phase E of the housing. Is measured to recognize the ground phase of the system power supply Eg of the interconnection destination.

  For example, if the U (R) phase voltage is about 100V, the V (S) phase voltage is about 100V, and the W (T) phase voltage is about 173V with respect to the ground phase E of the housing, U (R) Recognize that there is a ground point between -V (S).

  Based on the result, the control unit 30 performs PWM control of the three-phase inverter 3 so as to match the ground phase of the system power source of the interconnection destination with reference to the virtual ground point, so that the potential fluctuation of the commercial frequency on the DC side Is suppressed, and the leakage current at the commercial frequency can be reduced.

  Further, similarly to the above, the control unit 30 determines the ground phase of the system power source of the connection destination based on the phase voltage or the line voltage of the system power source based on the ground phase E of the housing, and the virtual ground point is The switch circuit 7 is controlled so as to match with the ground phase of the system power source of the connection destination, and the DC neutral point NP and the connection points of a plurality of capacitors constituting the LC filter 4 are automatically connected. .

  FIG. 2 shows a case where the system power supply is a three-phase three-wire system power supply with V (S) phase grounding. The capacitors constituting the LC filter 4 are delta-connected, and the virtual ground point is formed by a connection point between the capacitors between the delta-connected phases.

  When the system power supply is a three-phase three-wire system power supply with V (S) phase grounding and the capacitors constituting the LC filter are delta-connected, the connection point between the delta-connected capacitors is the virtual grounding point. be able to.

  FIG. 3 shows another example in which the system power supply is a three-phase four-wire system power supply with O (N) phase grounding. A capacitor constituting the LC filter 4 is star-connected to each phase, and a virtual ground point is configured by a neutral point of the capacitor star-connected.

  When the system power supply is a three-phase four-wire system power supply with O (N) phase grounding and the capacitors constituting the LC filter are star-connected, the neutral point of the star-connected capacitor is set as a virtual grounding point. be able to.

  Furthermore, when the system power supply is a three-phase three-wire system power supply with V (S) phase grounding and the capacitors constituting the LC filter 4 are star-connected, the neutral point of the star-connected capacitors is It can be a virtual ground point.

  In any of the cases described above, the control unit 30 determines the ground phase of the grid system power source based on the phase voltage or line voltage of the system power source with reference to the ground phase E of the housing, and the virtual ground point The three-phase inverter is PWM-controlled so as to match the ground phase of the system power supply Rg of the connection destination with reference to.

  Since the three-phase inverter is controlled so that it matches the ground phase of the grid power supply system with reference to the virtual ground point, fluctuations in the commercial frequency potential on the DC side are suppressed, and the leakage current at the commercial frequency is also reduced. it can.

It is preferable in terms of cost that the three-phase inverter 3 is composed of a two-level inverter that is sinusoidally PWM controlled by the control unit 30.
FIG. 5 shows a circuit example corresponding to a two-level inverter. Three switching arms in which a high-side switch and a low-side switch are connected in series are connected in parallel, and phase voltages of U, V, and W are output from each midpoint.

  If the three-phase inverter 3 is composed of a three-level inverter, high-frequency leakage current can be effectively suppressed, and the reactor current ripple can be reduced, so that the loss is improved.

  FIG. 6 shows an NPC type three-level inverter, and FIG. 7 shows a one-phase switching arm constituting a T type three-level inverter. Any configuration can be suitably used.

  The control unit 30 includes a PWM control unit that generates a PWM signal obtained by comparing a sine wave as a command value and a triangular wave as a carrier as a drive signal for the inverter 3. When the three-phase inverter 3 is driven, it is preferable that the triangular wave has a symmetrical waveform with respect to the reference line connecting the zero points of the sine wave.

  8A and 8B show PWM signals when the triangular wave has a symmetrical waveform with respect to the reference line. The upper part of FIG. 8A shows a sine wave, which is a command value normalized by ± 1, an upper triangular wave (solid line), and a lower triangular wave (dashed line), and the lower part of FIG. Indicates the output voltage of the U phase. 8B shows the output voltage for the U-phase, the middle stage shows the output voltage for the V-phase, and the lower stage shows the line voltage between the U-phase and the V-phase.

  9A and 9B show PWM signals when the triangular wave is asymmetric with respect to the reference line and has the same waveform. The upper part of FIG. 9A shows a sine wave, which is a command value normalized by ± 1, an upper triangular wave (solid line), and a lower triangular wave (dashed line), and the lower part of FIG. 9A. Indicates the output voltage of the U phase. Furthermore, the upper stage of FIG. 9B shows the output voltage for the U phase, the middle stage shows the output voltage for the V phase, and the lower stage shows the line voltage between the U phase and the V phase.

  In order to generate the PWM signal for the inverter 3, any of the systems shown in FIGS. 8 and 9 may be adopted. However, as shown in FIG. 8, the positive side and the negative side are symmetrical with respect to the reference line. If the PWM signal is generated based on the triangular wave respectively prepared on the side, the symmetry of the output voltage waveform seen from the DC neutral point NP is improved, and the symmetry of the current flowing through the reactor of each phase when the inverter 3 is switched is improved. Therefore, the common mode current generated in the reactor is effectively suppressed.

  As shown in FIG. 13, a circuit simulator PSIM provided by Myway Plus Co., Ltd. is provided for the five types of power conditioners of Examples 1 to 5 and the two types of power conditioners of Comparative Example 1 and Comparative Example 2. This was used to simulate the operation.

  The first embodiment corresponds to the circuit diagram shown in FIG. 1 and uses a two-level inverter, the LC filter capacitor is delta-connected, and the virtual ground point connected to the DC neutral point NP is the O (N) phase ground. This is a mode in which the position corresponding to the three-phase four-wire system power source is selected and the PWM output is an output based on the control shown on the right side of the lowermost stage in FIG.

  The second embodiment corresponds to the circuit diagram shown in FIG. 1 and uses a three-level inverter, the capacitor of the LC filter is delta connected, and the virtual ground point connected to the DC neutral point NP is the O (N) phase ground. The triangular wave used for PWM control is a line symmetrical waveform (see FIG. 8), and the PWM output is an output based on the control shown on the right side of the lowermost stage in FIG. It is an aspect.

  The third embodiment is an aspect in which a triangular wave having the same shape (see FIG. 9) that is asymmetrical is employed instead of the triangular wave that is a line-symmetric waveform of the second embodiment.

  Example 4 corresponds to the circuit diagram shown in FIG. 2 and uses a three-level inverter, the capacitor of the LC filter is delta-connected, and the virtual ground point connected to the DC neutral point NP is V (S) -phase grounding. This is a mode in which a triangular wave used for PWM control is selected as a position corresponding to the three-phase three-wire system power supply and is a line-symmetric waveform, and the PWM output is an output based on the control shown in the lower left part of FIG.

  Example 5 corresponds to the circuit diagram shown in FIG. 3 and uses a three-level inverter, the LC filter capacitor is star-connected, and the virtual ground point connected to the DC neutral point NP is selected as the neutral point of the capacitor. The triangular wave used for PWM control is a line-symmetric waveform, and the PWM output is an output based on the control shown on the right side of the lowermost stage in FIG.

  Comparative Example 1 is a mode in which the neutral point is opened without connecting to the virtual ground point with respect to Example 2, and Comparative Example 2 is a triangular wave of PWM control with respect to Example 4 having an asymmetric waveform, and the system power supply is This is a conventional mode which is a three-phase four-wire system power supply with O (N) phase grounding.

As shown in FIG. 10, assuming that the solar cell panel PV to be simulated is a panel that is 160% overloaded with a three-phase 10 kW power conditioner, the stray capacitance C _p2 between the N terminal side and the ground is 3 μF.

  The stray capacity is inferior in the power generation per module than the crystalline system, and for compound solar cells that are the types of modules that require more modules (area) if the rated power is the same. The value is determined assuming severe rainy weather.

That is, it is assumed that a parasitic capacitance C _{p2 of 3} μF exists between the cells of the solar battery panel PV and the solar battery frame, and that the cell frame and the ground are connected via the grounding resistance R _g1. did. The same applies to a solar cell having a floating capacity on the positive electrode side, or a solar cell having a capacity on both the positive electrode and the negative electrode.

FIG. 11 shows an example of a simulation circuit on the load side with respect to the circuit diagram shown in FIG. A three-phase, four-wire system is assumed to be connected to a low-voltage interconnection that is connected to a power / power-shared midpoint grounding transformer. System interconnection operation was performed with a circuit having the O (N) phase between U (R) and V (S) as a ground point. System impedances R _S and Ls are inserted between the power conditioners. Further, the O (N) phase of the transformer is assumed to be grounded via a grounding resistor _Rg3 , and the E terminal of the power conditioner is grounded via a grounding resistor _Rg2 .

FIG. 12 shows an example of a load-side simulation circuit for the circuit diagram shown in FIG. Three-phase three-wire Δ connection A low-voltage interconnection that is connected to a V (S) -phase grounding transformer is assumed. System impedances R _S and Ls are inserted between the power conditioners. Further, the V (S) phase of the transformer is assumed to be grounded via a grounding resistor _Rg3 , and the E terminal of the power conditioner is grounded via a grounding resistor _Rg2 .

  FIG. 14 shows circuit constants used for the simulation. Based on these circuit constants, the leakage current in the case of simulating grid interconnection operation was obtained and evaluated.

  FIG. 15 shows the magnitude of leakage current flowing from the output of the inverter, which is the result of the simulation, to the DC side stray capacitance via the system. In Comparative Example 2 in which a conventional V (S) phase grounding power conditioner is connected to the O (N) phase grounding system, the leakage current is 170 mA, and the standard sensitivity of the leakage breaker of the 10 kW class power conditioner Since the current has exceeded 100 mA, it can be seen that the earth leakage circuit breaker operates unnecessary, and the generated power cannot be reversely flowed.

  In Comparative Example 1, even if PWM control is performed using a triangular wave having a symmetric waveform using a three-level inverter, the current is 73 mA when the inverter output capacitor and the DC neutral point capacitor are not connected, and the sensitivity of the leakage breaker Since the rated inactive current is 50% or more when the current is 100 mA, the possibility of unnecessary operation remains.

  In Examples 1 to 5, it can be evaluated that they are substantially equivalent from the viewpoint of leakage current. However, this simulation is a state in which the inverter is operated with one unit, and it is necessary to consider that the leakage current tends to increase due to the circulating current between the inverters when operating with a plurality of units. It is important to reduce the leakage current.

  From this point of view, a three-level inverter is used, a line-symmetric triangular wave is used for the carrier signal, a capacitor on the inverter output side is delta-connected, and a DC neutral point capacitor is connected to the same location as the ground point of the system. The second embodiment and the fourth embodiment, which are connected to each other, are most preferable. Next, a three-level inverter is used, a line-symmetric triangular wave is adopted as the carrier signal, and the capacitor on the inverter output side is star-connected. The embodiment of Example 5, which is a system in which the sex point is connected to a DC neutral point capacitor, is preferred.

Another embodiment of the present invention will be described below.
In the above-mentioned embodiment, each phase of the capacitors of the delta-connected LC filter is composed of two capacitors connected in series, and the switch circuit includes a semiconductor switch that connects the neutral point of the capacitors and the DC neutral point NP. 7 is provided, and the switch circuit 7 is controlled by the control unit 30. However, for example, the terminal block of the power conditioner 2 is connected to each midpoint of two capacitors connected in series. Three connected terminals and one terminal connected to the DC neutral point NP may be provided so that terminals corresponding to the ground phase on the system power supply side can be connected manually.

  Further, three male connectors connected to the respective midpoints of two capacitors connected in series instead of the terminals and one female connector connected to the DC neutral point NP are provided, and the ground phase on the system power supply side is provided. Connectors corresponding to the above may be configured to be connectable by manual operation.

  In addition, this invention is not limited to the structure by which the power supply device connected to the non-insulated power converter 2 is the solar cell panel PV, Non-insulated power converter 2 and system power supplies, such as a storage battery and a fuel cell, The present invention can be widely applied to a DC power source that may cause unnecessary operation of a leakage breaker connected between the two. Further, a DC boost converter may be provided between the DC power supply and the three-phase inverter, and the output of the DC boost converter may be connected to the three-phase inverter to adopt another configuration.

  The embodiment described above is merely an example of a non-insulated power conversion apparatus and a non-insulated power conversion system to which the present invention is applied. Specific circuit configurations, circuit constants, and the like of an inverter, a control unit, an LC filter, etc. Needless to say, the design can be changed as appropriate as long as the effects of the present invention are achieved.

1: Non-insulated power conversion system (solar cell power generator)
2: Non-insulated power converter (power conditioner)
3: Inverter 4: LC filter 5: Common mode filter 7: Switch circuit 8: Housing 30: Control unit NP: DC neutral point (virtual ground point)

Claims (11)

A three-phase inverter, a plurality of input-side capacitors connected in series between the DC input terminals of the three-phase inverter, an LC filter composed of a reactor and a capacitor connected to the AC output terminal of the three-phase inverter, A power conversion device comprising a control unit for controlling a three-phase inverter,
In order to match the ground phase of the system power source of the interconnection destination, the connection point between the input side capacitors and the connection point of any of the plurality of capacitors constituting the LC filter can be connected as a virtual ground point. In addition, a common mode filter is connected to the subsequent stage of the LC filter,
The said control part controls the said three-phase inverter so that it may match | combine with the ground phase of the system power source of a connection destination on the basis of the said virtual ground point, The non-insulated power converter device characterized by the above-mentioned. The system power supply is a three-phase four-wire system power supply with O (N) phase grounding,
The non-conducting circuit according to claim 1, wherein the capacitors constituting the LC filter are constituted by a plurality of divided capacitors connected in delta, at least one of which is connected in series, and the virtual ground point is constituted by a connection point between the divided capacitors. Insulated power converter. The system power supply is a V (S) phase grounded three-phase three-wire system power supply,
The non-insulated power converter according to claim 1, wherein the capacitors constituting the LC filter are delta-connected, and the virtual ground point is formed by a connection point between the delta-connected capacitors. The system power supply is a three-phase four-wire system power supply with O (N) phase grounding,
The non-insulated power conversion device according to claim 1, wherein a capacitor constituting the LC filter is star-connected, and the virtual ground point is a neutral point of the capacitor star-connected. The system power supply is a V (S) phase grounded three-phase three-wire system power supply,
The non-insulated power conversion device according to claim 1, wherein a capacitor constituting the LC filter is star-connected, and the virtual ground point is a neutral point of the capacitor star-connected.   The control unit determines the ground phase of the system power source of the connection destination based on the phase voltage or the line voltage of the system power source based on the ground phase of the housing, and connects to the connection destination based on the virtual ground point. The non-insulated power converter according to any one of claims 1 to 5, wherein the non-insulated power converter is configured to control the three-phase inverter so as to be matched with a ground phase of the system power supply.   The control unit determines the ground phase of the grid system power source based on the phase voltage or line voltage of the grid power source with respect to the ground phase of the housing, and the virtual ground point is the grid system power source The connection point of the said input side capacitors and the connection point of the several capacitor | condenser which comprises the said LC filter are automatically connected so that it may match with the earthing phase of this, The structure in any one of Claim 1 to 6 Non-insulated power converter.   The non-insulated power converter according to any one of claims 1 to 7, wherein the three-phase inverter is configured by a two-level inverter that is sinusoidally PWM controlled.   The non-insulated power converter according to any one of claims 1 to 7, wherein the three-phase inverter is configured by a three-level inverter that is sinusoidally PWM controlled.   The control unit includes a PWM control unit that drives the three-phase inverter by a PWM signal obtained by comparing a reference sine wave and a triangular wave, and the triangular wave has a vertically symmetrical waveform with a zero point as a reference. Item 10. The non-insulated power converter according to Item 9.   The non-insulated power conversion device according to any one of claims 1 to 10, and any one of a solar cell, a storage battery, and a fuel cell that supply DC power to a three-phase inverter provided in the non-insulated power conversion device, or those A non-insulated power conversion system comprising a combination of