Control method of two-stage bidirectional AC-DC converter

Abstract

The invention discloses a control method of a two-stage bidirectional AC-DC converter, and relates to the technical field of two-stage bidirectional AC-DC converters, and the two-stage bidirectional AC-DC converter comprises a front-stage interleaved bridgeless PFC circuit which is used for converting an AC input voltage into a DC voltage; the back-stage bidirectional full-bridge CLLLC resonant circuit can realize zero-voltage soft switching-on and zero-current soft switching-off of a switching tube, an AC-DC part of the two-stage bidirectional AC-DC converter is an interleaved bridgeless PFC circuit, two paths of input inductive current are interleaved, so that input current ripples are greatly reduced, a power factor correction function is realized, a DC-DC part is a bidirectional full-bridge CLLLC resonant circuit, and the two paths of input inductive current are interleaved, so that the two paths of input inductive current are interleaved. The wide-range voltage regulation function can be achieved under phase shift-frequency conversion control, the two-stage bidirectional AC-DC converter can achieve bidirectional energy flow, and meanwhile the converter is provided with a high-frequency transformer so that electrical isolation can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of two-stage bidirectional AC-DC converters, and in particular to a control method of a two-stage bidirectional AC-DC converter. Background Art

[0002] The two-stage bidirectional AC-DC converter is a key device for realizing bidirectional conversion of electric energy and is widely used in distributed power generation, electric vehicles, microgrid energy storage systems, and smart grids.

[0003] The AC-DC converter of the front stage can realize power factor correction and provide stable voltage for the back stage at the same time. By connecting the converters of the front and back stages with the DC bus voltage, the coupling relationship between input and output can be weakened. The DC-DC converter of the back stage can output a stable and wide range of DC voltage. The front and back stage converters of the two-stage bidirectional converter can be designed relatively independently, which can reduce the degree of coupling during control and can also play an isolation role. In addition, compared with the single-stage converter, there are great improvements in power conversion efficiency, power factor, and widening of output voltage range. It has higher performance and stability and can better meet the needs.

[0004] The single-stage AC-DC converter has the disadvantages of low power factor, poor dynamic performance, high requirements for protection circuits, and a narrow output voltage range. The above-mentioned problems limit the transmission efficiency of the AC-DC converter, affect the system stability of the AC-DC converter, and limit the application range of the converter. It is necessary to improve and adjust it, so a control method for a two-stage bidirectional AC-DC converter is proposed. Summary of the invention

[0005] The object of the present invention is to provide a control method for a two-stage bidirectional AC-DC converter to solve the problems of a single-stage AC-DC converter such as low power factor, poor dynamic performance, and a narrow output voltage range.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A control method for a two-stage bidirectional AC-DC converter comprises the following steps:

[0008] Step 1: Establish a model of a two-stage bidirectional AC-DC converter, analyze the working principle of the two-stage bidirectional AC-DC converter, and obtain the working characteristics of the front-stage interleaved parallel bridgeless PFC circuit and the rear-stage bidirectional full-bridge CLLLC resonant circuit;

[0009] Step 2: According to the working characteristics of the front-stage interleaved parallel bridgeless PFC circuit, a voltage and current double closed-loop control model is established for the front-stage interleaved parallel bridgeless PFC circuit during forward and reverse operation. The working process of the front-stage interleaved parallel bridgeless PFC circuit is basically the same during forward and reverse operation. During forward operation, the current inner loop makes the input inductor current change with the input voltage, making the input inductor current closer to a sine wave, and the voltage outer loop keeps the output of the PFC circuit stable. The sampled bus voltage V dc and bus voltage reference value V dc_ref The bus voltage error signal is obtained by comparison. The bus voltage error signal is multiplied by the input current unit after passing through the PI controller to obtain the reference value of the two-way input inductor current. The two-way input inductor current reference value and the two-way input inductor current I L1 with I L2 By comparing the two input inductor current error signals, the duty cycle change is obtained through the PI controller, and then compared with the sawtooth wave to obtain the PWM signal of the high-frequency switch tube, in which the two high-frequency bridge arm drive signals are fixedly 180° apart. The low-frequency switch tubes Q5 and Q6 are controlled to be on and off by judging the positive and negative half cycles through the input voltage, and the input voltage also controls the circuit zero-crossing drive blockage;

[0010] Step 3: Establish a phase-shift-frequency control model of the subsequent bidirectional full-bridge CLLLC resonant circuit according to the operating characteristics of the subsequent bidirectional full-bridge CLLLC resonant circuit. When running in the forward direction, the reference output voltage V o_ref and the actual output voltage V o is the input signal of the voltage loop PI controller, and the actual output current I o The output signal of the voltage loop PI controller is the input signal of the current loop PI controller. In the variable frequency mode, the output voltage is controlled by changing the switching frequency of the switch tubes S1 and S4, S2 and S3. In the phase shift mode, the output voltage is controlled by changing the phase shift angle of the switch tubes S1 and S4, S2 and S3. The latter bidirectional full-bridge CLLLC resonant circuit adopts a variable frequency control mode when it works in the forward voltage gain M>1, and a phase shift control mode is adopted if it works in the voltage gain M<1. The latter bidirectional full-bridge CLLLC resonant circuit refers to the input voltage V when it is reversely operated. dc_ref and the actual input voltage V dc is the input signal of the voltage loop PI controller, the actual input current I dc The output signal of the voltage loop PI controller is the input signal of the current loop PI controller. The back-stage bidirectional full-bridge CLLLC resonant circuit adopts the variable frequency control mode when the reverse voltage gain M>1, and adopts the phase shift control mode when the reverse voltage gain M<1. In the variable frequency mode, the output voltage is controlled by changing the switching frequency of the switch tubes S5 and S8, S6 and S7, and in the phase shift mode, the output voltage is controlled by changing the phase shift angle of the switch tubes S5 and S8, S6 and S7;

[0011] Step 4: Apply the above control method to realize the operation of the two-stage bidirectional AC-DC converter under constant current control and constant voltage control.

[0012] A further improvement of the technical solution of the present invention is that the specific process of step 1 is as follows:

[0013] Step 1.1: The front-stage interleaved parallel bridgeless PFC circuit adopts a synchronous rectification scheme. Q1, Q2, Q3, and Q4 are used as high-frequency switches. When the input current is in the positive half cycle, the power frequency switch Q5 is always off and Q6 is always on; when the input current is in the negative half cycle, the power frequency switch Q5 is always on and Q6 is always off.

[0014] Step 1.2: The switch tubes S1 to S4 of the rear bidirectional full-bridge CLLLC resonant circuit form the primary side full bridge, and S5 to S8 form the secondary side full bridge. s1 ~D s8 They are the body diodes of S1 to S8, C s1 ~C s8 The drain-source parasitic capacitances of S1 to S8 are shown in Figure 1. The transformer ratio is n:1, and also includes the excitation inductance L. m , the equivalent symmetrical resonant inductor L on the primary and secondary sides r1 and L r2 , resonant capacitor C r1 and C r2 , high frequency transformer for electrical isolation. V dc is the input voltage, V o is the load or energy storage battery voltage, C o is the filter capacitor. When the converter is working in the forward direction, the power is from V dc To V o Transfer, when working in reverse, the power is V o To V dc transfer;

[0015] Step 1.3: The two-stage bidirectional AC-DC converter can transfer energy in both forward and reverse modes, thus achieving bidirectional energy flow.

[0016] A further improvement of the technical solution of the present invention is that the specific process of step 2 is as follows:

[0017] Step 2.1: Calculate the expression of the current inner loop transfer function of the front-stage interleaved parallel bridgeless PFC circuit as follows:

[0018]

[0019] Among them, G id(s) is the current controller transfer function when PI control is used, KPi1 , K Ii1 They are the proportional coefficient and integral coefficient of the current inner loop controller of the interleaved parallel bridgeless PFC circuit respectively;

[0020] Step 2.2: Find the expression of the voltage outer loop transfer function of the front-stage interleaved parallel bridgeless PFC circuit:

[0021]

[0022] Among them, G vd(s) is the voltage controller transfer function when PI control is used, K Pv1 , K Iv1 They are the proportional coefficient and integral coefficient of the voltage outer loop controller of the interleaved parallel bridgeless PFC circuit respectively;

[0023] Step 2.3: The control strategy of the front-stage interleaved parallel bridgeless PFC circuit is obtained from the transfer function;

[0024] Step 2.4: Use the control strategy to obtain the output waveform of the front-stage interleaved parallel bridgeless PFC circuit.

[0025] A further improvement of the technical solution of the present invention is that the specific process of step 3 is as follows:

[0026] Step 3.1: Define the impedance expression of the bidirectional full-bridge CLLLC resonant circuit as:

[0027]

[0028] Where Z1 is the primary series resonant impedance; Z2 is the equivalent secondary series resonant impedance; Z m is the excitation inductance impedance; L r2 ′、C r2 ′ is L r2 , C r2 The values ​​of capacitance and inductance converted to the primary side of the transformer;

[0029] Step 3.2: Find the transfer function of the bidirectional full-bridge CLLLC resonant circuit as:

[0030]

[0031] Among them, V AB_FHA(t) V is the square wave fundamental component of the input DC bus voltage after full-bridge inversion. CD_FHA(t) is the square wave fundamental component of the output voltage after full-bridge rectification, R eq is the equivalent load converted to the original side;

[0032] Step 3.3: Calculate the voltage gain expression of the bidirectional full-bridge CLLLC resonant circuit under variable frequency control:

[0033]

[0034] Where, k is the inductance coefficient, Q is the quality factor; f n is the normalized frequency, f s is the actual switching frequency;

[0035] Step 3.4: The expression of the fundamental component of the square wave of the input voltage under phase shift control is:

[0036]

[0037] Step 3.5: The voltage gain expression under phase shift control is:

[0038]

[0039] Where D is the shift ratio, the voltage gain is approximately in a cosine relationship with D, and the range of variation is between 0 and 1;

[0040] Step 3.6: It can be concluded that when the voltage gain M>1, the frequency conversion control method is adopted, and when the voltage gain M<1, the phase shift control method is adopted;

[0041] Step 3.7: The working results of the bidirectional full-bridge CLLLC resonant circuit under variable frequency control and the working results under phase shift control can be obtained.

[0042] Due to the adoption of the above technical solution, the present invention has the following technical advances compared with the prior art:

[0043] 1. The present invention provides a control method for a two-stage bidirectional AC-DC converter, which solves the problems of a single-stage AC-DC converter, such as low power factor, poor dynamic performance, high requirements for protection circuits, and a narrow output voltage range. The voltage and power of the two-stage bidirectional AC-DC converter can meet the requirements, greatly reducing system losses and improving system efficiency.

[0044] 2. The present invention provides a control method for a two-stage bidirectional AC-DC converter, which broadens the practical application scope of the AC-DC converter and makes a certain contribution to the future development of the two-stage bidirectional AC-DC converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a block diagram of the overall control strategy of the two-stage bidirectional AC-DC converter of the present invention;

[0046] Figure 2 It is an equivalent circuit diagram of the front-stage interleaved parallel bridgeless PFC circuit of the present invention when it is in operation;

[0047] Figure 3It is a waveform diagram of the front-stage interleaved parallel bridgeless PFC circuit under the rated state of the present invention;

[0048] Figure 4 It is an equivalent circuit diagram of the rear-stage bidirectional full-bridge CLLLC resonant circuit of the present invention when it is in operation;

[0049] Figure 5 It is a voltage gain diagram of the rear-stage bidirectional full-bridge CLLLC resonant circuit of the present invention;

[0050] Figure 6 It is a variable waveform diagram under phase shift control of the rear-stage bidirectional full-bridge CLLLC resonant circuit of the present invention;

[0051] Figure 7 It is a variable waveform diagram under the frequency conversion control of the rear-stage bidirectional full-bridge CLLLC resonant circuit of the present invention;

[0052] Figure 8 It is a variable waveform diagram of the two-stage bidirectional AC-DC converter under constant current control of the present invention;

[0053] Fig. 9 The figure is a variable waveform diagram of the two-stage bidirectional AC-DC converter of the present invention under constant voltage control. DETAILED DESCRIPTION

[0054] The present invention is further described in detail below in conjunction with embodiments:

[0055] Example 1

[0056] like Figure 1-9 As shown, the present invention provides a control method for a two-stage bidirectional AC-DC converter, comprising the following steps:

[0057] Step 1: Establish a model of a two-stage bidirectional AC-DC converter, analyze the working principle of the two-stage bidirectional AC-DC converter, and obtain the working characteristics of the front-stage interleaved parallel bridgeless PFC circuit and the rear-stage bidirectional full-bridge CLLLC resonant circuit.

[0058] The overall control block diagram of the two-stage bidirectional AC-DC converter is as follows: Figure 1 As shown, it includes the current inner loop and voltage outer loop dual closed-loop control of the front-stage interleaved parallel bridgeless PFC circuit and the phase-shift-frequency conversion hybrid control of the rear-stage bidirectional full-bridge CLLLC resonant circuit.

[0059] Step 2: According to the working characteristics of the front-stage interleaved parallel bridgeless PFC circuit, a voltage and current double closed-loop control model is established for the front-stage interleaved parallel bridgeless PFC circuit during forward and reverse operation. The working process of the front-stage interleaved parallel bridgeless PFC circuit is basically the same during forward and reverse operation. Figure 1As shown in the figure, during forward operation, the inner current loop makes the input inductor current change with the input voltage, making the input inductor current closer to a sine wave, and the outer voltage loop keeps the output of the PFC circuit stable. The sampled bus voltage V dc and bus voltage reference value V dc_ref The bus voltage error signal is obtained by comparison. The bus voltage error signal is multiplied by the input current unit after passing through the PI controller to obtain the reference value of the two-way input inductor current. The two-way input inductor current reference value and the two-way input inductor current I L1 with I L2 By comparing the two input inductor current error signals, the duty cycle change is obtained through the PI controller, and then compared with the sawtooth wave to obtain the PWM signal of the high-frequency switch tube, in which the two high-frequency bridge arm drive signals are fixedly 180° apart. The low-frequency switch tubes Q5 and Q6 control the on and off by judging the positive and negative half cycles through the input voltage, and the input voltage also controls the circuit zero-crossing drive blockage.

[0060] Step 3: According to the working characteristics of the subsequent bidirectional full-bridge CLLLC resonant circuit, a phase-shift-frequency control model of the subsequent bidirectional full-bridge CLLLC resonant circuit is established. When running in the forward direction, the reference output voltage V o_ref and the actual output voltage V o is the input signal of the voltage loop PI controller, and the actual output current I o The output signal of the voltage loop PI controller is the input signal of the current loop PI controller. In the variable frequency mode, the output voltage is controlled by changing the switching frequency of the switch tubes S1 and S4, S2 and S3. In the phase shift mode, the output voltage is controlled by changing the phase shift angle of the switch tubes S1 and S4, S2 and S3. The subsequent bidirectional full-bridge CLLLC resonant circuit adopts the variable frequency control method when it works in the forward voltage gain M>1, and adopts the phase shift control method if it works in the voltage gain M<1. When the subsequent bidirectional full-bridge CLLLC resonant circuit is in reverse operation, the reference input voltage V dc_ref and the actual input voltage V dc is the input signal of the voltage loop PI controller, the actual input current I dc The output signal of the voltage loop PI controller is the input signal of the current loop PI controller. The rear bidirectional full-bridge CLLLC resonant circuit adopts the variable frequency control mode when the reverse voltage gain M>1, and adopts the phase shift control mode when the reverse voltage gain M<1. In the variable frequency mode, the output voltage is controlled by changing the switching frequency of the switch tubes S5 and S8, S6 and S7, and in the phase shift mode, the output voltage is controlled by changing the phase shift angle of the switch tubes S5 and S8, S6 and S7.

[0061] Step 4: Apply the above control method to realize the operation of the two-stage bidirectional AC-DC converter under constant current control and under constant voltage control.

[0062] Example 2

[0063] like Figure 1-9 As shown, a control method for a two-stage bidirectional AC-DC converter comprises the following steps:

[0064] Step 1: Establish a model of a two-stage bidirectional AC-DC converter, analyze the working principle of the two-stage bidirectional AC-DC converter, and obtain the working characteristics of the front-stage interleaved parallel bridgeless PFC circuit and the rear-stage bidirectional full-bridge CLLLC resonant circuit.

[0065] The specific process is as follows:

[0066] Step 1.1: The front-stage interleaved parallel bridgeless PFC circuit adopts a synchronous rectification scheme. Q1, Q2, Q3, and Q4 are used as high-frequency switches. When the input current is in the positive half cycle, the power frequency switch Q5 is always off and Q6 is always on; when the input current is in the negative half cycle, the power frequency switch Q5 is always on and Q6 is always off.

[0067] Step 1.2: The switch tubes S1 to S4 of the rear bidirectional full-bridge CLLLC resonant circuit form the primary side full bridge, and S5 to S8 form the secondary side full bridge. s1 ~D s8 They are the body diodes of S1 to S8, C s1 ~C s8 The drain-source parasitic capacitances of S1 to S8 are shown in Figure 1. The transformer ratio is n:1, and also includes the excitation inductance L. m , the equivalent symmetrical resonant inductor L on the primary and secondary sides r1 and L r2 , resonant capacitor C r1 and C r2 , high frequency transformer for electrical isolation. V dc is the input voltage, V o is the load or energy storage battery voltage, C o is the filter capacitor. When the converter is working in the forward direction, the power is from V dc To V o Transfer, when working in reverse, the power is V o To V dc transfer;

[0068] Step 1.3: The two-stage bidirectional AC-DC converter can transfer energy in both forward and reverse modes, achieving bidirectional energy flow.

[0069] Step 2: According to the working characteristics of the front-stage interleaved parallel bridgeless PFC circuit, a voltage and current double closed-loop control model is established for the front-stage interleaved parallel bridgeless PFC circuit during forward and reverse operation. The working process of the front-stage interleaved parallel bridgeless PFC circuit is basically the same during forward and reverse operation. Figure 1As shown in the figure, during forward operation, the inner current loop makes the input inductor current change with the input voltage, making the input inductor current closer to a sine wave, and the outer voltage loop keeps the output of the PFC circuit stable. The sampled bus voltage V dc and bus voltage reference value V dc_ref The bus voltage error signal is obtained by comparison. The bus voltage error signal is multiplied by the input current unit after passing through the PI controller to obtain the reference value of the two-way input inductor current. The two-way input inductor current reference value and the two-way input inductor current I L1 with I L2 By comparing the two input inductor current error signals, the duty cycle change is obtained through the PI controller, and then compared with the sawtooth wave to obtain the PWM signal of the high-frequency switch tube, in which the two high-frequency bridge arm drive signals are fixedly 180° apart. The low-frequency switch tubes Q5 and Q6 control the on and off by judging the positive and negative half cycles through the input voltage, and the input voltage also controls the circuit zero-crossing drive blockage.

[0070] The specific process is as follows:

[0071] Step 2.1: Figure 2 The expression of the current inner loop transfer function of the front-stage interleaved parallel bridgeless PFC circuit is shown as:

[0072]

[0073] Among them, G id(s) is the current controller transfer function when PI control is used, K Pi1 , K Ii1 They are the proportional coefficient and integral coefficient of the current inner loop controller of the interleaved parallel bridgeless PFC circuit respectively.

[0074] Step 2.2: Find the expression of the voltage outer loop transfer function of the front-stage interleaved parallel bridgeless PFC circuit:

[0075]

[0076] Among them, G vd(s) is the voltage controller transfer function when PI control is used, K Pv1 , K Iv1 They are the proportional coefficient and integral coefficient of the voltage outer loop controller of the interleaved parallel bridgeless PFC circuit respectively.

[0077] Step 2.3: The control strategy of the front-stage interleaved parallel bridgeless PFC circuit is obtained from the transfer function.

[0078] Step 2.4: If Figure 3 The output waveform of the front-stage interleaved parallel bridgeless PFC circuit is obtained using the control strategy shown.

[0079] Step 3: According to the working characteristics of the subsequent bidirectional full-bridge CLLLC resonant circuit, a phase-shift-frequency control model of the subsequent bidirectional full-bridge CLLLC resonant circuit is established. Reference output voltage V o_ref and the actual output voltage V o is the input signal of the voltage loop PI controller, and the actual output current I o The output signal of the voltage loop PI controller is the input signal of the current loop PI controller. In the variable frequency mode, the output voltage is controlled by changing the switching frequency of the switch tubes S1 and S4, S2 and S3. In the phase shift mode, the output voltage is controlled by changing the phase shift angle of the switch tubes S1 and S4, S2 and S3. The subsequent bidirectional full-bridge CLLLC resonant circuit adopts the variable frequency control method when it works in the forward voltage gain M>1, and adopts the phase shift control method if it works in the voltage gain M<1. When the subsequent bidirectional full-bridge CLLLC resonant circuit is in reverse operation, the reference input voltage V dc_ref and the actual input voltage V dc is the input signal of the voltage loop PI controller, the actual input current I dc The output signal of the voltage loop PI controller is the input signal of the current loop PI controller. The rear bidirectional full-bridge CLLLC resonant circuit adopts the variable frequency control mode when the reverse voltage gain M>1, and adopts the phase shift control mode when the reverse voltage gain M<1. In the variable frequency mode, the output voltage is controlled by changing the switching frequency of the switch tubes S5 and S8, S6 and S7, and in the phase shift mode, the output voltage is controlled by changing the phase shift angle of the switch tubes S5 and S8, S6 and S7.

[0080] The specific process is as follows:

[0081] Step 3.1: If Figure 4 The impedance expression for the bidirectional full-bridge CLLLC resonant circuit is shown as:

[0082]

[0083] Where Z1 is the primary series resonant impedance; Z2 is the equivalent secondary series resonant impedance; Z m is the excitation inductance impedance; L r2 ′、C r2 ′ is L r2 , C r2 The values ​​of capacitance and inductance converted to the primary side of the transformer;

[0084] Step 3.2: Find the transfer function of the bidirectional full-bridge CLLLC resonant circuit as:

[0085]

[0086] Among them, V AB_FHA(t) V is the square wave fundamental component of the input DC bus voltage after full-bridge inversion.CD_FHA(t) is the square wave fundamental component of the output voltage after full-bridge rectification, R eq is the equivalent load converted to the original side;

[0087] Step 3.3: Calculate the voltage gain expression of the bidirectional full-bridge CLLLC resonant circuit under variable frequency control:

[0088]

[0089] Where, k is the inductance coefficient, Q is the quality factor; f n is the normalized frequency, f s is the actual switching frequency;

[0090] Step 3.4: The expression of the fundamental component of the square wave of the input voltage under phase shift control is:

[0091]

[0092] Step 3.5: The voltage gain expression under phase shift control is:

[0093]

[0094] Where D is the shift ratio, the voltage gain is approximately in a cosine relationship with D, and the range of variation is between 0 and 1;

[0095] Step 3.6: If Figure 5 As shown, it can be concluded that when the voltage gain M>1, the frequency conversion control method is adopted, and when the voltage gain M<1, the phase shift control method is adopted.

[0096] Step 3.7: The working results of the bidirectional full-bridge CLLLC resonant circuit under phase shift control can be obtained as follows Figure 6 The working results under variable frequency control are shown as Figure 7 As shown;

[0097] Step 4: Apply the above control method to realize the operation of the two-stage bidirectional AC-DC converter under constant current control. Figure 8 as shown and operates under constant pressure control as Fig. 9 shown.

[0098] The above generally describes the present invention in detail, but it is obvious to a person skilled in the art that some modifications or improvements can be made to the present invention. Therefore, modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A control method for a two-stage bidirectional AC-DC converter, characterized in that: The following steps are involved: Step 1: Establish a model of a two-stage bidirectional AC-DC converter, analyze the working principle of the two-stage bidirectional AC-DC converter, and obtain the working characteristics of the front-stage interleaved parallel bridgeless PFC circuit and the rear-stage bidirectional full-bridge CLLLC resonant circuit; Step 2: According to the working characteristics of the front-stage interleaved parallel bridgeless PFC circuit, a voltage and current double closed-loop control model of the front-stage interleaved parallel bridgeless PFC circuit during forward and reverse operation is established. The working process of the front-stage interleaved parallel bridgeless PFC circuit is basically the same during forward and reverse operation. During forward operation, the current inner loop makes the input inductor current change with the input voltage, making the input inductor current closer to a sine wave. The voltage outer loop keeps the output of the PFC circuit stable. The sampled bus voltage V dc and bus voltage reference value V dc_ref The bus voltage error signal is obtained by comparison. The bus voltage error signal is multiplied by the input current unit after passing through the PI controller to obtain the reference value of the two-way input inductor current. The two-way input inductor current reference value and the two-way input inductor current I L1 with I L2 By comparing the two input inductor current error signals respectively, the duty cycle change is obtained through the PI controller, and then compared with the sawtooth wave to obtain the PWM signal of the high-frequency switch tube. The two high-frequency bridge arm drive signals are fixed with a phase difference of 180°. The low-frequency switch tubes Q5 and Q6 are controlled to be on and off by judging the positive and negative half-cycles through the input voltage. At the same time, the input voltage also controls the circuit to drive the blockade at the zero crossing point. Step 3: Establish a phase-shift-frequency control model of the subsequent bidirectional full-bridge CLLLC resonant circuit according to the operating characteristics of the subsequent bidirectional full-bridge CLLLC resonant circuit. When running in the forward direction, the reference output voltage V o_ref and the actual output voltage V o is the input signal of the voltage loop PI controller, and the actual output current I o The output signal of the voltage loop PI controller is the input signal of the current loop PI controller. In the variable frequency mode, the output voltage is controlled by changing the switching frequency of the switch tubes S1 and S4, S2 and S3. In the phase shift mode, the output voltage is controlled by changing the phase shift angle of the switch tubes S1 and S4, S2 and S3. The latter bidirectional full-bridge CLLLC resonant circuit adopts a variable frequency control mode when the forward voltage gain M>1 is operated. If it works at a voltage gain M<1, a phase shift control mode is adopted. The latter bidirectional full-bridge CLLLC resonant circuit refers to the input voltage V when it is reversely operated. dc_ref and the actual input voltage V dc is the input signal of the voltage loop PI controller, the actual input current I dc The output signal of the voltage loop PI controller is the input signal of the current loop PI controller. The rear-stage bidirectional full-bridge CLLLC resonant circuit adopts a variable frequency control mode when the reverse voltage gain M>1, and adopts a phase shift control mode when the reverse voltage gain M<1. In the variable frequency mode, the output voltage is controlled by changing the switching frequency of the switch tubes S5 and S8, S6 and S7. In the phase shift mode, the output voltage is controlled by changing the phase shift angle of the switch tubes S5 and S8, S6 and S7. Step 4: Apply the above control method to realize the operation of the two-stage bidirectional AC-DC converter under constant current control and constant voltage control.

2. The control method of a two-stage bidirectional AC-DC converter according to claim 1, characterized in that: The specific process of step 1 is as follows: Step 1.1: The front-stage interleaved parallel bridgeless PFC circuit adopts a synchronous rectification scheme. Q1, Q2, Q3, and Q4 are used as high-frequency switches. When the input current is in the positive half cycle, the power frequency switch Q5 is always off and Q6 is always on; when the input current is in the negative half cycle, the power frequency switch Q5 is always on and Q6 is always off. Step 1.2: The switch tubes S1~S4 of the rear bidirectional full-bridge CLLLC resonant circuit form the primary side full bridge, S5~S8 form the secondary side full bridge, D s1 ~D s8 They are the body diodes of S1 to S8, C s1 ~C s8 They are the drain-source parasitic capacitances of S1 to S8, the transformer ratio is n:1, and also includes the excitation inductance L m , the equivalent symmetrical resonant inductor L on the primary and secondary sides r1 and L r2 , resonant capacitor C r1 and C r2 , high frequency transformer for electrical isolation, V dc is the input voltage, V o is the load or energy storage battery voltage, C o is the filter capacitor. When the converter is working in the forward direction, the power is V dc To V o Transfer, when working in reverse, the power is V o To V dc transfer; Step 1.3: The two-stage bidirectional AC-DC converter can transfer energy in both forward and reverse modes, thus achieving bidirectional energy flow.

3. The control method of a two-stage bidirectional AC-DC converter according to claim 1, characterized in that: The specific process of step 2 is as follows: Step 2.1: Calculate the expression of the current inner loop transfer function of the front-stage interleaved parallel bridgeless PFC circuit as follows: Among them, G id(s) is the current controller transfer function when PI control is used, K Pi1 , K Ii1 They are the proportional coefficient and integral coefficient of the current inner loop controller of the interleaved parallel bridgeless PFC circuit respectively; Step 2.2: Find the expression of the voltage outer loop transfer function of the front-stage interleaved parallel bridgeless PFC circuit: Among them, G vd(s) is the voltage controller transfer function when PI control is used, K Pv1 , K Iv1 They are the proportional coefficient and integral coefficient of the voltage outer loop controller of the interleaved parallel bridgeless PFC circuit respectively; Step 2.3: The control strategy of the front-stage interleaved parallel bridgeless PFC circuit is obtained from the transfer function; Step 2.4: Use the control strategy to obtain the output waveform of the front-stage interleaved parallel bridgeless PFC circuit.

4. The control method of a two-stage bidirectional AC-DC converter according to claim 1, characterized in that: The specific process of step 3 is as follows: Step 3.1: Define the impedance expression of the bidirectional full-bridge CLLLC resonant circuit as: Where Z1 is the primary series resonant impedance; Z2 is the equivalent secondary series resonant impedance; Z m is the excitation inductance impedance; L r2 ′、C r2 ′ is L r2 , C r2 The values ​​of capacitance and inductance converted to the primary side of the transformer; Step 3.2: Find the transfer function of the bidirectional full-bridge CLLLC resonant circuit as: Among them, V AB_FHA(t) V is the square wave fundamental component of the input DC bus voltage after full-bridge inversion. CD_FHA(t) is the square wave fundamental component of the output voltage after full-bridge rectification, R eq is the equivalent load converted to the original side; Step 3.3: Calculate the voltage gain expression of the bidirectional full-bridge CLLLC resonant circuit under variable frequency control: Where, k is the inductance coefficient, Q is the quality factor; f n is the normalized frequency, f s is the actual switching frequency; Step 3.4: The expression of the fundamental component of the square wave of the input voltage under phase shift control is: Step 3.5: The voltage gain expression under phase shift control is: Where D is the shift ratio, the voltage gain is approximately in a cosine relationship with D, and the range of variation is between 0 and 1; Step 3.6: It can be concluded that when the voltage gain M>1, the frequency conversion control method is adopted, and when the voltage gain M<1, the phase shift control method is adopted; Step 3.7: The working results of the bidirectional full-bridge CLLLC resonant circuit under variable frequency control and the working results under phase shift control can be obtained.

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