Control circuit and method of three-phase single-stage AC / DC converter

Abstract

The invention discloses a control circuit and method for a three-phase single-stage AC / DC converter, and belongs to the technical field of electric energy conversion, and the method comprises the steps: collecting the resonance current in a DC / DC resonance circuit, calculating the integral value of the resonance current, outputting a signal after modulation, and determining the drive logic of a switch in the DC / DC resonance circuit. According to the control circuit and method of the three-phase single-stage AC / DC converter, energy transmitted by the resonant cavity can be directly controlled, the resonance condition of each switching period element does not need to be considered, parameter design is simple, the dynamic performance of a system can be improved, and the control speed of three-phase current can be increased.

Description

Technical Field

[0001] The present invention relates to the technical field of electric energy conversion, and in particular to a control circuit and method of a three-phase single-stage AC / DC converter. Background Art

[0002] With the explosive growth of distributed energy storage, microgrids and vehicle-to-grid (V2G) applications, isolated AC / DC converters, as key power electronic devices that convert grid AC power into DC power, have received widespread attention.

[0003] Among them, the single-stage AC / DC converter structure can improve the overall efficiency and power density of the converter by reducing the energy conversion level and removing the intermediate DC bus capacitor, which is more in line with the design requirements of current AC / DC power supply equipment. In recent years, the single-stage AC / DC converter structures that have been widely studied are divided into two categories: one is the dual active bridge structure based on phase shift control (Baranwal R, Iyer KV, Basu K, et al. AReduced Switch Count Single-Stage Three-Phase Bidirectional Rectifier With High-Frequency Isolation [J]. IEEE Transactions on Power Electronics, 2018.). The other is the matrix conversion structure composed of bidirectional switches with complex conduction timing (Afsharian J, Xu DD, Wu B, et al. The Optimal PWM Modulation and Commutation Scheme for a Three-Phase Isolated Buck Matrix-Type Rectifier [J]. IEEE Transactions on Power Electronics, 2017: 110-124.). Although these structures can achieve single-stage AC / DC conversion through complex control strategies, they cannot guarantee soft switching of all switches under full load conditions, which limits the promotion and application of such converters.

[0004] The literature (Zhang B, Xie S, Li Z, et al. An Optimized Single-Stage Isolated Swiss-type AC / DC converter Based on Single Full-Bridge with Midpoint-Clamper [J]. IEEE Transactions on Power Electronics, 2021, PP (99): 1-1.) proposes a three-phase single-stage AC / DC converter based on a Swiss rectifier. The LLC resonant circuit is added to the Swiss-type AC / DC conversion process, and the LLC resonant cavity is used to realize the soft switching of the high-frequency switch tube to reduce the switching loss. At the same time, the wide gain characteristics of the LLC are used to adjust the switching frequency of the LLC resonant cavity to complete the three-phase input current control and output voltage control.

[0005] The current three-phase single-stage AC / DC resonant converter based on Swiss rectifier adopts input current sampling, direct switching frequency modulation combined with duty cycle adjustment. Like the traditional AC / DC converter, the control loop of output voltage is the outer loop, and the output of the control loop is the maximum value of input current. The control loop of input current is the inner loop, and the output of the control loop is the switching frequency and duty cycle. A 、u B 、u C Redefined: The phase with the largest absolute value of instantaneous voltage is defined as L phase, and its phase voltage is u L ; The phase with the smallest absolute value of instantaneous voltage is defined as phase S, and its phase voltage is u S ; The remaining phase is defined as phase M, and its phase voltage is u M . However, the disadvantage of this control method is that the working characteristics of the LLC resonant cavity are different under different working conditions, and the amount of energy it can transfer is also different, so the output voltage and input current will change with the change of the switching frequency. But the change law of the working state of the LLC resonant cavity is very complicated, and it does not change linearly with the change of the switching frequency. This makes the corresponding controller design very complicated, and it is necessary to design multiple sets of control parameters to cope with the working state requirements of the LLC resonant cavity at different phases, and the control effect is not good. Moreover, the switching frequency can only indirectly control the energy of the LLC resonant cavity, which limits the dynamic adjustment ability and current control loop bandwidth of the direct frequency control strategy. In addition, in AC / DC, where external conditions (voltage, power) are always changing, the dependence on the current loop bandwidth is very large. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a control circuit and method for a three-phase single-stage AC / DC converter, which samples the resonant current for direct control.

[0007] To achieve the above object, the technical solution of the present invention is:

[0008] A control method for a three-phase single-stage AC / DC converter is applied to a three-phase single-stage AC / DC converter, wherein the three-phase single-stage AC / DC converter comprises an AC / DC rectifier circuit and a DC / DC resonant circuit, wherein the input of the AC / DC rectifier circuit is connected to a three-phase AC voltage, the AC / DC rectifier circuit outputs a DC power to the input of the DC / DC resonant circuit, and the DC / DC resonant circuit outputs a DC voltage; comprising:

[0009] Determining the phase angle of the three-phase AC voltage according to the three-phase AC voltage, and determining the driving logic of the switch in the AC / DC rectifier circuit;

[0010] The output voltage is compared with the output voltage reference value and the maximum current value I is output after modulation MAX ;

[0011] According to the three-phase AC voltage and the three-phase AC current, the L, M, and S phases are determined, and the first current reference value I is output after processing. Mref , the second current reference value I Lref 、Current i M The absolute value of |i M |With current i L The absolute value of |i L |; Collect the resonant current in the DC / DC resonant circuit, calculate the integral value of the resonant current, output the signal after modulation, and determine the driving logic of the switch in the DC / DC resonant circuit.

[0012] Furthermore, the phase with the largest absolute value of instantaneous voltage is defined as phase L, and its phase voltage is u L ; The phase with the smallest absolute value of instantaneous voltage is defined as phase S, and its phase voltage is u S ; The remaining phase is defined as phase M, and its phase voltage is u M , the expression of each phase voltage is as follows:

[0013]

[0014] Among them, the current i L and phase angle θ L is the phase voltage u L The corresponding phase current and phase angle, current i S and phase angle θ S is the phase voltage u S The corresponding phase current and phase angle, current iM and phase angle θ M is the phase voltage u M The corresponding phase current and phase angle.

[0015] Furthermore, the current i M Converted into current i M The absolute value of |i M |, the current i L Converted into current i L The absolute value of |i L |, the phase angle θ M Sine of sin(θ M ) is transformed into a phase angle θ M The absolute value of sine | sin(θ M )|, the phase angle θ L The sine of sin(θ L ) is transformed into a phase angle θ L The absolute value of sine | sin(θ L )|, the phase angle θ M The absolute value of sine | sin(θ M )| and the maximum current value I MAX Multiply to obtain the first current reference value I Mref , the phase angle θ L The absolute value of sine | sin(θ L )| and the maximum current value I MAX Multiply to obtain the second current reference value I Lref .

[0016] Furthermore, the above resonant current integral value includes the interval [0-D PN T s ] and the first resonant current integral value in the interval [0-T s / 2] within the second resonant current integral value.

[0017] In a specific embodiment, a first resonant current average value is obtained according to the first resonant current integral value, a second resonant current average value is obtained according to the second resonant current integral value, and the first current reference value I Mref Subtract the first resonant current average value after modulation to obtain the duty cycle D PN ; Subtract the second current reference value I from the second resonant current average value Lref After modulation, the switching frequency f s , where the duty cycle D PN is the voltage u in half a cycle PN The proportion of working hours.

[0018] In a specific embodiment, the second current reference value I LrefSubtract the current i L The absolute value of |i L |Get the current I Le , the current I Le After modulation, the first integration threshold v is obtained comp1 ; The first current reference value I Mref Subtract the current i M The absolute value of |i M |Get the current I Me , the current I Me After modulation, the second integration threshold v is obtained comp2 If the second resonant current integral value exceeds the first integral threshold value v comp1 , and obtain the half switching cycle length Ts / 2; if the first resonant current integral value exceeds the second integral threshold value v comp2 , get the working time D PN T s .

[0019] Furthermore, if the DC / DC resonant circuit includes a plurality of resonant cavities, the current of a single resonant cavity may be sampled for control, and a driving signal may be obtained and then output to other resonant cavities.

[0020] The present invention also provides a control circuit of a three-phase single-stage AC / DC converter, which executes the control method of the three-phase single-stage AC / DC converter as described above, wherein the control circuit includes a phase-locked loop module, a current loop module, a voltage loop module, a resonant current control module, a first drive logic module and a second drive logic module;

[0021] The phase-locked loop module outputs the phase angle of the three-phase AC voltage according to the three-phase AC voltage and outputs it to the first driving logic module, and the first driving logic module determines the driving logic of the switch in the AC / DC rectifier circuit according to the phase angle of the three-phase AC voltage;

[0022] The voltage loop module compares the output voltage with the output voltage reference value and modulates the output maximum current value I MAX To the current loop module;

[0023] The current loop module determines the L, M, and S phases according to the three-phase AC voltage and the three-phase AC current, and outputs the first current reference value I after processing. Mref , the second current reference value I Lref 、Current i M The absolute value of |i M |With current i L The absolute value of |i L | to the resonant current control module;

[0024] The resonant current control module collects the resonant current in the DC / DC resonant circuit, calculates the integral value of the resonant current, and outputs a signal to the second drive logic module after modulation. The second drive logic module determines the drive logic of the switch in the DC / DC resonant circuit.

[0025] Furthermore, the resonant current control module comprises a first integrator, a second integrator, a first sample holder and a second sample holder, wherein the first integrator performs a sampling operation on the interval [0-D PN T s ], the second integrator integrates the resonant current in the interval [0-T s / 2], the first sample holder maintains t=D PN T s The first resonant current integral value at the moment t=T s / 2 time the second resonant current integration value.

[0026] Furthermore, the resonant current control module further includes a PWM counter, a first comparator and a second comparator, wherein the first comparator compares the first resonant current integral value with the second integral threshold value v comp2 After comparison, the third trigger signal v is obtained trig3 The second comparator compares the second resonant current integral value with the first integral threshold value v comp1 After comparison, the fourth trigger signal v is obtained trig4 , the third trigger signal v trig3 With the fourth trigger signal v trig4 Output to the PWM counter, the PWM counter according to the third trigger signal v trig3 With the fourth trigger signal v trig4 The switching frequency f is obtained s and duty cycle D PN .

[0027] Furthermore, the above-mentioned resonant current control module also includes a rectifier, the input of the rectifier is connected to the two ends of the current transformer, the current transformer detects the resonant current, the output of the rectifier is connected to the first inverter and the second inverter, the output of the first inverter is connected to the first integrator, and the output of the second inverter is connected to the second integrator.

[0028] Furthermore, the current loop module converts the current i M Converted into current i M The absolute value of |i M |, the current i L Converted into current i L The absolute value of |i L |, the phase angle θM The sine of sin(θ M ) is transformed into a phase angle θ M The absolute value of sine | sin(θ M )|, the phase angle θ L The sine of sin(θ L ) is transformed into a phase angle θ L The absolute value of sine | sin(θ L )|, the phase angle θ M The absolute value of sine | sin(θ M )| and the maximum current value I MAX Multiply to obtain the first current reference value I Mref , the phase angle θ L The absolute value of sine | sin(θ L )| and the maximum current value I MAX Multiply to obtain the second current reference value I Lref .

[0029] Beneficial effect: The control circuit and method of the three-phase single-stage AC / DC converter of the present invention can directly control the energy transmitted by the resonant cavity without considering the resonance of the components in each switching cycle. The parameter design is simple, and the dynamic performance of the system can be improved, and the control speed of the three-phase current can be increased.

[0030] In order to make the above features and advantages of the invention more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a control block diagram of a three-phase single-stage AC / DC converter.

[0032] Figure 2 for Figure 1 A schematic diagram of a specific embodiment of the circuit in FIG.

[0033] Figure 3 for Figure 2 Switching logic and voltage waveform diagram of the embodiment in FIG.

[0034] Figure 4 (a) is the voltage u PY Greater than voltage u YN The switching logic and resonant voltage and current waveforms in the DC / DC resonant circuit; Figure 4 (b) is the voltage u YN Greater than voltage u PY The switching logic and resonant voltage and current waveforms in the DC / DC resonant circuit.

[0035] Figure 5 for Figure 2A schematic diagram of a specific embodiment of a resonant current control module.

[0036] Figure 6 (a) Figure 5 In the embodiment in the interval [0-D PN T s ] schematic diagram of the resonant voltage and current waveforms; Figure 6 (b) Figure 5 In the embodiment in the interval [0-T s / 2] Schematic diagram of the resonant voltage and current waveforms.

[0037] Figure 7 for Figure 2 A schematic diagram of another specific embodiment of the resonant current control module.

[0038] Figure 8 (a) Figure 7 Schematic diagram of the resonant voltage and current waveforms of the embodiment; Figure 8 (b) is the trigger signal v trig3 Schematic diagram of the resonant voltage and current waveforms when the triggering duration is shorter than the shortest operating duration.

[0039] Fig. 9 Circuit diagram of the Swiss-LLC topology with four LLC cavities connected in parallel.

[0040] In the drawings, like reference numerals refer to the same drawing elements. DETAILED DESCRIPTION

[0041] In order to make the purpose and technical solution of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Figure 1 1 is a control block diagram of a three-phase single-stage AC / DC converter of the present invention. More specifically, the three-phase AC voltage u A 、u B 、u C The input is to the AC / DC rectifier circuit 11, the AC / DC rectifier circuit 11 outputs direct current to the three terminals PYN, and the DC / DC resonant circuit 12 converts the electric energy at the three terminals PYN to output the voltage Vo to the load. The DC / DC resonant circuit 12 adjusts the output voltage Vo and the three-phase AC current i A 、i B 、i C, or adjust the output current Io and the three-phase AC current i A 、i B 、i C The control circuit 13 receives the three-phase AC voltage u A 、u B 、u C , the output voltage Vo and the resonant current of the DC / DC resonant circuit 12 are calculated and then output as a driving signal to the switch tubes of the AC / DC rectifier circuit 11 and the DC / DC resonant circuit 12.

[0043] Further, the control circuit 13 includes a phase-locked loop module 131, a current loop module 132, a voltage loop module 133, a resonant current control module 134, a first drive logic module 135 and a second drive logic module 136. The input of the phase-locked loop module 131 is connected to the three-phase AC voltage, the output of the phase-locked loop module 131 is connected to the input of the first drive logic module 135 and the input of the second drive logic module 136, the output of the first drive logic module 135 is connected to the AC / DC rectifier circuit 11, the input of the voltage loop module 133 is connected to the output voltage Vo, the output of the voltage loop module 133 is connected to the current loop module 132, the output of the phase-locked loop module 131 and the three-phase AC voltage are both connected to the current loop module 132, the output of the current loop module 132 is connected to the resonant current control module 134, the resonant current control module 134 is connected to the DC / DC resonant circuit 12, the output of the resonant current control module 134 is connected to the second drive logic module 136, and the output of the second drive logic module 136 is connected to the DC / DC resonant circuit 12.

[0044] Furthermore, the input of the phase-locked loop module 131 is a three-phase AC voltage u A 、u B 、u C , after processing, the output three-phase AC voltage u A 、u B 、u C The phase angle θ A ,θ B ,θ C to the first driving logic module 135, and the first driving logic module 135 generates a signal according to the phase angle θ A ,θ B ,θ C Determine the driving logic of the switch in the AC / DC rectifier circuit 11.

[0045] The voltage loop module 133 compares the output voltage Vo with the voltage reference value V ref After comparison and PI modulation, the maximum current value I is output MAX to the current loop module 132 .

[0046] The current loop module 132 generates a three-phase AC voltage uA 、u B 、u C and the three-phase alternating current i A 、i B 、i C , determine the L, M, and S phases, where the phase with the largest absolute value of instantaneous voltage is defined as the L phase, and its phase voltage is u L ; The phase with the smallest absolute value of instantaneous voltage is defined as phase S, and its phase voltage is u S ; The remaining phase is defined as phase M, and its phase voltage is u M , the expression of each phase voltage is as follows:

[0047]

[0048] Among them, the current i L and phase angle θ L is the phase voltage u L The corresponding phase current and phase angle, current i S and phase angle θ S is the phase voltage u S The corresponding phase current and phase angle, current i M and phase angle θ M is the phase voltage u M The corresponding phase current and phase angle.

[0049] The current loop module 132 converts the current i M Converted into current i M The absolute value of |i M |, the current i L Converted into current i L The absolute value of |i L |, the phase angle θ M The sine of sin(θ M ) is transformed into a phase angle θ M The absolute value of sine | sin(θ M )|, the phase angle θ L The sine of sin(θ L ) is transformed into a phase angle θ L The absolute value of sine | sin(θ L )|, the phase angle θ M The absolute value of sine | sin(θ M )| and the maximum current value I MAX Multiply to obtain the first current reference value I Mref . Set the phase angle θ L The absolute value of sine | sin(θ L )| and the maximum current value I MAX Multiply to obtain the second current reference value I Lref .

[0050] The first current reference value I Mref , the second current reference value I Lref 、Current i M The absolute value of |i M |With current i L The absolute value of |i L The resonant current control module 134 is input, and the resonant current control module 134 collects the resonant current in the DC / DC resonant circuit 12, and outputs a signal G1 to the second drive logic module 136 after the resonant current control to determine the drive logic of the switch in the DC / DC resonant circuit 12.

[0051] Figure 2 for Figure 1 In this specific embodiment, the AC / DC rectifier circuit 21 is a Swiss rectifier circuit, and the DC / DC resonant circuit 22 includes a three-level bridge module 221, a resonant module 222, and a secondary rectifier module 223. The three-level bridge module 221, the resonant module 222, and the secondary rectifier module 223 are connected in parallel in sequence. Figure 2 The resonant module 222 in the embodiment is of LLC topology.

[0052] It should be noted that the resonance module 222 may also be an LC topology or a DAB topology.

[0053] The AC / DC rectifier circuit 21 includes bidirectional switch tubes Say, Sby, and Scy, which are switched on at a low frequency when the two-phase voltages intersect. The bidirectional switch of the phase with the larger absolute value of the voltage amplitude of the two intersecting phases is turned off, and the bidirectional switch of the phase with the smaller amplitude is turned on. In this way, the phase with the larger amplitude in the forward voltage is connected to the P terminal through the upper diode Dp, the phase with the larger amplitude in the negative voltage is connected to the N terminal through the lower diode Dn, and the remaining phase is connected to the Y terminal through the turned-on bidirectional switch Sy. Figure 3 (a) with Figure 3 (b), will u A 、u B 、u C becomes u P 、u N 、u Y , we get three positive line voltages u PN 、u PY and u YN , where u PN It is always the largest one, no matter the input voltage is normal or distorted or there is three-phase imbalance. PN Always the largest one, the other two u PY and u YN Alternate changes.

[0054] The input voltage of the DC / DC resonant circuit 22 is three line voltages u PN 、u PY and u YN , high frequency switching of the switches in the three-level bridge module 221, the voltage u PN 、u PY 、u YN The 0 level and the 10 level are fed to the resonance module 222 , and the resonance module 222 is used to provide a soft switching condition for the switches in the three-level bridge module 221 .

[0055] Figure 4 (a) is the voltage u PY Greater than voltage u YN The switching logic and the resonant voltage and current waveforms in the DC / DC resonant circuit 22; Figure 4 (b) is the voltage u YN Greater than voltage u PY The switching logic and the resonant voltage and current waveforms in the DC / DC resonant circuit 22 are shown in FIG. PN is the LLC input voltage u in half a cycle PN The duty cycle of the working time is used to change the resonant current i from half a cycle Lr The appropriate current is separated to become the L phase current. Voltage u PY Duty cycle D PY 0.5-D PN , voltage u YN Duty cycle D YN 0.5-D PN .

[0056] Figure 2 The control circuit 23 and Figure 1 The structure and principle of the control circuit 13 are the same, and will not be repeated here. The resonant current control module 234 samples the resonant current i in the resonant module 222. Lr .

[0057] Figure 5 for Figure 2 Schematic diagram of a specific embodiment of the resonant current control module in FIG. Lr Integrate and average, use the average value of the resonant current to directly control the energy transferred by the LLC resonant cavity, and adjust the input current directly by changing the average value of the resonant current in the LLC resonant cavity. The resonant current control module 534 includes an integrator 5341, an integrator 5342, a sample holder 5343 and a sample holder 5344, and the resistor R1 is connected in parallel at both ends of the current transformer CT1, and the resistor R1 is a resonant current sampling resistor.

[0058] In the integrator 5341, the negative input terminal of the operational amplifier A1 is connected to the first terminal of the resistor R1 and grounded, the positive input terminal is connected to the second terminal of the resistor R1 through the resistor R2, the first terminal of the capacitor C1 is connected to the positive input terminal of the operational amplifier A1, the second terminal of the capacitor C1 is connected to the output terminal of the operational amplifier A1, and the switch Q1 is connected in parallel to both ends of the capacitor C1. Among them, the capacitor C1 is an integrating capacitor, the switch Q1 is a bidirectional switch, and the switch Q1 is connected in series with the resistor R2 for discharge.

[0059] In the integrator 5342, the negative input terminal of the operational amplifier A2 is connected to the first terminal of the resistor R1 and grounded, the positive input terminal is connected to the second terminal of the resistor R1 through the resistor R3, the first terminal of the capacitor C1 is connected to the positive input terminal of the operational amplifier A2, the second terminal of the capacitor C1 is connected to the output terminal of the operational amplifier A2, and the switch Q2 is connected in parallel to both ends of the capacitor C2. Among them, the capacitor C2 is an integrating capacitor, the switch Q2 is a bidirectional switch, and the switch Q2 is connected in series with the resistor R3 for discharge.

[0060] Optionally, sample holder 5343 and sample holder 5344 are in the DSP.

[0061] More specifically, the resonant current i is sampled using the current transformer CT1. Lr The voltage across the resistor R1 is integrated using integrators 5341 and 5342. The integrated value of the resonant current at a specific moment is obtained using sample holders 5343 and 5344.

[0062] Furthermore, the integrator 5341 is responsible for the integration interval [0-D PN T s ] resonant current, the voltage across capacitor C1 is v int1 represents the current integral in this interval. Switch Q1 is the discharge switch of integrator 5341. After switch Q1 is turned on, the voltage across capacitor C1 becomes 0V. trig1 is the trigger signal of the sample and hold 5343. PN T s , trigger signal v trig1 =1, the sample holder 5343 maintains t=D PN T s The first resonant current integral value at time The waveform diagram of the relevant voltage and current is as follows Figure 6 (a) shown.

[0063] Integrator 5342 is responsible for the integration interval [0-T s / 2], the resonant current in the capacitor C2, and the voltage v int2represents the current integral in this interval. Switch Q2 is the discharge switch of integrator 5342. After switch Q2 is turned on, the voltage across capacitor C2 becomes 0V. trig2 is the trigger signal of the sample and hold 5344. s / 2, trigger signal v trig2 =1, the sample holder 5344 maintains t=T s The second resonant current integral value at time / 2 The schematic diagram of the relevant voltage and current is as follows Figure 6 (b) as shown.

[0064] Then, the first resonant current integral value and the second resonant current integral value are divided by half the period T S / 2 to obtain the first resonant current average value and the second resonant current average value; the first current reference value I Mref Subtract the average value of the first resonant current and get the duty cycle D after PI modulation PN ; Subtract the second current reference value I from the second resonant current average value Lref After PI modulation, the switching frequency f s .

[0065] The duty cycle D PN and the switching frequency f s The output is sent to the second driving logic module 236 to drive the switch in the DC / DC resonant circuit 22 .

[0066] In this specific embodiment, the use of the average value of the resonant current for control can directly control and distribute the current of the resonant cavity, eliminate the interference of the input filter circuit, and increase the speed of the control loop.

[0067] Figure 7 for Figure 2 Schematic diagram of another specific embodiment of the resonant current control module in FIG. Lr Integrate to obtain the charge information of the energy transferred in the DC / DC resonant circuit 12 and perform charge control. The essence of charge control is the hysteresis control of the resonant current integration, which belongs to nonlinear control. In charge control, the switching frequency f s and duty cycle D PN They are all generated by the comparator and PWM counter, with faster adjustment speed, which is suitable for occasions where external conditions change quickly such as AC / DC conversion.

[0068] Optionally, the comparator is an analog comparator located in the DSP.

[0069] The integrator 7341, the integrator 7342, the sample holder 7343 and the sample holder 7344 in the resonant current control module 734 are connected to the Figure 5The structure and principle are the same as those in FIG. 7 , and will not be described in detail here. The resonant current control module 734 also includes a PWM counter 7345 .

[0070] More specifically, the resonant current i is sampled using the current transformer CT1. Lr The voltage across the resistor R1 is integrated using integrators 7341 and 7342. The integrated value of the resonant current at a specific moment is obtained using sample holders 7343 and 7344.

[0071] Furthermore, the integrator 7341 is responsible for the integration interval [0-D PN T s ] resonant current, the voltage across capacitor C1 is v int1 represents the current integral in this interval. Switch Q1 is the discharge switch of integrator 7341. After switch Q1 is turned on, the voltage across capacitor C1 becomes 0V. trig1 is the trigger signal of the sample and hold 7343. PN T s , trigger signal v trig1 =1, the sample holder 7343 maintains t=D PN T s The first resonant current integral value at time

[0072] Integrator 7342 is responsible for the integration interval [0-T s / 2], the resonant current in the capacitor C2, and the voltage v int2 represents the current integral in this interval. Switch Q2 is the discharge switch of integrator 7342. After switch Q2 is turned on, the voltage across capacitor C2 becomes 0V. trig2 is the trigger signal of the sample and hold 7344. s / 2, trigger signal v trig2 =1, the sample holder 7344 maintains t=T s The second resonant current integral value at time / 2

[0073] The second current reference value I Lref Subtract the current i L The absolute value of |i L |Get the current I Le , the current I Le After PI modulation, the first integral threshold v is obtained comp1 ; The first current reference value I Mref Subtract the current i M The absolute value of |i M |Get the current I Me , the current I MeAfter PI modulation, the second integration threshold v is obtained comp2 The first resonant current integral value and the second integral threshold value v comp2 After comparison by comparator A5, the third trigger signal v is obtained trig3 ; The second resonant current integral value and the first integral threshold value v comp1 After comparison by comparator A6, the fourth trigger signal v trig4 . The third trigger signal v trig3 With the fourth trigger signal v trig4 Output to PWM counter 7345.

[0074] If the first resonant current integral value exceeds the first integral threshold value v comp2 , it means that the input energy of the LLC resonant cavity in half a cycle meets the input requirement. At this time, the PWM counter 7345 is triggered to obtain the half switching cycle length Ts / 2; if the second resonant current integral value exceeds the second integral threshold value v comp1 , it means that the energy input by LLC resonant cavity reaches the requirement of M phase input. At this time, PWM counter 7345 obtains the voltage u between P and N points. PN Working hours D PN T s .

[0075] After the positive half cycle count is completed, the resonant current integral value is reset to 0V. Figure 5 As in the embodiment, the switch Q1 and the switch Q2 are used for resetting. After the switch Q1 or the switch Q2 is turned on, the voltage across the capacitor C1 or the voltage across the capacitor C2 becomes 0V.

[0076] The negative half cycle is symmetrical to the positive half cycle. At the beginning of the negative half cycle, the voltage -u PN Working hours loading D PN T s , that is, its working area is [Ts / 2~(D PN T s +T s / 2)], the switching cycle load T s The waveforms of the trigger signal, resonant current, and capacitor voltage in this process are shown in Figure 8 (a).

[0077] In addition, if the trigger signal v trig3 The triggering time is shorter than the shortest working time (0.5T min ), the switching logic of the DC / DC conversion circuit 72 is converted into the determination logic of the PWM mode, that is, the fixed switching cycle length is T s =T min , the first integration threshold v comp1 Responsible for controlling the duration D PWM*Ts, the second integration threshold v comp2 Responsible for control Get control Get duration D PN *T s The waveforms of the trigger signal, resonant current, and capacitor voltage in this process are shown in Figure 8 (b) Where T min is the lower limit of the switching period, corresponding to the maximum operating frequency f of the LLC resonant module smax , D PWM is the duty cycle of the LLC resonant cavity input energy. If the switching frequency f s >f smax , the circuit works in PWM mode, fixing f s =f smax , by reducing D PWM To reduce the effective value of the input voltage and thus reduce the output voltage.

[0078] In summary, the application of charge control is equivalent to adding a nonlinear closed loop in the current inner loop, improving the current inner loop regulation speed and the dynamic load shedding responsiveness of the system. Moreover, the three-phase single-stage AC / DC resonant converter controlled by this control strategy can output a higher quality single-phase input current waveform, with better THD and simpler control parameter design.

[0079] It should be noted that the control method of a three-phase single-stage AC / DC converter of the present invention can also be used for a Swiss-LLC topology, a Swiss-LC topology, or a Swiss-DAB topology with multiple cavities in parallel, and the resonant current or the integral of the resonant current can also be controlled.

[0080] The following is an example of a resonant circuit using four LLC resonant cavities in parallel with charge control. Fig. 9 , sample the current of a single LLC resonant cavity for control, obtain a three-level drive signal, shift the corresponding phase and assign it to the three-level switch network of other LLC resonant cavities. The drive signals of the four LLC resonant cavities are consistent but there is a phase difference. In addition, the integral control of the resonant current is performed for the positive and negative half cycles of each switching cycle, respectively, within 1 / 2Ts time and D PN T s The resonant current is integrated over time.

[0081] The resonant current control module 934 includes a rectifier 9348, an inverter 9346, an inverter 9347, an integrator 9341, an integrator 9342, a sample holder 9343, a sample holder 9344 and a PWM counter 9345. The structures and functions of the integrator 9341, the integrator 9342, the sample holder 9343, the sample holder 9344 and the PWM counter 9345 are similar to those of the Figure 7The same as in, no further description is given here.

[0082] The input of rectifier 9348 is connected to the two ends of current transformer CT1, the output of rectifier 9348 is connected to inverter 9346 and inverter 9347, the output of inverter 9346 is connected to integrator 9341, and the output of inverter 9347 is connected to integrator 9342.

[0083] The rectifier 9348 includes a switch Q1, a switch Q2, a switch Q3, and a switch Q4. The first end of the switch Q1 is connected to the second end of the resistor R1, the second end of the switch Q1 is connected to the first end of the resistor R5, the first end of the switch Q2 is connected to the second end of the resistor R1, the second end of the switch Q2 is connected to the positive input end of the operational amplifier A3, the first end of the switch Q3 is connected to the first end of the resistor R1, the second end of the switch Q3 is connected to the second end of the switch Q1, the first end of the switch Q4 is connected to the first end of the resistor R1, and the second end of the switch Q4 is connected to the second end of the switch Q2. The second end of the resistor R5 is connected to the positive input end of the operational amplifier A3, the first end of the resistor R4 is connected to the second end of the resistor R5, the second end of the resistor R4 is connected to the output end of the operational amplifier A3, and the output end of the operational amplifier A3 is connected to the resistor R3. The first end of the resistor R7 is connected to the second end of the switch Q4, the second end of the resistor R7 is connected to the negative input end of the operational amplifier A4, the first end of the resistor R6 is connected to the second end of the resistor R7, and the second end of the resistor R6 is connected to the output end of the operational amplifier A4.

[0084] Since the resonant current is both positive and negative, the function of the rectifier 9348 is to switch the switch so that both the positive half-cycle current and the negative half-cycle current can be extracted.

[0085] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person having ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope of the attached patent application.

Claims

1. A control method for a three-phase single-stage AC / DC converter, characterized in that: Applied to a three-phase single-stage AC / DC converter, the three-phase single-stage AC / DC converter comprises an AC / DC rectifier circuit and a DC / DC resonant circuit, the input of the AC / DC rectifier circuit is connected to a three-phase AC voltage, the AC / DC rectifier circuit outputs DC power to the input of the DC / DC resonant circuit, and the DC / DC resonant circuit outputs a DC voltage; include, Determining the phase angle of the three-phase AC voltage according to the three-phase AC voltage, and determining the driving logic of the switch in the AC / DC rectifier circuit; The output voltage is compared with the output voltage reference value and the maximum current value I is output after modulation MAX ; According to the three-phase AC voltage and the three-phase AC current, the L, M, and S phases are determined, and the first current reference value I is output after processing. Mref , the second current reference value I Lref 、Current i M The absolute value of |i M |With current i L The absolute value of |i L |; Collect the resonant current in the DC / DC resonant circuit, calculate the integral value of the resonant current, output the signal after modulation, and determine the driving logic of the switch in the DC / DC resonant circuit.

2. A control method for a three-phase single-stage AC / DC converter as claimed in claim 1, characterized in that: The phase with the largest absolute value of instantaneous voltage is defined as L phase, and its phase voltage is u L ; The phase with the smallest absolute value of instantaneous voltage is defined as phase S, and its phase voltage is u S ; The remaining phase is defined as phase M, and its phase voltage is u M , the expression of each phase voltage is as follows: Among them, the current i L and phase angle θ L is the phase voltage u L The corresponding phase current and phase angle, current i S and phase angle θ S is the phase voltage u S The corresponding phase current and phase angle, current i M and phase angle θ M is the phase voltage u M The corresponding phase current and phase angle.

3. A control method for a three-phase single-stage AC / DC converter as claimed in claim 2, characterized in that: The current i M Converted into current i M The absolute value of |i M |, the current i L Converted into current i L The absolute value of |i L |, the phase angle θ M The sine of sin(θ M ) is transformed into a phase angle θ M The absolute value of sine | sin(θ M )|, the phase angle θ L The sine of sin(θ L ) is transformed into a phase angle θ L The absolute value of sine | sin(θ L )|, the phase angle θ M The absolute value of sine | sin(θ M )| and the maximum current value I MAX Multiply to obtain the first current reference value I Mref , the phase angle θ L The absolute value of sine | sin(θ L )| and the maximum current value I MAX Multiply to obtain the second current reference value I Lref .

4. A control method for a three-phase single-stage AC / DC converter as claimed in claim 3, characterized in that: The resonant current integral value includes an interval [0-D PN T s ] and the first resonant current integral value in the interval [0-T s / 2] within the second resonant current integral value.

5. A control method for a three-phase single-stage AC / DC converter as claimed in claim 4, characterized in that: The first resonant current average value is obtained according to the first resonant current integral value, the second resonant current average value is obtained according to the second resonant current integral value, and the first current reference value I Mref Subtract the first resonant current average value after modulation to obtain the duty cycle D PN ; Subtract the second current reference value I from the second resonant current average value Lref After modulation, the switching frequency f s , where the duty cycle D PN is the voltage u in half cycle PN The proportion of working hours.

6. A control method for a three-phase single-stage AC / DC converter as claimed in claim 4, characterized in that: The second current reference value I Lref Subtract the current i L The absolute value of |i L |Get the current I Le , the current I Le After modulation, the first integration threshold v is obtained comp1 ; The first current reference value I Mref Subtract the current i M The absolute value of |i M |Get the current I Me , the current I Me After modulation, the second integration threshold v is obtained comp2 If the second resonant current integral value exceeds the first integral threshold value v comp1 , and obtain the half switching cycle length Ts / 2; if the first resonant current integral value exceeds the second integral threshold value v comp2 , get the working time D PN T s .

7. A control method for a three-phase single-stage AC / DC converter as claimed in claim 4, characterized in that: If the DC / DC resonant circuit includes multiple resonant cavities, the current of a single resonant cavity can be sampled for control, and a driving signal can be obtained and then output to other resonant cavities.

8. A control circuit for a three-phase single-stage AC / DC converter, characterized in that: Execute the control method of a three-phase single-stage AC / DC converter as described in any one of claims 1 to 7, the control circuit includes a phase-locked loop module, a current loop module, a voltage loop module, a resonant current control module, a first drive logic module and a second drive logic module; The phase-locked loop module outputs the phase angle of the three-phase AC voltage according to the three-phase AC voltage and outputs it to the first driving logic module, and the first driving logic module determines the driving logic of the switch in the AC / DC rectifier circuit according to the phase angle of the three-phase AC voltage; The voltage loop module compares the output voltage with the output voltage reference value and modulates the output maximum current value I MAX To the current loop module; The current loop module determines the L, M, and S phases according to the three-phase AC voltage and the three-phase AC current, and outputs the first current reference value I after processing. Mref , the second current reference value I Lref 、Current i M The absolute value of |i M |With current i L The absolute value of |i L | to the resonant current control module; The resonant current control module collects the resonant current in the DC / DC resonant circuit, calculates the integral value of the resonant current, and outputs a signal to the second drive logic module after modulation. The second drive logic module determines the drive logic of the switch in the DC / DC resonant circuit.

9. A control circuit for a three-phase single-stage AC / DC converter as claimed in claim 8, characterized in that: The resonant current control module includes a first integrator, a second integrator, a first sample holder and a second sample holder. The first integrator performs a sampling operation on the interval [0-D PN T s ], the second integrator integrates the resonant current in the interval [0-T s / 2], the first sample holder maintains t=D PN T s The first resonant current integral value at the moment t=T s / 2 time the second resonant current integration value.

10. A control circuit for a three-phase single-stage AC / DC converter as claimed in claim 9, characterized in that: The resonant current control module further includes a PWM counter, a first comparator and a second comparator. The first comparator compares the first resonant current integral value with the second integral threshold value v comp2 After comparison, the third trigger signal v is obtained trig3 The second comparator compares the second resonant current integral value with the first integral threshold value v comp1 After comparison, the fourth trigger signal v is obtained trig4 , the third trigger signal v trig3 With the fourth trigger signal v trig4 Output to the PWM counter, the PWM counter according to the third trigger signal v trig3 With the fourth trigger signal v trig4 The switching frequency f is obtained s and duty cycle D PN .

11. A control circuit for a three-phase single-stage AC / DC converter as claimed in claim 10, characterized in that: The resonant current control module also includes a rectifier, the input of the rectifier is connected to the two ends of the current transformer, the current transformer detects the resonant current, the output of the rectifier is connected to a first inverter and a second inverter, the output of the first inverter is connected to a first integrator, and the output of the second inverter is connected to a second integrator.

12. A control circuit for a three-phase single-stage AC / DC converter as claimed in claim 8, characterized in that: The current loop module converts the current i M Converted into current i M The absolute value of |i M |, the current i L Converted into current i L The absolute value of |i L |, the phase angle θ M The sine of sin(θ M ) is transformed into a phase angle θ M The absolute value of sine | sin(θ M )|, the phase angle θ L The sine of sin(θ L ) is transformed into a phase angle θ L The absolute value of sine | sin(θ L )|, the phase angle θ M The absolute value of sine | sin(θ M )| and the maximum current value I MAX Multiply to obtain the first current reference value I Mref , the phase angle θ L The absolute value of sine | sin(θ L )| and the maximum current value I MAX Multiply to obtain the second current reference value I Lref .

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