Control method of wide-range isolated dc-ac converter and circuit thereof

Abstract

The application relates to the field of power electronics, and provides a control method for a wide-range isolated DC-AC converter, specifically: cascading an FSBB converter in front of a DAB converter, multiplexing switch tubes S 3 and S 4; setting the duty cycle of the switch tube S 1 to be d 1, setting the duty cycle of the switch tube S 2 to be 1- d 1， setting the duty cycles of the switch tubes S 3 and S 4 to be both 0.5. Defining the ratio of a DAB output-input voltage ratio to a double transformer primary-secondary side ratio as M , deducing a calculation formula of M and the duty cycle d 1; based on the relationship between M and the minimum current stress and full-range soft switching in a circuit topology, obtaining an optimal solution of M , inversely solving the value of the switch tube duty cycle d 1, completing the control strategy, and realizing the minimum current stress and full-range soft switching of the DAB circuit. On this basis, the bus voltage reference value V bus is flattened at the maximum voltage value that can be output by the FSBB converter, so that the overall system loss is further reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to a control method of a wide-range isolated DC-AC converter. BACKGROUND

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

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

[0004] The progress of power electronic devices and control technology has promoted the single-phase DAB DC-AC converter to develop in the direction of high switching frequency and high power density. With the improvement of the switching frequency and power density of the single-phase DAB DC-AC converter, the limitations of the DAB converter gradually appear. In the application scenario of wide input voltage range, the DAB converter is to maintain the matching of the output input voltage and the transformer ratio, which leads to the problems of limited soft switching range of the converter, large current stress and the like. Therefore, the efficiency of the converter is low. SUMMARY

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

[0006] The application solves the above technical problems by the following technical means:

[0007] The application provides a control method of a wide-range isolated DC-AC converter, comprising the following steps:

[0008] S1, a four-switch Buck-Boost converter is cascaded in front of the DAB converter, and the four switches are respectively a first bridge arm switch tube S 1、 S 2, a second bridge arm switch tube S 3、 S 4, a switch tube of the DAB converter and the four-switch Buck-Boost converter S 3 and S 4 are multiplexed;

[0009] S2, setting switch tube S 1 is 0.5 d 1, switch tube S 2 is 1 d 1， switch tube S 3 is 0.5 d 3= 0.5, switch tube S 4 is 0.5 d 4= 0.5;

[0010] S3, define the ratio of DAB output input voltage ratio and the ratio of primary and secondary side of double transformer as M , derive the calculation M and the duty cycle d 1 relationship formula;

[0011] S4, based on M The relationship between current stress and soft switching range in circuit topology, the value of M Satisfy the minimum current stress and full range soft switching condition;

[0012] S5, based on the desired output voltage reference value V ac And the value of M Step S4, calculate the output value of duty cycle d 1;

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

[0014] Further, step S3 is specifically:

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

[0016] (1)

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

[0018] Define the ratio of DAB output input voltage ratio and the ratio of primary and secondary side of double transformer as M , then M Indicated as:

[0019] (2)

[0020] Where,v ac It is the power frequency AC output voltage; v s This refers to the AC side voltage of the transformer. v p The DC side voltage of the transformer; substituting equation (1) into equation (2) yields:

[0021]

[0022] Further, the steps described in step S4 M The specific relationship between the value and the current stress in the circuit topology is as follows:

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

[0024] (4)

[0025] in, i Lk-p Leakage Lk Maximum current stress; f s The switching frequency of the switching transistor; D For switching transistors S 3. High-frequency operating switch tube with positive voltage output on AC side Q 1 or AC side negative voltage output high-frequency action switch tube Q 4. Phase shift angle between driving pulses; L k This is the equivalent leakage inductance value of the transformer referred to the AC side;

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

[0027] (5)

[0028] In the formula L k * for L k The normalized value, when L k * When the value is constant, it can be solved from equation (5) to obtain M= At 1 o'clock, i * Lk-p The smallest value.

[0029] Further, the steps described in step S4 MThe specific relationship between the value and the soft-switching range in the circuit topology is as follows:

[0030] Different M Switching transistors in the DAB circuit topology with the following values S 5~ S 6. Q 1~ Q For all 4 elements to achieve ZVS, the following conditions must be met:

[0031] (6)

[0032] in, S 5. S 6 is the DC-side third bridge arm switch. S 5 and S 6. They are complementary tubes; Q 1. AC side positive voltage output high-frequency action switching transistor. Q 4 is a high-frequency operating switch for AC side negative voltage output. Q 3 and Q 1. They are complementary tubes. Q 2 and Q 4. Complementary tubes;

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

[0034] (7)

[0035] in, t 0 is the switching transistor S 1 and S3 activation times; t 1 is a switching transistor Q 1. Opening time;

[0036] Combining equations (6) and (7), we can derive different results. M Down switch transistor S 5~ S 6. Q 1~ Q 4. Soft switching range and phase shift angle D The relationship between them; when M When =1, the inductor node current described in equation (7) all satisfy the switching transistor current set in equation (6). S 5~ S 6. Q 1~ Q The ZVS condition of equation (4) remains unchanged and is not affected by changes in other system parameters involved in equation (7). S 5~ S 6. Q 1~ Q 4 at any phase shift angleD ZVS is implemented everywhere.

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

[0038] S51, Set the desired output voltage reference value V ac ;

[0039] S52, Based on the output voltage reference value V ac Calculated by formula (2) when M= The expected reference value of bus voltage at time 1 V bus ;

[0040] S53, Based on the bus voltage reference value V bus And in combination with the specific input DC voltage V dc The duty cycle is calculated using formula (1). d 1.

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

[0042] S61. Calculate the maximum output value of the converter's front-end FSBB based on the input voltage value. V bus-p1 ,get:

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

[0044] S62. Based on the determined transformer turns ratio and the peak value of the output AC voltage. V ac-p Find the required peak value of the sinusoidal wave of the intermediate busbar. V bus-p2 ;get: V bus-p2 = V ac-p / (2*n)

[0045] S63, according to V bus-p2 Set bus voltage reference value V bus ,get: V bus = V bus-p2 *sin(2*Π*f*t), where f is the AC voltage frequency;

[0046] S64, when the voltage value V bus-p1 Greater than the set bus voltage reference value V bus At that time, set the intermediate bus voltage of the converter. v bus The actual output voltage value follows the bus voltage reference value. V bus ,Right now V bus = V bus-p2 *sin(2*Π*f*t); otherwise, proceed to step S65;

[0047] S65, Reference value for bus voltage V bus The voltage at the maximum output voltage of the FSBB is clipped to serve as the reference voltage value for the intermediate bus voltage output. V bus = V bus-p1 .

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

[0049] A four-switch Buck-Boost converter and a DAB converter; the four-switch Buck-Boost converter consists of switching transistors S 1~ S 4 and inductance L b It is composed of multiplexed switching transistors with the subsequent DAB converter via the second bridge arm on the DC side. S 3~ S 4. A DC-AC converter is formed; in the subsequent DAB converter, the switching transistors... S 3~ S A full-bridge circuit is formed by 6 components, and the voltage at the midpoint of each bridge arm is... v p AC side bidirectional switch Q 1~ Q 4 and capacitor C 1. C Two components form a half-bridge circuit, with the voltage at the midpoint of each bridge arm being... v s ; v p and v s Connected via a high-frequency transformer, the primary-to-secondary turns ratio of the transformer is 1: n The equivalent leakage of the communication side is L k The equivalent magnetizing inductance on the DC side isL m .

[0050] Set capacitor C f Located on the DC side of the transformer primary winding, it is a DC blocking capacitor used to isolate the inductor of the preceding FSBB converter. L b The DC bias current present on it.

[0051] The advantages of this invention are:

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

[0053] (2) The single-phase DC-AC converter control method provided by the present invention can realize soft switching of DAB switching transistors in both the input voltage range and the full power range, solving the problem that it is difficult to realize full-range soft switching of DAB converter under light load, reducing the switching loss of converter and improving the efficiency of 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 and phase shift modulation with fixed duty cycle of multiplexed bridge arms. The control strategy is simple and easy to implement, so that the output-input voltage ratio of DAB matches the transformer turns ratio. The converter provided by the present invention adds a DC blocking capacitor to the DC side of the transformer to eliminate the problem of primary current bias of transformer in quasi-single-stage and two-stage converters.

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

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

[0057] Figure 2 Different from Embodiment 1 of the present invention M DAB current stress and inductance at various values L k Relationship diagram;

[0058] Figure 3 For the DAB switching transistor under different values ​​of M in Embodiment 1 of the present invention S 3~ S 4.Q 1~ Q Schematic diagram of the soft opening range of 4. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] Example 1

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

[0062] S1. A four-switch Buck-Boost converter is cascaded before the DAB converter, wherein the four switches are the first bridge arm switches. S 1. S 2; Second bridge arm switch tube S 3. S 4; Multiplexing the switching transistors of the DAB converter and the four-switch Buck-Boost converter S 3 and S 4.

[0063] S2, Setting the switching transistor S The duty cycle of 1 is d 1. Switching transistor S The duty cycle of 2 is 1- d 1， Switching transistor S The duty cycle of 3 is d 3 = 0.5, switching transistor S The duty cycle of 4 is d 4 = 0.5;

[0064] S3. Define the ratio of the DAB output-input voltage ratio to twice the primary-secondary transformation ratio of the transformer as: M Derivation and calculation M With the duty cycle d The relational expression is 1. The specific derivation process is as follows:

[0065] Based on the voltage gain of the Buck-Boost circuit, we obtain

[0066] (1)

[0067] in, v bus This refers to the intermediate bus voltage.V dc DC input voltage;

[0068] Define the ratio of the DAB output-input voltage to twice the primary-secondary transformation ratio of the transformer as: M ,but M Represented as:

[0069] (2)

[0070] in, v ac It is the power frequency AC output voltage; v s This refers to the AC side voltage of the transformer. v p The DC side voltage of the transformer; substituting equation (1) into equation (2) yields:

[0071]

[0072] S4, based on M By relating the current stress and soft-switching range in the circuit topology, we can obtain the conditions that satisfy both minimum current stress and full-range soft-switching. M Values.

[0073] (1) Satisfying the minimum current stress condition M The specific derivation process for the value is as follows:

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

[0075] (4)

[0076] in, i Lk-p Leakage Lk Maximum current stress; f s The switching frequency of the switching transistor; D For switching transistors S 3. High-frequency operating switch tube with positive voltage output on AC side Q 1 or AC side negative voltage output high-frequency action switch tube Q 4. Phase shift angle between driving pulses; L k This is the equivalent leakage inductance value of the transformer referred to the AC side;

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

[0078] (5)

[0079] In the formula L k * for L k The normalized value, when L k * When the value is constant, it can be solved from equation (5) to obtain the value. M= At 1 o'clock, i * Lk-p The smallest value. For example... Figure 2 As shown, when M= At time 1, inductance L k The current stress is significantly reduced. And the inductance... L k Size has a relatively small impact.

[0080] (2) Satisfies the full-range soft-switching condition of the DAB converter M The specific derivation process for the value is as follows:

[0081] Different M Switching transistors in the DAB circuit topology with the following values S 5~ S 6. Q 1~ Q To achieve ZVS for all 4, equation (6) must be satisfied:

[0082] (6)

[0083] in, S 5. S 6 is the DC-side third bridge arm switch. S 5 and S 6. They are complementary tubes; Q 1. AC side positive voltage output high-frequency action switching transistor. Q 4 is a high-frequency operating switch for AC side negative voltage output. Q 3 and Q 1. They are complementary tubes. Q 2 and Q 4. They are complementary tubes.

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

[0085] (7)

[0086] in, t 0 is the switching transistor S1 and S3 activation times; t 1 is a switching transistor Q 1. Opening time;

[0087] Combining equations (6) and (7), we can derive different results. M Down switch transistor S 5~ S 6. Q 1~ Q 4. Soft switching range and phase shift angle D The relationship between them; when M When =1, the inductor node current described in equation (7) all satisfy the switching transistor current set in equation (6). S 5~ S 6. Q 1~ Q The ZVS condition of equation (4) remains unchanged and is not affected by changes in other system parameters involved in equation (7). S 5~ S 6. Q 1~ Q 4 at any phase shift angle D ZVS is achieved everywhere; conversely, when M Deviation 1, switching transistor S 5~ S 6. Q 1~ Q 4. Due to the change in phase shift angle, the soft switching condition described in equation (6) cannot be satisfied by equation (7). Therefore, by controlling... M =1, the switching transistor in the proposed converter S 5~ S 6. Q 1~ Q 4. Achieve full-range ZVS under wide input voltage conditions. For example... Figure 3 As shown, according to M Based on the values ​​and ZVS ranges of each switch, the region is divided into three regions: Region I contains only the switch. S 5~ S 6. Achieve ZVS; Region II contains only switching transistors. Q 1~ Q 4. Implement ZVS; Switching transistors in Zone III S 5~ S 6. Q 1~ Q All four can achieve ZVS. Furthermore, the four black lines represent different... M The ZVS range of the switching transistor is given, where the solid line represents the switching transistor. S 5~ S 6. Q 1~ Q All four can achieve ZVS.

[0088] S5, based on the desired output voltage reference value V ac and the result obtained in step S4 M The duty cycle is calculated by taking the value. d The output value of 1. The specific steps are as follows:

[0089] S51, Set the desired output voltage reference value V ac ;

[0090] S52, Based on the output voltage reference value V ac Calculated by formula (2) when M= The expected reference value of bus voltage at time 1 V bus ;

[0091] S53, Based on the bus voltage reference value V bus And in combination with the specific input DC voltage V dc The duty cycle is calculated using formula (1). d 1.

[0092] To further reduce overall system losses, the transformer turns ratio can be reduced. n Reduce the primary inductance of the converter L b Current, that is, under the premise of transmitting the same power, increasing the output voltage of the Buck-Boost converter reduces the required output current of the Buck-Boost converter, thereby reducing the inductance. L b The current flowing through the system further reduces overall system losses. The steps involved are as follows:

[0093] S6. By using the bus voltage reference value V bus The voltage is clipped at the maximum output voltage of the four-switch Buck-Boost converter to reduce overall system losses. The specific steps are as follows:

[0094] S61. Calculate the maximum output value of the converter's front-end FSBB based on the input voltage value. V bus-p1 ,get:

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

[0096] S62. Based on the determined transformer turns ratio and the peak value of the output AC voltage. V ac-p Find the required peak value of the sinusoidal wave of the intermediate busbar. V bus-p2 ;get: V bus-p2 = V ac-p / (2*n)

[0097] S63, according to V bus-p2 Set bus voltage reference value V bus ,get: V bus = V bus-p2 *sin(2*Π*f*t), where f is the AC voltage frequency;

[0098] S64, when the voltage value V bus-p1 Greater than the set bus voltage reference value V bus At that time, set the intermediate bus voltage of the converter. v bus The actual output voltage value follows the bus voltage reference value. V bus ,Right now V bus = V bus-p2 *sin(2*Π*f*t); otherwise, proceed to step S65;

[0099] S65, Reference value for bus voltage V bus The voltage at the maximum output voltage of the FSBB is clipped to serve as the reference voltage value for the intermediate bus voltage output. V bus = V bus-p1 .

[0100] The primary side of the converter implements a reference value for the bus voltage. V bus The voltage can be freely adjusted, and as can be seen from the above analysis, there are two forms of setting the reference value of the intermediate bus voltage according to the actual circuit parameters: 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, such as Figure 1As shown, the present invention also provides a wide-range isolated DC-AC converter circuit, employing the control method described in Embodiment 1. The circuit includes: a four-switch Buck-Boost converter and a DAB converter cascaded via multiplexed switches, wherein the four-switch Buck-Boost converter consists of multiplexed switches... S 1~ S 4 and inductance L b It is composed of multiplexed switching transistors with the subsequent DAB-DC / AC converter via the second bridge arm on the DC side. S 3~ S 4. The proposed wide-range isolated DC-AC converter topology is constructed. The proposed converter is followed by a DAB-DC / AC converter. S 3~ S A full-bridge circuit is formed by 6 components, and the voltage at the midpoint of each bridge arm is... v p AC side bidirectional switch Q 1~ Q 4 and capacitor C 1. C Two components form a half-bridge circuit, with the voltage at the midpoint of each bridge arm being... v s . v p and v s Connected via a high-frequency transformer, the primary-to-secondary turns ratio of the transformer is 1: n The equivalent leakage of the communication side is L k The equivalent magnetizing inductance on the DC side is L m .

[0103] Set capacitor C f As a DC blocking capacitor, since the proposed converter structure consists of an FSBB converter and a DAB converter cascaded via multiplexed switching transistors, the inductor of the preceding FSBB converter is used to ensure the power output of the subsequent DAB converter. L b The transformer will have a large DC bias current. Since the transformer in practical applications is not an ideal transformer, it will have magnetizing inductance. L m The path will be for the inductor. L b To provide a path for the flow of direct current, a capacitor is needed to prevent direct current from flowing into the transformer and causing magnetic saturation. C f It isolates direct current from flowing into the transformer.

[0104] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate 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 isolated DC-AC converter, characterized in that, Includes the following steps: S1. A four-switch Buck-Boost converter is cascaded before the DAB converter, wherein the four switches are the first bridge arm switches. S 1. S 2; Second bridge arm switch tube S 3. S 4; Multiplexing the switching transistors of the DAB converter and the four-switch Buck-Boost converter S 3 and S 4; S2, Setting the switching transistor S The duty cycle of 1 is d 1. Switching transistor S The duty cycle of 2 is 1- d 1， Switching transistor S The duty cycle of 3 is d 3 = 0.5, switching transistor S The duty cycle of 4 is d 4 = 0.5; S3. Define the ratio of the DAB output-input voltage ratio to twice the primary-secondary transformation ratio of the transformer as: M Derivation and calculation M With the duty cycle d The relational expression of 1; S4, based on M By relating the current stress and soft-switching range in the circuit topology, we can obtain the conditions that satisfy both minimum current stress and full-range soft-switching. M Values; The specific relationship between the value of M and the current stress in the circuit topology is as follows: When M changes, the current stress through the DAB converter is: (4) Where iLk-p is the maximum value of the leakage inductance Lk current stress; fs is the switching frequency of the switching transistor; D is the phase shift angle between the driving pulses of the switching transistor S3 and the AC side positive voltage output high-frequency operating switching transistor Q1 or AC side negative voltage output high-frequency operating switching transistor Q4; Lk is the equivalent leakage inductance value of the transformer referred to the AC side. The maximum normalized current stress value of inductor Lk, i*Lk-p, is: (5) In the formula, Lk* is the normalized value of Lk. When Lk* is a constant, the value of i*Lk-p can be minimized when M=1 by formula (5). The specific relationship between the value of M and the soft-switching range in the circuit topology is as follows: For the switching transistors S5~S6 and Q1~Q4 of the DAB circuit topology to achieve ZVS under different values ​​of M, the following must be satisfied: (6) Among them, S5 and S6 are DC side third bridge arm switches, and S5 and S6 are complementary switches; Q1 is AC side positive voltage output high-frequency action switch, Q4 is AC side negative voltage output high-frequency action switch, Q3 and Q1 are complementary switches, and Q2 and Q4 are complementary switches. When M changes, the formula for the node current of inductor Lk is as follows: (7) Where t0 is the turn-on time of switches S1 and S3; t1 is the turn-on time of switch Q1; Combining equations (6) and (7), the relationship between the soft switching range of switching transistors S5~S6 and Q1~Q4 and the phase shift angle D under different M values ​​is obtained. When M=1, the current at the inductor Lk node described in equation (7) satisfies the ZVS condition set by equation (6) for switching transistors S5~S6 and Q1~Q4, and will not change due to changes in other system parameters involved in equation (7). Switching transistors S5~S6 and Q1~Q4 achieve ZVS at any phase shift angle D. S5, based on the desired output voltage reference value V ac and the result obtained in step S4 M The duty cycle is calculated by taking the value. d The output value of 1; S6. By using the bus voltage reference value V bus The voltage is clipped at the maximum output voltage of the four-switch Buck-Boost converter to reduce overall system losses.

2. The control method for a wide-range isolated DC-AC converter according to claim 1, characterized in that, Step S3 is as follows: Based on the voltage gain of the Buck-Boost circuit, we obtain (1) in, v bus This refers to the intermediate bus voltage. V dc DC input voltage; Define the ratio of the DAB output-input voltage to twice the primary-secondary transformation ratio of the transformer as: M ,but M Represented as: (2) in, v ac It is the power frequency AC output voltage; v s This refers to the AC side voltage of the transformer. v p The DC side voltage of the transformer; substituting equation (1) into equation (2) yields: 。 3. The control method for a wide-range isolated DC-AC converter according to claim 1, characterized in that, Step S5 includes the following steps: S51, Set the desired output voltage reference value V ac ; S52, Based on the output voltage reference value V ac Calculated by formula (2) when M= The expected reference value of bus voltage at time 1 V bus ; S53, Based on the bus voltage reference value V bus And in combination with the specific input DC voltage V dc The duty cycle is calculated using formula (1). d 1.

4. The control method for a wide-range isolated DC-AC converter according to claim 3, characterized in that, Step S6 includes the following steps: S61. Calculate the maximum output value of the converter's front-end FSBB based on the input voltage value. V bus-p1 ,get: V bus-p1 = 1.8 V dc , where, according to equation (1), the maximum boost ratio is 1.8; S62. Based on the determined transformer turns ratio and peak output AC voltage... V ac-p Find the required peak value of the sinusoidal wave of the intermediate busbar. V bus-p2 ;get: V bus-p2 = V ac-p / (2*n) S63, according to V bus-p2 Set bus voltage reference value V bus ,get: V bus = V bus-p2 *sin(2*Π*f*t), where f is the frequency of the AC voltage; S64, when the voltage value V bus-p1 Greater than the set bus voltage reference value V bus At that time, set the intermediate bus voltage of the converter. v bus The actual output voltage value follows the bus voltage reference value. V bus ,Right now V bus = V bus-p2 *sin(2*Π*f*t); otherwise, proceed to step S65; S65, Reference value for bus voltage V bus The voltage at the maximum output voltage of the FSBB is clipped to serve as the reference voltage value for the intermediate bus voltage output. V bus = V bus-p1 .

5. A DAB converter circuit employing the control method described in any one of claims 1-4, characterized in that, The circuit includes: A four-switch Buck-Boost converter and a DAB converter; the four-switch Buck-Boost converter consists of switching transistors S 1~ S 4 and inductance L b It is composed of multiplexed switching transistors with the subsequent DAB converter via the second bridge arm on the DC side. S 3~ S 4. A DC-AC converter is formed; in the subsequent DAB converter, the switching transistors... S 3~ S A full-bridge circuit is formed by 6 components, and the voltage at the midpoint of each bridge arm is... v p AC side bidirectional switch Q 1~ Q 4 and capacitor C 1. C Two components form a half-bridge circuit, with the voltage at the midpoint of each bridge arm being... v s ; v p and v s Connected via a high-frequency transformer, the primary-to-secondary turns ratio of the transformer is 1: n The equivalent leakage of the communication side is L k The equivalent magnetizing inductance on the DC side is L m Set capacitor C f Located on the DC side of the transformer primary winding, it is a DC blocking capacitor used to isolate the inductor of the preceding FSBB converter. L b The DC bias current present on it.

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