Control method and circuit of wide-range high-efficiency isolated DC-AC converter

Abstract

The invention relates to the technical field of power electronics, and provides a control method for a wide-range high-efficiency isolated DC-AC converter, and the method specifically comprises the steps: cascading an FSBB converter in front of a DAB converter, and multiplexing switching tubes S3 and S4; the duty ratio of the switch tube S1 is set to be d1, the duty ratio of the switch tube S2 is set to be 1-d1, and the duty ratios of the switch tube S3 and the switch tube S4 are set to be 0.5. Defining the ratio of the output-input voltage ratio of the DAB to the transformation ratio of the primary side and the secondary side of the double transformer as M, and deducing and calculating a relational expression between M and the duty ratio d1; based on the relation between M and the minimum current stress and the full-range soft switching in the circuit topology, the optimal solution of M is obtained, then the value of the duty ratio d1 of a switching tube is inversely solved, the control strategy is completed, and the DAB circuit with the minimum current stress and the full-range soft switching are achieved. On this basis, the overall loss of the system is further reduced by smoothing the initial reference voltage of the bus voltage Vbus at the maximum voltage value which can be output by the FSBB converter.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a control method for a wide-range high-efficiency isolated DC-AC converter. Background Art

[0002] The DC-AC converter based on DAB has the advantages of high power conversion efficiency, bidirectional power conversion, fault tolerance and high reliability. It has good application prospects in the fields of electric vehicle charging piles, renewable energy power generation systems, etc.

[0003] There are many single-phase DAB DC-AC topologies. The commonly used single-phase DAB DC-AC converter structure is mainly composed of three units: the primary DC-AC converter, the transformer and the secondary AC-AC converter. The primary converter converts the DC input into a high-frequency AC square wave, the transformer changes the voltage amplitude, and the secondary converter converts the input high-frequency AC quantity into the desired industrial frequency AC output.

[0004] The progress of power electronic devices and control technology has promoted the development of single-phase DAB DC-AC converters towards high switching frequency and high power density. With the increase of switching frequency and power density of single-phase DAB DC-AC converters, the limitations of DAB converters have gradually emerged. In the application scenario of wide input voltage range, DAB converters maintain the matching of output input voltage and transformer ratio, which leads to problems such as limited soft switching range of converters and high current stress. Therefore, the converter efficiency is low. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to reduce the current stress of a single-phase DAB DC-AC converter and realize full-range soft switching of the DAB converter in applications with wide input, high frequency and high power density.

[0006] The present invention solves the above technical problems through the following technical means:

[0007] The present invention provides a control method for a wide range high efficiency isolated DC-AC converter, comprising the following steps:

[0008] S1, a four-switch Buck-Boost converter is cascaded before the DAB converter, wherein the four switches are the first bridge arm switch tubes S1 and S2; the second bridge arm switch tubes S3 and S4; the switch tubes S3 and S4 of the DAB converter and the four-switch Buck-Boost converter are reused;

[0009] S2, set the duty cycle of switch S1 to d1, and the duty cycle of switch S2 to 1-d 1，The duty cycle of the switch tube S3 is d3=0.5, and the duty cycle of the switch tube S4 is d4=0.5;

[0010] S3, define the ratio of the DAB output-input voltage ratio to the double transformer primary-to-secondary transformation ratio as M, and derive and calculate the relationship between M and the duty cycle d1;

[0011] S4, based on the relationship between M and the current stress and soft switching range in the circuit topology, obtain the M value that satisfies the minimum current stress and full range soft switching conditions;

[0012] S5, based on the desired output voltage reference value V ac and the value of M obtained in step S4, the output value of the duty cycle d1 is calculated;

[0013] S6, through the bus voltage V bus The initial reference voltage is clipped at the maximum voltage value that the four-switch Buck-Boost converter can output, thereby reducing the overall system loss.

[0014] Furthermore, step S3 is specifically as follows:

[0015] According to the Buck-Boost circuit voltage gain, we get

[0016]

[0017] Among them, v bus is the intermediate bus voltage; V dc is the DC input voltage;

[0018] Define the ratio of the DAB output-input voltage ratio to the double transformer primary-to-secondary ratio as M, then M is expressed as:

[0019]

[0020] Among them, v ac is the industrial frequency AC output voltage; v s is the voltage on the AC side of the transformer; v p is the voltage on the DC side of the transformer; Substituting formula (1) into formula (2), we can get:

[0021]

[0022] Furthermore, the relationship between the value of M in step S4 and the current stress in the circuit topology is specifically:

[0023] When M changes, the current stress through the DAB converter is:

[0024]

[0025] Among them, i Lk-pis the maximum value of the leakage inductance Lk current stress; f s is the switching frequency of the switch tube; D is the phase shift angle between the driving pulses of the switch tube S3 and the AC side positive voltage output high-frequency action switch tube Q1 or the AC side negative voltage output high-frequency action switch tube Q4; L k The equivalent leakage inductance value of the transformer converted to the AC side;

[0026] Inductance L k Normalized current stress maximum value i * Lk-p for:

[0027]

[0028] Where L k * For L k The normalized value, when L k * When M is a constant, equation (5) can be used to solve for M = 1, i * Lk-p The minimum value.

[0029] Furthermore, the relationship between the value of M in step S4 and the soft switching range in the circuit topology is specifically:

[0030] Under different M values, the switch tubes S5~S6, Q1~Q4 of the DAB circuit topology all achieve ZVS, which must meet the following requirements:

[0031]

[0032] Among them, S5 and S6 are the third bridge arm switch tubes on the DC side, and S5 and S6 are complementary tubes to each other; Q1 is the high-frequency action switch tube for positive voltage output on the AC side, Q4 is the high-frequency action switch tube for negative voltage output on the AC side, Q3 and Q1 are complementary tubes to each other, and Q2 and Q4 are complementary tubes to each other;

[0033] When M changes, the inductance L k The node current formula is as follows:

[0034]

[0035] Among them, t0 is the turn-on time of switch tubes S1 and S3; t1 is the turn-on time of switch tube Q1;

[0036] Combining equations (6) and (7), the relationship between the soft switching range of the switch tubes S5-S6, Q1-Q4 and the phase shift angle D under different M is obtained; when M=1, the node current of the inductor Lk described in equation (7) satisfies the ZVS condition of the switch tubes S5-S6, Q1-Q4 set by equation (6), and will not change due to changes in other system parameters involved in equation (7). The switch tubes S5-S6, Q1-Q4 achieve ZVS at any phase shift angle D.

[0037] Further, step S5 includes the following steps:

[0038] S51, set the desired output voltage reference value v ac ;

[0039] S52, according to the output voltage reference value v ac , the expected bus voltage reference value V when M = 1 is calculated by formula (2) bus ;

[0040] S53, according to the bus voltage reference value V bus , and combined with the specific input DC voltage V dc The duty cycle d1 is calculated by formula (1).

[0041] Furthermore, step S6 includes the following steps:

[0042] S61, according to the input voltage value, obtain the maximum value V that the converter front stage FSBB can output bus-p1 ,get:

[0043] V bus-p1 =1.8V dc , where, according to formula (1), the maximum boost ratio is 1.8;

[0044] S62, according to the determined transformer ratio and output AC voltage peak value V ac-p , find the required intermediate bus sinusoidal wave peak value V bus-p2 ; Get: V bus-p2 =V ac-p / (2*n);

[0045] S63, according to V bus-p2 Set bus voltage V bus Initial reference voltage, get: V bus =V bus-p2 *sin(2*Π*f*t)

[0046] S64, when the voltage value V bus-p1 Greater than the set bus voltage V bus When the initial reference voltage is set, the converter bus voltage V busThe actual output voltage value follows the bus voltage V bus The initial reference voltage, V bus =V bus-p2 *sin(2*Π*f*t); otherwise, execute step S65;

[0047] S65, bus voltage V bus The initial reference voltage is flattened at the maximum voltage value that FSBB can output and used as the reference voltage value of the intermediate bus voltage output, that is, V bus =V bus-p1 .

[0048] The present invention also provides a DAB converter circuit using the above control method, characterized in that the circuit comprises:

[0049] Four-switch tube Buck-Boost converter and DAB converter; the four-switch tube Buck-Boost converter consists of switch tubes S1~S4 and inductor L b The DC-AC converter is composed of the second bridge arm on the DC side and the subsequent DAB converter by multiplexing the switch tubes S3-S4; in the subsequent DAB converter, the switch tubes S3-S6 form a full-bridge circuit, and the midpoint voltage of the bridge arm is v p The AC side bidirectional switches Q1~Q4 and capacitors C1 and C2 form a half-bridge circuit, and the midpoint voltage of the bridge arm is v s ;v p and v s Connected through a high-frequency transformer, the transformer primary and secondary turns ratio is 1:n, and the equivalent leakage inductance on the AC side is L k , the equivalent excitation inductance on the DC side is L m .

[0050] Setting the capacitor C f , located on the DC side of the transformer primary side, is a DC blocking capacitor used to isolate the inductor L of the previous FSBB converter b The DC bias current present on the

[0051] The advantages of the present invention are:

[0052] (1) The present invention proposes a wide-range high-efficiency isolated DC-AC converter control strategy, which can adjust the DAB input voltage to a desired voltage in applications with a wide input voltage range, maintain the DAB output-input voltage ratio matching the transformer ratio within the power frequency cycle, reduce the converter current stress, and improve the converter efficiency.

[0053] (2) The single-phase DC-AC converter control method provided by the present invention can realize soft switching of the DAB switch tube within the input voltage range and the full power range, thereby solving the problem that it is difficult to realize full-range soft switching of the DAB converter when the DAB converter is lightly loaded, reducing the switching loss of the converter and improving the efficiency of the converter.

[0054] (3) The voltage regulation function of the Buck-Boost structure in the converter provided by the present invention adopts a hybrid modulation strategy of pulse width modulation with a fixed bridge arm duty cycle and phase shift modulation. The control strategy is simple and easy to implement, so that the DAB output-input voltage ratio matches the transformer ratio. In the converter provided by the present invention, a DC blocking capacitor is added to the DC side of the transformer to eliminate the current bias problem of the primary side of the transformer in the quasi-single-stage and two-stage converters.

[0055] (4) The control method and circuit topology provided by the present invention realize quasi-single-stage bidirectional isolated DC-AC power conversion instead of multi-stage power converter, thereby reducing the number of system power devices, reducing losses, and optimizing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a full-bridge circuit diagram of a DAB DC-AC converter according to Embodiment 1 of the present invention;

[0057] Figure 2 The DAB current stress and the inductance L under different M values ​​in Example 1 of the present invention are shown in FIG. k Relationship diagram;

[0058] Figure 3 Schematic diagram of the soft-opening range of DAB switch tubes S3-S4 and Q1-Q4 under different M values ​​in Example 1 of the present invention. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] Example 1

[0061] This embodiment provides a control method for a wide range high efficiency isolated DC-AC converter, comprising the following steps:

[0062] S1, a four-switch Buck-Boost converter is cascaded before the DAB converter, wherein the four switches are first arm switch tubes S1 and S2; second arm switch tubes S3 and S4; and the switch tubes S3 and S4 of the DAB converter and the four-switch Buck-Boost converter are multiplexed.

[0063] S2, set the duty cycle of switch S1 to d1, and the duty cycle of switch S2 to 1-d 1， The duty cycle of the switch tube S3 is d3=0.5, and the duty cycle of the switch tube S4 is d4=0.5;

[0064] S3, define the ratio of the DAB output-input voltage ratio to the double transformer primary-to-secondary ratio as M, and derive and calculate the relationship between M and the duty cycle d1. The specific derivation process is:

[0065] According to the Buck-Boost circuit voltage gain, we get

[0066]

[0067] Among them, v bus is the intermediate bus voltage; V dc is the DC input voltage;

[0068] Define the ratio of the DAB output-input voltage ratio to the double transformer primary-to-secondary ratio as M, then M is expressed as:

[0069]

[0070] Among them, v ac is the industrial frequency AC output voltage; v s is the voltage on the AC side of the transformer; v p is the voltage on the DC side of the transformer; Substituting formula (1) into formula (2), we can get:

[0071]

[0072] S4. Based on the relationship between M and the current stress and soft switching range in the circuit topology, obtain the M value that meets the minimum current stress and full-range soft switching conditions.

[0073] (1) The specific derivation process of the M value that meets the minimum current stress condition is:

[0074] When M changes, the current stress through the DAB converter is:

[0075]

[0076] Among them, i Lk-p is the maximum value of the leakage inductance Lk current stress; f sis the switching frequency of the switch tube; D is the phase shift angle between the driving pulses of the switch tube S3 and the AC side positive voltage output high-frequency action switch tube Q1 or the AC side negative voltage output high-frequency action switch tube Q4; L k The equivalent leakage inductance value of the transformer converted to the AC side;

[0077] Inductance L k Normalized current stress maximum value i * Lk-p for:

[0078]

[0079] Where L k * For L k The normalized value, when L k * When M is a constant, equation (5) can be used to solve for M = 1, i * Lk-p The value is the smallest. Figure 2 As shown, when M = 1, the inductance L k The current stress is significantly reduced. And affected by the inductance L k Size has less of an effect.

[0080] (2) The specific derivation process of the M value that satisfies the full range soft switching conditions of the DAB converter is as follows:

[0081] Under different M values, the switch tubes S5~S6, Q1~Q4 of the DAB circuit topology all achieve ZVS and must satisfy equation (6):

[0082]

[0083] Among them, S5 and S6 are the third bridge arm switch tubes on the DC side, and S5 and S6 are complementary tubes to each other; Q1 is the high-frequency action switch tube for positive voltage output on the AC side, Q4 is the high-frequency action switch tube for negative voltage output on the AC side, Q3 and Q1 are complementary tubes to each other, and Q2 and Q4 are complementary tubes to each other.

[0084] When M changes, the inductance L k The node current formula is as follows:

[0085]

[0086] Among them, t0 is the turn-on time of switch tubes S1 and S3; t1 is the turn-on time of switch tube Q1;

[0087] Combining equations (6) and (7), the relationship between the soft switching range of the switch tubes S5~S6, Q1~Q4 and the phase shift angle D under different M is obtained; when M=1, the node current of the inductor Lk described in equation (7) satisfies the ZVS condition of the switch tubes S5~S6, Q1~Q4 set by equation (6), and will not change due to changes in other system parameters involved in equation (7). The switch tubes S5~S6, Q1~Q4 achieve ZVS at any phase shift angle D; on the contrary, when M deviates from 1, the switch tubes S5~S6, Q1~Q4 will not be able to meet the soft switching condition described in equation (6) through equation (7) due to the change in the phase shift angle. Therefore, by controlling M=1, the switch tubes S5~S6, Q1~Q4 in the proposed converter achieve full range ZVS under a wide input voltage. Figure 3 As shown in the figure, according to the M value and the ZVS range of each switch tube, it is divided into three areas: in area I, only switch tubes S5~S6 achieve ZVS; in area II, only switch tubes Q1~Q4 achieve ZVS; in area III, switch tubes S5~S6 and Q1~Q4 can all achieve ZVS. In addition, the four black line segments represent the ZVS range of the switch tubes under different M values, among which the solid line part switch tubes S5~S6 and Q1~Q4 can all achieve ZVS.

[0088] S5, based on the desired output voltage reference value V ac The output value of the duty cycle d1 is calculated by combining the value of M obtained in step S4. The specific steps are:

[0089] S51, set the desired output voltage reference value v ac ;

[0090] S52, according to the output voltage reference value v ac , the expected bus voltage reference value V when M = 1 is calculated by formula (2) bus ;

[0091] S53, according to the bus voltage reference value V bus , and combined with the specific input DC voltage V dc The duty cycle d1 is calculated by formula (1).

[0092] In order to further reduce the overall system loss, the transformer ratio n can be reduced to reduce the primary inductance L of the converter. b Current, that is, under the premise of transmitting the same power, increase the output voltage of the Buck-Boost converter, reduce the required output current of the Buck-Boost converter, and thus reduce the inductance L b The current flowing through the circuit further reduces the overall system loss. The steps adopted are as follows:

[0093] S6, through the bus voltage V busThe initial reference voltage is flattened at the maximum voltage value that the four-switch Buck-Boost converter can output, reducing the overall system loss. The specific steps are:

[0094] S61, according to the input voltage value, obtain the maximum value V that the converter front stage FSBB can output bus-p1 ,get:

[0095] V bus-p1 =1.8V dc , where, according to formula (1), the maximum boost ratio is 1.8;

[0096] S62, according to the determined transformer ratio and output AC voltage peak value V ac-p , find the required intermediate bus sinusoidal wave peak value V bus-p2 ; Get: V bus-p2 =V ac-p / (2*n);

[0097] S63, according to V bus-p2 Set bus voltage V bus Initial reference voltage, get: V bus =V bus-p2 *sin(2*Π*f*t)

[0098] S64, when the voltage value V bus-p1 Greater than the set bus voltage V bus When the initial reference voltage is set, the converter bus voltage V bus The actual output voltage value follows the bus voltage V bus The initial reference voltage, V bus =V bus-p2 *sin(2*Π*f*t); otherwise, execute step S65;

[0099] S65, bus voltage V bus The initial reference voltage is flattened at the maximum voltage value that FSBB can output and used as the reference voltage value of the intermediate bus voltage output, that is, V bus =V bus-p1 .

[0100] The primary side of the converter realizes the bus voltage V bus It can be freely adjusted, and according to the above analysis, it can be known that according to the actual circuit parameters, the reference value setting of the intermediate bus voltage will have two forms: a complete sinusoidal steamed bun wave voltage and a steamed bun wave voltage with a flat peak.

[0101] Example 2

[0102] Based on the same inventive concept, Figure 1As shown, the present invention also provides a wide range high efficiency isolated DC-AC converter circuit, which adopts the control method described in Example 1. The circuit comprises: a four-switch tube Buck-Boost converter and a DAB converter cascaded by multiplexing switch tubes, wherein the four-switch tube Buck-Boost converter is composed of switch tubes S1 to S4 and an inductor L b The proposed wide range high efficiency isolated DC-AC converter topology is formed by reusing the switch tubes S3~S4 in the second bridge arm of the DC side and the subsequent DAB-DC / AC converter. In the proposed converter subsequent DAB-DC / AC converter, S3~S6 form a full bridge circuit, and the midpoint voltage of the bridge arm is v p The AC side bidirectional switches Q1~Q4 and capacitors C1 and C2 form a half-bridge circuit, and the midpoint voltage of the bridge arm is v s .v p and v s Connected through a high-frequency transformer, the transformer primary and secondary turns ratio is 1:n, and the equivalent leakage inductance on the AC side is L k , the equivalent excitation inductance on the DC side is L m .

[0103] Setting the capacitor C f is a DC blocking capacitor. Since the proposed converter structure is composed of a FSBB converter and a DAB converter cascaded by multiplexing the switch tube, in order to ensure the power output of the subsequent DAB converter, the inductor L of the previous FSBB converter is b There will be a large DC bias current. Since the transformer in actual application is not an ideal transformer, there is an excitation inductance L m path, will be the inductor L b To provide a path for the DC current to flow, capacitor C is needed to prevent the DC current from flowing into the transformer and causing the transformer to be magnetically saturated. f Isolate DC current from flowing into the transformer.

[0104] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for a wide range high efficiency isolated DC-AC converter, characterized in that: The following steps are involved: S1, a four-switch Buck-Boost converter is cascaded before the DAB converter, wherein the four switches are the first bridge arm switch tubes S1 and S2; the second bridge arm switch tubes S3 and S4; the switch tubes S3 and S4 of the DAB converter and the four-switch Buck-Boost converter are reused; S2, set the duty cycle of switch S1 to d1, and the duty cycle of switch S2 to 1-d 1， The duty cycle of the switch tube S3 is d3=0.5, and the duty cycle of the switch tube S4 is d4=0.5; S3, define the ratio of the DAB output-input voltage ratio to the double transformer primary-to-secondary transformation ratio as M, and derive and calculate the relationship between M and the duty cycle d1; S4, based on the relationship between M and the current stress and soft switching range in the circuit topology, obtain the M value that satisfies the minimum current stress and full range soft switching conditions; S5, based on the desired output voltage reference value V ac and the value of M obtained in step S4, the output value of the duty cycle d1 is calculated; S6, through the bus voltage V bus The initial reference voltage is clipped at the maximum voltage value that the four-switch Buck-Boost converter can output, thereby reducing the overall system loss.

2. The control method of a wide range high efficiency isolated DC-AC converter according to claim 1, characterized in that: Step S3 is specifically as follows: According to the Buck-Boost circuit voltage gain, we get Among them, v bus is the intermediate bus voltage; V dc is the DC input voltage; Define the ratio of the DAB output-input voltage ratio to the double transformer primary-to-secondary ratio as M, then M is expressed as: Among them, v ac is the industrial frequency AC output voltage; v s is the voltage on the AC side of the transformer; v p is the voltage on the DC side of the transformer; Substituting formula (1) into formula (2), we can get:

3. The control method of a wide range high efficiency isolated DC-AC converter according to claim 2, characterized in that: The relationship between the value of M in step S4 and the current stress in the circuit topology is specifically: When M changes, the current stress through the DAB converter is: Among them, i Lk-p is the maximum value of the leakage inductance Lk current stress; f s is the switching frequency of the switch tube; D is the phase shift angle between the driving pulses of the switch tube S3 and the AC side positive voltage output high-frequency action switch tube Q1 or the AC side negative voltage output high-frequency action switch tube Q4; L k The equivalent leakage inductance value of the transformer converted to the AC side; Inductance L k Normalized current stress maximum value i * Lk-p for: Where L k * For L k The normalized value is k * When M is a constant, equation (5) can be used to solve for M = 1, i * Lk-p The minimum value.

4. The control method of a wide range high efficiency isolated DC-AC converter according to claim 3, characterized in that: The relationship between the M value in step S4 and the soft switching range in the circuit topology is specifically: Under different M values, the switch tubes S5~S6, Q1~Q4 of the DAB circuit topology all achieve ZVS, which must meet the following requirements: Among them, S5 and S6 are the third bridge arm switch tubes on the DC side, and S5 and S6 are complementary tubes to each other; Q1 is the high-frequency action switch tube for positive voltage output on the AC side, Q4 is the high-frequency action switch tube for negative voltage output on the AC side, Q3 and Q1 are complementary tubes to each other, and Q2 and Q4 are complementary tubes to each other; When M changes, the inductance L k The node current formula is as follows: Among them, t0 is the turn-on time of switch tubes S1 and S3; t1 is the turn-on time of switch tube Q1; Combining equations (6) and (7), the relationship between the soft switching range of the switch tubes S5-S6, Q1-Q4 and the phase shift angle D under different M is obtained; when M=1, the node current of the inductor Lk described in equation (7) satisfies the ZVS condition of the switch tubes S5-S6, Q1-Q4 set by equation (6), and will not change due to changes in other system parameters involved in equation (7). The switch tubes S5-S6, Q1-Q4 achieve ZVS at any phase shift angle D.

5. The control method of a wide range high efficiency isolated DC-AC converter according to claim 4, characterized in that: Step S5 includes the following steps: S51, set the desired output voltage reference value v ac ; S52, according to the output voltage reference value v ac , the expected bus voltage reference value V when M = 1 is calculated by formula (2) bus ; S53, according to the bus voltage reference value V bus , and combined with the specific input DC voltage V dc The duty cycle d1 is calculated by formula (1).

6. The control method of a wide range high efficiency isolated DC-AC converter according to claim 5, characterized in that: The step S6 comprises the following steps: S61, according to the input voltage value, obtain the maximum value V that the converter front stage FSBB can output bus-p1 ,get: V bus-p1 =1.8V dc , where, according to formula (1), the maximum boost ratio is 1.8; S62, according to the determined transformer ratio and output AC voltage peak value V ac-p , find the required intermediate bus sinusoidal wave peak value V bus-p2 ; Get: V bus-p2 =V ac-p / (2*n); S63, according to V bus-p2 Set bus voltage V bus Initial reference voltage, get: V bus =V bus-p2 *sin(2*Π*f*t) S64, when the voltage value V bus-p1 Greater than the set bus voltage V bus When the initial reference voltage is set, the converter bus voltage V bus The actual output voltage value follows the bus voltage V bus The initial reference voltage, V bus =V bus-p2 *sin(2*Π*f*t); otherwise, execute step S65; S65, bus voltage V bus The initial reference voltage is flattened at the maximum voltage value that FSBB can output and used as the reference voltage value of the intermediate bus voltage output, that is, V bus =V bus-p1 .

7. A DAB converter circuit using the control method according to any one of claims 1 to 6, characterized in that: The circuit comprises: Four-switch tube Buck-Boost converter and DAB converter; the four-switch tube Buck-Boost converter consists of switch tubes S1~S4 and inductor L b The DC-AC converter is composed of the second bridge arm on the DC side and the subsequent DAB converter by multiplexing the switch tubes S3-S4; in the subsequent DAB converter, the switch tubes S3-S6 form a full-bridge circuit, and the midpoint voltage of the bridge arm is v p The AC side bidirectional switches Q1~Q4 and capacitors C1 and C2 form a half-bridge circuit, and the midpoint voltage of the bridge arm is v s ;v p and v s Connected through a high-frequency transformer, the transformer primary and secondary turns ratio is 1:n, and the equivalent leakage inductance on the AC side is L k , the equivalent excitation inductance on the DC side is L m ; Set the capacitor C f , located on the DC side of the transformer primary side, is a DC blocking capacitor used to isolate the inductor L of the previous FSBB converter b The DC bias current present on the

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