A two-stage DC-AC converter system based on DAB and its ripple suppression method

Abstract

The present invention discloses a two-stage DC-AC converter system based on DAB, which is composed of a dual-active full-bridge DC-DC converter and a single-phase grid-connected inverter. The dual-active full-bridge DC-DC converter is composed of a primary full bridge and a secondary full bridge through a high-frequency transformer HFL and a C r 、 L r The single-phase grid-connected inverter consists of a resonant circuit composed of a switching tube. K 1 ～K 4 The inverter full bridge and the inductor L 1. L 2 and capacitor C The invention discloses an LCL type grid-connected filter circuit; and discloses a secondary ripple suppression method and control strategy thereof, which transfers the doubled frequency pulsating power in the DC bus capacitor to the LC power decoupling branch through an LC passive branch connected at the midpoint of the secondary side of the dual active bridge, thereby achieving power decoupling and further suppressing the secondary ripple in the DC bus voltage to maintain bus voltage stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a two-stage DC-AC converter system based on DAB, and a ripple suppression method thereof. Background Art

[0002] In a two-stage DC-AC grid-connected structure, maintaining a constant voltage at the grid-connected inverter is crucial for improving power quality. However, in a DC converter with an inverter, secondary ripple in the grid power results from the power conservation principle, which results in secondary ripple in the inverter input voltage. This ripple increases switching losses in the inverter's switches and significantly impacts power quality.

[0003] In addition, in order to suppress voltage ripple, while ensuring that the downstream grid-connected inverter can work normally, it is best to select a decoupling capacitor with a smaller capacitance value, so that the volume and weight of the whole machine can be reduced and the power density can be improved.

[0004] Therefore, a technology is needed that can suppress the DC bus secondary ripple voltage and reduce the decoupling capacitance to improve power quality and power density. Summary of the Invention

[0005] One of the objectives of the present invention is to provide a two-stage DC-AC converter system based on DAB, which can be applied to various new energy combined power generation systems, new energy and energy storage device combined power generation systems, etc.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a two-stage DC-AC converter system based on DAB, which is composed of a dual-active full-bridge DC-DC converter and a single-phase grid-connected inverter. The dual-active full-bridge DC-DC converter is composed of a primary full bridge and a secondary full bridge through a high-frequency transformer HFL and a C r 、L r The resonant circuit is connected, the primary full bridge is composed of primary switch tubes S1~S4, the secondary full bridge is composed of secondary switch tubes Q1~Q4, the DC port 1 and port 2 of the primary full bridge and the inductor L s1 、L s2 Together with the switch tubes S1 and S2, a dual Boost circuit is formed. The inductor L s1 =L s2 =L s The middle point of the left arm of the secondary full bridge is connected to the inductor L r1 , capacitor C r1The single-phase grid-connected inverter comprises an inverter full-bridge composed of switch tubes K1 to K4 and an LCL type grid-connected filter circuit composed of inductors L1, L2 and capacitor C. The LCL type grid-connected filter circuit is connected to the AC grid through port 3.

[0007] In the ripple suppression method of the two-stage DC-AC converter system based on DAB, port 1 is an energy storage port connected to a battery, and port 2 is connected to a new energy port of a photovoltaic power generation module.

[0008] A second object of the present invention is to provide a ripple suppression method for a two-stage DC-AC converter system based on DAB, comprising the following steps:

[0009] S1, start running, system initialization ref Given: given reference DC bus voltage u ref ;

[0010] S2, after completing the initialization operation, gives the reference DC bus voltage u ref The DC bus voltage u measured by the voltage sensor dc The double frequency ripple voltage v is obtained through negative feedback comparison m =u ref -u dc , thereby separating the double frequency ripple voltage v m ;

[0011] S3, double frequency ripple voltage v m The capacitor current inner loop given value i is obtained through the quasi-proportional resonant regulator PR output. ref , the LC power decoupling branch capacitor current i measured by the current sensor r The output after comparison is adjusted by the proportional controller P, and after voltage and current double closed-loop control, the fluctuation of the duty cycle D2 of the secondary switch tubes Q1~Q4 is finally output. D ;

[0012] S4, take the duty cycle steady-state operating point D0 of the secondary full bridge when the transmission power reaches the maximum, and the fluctuation amount δ of the duty cycle D2 D After adding, the actual secondary side duty cycle D2 is obtained. The fluctuation amount δ is added to the stable point D0 and the actual secondary side switch duty cycle D2 = D0 + δ is obtained.

[0013] S5, using D2 to perform PWM modulation to form the secondary side switch tube drive pulse: D2 is used as the secondary side switch tube duty cycle to generate the secondary side switch tube PWM modulation signal to control the secondary side switch tubes Q1 to Q4;

[0014] S6, makes the fluctuating power of LC power decoupling branch compensate the double frequency ripple power: by controlling the duty cycle of switch tubes Q1~Q2, the capacitor voltage u on the LC power decoupling branch is c Periodic fluctuations occur, thereby releasing or absorbing secondary pulsating power, transferring the power that needs to be buffered by the DC bus to the LC power decoupling branch, maintaining a constant DC bus voltage and suppressing the DC bus double frequency ripple voltage;

[0015] S7, determine whether to shut down: if no shutdown instruction is received, repeat steps S2 to S6, otherwise exit the running state.

[0016] Furthermore, the control strategy of the secondary side switches Q1 to Q4 adopts a dual closed-loop control consisting of a DC bus voltage outer loop and a capacitor current inner loop. When the duty cycle of the secondary side switches Q1 and Q2 is D2, and the LC power decoupling branch realizes buffering of the doubled frequency power, the duty cycle of the secondary side switches Q3 and Q4 is 1-D2.

[0017] Furthermore, the reference DC bus voltage u ref The actual bus voltage u after low-pass filter dc The difference between the two is compared through negative feedback, and the PI regulator outputs the phase shift angle θ, which participates in the PWM modulation of the secondary side switches Q1~Q4.

[0018] Furthermore, the single-phase grid-connected inverter adopts dual current loop control based on the capacitor current inner loop and the grid current outer loop, the capacitor current inner loop adopts proportional control, and the grid current outer loop adopts direct control of the grid current; let u g is the grid voltage sampling value, u g To output the grid voltage phase through the phase-locked loop, ensure that the grid current and grid voltage phase are close, I g * The grid current amplitude is given, and the given value I can be obtained from the power balance g * =2(P pv +P bat ) / U g , I g * The instantaneous given value of the grid current i is obtained by multiplying the phase product of the phase-locked loop g * , change i g * and the grid current sampling value i g The error of the grid current outer loop quasi-proportional resonant regulator PR generates the reference value i of the capacitor current inner loop c * , then i c *The measured value of the capacitor current i c The feedback is compared, and the error between the two is generated by the capacitor current inner loop proportional controller P to generate the SPWM modulation signal of the inverter full bridge, thereby realizing the control of the inverter full bridge switch tubes K1~K4.

[0019] The beneficial effects of the present invention are as follows: the present invention is based on DAB two-stage DC-AC conversion, and by connecting an LC power decoupling branch to the secondary bridge arm of the dual active bridge, the problem of the DC bus voltage of the input inverter containing secondary ripples and the problem of improving the system power density are effectively solved.

[0020] The present invention adopts a double closed loop control method to output the duty cycle of the secondary full bridge. By using this circuit structure and control strategy, it can be achieved: the ripple power in the system is transferred from the bus capacitor C dc The power is transferred to the LC power decoupling branch to suppress the secondary ripple voltage of the DC bus, so that the DC bus voltage remains constant and the power quality is improved. Under the same ripple suppression effect, the total decoupling capacitor capacitance is reduced, and the power density of the system is relatively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of a two-stage DC-AC converter system based on DAB according to the present invention;

[0022] Figure 2 This is a flow chart of the LC power decoupling branch of the present invention to achieve double frequency power decoupling control;

[0023] Figure 3 It is the secondary DC bus voltage waveform when the LC power decoupling branch is not added;

[0024] Figure 4 It is the secondary DC bus voltage waveform when the LC power decoupling branch is added. DETAILED DESCRIPTION

[0025] The present invention will be described in further detail below with reference to the embodiments and the accompanying drawings.

[0026] Reference Figure 1 As shown in the figure, the present invention discloses a two-stage DC-AC converter system based on DAB, the main circuit consists of two parts: a dual-active full-bridge DC-DC converter and a single-phase grid-connected inverter, wherein the dual-active full-bridge DC-DC converter consists of a primary full bridge and a secondary full bridge through a high-frequency transformer HFL and a C r 、L rThe resonant circuit formed is connected to form a resonant partially isolated DC-DC converter. The primary full bridge is composed of primary switch tubes S1~S4, and the secondary full bridge is composed of secondary switch tubes Q1~Q4. Port 1 is the energy storage port and is analyzed by taking the battery as an example. Port 2 is the new energy port and is analyzed by taking photovoltaic power generation as an example. Ports 1 and 2 of the primary full bridge and the inductor L s1 、L s2 And the switch tubes S1~S2 form a dual Boost circuit, where the inductor L s1 =L s2 =L s This structure can boost the photovoltaic voltage through the Boost circuit, increase the bus voltage and achieve voltage matching between port 1 and port 2. By reusing the switch tubes S1 and S2, the number of power switch tubes is reduced, which reduces the cost. The midpoint of the left arm of the secondary full bridge is connected to the inductor L r1 , capacitor C r1 The LC power decoupling branch is composed of a small fluctuation in the duty cycle of the secondary side switch tube near 0.5, which makes the capacitor voltage on the LC power decoupling branch fluctuate to achieve power decoupling. The LC power decoupling branch is used to filter out the secondary ripple component in the circuit. The capacitor C d Very small to absorb the high frequency noise of the primary switch tube, capacitor C dc This is a high-side stabilizing capacitor. The single-phase grid-connected inverter is a DC-AC inverter consisting of an inverter full-bridge consisting of switches K1-K4, and an LCL-type grid-connected filter circuit consisting of inductors L1, L2, and capacitor C. Port 3 of the LCL-type grid-connected filter circuit is connected to the AC grid. The front-stage DC-DC converter controls the duty cycle of the primary-side switches to achieve MPPT control of the photovoltaic cells. The battery port acts as a free port, charging or discharging according to changes in photovoltaic output power to compensate for system energy.

[0027] The control strategy for the secondary side switches Q1 to Q4 in the front-stage DC-DC section is a dual closed-loop control consisting of a DC bus voltage outer loop and a capacitor current inner loop. When the duty cycle of the secondary side switches Q1 and Q2 is D2, and the LC power decoupling branch buffers the doubled frequency power, the duty cycle of the secondary side switches Q3 and Q4 is 1-D2. Take the duty cycle modulation frequency ω r Equal to twice the grid frequency ω gBy controlling the duty cycle of the secondary side switch tube to produce a small fluctuation near 0.5, the capacitor voltage on the LC power decoupling branch fluctuates, thereby transferring the secondary pulsating power to the LC power decoupling branch to achieve power decoupling, thereby suppressing the secondary ripple of the DC bus voltage and maintaining DC voltage stability. Dual closed-loop control is used to achieve power decoupling, where the outer loop is the bus voltage loop and the inner loop is the LC power decoupling branch current loop. The small fluctuation of the secondary side full-bridge duty cycle controlled by the dual closed-loop output is δ D , so the secondary full-bridge duty cycle is D2=0.5+δ D After adding the LC power decoupling branch and related controls, the secondary ripple in the circuit is effectively suppressed, the voltage input to the grid-connected inverter is more stable, and the quality of the grid-connected current is improved. In addition, this decoupling method can greatly reduce the decoupling capacitance and increase the power density.

[0028] When the DC converter is loaded with an inverter, a double frequency ripple will be generated in the DC bus. When the inverter output voltage angular frequency is ω, the instantaneous power will contain a double frequency pulsating power of 2ω. Due to the law of power conservation, the DC bus side will inevitably contain a double frequency pulsating power. Figure 2 As shown, the present invention discloses a ripple suppression method for a two-stage DC-AC converter system based on DAB, and the process of controlling the double frequency ripple suppression in the circuit by the LC power decoupling branch is as follows.

[0029] S1, start running, system initialization ref Given: given reference DC bus voltage u ref First, at the initial stage of system power-on, perform the software and hardware initialization work related to system control. The important work is to set the duty cycle D2 in the program to output the dynamic fluctuation delta. D =0 and D2 steady-state point output is 0.5.

[0030] S2, after completing the initialization operation, gives the reference DC bus voltage u ref The DC bus voltage u measured by the voltage sensor dc The double frequency ripple voltage v is obtained through negative feedback comparison m =u ref -u dc , thereby separating the double frequency ripple voltage v m .

[0031] S3, double frequency ripple voltage v m The capacitor current inner loop given value i is obtained through the quasi-proportional resonant regulator PR output. ref , the LC power decoupling branch capacitor current i measured by the current sensor rThe output after comparison is adjusted by the proportional controller P, and after voltage and current double closed loop control, the output is the fluctuation of the duty cycle D2 of the secondary switch tubes Q1~Q4 δ D .

[0032] S4, take the duty cycle steady-state operating point D0 of the secondary full bridge when the transmission power reaches the maximum, and the fluctuation amount δ of the duty cycle D2 D After adding, we get the actual secondary side duty cycle D2. From the analysis, we know that when D2 is around 0.5, the transmission power can reach the maximum. When D2 deviates greatly from 0.5, it is not conducive to power transmission. Therefore, the duty cycle steady-state operating point of the secondary full bridge is 0.5. Add the fluctuation amount δ to the stable point D0 = 0.5, that is, the fluctuation amount δ of the duty cycle D2 D After adding D0=0.5, the actual secondary side switch duty cycle D2=D0+δ is obtained.

[0033] S5, using D2 to perform PWM modulation to form a secondary side switch tube drive pulse: using D2 as the secondary side switch tube duty cycle to generate a PWM modulation signal for the secondary side switch tube to control the secondary side switch tubes Q1 to Q4.

[0034] S6, makes the fluctuating power of LC power decoupling branch compensate the double frequency ripple power: by controlling the duty cycle of switch tubes Q1~Q2, the capacitor voltage u on the LC power decoupling branch is c Periodic fluctuations occur, thereby releasing or absorbing secondary pulsating power, transferring the power that needs to be buffered by the DC bus to the LC power decoupling branch, keeping the DC bus voltage constant and achieving the purpose of suppressing the DC bus double frequency ripple voltage.

[0035] S7, determine whether to shut down: if no shutdown instruction is received, repeat steps S2 to S6, otherwise exit the running state.

[0036] For the front-stage dual active full-bridge DC-DC converter, according to the attached Figure 2 Provide explanation.

[0037] The port 1 is an energy storage port connected to the battery, and the port 2 is a new energy port connected to the photovoltaic power generation module.

[0038] Taking the battery as port 1 and the photovoltaic cell as port 2 as an example, similar to the setting of the switch tube duty cycle D2, D1 is the duty cycle of the primary full-bridge switch tubes S1 and S2, which is used to realize the MPPT control of the photovoltaic cell, then the duty cycle of the switch tubes S3 and S4 is (1-D1); θ is the angle at which the primary side midpoint voltage of the high-frequency transformer HFL leads the secondary side midpoint voltage, which is used to control the direction of energy transfer. This patent sets 0≤θ≤π, that is, power is transferred in the forward direction from the DC side to the AC side to realize the combined grid-connected power generation of new energy and energy storage.

[0039] The maximum power point tracking (MPPT) control strategy of photovoltaic cells is designed by using the conductance increment method. The reference value of the photovoltaic cell voltage is output by MPPT to make it consistent with the photovoltaic voltage u measured by the actual voltage sensor. pv Negative feedback is used for comparison, and the difference between the two is output by the PI regulator as the duty cycle D1 of the primary-side switch of the dual active bridge. After PWM modulation, the primary-side switches S1 to S4 are controlled. The secondary-side switch duty cycle D2 is used to suppress the secondary ripple in the bus voltage.

[0040] The reference DC bus voltage u ref The actual bus voltage u after low-pass filter dc Negative feedback is used for comparison, and the difference between the two is passed through the PI regulator to output a phase-shift angle θ, which is used to modulate the PWM of the secondary switches Q1-Q4. Using the phase-shift angle θ between the primary and secondary sides, a single voltage loop is designed to control the DC bus voltage constantly, ensuring bus voltage stability to meet the grid-connected inverter's requirements. This dual-PWM + phase-shift modulation strategy achieves MPPT control of the new energy port, secondary bus voltage regulation, and secondary ripple suppression.

[0041] Given rated bus voltage u ref As the reference value of the voltage outer loop, the actual bus voltage u dc As negative feedback, the difference between the two is output through the voltage outer loop PR quasi-proportional resonant regulator to obtain the reference value i of the LC power decoupling branch capacitor current. ref , and the capacitor current i measured by the current sensor r After comparison, the capacitance current inner loop proportional controller P outputs the fluctuation of the secondary side switch tube δ D , and the steady-state value 0.5 is added to obtain the duty cycle D2 of the secondary switch tube, which is then modulated by PWM to control the secondary switch tubes Q1 to Q4. The single voltage loop is designed to control the DC bus voltage by using the phase shift angle θ between the primary and secondary sides to ensure the bus voltage is stable to meet the grid-connected requirements of the grid-connected inverter. ref The actual bus voltage u after low-pass filter dc Negative feedback is used for comparison, and the difference between the two is passed through the PI regulator to output the phase shift angle θ, which is used to modulate the PWM of the secondary switches Q1 to Q4. This dual PWM + phase shift modulation strategy achieves MPPT control of the new energy port, secondary bus voltage regulation, and secondary ripple suppression.

[0042] Explanation of the subsequent single-phase grid-connected inverter: The control strategy of the single-phase grid-connected inverter adopts a dual current loop control strategy of a capacitor current inner loop and a grid current outer loop; the use of proportional control in the capacitor current inner loop can effectively damp the resonant peak of the LCL filter and improve the system speed and stability; the grid current outer loop adopts a direct control scheme of the grid current to achieve unity power factor grid connection and reduce grid current harmonics. g is the grid voltage sampling value, u g The grid voltage phase is output through the phase-locked loop to ensure that the grid current and grid voltage are close to the same phase, I g * The grid current amplitude is given, and the given value I can be obtained from the power balance g * =2(P pv +P bat ) / U g , I g * The instantaneous given value of the grid current i is obtained by multiplying the phase product of the phase-locked loop g * , change i g * and the grid current sampling value i g The error of the grid current outer loop quasi-proportional resonant regulator PR generates the reference value i of the capacitor current inner loop c * , then i c * The measured value of the capacitor current i c The feedback is compared, and the error between the two is generated by the capacitor current inner loop proportional controller P to generate the SPWM modulation signal of the inverter full bridge, thereby realizing the control of the inverter full bridge switch tubes K1~K4.

[0043] The present invention provides an LC power decoupling control technology for suppressing secondary ripple of the DC bus voltage of the input inverter. In order to suppress the double frequency ripple power output by the DC bus, for the dual active full-bridge DC-DC converter, an LC passive branch is connected at the midpoint of the secondary full-bridge, so that a Boost circuit is formed between the LC power decoupling branch and the secondary side switch tube of the dual active bridge and the bus voltage without adding additional components, and is connected to the switch tubes Q1, Q3, and the bus voltage U dc A Boost circuit is formed between them. Assuming that the duty cycle of the secondary side switch of the full bridge is D2, the decoupling capacitor voltage U is obtained. c Equal to the DC bus voltage U dc The product of duty cycle D2.

[0044] In terms of control, the present invention adopts a dual closed-loop control strategy of voltage outer loop and current inner loop to realize the control of the duty cycle of the DAB secondary side switch tube. The dual closed-loop control is used to make the duty cycle D2 fluctuate slightly around 0.5, so that the decoupling capacitor voltage on the LC power decoupling branch fluctuates periodically to absorb or release the secondary pulsating power required by the system, and transfer the decoupling power from the original DC bus to the LC power decoupling branch, ensuring the constant DC bus voltage while realizing power decoupling.

[0045] Figure 3 The left figure is the DC bus voltage waveform when the LC power decoupling branch is not added, and the right figure is the DC bus voltage waveform. Figure 3 It can be seen that the DC bus voltage is essentially stable at 300V, with a 100Hz secondary ripple with an amplitude of 6V, which is consistent with the analysis of the bus voltage experiencing double-frequency ripple. Without the addition of an LC power decoupling branch, the system's secondary pulsating power is primarily buffered by the bus capacitor. The figure shows that the DC bus voltage is 300V, and the voltage ripple is 6V, or 2%, with a bus capacitor value of 2000μF. This shows that simply connecting a large capacitor in parallel with the secondary DC bus for power decoupling does not effectively suppress the secondary ripple in the circuit. A significant amount of secondary ripple still exists in the circuit. Moreover, in this configuration, the decoupling capacitor value is very large, resulting in low power density.

[0046] Figure 4 This is the secondary DC bus voltage waveform when the LC power decoupling branch is added. The left figure is the DC bus voltage waveform, and the right figure is the DC bus voltage partial amplified waveform. Figure 3 and Figure 4 It can be seen that after implementing the LC power decoupling method, the DC bus voltage remains stable before and after the light intensity decreases at t = 1s, demonstrating the correctness of the patent's overall energy management strategy for the system. The addition of the LC power decoupling branch reduces the DC bus voltage fluctuation from 6V to 1.5V, and the total power decoupling capacitor capacitance is reduced, effectively suppressing the secondary ripple content in the circuit and improving the system's power density.

[0047] It is easy for those skilled in the art to understand that the above description is only a preferred use case of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A ripple suppression method for a two-stage DC-AC converter system based on DAB, characterized in that: The DC-AC converter system consists of a dual-active full-bridge DC-DC converter and a single-phase grid-connected inverter. The dual-active full-bridge DC-DC converter consists of a primary full-bridge and a secondary full-bridge through a high-frequency transformer and a C r 、 L r The resonant circuit is connected, and the primary full bridge is composed of the primary switch tube S 1 ～S 4 The secondary side full bridge is composed of the secondary side switch tube Q 1 ～Q 4 constitute, Q 1 and Q 3 As the left bridge arm, Q 2 and Q 4 As the right bridge arm, the DC ports 1 and 2 of the primary full bridge and the inductor L s1 、 L s2 and switch tube S 1 ～S 2 It forms a dual Boost circuit, port 1 is connected to the energy storage port of the battery, port 2 is connected to the new energy port of the photovoltaic power generation module, and the inductor L s1 = L s2 = L s , an inductor is connected between the midpoint of the left arm of the secondary full bridge and the output negative pole L r1 ,capacitance C r1 The single-phase grid-connected inverter comprises a switching tube K 1 ～K 4 The inverter full bridge and the inductor L 1. L 2 and capacitor C The LCL type grid-connected filter circuit is connected to the AC grid through port 3 and includes the following steps: S1, given the reference DC bus voltage of the secondary full-bridge output bus u ref ; S2, will refer to the DC bus voltage u ref The DC bus voltage measured by the voltage sensor u dc The double frequency ripple voltage is obtained by negative feedback comparison v m = u ref - u dc ; S3, double the frequency ripple voltage v m After inputting the quasi-proportional resonant regulator PR, the output capacitor current inner loop set value i ref , and the LC power decoupling branch capacitor current measured by the current sensor i r The output after comparison is adjusted by the proportional controller P, and the output secondary side switch tube Q 1 ～Q 4 Duty cycle D Fluctuation of 2 δ D ; S4, take the duty cycle steady-state operating point of the secondary full bridge when the transmission power reaches the maximum D 0, with duty cycle D Fluctuation of 2 δ D After adding, we get the actual secondary duty cycle D 2. At the stable point D Add the fluctuation amount based on 0 δ D Get the actual secondary side switch duty cycle D 2 = D 0 + δ D ; S5, will D 2 as the duty cycle of the secondary side switch tube to generate the PWM modulation signal of the secondary side switch tube and control the secondary side switch tube Q 1 ～Q 4 ; S6, by controlling the switch Q 1 ～Q 2 The duty cycle changes, making the capacitor voltage on the LC power decoupling branch u c Periodic fluctuations occur, thereby releasing or absorbing secondary pulsating power, transferring the power that needs to be buffered by the DC bus to the LC power decoupling branch, and keeping the DC bus voltage constant; S7, if no stop command is received, repeat steps S2 to S6, otherwise exit the running state.

2. The ripple suppression method of a two-stage DC-AC converter system based on DAB according to claim 1, characterized in that: The secondary side switch tube Q 1 ～Q 4 The double closed loop control consisting of DC bus voltage outer loop and capacitor current inner loop is adopted. Q 1 and Q 2 The duty cycle is D 2. The LC power decoupling branch realizes the buffering of the double frequency power and the secondary side switch tube switch tube Q 3 and Q 4 The duty cycle is 1- D 2.

3. The ripple suppression method of a two-stage DC-AC converter system based on DAB according to claim 2, characterized in that: The reference DC bus voltage u ref The actual bus voltage after low-pass filter u dc The difference between the two is compared with the negative feedback, and the PI regulator outputs the phase shift angle θ , participate in the secondary side switch Q 1 ～Q 4 PWM modulation.

4. The ripple suppression method of a two-stage DC-AC converter system based on DAB according to claim 3, characterized in that: The single-phase grid-connected inverter adopts dual current loop control based on the capacitor current inner loop and the grid current outer loop. The capacitor current inner loop adopts proportional control, and the grid current outer loop directly controls the grid current. make u g is the grid voltage sampling value, u g To output the grid voltage phase through the phase-locked loop and ensure that the grid current and grid voltage phase are close, I g * The grid-connected current amplitude is given, and the given value can be obtained from the power balance I g * =2（P pv +P bat ） / U g ,in P pv Indicates the power of the photovoltaic power generation module, P bat Indicates the power of the battery. I g * The instantaneous given value of the grid current is obtained by multiplying the phase product of the phase-locked loop. i g * ,Will i g * and grid current sampling value i g The error of the grid current outer loop quasi-proportional resonant regulator PR generates the reference value of the capacitor current inner loop i c * , and then i c * The measured value of the capacitor current i c The error between the two is compared and the capacitor current inner loop proportional controller P is used to generate the SPWM modulation signal of the inverter full bridge to realize the full bridge switch of the inverter. K 1 ～K 4 control.

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