Two-stage DC-AC converter system based on DAB and ripple suppression method thereof

Abstract

The invention discloses a DAB-based two-stage DC-AC converter system, which is composed of a dual-active full-bridge DC-DC converter and a single-phase grid-connected inverter, and is characterized in that the dual-active full-bridge DC-DC converter is formed by connecting a primary side full bridge and a secondary side full bridge through a high-frequency transformer HFL and a resonance circuit composed of Cr and Lr; the single-phase grid-connected inverter comprises an inverter full bridge composed of switch tubes K1-K4 and an LCL type grid-connected filter circuit composed of inductors L1 and L2 and a capacitor C; the invention further discloses a secondary ripple suppression method and a control strategy, the pulse power of double frequency multiplication in the direct-current bus capacitor is transferred to the LC power decoupling branch through the LC passive branch connected to the middle point of the secondary side of the double active bridge, so that power decoupling is achieved, and the secondary ripple suppression in the direct-current bus voltage keeps the bus voltage stable.

Description

Technical Field

[0001] The 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 the two-stage DC-AC grid-connected structure, keeping the voltage of the input grid-connected inverter constant is of great significance to improving the power quality. However, in the structure of the DC converter with inverter grid-connected, due to the existence of a secondary pulsating power in the grid power, according to the principle of power conservation, there is a secondary ripple in the voltage of the input inverter, which will increase the switching loss of the inverter switch tube and have a great impact on the power quality.

[0003] In addition, in order to suppress voltage ripple, under the premise of ensuring that the subsequent grid-connected inverter can work normally, try to select a decoupling capacitor with a smaller capacitance, so that the size 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 secondary ripple voltage of the DC bus and reduce the decoupling capacitance to improve the power quality and power density. Summary of the invention

[0005] One of the purposes 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 The switch tubes S1 and S2 form a dual Boost circuit. The inductor L s1 =L s2 =L s The left bridge arm midpoint of the secondary side 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 a 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 a reference DC bus voltage u ref The DC bus voltage u measured by the voltage sensor dc After negative feedback comparison, the double frequency ripple voltage v is obtained m =u ref -u dc , thus 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 the 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. After adding the fluctuation amount δ to the stable point D0, the actual secondary side switch tube duty cycle D2 = D0 + δ is obtained.

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

[0014] S6, the fluctuating power of the LC power decoupling branch compensates the double frequency ripple power: by controlling the duty cycle of the switch tubes Q1~Q2, the capacitor voltage u on the LC power decoupling branch 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 double frequency ripple voltage of the DC bus;

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

[0016] Furthermore, the control strategy of the secondary side switches Q1~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 filtering dc The negative feedback is compared, and the difference between the two is output through the PI regulator to form a phase shift angle θ, which participates in the PWM modulation of the secondary side switch tubes 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-connected 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 grid current given value 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 secondary full-bridge duty cycle. By using this circuit structure and control strategy, it can be achieved that: the ripple power in the system is transferred from the bus capacitor C dc It 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 It is a schematic diagram of a two-stage DC-AC converter system based on DAB of the present invention;

[0022] Figure 2 It is a flow chart of the LC power decoupling branch of the present invention to realize 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 is further described in detail below in conjunction with the embodiments and the accompanying drawings.

[0026] Reference Figure 1 As shown, the present invention discloses a two-stage DC-AC converter system based on DAB, wherein the main circuit is composed 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 is composed 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 switch tubes S1 and S2, the number of power switch tubes is reduced, reducing 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 switch tube near 0.5, so that the capacitor voltage on the LC power decoupling branch fluctuates 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 It is a high-voltage side voltage stabilizing capacitor. The single-phase grid-connected inverter is a DC-AC inverter, including 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. Port 3 of the LCL type grid-connected filter circuit is connected to the AC grid. The front-stage DC-DC part realizes the MPPT control of the photovoltaic cell by controlling the duty cycle of the primary switch tube. The battery port is a free port that charges or discharges according to the change of photovoltaic output power to compensate for the system energy.

[0027] The control strategy of the secondary switch tubes Q1~Q4 of the front-stage DC-DC part adopts a double closed-loop control consisting of a DC bus voltage outer loop and a capacitor current inner loop. When the duty cycle of the secondary switch tubes Q1 and Q2 is D2, the duty cycle of the secondary switch tubes Q3 and Q4 is 1-D2 after the LC power decoupling branch realizes the buffering of the double frequency power. Take the duty cycle modulation frequency ω r Equal to twice the grid frequency ω gBy controlling the duty cycle of the secondary 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, and then suppressing the secondary ripple of the DC bus voltage to maintain DC voltage stability. Dual closed-loop control is used to achieve power decoupling, in which 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 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 control, 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 capacitor and improve 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 the LC power decoupling branch controlling the double frequency ripple suppression in the circuit 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 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 fluctuation momentum δ D =0 and D2 steady-state point output is 0.5.

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

[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 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 on the basis of 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 switch tube drive pulse: using D2 as the secondary switch tube duty cycle to generate a PWM modulation signal of the secondary switch tube to control the secondary switch tubes Q1 to Q4.

[0034] S6, the fluctuating power of the LC power decoupling branch compensates the double frequency ripple power: by controlling the duty cycle of the switch tubes Q1~Q2, the capacitor voltage u on the LC power decoupling branch 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 double-frequency ripple voltage of the DC bus.

[0035] S7, determine whether to shut down: if no shutdown command 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 a battery, and the port 2 is a new energy port connected to a 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 midpoint voltage of the high-frequency transformer HFL leads the secondary midpoint voltage, which is used to control the direction of energy transfer. This patent sets 0≤θ≤π, that is, power is forwardly transferred from the DC side to the AC side to realize the joint 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 The difference between the two is compared by negative feedback, and the duty cycle D1 of the primary switch tube of the dual active bridge is output by the PI regulator, and the primary switch tubes S1 to S4 are controlled after PWM modulation. The duty cycle D2 of the secondary switch tube 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 filtering dc The negative feedback is compared, and the difference between the two is output through the PI regulator phase shift angle θ, which participates in the PWM modulation of the secondary switch tubes Q1~Q4. The single voltage loop is designed using the phase shift angle θ between the original and secondary sides to perform constant voltage control on the DC bus to ensure the bus voltage stability to meet the grid-connected requirements of the grid-connected inverter. Under the dual PWM+phase shift modulation strategy, the MPPT control of the new energy port, the secondary bus voltage stabilization control, and the secondary ripple suppression control are realized.

[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 fluctuation amount δ of the secondary switch tube is output through the capacitor current inner loop proportional controller P. D , and the steady-state value 0.5 is added to obtain the duty cycle D2 of the secondary switch tube, and the secondary switch tubes Q1~Q4 are controlled after PWM modulation. The single voltage loop is designed to control the DC bus voltage by using the phase shift angle θ between the original 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 filtering dc The negative feedback is compared, and the difference between the two is output through the PI regulator phase shift angle θ, which participates in the PWM modulation of the secondary switch tubes Q1~Q4. Under the dual PWM+phase shift modulation strategy, the MPPT control of the new energy port, the secondary bus voltage regulation control, and the secondary ripple suppression control are realized.

[0042] Description of the subsequent single-phase grid-connected inverter: The control 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 resonance 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-connected 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 grid current given value 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 dual active bridge secondary switch tube and the bus voltage without adding additional components, and the LC power decoupling branch 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 switch of the full-bridge is D2, the decoupling capacitor voltage U 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 a voltage outer loop and a 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, thereby ensuring the constant DC bus voltage and realizing power decoupling.

[0045] Figure 3 The figure below is the DC bus voltage waveform on the secondary side when the LC power decoupling branch is not added. The left figure is the DC bus voltage waveform, and the right figure is the partial amplified DC bus voltage waveform. Figure 3 It can be seen that the DC bus voltage is basically stable at 300V, and there is a fluctuation of 100Hz with an amplitude of 6V, which is the secondary ripple. This is consistent with the analysis of the bus voltage having a double frequency ripple. Without adding an LC power decoupling branch, the secondary pulsating power of the system is mainly buffered by the bus capacitor. It can be seen from the figure that the DC bus is 300V, and the voltage ripple is 6V, or 2%. At this time, the bus capacitance value is 2000μF. It can be seen that only when the secondary DC bus is connected in parallel with a large capacitor for power decoupling, the secondary ripple in the circuit cannot be effectively suppressed. There is still a large amount of secondary ripple in the circuit, and in this way, the decoupling capacitor value is large and the power density is low.

[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 magnified waveform. Figure 3 and Figure 4 It can be seen that after adopting the LC power decoupling method, the DC bus voltage can maintain a stable voltage before and after the light intensity decreases at t=1s, which shows that the overall energy management strategy of the system in this patent is correct. After adding the LC power decoupling branch, the DC bus voltage fluctuation is reduced from the original 6V to 1.5V, and the total power decoupling capacitor capacitance is reduced, which effectively suppresses the secondary ripple content in the circuit and improves the power density of the system.

[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 protection scope of the present invention.

Claims

1. A two-stage DC-AC converter system based on DAB, characterized in that: The dual-active full-bridge DC-DC converter and the single-phase grid-connected inverter are composed 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, 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 The switch tubes S1 and S2 form a dual Boost circuit. The inductor L s1 =L s2 =L s The left bridge arm midpoint of the secondary side full bridge is connected to the inductor L r1 , capacitor C r1 The 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.

2. A two-stage DC-AC converter system based on DAB according to claim 1, characterized in that: The port 1 is an energy storage port connected to a battery, and the port 2 is a new energy port connected to a photovoltaic power generation module.

3. A ripple suppression method for a DC-AC converter system as claimed in claim 1, characterized in that: The steps include: S1, given reference DC bus voltage u ref ; S2, the reference DC bus voltage u ref The DC bus voltage u measured by the voltage sensor dc After negative feedback comparison, the double frequency ripple voltage v is obtained m =u ref -u dc ; S3, doubles the frequency ripple voltage v m After inputting the quasi-proportional resonant regulator PR, the output capacitor current inner loop given value i ref , and the LC power decoupling branch capacitor current i measured by the current sensor r The compared output is adjusted by the proportional controller P, and the fluctuation of the duty cycle D2 of the output secondary switch tubes Q1~Q4 is δ D ; 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. On the basis of the stable point D0, the fluctuation amount δ is added to obtain the actual secondary side switch tube duty cycle D2 = D0 + δ; S5, using D2 as the duty cycle of the secondary switch tube to generate a PWM modulation signal of the secondary switch tube to control the secondary switch tubes Q1 to Q4; S6, by controlling the duty cycle of the 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, and keeping the DC bus voltage constant; S7, if no stop command is received, repeat steps S2 to S6, otherwise exit the running state.

4. The ripple suppression method of a two-stage DC-AC converter system based on DAB according to claim 3, characterized in that: The secondary side switches Q1~Q4 adopt 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 double frequency power, the duty cycle of the secondary side switches Q3 and Q4 is 1-D2.

5. The ripple suppression method of a two-stage DC-AC converter system based on DAB according to claim 4, characterized in that: The reference DC bus voltage u ref The actual bus voltage u after low-pass filtering dc The negative feedback is compared, and the difference between the two is output through the PI regulator to form a phase shift angle θ, which participates in the PWM modulation of the secondary side switch tubes Q1~Q4.

6. The ripple suppression method of a two-stage DC-AC converter system based on DAB according to claim 5, 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. 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-connected 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 grid current given value 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.

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