Control method of single-stage three-phase isolation type alternating current and direct current rectifying device

Abstract

The invention discloses a control method of a single-stage three-phase isolation type alternating current and direct current rectifying device. The device comprises an input filtering unit, a power conversion unit and an output filtering unit. The input filtering unit receives three-phase AC input and outputs three-phase AC voltage. The power conversion unit comprises three same single-phase power conversion units, each phase of three-phase alternating voltage is connected with an alternating current input connection port of one single-phase power conversion unit, voltage isolation is carried out through a high-frequency isolation transformer, each single-phase power conversion unit is connected with the output filtering unit, and the output filtering unit is connected with the output filtering unit. The output filtering unit outputs rectified direct-current voltage; according to the method, energy storage and energy release are carried out by applying a PWM driving signal to a switching tube; according to the invention, the complexity of multi-stage circuit conversion is simplified, and the voltage stabilization requirement of a wide-range converter at a direct-current end is met.

Description

Technical Field

[0001] The present invention relates to a control method for an AC / DC rectifier device, in particular to a control method for a single-stage three-phase isolated AC / DC rectifier device. Background Art

[0002] With the emergence of new energy, many battery energy storage applications, such as vehicle charging stations and industrial and commercial energy storage, are driving increasing power consumption. A growing number of these devices rely on three-phase power supply. Furthermore, with the recent development of artificial intelligence (AI), data centers are increasingly demanding power, and most of this power is supplied by three-phase rectifiers or high-power UPSs. Therefore, if power supply equipment lacks power factor correction (PFC), it can significantly degrade grid power quality and, in severe cases, even paralyze the grid. To meet grid quality requirements and reduce harmonic pollution and unnecessary transmission burdens on the distribution network, three-phase power consumption equipment must have PFC functionality or incorporate filtering devices.

[0003] Traditionally, three-phase rectifiers employ a two-stage conversion scheme. The first stage, a non-isolated PFC, performs AC / DC conversion, converting sinusoidal AC into a more stable DC voltage, such as 800V or higher, while meeting the high power factor requirements of the AC input. The second stage, a DC / DC converter, currently employs soft-switching LLC topologies or phase-shifted full-bridge topologies. Consequently, two-stage converters require a relatively large number of components and are costly. To address the power device limitations of the DC converter behind the rectifier while also balancing efficiency and other factors, single-stage bidirectional converters, such as matrix converters or matrix-like converters, have become a hot topic of research in recent years. However, because these topologies employ hard switching, the input matrix bridge and the DC-side converter experience hard-turn-off spikes, resulting in high voltage stress. Furthermore, the switching logic control of the matrix bridge is complex, making it difficult to ensure soft switching under all conditions. Furthermore, their performance is limited across a wide range of DC or AC voltages. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a control method for a single-stage three-phase isolated AC / DC rectifier device to solve the technical problems in the prior art that the device cannot meet the wide AC / DC range or requires multiple step-up and step-down conversions of a two-stage converter, resulting in large losses and complex conversions, making it unsuitable for application in places with limited volume or relatively high cost requirements.

[0005] Technical solution: The control method of the single-stage three-phase isolated AC / DC rectifier device described in the present invention includes an input filter unit, a power conversion unit and an output filter unit;

[0006] The input filter unit receives a three-phase AC input and outputs a three-phase AC voltage;

[0007] The power conversion unit includes three identical single-phase power conversion units, each of which has an AC input connection port V ac-L 、AC negative terminal V ac-N Connect the midpoint V to the original side of the transformation unit p-Mid The primary sides of the three single-phase power conversion units are connected to the midpoint V p-Mid connected together; the U A / U B / U C The AC negative terminal V of the three single-phase power conversion units ac-N Connect together;

[0008] Each phase of the three-phase AC voltage is connected to the AC input connection port V of a single-phase power conversion unit. ac-L The voltage is isolated by a high-frequency isolation transformer. Each of the single-phase power conversion units is connected to the output filter unit. The output filter unit is connected to the output port V out+ and V out- Outputting rectified DC voltage; each of the single-phase power conversion units includes fourth to fifth capacitors, a high-frequency isolation transformer, first to second switching tubes, fifth to sixth diodes, and a bidirectional switch;

[0009] The fourth capacitor, the first switch tube and the second switch tube are connected to the V ac-L and V ac-N The drain of the first switch tube at the positive end of the fourth capacitor is connected to V ac-L The source of the second switch tube at the negative end of the fourth capacitor is connected to V ac-N port;

[0010] The source of the first switch tube and the drain of the second switch tube are connected to one end of the primary coil of the high-frequency isolation transformer to V p-K The other end of the primary coil of the high-frequency isolation transformer is connected to one end of the fifth capacitor, and the other end of the fifth capacitor is connected to the midpoint V of the primary side of the high-frequency isolation transformer. p-Mid Connection; one end of the secondary coil of the high-frequency isolation transformer is connected to one end of the inductor, and the other end of the inductor is connected to the anode of the fifth diode, the cathode of the sixth diode and one end of the bidirectional switch. s-D The other end of the secondary coil of the high-frequency isolation transformer and the other end of the bidirectional switch are connected to V s-Mid point;

[0011] The cathode of the fifth diode is connected to the output port V out+ The anode of the sixth diode is connected to the output port V out-;

[0012] The control method comprises the following steps:

[0013] Step 1: Calculate the phase and interval of each phase AC voltage at the current moment, and calculate the instantaneous value V of the voltage of each single-phase power conversion unit. ac ;

[0014] Step 2: Apply a PWM drive signal to the first switch tube, and apply a PWM drive signal complementary to the first switch tube to the second switch tube; based on the phase and interval of the AC voltage at the current moment, when the first switch tube or the second switch tube is turned on, apply a PWM drive signal to the bidirectional switch or to one of the bidirectional switches to boost the voltage and store energy;

[0015] The duty cycle calculation method of the PWM drive signal of the bidirectional switch is: Where k is a coefficient of 0 to 1, N is the ratio of the secondary side to the primary side of the high-frequency isolation transformer, V out is the output DC voltage, D PI is the duty cycle obtained through PI feedback control operation;

[0016] Step 3: After completing the boost energy storage, turn off the PWM drive of the bidirectional switch to perform boost energy release.

[0017] Furthermore, the operating frequency of the first switch tube and the second switch tube is f s =a*f, where a is a constant, 0.6 <a<1, L s It is the sum of the inductance and the equivalent inductance of the high-frequency isolation transformer, and C5 is the fifth capacitor.

[0018] Furthermore, when the inductance is much larger than the equivalent inductance of the high-frequency isolation transformer, the L s Equivalent to the inductor.

[0019] Furthermore, the PWM driving signals applied to the first switching tube, the second switching tube and the bidirectional switch in each single-phase power conversion unit are edge-aligned or center-aligned.

[0020] Furthermore, the fourth capacitor is a high-frequency non-polarized capacitor or a high-frequency polarized capacitor, and the fifth capacitor is a high-frequency non-polarized capacitor.

[0021] Furthermore, it also includes a high-frequency switch tube provided with anti-parallel diodes, wherein the anti-parallel diodes serve as the fifth diode and the sixth diode respectively.

[0022] Furthermore, the inductor is an inductor element external to the high-frequency isolation transformer, or an equivalent leakage inductance of the high-frequency isolation transformer, or the sum of the inductor element external to the high-frequency isolation transformer and the equivalent leakage inductance of the high-frequency isolation transformer.

[0023] Furthermore, the bidirectional switch includes a third switch tube and a fourth switch tube, and one end of the third switch tube is connected to V s-D point, and the other end is connected to the fourth switch tube; the third switch tube and the fourth switch tube are connected to a common source or a common drain;

[0024] If the AC voltage is in the positive half cycle at the current moment, when the first switch tube is turned on, a PWM drive signal is applied to the third switch tube and the fourth switch tube, or only to the fourth switch tube, to boost and store energy; when the second switch tube is turned on, a PWM drive signal is applied to the third switch tube and the fourth switch tube, or only to the third switch tube, to boost and store energy.

[0025] If the AC voltage is in the negative half cycle at the current moment, when the first switch tube is turned on, a PWM drive signal is applied to the third switch tube and the fourth switch tube, or only to the third switch tube, to boost and store energy; when the second switch tube is turned on, a PWM drive signal is applied to the third switch tube and the fourth switch tube, or only to the fourth switch tube, to boost and store energy.

[0026] Furthermore, the output filter unit includes first to third capacitors, and the positive terminals of the first capacitor and the second capacitor are connected to V out+ port, the negative terminals of the first and third capacitors are connected to V out- The negative terminal of the second capacitor and the positive terminal of the third capacitor are connected to V s-Mid port.

[0027] Furthermore, it also includes a control unit for controlling the power conversion unit to achieve power conversion.

[0028] Beneficial effects: Compared with the prior art, the advantages of the present invention are: (1) the single-stage AC / DC rectifier simplifies the complexity of multi-stage circuit conversion; (2) the number of switching tubes is reduced to about half of the traditional one; (3) in terms of performance, it can meet the converter voltage regulation requirements over a wide range at the DC end; (4) in terms of efficiency, it is much better than the traditional multi-stage circuit or single-stage matrix conversion circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a block diagram of a single-stage three-phase isolated AC / DC rectifier device of the present invention.

[0030] Figure 2 It is a specific schematic diagram of the single-stage three-phase isolated AC / DC rectifier device of the present invention.

[0031] Figure 3Schematic diagram of a single-phase power conversion unit according to the present invention.

[0032] Figure 4 Schematic diagram of three-phase AC voltage waveform and intersection point definition in an embodiment of the present invention.

[0033] Figure 5 Schematic diagram of a single-phase power conversion unit in boost mode according to an embodiment of the present invention.

[0034] Figure 6 Schematic diagram of boost mode 2 of a single-phase power conversion unit in an embodiment of the present invention.

[0035] Figure 7 Schematic diagram of the simulation waveform of the present invention.

[0036] Figure 8 FIG. 1 is a schematic diagram of an energy release mode of a single-phase power conversion unit according to an embodiment of the present invention.

[0037] Figure 9 FIG. 2 is a schematic diagram of a second energy release mode of a single-phase power conversion unit according to an embodiment of the present invention.

[0038] Figure 10 This is a classic dual-loop PI control block diagram in an embodiment of the present invention.

[0039] Figure 11 This is a composite control block diagram of feedforward plus feedback in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0041] like Figure 1 As shown, the single-stage three-phase isolated AC / DC rectifier device in the control method of the single-stage three-phase isolated AC / DC rectifier device includes an input filter unit, a power conversion unit, an output filter unit and a control unit. The power conversion unit includes U A / U B / U C Three identical single-phase power conversion units (referred to as A conversion unit, B conversion unit and C conversion unit in this embodiment), each single-phase power conversion unit has an AC input connection port V ac-L 、AC negative terminal V ac-N , the transformation unit primary side connection midpoint V p-Mid The output filter unit includes the first to third capacitors, and the output connection port V out+ and V out- And the output side connects the midpoint V s-Mid The control unit is a hardware unit used to control the power conversion unit to achieve power conversion, including signal sampling, calculation control, switch tube drive control signal, internal and external communication circuits.

[0042] like Figure 2 As shown, the input filter unit is connected to the three-phase AC input, and the output port of the input filter unit outputs the three-phase AC voltage A, B, C. The port V ac-L Connect to the A phase of the three-phase three-wire power supply and the V ac-L Connect to the B phase of the three-phase three-wire power supply and the V port of the C conversion unit ac-L Connect to the C phase of the three-phase three-wire power supply, and the primary side of the three single-phase power conversion units is connected to the midpoint V p-Mid Connect together, the AC negative terminal V of the three single-phase power conversion units ac-N The positive ends of the first capacitor C1 and the second capacitor C2 are connected to the output connection ports V of the three single-phase power conversion units. out+ The negative ends of the first capacitor C1 and the third capacitor C3 are connected to the output connection ports V out- The negative end of the second capacitor C2 and the positive end of the third capacitor C3 are connected together with the output of the three single-phase power conversion units to the midpoint V s-Mid Connected together.

[0043] like Figure 3 As shown, the single-phase power conversion unit includes first to fourth switch tubes (Q1 to Q4), fourth to fifth capacitors (C4 to C5), and fifth to sixth diodes (D5 to D6). The fourth capacitor C4, the first switch tube Q1 and the second switch tube Q2 are connected to the port V of the single-phase power conversion unit. ac-L And the AC negative terminal V ac-N The drain of the first switch tube Q1 at the positive end of the fourth capacitor C4 is connected to the AC input port V ac-L The source of the second switch tube Q2 at the negative end of the fourth capacitor C4 is connected to the AC negative terminal V ac-N The source of the first switch tube Q1 and the drain of the second switch tube Q2 are connected to the high frequency isolation transformer T R One end of the primary coil is connected to "V p-K ” point, high frequency isolation transformer T R The other end of the primary coil is connected to one end of the fifth capacitor C5, and the other end of the fifth capacitor C5 is connected to the midpoint V p-Mid Connection. High frequency isolation transformer T R One end of the secondary coil is connected to the inductor L s1 One end of the inductor is connected; s1 The anode of the fifth diode D5, the cathode of the sixth diode D6 and the drain of the third switch tube Q3 are connected to "V s-D "Point; High frequency isolation transformer T RThe other end of the secondary coil and the drain of the fourth switch tube Q4 are connected to the output connection port V s-Mid The cathode of the fifth diode D5 is connected to the output port V out+ The anode of the sixth diode D6 is connected to the output port V out- ; The sources of the third switch tube Q3 and the fourth switch tube Q4 are connected together.

[0044] The fourth capacitor C4 of this embodiment is a high-frequency non-polarized capacitor or a high-frequency polarized capacitor, and the fifth capacitor C5 is a high-frequency non-polarized capacitor, and the fifth capacitor C5 is connected to the high-frequency isolation transformer T R The primary coils of the transistors are in a series relationship in the loop, and their positions in the loop are not fixed and are only shown as a series relationship. The fifth to sixth diodes D5~D6 can also be high-frequency switching tubes with anti-parallel diodes. The high-frequency switching tubes are used for synchronous rectification, and the direction of the anti-parallel diodes is consistent with that of the fifth to sixth diodes D5~D6. The third switching tube Q3 and the fourth switching tube Q4 of this embodiment adopt a common source connection method, or a common drain connection method, or other equivalent controllable bidirectional switches. For example, the positions of the switching tubes of this embodiment are simply changed or replaced with IGBTs and other equivalent controllable bidirectional switches. Other combinations that can realize the functions of the controllable switches of the present invention also fall within the scope of the present invention.

[0045] like Figure 4 As shown, the input three-phase AC power source includes Phase A, Phase B, and Phase C. Because the actual input AC voltage may be transient or distorted, the voltage waveform in this embodiment uses a standard waveform as a reference for ease of description. Furthermore, the three-phase voltages are assumed to be sinusoidal with a phase difference of 120°, and each 360° (or 2π) constitutes a cycle. For intuitive and convenient expression, a complete cycle is defined as 30° to 390°, i.e., the 30° point of the next cycle. The intersection points are defined as AC (30°), BC (90°), BA (150°), CA (210°), CB (270°), AB (330°), and AC (30° or 390°). The zero crossing point is designated as "0." The control method for the single-stage three-phase isolated AC / DC rectifier device of the present invention is described below using the AC-0 interval as an example.

[0046] S1: Determine whether the rectification mode is met based on the external input control information, program settings, and external AC and DC judgment. Assume that the control unit determines that the rectification working conditions are met based on the relevant sampling information and program settings and proceeds to the next step.

[0047] S2: Diodes D5 and D6 (or freewheeling diodes) in the single-phase power conversion unit can also be switches without applying PWM drive signals or only applying synchronous rectification drive signals. A high-level direct drive signal is applied to the switch that needs to perform direct operation. No PWM drive signal is applied to the switch that does not need to conduct, or a low-level non-conduction signal is applied.

[0048] S3: Analyze the phase and interval of each phase power supply at the current moment according to the phase lock of the input three-phase three-wire power supply voltage signal (or the AC phase table set by the program); analyze the AC-0 interval, at this time, phase A and phase C are positive half-waves, and phase B is negative half-waves, and analyze the instantaneous value V of the voltage of each phase power supply of the three single-phase power conversion units according to the phase ac .

[0049] S4: The control unit sets the operating frequency of the switch tube of the single-phase power conversion unit to a fixed value within the range of 60% to 100% of the resonant frequency; s The resonant frequency of the resonant unit composed of C5 L s Contains external inductor L s1 and the sum of the transformer equivalent leakage inductance. Assuming the operating frequency f s =0.9f; then the operating frequency f is applied to the first to second switching tubes (Q1-Q2) s =0.9f, and a fixed 50% duty cycle drive signal with a dead time (assumed to be 200ns).

[0050] S5: According to the above current determination that the AC input of the A conversion unit and the C conversion unit is in the positive half cycle, when the Q1 switch is turned on, a PWM drive signal is applied to Q3 and Q4 or only to Q4 to boost and store energy; when the Q2 switch is turned on, a PWM drive signal is applied to Q3 and Q4 or only to Q3 to boost and store energy. In addition, in step S5, a PWM drive signal D with a duty cycle of 50% or less than 50% is applied to the Q1 switch. pwm-p , apply a PWM drive signal complementary to Q1 to the Q2 switch tube.

[0051] According to the above, it is currently determined that the AC input of the B conversion unit is in the negative half cycle. When the Q1 switch tube is turned on, a PWM drive signal is applied to Q3 and Q4 or only to Q3 to boost and store energy; when the Q2 switch tube is turned on, a PWM drive signal is applied to Q3 and Q4 or only to Q4 to boost and store energy; the PWM drive duty cycle required to be applied to Q3 and Q4 is calculated according to the classic PI control method. After completing the boost energy storage, the PWM drive of Q3 and Q4 is turned off to enter the boost energy release stage.

[0052] The specific implementation method and working status of boost energy release are analyzed in detail below.

[0053] like Figure 5 The figure shows a schematic diagram of the boost mode of a single-phase power conversion unit. When Q1 is turned on in the A conversion unit and the C conversion unit, Q3 and Q4 are also turned on, then "V p-K ” is a high level potential, V p-Mid Point is low level potential, high frequency isolation transformer T R The coupling voltage of the secondary coil is all applied to the inductor L s1 On the inductor L s1 In boost energy storage mode, the current path is as follows Figure 5 As shown in .

[0054] like Figure 6 The figure shows the schematic diagram of the boost mode 2 of the single-phase power conversion unit. In the B conversion unit, when the Q1 switch is turned on, Q3 and Q4 are also turned on, then "V p-K ” is a low level potential, V p-Mid The point is high level potential, and the current of conversion unit A and conversion unit C can flow back to the grid through conversion unit B. At this time, the current can pass through the Q1 switch tube or the reverse parallel diode of the Q1 switch tube. High frequency isolation transformer T R The coupling voltage of the secondary coil is all applied to the inductor L s1 On the inductor L s1 In boost energy storage mode, the current path is as follows Figure 6 As shown in , and the current flow direction is the same as Figure 5 In the above working process, due to the AC negative terminal V ac-N The voltage is equal to or lower than V ac-L (In actual work, the negative terminal V ac-N The voltage will be lower than a certain platform voltage of the three-phase AC voltage A, B, and C, which is recorded as the bias voltage V-bais; it varies depending on the size of the output load and the parameters of the converter. Therefore, when Q2 is not turned on, no short circuit will be formed on C4.

[0055] like Figure 7 As shown in the figure, it is a simulation waveform diagram of the single-stage three-phase isolated AC / DC rectifier device of this embodiment. UA-N, UB-N, and UC-N respectively represent the voltages of the input capacitors in the three single-phase power units A / B / C. Under different output voltages, the bias voltage V-bais shown in the figure will be different. The higher the output voltage boost, the higher the V-bais, and the higher the UA-N, UB-N, and UC-N. Therefore, in actual use, it is necessary to pay attention to this voltage and select the appropriate switch tube.

[0056] like Figure 8The figure shows a schematic diagram of the energy release mode of the single-phase power conversion unit. After the boost energy storage is completed in the A conversion unit and the C conversion unit, the PWM drive of Q3 and Q4 is turned off and the energy release boost is started. The Q1 switch tube continues to be turned on, then "V p-K ” is a high level potential, V p-Mid Point is at low level potential, and the original current direction remains unchanged; due to the inductance L s1 In the voltage reverse energy release mode, the high-frequency isolation transformer T R The coupling voltage of the secondary coil and the inductance L s1 The energy release voltage on the output is superimposed in series, and the A conversion unit and the C conversion unit form a boost rectifier output mode. The current path is shown in the figure. The output end D5 diode is turned on by the forward bias voltage, and the current flows through D5 to the output capacitors C1 and C2 and the load. At the same time, the current flows through V s-Mid Reflow; complete high frequency isolation transformer T R The secondary coil and inductance L s1 The rectified output of the discharge voltage.

[0057] like Figure 9 The figure shows the second energy release mode of the single-phase power conversion unit. After the boost energy storage is completed in the B conversion unit, the PWM drive of Q3 and Q4 is turned off and the energy release boost is started. The Q1 switch tube continues to be turned on, then "V p-K ” is a low level potential, V p-Mid The point is high level potential, the current of A conversion unit and C conversion unit can pass through V p-Mid The current flows back to the grid, and the original current direction remains unchanged; due to the inductance L s1 In the voltage reverse energy release mode, the high-frequency isolation transformer T R The coupling voltage of the secondary coil and the inductance L s1 The energy release voltages on the B converter are superimposed in series, and the B converter unit forms a boost rectifier output mode, and the current direction is the same as Figure 8 In contrast to the example shown in Figure 2, the output diode D6 is forward biased and conducts, and the current flows through V s-Mid The potential point supplies power to the output capacitors C3, C1, and the load, while the current flows back through D6; completing the high-frequency isolation transformer T R The secondary coil and inductance L s1 The rectified output of the discharge voltage.

[0058] At the same time, in the above working process, C5 in the three single-phase power conversion units constitutes a voltage-dividing energy storage, and L s The resonant frequency of the resonant unit composed of C5 L s Contains external inductor L s1 and the sum of the transformer equivalent leakage inductance. s1If the inductance value is much larger than the equivalent leakage inductance of the transformer, it is assumed to be approximately equal to the sum of the external inductance and the equivalent leakage inductance of the transformer. s It can be simplified to directly use the single external inductor value L s1 .

[0059] Similarly, when the above-mentioned rectification and conversion process is completed and the dead time (assuming 200ns) has passed, when the Q2 switch tube is turned on, a PWM drive signal is applied to Q3 and Q4 or only Q4 to boost and store energy; at this time, the power supply of the primary side of the transformer is released by C5 and is transmitted through V p-Mid point and the AC negative terminal V ac-N The three single-phase power conversion units form a power supply loop. The principle is consistent with the above analysis. Those skilled in the art can refer to the reasoning to derive the relevant working process, which will not be repeated here.

[0060] The following describes the PI control method of the single-stage three-phase isolated AC / DC rectifier device of this embodiment.

[0061] like Figure 10 The figure shows the classic dual-loop (voltage outer loop, current inner loop) PI control block diagram of the single-stage three-phase isolated AC / DC rectifier device of this embodiment. It is similar to the traditional PFC control implementation method. In the control unit, the current loop sampling involved in the control is achieved by using a high-frequency isolation transformer T R The primary current I Tr , used to replace the inductor current of the traditional non-isolated PFC; the output voltage V out With reference voltage V * out Compare to obtain the voltage error; then process the error through the PI controller (proportional integral) and output the reference signal I of the current amplitude ref , generating the current reference signal: Where V ac(t) is the input voltage sampling waveform, V vac_peak Then connect it to the high frequency isolation transformer T R The primary current I Tr By comparison, the current error is obtained, and the current reference is quickly tracked by the P or PI controller to generate the PWM drive duty cycle D required for Q3 and Q4. PI , that is, D pwm = Duty cycle D obtained by feedback control operation PI .

[0062] Because it is difficult to achieve the unity of control system stability and high precision by using the classic feedback control structure and conventional PID algorithm. In order to improve the dynamic response and zero-crossing current distortion and other problems, the system correction method combining feedback control and feedforward in the system correction theory of classic control can be referred to to perform system correction. Figure 11 As shown, in Figure 10 Based on the control block diagram, feedforward control is introduced. The feedforward part calculates the duty cycle D c =1-N*V ac / V out Among them, the high-frequency isolation transformer T R The ratio of the secondary side to the primary side is N, V ac It is the instantaneous value of the voltage of each phase power supply.

[0063] The controller can adopt a composite control method of partial or complete feedforward plus feedback according to actual needs, that is, the duty cycle Dc calculated by the feedforward part is multiplied by the coefficient k and then combined with the duty cycle D obtained by the feedback control operation. PI Add, that is, D pwm =k*D c +D PI k is a value between 0 and 1. When k is 0, the control system is a traditional classic dual-loop non-feedforward control; when k is 1, it is a full feedforward plus feedback composite control method; when 0<k<1, it is a partial feedforward plus feedback composite control method.

[0064] Feedforward control is essentially an open-loop regulation. Its fundamental difference from closed-loop feedback is that it doesn't wait until the controlled variable deviates before correcting the deviation. Instead, it takes effect as soon as the control action is applied to the system. Therefore, it is more "timely" than feedback control and is not affected by system delays. This allows for better tracking of current and voltage, resulting in higher power factors (PF) and lower current harmonics (THDI).

[0065] According to the aforementioned control method, after obtaining the PWM drive duty cycle Dpwm required to be applied to Q3 and Q4, when applying the PWM drive signal to the Q1 to Q4 switch tubes in the three single-phase power conversion units, the PWM drive signal adopts edge alignment or center alignment.

[0066] Through the above control method, according to the voltage magnitude relationship of each phase voltage in each interval segment, the switching tubes in the three single-phase power conversion units are applied with appropriate drive in an orderly manner, which can effectively ensure that current flows in all three phases in each switching cycle. At the same time, the duty cycle of the PWM drive signal is modulated according to real-time control, so that the current waveform and the voltage waveform can be kept consistent, thereby obtaining a higher PF value.

Claims

1. A control method for a single-stage three-phase isolated AC / DC rectifier, characterized in that: The single-stage three-phase isolated AC / DC rectifier device includes an input filter unit, a power conversion unit and an output filter unit; The input filter unit receives a three-phase AC input and outputs a three-phase AC voltage; The power conversion unit includes three identical single-phase power conversion units, each of which has an AC input connection port V ac-L 、AC negative terminal V ac-N Connect the midpoint V to the original side of the transformation unit p-Mid The primary sides of the three single-phase power conversion units are connected to the midpoint V p-Mid connected together; the U A / U B / U C The AC negative terminal V of the three single-phase power conversion units ac-N Connect together; Each phase of the three-phase AC voltage is connected to the AC input connection port V of a single-phase power conversion unit. ac-L The voltage is isolated by a high-frequency isolation transformer. Each of the single-phase power conversion units is connected to the output filter unit. The output filter unit is connected to the output port V out+ and V out- Outputting rectified DC voltage; each of the single-phase power conversion units includes fourth to fifth capacitors, a high-frequency isolation transformer, first to second switching tubes, fifth to sixth diodes, and a bidirectional switch; The fourth capacitor, the first switch tube and the second switch tube are connected to the V ac-L and V ac-N The drain of the first switch tube at the positive end of the fourth capacitor is connected to V ac-L The source of the second switch tube at the negative end of the fourth capacitor is connected to V ac-N port; The source of the first switch tube and the drain of the second switch tube are connected to one end of the primary coil of the high-frequency isolation transformer to V p-K The other end of the primary coil of the high-frequency isolation transformer is connected to one end of the fifth capacitor, and the other end of the fifth capacitor is connected to the midpoint V of the primary side of the high-frequency isolation transformer. p-Mid Connection; one end of the secondary coil of the high-frequency isolation transformer is connected to one end of the inductor, and the other end of the inductor is connected to the anode of the fifth diode, the cathode of the sixth diode and one end of the bidirectional switch. s-D The other end of the secondary coil of the high-frequency isolation transformer and the other end of the bidirectional switch are connected to V s-Mid point; The cathode of the fifth diode is connected to the output port V out+ The anode of the sixth diode is connected to the output port V out- ; The control method comprises the following steps: Step 1: Calculate the phase and interval of each phase AC voltage at the current moment, and calculate the instantaneous value V of the voltage of each single-phase power conversion unit. ac ; Step 2: Apply a PWM drive signal to the first switch tube, and apply a PWM drive signal complementary to the first switch tube to the second switch tube; based on the phase and interval of the AC voltage at the current moment, when the first switch tube or the second switch tube is turned on, apply a PWM drive signal to the bidirectional switch or to one of the bidirectional switches to boost the voltage and store energy; The duty cycle calculation method of the PWM drive signal of the bidirectional switch is: Where k is a coefficient of 0 to 1, N is the ratio of the secondary side to the primary side of the high-frequency isolation transformer, V out is the output DC voltage, D PI is the duty cycle obtained through PI feedback control operation; Step 3: After completing the boost energy storage, turn off the PWM drive of the bidirectional switch to perform boost energy release.

2. The control method of the single-stage three-phase isolated AC / DC rectifier according to claim 1, characterized in that: The operating frequency of the first switching tube and the second switching tube is f s =a*f, where a is a constant, 0.6 <a<1, L s It is the sum of the inductance and the equivalent inductance of the high-frequency isolation transformer, and C5 is the fifth capacitor.

3. The control method of the single-stage three-phase isolated AC / DC rectifier according to claim 2, characterized in that: When the inductance is much larger than the equivalent inductance of the high-frequency isolation transformer, the L s Equivalent to the inductor.

4. The control method of the single-stage three-phase isolated AC / DC rectifier according to claim 1, characterized in that: The PWM driving signals applied to the first switching tube, the second switching tube and the bidirectional switch in each single-phase power conversion unit are edge-aligned or center-aligned.

5. The control method of the single-stage three-phase isolated AC / DC rectifier according to claim 1, characterized in that: The fourth capacitor is a high-frequency non-polarized capacitor or a high-frequency polarized capacitor, and the fifth capacitor is a high-frequency non-polarized capacitor.

6. The control method of the single-stage three-phase isolated AC / DC rectifier according to claim 1, characterized in that: It also includes a high-frequency switch tube provided with anti-parallel diodes, wherein the anti-parallel diodes serve as the fifth diode and the sixth diode respectively.

7. The control method of the single-stage three-phase isolated AC / DC rectifier according to claim 1, characterized in that: The inductor is an inductor element external to the high-frequency isolation transformer, or an equivalent leakage inductance of the high-frequency isolation transformer, or the sum of the inductor element external to the high-frequency isolation transformer and the equivalent leakage inductance of the high-frequency isolation transformer.

8. The control method of the single-stage three-phase isolated AC / DC rectifier according to claim 1, characterized in that: The bidirectional switch includes a third switch tube and a fourth switch tube, one end of the third switch tube is connected to V s-D point, and the other end is connected to the fourth switch tube; the third switch tube and the fourth switch tube are connected to a common source or a common drain; If the AC voltage is in the positive half cycle at the current moment, when the first switch tube is turned on, a PWM drive signal is applied to the third switch tube and the fourth switch tube, or only to the fourth switch tube, to boost and store energy; when the second switch tube is turned on, a PWM drive signal is applied to the third switch tube and the fourth switch tube, or only to the third switch tube, to boost and store energy. If the AC voltage is in the negative half cycle at the current moment, when the first switch tube is turned on, a PWM drive signal is applied to the third switch tube and the fourth switch tube, or only to the third switch tube, to boost and store energy; when the second switch tube is turned on, a PWM drive signal is applied to the third switch tube and the fourth switch tube, or only to the fourth switch tube, to boost and store energy.

9. The control method of the single-stage three-phase isolated AC / DC rectifier according to claim 1, characterized in that: The output filter unit includes first to third capacitors, and the positive ends of the first capacitor and the second capacitor are connected to V out+ port, the negative terminals of the first and third capacitors are connected to V out- The negative terminal of the second capacitor and the positive terminal of the third capacitor are connected to V s-Mi d port.

10. The control method of the single-stage three-phase isolated AC / DC rectifier according to claim 1, characterized in that: It also includes a control unit for controlling the power conversion unit to achieve power conversion.

Images