Soft-switching single-stage isolated three-phase ACDC converter and control method thereof

Abstract

The present invention discloses a soft-switching single-stage isolated three-phase ACDC converter and a control method thereof, wherein the converter comprises a three-phase uncontrolled rectifier bridge, a charge and discharge control branch, a sector selection switch group, a DC blocking capacitor C1, an isolation transformer, a DC side rectifier circuit, and a controller, wherein the three-phase uncontrolled rectifier bridge converts alternating current into direct current, the charge and discharge control branch connects two output ends of the direct current, the sector selection switch group selects one of the three-phase electricity to connect to the neutral line O of the charge and discharge control branch, the controller controls the switch actions in the charge and discharge control branch and the sector selection switch group, and outputs alternating current to the primary winding of the isolation transformer. The present invention realizes a step-down type rectification mode, avoids the startup impact problem of the previous boost rectification mode, and realizes electrical isolation only with a single-stage power conversion circuit; all switches can realize soft switching within a wide load range, reduce the loss of the rectifier, and improve the overall efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of AC / DC converters, in particular to a wide-range soft-switching single-stage isolated three-phase ACDC converter and a control method thereof. Background Art

[0002] At present, three-phase power converters mainly adopt a two-stage structure, such as car charging piles. The front stage adopts a boost topology such as Vienna PFC or six-switch PFC to achieve power factor correction, and the back stage adopts LLC or full-bridge topology to achieve DC / DC power conversion. Three-phase AC / DC can be divided into two categories according to whether there is a DC side inductor: current source type and voltage source AC / DC converter; according to whether there is a high-frequency isolation transformer, it can be divided into isolated type and non-isolated type.

[0003] The non-isolated three-phase voltage source AC / DC converter composed of a three-phase bridge circuit has a boost characteristic on the DC side during rectification. The three-phase 380V AC voltage is usually converted to a DC voltage of 600-800V. It usually needs to be connected to the low-voltage DC bus after being stepped down by an isolation transformer or a DC / DC converter at the later stage. In addition, the rectification mode of the voltage source AC / DC converter is a boost type, which has a startup impact problem. It is necessary to add startup current limiting measures in the power transmission path, which affects the converter efficiency and power density. At the same time, when the boost circuit is working at no load or light load, the closed-loop control of the system is also very difficult, and it is difficult to take into account the stability of control and the fast dynamic response characteristics. Isolated AC / DC converters usually require a two-stage structure. One is to add an industrial frequency isolation transformer in the front stage, which will result in a large overall size and weight of the converter and high cost; the other is to add a high-frequency isolated DC / DC converter in the back stage. However, the two-stage power conversion has a great negative impact on system efficiency, and the existing high-frequency isolated DC / DC converter has poor characteristics under a wide voltage variation range. This type of converter is difficult to adapt to application requirements with wide input and output voltage variations.

[0004] At present, there are single-stage three-phase AC-DC converters, which usually have multiple switching devices and complex circuits, and the control is not simple. For example, the Chinese patent application (publication number: CN112202351A) has high technical advancement, such as single-stage isolated AC-DC and primary high-frequency switching devices to achieve soft switching, but there are many active switching power devices, requiring 8 high-frequency power switching devices and multiple magnetic devices.

[0005] Therefore, designing a three-phase ACDC rectifier with simple circuit, convenient control, relatively few components and relatively low preparation cost is a technical problem that needs to be solved urgently in the industry. Summary of the invention

[0006] In order to solve the above defects in the prior art, the present invention proposes a soft-switching single-stage isolated three-phase ACDC converter and a control method thereof.

[0007] The technical solution adopted by the present invention is to design a soft-switching single-stage isolated three-phase ACDC converter, which includes a three-phase uncontrolled rectifier bridge, a charge and discharge control branch, a sector selection switch group, a DC blocking capacitor C1, an isolation transformer, a DC side rectifier circuit, and a controller, wherein the A-phase input terminal, the B-phase input terminal and the C-phase input terminal of the three-phase uncontrolled rectifier bridge are connected to the three-phase alternating current, and the charge and discharge control branch is connected between the positive DC bus P and the negative DC bus N; the charge and discharge control branch includes a first switch SW1, a second switch SW2, a third switch SW3, and a fourth switch SW4 connected in series in sequence, the first switch SW1 and the second switch SW2 are connected as a P-connection point, the second switch SW2 and the third switch SW3 are connected as a neutral line O, and the third switch SW3 and the fourth switch SW4 are connected as an N+ connection point; the sector selection switch group includes an A-phase switch (SWA1, SWA2), a B-phase switch (SWB1, SWB2), and a C-phase switch (SWC1, SWC2), the A-phase switch is connected in series between the A-phase input terminal and the neutral line O, the B-phase switch is connected in series between the B-phase input terminal and the neutral line O, and the C-phase switch is connected in series between the C-phase input terminal and the neutral line O; the DC blocking capacitor C1 is connected in series with the primary winding of the isolation transformer and then connected between the P-connection point and the N+connection point; the DC side rectifier circuit is connected to the secondary winding of the isolation transformer to provide DC power to the load; the controller controls the switch actions in the charge and discharge control branch and the sector selection switch group, outputs alternating current to the primary winding of the isolation transformer, and the secondary winding of the isolation transformer and the DC side rectifier circuit output DC power.

[0008] A three-phase EMI filter is provided between the A-phase input terminal, the B-phase input terminal and the C-phase input terminal and the three-phase alternating current.

[0009] The A-phase switch is composed of an A-phase first switch SWA1 and an A-phase second switch SWA2 connected in series in an inversely symmetrical manner, the B-phase switch is composed of a B-phase first switch SWB1 and a B-phase second switch SWB2 connected in series in an inversely symmetrical manner, and the C-phase switch is composed of a C-phase first switch SWC1 and a C-phase second switch SWC2 connected in series in an inversely symmetrical manner.

[0010] The DC side rectification circuit adopts one of a full-bridge rectification circuit, a current doubler rectification circuit and a full-wave rectification circuit.

[0011] The present invention also designs a control method for a soft-switching single-stage isolated three-phase ACDC converter. The converter adopts the above-mentioned soft-switching single-stage isolated three-phase ACDC converter. The control method includes a controller controlling the sector selection switch group to act, dividing a power frequency cycle of the three-phase AC power into 6 sectors, with the A phase voltage at a time when the positive half-cycle amplitude is the highest at 0, the negative half-cycle amplitude is the highest at π, and the positive half-cycle amplitude is the highest again at 2π, and the B phase lags behind Phase A is 2π / 3, and phase C lags behind phase B by 2π / 3; the first sector is 0-π / 3, and only the B phase enable switch is turned on; the second sector is π / 3-2π / 3, and only the A phase enable switch is turned on; the third sector is 2π / 3-π, and only the C phase enable switch is turned on; the fourth sector is π-4π / 3, and only the B phase enable switch is turned on; the fifth sector is 4π / 3-5π / 3, and only the A phase enable switch is turned on; the sixth sector is 5π / 3-2π, and only the C phase enable switch is turned on.

[0012] The duty cycle of the first switch SW1 is DP, and the duty cycle of the fourth switch SW4 is DN;

[0013] To simplify the discussion, the following descriptions are based on ideal conditions: all switching devices are ideal devices with no conduction loss and switching loss; inductors and capacitors are ideal devices with no loss; and the inductor is large enough.

[0014] In the first fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using formula 1.

[0015] D p (t) = i a / I dc k, D n (t) = i c / I dc· k (Formula 1);

[0016] In the second fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using formula 2:

[0017] D p (t) = i b / I dc k, D n (t) = i c / I dc k (Formula 2);

[0018] In the third fan, the duty cycle of the first switch SW1 and the fourth switch SW4 is calculated using Formula 3:

[0019] D p (t) = i b / I dc k, D n (t) = ia / I dc k (Formula 3);

[0020] In the fourth fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using formula 4:

[0021] D p (t) = i c / I dc· k, D n (t) = i a / I dc k (Formula 4);

[0022] In the fifth fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using Formula 5,

[0023] D p (t) = i c / I dc k, D n (t) = i b / I dc k (Formula 5);

[0024] In the sixth fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using Formula 6:

[0025] D p (t) = i a / I dc k, D n (t) = i b / I dc k (Formula 6);

[0026] In the above formula, ia is the A phase current, ib is the B phase current, ic is the C phase current, Idc is the output current of the DC side rectifier circuit, and k is the primary-secondary transformation ratio of the isolation transformer.

[0027] The first switch SW1 and the second switch SW2 are a pair of complementary conduction tubes with a dead zone, and the third switch SW3 and the fourth switch SW4 are a pair of complementary conduction tubes with a dead zone. The controller controls the first switch SW1 to the fourth switch SW4 to switch, realizes zero voltage switching in a wide load range, charges and discharges the DC blocking capacitor C1, and outputs alternating current to the primary winding of the isolation transformer.

[0028] The controller samples the three-phase alternating current, and controls the action of the sector selection switch group after calculation by the sector selection function module;

[0029] The controller controls the voltage Vp of the positive DC bus P and the voltage V N, the output current Idc of the DC side rectifier circuit, and the output voltage Vout of the DC side rectifier circuit are sampled respectively;

[0030] The voltage Vp is multiplied by the control loop optimization parameter Kin to generate a positive input sampling value, and sent to the first adder;

[0031] The voltage VN is inverted and then multiplied with the control loop optimization parameter Kin to generate a negative input sampling value, which is sent to the second adder;

[0032] The output voltage reference value Vout* is subtracted from the output voltage Vout, and then the output voltage loop control (R(S)) is performed, and then the output current Idc is subtracted, and then the output current loop control (G(S)) is performed to generate the duty cycle error adjustment amount △d, which is then sent to the first adder (J1);

[0033] In a first adder (J1), the positive input sampling value and the duty cycle error adjustment value Δd are added and sent to a first PWM generator to generate a first PWM control signal;

[0034] In the second adder (J2), the negative input sampling value and the duty cycle error adjustment value Δd are added and sent to the second PWM generator to generate a second PWM control signal;

[0035] The first PWM control signal is sent to the control end of the first switch SW1, and at the same time, a signal which is opposite to the first PWM control signal and has a dead zone is generated by the first NOT gate and sent to the control end of the second switch SW2;

[0036] The second PWM control signal is sent to the control end of the fourth switch SW4, and at the same time, a signal which is opposite to the second PWM control signal and has a dead zone is generated by the second NOT gate and sent to the control end of the third switch SW3.

[0037] The control loop optimization parameter Kin is equal to 2Vout×n / 3Um 2 , wherein Vout is the output voltage Vout, n is the turns ratio of the primary side to the secondary side of the isolation transformer, and Um is the phase voltage peak value of the three-phase AC input.

[0038] The beneficial effects of the technical solution provided by the present invention are:

[0039] The present invention realizes a step-down type rectification mode, avoids the startup impact problem of the previous boost rectification mode, and solves the problem in the prior art that a three-phase bidirectional AC / DC converter must adopt a two-stage structure when converting a three-phase 380V AC voltage into a low-voltage DC voltage or a low-voltage DC voltage into a three-phase 380V AC voltage, and realizes electrical isolation with only a single-stage power conversion circuit; all high-frequency switching tubes can realize soft switching within a wide load range, thereby reducing the loss of the rectifier and improving the overall efficiency; in addition, it also has the advantages of good grid-side current sinusoidality, high grid-side power factor, and efficient power transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention is described in detail below with reference to the embodiments and accompanying drawings, wherein:

[0041] Figure 1 is a circuit diagram of a power conversion circuit in an embodiment;

[0042] Figure 2 It is the AC sector division and the voltage and current waveform comparison diagram of key branches and nodes;

[0043] Figure 3a This is the conduction state diagram of SW1 and SW4;

[0044] Figure 3b This is the SW1 conduction state diagram (the transient process of achieving SW3 ZVS);

[0045] Figure 3c This is the conduction state diagram of SW1 and SW3;

[0046] Figure 3d This is the SW3 conduction state diagram (the transient process of achieving SW2 ZVS);

[0047] Figure 3e This is the conduction state diagram of W2 and SW3;

[0048] Figure 3f This is the state diagram of SW1, SW2, SW3, and SW4 being fully disconnected (realizing the transient process of SW1 and ZV4 ZVS);

[0049] Figure 4 It is the waveform diagram of Dp, Dn and Io, Ip, In;

[0050] Figure 5 It is a circuit diagram of a DC side rectifier circuit using a current doubler rectifier circuit;

[0051] Figure 6 This is a circuit diagram in which the DC side rectifier circuit adopts a full-wave rectifier circuit;

[0052] Figure 7 It is a control principle block diagram of a preferred embodiment. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0054] The present invention discloses a soft-switching single-stage isolated three-phase ACDC converter. Figure 1 The circuit diagram shown includes a three-phase uncontrolled rectifier bridge (6 diodes), a charge and discharge control branch, a sector selection switch group, a DC blocking capacitor C1, an isolation transformer (Tr2), a DC side rectifier circuit (4 diodes), and a controller, wherein the A-phase input terminal, the B-phase input terminal, and the C-phase input terminal of the three-phase uncontrolled rectifier bridge are connected to the three-phase alternating current, and the charge and discharge control branch is connected between the positive DC bus P and the negative DC bus N; the charge and discharge control branch includes a first switch SW1, a second switch SW2, a third switch SW3, and a fourth switch SW4 connected in series in sequence, the first switch SW1 and the second switch SW2 are connected to a P-connection point, the second switch SW2 and the third switch SW3 are connected to a neutral line O, and the third switch SW3 and the fourth switch SW4 are connected to an N+ connection point; The sector selection switch group includes an A-phase switch (SWA1, SWA2), a B-phase switch (SWB1, SWB2), and a C-phase switch (SWC1, SWC2). The A-phase switch is connected in series between the A-phase input terminal and the neutral line O, the B-phase switch is connected in series between the B-phase input terminal and the neutral line O, and the C-phase switch is connected in series between the C-phase input terminal and the neutral line O; the DC blocking capacitor C1 is connected in series with the primary winding of the isolation transformer and then connected between the P-connection point and the N+connection point; the DC side rectifier circuit is connected to the secondary winding of the isolation transformer to provide DC power to the load; the controller controls the switch actions in the charge and discharge control branch and the sector selection switch group to output alternating current to the primary winding of the isolation transformer, and the secondary winding of the isolation transformer and the DC side rectifier circuit output DC power.

[0055] The present invention is based on a three-phase AC / DC rectifier injected with third harmonics, and has wide-range soft switching, single-stage isolation transformer, voltage change ratio adjustment and electrical isolation functions. The input three-phase 380V AC voltage provides a low-frequency periodically changing pulsating DC voltage for the high-frequency working structure through a three-phase uncontrolled rectifier bridge and a sector selection switch group, and the positive and negative busbars (P, N) provide a multi-level high-frequency power pulse voltage to the isolation transformer through a series connection of four high-frequency switches (SW1, SW2, SW3, SW4) in the charge and discharge control branch, and the power is transmitted to the load through the transformer coupling to the secondary DC side rectifier circuit. During the power transmission process, the appropriate duty cycle of the four high-frequency switches (SW1, SW2, SW3, and SW4) is adjusted so that the high-frequency periodic average current flowing from the positive bus to the series branch of the four high-frequency switches is proportional to the positive bus voltage to the neutral point of the AC power, and the high-frequency periodic average current flowing through the series branch of the four high-frequency switches from the negative bus is proportional to the negative bus voltage to the neutral point of the AC power, and the sector selection switch group is turned on and off at an appropriate time to achieve single-stage isolated three-phase AC / DC conversion.

[0056] See also Figure 1 In the preferred embodiment shown, a three-phase EMI filter is provided between the A-phase input terminal, the B-phase input terminal and the C-phase input terminal and the three-phase alternating current.

[0057] exist Figure 1 In the preferred embodiment shown, the A-phase switch is composed of an A-phase first switch SWA1 and an A-phase second switch SWA2 connected in series in an inversely symmetrical manner, the B-phase switch is composed of a B-phase first switch SWB1 and a B-phase second switch SWB2 connected in series in an inversely symmetrical manner, and the C-phase switch is composed of a C-phase first switch SWC1 and a C-phase second switch SWC2 connected in series in an inversely symmetrical manner.

[0058] The DC side rectification circuit adopts one of a full-bridge rectification circuit, a current doubler rectification circuit and a full-wave rectification circuit. Figure 1 In the illustrated embodiment, the DC side rectifier circuit adopts a full-bridge rectifier circuit composed of four rectifier diodes, two input ends of the full-bridge rectifier circuit are connected to the secondary winding of the isolation transformer, and one output end of the full-bridge rectifier circuit is connected in series with the DC side filter inductor L1 to form an output end, and a DC side filter capacitor C2 is connected between the output end and the other output end of the rectifier module.

[0059] Figure 5The circuit diagram of the DC side rectifier circuit using a current doubler rectifier circuit is shown. There are two diodes D11 and D12 with a common anode in the figure. The cathode of diode D11 is connected to one end of the isolation transformer Tr2 and one end of the inductor L3, and the cathode of diode D12 is connected to the other end of the isolation transformer Tr2 and one end of the inductor L2. The anodes of diodes D11 and D12 are connected to one end of capacitor C3, and the two ends of capacitor C3 are connected to the load. The secondary winding of the isolation transformer Tr2 generates symmetrical high-frequency positive and negative square wave voltages. When the upper end voltage of the secondary winding is positive, the secondary current passes through L3, C3 and the load, D12 and then returns to the secondary winding; when the lower end voltage of the secondary winding is positive, the secondary current passes through L2, C3 and the load, D11 and then returns to the secondary winding. According to this process, the current doubler rectifier rectifies the high-frequency AC square wave voltage into a DC output voltage. The purpose of low voltage and high current can be achieved.

[0060] Figure 6 What is shown is a circuit diagram of a DC side rectifier circuit using a full-wave rectifier circuit. In the figure, there are two secondary windings S1 and S2 connected head to tail. The head end of S1 is connected to the cathode of D13, and the anode of D13 is grounded. The tail end of S2 is connected to the cathode of D14, and the anode of D14 is grounded. The tail end of S1 is connected to the head end of S2 and connected to one end of inductor L4. The other end of L4 is connected to capacitor C4 and the ground. Both ends of capacitor C4 are connected to the load.

[0061] The present invention also discloses a control method for a soft-switching single-stage isolated three-phase ACDC converter. The converter adopts the above-mentioned soft-switching single-stage isolated three-phase ACDC converter. The control method includes a controller controlling a sector selection switch group to act, dividing a power frequency cycle of the three-phase AC power into 6 sectors, with the A phase voltage at a time when the positive half-cycle amplitude is the highest at 0, the negative half-cycle amplitude is the highest at π, and the positive half-cycle amplitude is the highest again at 2π, and the B phase lags behind. Phase A is 2π / 3, and phase C lags behind phase B by 2π / 3; the first sector is 0-π / 3, and only the B phase enable switch is turned on; the second sector is π / 3-2π / 3, and only the A phase enable switch is turned on; the third sector is 2π / 3-π, and only the C phase enable switch is turned on; the fourth sector is π-4π / 3, and only the B phase enable switch is turned on; the fifth sector is 4π / 3-5π / 3, and only the A phase enable switch is turned on; the sixth sector is 5π / 3-2π, and only the C phase enable switch is turned on. Figure 1 The A-phase switch includes SWA1+SWA2, the B-phase switch includes SWB1+SWB2, and the C-phase switch includes SWC1+SWC2 to form three bidirectional switches, each of which is enabled twice in each power frequency cycle.

[0062] Below Figure 1 The illustrated embodiment combines Figure 2The waveform comparison diagram shown illustrates the working principle of the rectifier. Before the analysis, the following assumptions are made: 1) All switches and diodes are ideal devices; 2) All inductors, capacitors, and transformers are ideal components; 3) The three-phase symmetrical ideal power grid; 4) The DC side filter inductor L1 is large enough to be regarded as an ideal current source, and idc is the DC side rectifier output current; 5) The DC side filter capacitor C2 is large enough to be regarded as an ideal voltage source, and U dc is the DC side rectifier output voltage. Figure 2 The following is a schematic diagram of the sector division of the three-phase voltage in the present invention. The cosine voltage Ua of phase A is defined as the maximum value at 0 angle, and the sine voltage Ua of phase A is defined as the minimum value at π angle. The voltage of phase B lags the voltage of phase A by 2π / 3, and the voltage of phase C lags the voltage of phase B by 4π / 3. 0-π / 3 is set as sector 1, and so on. The sector selection switch group only operates when the sector is switched. The switch state of the switch tube when each sector is switched is as follows:

[0063] As shown in Table 1, 1 represents on and 0 represents off.

[0064]

[0065] Table 1

[0066] When the sector selection switch group is in operation, the voltage U po between the positive DC bus P and the neutral line O, and the voltage U on between the neutral line O and the negative DC bus N also change in the low-frequency pulsation cycle. Taking the first sector as an example, at this time, the voltage U po is the difference U AB between the A phase voltage and the B phase voltage, and the voltage U on is the difference U BC between the B phase voltage and the C phase voltage. Therefore, the voltage U po and voltage U on conversion cycle is three times the power frequency cycle. In addition to splitting the three-phase voltage, the low-frequency sector also splits the three-phase current. The positive DC bus P current ip, the negative DC bus N current in, and their current difference (neutral line O current io) are also divided according to Figure 2 The low-frequency pulsation shown in the figure can achieve a sinusoidal converter AC current and a unity power factor.

[0067] The following uses the first sector as an example to calculate the mode conduction time, such as Figure 4 As shown, assuming that Dp is the chopping current width on the positive bus, Dn is the chopping current width on the negative bus, and the difference between the two is the chopping current width injected into the neutral line O. Since the DC side filter inductor (L1) of the DC side rectifier circuit can be regarded as a constant DC source, the positive DC bus P current ip can be regarded as the chopping current of the DC side rectifier output current idc, and similarly, the negative DC bus N current in can be regarded as the chopping current of the DC side rectifier output current idc.

[0068] In the first sector, the positive DC bus P current ip is the A-phase power frequency current, the DC bus N current in is the C-phase power frequency current, and the neutral line O current io is the B-phase power frequency current. According to the average value equivalent principle, the average current ip of any switching cycle can be expressed as:

[0069] i p (t) = D p (t)·I dc ·k where k is the secondary-to-primary ratio of the isolation transformer. Similarly, we have:

[0070] |i o (t)|=|D p (t)-D n (t)|·I dc ·ki n (t) = D n (t)·I dc ·k

[0071] When the periodic average values ​​of the current ip and in at any time are equal to the instantaneous value of the AC side current, the AC current sinusoidal degree and unity power factor control are achieved. Therefore, the expressions of the two current control widths in the first sector are:

[0072] D p (t) = i a / I dc k, D n (t) = i c / I dc .k

[0073] The other five sectors can be deduced in the same way.

[0074] In a preferred embodiment, the duty cycle of the first switch SW1 is DP, and the duty cycle of the fourth switch SW4 is DN;

[0075] In the first fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using formula 1.

[0076] D p (t) = i a / I dc k, D n (t) = i c / I dc .k (Formula 1);

[0077] In the second fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using formula 2:

[0078] D p (t) = i b / I dc k, Dn (t) = i c / I dc k (Formula 2);

[0079] In the third fan, the duty cycle of the first switch SW1 and the fourth switch SW4 is calculated using Formula 3:

[0080] D p (t) = i b / I dc k, D n (t) = i a / I dc k (Formula 3);

[0081] In the fourth fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using formula 4:

[0082] D p (t) = i c / I dc k, D n (t) = i a / I dc k (Formula 4);

[0083] In the fifth fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using Formula 5,

[0084] D p (t) = i c / I dc k, D n (t) = i b / I dc k (Formula 5);

[0085] In the sixth fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using Formula 6:

[0086] D p (t) = i a / I dc k, D n (t) = i b / I dc k (Formula 6);

[0087] In the above formula, ia is the A phase current, ib is the B phase current, ic is the C phase current, Idc is the output current of the DC side rectifier circuit, and k is the primary-secondary transformation ratio of the isolation transformer.

[0088] The driving signal of the first switch SW1 generates the driving signal of the second switch SW2 through an inverter with a dead zone, that is, SW1 and SW2 are driven by complementary driving signals with a dead zone, and the driving signal of the third switch SW3 generates the driving signal of the fourth switch SW4 through an inverter with a dead zone, that is, SW3 and SW4 are driven by complementary driving signals with a dead zone, so that zero voltage switching is achieved in a wide load range, the DC blocking capacitor C1 is charged and discharged, and an alternating current is output to the primary winding of the isolation transformer.

[0089] Figure 3a The diagram shows the conduction state of SW1 and SW4. SW1 and SW4 are turned on, and SW2 and SW3 are turned off. In this process, the primary current flows from the positive DC bus P through SW1, the DC blocking capacitor, the isolation transformer, and SW4 to the negative DC bus N.

[0090] Figure 3b The diagram shows the SW1 conduction state (the transient process of realizing SW3 ZVS). SW1 is turned on, and SW2, SW3, and SW4 are turned off. The transformer primary current switches from the channel of Sw4 to the charging and discharging of the parasitic junction capacitance of Sw3 and Sw4. When the charging and discharging is completed, the potential of the node N+ is equal to the potential of the node O, and the process ends. After this process, the soft turn-on of the next mode SW3 can be realized. This mode is the transient process of the switching device.

[0091] Figure 3c The diagram shows the conduction state of SW1 and SW3. SW1 and SW3 are turned on, and SW2 and SW4 are turned off. In this process, the primary current flows from the positive DC bus P through SW1, the DC blocking capacitor, the isolation transformer, and SW3 to the common node O of the three-phase selection.

[0092] Figure 3d The diagram shows the SW3 conduction state (the transient process of realizing SW2 ZVS). SW3 is turned on, and SW1, SW2, and SW4 are turned off. The transformer primary current switches from the channel of Sw1 to the charging and discharging of the parasitic junction capacitance of Sw1 and Sw2. When the charging and discharging are completed, the P-connection point is equal to the potential of the neutral line O, and the process ends. After this process, the soft opening of SW2 in the next mode can be realized, preparing for the turning off of Sw1 and Sw4 and the turning on of Sw2 and Sw3. This mode is the transient process of the switching device.

[0093] Figure 3e The diagram shows the on-state of W2 and SW3. Sw1 and Sw4 are off, and Sw2 and Sw3 are on. The primary current loop is the DC blocking capacitor, SW2, SW3, and transformer.

[0094] Figure 3fThe diagram shows the fully disconnected state of SW1, SW2, SW3, and SW4 (realizing the transient process of SW1 and ZV4 ZVS). SW1 to SW4 are turned off. The primary current of the transformer switches from the channel of Sw2 and SW3 to the parasitic junction capacitance charging and discharging of Sw1, Sw2 and SW3 and SW4. When the charging and discharging is completed, that is, when the potential of the P- and N- nodes reaches the nodes P and N respectively, the process ends, and the zero voltage turn-on of SW1 and SW4 can be realized. This mode is the transient process of the switching device.

[0095] See also Figure 7 The control principle block diagram of the preferred embodiment shown, the controller samples the three-phase AC power, and controls the sector selection switch group to operate after the sector selection function module calculates;

[0096] The controller controls the voltage Vp of the positive DC bus P and the voltage V N , the output current Idc of the DC side rectifier circuit, and the output voltage Vout of the DC side rectifier circuit are sampled respectively; the voltage Vp is multiplied by the control loop optimization parameter Kin to generate a positive input sampling value, and sent to the first adder;

[0097] The voltage VN is inverted and then multiplied with the control loop optimization parameter Kin to generate a negative input sampling value, which is sent to the second adder;

[0098] The output voltage reference value Vout* is subtracted from the output voltage Vout, and then the output voltage loop control (transfer function R(S)) is performed, and then the output current Idc is subtracted, and then the output current loop control (transfer function G(S)) is performed to generate the duty cycle error adjustment amount △d, which is then sent to the first adder J1;

[0099] In the first adder J1, the positive input sampling value and the duty cycle error adjustment value Δd are added and sent to the first PWM generator to generate a first PWM control signal;

[0100] In the second adder J2, the negative input sampling value and the duty cycle error adjustment value Δd are added and sent to the second PWM generator to generate a second PWM control signal;

[0101] The first PWM control signal is sent to the control end of the first switch SW1, and at the same time, a signal which is opposite to the first PWM control signal and has a dead zone is generated by the first NOT gate and sent to the control end of the second switch SW2;

[0102] The second PWM control signal is sent to the control end of the fourth switch SW4, and at the same time, a signal which is opposite to the second PWM control signal and has a dead zone is generated by the second NOT gate and sent to the control end of the third switch SW3.

[0103] In a preferred embodiment, the control loop optimization parameter Kin is equal to 2Vout×n / 3Um 2 , wherein Vout is the output voltage Vout, n is the turns ratio of the primary side to the secondary side of the isolation transformer, and Um is the phase voltage peak value of the three-phase AC input.

[0104] Unless otherwise defined in the art, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by ordinary technicians in the field to which the invention belongs. It should also be understood that those terms such as those defined in general dictionaries should be understood to have the meaning consistent with the meaning in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0105] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A control method for a soft-switching single-stage isolated three-phase ACDC converter, characterized in that: The converter includes a three-phase uncontrolled rectifier bridge, a charge and discharge control branch, a sector selection switch group, a DC isolation capacitor C1, an isolation transformer, a DC side rectifier circuit, and a controller, wherein The A-phase input terminal, the B-phase input terminal and the C-phase input terminal of the three-phase uncontrolled rectifier bridge are connected to the three-phase alternating current, and the positive DC bus P and the negative DC bus N are connected to the charge and discharge control branch; The charge and discharge control branch includes a first switch SW1, a second switch SW2, a third switch SW3, and a fourth switch SW4 connected in series in sequence, the first switch SW1 and the second switch SW2 are connected as a P-connection point, the second switch SW2 and the third switch SW3 are connected as a neutral line O, and the third switch SW3 and the fourth switch SW4 are connected as an N+ connection point; The sector selection switch group includes an A-phase switch, a B-phase switch, and a C-phase switch, wherein the A-phase switch is connected in series between the A-phase input terminal and the neutral line O, the B-phase switch is connected in series between the B-phase input terminal and the neutral line O, and the C-phase switch is connected in series between the C-phase input terminal and the neutral line O; The DC blocking capacitor C1 is connected in series with the primary winding of the isolation transformer and then connected between the P-connection point and the N+ connection point; The DC side rectifier circuit is connected to the secondary winding of the isolation transformer to provide DC power to the load; The controller controls the switch actions in the charge and discharge control branch and the sector selection switch group, outputs alternating current to the primary winding of the isolation transformer, and the secondary winding of the isolation transformer and the DC side rectifier circuit output direct current power; A three-phase EMI filter is provided between the A-phase input terminal, the B-phase input terminal and the C-phase input terminal and the three-phase alternating current; The A-phase switch is composed of an A-phase first switch (SWA1) and an A-phase second switch (SWA2) connected in series in an anti-symmetrical manner, the B-phase switch is composed of a B-phase first switch (SWB1) and a B-phase second switch (SWB2) connected in series in an anti-symmetrical manner, and the C-phase switch is composed of a C-phase first switch (SWC1) and a C-phase second switch (SWC2) connected in series in an anti-symmetrical manner; The control method includes: a controller controls a sector selection switch group to operate, and a three-phase alternating current is switched to a working The frequency cycle is divided into 6 sectors, with the highest amplitude of the positive half cycle of the A phase voltage at one moment being 0, the highest amplitude of the negative half cycle being π, and the highest amplitude of the positive half cycle being 2π. The B phase lags the A phase by 2π / 3, and the C phase lags the B phase by 2π / 3. The first sector is 0-π / 3, and only the B phase gate switch is turned on. The second sector is π / 3-2π / 3, and only the A phase gate switch is turned on. The third sector is 2π / 3-π, and only the C phase gate switch is turned on. The fourth sector is π-4π / 3, and only the B phase gate switch is turned on. The fifth sector is 4π / 3-5π / 3, and only the A phase gate switch is turned on. The sixth sector is 5π / 3-2π, and only the C phase gate switch is turned on. The duty cycle of the first switch SW1 is DP, and the duty cycle of the fourth switch SW4 is DN; In the first fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using formula 1. D p D(t) = i a / I dc ·k, D n D(t) = i c / I dc ·k (Formula 1); In the second fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using formula 2: D p D(t) = i b / I dc ·k, D n D(t) = i c / I dc ·k (Formula 2); In the third fan, the duty cycle of the first switch SW1 and the fourth switch SW4 is calculated using Formula 3: D p D(t) = i b / I dc ·k, D n D(t) = i a / I dc ·k (Equation 3); In the fourth fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using formula 4: D p D(t) = i c / I dc ·k, D n D(t) = i a / I dc ·k (Equation 4); In the fifth fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using Formula 5, D p D(t) = i c / I dc ·k, D n D(t) = i b / I dc ·k (Formula 5); In the sixth fan, the duty ratio of the first switch SW1 and the fourth switch SW4 is calculated using Formula 6: D p D(t) = i a / I dc ·k, D n D(t) = i b / I dc ·k (Formula 6); In the above formula, ia is the A phase current, ib is the B phase current, ic is the C phase current, Idc is the output current of the DC side rectifier circuit, and k is the primary-secondary ratio of the isolation transformer; The first switch SW1 and the second switch SW2 are a pair of complementary conduction transistors with a dead zone, and the third switch SW3 and the fourth switch SW4 are a pair of complementary conduction transistors with a dead zone. The controller controls the first switch SW1 to the fourth switch SW4 to switch, realizes zero voltage switching in a wide load range, charges and discharges the DC blocking capacitor C1, and outputs an alternating current to the primary winding of the isolation transformer; The controller samples the three-phase alternating current, and controls the action of the sector selection switch group after calculation by the sector selection function module; The controller controls the voltage Vp of the positive DC bus P and the voltage V N , the output current Idc of the DC side rectifier circuit, and the output voltage Vout of the DC side rectifier circuit are sampled respectively; The voltage Vp is multiplied by the control loop optimization parameter Kin to generate a positive input sampling value, and sent to the first adder; The voltage V N After inversion, it is multiplied with the control loop optimization parameter Kin to generate the negative input sampling value and sent to the second adder; The output voltage reference value Vout* is subtracted from the output voltage Vout, and then the output voltage loop control (R(S)) is performed, and then the output current Idc is subtracted, and then the output current loop control (G(S)) is performed to generate the duty cycle error adjustment amount △d, which is then sent to the first adder (J1); In a first adder (J1), the positive input sampling value and the duty cycle error adjustment value Δd are added and sent to a first PWM generator to generate a first PWM control signal; In the second adder (J2), the negative input sampling value and the duty cycle error adjustment value Δd are added and sent to the second PWM generator to generate a second PWM control signal; The first PWM control signal is sent to the control end of the first switch SW1, and at the same time, a signal which is opposite to the first PWM control signal and has a dead zone is generated by the first NOT gate and sent to the control end of the second switch SW2; The second PWM control signal is sent to the control end of the fourth switch SW4, and at the same time, a signal which is opposite to the second PWM control signal and has a dead zone is generated by the second NOT gate and sent to the control end of the third switch SW3.

2. The control method of the soft-switching single-stage isolated three-phase ACDC converter according to claim 1, characterized in that: The control loop optimization parameter Kin is equal to 2Vout×n / 3Um 2 , wherein Vout is the output voltage Vout, n is the turns ratio of the primary side to the secondary side of the isolation transformer, and Um is the phase voltage peak value of the three-phase AC input.

3. The control method of the soft-switching single-stage isolated three-phase ACDC converter according to claim 1, characterized in that: The DC side rectification circuit adopts one of a full-bridge rectification circuit, a current doubler rectification circuit and a full-wave rectification circuit.

Images