SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method

Abstract

The invention relates to the technical field of converters, and discloses a SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method, which comprises the following steps of: a modulation method: converting three-phase voltage of a low-frequency Swiss rectifying circuit into port voltage; high-frequency resonance is input into the resonant cavity through high-frequency switching change, and the input time is determined by the duty ratio; a control method: adopting a charge control method; the digital control method comprises the following steps of: setting a normal working mode and a PWM (Pulse-Width Modulation) mode of switching on and switching off a tube in a state 1 and a state 2 by adopting frequency counting and duty ratio counting of a cavity a; and entering a normal working mode and a PWM mode of the cavity b, staggering the cavity b and the cavity a by 90 degrees, and then entering a cavity c and cavity d mode. Through a four-cavity parallel connection scheme and charge cycle-by-cycle control, the dynamic performance of the converter is improved, the response speed of the converter is improved, the closed-loop PI can be corrected, the result is more accurate, and the response is faster. And the design difficulty of the compensator is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of level charge control of new energy converters, and in particular to a SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method. Background Art

[0002] In recent years, with the rapid economic development, problems such as energy shortage, environmental pollution and climate warming have become increasingly prominent. Finding economical, clean and renewable new energy is an effective means to solve these problems.

[0003] Building a new power system dominated by new energy is the future development direction of the power industry. In the new power system, the isolated AC / DC converter is the grid interface and core unit connecting photovoltaic, wind power and other new energy power generation and energy storage systems. Therefore, in many application scenarios, the research on isolated AC / DC converters is of great significance.

[0004] At present, isolated AC / DC converters usually adopt a two-stage structure. The front stage adopts a three-phase PFC converter structure to complete the three-phase current control task, cope with various grid distortion problems, and ensure the power quality of the grid. The back stage adopts an isolated DCDC structure to achieve electrical isolation between the power supply side and the power consumption side, and achieve output voltage stability under different load conditions. However, due to the two-stage power conversion, this structure has the disadvantages of low conversion efficiency and high cost. In addition, the two-stage structure also requires a large bus capacitor (usually a cheap and short-life electrolytic capacitor) to buffer the energy of the front and rear converters, which will reduce the reliability of the converter and limit the optimization of its power density.

[0005] With the continuous updating and development of power electronics technology, academia and industry hope to find an AC / DC converter structure with higher energy transmission efficiency, more compact structure and lower cost. Compared with the two-stage structure, the single-stage ACDC 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 studied are divided into two categories: 1) using a dual active bridge structure based on phase shift control (Baranwal R, Iyer KV, Basu K, et al. A Reduced Switch Count Single-Stage Three-Phase Bidirectional Rectifier With High-Frequency Isolation [J]. IEEE Transactions on Power Electronics, 2018.) and 2) using a 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-PhaseIsolated Buck Matrix-Type Rectifier [J]. IEEE Transactions on Power Electronics, 2017: 110-124.). Although these structures can also achieve single-stage ACDC energy conversion through complex control strategies, they cannot guarantee that all switch tubes can achieve soft switching under full load conditions, which limits the promotion and application of this type of converter.

[0006] Technical terms:

[0007] Three-phase single-stage AC / DC resonant converter: A resonant converter is used to achieve three-phase AC / DC conversion, such as Figure 1 As shown. This converter controls the transmission energy of the resonant converter by adjusting the switching frequency to control the input current and output voltage. The converter uses the resonant converter to achieve soft switching of high-frequency switches, reduce switching losses, and obtain higher converter efficiency. In addition, compared with the two-stage AC / DC converter, the single-stage AC / DC converter does not require bus capacitors, and only requires a single-stage structure to complete energy conversion, thereby obtaining a higher power density.

[0008] SWISS rectifier: SWISS rectifier is a new type of unidirectional, step-down, three-phase AC-DC rectifier with power factor correction function, such as Figure 2 As shown. It has excellent performances such as unity power factor operation, small switching loss, low switching stress, low current harmonic distortion rate, and full range adjustable output bus voltage. It can achieve single-stage electrical isolation and is very suitable for electric vehicle charging.

[0009] Charge control strategy: Figure 3 As shown, a current transformer is used to sample the resonant cavity current, and the sampled current passes through a resistor. Parameter Voltage ,Voltage A current signal is generated by a voltage-controlled current source, and the integrated voltage is obtained by integrating it on the capacitor. In order to suppress subharmonic oscillation and improve stability, two current sources are used to compensate the slope capacitor. Linear charging or discharging, the charging and discharging currents are , get the slope compensation voltage The integral voltage is added to the slope compensation voltage to obtain . Input to two comparators, and compared with the integration threshold and 0 respectively. Equal to 0 triggers the RS trigger to set, and the resonant cavity begins to flow current. Start to rise. Equal to the integration threshold The RS trigger is reset, and the reset signal res is pulled high, causing the integral capacitor to discharge.

[0010] The solution of prior art one:

[0011] The literature (Du Shixiang. Charge control of LLC converter and its digital implementation [D]. Nanjing University of Aeronautics and Astronautics, 2021. DOI: 10.27239 / d.cnki.gnhhu.2021.000434.) proposed an LLC charge control strategy, which greatly improved the dynamic response of LLC. Disadvantages of the prior art 1: The charge control method is only applicable to two levels and only uses PI for adjustment, and the compensator is difficult to design at high power.

[0012] The solution of the second prior art:

[0013] Literature (Zhang Binfeng. Research on Single-stage Isolation SWISS-type Three-phase AC / DC Converter [D]. Nanjing University of Aeronautics and Astronautics, 2020. DOI: 10.27239 / d.cnki.gnhhu.2020.002412.) Based on the research on the basic principles and control strategies of SWISS-type converters, combined with the characteristics of the full-bridge structure, a single-stage isolation SWISS-type ACDC converter based on a dual full-bridge structure suitable for the mixed use of Si and SiC devices is proposed, and a new modulation strategy is proposed to solve the power coupling problem of the two groups of full bridges, while realizing the soft switching of the main power devices. Disadvantages of the second existing technology: The switching frequency is still limited to 90kHz, which has not yet fully reflected the application advantages of SiCMOSFET.

[0014] Technical solution of prior art three:

[0015] The literature (X. Li, J. Sun, L. Guo, M. Gao, H. Hu and M. Xu, "A Three-Phase Single-Stage ac / dc Converter Based on Swiss Rectifier and Three-Level LLC Topology," in IEEE Transactions on Power Electronics, vol. 38, no. 2, pp.1958-1972, Feb. 2023, doi: 10.1109.) proposed a three-phase single-stage AC / DC converter topology based on Swiss rectification and series half-bridge three-level LLC resonant cavity. Three levels are input in one cycle, and the LLC input voltage is changed by adjusting the switching frequency fs and duty cycle DPN. Disadvantages of the existing technology three: using average current control, slow dynamic response speed, and difficult to adjust closed-loop control.

[0016] The solution of prior art four:

[0017] The literature (B. Zhang, S. Xie, Z. Li, P. Zhao and J. Xu, "An Optimized Single-Stage Isolated Swiss-Type AC / DC Converter Based on Single Full-BridgeWith Midpoint-Clamper," in IEEE Transactions on Power Electronics, vol. 36, no. 10, pp. 11288-11297, Oct. 2021, doi: 10.1109.) adopts a Swiss-type DAB single-stage AC / DC converter, introduces space current vector modulation to share the pressure of phase shift control, reduces the adjustment range of the phase shift angle, and thus expands the soft switching range. Disadvantages of the prior art four: It is difficult for a single-stage AC / DC converter based on the DAB topology to achieve soft switching in the full load range. Summary of the invention

[0018] In order to overcome the deficiencies of the prior art, the present invention adopts a SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method; it is capable of increasing the transmission power and improving the response speed of the converter.

[0019] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0020] A SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method, the steps of which are as follows:

[0021] 1) Modulation strategy and control method;

[0022] (1) Three sets of bidirectional switches in a low-frequency Swiss rectifier circuit , , The switching logic and three-phase voltage ( , , ) and port voltage ( , , ), the conversion relationship between the bidirectional switch , , When the two-phase voltage crosses, it is opened alternately. When the three-phase voltage changes, the three-phase voltage , , All become port voltage , , ;

[0023] (2) High-frequency resonance change part, through high-frequency switching - and - , the voltage , , Input to the resonant cavity; within one cycle, the input , , Three levels to the resonant cavity, half cycle input The largest one among them, the remaining two phases are input in the other half cycle, and the input time is determined by the duty cycle D;

[0024] 2) Control adopts charge control method:

[0025] The output current is used as the outer loop, which is used to control the output current stability. Its output is the peak value of the input current. ;Will Multiply the phase information of P phase and N phase ( )and( ) to obtain the reference current of P phase and N phase ( and ); Inner loop control and Tracking reference current and , realize the PFC of three-phase current, and output the integral threshold of charge control through PI and ;

[0026] like > , then control , control ;

[0027] like < , then control , control ;

[0028] The resonant current of a resonant cavity is sampled by a current transformer. The sampled current passes through the resistor Rs and the parameter voltage Vs. The voltage Vs is inverted by the inverter and integrated on the integrator. A bias voltage is connected to the non-inverting input of This bias voltage provides an additional constant integral current for the integral capacitor, namely the slope compensation current Iramp. Finally, the integral capacitor generates an integral voltage ;

[0029] The resonant circuit sampling factor is written as:

[0030]

[0031] Integral voltage Through the comparator and the integration threshold , Compare and output the rising edge to the digital control, thereby controlling the operating frequency fs and duty cycle D of the high-frequency switch;

[0032] If there is external interference, such as the output current drops below the reference value, the error increases, and the IMAX output by the outer loop PI will rise, and the final IPref and INref will rise, and the error with IP and IN will also increase. After passing through the inner loop PI, the two integral thresholds will also rise, the frequency will decrease, and the duty cycle will increase, so that the gain will increase, thereby increasing the output current until it is equal to the reference value; because the final cycle is controlled by comparing the integral threshold and the integral voltage through a comparator, it is a cycle-by-cycle control with a fast response speed;

[0033] Digital control process:

[0034] ①. At the initial moment, the count Count1 of cavity a is 0, and the integral capacitor voltage is 0; after power supply, the integral capacitor Ci starts to charge.

[0035] The frequency count Count1 and duty cycle count Count_PFC of cavity a also start to accumulate;

[0036] At the same time, when > When , it is set to state 1, and the tube S1 is turned on; when < When , it is set to state 2 and the tube S2 is turned on;

[0037] ② When the integral capacitor voltage When the integral threshold Vcomp2 of the duty cycle D is just reached, a rising edge posedge2 is output;

[0038] ③. If the rising edge posedge2 is detected, the count of Count_PFC is cleared to zero, and at the same time, the tube S1 (state 1) or S2 (state 2) is turned off;

[0039] ④. When the voltage of the integrating capacitor just reaches the frequency integration threshold Vcomp1, a rising edge posedge1 is output, and the reset switch res on the integrating capacitor Ci is closed to discharge;

[0040] ⑤. If the rising edge posedge1 is detected, the count Count1 of cavity a starts to decrease; if the count Count1 of cavity 1 has not reached the lower limit of the cycle length at this time, the count continues to accumulate until the count value equals the lower limit of the cycle, then the count starts to decrease again and enters the PWM mode;

[0041] ⑥. When Count1 starts to decrease, turn on tube S2 (state 1) or S1 (state 2); if it enters PWM mode, when the rising edge posedge2 is detected, turn on tube S2 (state 1) or S1 (state 2);

[0042] ⑦. When Count1 decreases to 0, turn off tube S2 (state 1) or S1 (state 2);

[0043] ⑧. During the period from when Count_PFC is cleared to when the rising edge posedge1 is detected, turn on the tube Sy1;

[0044] The drive of cavity b is exactly the same as that of cavity a, staggered by 90°. In order to achieve 90° staggering through charge control, the following control strategy is made:

[0045] 1) When cavity a detects the rising edge posedge1, the value of Count1 at this time is assigned to the intermediate quantity Temp2 and T_PWM at the same time. If the PWM mode is entered, Temp2 is equal to the minimum cycle time;

[0046] 2) When cavity a detects the rising edge posedge2, the value of Count_PFC at this time is assigned to an intermediate quantity DB;

[0047] 3) At the initial moment, the count Count2 of cavity b starts the same as cavity a. When Count1 is equal to 0.5*Temp2 in the second cycle, Count2 is set to 0; then Count2 starts counting again, so as to achieve the purpose of staggering 90°.

[0048] 4) When Count2 is greater than 0 and less than DB, turn on tube S4 (state 1) or S3 (state 2);

[0049] 5) When Count2 is greater than DB and less than Temp2, Sy2 is turned on;

[0050] 6) When Count2 is greater than Temp2, turn on tube S3 (state 1) or S4 (state 2);

[0051] 7) If the PWM mode is entered, the tube Sy2 is turned on when Count2 is less than Temp2-T_PWM; the tube S3 (state 1) or S4 (state 2) is turned on when Count2 is greater than Temp2-T_PWM;

[0052] Similarly, for the detection and setting of cavity C and cavity D, cavity C sets Count3 to 0 when cavity 1 detects the rising edge posedge1, and sets Count3 to 0 when Count1 equals the minimum value of the cycle in PWM mode; cavity D sets Count4 to 0 when cavity 1 counts Count1 and equals 0.5*Temp2 when it decreases.

[0053] A SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method adopts a charge control method: the charge charged to the integral voltage by the current of the main circuit is Vsum minus the slope compensation voltage Vramp, then the integral threshold v comp1 、v comp2 With the charge Q in1 , Q in2 The corresponding relationship is

[0054] Q i n 1 = C i K S [ v s u m ( t 2 ) − v r a m p ( t 2 ) ] Q i n 2 = C i K S [ v s u m ( t 1 ) − v r a m p ( t 1 ) ]

[0055] v ramp (t1) and v ramp (t2) corresponds to the slope compensation voltage values ​​of t1 and t2 respectively;

[0056] Slope compensation is generated by the slope compensation current charging the slope compensation capacitor, so:

[0057]

[0058] The charge can be expressed as the integral of the resonant current

[0059]

[0060] Taking cavity a as an example, when 0-t1, the switch tube S2 is turned on and the current Flows into the resonant cavity. At the moment t1-t2, the switch tube Sy1 is turned on and the current Flow into the resonant cavity;

[0061]

[0062] From the above formulas, we can get the expression of the integral threshold;

[0063]

[0064]

[0065] According to the parameters involved in the above formula, the integral threshold v comp1 and v comp2 To calculate, use the switching frequency of the previous switching cycle and duty cycle Instead, combined with the current reference value i of the N phase and Y phase at this time Y_ref and i N_ref To calculate the required V comp1 and V comp2 :

[0066]

[0067] In PWM working mode, the integral threshold v comp1 and v comp2 The calculation formula of is similar to that of the PFM working mode and can be expressed as:

[0068]

[0069] Where D PWM_pre The ratio of the time of entering PWM mode to half cycle time in the previous cycle;

[0070] Since there are certain errors between the switching frequency of the previous cycle and the switching frequency of the current cycle, and between the duty cycle of the previous cycle and the duty cycle of the current cycle, and there are also various errors in actual experiments, only direct calculation is used to obtain the integral threshold v comp1 and v comp2 This will result in poor control effect of the three-phase input current; therefore, based on direct calculation, the calculation error is corrected through closed-loop adjustment; after obtaining the integral threshold.

[0071] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0072] The present invention discloses a SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method, which adds an LLC resonant circuit to the SWISS type AC / DC conversion process, uses the LLC resonant cavity to realize the soft switching of the high-frequency switch tube to reduce the switching loss, and uses the wide gain characteristics of the LLC to adjust the switching frequency of the LLC resonant cavity to complete the three-phase input current control and output voltage control. In order to increase the transmission power, the resonant cavity adopts a four-cavity parallel LLC solution. At the same time, in order to improve the response speed of the converter, a charge control strategy is introduced; and the charge control adopts a direct calculation plus closed-loop correction method, which further improves the response speed of the converter and reduces the difficulty of compensator design. The specific features are as follows:

[0073] 1) The present invention proposes a three-level charge control strategy for the SWISS-four-cavity LLC multi-connected three-phase single-stage AC / DC conversion module, integrates the resonant current, controls the on and off of the high-frequency tube by comparing the integrated voltage with the integrated threshold, and describes in detail the digital control logic of charge control under three-level input and the control logic of the four-cavity interleaving, and improves the dynamic performance of the converter through the cycle-by-cycle control of charge control. It solves the problems of slow dynamic response speed of SWISS-three-phase single-stage ACDC under direct frequency control, difficult closed-loop control, and difficult compensator design.

[0074] 2) In order to solve the problems of the difficulty in designing PI controllers and closed-loop control under high-power ACDC in traditional charge control, this paper proposes a charge control strategy with direct calculation and closed-loop error correction. Mainly through mathematical derivation, the integral threshold is expressed by reference current, switching frequency and duty cycle, so that the size of the integral threshold can be directly calculated in digital control. Since the switching frequency and duty cycle cannot be known in real time, the switching frequency and duty cycle of the previous cycle are used, which has a certain error, so the closed-loop PI correction is introduced to make the result more accurate and the response faster. The problem of the difficulty in designing PI controllers in the application scenario of high-power ACDC in traditional charge control is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 This is the structural diagram of a three-phase single-stage AC / DC resonant converter.

[0076] Figure 2 This is the structure diagram of the SWISS rectifier.

[0077] Figure 3 This is the structural diagram of the charge control strategy.

[0078] Figure 4 This is the topology diagram of a 40kW SWISS-4 cavity LLC three-phase single-stage AC / DC.

[0079] Figure 5 is the three-phase voltage ( , , ) and port voltage ( , , ) conversion relationship diagram.

[0080] Figure 6 is the charge control diagram.

[0081] Figure 7 It is a control block diagram for controlling the operating frequency fs and duty cycle D of the high-frequency switch.

[0082] Figure 8 It is the charge Vsum charged by the main circuit current to the integrated voltage minus the slope compensation voltage Vramp.

[0083] Fig. 9 This is the final control block diagram.

[0084] Fig.10 This is the normal working mode diagram of cavity a.

[0085] Fig.11 This is the PWM working mode diagram of cavity a.

[0086] Fig.12 This is the normal working mode diagram of cavity b.

[0087] Fig.13 This is the PWM working mode diagram of cavity b. DETAILED DESCRIPTION

[0088] A SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method adopts the topology of a 40kW SWISS-4-cavity LLC three-phase single-stage AC / DC. Four groups of LLC circuits are connected in parallel, using the same switching frequency, and the switching logic is 90 degrees different from each other, such as Figure 4 As shown in the figure, the parameters of the four LLC resonant cavities are completely equal. Although their input voltages differ by 90 degrees, their voltage waveforms are completely equal. Therefore, the currents in the four resonant cavities are completely symmetrical, also differ by 90 degrees, and satisfy the equal relationship. =0.

[0089] Modulation strategies and control methods

[0090] Three sets of bidirectional switches in low-frequency Swiss rectifier circuit , , The switching logic and three-phase voltage ( , , ) and port voltage ( , , ) is as follows Figure 5 As shown, the bidirectional switch , , It is only switched on alternately when the two-phase voltage crosses. No matter how the three-phase voltage changes, the three-phase voltage , , All become port voltage , , .

[0091] The high-frequency resonance change part is switched by high-frequency - and - , the voltage , , Input to the resonant cavity. In one cycle, the input , , Three levels to the resonant cavity, half cycle input The largest one among them is input, and the remaining two phases are input in the other half cycle. The input time is determined by the duty cycle D.

[0092] Control adopts charge control strategy:

[0093] Charge Control Strategy 1:

[0094] The output current is used as the outer loop, which is used to control the output current stability. Its output is the peak value of the input current. .Will Multiply the phase information of P phase and N phase ( )and( ) can get the reference current of P phase and N phase ( and ). Inner loop control and Tracking reference current and , in order to achieve three-phase current PFC, the integral threshold of charge control is output through PI and .like > , then control , control .like < , then control , control The charge control part is as follows Figure 6 As shown, a current transformer is used to sample the resonant current of a resonant cavity. The sampled current passes through the resistor Rs and the parameter voltage Vs. The voltage Vs is inverted by the inverter and integrated on the integrator. A bias voltage is connected to the non-inverting input of This bias voltage provides an additional constant integral current for the integral capacitor, namely the slope compensation current Iramp. Finally, the integral capacitor generates an integral voltage .

[0095] The resonant circuit sampling factor can be written as:

[0096]

[0097] Integral voltage Through the comparator and the integration threshold , After comparison, the rising edge is output to the digital control, thereby controlling the operating frequency fs and duty cycle D of the high-frequency switch.

[0098] Control block diagram Figure 7 As shown:

[0099] If there is external interference, such as the output current drops below the reference value, the error increases, and the IMAX output by the outer loop PI will rise, and the final IPref and INref will rise, and the error with IP and IN will also increase. After passing through the inner loop PI, the two integral thresholds will also rise, the frequency will decrease, and the duty cycle will increase, making the gain larger, thereby increasing the output current until it is equal to the reference value. Since the final cycle is controlled by comparing the integral threshold and the integral voltage through a comparator, it is a cycle-by-cycle control with a fast response speed.

[0100] Charge Control Strategy 2:

[0101] In charge control strategy 1, only PI is used for closed-loop control, but in ACDC, the current reference value and When the AC changes, the gain of the PI regulator is infinite at the DC point, but it is difficult to achieve zero-static tracking of the AC quantity. In order to improve the control rate and dynamic response speed, reduce THD, and reduce the difficulty of compensator design, a direct calculation method is introduced.

[0102] The charge of the integrated voltage by the current of the main circuit is actually Vsum minus the slope compensation voltage Vramp. Figure 8 As shown, the integral threshold v comp1 、v comp2 With the charge Q in1, Q in2 The corresponding relationship is

[0103] Q i n 1 = C i K S [ v s u m ( t 2 ) − v r a m p ( t 2 ) ] Q i n 2 = C i K S [ v s u m ( t 1 ) − v r a m p ( t 1 ) ]

[0104] v ramp (t1) and v ramp (t2) corresponds to the slope compensation voltage values ​​of t1 and t2 respectively.

[0105] Slope compensation is generated by the slope compensation current charging the slope compensation capacitor, so:

[0106]

[0107] The charge can be expressed as the integral of the resonant current

[0108]

[0109] Taking cavity a as an example, when 0-t1, the switch tube S2 is turned on and the current Flows into the resonant cavity. At the moment t1-t2, the switch tube Sy1 is turned on and the current into the resonant cavity.

[0110]

[0111] From the above formulas, we can get the expression of the integral threshold.

[0112]

[0113]

[0114] We can directly calculate the integral threshold v according to the parameters involved in the above formula comp1 and v comp2 Calculation is performed, but the frequency fs and duty cycle D in the formula cannot be known in advance, and the frequency and duty cycle of adjacent switching cycles will not differ greatly, so the switching frequency of the previous switching cycle can be used and duty cycle Combined with the current reference values ​​i of the N phase and Y phase at this time Y_ref and i N_ref To calculate the required V comp1 and V comp2 :

[0115]

[0116] In PWM working mode, the integral threshold v comp1 and v comp2 The calculation formula of is similar to that of the PFM working mode and can be expressed as:

[0117]

[0118] Where D PWM_pre It is the ratio of the time of entering PWM mode to half cycle time in the previous cycle.

[0119] Since there are certain errors between the switching frequency of the previous cycle and the switching frequency of the current cycle, and between the duty cycle of the previous cycle and the duty cycle of the current cycle, and there are also various errors in actual experiments, only direct calculation is used to obtain the integral threshold v comp1 and v comp2 This will result in poor control of the three-phase input current. Therefore, the calculation error can be corrected through closed-loop regulation based on direct calculation. After obtaining the integral threshold, the subsequent process is the same as charge control strategy 1.

[0120] The final control block diagram is as follows: Fig. 9 Shown are:

[0121] Charge control strategy 2 introduces a direct calculation method based on strategy 1. Because PI calculation is a cumulative calculation, the calculation process is relatively slow. If direct calculation is introduced, most of the calculations will be performed before PI, which can greatly reduce the time for PI to perform cumulative calculations, thereby improving the speed of dynamic response and greatly reducing the difficulty of PI controller design.

[0122] Digital control process:

[0123] 1. At the initial moment, the count Count1 of cavity a is 0, and the integral capacitor voltage is 0. After power is supplied, the integral capacitor Ci starts to charge, and the frequency count Count1 and duty cycle count Count_PFC of cavity a also start to accumulate. > When the state is set to 1, the tube S1 is turned on. < When , it is set to state 2 and the tube S2 is turned on.

[0124] 2. When the integral capacitor voltage When the integral threshold Vcomp2 of the duty cycle D is just reached, a rising edge posedge2 is output.

[0125] 3. If the rising edge posedge2 is detected, the count of Count_PFC is cleared and at the same time, the tube S1 (state 1) or S2 (state 2) is turned off.

[0126] 4. When the voltage of the integrating capacitor just reaches the frequency integration threshold Vcomp1, a rising edge posedge1 is output, and the reset switch res on the integrating capacitor Ci is closed to discharge.

[0127] 5. If the rising edge posedge1 is detected, the count Count1 of cavity a starts to decrease. If the count Count1 of cavity 1 has not reached the lower limit of the cycle length at this time, the count continues to accumulate until the count value equals the lower limit of the cycle, then the count starts to decrease again and enters the PWM mode.

[0128] 6. When Count1 starts to decrease, turn on tube S2 (state 1) or S1 (state 2). If the PWM mode is entered, when the rising edge posedge2 is detected, tube S2 (state 1) or S1 (state 2) is turned on.

[0129] 7. When Count1 decreases to 0, turn off tube S2 (state 1) or S1 (state 2).

[0130] 8. During the period from when Count_PFC is cleared to when the rising edge posedge1 is detected, the tube Sy1 is turned on.

[0131] like Fig.10 is the normal working mode diagram of cavity a and Fig.11 The PWM working mode of cavity a is shown in the figure.

[0132] The drive of cavity b is exactly the same as that of cavity a, staggered by 90°. In order to achieve 90° staggering through charge control, the following control strategy is made:

[0133] 1. When cavity a detects the rising edge posedge1, the value of Count1 at this time is assigned to the intermediate quantity Temp2 and T_PWM at the same time. If the PWM mode is entered, Temp2 is equal to the minimum cycle time.

[0134] 2. When cavity a detects the rising edge posedge2, the value of Count_PFC at this time is assigned to an intermediate quantity DB.

[0135] 3. At the initial moment, the count Count2 of cavity b starts the same as cavity a. When Count1 is equal to 0.5*Temp2 in the second cycle, Count2 is set to 0. Then Count2 starts counting again, so as to achieve the purpose of staggering 90°.

[0136] 4. When Count2 is greater than 0 and less than DB, turn on tube S4 (state 1) or S3 (state 2).

[0137] 5. When Count2 is greater than DB and less than Temp2, Sy2 is turned on.

[0138] 6. When Count2 is greater than Temp2, turn on tube S3 (state 1) or S4 (state 2).

[0139] 7. If the PWM mode is entered, the tube Sy2 is turned on when Count2 is less than Temp2-T_PWM; the tube S3 (state 1) or S4 (state 2) is turned on when Count2 is greater than Temp2-T_PWM.

[0140] like Fig.12 This is the normal working mode diagram of cavity b and Fig.13 The PWM working mode of cavity b is shown in the figure.

[0141] The idea of ​​C and D cavities is the same. C cavity sets Count3 to 0 when Cavity 1 detects the rising edge posedge1. In PWM mode, Count3 is set to 0 when Count1 is equal to the minimum value of the cycle. Cavity d sets Count4 to 0 when Cavity 1 counts Count1 and 0.5*Temp2 when it decreases.

[0142] The three-level charge control strategy of the above-mentioned SWISS-four-cavity LLC multi-connected three-phase single-stage AC / DC conversion module integrates the resonant current, controls the on and off of the high-frequency tube by comparing the integrated voltage with the integrated threshold, and describes in detail the digital control logic of the charge control at three-level input and the control logic of the four-cavity interleaving, and improves the dynamic performance of the converter through cycle-by-cycle control of charge control.

[0143] The invention solves the problems that the PI controller of the traditional charge control is difficult to design and the closed loop is difficult to control under the high power of ACDC. The invention proposes a charge control strategy of direct calculation plus closed loop error correction. It is mainly through mathematical derivation, using the reference current, switching frequency and duty cycle to express the integral threshold, so that the size of the integral threshold can be directly calculated in digital control. Since the switching frequency and duty cycle cannot be known in real time, the switching frequency and duty cycle of the previous cycle are used, which has a certain error, so the correction of the closed loop PI is introduced to make the result more accurate and the response faster.

[0144] The application fields of the present invention include: 1) charging piles; 2) distributed systems; 3) energy storage systems; 4) AC / DC microgrids; 5) power electronic transformers; 6) large-scale new energy delivery. Among them, when applied to charging piles, the multi-cavity topology can make the charging piles very powerful and increase the charging speed of the charging piles. By applying the current charge control method, it can quickly output a more stable output voltage and current suitable for specific electric vehicles, and can also make faster adjustments to external interference, and quickly stabilize the output voltage and current.

Claims

1. A SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method, characterized by: The steps as follows: 1) Modulation strategy and control method; (1) Three sets of bidirectional switches in the low-frequency Swiss rectifier circuit , , The switching logic and three-phase voltage ( , , ) and port voltage ( , , ), the conversion relationship between the bidirectional switch , , When the two-phase voltage crosses, it is turned on alternately. When the three-phase voltage changes, the three-phase voltage , , All become port voltage , , ; (2) High-frequency resonance change part, through high-frequency switching - and - , the voltage , , Input to the resonant cavity; within one cycle, the input , , Three levels to the resonant cavity, half cycle input The largest one among them, the remaining two phases are input in the other half cycle, and the input time is determined by the duty cycle D; 2) Control adopts charge control method: The output current is used as the outer loop, which is used to control the output current stability. Its output is the peak value of the input current. ;Will Multiply the phase information of P phase and N phase ( )and( ) to obtain the reference current of P phase and N phase ( and ); Inner loop control and Tracking reference current and , realize the PFC of three-phase current, and output the integral threshold of charge control through PI and ; like > , then control , control ; like < , then control , control ; The resonant current of a resonant cavity is sampled by a current transformer. The sampled current passes through the resistor Rs and the parameter voltage Vs. The voltage Vs is inverted by the inverter and integrated on the integrator. A bias voltage is connected to the non-inverting input of This bias voltage provides an additional constant integral current for the integral capacitor, namely the slope compensation current Iramp. Finally, the integral capacitor generates an integral voltage ; The resonant circuit sampling factor is written as: Integral voltage Through the comparator and the integration threshold , Compare and output the rising edge to the digital control, thereby controlling the operating frequency fs and duty cycle D of the high-frequency switch; If there is external interference, such as the output current drops below the reference value, the error increases, and the IMAX output by the outer loop PI will rise, and the final IPref and INref will rise, and the error with IP and IN will also increase. After passing through the inner loop PI, the two integral thresholds will also rise, the frequency will decrease, and the duty cycle will increase, so that the gain will increase, thereby increasing the output current until it is equal to the reference value; because the final cycle is controlled by comparing the integral threshold and the integral voltage through a comparator, it is a cycle-by-cycle control with a fast response speed; Digital control method: ①. At the initial moment, the count Count1 of cavity a is 0, and the integral capacitor voltage is 0; after power supply, the integral capacitor C i Start charging. The frequency count Count1 and duty cycle count Count_PFC of cavity a also start to accumulate; At the same time, when > When , it is set to state 1, and the tube S1 is turned on; when < When , it is set to state 2 and the tube S2 is turned on; ② When the integral capacitor voltage When the integral threshold Vcomp2 of the duty cycle D is just reached, a rising edge posedge2 is output; ③. If the rising edge posedge2 is detected, the count of Count_PFC is cleared to zero, and at the same time, the tube S1 (state 1) or S2 (state 2) is turned off; ④. When the voltage of the integral capacitor just reaches the frequency integral threshold Vcomp1, a rising edge posedge1 is output, and the integral capacitor C is closed at the same time. i The reset switch res on the switch is discharged; ⑤. If the rising edge posedge1 is detected, the count Count1 of cavity a starts to decrease; if the count Count1 of cavity 1 has not reached the lower limit of the cycle length at this time, the count continues to accumulate until the count value equals the lower limit of the cycle, then the count starts to decrease again and enters the PWM mode; ⑥. When Count1 starts to decrease, turn on tube S2 (state 1) or S1 (state 2); if it enters PWM mode, when the rising edge posedge2 is detected, turn on tube S2 (state 1) or S1 (state 2); ⑦. When Count1 decreases to 0, turn off tube S2 (state 1) or S1 (state 2); ⑧. During the period from when Count_PFC is cleared to when the rising edge posedge1 is detected, turn on the tube Sy1; Cavity b is driven exactly the same as cavity a, staggered 90°; Similarly, for the detection and setting of cavity C and cavity D, cavity C sets Count3 to 0 when cavity 1 detects the rising edge posedge1, and sets Count3 to 0 when Count1 equals the minimum value of the cycle in PWM mode; cavity D sets Count4 to 0 when cavity 1 counts Count1 and equals 0.5*Temp2 when it decreases.

2. A SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method as claimed in claim 1, characterized in that: Control adopts charge control method: The charge of the integral voltage charged by the current of the main circuit is Vsum minus the slope compensation voltage Vramp, so the integral threshold v comp1 、v comp2 With the charge Q in1 , Q in2 The corresponding relationship is v ramp (t1) and v ramp (t2) corresponds to the slope compensation voltage values ​​of t1 and t2 respectively; Slope compensation is generated by the slope compensation current charging the slope compensation capacitor, so: The charge can be expressed as the integral of the resonant current Taking cavity a as an example, when 0-t1, the switch tube S2 is turned on and the current Flows into the resonant cavity. At the moment t1-t2, the switch tube Sy1 is turned on and the current Flow into the resonant cavity; From the above formulas, we can get the expression of the integral threshold; According to the parameters involved in the above formula, the integral threshold v comp1 and v comp2 To calculate, use the switching frequency of the previous switching cycle and duty cycle Instead, combined with the current reference value i of the N phase and Y phase at this time Y_ref and i N_ref To calculate the required V comp1 and V comp2 : In PWM working mode, the integral threshold v comp1 and v comp2 The calculation formula of is similar to that of the PFM working mode and can be expressed as: Where D PWM_pre The ratio of the time of entering PWM mode to half cycle time in the previous cycle; Since there are certain errors between the switching frequency of the previous cycle and the switching frequency of the current cycle, and between the duty cycle of the previous cycle and the duty cycle of the current cycle, and there are also various errors in actual experiments, only direct calculation is used to obtain the integral threshold v comp1 and v comp2 This will result in poor control effect of the three-phase input current; therefore, based on direct calculation, the calculation error is corrected through closed-loop adjustment; after obtaining the integral threshold.

3. A SWISS-multi-cavity LLC three-phase single-stage AC / DC three-level charge control method as claimed in claim 1, characterized in that: The digital control method adopts charge control to achieve 90° staggering, and the specific control method is as follows: 1) When cavity a detects the rising edge posedge1, the value of Count1 at this time is assigned to the intermediate quantity Temp2 and T_PWM at the same time. If the PWM mode is entered, Temp2 is equal to the minimum cycle time; 2) When cavity a detects the rising edge posedge2, the value of Count_PFC at this time is assigned to an intermediate quantity D B ; 3) At the initial moment, the count Count2 of cavity b starts the same as cavity a. When Count1 is equal to 0.5*Temp2 when accumulated in the second cycle, Count2 is set to 0; then Count2 starts counting again, so as to achieve the purpose of staggering 90°. 4) When Count2 is greater than 0 and less than DB, turn on tube S4 (state 1) or S3 (state 2); 5) When Count2 is greater than D B When it is less than Temp2, Sy2 is turned on; 6) When Count2 is greater than Temp2, turn on tube S3 (state 1) or S4 (state 2); 7) If the PWM mode is entered, the tube Sy2 is turned on when Count2 is less than Temp2-T_PWM; the tube S3 (state 1) or S4 (state 2) is turned on when Count2 is greater than Temp2-T_PWM.

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