Multi-mode frequency conversion control method of three-phase four-wire system Vienna rectifier

Abstract

The invention discloses a multi-mode frequency conversion control method of a three-phase four-wire system Vienna rectifier. A carrier reset pulse generation unit and a modulation unit are included. The carrier reset pulse generation unit comprises an AND gate, a first integrator and a first RS trigger; the modulation unit comprises an OR gate, a second integrator and a second RS trigger. The output of the OR gate is used as the input of the first input port of the OR gate. According to the invention, CCM-CRM-DCM multi-mode frequency conversion control is realized by using the logic circuit, and the input current quality during light load is improved; gain compensation is added to modulation signal voltage in a control loop, so that control loop gain change caused by frequency conversion control is offset, uniform control of average current in different working modes is realized, zero-crossing distortion of current in a DCM mode is reduced, oscillation and impact caused by control switching of different modes are avoided, and the reliability of the control loop is improved. The current quality is further improved, and the performance of the rectifier is improved.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a control method for a three-phase four-wire Vienna rectifier. Background Art

[0002] The Vienna rectifier generally adopts output voltage and input current control, the purpose is to stabilize the output DC voltage and make the input current of the Vienna rectifier sinusoidal. Near the zero-crossing point of the input voltage, since the inductor current rise rate of the Vienna rectifier is very small, it is difficult for the inductor current to track the upper reference current. In addition, when the load is very light, the inductor current works in a discontinuous state, the current loop gain and bandwidth of the converter are very small, and it is more difficult for the inductor current to track the upper reference current, so that the input current is distorted when the input voltage passes through zero, especially in applications with high grid frequency, the input current zero-crossing distortion is more obvious. Under light load conditions, due to the phase difference between the reference voltage and the input current, the output current zero-crossing distortion is generated, resulting in an increase in input harmonics and the degradation of other electrical performance parameters, affecting the output quality of the rectifier. At the same time, the current Vienna rectifier control methods are all oriented to a single mode. Under the same set of control methods, it is impossible to simultaneously meet the operation of multiple working modes. Therefore, it is very important to seek a control method that can realize the multi-mode operation of the Vienna rectifier. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide a multi-mode frequency conversion control method for a three-phase four-wire Vienna rectifier, so as to solve the technical problem that when the Vienna rectifier is under average current control, the power factor at the input end decreases due to the appearance of the discontinuous mode of the inductor current when it is lightly loaded or near the zero point, thereby affecting the current quality, and to solve the problem that a set of control methods cannot be universally applied to multiple working modes such as CCM / CRM / DCM.

[0004] The multi-mode frequency conversion control method of the three-phase four-wire Vienna rectifier of the present invention comprises a carrier reset pulse generating unit and a modulation unit;

[0005] The carrier reset pulse generating unit comprises an AND gate, a first integrator and a first RS trigger; the maximum switching frequency of the switch tube is used as the first input of the first integrator, and when the output of the first integrator is ≥1, the output of the first integrator is used as the second input of the first integrator; the output of the first integrator is used as the input of the S port of the first RS trigger, and the output of the AND gate is used as the input of the R port of the first RS trigger; the input logic of the first input port of the AND gate is always 1, and the second input port of the AND gate takes the output of the Q port of the first RS trigger as input;

[0006] The modulation unit includes an OR gate, a second integrator and a second RS trigger, the output of the AND gate is used as the input of the first input port of the OR gate; the minimum switching frequency of the switch tube is used as the first input of the second integrator, and the output of the OR gate is used as the second input of the second integrator; when the output of the second integrator is ≥1, the output of the second integrator is used as the second input of the OR gate, and the output of the OR gate is subtracted from the modulation signal voltage of the phase where the controlled switch tube is located as the input of the R port of the second RS trigger; the output of the OR gate is used as the input of the S port of the second RS trigger; the Q port of the second RS trigger outputs a control signal to the controlled switch tube;

[0007] In the CCM working mode, the output logic of the AND gate to the OR gate is always 0, the second integrator is not reset, and the output frequency of the second integrator is a triangular carrier with the minimum switching frequency, that is, in the CCM mode, the operating frequency of the control switch tube is always the minimum switching frequency;

[0008] In the CRM working mode, when the inductor current of the phase where the controlled switch tube is located gradually decreases to the moment when it passes through 0, the logic output of the AND gate to the OR gate is 1, so that the OR gate outputs a high-level signal to reset the second integrator to change the frequency of the output triangular carrier, and at this moment, the controlled switch tube is turned on to make the inductor current rise again to maintain the CRM working mode;

[0009] In the DCM working mode, when the inductor finishes discharging and the inductor current is equal to zero, the falling edge of the first integrator output has not yet appeared, that is, the output logic of the first RS trigger has not yet been set to 1, and the output logic of the AND gate is 0. When the falling edge of the first integrator output arrives, the output logic of the AND gate is 1, that is, the switching frequency is maintained at the maximum switching frequency in the DCM mode.

[0010] Furthermore, the modulation signal voltage is composed of the product of the carrier amplitude, the working time of the controlled switch tube and the power factor correction control output based on the input impedance;

[0011] The carrier amplitude is obtained in real time by performing low-pass filtering on the triangular carrier output by the second integrator and then doubling it;

[0012] The working time of the controlled switch tube is obtained by judging whether the inductor current of the phase where the controlled switch tube is located is greater than zero and performing low-pass filtering.

[0013] Further, the power factor correction control output based on the input impedance is obtained as follows:

[0014] The rated output voltage and actual output voltage of the Vienna rectifier are subtracted and then proportional-integrated to obtain the output voltage control signal voltage. The voltages of the two split capacitors in the Vienna rectifier are subtracted and proportionally amplified to obtain the equalizing control output. The equalizing control output is added to the inductor current of the phase where the controlled switch tube is located, and the absolute value is taken, which is then divided by the output voltage control signal voltage, and then limited to obtain the power factor correction control output based on the input impedance.

[0015] Beneficial effects of the present invention:

[0016] 1. The multi-mode frequency conversion control method of the three-phase four-wire Vienna rectifier of the present invention is based on the design of the input side inductance and the frequency conversion boundary, and uses a logic circuit to realize CCM-CRM-DCM multi-mode frequency conversion control, thereby improving the input current quality under light load.

[0017] 2. The multi-mode frequency conversion control method of the three-phase four-wire Vienna rectifier of the present invention offsets the change in control loop gain caused by frequency conversion control by adding gain compensation to the modulation signal voltage in the control loop, realizes unified control of average current in different working modes, reduces the zero-crossing distortion of current in DCM mode, avoids the oscillation and impact caused by switching of different mode controls, further improves the current quality, and improves the rectifier performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The schematic diagram of the CCM-CRM-DCM multi-mode frequency conversion control method for a three-phase four-wire Vienna rectifier; where N is the midpoint of the three-phase input of the power grid, v a 、v b 、v c They are abc three-phase input voltage, L a , L b , L c They are abc three-phase input inductance, i La 、i Lb 、i Lc abc are the three-phase input inductor currents, D1-D6 are diodes, Q1-Q6 are switch tubes, C1 and C2 are split capacitors, V p 、V n are the voltages of split capacitors C1 and C2, R load is the load resistance, V out is the output voltage, V cdiff is the output of the voltage-balanced control, V ref is the rated output voltage, V loop is the output voltage control signal voltage, V cona a is the three-phase modulation signal voltage, f max 、f minare the maximum switching frequency and the minimum switching frequency, Pulse a is the a-phase carrier reset pulse, Ramp a is the a-phase carrier, V ma is the carrier amplitude of phase a, D a is the working time of the a-phase switch tube, PWM a 、PWM b 、PWM c They are respectively the abc phase switch control signals.

[0019] Figure 2 is the A-phase inductor current i when the rectifier load is 10% La , the inductor current of phase A after filtering and carrier waveform diagram;

[0020] Figure 3 is the inductor current i when the rectifier load is 10% L , the inductor current after filtering Input voltage in , output voltage V out and the split capacitor voltage V p 、V n Waveform graph. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0022] like Figure 1 As shown, the multi-mode frequency conversion control method of the three-phase four-wire Vienna rectifier in this embodiment includes a carrier reset pulse generating unit and a modulation unit.

[0023] The carrier reset pulse generating unit includes an AND gate, a first integrator and a first RS trigger; the maximum switching frequency of the switch tube is used as the first input of the first integrator, and when the output of the first integrator is ≥1, the output of the first integrator is used as the second input of the first integrator; the output of the first integrator is used as the input of the S port of the first RS trigger, and the output of the AND gate is used as the input of the R port of the first RS trigger; the input logic of the first input port of the AND gate is always 1, and the second input port of the AND gate uses the output of the Q port of the first RS trigger as input.

[0024] The modulation unit includes an OR gate, a second integrator and a second RS trigger, the output of the AND gate is used as the input of the first input port of the OR gate; the minimum switching frequency of the switch tube is used as the first input of the second integrator, and the output of the OR gate is used as the second input of the second integrator; when the output of the second integrator is ≥1, the output of the second integrator is used as the second input of the OR gate, the output of the OR gate and the modulation signal voltage of the phase where the controlled switch tube is located are subtracted as the input of the R port of the second RS trigger, and the output of the OR gate is used as the input of the S port of the second RS trigger; the Q port of the second RS trigger outputs a control signal to the controlled switch tube.

[0025] The switch control method of the three-phase abc of the three-phase four-wire Vienna rectifier is the same. The following takes phase a as an example:

[0026] In the continuous conduction mode (CCM), the inductor current i La It is always greater than 0, and the output logic of the AND gate to the OR gate is always 0, that is, the carrier reset pulse Pulse output by the AND gate a It is always low, the second integrator is not reset, and the output frequency of the second integrator is a triangular carrier with the minimum switching frequency, that is, in CCM mode, the operating frequency of the control switch tube is always the minimum switching frequency;

[0027] In the critical conduction mode (CRM), when the inductor current of the phase where the controlled switch is located gradually decreases to the moment when it passes through zero (i.e., i La Gradually decreases to the moment when it passes through 0), at this time, the output of the AND gate is judged to be high level. Since the R port of the first RS flip-flop is low at the previous moment, the Q end is high at this time, and the output of the AND gate is high. This output sets the R end high again, so that the Q end is reset to low at the next moment. Therefore, the output of the AND gate is high at i La The moment it reaches 0 is represented by a very short high-level pulse signal Pulse a , that is, the logic of the AND gate output to the OR gate is 1. The pulse signal causes the OR gate to output a high-level signal to reset the second integrator to change the frequency of the triangular carrier output by the second integrator, and at this moment, the controlled switch tube is turned on to make the inductor current rise again to maintain the CRM working mode. The switching frequency in CRM mode must be greater than that in CCM mode. In CRM mode, the second integrator will only be a Reset. That is, in CRM mode, the operating frequency of the switch tube is at the minimum switching frequency f min ~Maximum switching frequency f max Changes between.

[0028] In the discontinuous conduction mode (DCM), the inductor is discharged and the inductor current i La At the moment when θ is equal to zero, the falling edge of the first integrator output has not yet appeared, that is, the output logic of the first RS flip-flop has not yet been set to 1, and the output logic of the AND gate is 0. When the falling edge of the first integrator output arrives, the output logic of the AND gate is 1, that is, the switching frequency is maintained at the maximum switching frequency in DCM mode.

[0029] In DCM mode, according to the voltage volt-second balance of the inductor, we get:

[0030]

[0031] Where T ona , T offa , T sw are the on-time, off-time and switching cycle of the switch tube, respectively. offa is the off-time duty cycle. a =D ona +D offa , in CCM and CRM modes D a =1, in DCM mode D a <1. In DCM mode, the input impedance of phase a is Z ina for:

[0032]

[0033] Will Substituting into the above formula, we get:

[0034]

[0035] It can be seen that the input impedance will be affected by D a Influence, and D a It can be expressed by the following formula:

[0036]

[0037] From the expression we can see that D a Make Z ina During DCM mode, it no longer presents a pure resistance characteristic. Therefore, it is necessary to modulate the signal V in phase a. cona Compensation is added to offset as follows:

[0038]

[0039] Where V ma is the carrier amplitude of phase a, is the filtered a-phase inductor current, V loopis the output voltage control signal voltage;

[0040] Therefore, as an improvement to the above-mentioned multi-mode frequency conversion control method of the three-phase four-wire Vienna rectifier, the modulation signal V cona To compensate, the modulation signal voltage V cona The carrier amplitude V m , Working time of controlled switch tube D a And the power factor correction control output V based on the input impedance ca The product of .

[0041] By outputting the triangular carrier Ramp to the second integrator a The carrier amplitude V is obtained in real time by doubling after low-pass filtering. ma .

[0042] By controlling the inductor current of the phase where the controlled switch tube is located |i La |Judge whether it is greater than zero and perform low-pass filtering to obtain the working time D of the controlled switch tube a .

[0043] The power factor correction control output V based on the input impedance in this embodiment ca Obtained by:

[0044] The rated output voltage V of the Vienna rectifier ref and the actual output voltage V dc After subtraction, proportional-integral processing is performed to obtain the output voltage control signal voltage V loop , the voltage V of the two split capacitors in the Vienna rectifier p and V n After subtraction, proportional amplification is performed to obtain the voltage control output V cdiff , the voltage control output V cdiff The a-phase inductor current i of the Vienna rectifier La After adding, take the absolute value and then divide it by the output voltage control signal voltage V loop , and then the power factor correction control output V based on the input impedance is obtained by limiting. ca .

[0045] The output voltage control output result is:

[0046]

[0047] The output result of the voltage equalization control is:

[0048] V cdiff =k pc (V p -V n )

[0049] The power factor correction control output based on the input impedance is:

[0050]

[0051] The following is a simulation verification of the multi-mode frequency conversion control method of the three-phase four-wire Vienna rectifier described in this embodiment. The relevant parameters of the rectifier are shown in Table 1:

[0052] Table 1

[0053]

[0054] Simulation verification 1: Figure 2 is the A-phase inductor current i when the rectifier load is 10% La , the inductor current of phase A after filtering and carrier waveform diagram.

[0055] from Figure 2 It can be seen that in one cycle of phase A operation, there are three conditions: CCM, CRM, and DCM. In CCM mode, it operates at the minimum frequency, in CRM mode, the operating frequency changes continuously, and in DCM mode, it operates at the maximum frequency, and the inductor current is sinusoidal and stable. This shows that the control method can realize CCM-CRM-DCM multi-mode variable frequency operation of the Vienna rectifier.

[0056] Simulation verification 2: Figure 3 is the inductor current i when the rectifier load is 10% L , the inductor current after filtering Input voltage in , output voltage V out and the split capacitor voltage V p 、V n Waveform graph.

[0057] from Figure 3 It can be seen that the three phases of the inductor current and input voltage can maintain the same phase operation; the output voltage is maintained at about 800 V; and the voltages of the two split capacitors are maintained at about 400 V. This shows that the control method can achieve power factor correction, voltage midpoint balance, and input current zero-crossing problem suppression under light load conditions.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A multi-mode frequency conversion control method for a three-phase four-wire Vienna rectifier, characterized in that: It includes a carrier reset pulse generating unit and a modulation unit; The carrier reset pulse generating unit comprises an AND gate, a first integrator and a first RS trigger; the maximum switching frequency of the switch tube is used as the first input of the first integrator, and when the output of the first integrator is ≥1, the output of the first integrator is used as the second input of the first integrator; the output of the first integrator is used as the input of the S port of the first RS trigger, and the output of the AND gate is used as the input of the R port of the first RS trigger; the input logic of the first input port of the AND gate is always 1, and the second input port of the AND gate takes the output of the Q port of the first RS trigger as input; The modulation unit includes an OR gate, a second integrator, and a second RS trigger, the output of the AND gate is used as the input of the first input port of the OR gate; the minimum switching frequency of the switch tube is used as the first input of the second integrator, and the output of the OR gate is used as the second input of the second integrator; when the output of the second integrator is ≥1, the output of the second integrator is used as the second input of the OR gate, the output of the OR gate is subtracted from the modulation signal voltage of the phase where the controlled switch tube is located as the input of the R port of the second RS trigger, and the output of the OR gate is used as the input of the S port of the second RS trigger; The Q port of the second RS trigger outputs a control signal to the controlled switch tube; In the CCM working mode, the output logic of the AND gate to the OR gate is always 0, the second integrator is not reset, and the output frequency of the second integrator is a triangular carrier with the minimum switching frequency, that is, in the CCM mode, the operating frequency of the control switch tube is always the minimum switching frequency; In the CRM working mode, when the inductor current of the phase where the controlled switch tube is located gradually decreases to the moment when it passes through 0, the logic output of the AND gate to the OR gate is 1, so that the OR gate outputs a high-level signal to reset the second integrator to change the frequency of the output triangular carrier, and at this moment, the controlled switch tube is turned on to make the inductor current rise again to maintain the CRM working mode; In the DCM working mode, when the inductor finishes discharging and the inductor current is equal to zero, the falling edge of the first integrator output has not yet appeared, that is, the output logic of the first RS trigger has not yet been set to 1, and the output logic of the AND gate is 0. When the falling edge of the first integrator output arrives, the output logic of the AND gate is 1, that is, the switching frequency is maintained at the maximum switching frequency in the DCM mode.

2. The multi-mode frequency conversion control method of a three-phase four-wire Vienna rectifier according to claim 1, characterized in that: The modulation signal voltage is composed of the product of the carrier amplitude, the working time of the controlled switch tube and the power factor correction control output based on the input impedance; The carrier amplitude is obtained in real time by performing low-pass filtering on the triangular carrier output by the second integrator and then doubling it; The working time of the controlled switch tube is obtained by judging whether the inductor current of the phase where the controlled switch tube is located is greater than zero and performing low-pass filtering.

3. The multi-mode frequency conversion control method of a three-phase four-wire Vienna rectifier according to claim 1, characterized in that: The power factor correction control output based on the input impedance is obtained as follows: The rated output voltage and actual output voltage of the Vienna rectifier are subtracted and then proportional-integrated to obtain the output voltage control signal voltage. The voltages of the two split capacitors in the Vienna rectifier are subtracted and proportionally amplified to obtain the equalizing control output. The equalizing control output is added to the inductor current of the phase where the controlled switch tube is located, and the absolute value is taken, which is then divided by the output voltage control signal voltage, and then limited to obtain the power factor correction control output based on the input impedance.

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