JP2018182774A - Power conversion apparatus, power conversion method, and inductance estimation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a unit from unstably operating when inductance between a power conversion apparatus and a DC power supply is changed by changing wiring between them.SOLUTION: A power conversion apparatus (10) converting power by switching operation comprises a voltage detection section (31) detecting a voltage Vinv across a capacitor (CC) arranged at an input side of the power conversion apparatus and a capacity output section (52) specifying capacity of the capacitor. An inductance estimation device estimates an inductance L of wiring between a DC power supply (20) and the power conversion apparatus (10) on the basis of a frequency f of the voltage Vinv just after cutting off energization to a winding of a motor (40) through an inverter (30). If the inductance L is large, a target value I* of the power conversion is limited.SELECTED DRAWING: Figure 1

Description

  The present invention relates to power conversion in consideration of inductance due to wiring.

  BACKGROUND In recent years, power conversion devices that perform power conversion of power supplied by DC power supplies such as batteries, solar power generation panels, and fuel cells are widely used. In such a power conversion device, even if it is a DC / DC converter as well as an inverter for driving a multiphase motor etc., the DC of the power supply is once converted to an AC and then its voltage is converted or the amount of current Controls the power (see, for example, Patent Document 1 below).

JP, 2015-211589, A

  In such a power conversion device, in order to reduce the impedance of the DC power source viewed from the switching element constituting the inverter, it is general to connect a capacitor having a large capacity in parallel to the power source input line. In this case, since the wiring from the DC power supply to the power conversion device has an inductance, if the current flowing through the DC power supply line fluctuates due to the on / off of the switching element, the input voltage fluctuation may become large. . For this reason, when designing a power converter, it was necessary to estimate the inductance of the wiring and select an appropriate capacitor capacity accordingly. When the wiring distance from the DC power supply to the power conversion device changes, the inductance of the wiring also changes. For this reason, conventionally, such a power conversion device has designed the capacity of the capacitor to an appropriate value according to the distance to the DC power supply.

  When the value of the capacitor is not designed individually, if the wiring length is long and the inductance is high, the input voltage fluctuation may be large, which may cause various problems. For example, the ripple of the DC power supply line of the circuit becomes large, and the operation of the control device such as a computer becomes unstable, sometimes the voltage of the input power supply line of the inverter falls below the rating, and the operation as an inverter stops. It was also possible. Also, if the ripple becomes large, the capacitor will repeat charge and discharge, which will affect the durability and reliability.

  The present invention has been made to solve at least a part of the above-mentioned problems, and can be realized as the following aspects or application examples.

  A first aspect of the present invention is a power converter (10) connected to a direct current power supply (20) to perform power conversion. This power conversion device includes a capacitor (CC) connected between power supply lines on the input side connected to the DC power supply, a voltage detection unit (31) for detecting a voltage across the capacitor, the DC power supply, and An inductance estimation unit (51) that estimates an inductance between the capacitor and the voltage from the detected both-end voltage, and the power supply line are connected to perform power conversion in consideration of the magnitude of the estimated inductance. And a power converter (30, 50) for outputting.

  This power conversion device estimates the inductance between the DC power supply and the capacitor of the power conversion device from the voltage across the capacitor, performs power conversion in consideration of the magnitude of the estimated inductance, and outputs power. Therefore, even if the arrangement of the DC power supply and the power conversion device is different and the inductance of the wiring changes, the power conversion can be performed by estimating it and taking it into consideration.

  A second aspect of the present invention is a power conversion method connected to a DC power supply to perform power conversion. This power conversion method detects the voltage across the capacitor connected between the power supply lines on the input side connected to the DC power supply (step S110), and detects the inductance between the DC power supply and the capacitor. It estimates from the voltage between both ends (step S140), controls the switching element (Su, Sv, Sw) for power conversion connected to the power supply line on the downstream side of the capacitor, and the size of the estimated inductance Power conversion taking into consideration (steps S150 and S160). For this reason, also in the second aspect, even if the arrangement of the DC power supply and the power conversion device is different, even if the inductance of the wiring is changed, the power conversion can be performed by estimating and considering this.

  A third aspect of the present invention is an inductance estimation device (10) for estimating the inductance of a wire between a power conversion device and a DC power supply. The device for estimating the inductance includes a capacitance output unit (52) for outputting a capacitance of a capacitor connected between power supply lines on the input side of the power conversion device powered by the DC power supply, and a voltage across the capacitor From the detection result of the voltage detection unit (31) to be detected and the detection result of the voltage detection unit when the current flowing to the power conversion unit for performing power conversion in the power conversion device is sharply reduced, the vibration of the detected voltage is The circuit includes: a cycle detection unit that detects a cycle; and an inductance estimation unit (51) that calculates the inductance from the capacitance of the output capacitor and the cycle of the voltage oscillation detected by the voltage detection unit. According to this inductance estimation device, the inductance between the DC power supply and the capacitor of the power conversion device can be accurately estimated.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows the power converter device of embodiment. The schematic block diagram of the electric power control part of an electric power converter. The flowchart which shows the inductance calculation process which an inductance estimation part performs. Explanatory drawing which shows the mode of the fluctuation | variation of the both-ends voltage of the capacitor | condenser at the time of calculating an inductance. Explanatory drawing which shows the equivalent circuit of the inverter corresponded to a power conversion part. The circuit diagram which shows the equivalent circuit at the time of calculating | requiring the capacity | capacitance and resistance value of a capacitor | condenser. The graph which shows the electric current of each part at the time of a transient response. The graph which shows the relation between the electric current of each part at the time of transient response, and the both-ends voltage of a capacitor. The flowchart which shows the process which calculates the capacity | capacitance and resistance value of a capacitor | condenser.

A. Power converter hardware configuration:
As shown in FIG. 1, the power conversion device 10 according to the embodiment drives the motor 40, and receives an electric power supply from the DC power supply 20 to control the inverter 30 that drives the motor 40 and the power that controls the inverter 30. And a conversion control device 50.

  The electric motor 40 is a three-phase motor in which permanent magnets are used as a rotor in the present embodiment. Such a motor is used, for example, as a drive source of an electric vehicle or an auxiliary power source for assisting the power of an internal combustion engine. Of course, it can be used for other uses. In addition, other types of motors may be used. The three-phase armature windings of the motor 40 are referred to as U-phase, V-phase, and W-phase windings, respectively. Among them, V-phase and W-phase windings detect V-phase currents iv and iw respectively. A phase current sensor 41 and a W-phase current sensor 43 are provided. When three phases or their windings are handled collectively, they may be referred to as UVW phase and UVW phase windings, respectively.

  An inverter 30 that directly drives the motor 40 is connected to a DC power supply 20. Between the positive and negative power supply lines from the DC power supply 20, a voltage sensor 31, a capacitor CC, and three pairs of switching elements Su, Sv, Sw are connected. The capacitor CC is provided on the input side to which the DC power supply 20 is connected, and the three switching element pairs Su, Sv and Sw are provided on the output side to which the motor 40 is connected. The voltage sensor 31 corresponds to a voltage detection unit that detects the voltage Vinv. Each of the three pairs of switching elements Su, Sv, Sw connects in series a switching element whose one side is connected to the positive power supply line and a switching element whose one side is connected to the negative power supply line (ground line) The connection point of both switching elements is connected to each winding of the UVW phase. A protective diode is connected to each switching element. These three pairs of switching element pairs Su, Sv, Sw are turned on / off by shifting the electric angle of motor 40 by 120 degrees, respectively, to control the amount of current flowing through the UVW phase winding, that is, the driving force of motor 40. . The inverter 30 is also provided with a current sensor 33 for detecting the current Iinv flowing in the power supply line on the downstream side of the capacitor CC, but this current sensor 33 is not used in the first embodiment. It is drawn with a broken line. The handling of the current Iinv detected by the current sensor 33 will be described in the second embodiment.

  The direct current power supply 20 for supplying power to the inverter 30 is a direct current power supply such as a battery or a fuel cell. In the present embodiment, a high voltage secondary battery (battery) is used. Although the DC power supply 20 and the inverter 30 are electrically connected by a wire, an inductance component exists in the wire. This is shown as an inductance L in FIG. Although drawn on a positive power supply line in the drawing, the inductance L is representatively shown as an inductance component of the entire wiring. The inductance component of the wiring does not cause a problem if the constant current always flows because the power supply is the DC power supply 20, but the switching operation of the switching element pair Su, Sv, Sw in the inverter 30 The current flowing in the line fluctuates greatly on the time axis. The capacitor CC described above is provided on the input side of the inverter 30 in order to suppress such fluctuations and to reduce the impedance seen from the switching element pair Su, Sv, Sw side. Fluctuations in the amount of current flowing through the wires are inevitable. Therefore, the wiring inductance L is one of the considerations for the operation of the inverter 30.

  The power conversion control device 50 estimates the inductance L of the above-described wiring, the capacitance output unit 52 that outputs the size of the capacitance C of the capacitor CC provided in the inverter 30, and the UVW phase winding of the motor 40 And a voltage control unit 55 that controls the voltage applied to the The power conversion control device 50 controls the switching timing of the switching element pair Su, Sv, Sw of the inverter 30 so that a driving force corresponding to the externally set target value I * can be obtained from the motor 40, I have control. In the present embodiment, the inverter 30 and the voltage control unit 55 correspond to a power conversion unit. The target value I * commanded from the outside is output by the upper controller, and the power conversion state of the power conversion device 10 is set in order to set the rotational speed and torque of the motor 40 to a desired state. It is a target value instructing to control.

  The voltage value Vinv detected by the voltage sensor 31 of the inverter 30 and the capacitance C of the capacitor CC from the capacitance output unit 52 are input to the inductance estimation unit 51. The method of estimating the inductance L performed by the inductance estimation unit 51 will be described in detail later. In the first embodiment, the capacitance output unit 52 stores the value of the capacitance C of the capacitor CC provided in the inverter 30 in advance.

  The voltage control unit 55 receives the above-described target value I * and the estimated value of the inductance L estimated by the inductance estimation unit 51, as well as iv and iw detected by the V-phase current sensor 41 and the W-phase current sensor 43. It is input. Using these values, the voltage control unit 55 determines the on / off timings of the switching elements of the switching element pair Su, Sv, and Sw, and turns on / off the switching elements with control signals Vu *, Vv *, Vw * is output to the switching element pair Su, Sv, Sw. The affix “*” of each signal indicates that this is a target value.

  The detailed configuration of the voltage control unit 55 is shown in FIG. As illustrated, the voltage control unit 55 includes a target value limiting unit 61, a dq axis conversion unit 62, a voltage conversion unit 64, a coordinate inverse conversion unit 66, a coordinate conversion unit 67, and the like. The target value limiting unit 61 is a circuit that limits the target value I * instructed from the outside to within the output limit value IL as necessary. This limitation will be described later.

  The dq axis conversion unit 62 is a circuit that converts the target value I * into d axis and q axis currents id and iq. The current and voltage values are values on the time axis, but in the voltage control unit 55, for control of the motor 40, they are treated as values on the d and q axes. Therefore, the axis conversion unit 62 converts the target value I * from the outside into control values on the d axis and the q axis. Incidentally, in response to this conversion, the coordinate inverse transformation unit 66 at the final stage inversely transforms this to control signals Vu *, Vv * and Vw * which are control values on the time axis. The coordinate values of the current values iv and iw from the V-phase current sensor 41 and the W-phase current sensor 43 are also coordinate-converted to current values id and iq on the d and q axes.

  The target current values id * and iq * on the d and q axes converted by the axis conversion unit 62 are compared with the actual current values id and iq for feedback control, and differences Δid and Δiq are determined. This is input to the voltage conversion unit 64. The voltage conversion unit 64 converts the current values Δid and Δiq of the axes to be increased and decreased into voltage signals Vd * and Vq * that turn on / off the switching elements of the switching element pair Su, Sv and Sw.

  The voltage command values Vd * and Vq * on the d and q axes obtained in this manner are controlled by the coordinate inverse transformation unit 66 to control signals Vu * and Vv corresponding to the on / off instructions for the switching element pair Su, Sv and Sw. Inverts to *, Vw * and outputs to inverter 30.

  The internal configuration of the voltage control unit 55 has been described above, but the actual power conversion control device 50 includes the voltage control unit 55 as well as the inductance estimation unit 51 and the capacitance output unit 52 together with the computer and its control program. The operation is realized. Naturally, the inductance estimation unit 51, the capacitance output unit 52, the voltage control unit 55, and the like can also be realized by discrete electric circuits.

B. Processing in the First Embodiment:
Next, an inductance calculation process which is one of the processes performed by the power conversion control device 50 will be described with reference to FIG. The process shown in FIG. 3 implements the inductance estimating unit 51 and the target value limiting unit 61. The inductance calculation processing routine shown in FIG. 3 is executed each time control of the motor 40 is started. However, since the inductance L due to the wiring does not change in a short time although it changes over time, it is executed at the time of shipment, overhaul, replacement of parts, etc., and the processing result is stored in the non-volatile memory. The stored value may be referred to.

  When the process shown in FIG. 3 is started, the motor 40 is first energized for a short time to cut off the energization. At this time, the three-phase armature winding is energized for such a time that the rotor of the motor 40 does not rotate. This situation is shown in the lower part of FIG. By energizing for a short time, a large current Iinv flows through the inverter 30, whereby the voltage Vinv across the capacitor CC detected by the voltage sensor 31 drops momentarily. The DC power supply 20 is connected to the input terminal of the inverter 30, but charging of the capacitor CC is delayed due to the inductance L of the wiring and the impedance of the DC power supply 20 itself.

  As a result, when the energization is finished and the inverter current Iinv sharply decreases, the voltage Vinv at both ends of the capacitor CC vibrates as shown in the upper part of FIG. This is because an LC resonance circuit is formed by the inductance L by the wiring and the capacitance C of the capacitor CC. Therefore, the power conversion control device 50 next measures the fluctuation of this voltage (step S110), and detects the cycle Tf of the vibration (step S120). The period of oscillation Tf can be detected by measuring the voltage fluctuation and measuring the time from the positive (or negative) peak to the next positive (or negative) peak.

  Subsequently, the frequency f of the vibration is calculated from the period Tf (step S130), and the capacitance C of the capacitor CC necessary to obtain the inductance L is specified from the frequency f (step S135). In the present embodiment, the capacity C is specified by reading out a value stored in advance. As for the capacity C, a design value or an actual measurement value after manufacture may be stored in the memory of the power conversion control device 50 and read.

After the capacitance C is specified, the inductance L of the wiring is calculated (step S140). The calculation of the inductance L is an equation for obtaining the frequency f of the LC resonance,
1 / f = 2π√ (LC)
Formula (1) below transformed
L = 1 / {4C (πf) ² } (1)
From, you can easily ask.

  After the inductance L is thus determined, it is determined whether the inductance L is larger than a predetermined threshold Lth (step S150). If the calculated inductance L of the wiring is larger than the threshold Lth, the output limit value IL is set assuming that the output of 31 for driving the motor 40 is limited (step S160). Thereafter, the process exits to "END" and ends the processing routine.

  The output limit value IL set in step S160 is used to limit the target value I * in the target value limiting unit 61 shown in FIG. Now, if the determination in step S150 is "YES", that is, if the estimated inductance L of the interconnection is larger than threshold Lth, target value limiting unit 61 determines that target value I * given from the outside is larger than output limit value IL. For example, the target value I * is limited to the output limit value IL. When the inductance L of the wiring is larger than the threshold Lth assumed by the inverter 30 of the power conversion control device 50 as a design value, the voltage Vinv of the power supply line from the DC power supply 20 largely fluctuates, and the ripple of the power supply line becomes large. Although it is possible that the operation of the device having the same power supply line, for example, the computer becomes unstable, as described above, since the target value I * is limited to the output limit value IL, fluctuation of the power supply line is suppressed. Instability of the operation of the devices having the same line is prevented.

  Furthermore, according to the power conversion device 10 configured as described above, there is no need to change settings of the power conversion control device 50 even if the inductance L of the wiring changes, such as changing the length of the wiring. Therefore, it is necessary to change the arrangement of the DC power supply 20 and the power conversion control device 50, or change the design of the power conversion control device 50 in accordance with the respective arrangement, depending on the model etc. There is no

C. Second embodiment:
Next, a second embodiment will be described. In the second embodiment, a hardware configuration is used as in the first embodiment shown in FIG. However, in the second embodiment, the current sensor 33 shown in FIG. 1 is used. Further, the capacitance output unit 52 merely stores the capacitance C of the capacitor CC, and does not output this to the inductance estimation unit 51, but calculates the capacitance C of the capacitor CC. The method will be described below.

  First, the circuit around the capacitor CC will be described. FIG. 5 is a schematic view showing the current flowing through each part, as well as the connection relationship between the capacitor CC and the switching element pair Su, Sv, Sw. FIG. 6 is an equivalent circuit diagram showing the relationship between the capacitor CC and the motor 40. As shown in FIG. In FIG. 5, for each of the switching element pairs Su, Sv, Sw, the switching elements u1, v1, w1 connected to the positive power supply line side and the switching elements u2, v2, w2 connected to the negative power supply line side Is schematically shown as a switch. When switching elements u1, v2 and w2 are turned on among these switching elements, current Iinv of the power supply line flows from the U-phase winding of motor 40 to the V-phase and W-phase windings. This current is called an inverter current Iinv.

  The inverter current Iinv is approximately equal to the current (referred to as capacitor current) Ic supplied from the capacitor CC immediately after the switching element is turned on. Although the inverter current Iinv is finally supplied from the DC power supply 20, it is supplied from the DC power supply 20 in a state where the switching element is turned on and current starts to flow from the inductance L of the wiring and the internal impedance of the DC power supply 20. This is because the current (hereinafter referred to as battery current Ib) does not rise immediately and is delayed. Then, immediately after the switching element is turned on, it can be treated that there is no current from the DC power supply 20. The voltage Vinv, which is the voltage between the power supply lines and is detected by the voltage sensor 31, is at the same time equal to the voltage across the capacitor CC. Accordingly, as shown in the equivalent circuit of FIG. 6, the relationship between the capacitor CC and the load immediately after the switching element is turned on is, as shown in FIG. 6, the inverter Vin to the winding Lm of the motor 40 by the voltage Vinv of the capacitor CC. The current Iinv flows.

  Actually, the current Ic flowing through the capacitor CC immediately after turning on the switching element, the current Iinv flowing through the inverter 30, the current Ib flowing from the DC power supply 20, and the voltage Vinv between the power supply lines are measured in FIG. is there. As shown in the figure, immediately after the switching element is turned on, the inverter current Iinv and the capacitor current Ic are substantially the same, and as time passes, the battery current Ib from the DC power supply 20 may increase. I understand. Therefore, the inverter current Iinv can be treated as the capacitor current Ic in a short period immediately after the switching element is turned on, and in a period indicated by symbol DT in FIG. In the second embodiment, the inverter current Iinv is measured by the current sensor 33. However, as shown in FIG. 5, when the switching elements u1, v2, w2 are turned on, the inverter current Iinv is V Since it is equal to the sum of the currents iv and iw flowing in the phase winding and the W-phase winding, the inverter current Iinv may be determined using the detection results of the V-phase current sensor 41 and the W-phase current sensor 43.

  The period indicated by symbol DT in FIG. 7 is shown enlarged in FIG. The upper part of FIG. 8 shows the voltage Vinv at both ends of the capacitor CC, and the lower part shows the capacitor current Ic and the inverter current Iinv. The voltage Vinv across the capacitor CC and the capacitor current Ic show a transient response in the circuit shown in FIG. That is, when the switching element is turned on, the voltage Vinv across the capacitor CC decreases with time t, while the capacitor current Ic increases with time. The voltage Vinv and the capacitor current Ic follow the following equation (2). In the equation (2), Vinv (0) is a voltage at time t = 0, and in the present embodiment, the voltage is 12 V equal to the output voltage of the DC power supply 20. Further, a symbol C is a capacity of the capacitor CC, and Rc is a resistance value of the capacitor CC.

  Therefore, the voltages Vinv (t1) and Vinv (t2) across the capacitor CC at the first time t1 and the second time t2 and the capacitor currents Ic (t1) and Ic (t2) are measured, Substituting the equation (2) gives simultaneous equations for the variables Rc and C. As already described, since capacitor current Ic can be approximated by inverter current Iinv in period DT, inverter current Iinv (t1) and Iinv at first and second times t1 and t2 can be substituted for capacitor current Ic. The following equations (3) and (4) are for solving simultaneous equations using (t2) and solving for the resistance value Rc and the capacitance C of the capacitor CC.

  Therefore, if the above equations (3) and (4) are stored in advance, if the voltage Vinv across the capacitor CC at the first and second times t1 and t2 and the inverter current Iinv are measured, the capacitance C of the capacitor CC And the resistance value Rc can be known.

  Therefore, next, processing performed by the power conversion control device 50 in the power conversion device 10 according to the second embodiment will be described. FIG. 9 is a flow chart for explaining the operation of the power conversion control device 50, particularly the capacity output unit 52. In the second embodiment, as in the power converter of the first embodiment, the inductance calculation process shown in FIG. 3 is executed, but in the process of step S135 of FIG. 3, ie, when specifying the capacitance C of the capacitor CC, Instead of reading out the capacitance C of the capacitor CC stored in advance, the capacitance C is calculated using an inverter current or the like. This process will be described.

  The power conversion control device 50 of the second embodiment executes the process shown in FIG. 3 as in the first embodiment, and in the process of identifying the capacity of the capacitor in step S135, the capacity of the capacitor shown in FIG. Execute the resistance value calculation processing routine. When this process is started, first, energization of the three-phase winding of the motor 40 is started (step S200), and a process of measuring the voltage Vinv (t1) and the inverter current Iinv (t1) at the first time t1 is performed. Perform (step S210). The first time t1 is an elapsed time from the start of energization of the three-phase winding, and is any timing within the period DT shown in FIG. Here, it is 20 μsec.

  Subsequently, a process of measuring the voltage Vinv (t2) and the inverter current Iinv (t2) at the second time t2 is performed (step S220). The second time t1 is an elapsed time from the start of energization of the three-phase winding, and is an arbitrary timing within the period DT shown in FIG. 8 and after the first time t1. . Here, it is 40 μsec.

  The measurement results are put into the equations (3) and (4) described above to determine the capacitance C and the resistance value Rc of the capacitor CC (step S230). In particular, the capacitor capacitance C is specified for calculation of the inductance L Step S240). The identified capacitance C is used for the calculation of the inductance L shown in step S140 of FIG.

  Next, a process is performed to correct the output limit value IL based on the resistance value Rc of the capacitor CC obtained in step S230 (step S260). The output limit value IL is an upper limit value for limiting the target value I * of the power output from the inverter 30 to the motor 40 when the inductance L due to the wiring is larger than the threshold Lth, as described in the first embodiment. . In the second embodiment, the output limit value IL is corrected by the magnitude of the resistance value Rc of the capacitor CC. The correction is performed to correct the output limit value IL to a smaller value when the resistance value Rc is large. If the resistance value Rc of the capacitor CC is large, the fluctuation (ripple) of the voltage Vinv across the capacitor CC when the switching element pair Su, Sv, Sw of the inverter 30 is turned on / off becomes large. This is to further limit the target value I * if it is larger than Lth.

  After the above processing, the process exits to "END" and the operation routine ends. After the process shown in FIG. 9, the power conversion control device 50 executes the process after step S140 shown in FIG. As a result, calculation of the inductance L (step S140) and setting of the output limit value IL based on the magnitude thereof (step S160) are performed. In the calculation of the inductance L (step S140), the capacitance C of the capacitor CC specified in step S240 is used. Further, when setting the output limit value IL (step S160), the output limit value IL corrected in step S260 is used.

  According to the second embodiment described above, the capacitance L of the capacitor CC provided on the input side to which the inverter 30 is connected to the DC power supply 20 can be determined, and the inductance L of the wiring with the DC power supply 20 can be determined. . Therefore, in addition to the same operation and effect as the first embodiment, it is possible to obtain the advantage that the capacity C need not be stored in advance. Further, even if the capacitance C changes due to aging or the like, the inductance L can be obtained with high accuracy. Therefore, target value I * of power conversion device 10 can be appropriately limited based on the magnitude of inductance L. Further, since the capacitance C is obtained by calculation, it is not necessary to take measures to store different values for each device having a different capacitance of the capacitor CC.

  Further, in the second embodiment, the resistance value Rc of the capacitor CC is also determined, and the output limit value IL is thus corrected. Therefore, it is possible to take a more appropriate response to the aging of the capacitor CC and the like. it can.

D. Other embodiments:
As one of the other embodiments, it is possible to increase the switching frequency of the switching element pair Su, Sv, Sw as the inductance of the wiring between the DC power supply 20 and the inverter 30 is larger. The switching frequency is a frequency at which the voltage control unit 55 switches the current flowing to the switching element pair Su, Sv, Sw of the inverter 30. As in the first and second embodiments, when the motor 40 is driven, the U-phase, V-phase, and W-phase voltage is a pseudo sine wave of a frequency matched to the rotational speed of the rotor. As a result, PWM (pulse width modulation) is performed based on the switching control signal generated by comparing the carrier with the voltage command values Vu *, Vv *, Vw *. To increase the switching frequency when the wiring inductance is high corresponds to increasing the fundamental frequency of the carrier. It should be noted that in the inverter used in the case of a DC / DC converter or the like instead of the inverter for driving a motor or the like, pulse width modulation is performed according to the target value I * to be taken out without considering the rotational speed of the motor. It takes place. In this case, the switching frequency of this pulse width modulation may be increased or decreased according to the inductance L. As in the case of limiting the target value I * of the power conversion device 10 by adjusting the switching frequency of the pulse width modulation, the power conversion by the power conversion device 10 can be appropriately performed even in a device having different wiring inductance. it can. If the switching frequency is to be changed, modulation methods other than PWM such as PAM may be used.

  In the first embodiment and the above embodiment, it is not determined whether the inductance L of the wiring is higher than the threshold Lth, and a map or lookup table in which the inductance L is associated with the correction coefficient is prepared and calculated. The target value I * may be corrected by obtaining a correction coefficient corresponding to the inductance L. Moreover, in order to limit the size of the power conversion of the power conversion device 10, the upper limit value is not set for the control amount (for example, Vd * or Vq *) in each part shown in FIG. 2 instead of the target value I *. You may take measures such as

  Further, when the resistance value Rc of the capacitor CC is high, the switching frequency may be corrected instead of correcting the output limit value IL of the target value I * of the power conversion of the power conversion device 10. If the resistance value Rc is high, the switching frequency may be corrected to be high.

  In the equations (3) and (4), the capacitor current Ic flowing through the capacitor CC is approximated using the inverter current Iinv, but a sensor for directly measuring the capacitor current Ic is provided, and the output is used to The resistance value Rc may be determined. Alternatively, the capacitor current Ic may be estimated by another method and used. In those cases, the first and second times t1 and t2 do not have to be within the period DT under which it is assumed that the approximation holds. In addition, including the case of using the inverter current Iinv, the measurement may be performed at three or more timings such as the third time t3 other than the first and second times to improve the calculation accuracy.

  Although some embodiments of the present invention have been described above, the present invention is not limited to these embodiments and, of course, can be implemented in various aspects. For example, it can implement also as a power converter which drives apparatus other than an electric motor. Moreover, it can implement also as a method of estimating the inductance of the wiring between a power converter device and DC power supply. Alternatively, if the combination of the DC power supply and the power conversion device is different, or the wiring cable is different from the set product, and the estimated wiring inductance L differs from the design value, a warning such as this is also used. It is possible. In each of the above embodiments, the description has been made centering on the device that performs power conversion, but the configuration as the inductance estimation device can also be read. Furthermore, embodiments as a power conversion method and an inductance estimation method can be read together.

DESCRIPTION OF SYMBOLS 10 ... Power converter, 20 ... DC power supply, 30 ... Inverter, 31 ... Voltage sensor, 33 ... Current sensor, 40 ... Electric motor, 41 ... V phase current sensor, 43 ... W phase current sensor, 50 ... Power conversion control apparatus, 51: inductance estimation unit, 52: capacitance output unit, 55: voltage control unit, 61: target value limiting unit, 62: dq axis conversion unit, 64: voltage conversion unit, 66: coordinate inverse conversion unit, 67: coordinate conversion unit , CC ... capacitor

Claims (11)

A power converter (10) connected to a DC power supply (20) to perform power conversion,
A capacitor (CC) connected between power supply lines on the input side connected to the DC power supply;
A voltage detection unit (31) that detects a voltage across the capacitor;
An inductance estimation unit (51) for estimating an inductance between the DC power supply and the capacitor from the detected voltage across the terminals;
Power conversion units (30, 55) connected to the power supply line, performing power conversion in consideration of the magnitude of the estimated inductance, and outputting power;
Power converter equipped with.   The power conversion unit, when the estimated inductance is larger than a predetermined threshold, limits the output of the power to be converted, compared to the case where the estimated inductance is equal to or less than a predetermined threshold. Power converter as described.   When the estimated inductance is larger than a predetermined threshold value, the power conversion unit raises the switching frequency at the time of the power conversion as compared with the case where the estimated inductance is equal to or less than the predetermined threshold value. Power converter as described. The power converter according to any one of claims 1 to 3, wherein
And a capacitance output unit (52) for outputting the capacitance of the capacitor.
The inductance estimation unit
The period of the oscillation of the detected voltage is detected from the detection result of the voltage detection unit when the current flowing to the power conversion unit is suddenly reduced.
A power conversion device, which calculates the inductance from the capacitance of the output capacitor and the oscillation period of the detected voltage.   The power conversion device according to claim 4, wherein the capacitance output unit stores the capacitance of the capacitor measured in advance, and outputs the stored capacitance to the inductance estimation unit. The power converter according to claim 4, wherein
The capacitance output unit is
Detecting a current flowing in the power converter;
In a period (DT) which is a period after the power conversion unit starts energization from a state where the voltage of the power supply line is not fluctuating, and it can be approximated that the detected current is a current flowing in the capacitor A power conversion device, which calculates the capacitance of a capacitor to be output to the inductance estimation unit from the detected current and the detected voltage.   The power conversion device according to claim 6, wherein the capacitance output unit calculates the resistance value of the capacitor together with the capacitance of the capacitor from the detected current and the detected voltage. When the calculated resistance value of the capacitor is larger than a predetermined threshold value, the output of the power to be converted is further restricted compared to the case where the calculated resistance value is less than or equal to the predetermined threshold value. The power converter according to 7.   When the calculated resistance value of the capacitor is larger than a predetermined threshold value, the switching frequency at the time of the power conversion is increased compared to the case where the calculated resistance value is equal to or less than the predetermined threshold value. Power converter as described. A power conversion method connected to a DC power supply to perform power conversion, comprising:
The voltage across the capacitor connected between the power lines on the input side connected to the DC power source is detected (step S110).
The inductance between the DC power supply and the capacitor is estimated from the detected voltage across the terminals (step S140).
The power conversion switching element (Su, Sv, Sw) connected to the power supply line is controlled on the downstream side of the capacitor to perform power conversion in consideration of the estimated inductance (steps S150 and S160). )
Power conversion method. An inductance estimation device (10) for estimating the inductance of a wire between a power conversion device and a DC power supply, comprising:
A capacitance output unit (52) for outputting a capacitance of a capacitor connected between power supply lines on the input side of the power conversion device powered by the DC power supply;
A voltage detection unit (31) that detects a voltage across the capacitor;
The period of the oscillation of the detected voltage is detected from the detection result of the voltage detection unit when the current flowing in the power conversion unit for performing power conversion in the power conversion device is rapidly reduced, and the output is performed. An inductance estimation device comprising: an inductance estimation unit (51) that calculates the inductance from a capacitance of a capacitor and a period of vibration of a voltage detected by the voltage detection unit.

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