TWI452808B - A method and apparatus for applying a DC side injection compensation to an eighteen pulse wave AC / DC converter - Google Patents

Description

Method and device for applying DC side injection compensation to eighteen pulse wave AC/DC converter

The invention relates to the fields of power electronics, AC/DC rectification technology, automatic control, etc., and mainly relates to a method and a device for a high-power DC voltage output of an eight-pulse AC/DC converter, which are characterized by A three-phase converter is added to the pre-phase transformer pre-stage, and the control method is planned in a digital microprocessor to generate a compensation current command, and the switch width switching signal is generated by the pulse width modulation, thereby controlling the power switch driving circuit to drive the three-phase change. The power switch of the current generator generates a compensation current and is injected into the DC output terminals of three parallel six-pulse converters, thereby reducing the total harmonic distortion of the three-phase input power supply and improving the high-performance power factor of the three-phase input power supply. Method and apparatus for an AC/DC converter.

In the industrial field, in order to obtain a high-power DC power supply, a three-phase bridge rectifier is often used to rectify the three-phase voltage source, but for the power supply terminal, due to the three-phase bridge rectifier The non-linear load phenomenon caused by the conduction switching of the device causes serious current distortion at the power supply end, and has a very high harmonic content. These harmonics will cause the power quality to be low, and the life of the equipment on the power system is reduced, and the power is protected. Mistakes, etc., which are particularly serious for instruments that are increasingly demanding precision in recent years.

In order to improve this problem, Schaeffer, J proposed in 1965 to use a multi-group three-phase bridge rectifier with a three-phase power supply of a specific phase, and then use a phase-to-phase transformer for parallel supply to a DC load. In this way, a multi-pulse current waveform can be synthesized at the power supply end, and the output chopping voltage is also reduced, such as a twelve-pulse rectifier in which two sets of three-phase bridge rectifiers are connected in parallel, and three groups are connected in parallel to eighteen pulses. Wave rectifiers, etc., and so on. The method of generating multiple sets of three-phase power supplies with different phases is generally obtained by using a phase shifting transformer. When the rectifiers of the respective groups are connected in parallel, the instantaneous output voltages of the rectifiers are different due to different phase relationships, and cannot be directly connected in parallel. The transformer is designed to withstand the instantaneous unbalanced voltage and share the load current with its tight coupling characteristics. The traditional eight-wave pulse converter is a three-phase three-phase power supply with phase difference of 20 degrees by a phase-shifting transformer, and each is converted into a direct current through a group of six-pulse converters. The three groups of six-pulse converters can be directly independent. The power supply or the eight-phase pulse output DC voltage supply is connected in parallel through the three-phase phase transformer, and both of them can achieve the effect of eighteen pulses at the power supply end.

After the above basic multi-pulse parallel connection method, there are many methods for improving the input current harmonic distortion, such as S. Choi, P. Enjeti and Bang Sup Lee proposed in 1997, "suitable for high-power AC motors. New 24-pulse diode rectifier system for utility interface of high-power AC motor drives and B.Singh and S.Gairola The "Pulse Doubling in 18-pulse AC-DC Converters", which was proposed in 2007, uses a multi-tap phase-to-phase transformer and then connects the upper diodes in series. The number of current pulse waves at the power supply terminal is increased, and the total harmonic distortion of the current at the power supply end is reduced. However, the above method can only increase the pulse wave number, and still cannot achieve an ideal sine wave current at the power supply terminal. A new active interphase reactor for 12-pulse rectifiers provides clean power, which was proposed by S. Choi, P. Enjeti and Hoag-Hee Lee in 1996. Utility interface)", the active phase-to-phase transformer is applied to the 12-pulse converter system, and a triangular-wave current is injected into the secondary side of the active phase-to-phase transformer by a low-capacity (2.26% rated output power) converter. The harmonics of the power supply terminal can be effectively improved, and the power supply terminal current can maintain the low harmonic distortion current of the twelve pulse wave when the converter is damaged.

However, in applications where higher power requirements are considered, the harmonic specifications are more stringent. Therefore, the present invention proposes a DC side injection compensation strategy applied to an eighteen pulse converter system, using a set of low-capacity three-phase. The converter (2.39% rated output power) directly injects the compensation current into the junction between the output of the three sets of six-pulse bridge rectifiers and the phase transformer, without the need to increase the windings on the phase transformer, which can effectively improve The total amount of harmonic distortion of the power supply current. The three-phase converter matched by the injection compensation strategy proposed by the invention improves the traditional active filter placed on the AC side, which requires more cost and requires a larger capacity, and can simultaneously compensate the three-phase power supply current. Maintaining three-phase balance, and when the three-phase converter fails, it can still maintain the low harmonic distortion current of eighteen pulses at the power supply terminal. In response to the world's emphasis on energy conservation, the present invention is well suited for retrofitting an eighteen pulse converter system originally using an AC side active filter to the inventive circuit and using a DC side injection compensation strategy for energy saving purposes.

The object of the present invention is to provide a DC power supply with lower harmonic distortion, high efficiency, and suitable for higher power applications. For this reason, the present invention applies a current control type three-phase converter with an injection strategy to eighteen pulse wave communication. /DC converter, by injecting compensation current into the DC output of three parallel six-pulse rectifiers, so that the input current of the power supply terminal is improved from the original eighteen pulse wave to a sine wave with a low total harmonic distortion amount. The required three-phase converter device capacity is lower than that of the active filter applied to the AC side of the multi-pulse AC/DC converter, and the improvement of the single-phase current is compensated for the three-phase unbalance. The problem is that, when the three-phase converter fails, the current of the eight-pulse low harmonic distortion can be maintained at the power supply end. The present invention is very suitable for the eight-pulse wave originally using the AC-side active filter. Converter, and the case for energy saving purposes.

In order to achieve the above object, the present invention mainly utilizes a voltage/current sensing circuit in a control driving device to detect a voltage/current signal in a system, and returns a voltage/current signal to a digital microprocessor in a control driving device. Generate a command to inject current, and plan compensation current control loop on the digital microprocessor. The output signal will drive the power switch of the converter through the power switch drive circuit to instantly adjust the actual amplitude of the injection current to follow the compensation current. Command value. The input current of the power supply terminal is improved from the original eighteen pulse wave to a sinusoidal wave with extremely low total harmonic distortion to provide high efficiency, low input current harmonic distortion and AC/DC converter suitable for high power applications. .

The control driving device of the invention is mainly realized by a digital method, and only the current sensing circuit, the voltage sensing circuit and the power switch driving circuit are composed of analog components such as a resistor, a capacitor, an operational amplifier, an optical coupling isolation driver and the like. The current and voltage sensing circuit is mainly to convert the actual current and voltage into an analogy in a digital microprocessor. The range of signals that the digital module can accept. The digital method is implemented by a digital microprocessor, such as a digital signal processor (DSP) or a single-chip CPU. The programming program performs related settings, detection, calculation, and generation. The driving signal is driven, and the power switch of the converter is driven by the power switch driving circuit to complete the control driving device of the present invention.

The power switch and high-power solid-state electronic switch used in the converter of the present invention are controlled by high-power semiconductor components such as gate insulated bipolar transistor (IGBT) and bipolar junction transistor (BJT). composition.

The DC side injection compensation strategy disclosed by the present invention is applied to the main hardware circuit device 101 of the eighteen pulse wave AC/DC converter. As shown in FIG. 1, the system includes a three-phase input phase power source 102, and three sets of three-phase power sources are generated. A phase shift transformer 104 having a phase difference of 20 degrees, three sets of three-phase bridge rectifiers 105, an interphase transformer 106 required for parallel connection of three sets of three-phase bridge rectifiers, a three-phase converter 107 for generating a compensation current, and an output A DC load 108 and a control drive 109 for generating an injection current command and driving a converter power switch. The present invention returns a signal to the digital microprocessor 204 by the current sensing circuit 202, constructs a current command to be compensated in a table lookup manner, and uses the voltage sensing circuit 201 and the zero point detecting circuit 203 to connect the power phase reference point. It is sent to the digital microprocessor 204, and the current command phase is adjusted by using the reference point. After comparing with the actual feedback injection current, the gate insulating bipolar transistor 401 is driven to inject a compensation current into the three sets of three-phase bridge rectifier 105. The DC output and the front end of the phase transformer 106 can effectively improve the total harmonic distortion of the power supply current and improve its power factor. Efficiency, and advantages Another three-phase converter 107 requires a relatively small capacity, and the compensated power supply current can be balanced in three phases and is similar to a sine wave.

In order to achieve the above object, the eight-phase pulse transformer 103 needs to generate three sets of three-phase power sources each having a phase difference of 20° from the phase shift transformer 104, and can generate phase shifts of three sets of three-phase power sources each having a phase difference of 20 degrees. The transformer can be realized by various wiring methods. The phase shifting transformer 104 used in the practice of the present invention is composed of a set of delta/delta connected three-phase transformers 110 and two sets of delta/polygon connected three-phase transformers 111, wherein delta/delta The three-phase transformer 110 is used to generate a three-phase power supply of 0° group, and the other two sets of delta/polygon three-phase transformers 111 generate two sets of three-phase power sources with phase differences of ±20° by using different terminals.

According to the theory described in Chapter 8 of the book "Power Electronic Converter Harmonics-Multipulse Methods for Clean Power" by Derek.A.Paice, it can be seen that in the eighteen pulse converter system, the secondary side of the phase shifting transformer The 6 n ±1 harmonics other than 18 n ±1 in the output current are suppressed by the phase shift transformer and are synthesized as the power supply current, but the 18 n ±1 harmonics are Stacking each other and becoming more and more obvious in the power supply current, so when doing FFT analysis on the power supply current of the eighteen pulse converter system, it will see that it contains a large number of 18 n ± 1 harmonics and reduces the total harmonic distortion percentage. Therefore, if the 18 n ± 1 harmonic can be suppressed on the secondary side of the phase shifting transformer, the current generated by the current induced back to the primary side will naturally not contain 18 n ± 1 harmonics. It will only retain the fundamental wave and approximate the sine. For this reason, we must suppress the 18 n ± 1 harmonic contained in the original secondary current. To find such a waveform that does not contain any 18 n ± 1 harmonics, the amount of change in the injected current in the secondary side current of the phase shift transformer should have the following characteristics: 18 of this change waveform The size of the n ±1 harmonic component must be the same as the 18 n ± 1 harmonic component of the original waveform before compensation, and the phase angle of each corresponding harmonic component must be opposite, so that the harmonic component can be suppressed; The 6 n ± 1 harmonic component of this change waveform except for the 18 n ± 1 harmonic must be such that the change waveform is the same as the original waveform and remains at zero in the diode non-conducting section. From the above limitation, we find two suitable change waveforms. The 18 n ± 1 harmonic components of the two waveforms are the same in size as the original waveform, while the phase angle is just the opposite, the original waveform and the amount of change. After the two waveforms are added, the compensated secondary current waveform is obtained. After the compensated waveform is analyzed by FFT, the waveform does not contain any 18 n ± 1 harmonic components, indicating that it is 18 n ±1. The subharmonic component has been suppressed, and as a result, the power supply current after being transferred to the primary side via the phase shifting transformer and synthesized is a sine wave containing only the fundamental component. After the compensation, the secondary side current waveform of the transformer is sin0°~sin30° in the positive half cycle, and sin140°~sin180° in the falling edge; the negative half cycle is the reverse waveform of the positive half cycle, and the waveform does not contain any 18 n ± 1st harmonic. In order to make the secondary side currents i ₁ ~ i ₉ of the phase shift transformer become this waveform, we inject the compensation currents i _{x 1} , i _{x 2} and i _{x 3} into the DC output current of the three sets of bridge rectifiers, and the following will start to derive the compensation current. Waveform representation. Please refer to Figure 3 for the diode conduction function S ₁ corresponding to the input current i ₁ of the three-phase bridge rectifier with the power supply v _ab zero as the reference zero point. The waveform can be expanded by Fourier series as shown in equation (1). I corresponding to the other diode conduction function of the S ₂ ~ i _{9 2} ~ S ₉ S _1, respectively, may be displaced by -120 °, + 120 °, -20 °, -140 °, + 100 °, -40 °, -160 ° and +80 ° to obtain. Define the following two matrices first After that, the input current of the three-phase bridge rectifier 105 can be expressed by the formula (4). Referring to Figure 1, the phase-to-phase transformer wiring method, the relationship between the load current and the three rectifier output currents is as shown in equation (5): I _d = i _{d 1} + i _{d 2} + i _{d 3} (5) where I _d is ten The output currents of the eight-pulse converter 103, i _{d 1} , i _{d 2} and i _{d 3} are the output currents of the three-phase bridge rectifier 105, which are known from the concept of current sharing i _{d 1} , i _{d 2} and i _{d 3} Values are After the compensation currents i _{x 1} , i _{x 2} and i _{x 3 are} injected, the relationship between the three sets of rectifier output currents i _{d 1} , i _{d 2} and i _{d 3} and the compensation current is as follows: (6) and (7) And (8) By substituting equations (6), (7), and (8) into equation (4), the following equation can be rearranged. According to the relationship between i ₁ ~ i ₉ and the injection compensation current in equation (9), it can be inferred that if i ₁ ~ i _{9 are to} be compensated waveforms, the compensation currents i _{x 1} , i _{x 2} and i _{x 3 to} be injected are injected. Waveform, the waveform of which can be expressed by the following equation Where n =1,2,3; k =0,1,2,..., but since the waveform described in the above formula contains a DC component, and the three-phase converter has no neutral relationship, the waveform described in the above equation cannot be generated. Therefore, we replace it with an approximate sawtooth wave that does not contain a DC component, and the approximate sawtooth wave is expressed as shown in equation (11). Where n =1, 2, 3; k =0, 1, 2, .... In the digital microprocessor 204, in order to increase the speed of the processor operation, the current command is not calculated by the above equation, but the waveform is constructed in a built-in manner, and the amplitude is amplified/reduced according to the feedback load current value. Then, the actual command waveform is restored according to the controllable counter in the digital microprocessor 204.

The invention uses the control driving device 109 to generate the injection current command waveform as in the formula (11), and drives the gate insulated bipolar transistor 401 of the frequency converter to inject the compensation current to achieve the purpose of improving the total harmonic distortion of the power terminal. As shown in FIG. 3, the control driving device 109 is mainly implemented in a digital manner. Only the voltage sensing circuit 201, the current sensing circuit 202, and the power switch driving circuit 205 are composed of analog components such as a resistor, a capacitor, an operational amplifier, and a diode. It is composed of an optically coupled isolator. When the system is in operation, the current sensing circuit 202 is used to convert the load current and the three compensation currents into a range of electrical signals acceptable to the analog/digital module of the digital microprocessor 204, and then the voltage sensing circuit 201 and the zero point detection are used. The circuit 203 converts the positive and negative half cycles of the power supply line-to-line voltage v _ab into a High/Low signal to the digital microprocessor 204. Please refer to FIG. 4A, FIG. 4B and FIG. 4C for the circuit diagram. The voltage/current to be feedback is first converted into a current source signal output through the voltage sensor 301 and the current sensor 302, and then the current source is passed through the operational amplifier 303. The required ratio adjusts the output signal amplitude and the DC level, and is supplied to the analog/digital module of the digital microprocessor 204 to receive the signal, wherein the voltage signal needs to pass through the pivot circuit 305 and the comparator in the zero detection circuit 203. 304 converts the positive/negative half cycle of the voltage into a High/Low signal and eliminates the noise interference, and provides the digital microprocessor 204 with a zero point judgment. The program planning and control block of the digital microprocessor is shown in Figure 6A and Figure 6B. After the load current I _{d is} feedback and the compensation current command is constructed by looking up the table, the phase zero obtained by the feedback voltage v _{ab is} used. The synchronous command waveform, as described in the injection current control loop 501, is compared with the actual injected compensation current after the feedback to generate a power switch control signal, and the current control loop 501 compares the compensation current command with the actual current. As a result, a switch control signal is sent to change whether the switches are turned on or not, and the compensation current is injected into the output of the three sets of three-phase bridge rectifiers 105.

The three-phase converter 107 of the present invention uses a full-bridge three-phase converter as shown in FIG. Let the three-phase input phase power supply 102 be represented by the formula (12) Where V _LL is the primary side line voltage of the phase shifting transformer 104. The output voltages v _{d 1} and v _{d 2 of the} three-phase bridge rectifier 105 can be obtained as in equations (13) and (14), respectively. Referring to FIG. 5, it can be seen that the voltage across the two output terminals of the three-phase converter 107 v _delta is the output voltage difference between the two sets of three-phase bridge rectifier 105, as shown in equation (15) v _delta = v _{d 1} - v _{d 2} (15) Using the equation (15), the RMS value V _delta between the two output terminals of the three-phase converter 107 can be obtained, as shown in equation (16). Where V _d is the voltage across the DC load. Then, if it is assumed that there is a virtual neutral point between the three output ends of the three-phase converter 107, the voltage effective value of the output point of the three-phase converter to the virtual neutral point can be obtained by using the line voltage phase-inversion voltage. , here the symbol is defined as V _wye Then, the output current effective value I _{x of} the three-phase current transformer 107 is obtained by the equation (10) as shown in the equation (18). Here, let P _o = V _d I _d =1 pu , and the capacity of the three-phase current transformer 107 used in the present invention can be obtained by the equations (17) and (18), as shown in the formula (19), VA = 3 × V _wye × I _x =0.0239 pu =2.39% P _o (19) From the equation (19), the three-phase converter 107 required for the present invention has a capacity compared to the active filter applied to the eighteen-wave transform. The device is smaller, which is a very important advantage in the case of high power requirements where the harmonic specification is more stringent.

The invention utilizes a three-phase converter 107 with a very small capacity, and the compensation current is injected at the DC output end of the three-phase bridge rectifier 105 and the front end of the phase transformer 106, so that the input current of the power terminal is from the original The eighteen pulse waveform is compensated into a sine wave waveform with a lower total harmonic distortion, and the three-phase current can be simultaneously compensated to maintain the three-phase balance, and when the three-phase converter 107 fails, the power supply terminal current can also be maintained. In the case of low current distortion of the original eighteen pulse, it is very suitable for high power applications.

101‧‧‧Main hardware circuit device

102‧‧‧Three-phase input phase power supply

103‧‧‧18 pulse converter

104‧‧‧ Phase shift transformer

105‧‧‧Three-phase bridge rectifier

106‧‧‧Interphase transformer

107‧‧‧Three-phase converter

108‧‧‧ Output DC load

109‧‧‧Control drive

110‧‧‧delta/delta connected to three-phase transformer

111‧‧‧delta/polygon connected to three-phase transformer

201‧‧‧ voltage sensing circuit

202‧‧‧ Current sensing circuit

203‧‧‧ Zero detection circuit

204‧‧‧Digital microprocessor

205‧‧‧Power switch drive circuit

301‧‧‧ voltage sensor

302‧‧‧ Current Sensor

303‧‧‧Operational Amplifier

304‧‧‧ Comparator

305‧‧‧ pivot circuit

401‧‧‧ gate insulated bipolar transistor

402‧‧‧ diode

403‧‧‧Inductors

404‧‧‧DC voltage source

501‧‧‧Injection current control loop

v _a , v _b , v _c ‧‧‧ three-phase power input phase voltage

i _a , i _b , i _c ‧‧‧ three-phase power input line current

i _{a 1} , i _{a 2} , i _{a 3} , i _{b 1} , i _{b 2} , i _{b 3} , i _{c 1} , i _{c 2} , i _{c 3} ‧‧‧ phase shifting transformer input current

Number of turns of N _P , N _L , N _S ‧‧‧ phase shifting transformers

i ₁ , i ₂ , i ₃ , i ₄ , i ₅ , i ₆ , i ₇ , i ₈ , i ₉ ‧‧‧3-phase bridge rectifier input current

v _{d 1} , v _{d 2} , v _{d 3} ‧‧‧Three-phase bridge rectifier output voltage

i _{d 1} , i _{d 2} , i _{d 3} ‧‧‧Three-phase bridge rectifier output current

i _{x 1} , i _{x 2} , i _{x 3} ‧‧‧ converter output current

I _d ‧‧‧DC load current

V _d ‧‧‧DC load voltage

V _dc ‧‧‧ converter input DC voltage

V _delta ‧‧‧Three-phase converters across the two output terminals

V _delta ‧‧‧ RMS effective value between two output terminals of a three-phase converter

S ₁ , S ₂ , S ₃ , S ₄ , S ₅ , S ₆ ‧‧‧ power switch

1 is a schematic diagram of an overall system architecture of the present invention; FIG. 2 is a schematic diagram of a diode switching function S _{1 of the} present invention, corresponding to a three-phase bridge rectifier input current i ₁ with reference to a power supply v _ab phase; Schematic diagram of the control driving device; FIG. 4A, FIG. 4B and FIG. 4C are schematic diagrams of the voltage/current sensing circuit and the zero point detecting circuit of the present invention; FIG. 5 is a schematic diagram of the three-phase converter according to the present invention; FIG. 6B is a program planning flow chart and a control block diagram of the digital microprocessor of the present invention;

101‧‧‧Main hardware circuit device

102‧‧‧Three-phase input phase power supply

103‧‧‧18 pulse converter

104‧‧‧ Phase shift transformer

105‧‧‧Three-phase bridge rectifier

106‧‧‧Interphase transformer

107‧‧‧Three-phase converter

108‧‧‧ Output DC load

109‧‧‧Control drive

110‧‧‧delta/delta connected to three-phase transformer

111‧‧‧delta/polygon connected to three-phase transformer

v _a , v _b , v _c ‧‧‧ three-phase power input phase voltage

i _a , i _b , i _c ‧‧‧ three-phase power input current

i _{a 1} , i _{a 2} , i _{a 3} , i _{b 1} , i _{b 2} , i _{b 3} , i _{c 1} , i _{c 2} , i _{c 3} ‧‧‧ phase shifting transformer input current

Number of turns of N _P , N _L , N _S ‧‧‧ phase shifting transformers

i ₁ , i ₂ , i ₃ , i ₄ , i ₅ , i ₆ , i ₇ , i ₈ , i ₉ ‧‧‧3-phase bridge rectifier input current

v _{d 1} , v _{d 2} , v _{d 3} ‧‧‧Three-phase bridge rectifier output voltage

i _{d 1} , i _{d 2} , i _{d 3} ‧‧‧Three-phase bridge rectifier output current

i _{x 1} , i _{x 2} , i _{x 3} ‧‧‧ three-phase converter output current

I _d ‧‧‧DC load current

V _d ‧‧‧DC load voltage

Claims (6)

A device for an AC/DC converter for high-power DC voltage output, comprising: a phase-shift transformer: providing three sets of three-phase power voltages with phase differences of 20°; and a three-phase bridge rectifier: by power semiconductor components The three-phase AC voltage is rectified into a pulsating DC voltage; an interphase transformer: three windings are used to withstand the instantaneous output voltage difference when three sets of rectifiers are connected in parallel; and a three-phase converter: composed of a high-power solid-state electronic switch The converter device and the three inductors for converting the DC voltage source into a three-phase AC current conversion function are used for generating an injection current; and a control driving device includes a voltage sensing circuit, a zero point detecting circuit, and four The current sensing circuit, a digital microprocessor and a power switch driving circuit are used to generate a command for injecting current, and output a converter power switch driving signal; a constant current load: a load in which the input power source is a DC voltage. The apparatus for generating an AC/DC converter for high-power DC voltage output according to the first aspect of the patent application, wherein the phase shift transformer for generating three sets of phase-to-phase differential currents of 20° can be any wiring type. Phase shift transformer composition. The device for controlling an AC/DC converter for high-power DC voltage output according to the first aspect of the patent application, wherein the voltage sensing circuit, the current sensing circuit and the zero point detecting circuit of the control driving device are voltage/current The sensor, the operational amplifier and the comparator are configured to convert the voltage and current in the driving device into low-voltage, low-current electrical signals, and then adjust the amplitude to an appropriate value to provide a basis for controlling the driving output signal of the driving device. The apparatus for using an AC/DC converter for high-power DC voltage output according to the first aspect of the patent application, wherein the control driving device obtains a voltage/current signal, and then generates an injection current command after the operation of the control driving device to generate a switch. The drive signal is used to drive the high-power solid-state electronic switch of the converter, so that the output current of the converter has a controllable function to improve the total harmonic distortion of the current at the power supply end. The apparatus for using an AC/DC converter for high-power DC voltage output according to the first aspect of the patent application, wherein the power-on relationship of the converter is a high-power solid-state electronic switch, and the electronic opening relationship is performed by the power semiconductor component. composition. The current waveform injected in the DC side injection compensation strategy of the device for high-power DC voltage output AC/DC converter as described in claim 1 is not required to be 18 n ± It is inferred from the relationship between the secondary side output current of the transformer and the injection current of the first harmonic component that the optimum waveform equation of the injected current waveform is Approximate waveform equation