A method for determining the inductance range of dual active bridges suitable for single phase shift control

Abstract

The present invention discloses a method for determining the inductance range of a dual active bridge suitable for single phase shift control. This method takes into account the constraint that the maximum power output of the circuit should be greater than the given output power index requirement. In addition, it also takes into account the constraint that the power devices in the circuit should achieve zero voltage switching requirements. At the same time, the requirements for the direction of the characteristic current value, the inductance energy meeting the primary side commutation requirements, and the dead time matching the inductance value are discussed in detail and the minimum value of the inductance value range is obtained, thereby ensuring the zero voltage switching performance of the power devices in the DAB circuit and improving the reliability of the power devices and even the entire device. At the same time, since the power devices do not generate switching losses, the losses of the overall circuit will be reduced, thereby improving the working efficiency of the DAB device. After experimental verification, the inductance range determination method proposed by the present invention is comprehensive and has a clear process, which ensures the reliability of the normal operation of the dual active bridge circuit and has high practical value.

Description

Technical Field

[0001] The invention belongs to the field of transformer, rectifier and inductor manufacturing, and particularly relates to a method for determining the inductance range of a dual active bridge suitable for single phase shift control. Background Art

[0002] Medium-voltage direct current (DC) transmission technology is increasingly being used in power transmission due to its advantages, including high efficiency, high reliability, controllability, and low cost. Generally, the power a topology can transmit is proportional to the number of power semiconductors it contains. Therefore, among several common topologies, the Dual Active Bridge (DAB) is well-suited for use as a DC converter in high-power applications. Furthermore, compared to other resonant converters, DAB is easier to implement zero voltage switching (ZVS) and offers faster bidirectional conversion speeds. Therefore, DAB is widely used in medium-voltage, high-power transmission applications.

[0003] In recent years, wide bandgap power semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) have developed rapidly. Among them, SiC MOSFETs are widely used in high-voltage and high-frequency power electronic devices due to their fast switching speed, low on-resistance, and high operating temperature. DAB devices using SiC MOSFETs have been developed both domestically and internationally. However, when the circuit operating frequency is high and the power carrying capacity is large, the switching loss of the device will increase significantly, so it is necessary to achieve soft switching of the device. Among them, ZVS technology can make the voltage between the drain and source of the device 0V at the moment of conduction, thereby making the device turn-on loss almost equal to zero. As for DAB, previous studies have not studied the key factor that determines whether DAB can achieve soft switching - the selection of inductance range.

[0004] The inductance value range of DAB will affect two major working performances of the circuit. First, it affects the output power of the circuit. If an inductor with too large an inductance is selected, the maximum output power of the circuit cannot meet the design requirements. Second, it will directly affect whether the power devices in the DAB circuit can achieve soft switching or zero voltage switching.

[0005] In addition to the inductance range, the control strategy used for DAB also affects whether it can achieve ZVS. For DAB, the main control strategies include single-phase-shift control, dual-phase-shift control, and extended-phase-shift control. Single-phase-shift control (SPS) is the most widely used in practice due to its simple control and excellent dynamic performance. Under ideal SPS control, when the transformer ratio matches the input and output voltages, ZVS can be achieved across the entire power range. Otherwise, ZVS can only be achieved when the current direction at the moment of DAB inductor commutation meets the requirements. When considering the device's equivalent output capacitance, ZVS can only be achieved when the minimum inductor current at the end of device commutation meets the requirements. The inductance range, however, affects whether these requirements can be met in actual DAB operation.

[0006] Furthermore, in practical applications, the phase shift ratio under single-phase control depends on the inductor value. However, previous research has failed to combine the two, considering the impact of the power device output capacitance on achieving ZVS and providing an analytical inductance range for achieving zero-voltage switching. Furthermore, previous studies have largely overlooked the impact of dead time on the ZVS achieved by DAB. If the dead time is too short, the drain-source voltage of the device at turn-on will not drop to zero. If the dead time is too long, the DAB will produce a dead-zone effect, causing the drain-source voltage to rise again after dropping to zero, which can also lead to ZVS failure. In summary, previous research has not provided a detailed discussion of the inductance range that ensures high-reliability operation of the dual active bridge. Summary of the Invention

[0007] The present invention aims to provide a method for determining the inductance range of a dual-active bridge (DAB) suitable for single-phase-shift control, addressing the aforementioned issues with the incomplete considerations of existing DAB inductance selection ranges and their inability to ensure high-reliability circuit operation. By considering two major constraints: the maximum output power requirement of the circuit and the zero-voltage switching requirement of the circuit's power devices, the present invention simultaneously considers three conditions when analyzing the zero-voltage switching requirement: the characteristic current direction requirement, the inductor energy meeting the primary-side commutation requirement, and the dead-time matching requirement of the inductor value. This method, with its comprehensive and clear process, ensures that the dual-active bridge can meet the maximum power requirement exceeding the output power requirement while achieving zero-voltage switching of the SiC power devices in the circuit, thus ensuring the reliability of the normal operation of the dual-active bridge. The method can be applied to the design of dual-active bridge converters using single-phase-shift control under any technical specifications.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for determining an inductance range for a dual active bridge circuit includes the following steps:

[0010] S1: Given the design indicators and corresponding parameters of the dual active bridge;

[0011] S2: Substitute the design indicators and corresponding parameters into the maximum power requirement constraint to calculate the maximum value L of the inductance range. max ;

[0012] S3: Substitute the design indicators and corresponding parameters into the zero voltage switching requirement constraints, and obtain three minimum inductance values ​​L from the perspective of the three conditions that the characteristic current values ​​I1 and I2 are both > 0, the inductor energy meets the primary side commutation requirements, and the dead time and inductance value should match. min1 , L min2 , L min3 ;

[0013] S4: The minimum inductance L obtained by combining the three conditions min1 , L min2 , L min3 , take the maximum value of the three, and find the minimum value L of the inductance range that meets the three conditions min ;

[0014] S5: The maximum power requirement constraint and the zero voltage switching requirement constraint are combined to obtain the inductance value range that ensures high reliability operation of the dual active bridge.

[0015] The dual active bridge design indicators and corresponding parameters mainly include: input voltage V in , output voltage V out , output power P, operating frequency f s and the voltage ratio k, where k can be expressed as:

[0016]

[0017] Where n represents the DAB transformer ratio.

[0018] The maximum power requirement constraint can be expressed as:

[0019]

[0020] Where, L represents the inductance value, V out Represents the output current, η represents the output power extra margin set due to the existence of circuit loss, and is set to 1.1 in the present invention.

[0021] Furthermore, the maximum value L of the inductance range that meets the maximum power requirement constraint is obtained. max for:

[0022]

[0023] The zero voltage switching requirement constraint mainly includes three conditions: Condition 1: the characteristic current values ​​I1 and I2 are both > 0; Condition 2: the inductor energy meets the primary side commutation requirement; Condition 3: the dead time and the inductor value should match.

[0024] Furthermore, the characteristic current value I1 in Condition 1 represents the inductor current value when the DAB secondary side H-bridge starts commutating when the inductor current is in the positive half cycle; the characteristic current value I2 represents the inductor current value when the DAB primary side H-bridge starts commutating when the inductor current is in the positive half cycle. Condition 1 can be expressed as:

[0025]

[0026] Where D represents the phase shift of DAB using single phase shift control, which can be calculated by the following formula:

[0027]

[0028] Furthermore, the first minimum value L of the inductance range that satisfies condition 1 is obtained. min1 for:

[0029]

[0030] Furthermore, the condition 2 can be expressed as:

[0031]

[0032]

[0033] Among them, I2 can be obtained from (4); 2Q oss (V in ) represents the total charge flowing into the primary winding of the transformer; C oss (v) represents the output capacitance of the power device at different voltages. This parameter can be obtained from the device manual of the power device used.

[0034] Furthermore, the second minimum value L of the inductance range that satisfies condition 2 is obtained. min2 for:

[0035]

[0036] Among them, A, B and Δ are the intermediate variables to be solved:

[0037]

[0038] Furthermore, when k=1, the second minimum value L of the inductance range that satisfies condition 2 is min2 can be simplified to:

[0039]

[0040] Furthermore, the condition 3 requires setting the dead time of the power device in the DAB device. In the present invention, the dead time is set as:

[0041] t DT =S(t Imax +t II ) (12)

[0042] Among them, t DT represents the dead time between the upper and lower power devices of the H-bridge in DAB; S represents the safety margin set to ensure that the power devices achieve ZVS, which is set to 1.5 in the present invention; t Imax The maximum delay time between the device dynamic process and the driver dynamic process can be calculated by the following formula:

[0043] t Imax =(t PDHLmax +t d(off)max )-(t PDLHmin +t d(on)min ) (13)

[0044] Among them, t PDHLmax Indicates the maximum delay time of the gate drive falling edge; t d(off)max Indicates the maximum value of the power device shutdown delay time; t PDLHmin Indicates the minimum value of the gate drive rising edge delay time; t d(on)min Indicates the minimum turn-on delay time of the power device. These parameters can be obtained from the device manual of the power device used or the data sheet of the gate driver.

[0045] t Ⅱ The time of the device commutation process can be obtained by phase plane analysis:

[0046]

[0047] Among them, C eq It is used to calculate the equivalent capacitance of the transient commutation process, and its size is:

[0048]

[0049] Furthermore, the condition 3 can be expressed as:

[0050]

[0051] Among them, t Ⅲ Represents the total time from the end of resonance to the end of dead time. In order to obtain the sufficient condition of condition 3, tⅢ Set to:

[0052] t III =t DT -S'(t Imin +t II ) (17)

[0053] Wherein, S' is the safety margin of the minimum delay time and the resonance time, which is 0.5 in the present invention; t Imin Indicates the minimum value of the delay time, which can be calculated by the following formula:

[0054] t Imin =(t PDHLmin +t d(off)min )-(t PDLHmax +t d(on)max ) (18)

[0055] Among them, t PDHLmin Indicates the minimum value of the gate drive falling edge delay time; t d(off)min Indicates the minimum value of the power device shutdown delay time; t PDLHmax Indicates the maximum delay time of the gate drive rising edge; t d(on)max Indicates the maximum turn-on delay time of the power device. These parameters can be obtained from the device manual of the power device used or the data sheet of the gate driver.

[0056] I2' represents the inductor current at the end of resonance and can be calculated by the following formula:

[0057]

[0058] The third minimum value L of the inductance value range that satisfies the dead time and inductance value should match min3 It can be obtained from formula (20):

[0059]

[0060] The minimum inductance L obtained by combining the three conditions min1 , L min2 , L min3 Then, the minimum value L of the inductance range that meets all conditions can be obtained by the following formula: min :

[0061] L min =max(L min1 ,L min2 ,L min3 ) (twenty one)

[0062] The inductance range for ensuring high reliability operation of the dual active bridge by combining the maximum power requirement constraint and the zero voltage switching requirement constraint is:

[0063] L∈(L min ,L max )(twenty two)

[0064] Compared with the prior art, the present invention has the following beneficial technical effects:

[0065] The present invention proposes a method for determining the inductance range of a dual active bridge suitable for single phase shift control, which takes into account the constraint that the maximum output power of the circuit should be greater than a given output power index requirement, so that the inductance within this range can ensure the normal operation of DAB under given technical indicators.

[0066] The present invention proposes a method for determining the inductance range of a dual active bridge suitable for single-phase shift control. This method also considers the constraint that the power devices in the circuit must achieve zero-voltage switching. The method also discusses the three conditions—the characteristic current direction requirement, the inductor energy satisfying the primary-side commutation requirement, and the dead time matching the inductance value—in detail, deriving three corresponding minimum inductance constraints. By selecting the maximum of these three as the minimum value of the entire inductance range, the zero-voltage switching performance of the power devices in the DAB circuit is ensured, eliminating turn-on losses during operation of the power devices, significantly reducing their temperature rise, and improving the reliability of the power devices and, ultimately, the entire device. Furthermore, since the power devices do not generate switching losses, the overall circuit loss is reduced, improving the efficiency of the DAB device.

[0067] The method for determining the inductance range of a dual active bridge suitable for single phase shift control proposed in the present invention is comprehensive, has a clear process, and is highly practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0069] Figure 1 This is a typical circuit diagram of a dual active bridge;

[0070] Figure 2 This is the waveform diagram of the working principle of the dual active bridge;

[0071] Figure 3 It is the transient waveform diagram of the dual active bridge commutation process;

[0072] Figure 4 This is a flow chart of a method for determining the inductance range of a dual active bridge suitable for single phase shift control according to the present invention;

[0073] Figure 5 The waveforms of the input and output voltage and inductor current of the dual active bridge in the experimental test are shown;

[0074] Figure 6 This is the transient waveform of the primary-side commutation process of the dual active bridge in the experimental test;

[0075] Figure 7 The transient waveform diagram of the secondary side commutation process of the dual active bridge in the experimental test. DETAILED DESCRIPTION

[0076] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0077] In the description of the present invention, it should be noted that, unless otherwise expressly specified and limited, the terms "include" and "comprise" indicate the existence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the existence or addition of one or more other features, wholes, steps, operations, elements, components and / or their collections.

[0078] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0079] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0080] The specific steps of the method of the present invention are:

[0081] (1) Determine the design indicators and corresponding parameters of the designed dual active bridge, among which the required technical indicators and parameters mainly include the input voltage V in , output voltage V out , output power P, operating frequency f s and the voltage ratio k. See Figure 1 , Figure 1 A typical circuit diagram of a dual active bridge is given, and the meaning of each parameter circuit is as follows Figure 1 As shown. Where k can be expressed as:

[0082]

[0083] (2) Make the dual active bridge inductor design meet the maximum power requirement constraint. The maximum power requirement, i.e., the maximum power that the DAB can transmit, should be higher than the output power requirement, otherwise the DAB circuit cannot meet the design requirements. This constraint can be expressed as:

[0084]

[0085] Where, L represents the inductance value, V out Represents the output current, η represents the output power margin set due to the existence of circuit loss, which is set to 1.1 in the present invention. From formula (2), the maximum value L of the inductance range under the maximum power requirement constraint can be obtained: max for:

[0086]

[0087] (3) Ensure that the dual active bridge inductor design meets the zero voltage switching requirement constraints. The maximum zero voltage switching constraint is that the power devices on the primary and secondary sides of the DAB circuit must achieve zero voltage switching (ZVS) during normal operation. Otherwise, the power devices in the DAB circuit will have a safety hazard of excessive temperature rise. The zero voltage switching requirement constraint mainly includes three conditions: Condition 1: Both characteristic current values ​​I1 and I2 are greater than 0; Condition 2: The inductor energy meets the primary side commutation requirements; Condition 3: The dead time and inductor value must match. The three conditions are described below.

[0088] ① Make the dual active bridge inductor design meet condition 1. Please refer to Figure 2 , Figure 2 The working principle waveform of the dual active bridge is given, and the characteristic current values ​​I1 and I2 are as follows: Figure 2 The characteristic current value I1 represents the inductor current value when the DAB secondary side H-bridge starts commutating when the inductor current is in the positive half cycle; the characteristic current value I2 represents the inductor current value when the DAB primary side H-bridge starts commutating when the inductor current is in the positive half cycle. Figure 1 To achieve ZVS on the primary side of the transformer, the inductor current should be greater than zero before S1 and S4 are disconnected. During the dead time, the current continues to flow through diodes D2 and D3, so S2 and S3 can achieve ZVS conduction. Similarly, for ZVS on the secondary side of the transformer, the inductor current value should be greater than zero when the DAB secondary side H-bridge begins commutation. Therefore, condition 1 can be expressed as:

[0089]

[0090] Where D represents the phase shift of DAB using single phase shift control, which can be calculated by the following formula:

[0091]

[0092] From (4) and (5), we can get the first minimum value L of the inductance range that meets condition 1: min1 for:

[0093]

[0094] When k=1, L min1 =0, which means that DAB can always achieve ZVS when the input and output voltages are ideally matched with respect to the transformer ratio.

[0095] ② Ensure the dual active bridge inductor design meets condition 2. Condition 2 takes into account that the inductor energy should be sufficient at the moment the power device begins commutation to complete the charging and discharging of the power device's output capacitor. Since commutation occurs on both the primary and secondary sides of the DAB transformer, and the operating principles of the primary and secondary commutation processes are not exactly the same, they need to be considered separately.

[0096] During the commutation process on the secondary side of a DAB transformer, the inductor energy increases accordingly, reflecting an increase in the inductor current. Therefore, when the phase shift ratio D > 0 in single-phase control, the inductor energy always meets the requirements. Therefore, Condition 2 only focuses on whether the inductor energy meets the requirements during the primary-side commutation process. Therefore, Condition 2 can be expressed as the inductor energy meeting the primary-side commutation requirements.

[0097] During the commutation process on the primary side of the DAB transformer, the inductor energy decreases accordingly, which is reflected in the current as a decrease in the inductor current. To ensure that the drain-source voltage of the power device about to be turned on can completely drop to 0V, the inductor energy must be large enough to support the commutation. Therefore, the above condition 2 can be expressed as:

[0098]

[0099]

[0100] Among them, I2 can be obtained from (4); 2Q oss (V in ) represents the total charge flowing into the primary winding of the transformer; C oss (v) represents the output capacitance of the power device at different voltages. This parameter can be obtained from the device manual of the power device used. Substituting (1), (4) and (5) into (7), (7) can be rewritten as:

[0101]

[0102] This inequality is a quadratic inequality about L, and has two range solutions:

[0103] L <L a or L>L b (10)

[0104] Among them, L a and L b represents two solutions to a quadratic inequality. However, L <L a The solution obtained will show that I2<0, which conflicts with condition 1, so L>L b The second minimum value L of the inductance range that meets condition 2 can be obtained min2 for:

[0105]

[0106] Among them, A, B and Δ are the intermediate variables to be solved:

[0107]

[0108] Furthermore, when k=1, the second minimum value L of the inductance range that satisfies condition 2 is min2 can be simplified to:

[0109]

[0110] ③ Make the dual active bridge inductor design meet condition 3. Please refer to Figure 3 , Figure 3 The transient waveform of the dual active bridge commutation process is given, t PDHL , t d(off ), t PDLH , t d(on) , t Ⅱ and t Ⅲ The meaning is shown in the figure. Condition 3 takes into account the transient dead time effect of the device commutation process, which is a sufficient condition for DAB to achieve ZVS in practical applications. In order to prevent the two power devices above and below the same bridge arm from being directly connected, a dead time needs to be set in the application. However, the dead time should not be set too long to avoid the dead time effect, that is, voltage polarity reversal, voltage sag and other phenomena. On the contrary, if the dead time is set too short, not only will the DAB not be able to work in ZVS mode, it may even cause the power device to be directly connected. Therefore, it is necessary to first set the dead time of the power device in the DAB device. In the present invention, the dead time is set as follows

[0111] t DT =S(t Imax +t II ) (14)

[0112] Among them, t DTrepresents the dead time between the upper and lower power devices of the H-bridge in DAB; S represents the safety margin set to ensure that the power devices achieve ZVS, which is set to 1.5 in the present invention; t Imax It represents the maximum delay time between the device dynamic process and the driver dynamic process, and is defined by the following formula:

[0113] t Imax =(t PDHLmax +t d(off)max )-(t PDLHmin +t d(on)min ) (15)

[0114] Among them, t PDHLmax Indicates the maximum delay time of the gate drive falling edge; t d(off)max Indicates the maximum value of the power device shutdown delay time; t PDLHmin Indicates the minimum value of the gate drive rising edge delay time; t d(on)min Indicates the minimum turn-on delay time of the power device. These parameters can be obtained from the device manual of the power device used or the data sheet of the gate driver.

[0115] t Ⅱ The time of the device commutation process can be obtained by phase plane analysis:

[0116]

[0117] Among them, C eq It is used to calculate the equivalent capacitance of the transient commutation process, and its size is:

[0118]

[0119] After setting the dead time, you need to analyze the inductance range that meets condition 3. Figure 3 , t Ⅲ Represents the total time from the end of resonance to the end of dead time. During this period, the body diode of the power device S2 that is about to turn on begins to conduct freewheeling, and its drain-source voltage v ds2 is clamped to near zero. In this case, the inductor voltage v L is a constant value:

[0120] v L =-(V in +nV out ) (18)

[0121] At this time, the inductor current i L It decreases linearly. The power device S2 should be LTurn on before changing direction, otherwise, it will not be able to achieve zero voltage turn-on due to the dead time effect. Therefore, condition 3 can be expressed as:

[0122]

[0123] Among them, t Ⅲ Represents the total time from the end of resonance to the end of dead time. In order to obtain the sufficient condition of condition 3, t Ⅲ Set to:

[0124] t III =t DT -S'(t Imin +t II ) (20)

[0125] Wherein, S' is the safety margin of the minimum delay time and the resonance time, which is 0.5 in the present invention; t Imin Indicates the minimum value of the delay time, which can be calculated by the following formula:

[0126] t Imin =(t PDHLmin +t d(off)min )-(t PDLHmax +t d(on)max ) (twenty one)

[0127] Among them, t PDHLmin Indicates the minimum value of the gate drive falling edge delay time; t d(off)min Indicates the minimum value of the power device shutdown delay time; t PDLHmax Indicates the maximum delay time of the gate drive rising edge; t d(on)max Indicates the maximum turn-on delay time of the power device. These parameters can be obtained from the device manual of the power device used or the data sheet of the gate driver.

[0128] I2' represents the inductor current at the end of resonance and can be calculated by the following formula:

[0129]

[0130] The third minimum value L of the inductance value range that satisfies the dead time and inductance value should match min3 From formula (23), we can get:

[0131]

[0132] Since both the primary and secondary sides of the DAB transformer are set with dead time and the commutation process is not exactly the same, the secondary side commutation process and the dead time transient process also need to be considered. As mentioned above, for the commutation process on the secondary side of the DAB transformer, the inductor energy will increase accordingly during the commutation process. Therefore, as long as the inductance value range meets condition 1, the inductor current i L The direction will not change, so condition 3 only needs to focus on whether the inductance value of the primary side commutation process matches the dead time.

[0133] (IV) The three conditions are combined to make the dual active bridge inductor design meet the zero voltage switching requirement constraints. The minimum inductance L obtained by the three conditions is min1 , L min2 , L min3 Then, the minimum value L of the inductance range that meets all conditions can be obtained by the following formula: min :

[0134] L min =max(L min1 ,L min2 ,L min3 ) (twenty four)

[0135] (V) Combining the two constraints to obtain the inductance value range. Based on the above discussion of the maximum power requirement constraint and the zero voltage switching requirement constraint, the maximum and minimum values ​​of the inductance value range are obtained respectively. Therefore, the final inductance value range that ensures high reliability operation of the dual active bridge is:

[0136] L∈(L min ,L max ) (25)

[0137] See Figure 4 , Figure 4 A flow chart for the method for determining the inductance range of a dual-active bridge suitable for single-phase-shift control is provided. The accuracy and effectiveness of the proposed method for determining the inductance loss of a dual-active bridge suitable for single-phase-shift control are verified using a DAB device with an input voltage of 750V, an expected output voltage of 700V, an expected output power of 3500W, an operating frequency of 80kHz, a voltage ratio of 0.95, and a load resistance of 140Ω. Substituting the experimental conditions into the proposed inductance range determination method, the inductance range under these experimental conditions is obtained as follows:

[0138] L∈(83.3μH,108.7μH) (26)

[0139] Therefore, the inductance value selected in the experimental verification is 84.7μH, which falls within this range. Figure 5 , Figure 5The experimentally tested dual active bridge input and output voltage and inductor current waveforms are shown. The selected inductor value allows the circuit output voltage to reach the desired 700V. With a load resistance of 140Ω, the DAB output power can reach the desired 3500W. The selected inductor value meets the maximum power requirement. Figure 6 , Figure 6 The transient waveform of the primary commutation process of the dual active bridge in the experimental test is given, in which the commutation process is from Figure 1 The power devices S1 and S4 are switched to the power devices S2 and S3. Figure 6 It can be found that the S2 power device has a drain-source voltage v DS2 After dropping to 0V, its gate drive voltage v GS2 It starts to rise slowly, indicating that the selection of this inductor value has achieved ZVS of the primary power device. Figure 7 , Figure 7 The transient waveform of the secondary commutation process of the dual active bridge in the experimental test is given, in which the commutation process is from Figure 1 The power devices S6 and S7 are switched to the power devices S5 and S8. Figure 7 It can be found that the S5 power device has a drain-source voltage v DS5 After dropping to 0V, its gate drive voltage v GS5 The voltage then slowly begins to rise, indicating that the selection of this inductor value achieves ZVS for the secondary power device. In summary, the selection of an inductor value within this range satisfies both the maximum power demand constraint and the zero voltage switching constraint.

[0140] The present invention proposes a method for determining the inductance range of a dual active bridge suitable for single phase shift control. The present invention takes into account the constraint that the maximum power output of the circuit should be greater than the given output power index requirement, so that the inductance within this range can ensure the normal operation of the DAB under the given technical indicators. In addition, the method also takes into account the constraint that the power devices in the circuit should achieve zero voltage switching requirements. At the same time, the three major conditions of the characteristic current value direction requirement, the inductance energy meeting the primary side commutation requirement, and the dead time matching the inductance value are discussed in detail and the minimum value of the inductance value range is obtained, thereby ensuring the zero voltage switching performance of the power devices in the DAB circuit and improving the reliability of the power devices and even the entire device. At the same time, since the power devices do not generate switching losses, the overall circuit loss will be reduced, thereby improving the working efficiency of the DAB device. After experimental verification, the inductance range determination method proposed by the present invention is comprehensive and has a clear process, which ensures the reliability of the normal operation of the dual active bridge circuit and has high practical value.

[0141] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for determining the inductance range of a dual active bridge suitable for single phase shift control, characterized in that: The following steps are involved: S1: Given the design indicators and corresponding parameters of the dual active bridge; S2: Substitute the design indicators and corresponding parameters into the maximum power requirement constraint to calculate the maximum value L of the inductance range. max ; S3: Substitute the design indicators and corresponding parameters into the zero voltage switching requirement constraints, and obtain three minimum inductance values ​​L from the perspective of the three conditions that the characteristic current values ​​I1 and I2 are both > 0, the inductor energy meets the primary side commutation requirements, and the dead time and inductance value should match. min1 , L min2 , L min3 ; S4: The minimum inductance L obtained by combining the three conditions min1 , L min2 , L min3 , take the maximum value of the three, and find the minimum value L of the inductance range that meets the three conditions min ; S5: The maximum value of the inductance range L obtained by combining the maximum power demand constraint max The minimum value L of the inductance range obtained by the zero voltage switching requirement constraint min The inductance value range that ensures high reliability operation of the dual active bridge is obtained.

2. The method for determining the inductance range of a dual active bridge suitable for single phase shift control according to claim 1, characterized in that: The dual active bridge design indicators and corresponding parameters mainly include: input voltage V in , output voltage V out , output power P, operating frequency f s and the voltage ratio k, where k is expressed as: Where n represents the DAB transformer ratio.

3. The method for determining the inductance range of a dual active bridge suitable for single phase shift control according to claim 2, characterized in that: The maximum power requirement constraint is expressed as: Where, L represents the inductance value, I out Represents the output current, η represents the additional output power margin set due to the existence of circuit loss; The maximum value L of the inductance range under the maximum power requirement constraint max for:

4. The method for determining the inductance range of a dual active bridge suitable for single phase shift control according to claim 2, wherein: The characteristic current value I1 represents the inductor current value when the H-bridge on the secondary side of the DAB starts commutating when the inductor current is in the positive half cycle; The characteristic current value I2 represents the inductor current value when the DAB primary side H bridge starts commutating when the inductor current is in the positive half cycle; The characteristic current values ​​I1 and I2 are both >0, expressed as: Where D represents the phase shift of DAB using single phase shift control, which is calculated by the following formula: The first minimum value L of the inductance range that meets the characteristic current values ​​I1 and I2>0 is min1 for:

5. The method for determining the inductance range of a dual active bridge suitable for single phase shift control according to claim 4, characterized in that: The inductor energy that meets the primary side commutation requirement is expressed as: Among them, 2Q oss (V in ) represents the total charge flowing into the primary winding of the transformer; C oss (v) represents the output capacitance of the power device at different voltages, obtained from the device manual of the power device used; The second minimum value L of the inductance value range that meets the inductance energy to meet the primary side commutation requirements is min2 for: Among them, A, B and Δ are the intermediate variables to be solved: When k = 1, the second minimum value L of the inductance value range that meets the primary side commutation requirement is min2 Simplified to:

6. The method for determining the inductance range of a dual active bridge suitable for single phase shift control according to claim 4, characterized in that: The dead time should match the inductance value. First, the dead time of the power device in the DAB device is set as follows: t DT =S(t Imax +t II ) (12) Among them, t DT It represents the dead time between the upper and lower power devices of the H-bridge in DAB; S represents the safety margin set to ensure that the power devices achieve ZVS; t Imax It represents the maximum delay time generated by the device dynamic process and the driver dynamic process, and is calculated by the following formula: t Imax =(t PDHLmax +t d(off)max )-(t PDLHmin +t d(on)min ) (13) Among them, t PDHLmax Indicates the maximum delay time of the gate drive falling edge; t d(off)max Indicates the maximum value of the power device shutdown delay time; t PDLHmin Indicates the minimum value of the gate drive rising edge delay time; t d(on)min Indicates the minimum value of the power device turn-on delay time; t Ⅱ Represents the time of the device commutation process, which is obtained by phase plane analysis: Among them, C eq Represents the equivalent capacitance used to calculate the transient commutation process:

7. The method for determining the inductance range of a dual active bridge suitable for single phase shift control according to claim 6, characterized in that: The dead time and inductance value should match as follows: Among them, t Ⅲ Indicates the total time from the end of resonance to the end of dead time, t Ⅲ Set to: t III =t DT -S'(t Imin +t II ) (17) Where S' is the safety margin of the minimum delay time and resonance time; t Imin Indicates the minimum value of the delay time, which is calculated by the following formula: t Imin =(t PDHLmin +t d(off)min )-(t PDLHmax +t d(on)max ) (18) Among them, t PDHLmin Indicates the minimum value of the gate drive falling edge delay time; t d(off)min Indicates the minimum value of the power device shutdown delay time; t PDLHmax Indicates the maximum delay time of the gate drive rising edge; t d(on)max Indicates the maximum value of the power device turn-on delay time; I2' represents the inductor current at the end of resonance and is calculated by the following formula: The third minimum value L of the inductance value range that satisfies the dead time and inductance value should match min3 From formula (20), we can get:

8. The method for determining the inductance range of a dual active bridge suitable for single phase shift control according to claim 7, characterized in that: The minimum value of the inductance range is L min It is expressed as follows: L min =max(L min1 ,L min2 ,L min3 ) (21)。 9. The method for determining the inductance range of a dual active bridge suitable for single phase shift control according to claim 7, characterized in that: The inductance value range for ensuring high reliability operation of the dual active bridge is: L∈(L min ,L max ) (22)。

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