A dual active bridge converter and a DC bias suppression method thereof

Abstract

The invention discloses a dual active bridge converter and a DC bias suppression method thereof, belonging to the technical field of power electronic converters, comprising: when the dual active bridge converter is in steady state operation, according to the distribution coefficient p Perform bilateral single phase shift modulation; establish an inductor current function model of a dual active bridge converter taking into account high frequency link resistance; when the phase shift angle between the primary and secondary sides of the dual active bridge converter changes, calculate the transient phase shift ratio and distribute it to the primary and secondary sides for bilateral single phase shift modulation according to the circuit parameters of the dual active bridge converter, the inductor current function model and the shift ratio before and after the change. The present invention can eliminate the transient DC bias generated by the transient inductor current and the converter magnetic flux by introducing the transient phase shift ratio and distribution coefficient, combined with the bilateral phase shift control method, avoids excessive design of magnetic components, and can reach a stable state within one switching cycle for any high frequency link resistance value and shift ratio.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic converters, and in particular relates to a dual active bridge converter and a direct current bias suppression method thereof. Background Art

[0002] The dual active bridge (DAB) is a highly efficient isolated DC-DC converter that achieves electrical isolation through a high-frequency transformer. It has the characteristics of compact structure, soft switching, high power density, and bidirectional energy flow. It is widely used in electric vehicles, new energy power generation and other fields.

[0003] When the dual active bridge converter changes the transmission power, when the steady-state switching mode single phase shift modulation (SPS) is directly applied, the inductor current and the converter's excitation current, that is, the converter flux, will produce a transient DC bias. The transient DC bias generated by the inductor current will increase the peak current flowing through the switching device, increase the switching loss, and shorten its service life. The transient DC bias generated by the converter flux will cause the magnetic core to saturate or even burn out the switching device. Therefore, the suppression of DC bias is very critical for the stable operation of the dual active bridge converter. In the DC distribution network, the dual active bridge can be connected to a passive grid or an active grid at both ends. The demand for multiple working modes puts higher requirements on the DC bias suppression of the dual active bridge.

[0004] The prior art document "J. Hu, S. Cui and Y. He, Universal Flux Balancing Control to Suppress Transient DC-Bias of Phase-Shift Modulated Multi-Active-Bridge Converters, 2023 11th International Conference on Power Electronics and ECCE Asia (ICPE 2023 - ECCE Asia), Jeju Island, Republic of Korea, 2023, pp. 1898-1905." proposes a universal dynamic current balancing open-loop control scheme for a single-phase multi-active bridge converter. When the load angle changes, an intermediate phase shift angle is introduced to effectively eliminate the transient DC bias in the transformer current. However, the scheme does not take into account the high-frequency link resistance of the primary and secondary sides of the converter. The prior art document “SP Engel, N. Soltau, H. Stagge and RWDe Doncker, Improved instantaneous current control for high-power three phase dual-active bridge dc–dc converters, IEEE Transactions on Power Electronics, vol. 29, no. 8, pp. 4067–4077, 2014.” proposed a dynamic current balance control method considering high-frequency link resistance in a three-phase dual-active bridge converter. However, a sudden change in load angle will also cause an instantaneous DC bias in the transformer flux. The attenuation rate of the DC flux bias is related to the relatively large excitation inductance of the transformer, so it is easy to accumulate during the transient operation of the DAB converter. If the transformer is not designed with a large margin, this effect may cause the core material to saturate, ultimately affecting normal operation.The prior art document "J. Yin, J. Lu, H. Jiang, Y. Liu and J. Peng, Modified Phase-Shift Scheme for Optimal Transient Response of Dual-Active-Bridge DC / DC Converters Considering the Resistive Impact, in IEEE Access, vol. 9, pp. 87706-87714, 2021." analyzes the adverse effects of resistor elements on the transient performance of a single-phase DAB converter, and on this basis proposes a single-phase shift scheme, which eliminates the current bias by changing the three time periods of the original secondary side when the shift angle is switched. However, the transient process of this method is longer and the flux bias of the converter is not considered. The prior art document "J. Hu, S. Cui, S. Wang, and RW De Doncker, Instantaneous flux and current control for a three-phase dual-active bridge dc–dc converter," IEEE Transactions on Power Electronics, vol. 35, no. 2, pp. 2184–2195, 2020." proposed bilateral single phase shift modulation, which divides the transient phase shift angle into two parts and distributes them to the primary and secondary sides, effectively eliminating the transient flux bias; however, this method is combined with current dynamic balance control, and does not consider the high-frequency link resistance distributed on the primary and secondary sides, and it is only proved to be effective in the three-phase dual active bridge converter with a phase shift angle in the range of 0~60°. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a dual active bridge converter and a DC bias suppression method thereof. The present invention can eliminate the transient DC bias generated by the transient inductor current and the converter flux by introducing the transient phase shift ratio and distribution coefficient and combining the bilateral phase shift control method, avoiding the over-design of magnetic components, and achieving a stable state within one switching cycle for any high-frequency link resistance value and the phase shift ratio.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A method for suppressing direct current bias of a dual active bridge converter, comprising:

[0008] Step S1, when the dual active bridge converter is in steady state operation, according to the distribution coefficient pPerform bilateral single phase shift modulation;

[0009] Step S2, establishing an inductor current function model of a dual active bridge converter taking into account high frequency link resistance;

[0010] Step S3, when the phase shift angle between the primary and secondary sides of the dual active bridge converter changes, the transient phase shift ratio is calculated according to the circuit parameters of the dual active bridge converter, the inductor current function model and the shift ratio before and after the change. D int Assigned to the original secondary side for bilateral single phase shift modulation.

[0011] Furthermore, in step S1, the distribution coefficient p The expression is:

[0012] ,

[0013] N tr is the transformer primary-to-secondary turns ratio, L ' s is the secondary leakage inductance equivalent to the primary side, U p is the primary voltage, U s is the secondary voltage, L p is the primary side leakage inductance.

[0014] Furthermore, in step S1, the phase shift angle before the change φ 1 is divided into two parts, pφ 1 is assigned to the switch of the primary side, and the angle (1- p ) φ 1 is assigned to the switch on the secondary side, and the original secondary side shifts phase to the left and right directions respectively, among which the phase shift angle before the change is φ 1 is equal to D 1 T , T is half a switching cycle.

[0015] Further, in step S2, the inductor current function model is expressed as:

[0016]

[0017] in, k = N tr U s / U p is the voltage matching degree, R = R p +R ' s is the total high-frequency chain resistance of the primary side and the secondary side equivalent to the primary side, τ = L / R is the current decay time constant, D is the shift ratio of half a switching cycle, i p is the primary side inductor current, t For time.

[0018] Furthermore, in step S3, the transient shift ratio D int The calculation formula is:

[0019] ,

[0020] Among them, the function v and function λ The expression for 0 is as follows:

[0021]

[0022]

[0023] in, D 1 is the shift ratio of the first half of the switching cycle, D 2 is the shift ratio of the half switching cycle after the change.

[0024] Further, in step S3, the transient phase shift angle φ int Divide into two parts, pφ int Assigned to the switch of the primary side, the angle (1- p ) φ int The switches assigned to the secondary side shift the phase of the original secondary side to the left and right directions respectively, where the transient phase shift angle φ int equal D int T .

[0025] Furthermore, according to the distribution coefficient p or transient shift D int The output PWM signal drives the switches in the dual active bridge converter.

[0026] In a specific embodiment, the DC bias suppression method of the dual active bridge converter further includes that the duty cycle of the PWM signal is 0.5.

[0027] The present invention also provides a dual active bridge converter, which uses the above-mentioned DC bias suppression method of the dual active bridge converter, including a primary H-bridge, a secondary H-bridge, a transformer, multiple inductors and multiple resistors, the first input terminal and the second input terminal of the primary bridge are connected in parallel with the primary voltage, the first output terminal, the first resistor, the first inductor, the primary winding of the transformer, and the second output terminal of the primary H-bridge are connected in sequence, the first input terminal, the second resistor, the second inductor, the secondary winding of the transformer, and the second input terminal of the secondary H-bridge are connected in sequence, and the first output terminal and the second output terminal of the secondary H-bridge are connected in parallel with the secondary voltage.

[0028] Furthermore, the present invention provides a dual active bridge converter, according to the distribution coefficient p or transient shift D int Generates PWM signals to the switches of the dual active bridge converter.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: taking into account the high-frequency link resistance of the converter, by introducing the transient phase shift ratio and distribution coefficient, combined with the bilateral phase shift control method, the transient DC bias generated by the transient inductor current and the converter flux can be eliminated, avoiding excessive design of magnetic components, and achieving a stable state for any high-frequency link resistance value within one switching cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0031] Figure 1 This is the topological diagram of the dual active bridge converter.

[0032] Figure 2 The present invention is a flow chart of a method for suppressing direct current bias of a dual active bridge converter.

[0033] Figure 3 Schematic diagram of the equivalent circuit of the dual active bridge converter under single phase shift modulation.

[0034] Figure 4 To change the driving waveform and voltage of the original 8 switches on the secondary side when the front and rear shift ratios are both greater than 0 v ab With voltage v cd Waveform, primary inductor current i p Waveform diagram.

[0035] Figure 5This is the simulation result diagram of primary inductance current and converter flux under the traditional single-phase shift modulation method.

[0036] Figure 6 This is the simulation result diagram of the primary inductor current and converter flux under the transient bias elimination control method without considering the high-frequency link resistance.

[0037] Figure 7 This is a diagram of the simulation results of the primary inductance current and the converter flux under the method provided by the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other examples obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0039] Combine the following Figure 1 The dual active bridge converter of the present invention introduces a DC bias suppression method of the dual active bridge converter.

[0040] like Figure 1 As shown, the dual active bridge converter 1 includes a primary H bridge 11, a secondary H bridge 12, a transformer T1, a plurality of inductors and a plurality of resistors. The first input terminal and the second input terminal of the primary H bridge 11 are connected in parallel to the primary voltage U p , the first output terminal of the primary H bridge 11, the resistor R p ,inductance L p , the primary winding of the transformer T1, and the second output terminal of the primary H bridge 11 are connected in sequence, and the first input terminal of the secondary H bridge 12, the resistor R s ,inductance L s , the secondary winding of the transformer T1, and the second input terminal of the secondary H bridge 12 are connected in sequence, and the first output terminal and the second output terminal of the secondary H bridge 12 are connected in parallel to the secondary voltage U s .

[0041] Among them, the output voltage of the primary H bridge 11 is v ab , secondary side H bridge output voltage v cd .

[0042] Furthermore, the dual active bridge converter 1 further includes a capacitor C1 and a capacitor C2 , wherein the capacitor C1 is connected in parallel between the first input terminal and the second input terminal of the primary H bridge 11 , and the capacitor C2 is connected in parallel between the first output terminal and the second output terminal of the secondary H bridge 12 .

[0043] More specifically, the primary H-bridge 11 includes a switch S1 , a switch S2 , a switch S3 , and a switch S4 , which form a full-bridge topology.

[0044] More specifically, the secondary side H-bridge 12 includes a switch Q1 , a switch Q2 , a switch Q3 , and a switch Q4 , which form a full-bridge topology.

[0045] More specifically, the resistor R p is the primary high-frequency chain resistance, inductance L p is the primary side leakage inductance.

[0046] More specifically, the resistor R s is the secondary high-frequency chain resistance, inductance L s is the secondary side leakage inductance.

[0047] More specifically, the transformation ratio of transformer T1 is N tr :1.

[0048] Figure 2 Flow chart of a DC bias suppression method for a dual active bridge converter of the present invention, as shown in FIG. Figure 2 As shown, a DC bias suppression method for a dual active bridge converter of the present invention comprises:

[0049] Step S1, when the dual active bridge converter is in steady state operation, according to the distribution coefficient p Perform bilateral single phase shift modulation;

[0050] Step S2, establishing an inductor current function model of a dual active bridge converter taking into account high frequency link resistance;

[0051] Step S3, when the phase shift angle between the primary and secondary sides of the dual active bridge converter changes, the transient phase shift ratio is calculated according to the circuit parameters of the dual active bridge converter, the inductor current function model and the shift ratio before and after the change. D int Assigned to the original secondary side for bilateral single phase shift modulation.

[0052] Furthermore, the DC bias suppression method of the dual active bridge converter of the present invention further comprises: p or transient shift Dint The output PWM signal drives the switches in the dual active bridge converter.

[0053] Furthermore, according to the distribution coefficient p or transient shift D int Generate PWM signals to the switches of the dual active bridge converter to control its operation.

[0054] Optionally, for Figure 1 In the dual active bridge converter topology, the duty cycle of the PWM signal is 0.5.

[0055] More specifically, in step S1, the equivalent circuit of the dual active bridge converter under single phase shift modulation is as follows: Figure 3 Assume L M >> L p and L M >> L s , then according to the superposition theorem, the change in excitation flux is:

[0056] ,

[0057] in, L M is the magnetizing inductance of the dual active bridge converter, is the primary side switch voltage, is the switch voltage equivalent to the primary side from the secondary side, L p is the primary leakage inductance, L 's is the secondary leakage inductance equivalent to the primary side, R p is the primary high-frequency chain resistance, R 's is the secondary high-frequency chain resistance equivalent to the primary side, L = L p+ L 's is the total leakage inductance of the primary side and the secondary side equivalent to the primary side, R = R p+ R 's is the total high-frequency chain resistance of the primary side and the secondary side equivalent to the primary side, is the excitation flux, is the current when the primary voltage acts, is the current when the secondary voltage acts, t For time.

[0058] When the phase shift angle of the dual active bridge converter changes, the flux difference in the switching state should be 0. Since the conductor materials used in the primary and secondary sides of the transformer are the same, it is assumed that the distribution ratio of the high-frequency chain resistance and leakage inductance on the primary and secondary sides is the same, that is, L p / L = R p / R , we can get the formula:

[0059]

[0060] Among them, Δ φ is the phase shift angle variation, U p is the primary voltage, U s is the secondary voltage, T is half a switching cycle, L p is the primary side leakage inductance, L ' s is the secondary leakage inductance equivalent to the primary side, N tr is the transformer primary-to-secondary turns ratio, p is the distribution coefficient.

[0061] Among them, the distribution coefficient p The expression is:

[0062] .

[0063] When the phase shift angle of the dual active bridge converter changes, the double-sided shift term keeps the total phase shift angle unchanged, and the DC bias flux component induced on the primary side offsets the component induced on the secondary side. Therefore, the DC bias flux is offset in the transient state of the single phase shift modulation phase shift angle change, and the flux can instantly reach a new steady state.

[0064] Furthermore, in step S1, according to the distribution coefficient p Double-side single phase shift modulation is performed to eliminate the DC bias caused by the flux linkage, specifically including: changing the phase shift angle before the change φ 1 is divided into two parts, pφ 1 is assigned to the switch of the primary side, and the angle (1- p ) φ 1 is assigned to the switch on the secondary side, and the original secondary side shifts phase to the left and right directions respectively. Figure 4 As shown, the shift ratio at this time is D 1. Phase shift angle before change φ 1 is equal to D 1 T .

[0065] for Figure 1 In the dual active bridge converter topology, switches S1 and S4 are angularly spaced to the left. pφ 1 phase shift, switch Q1, switch Q4 to the right at an angle (1- p ) φ1 phase shift, the driving signals of switch S1 and switch S4 are 180° out of phase with the driving signals of switch Q1 and switch Q4, the driving signals of switch S2 and switch S3 are complementary to the driving signals of switch S1 and switch S4, and the driving signals of switch Q2 and switch Q3 are complementary to the driving signals of switch Q1 and switch Q4.

[0066] More specifically, in step S2, the inductor current function model within one cycle is expressed as:

[0067]

[0068] in, T is half a switching cycle, k = N tr U s / U p is the voltage matching degree, τ = L / R is the current decay time constant, D is the shift ratio of half a switching cycle, i p is the primary side inductor current.

[0069] Further, in step S3, when the phase shift angle between the primary and secondary sides of the dual active bridge converter changes, a transient shift ratio is introduced. D int , and is allocated to the original secondary side for bilateral single phase shift modulation, and the transient phase shift angle φ int Divide into two parts, pφ int Assigned to the switch of the primary side, the angle (1- p ) φ int The switches assigned to the secondary side shift the phase of the original secondary side to the left and right directions respectively to suppress the DC bias generated by the transient inductor current. φ int equal D int T .

[0070] Among them, the transient shift ratio D int The calculation formula is:

[0071] ,

[0072] Among them, the function v and function λ The expression for 0 is as follows:

[0073]

[0074]

[0075] in, D 1 is the shift ratio of the first half of the switching cycle, D 2 is the shift ratio of the half switching cycle after the change, D int is the transient shift ratio.

[0076] Furthermore, in the next cycle, the shift ratio of the half switching cycle after the change D 2. Change the phase shift angle φ 2 is divided into two parts, pφ 2 is assigned to the switch of the primary side, and the angle (1- p ) φ 2 is assigned to the switch on the secondary side, and the original secondary side shifts phase to the left and right directions respectively. Figure 4 As shown, the shift ratio at this time is D 2. Phase shift angle after change φ 2 is equal to D 2 T .

[0077] Taking the case where the shift ratio is greater than 0 before and after the change as an example, the relevant waveform is as follows Figure 4 As shown in the figure, it includes the driving waveforms of the 8 switches on the primary and secondary sides, the voltage v ab With voltage v cd Waveform, primary inductor current i p Waveform. Figure 4 The middle gray area is the transient shift ratio D int According to the transient process of the inductor current function model established in step S2 under steady-state conditions, the transient shift ratio is substituted into the inductor current function corresponding to each stage in the transient process, and the current after the transient process is equal to the steady-state current corresponding to the shift ratio after the change, and the transient shift ratio is calculated through the inductor current function waveform. D int , the transient shift ratio is allocated to the primary and secondary sides, so that the rising edge shift ratio of the primary switch tube S1 and S4 drive signal is pD int , the falling edge switches to pD 2, the rising edge shift ratio of the secondary switch tube Q1, Q4 drive signal is (1- p ) D int , the falling edge switches to (1- p ) D2. Realize the DC bias that suppresses transient inductor current.

[0078] For the case where the shift ratio of the half switching cycle before the change or the shift ratio of the half switching cycle after the change is not greater than 0, the above method can also be used for calculation, which will not be repeated here.

[0079] The method provided by the present invention is simulated and verified in the PLECS simulation platform, and compared with the conventional single phase shift modulation, instantaneous flux and current control method without considering the high-frequency chain resistance. The simulation sets the switching frequency to 10kHz, the primary leakage inductance value to 100μH, the primary high-frequency chain resistance to 1000mH, the secondary leakage inductance value to 30μH, the secondary high-frequency chain resistance to 300mH, the primary voltage to 1000V, the secondary voltage to 400V, the transformer primary-to-secondary turns ratio to 2, the phase shift angle to change from -10° to 60° and then back to -10°, the waveforms of the primary inductance current and the converter flux are as follows: Figure 5 , Figure 6 , Figure 7 Compared with the conventional single phase shift modulation and the instantaneous magnetic flux and current control method without considering the high frequency chain resistance, the method of the present invention can completely eliminate the DC bias of the current and magnetic flux, and the control method used is easy to implement.

[0080] According to the above experimental results, the dual active bridge converter and the DC bias suppression method thereof proposed in the present invention can be realized by simply shifting items without complicated adjustment process. By using this method, the dual active bridge converter can completely eliminate the current and flux bias and has good dynamic performance. The experiment verifies the effectiveness of the proposed method and proves that the elimination effect is better than that of the existing method.

Claims

1. A method for suppressing DC bias of a dual active bridge converter, characterized in that: include, Step S1, when the dual active bridge converter is in steady state operation, according to the distribution coefficient p Perform bilateral single phase shift modulation; Step S2, establishing an inductor current function model of a dual active bridge converter taking into account high frequency link resistance; Step S3, when the phase shift angle between the primary and secondary sides of the dual active bridge converter changes, the transient phase shift angle is calculated according to the circuit parameters of the dual active bridge converter, the inductor current function model and the phase shift angle before and after the change. D int Assigned to the original secondary side for bilateral single phase shift modulation; In step S2, the inductor current function model is expressed as: in, k = N tr U s / U p is the voltage matching, N tr is the transformer primary-to-secondary turns ratio, U p is the primary voltage, U s is the secondary voltage; R is the total high-frequency chain resistance of the primary side and the secondary side equivalent to the primary side, R p is the primary high frequency chain resistance, R ' s is the secondary high frequency chain resistance equivalent to the primary side, R = R p + R ' s ; τ = L / R is the current decay time constant, L It is the total leakage inductance of the primary side and the secondary side equivalent to the primary side; D is the shift phase of half a switching cycle, i p is the primary side inductor current, t For time, T is half a switching cycle; In step S3, the transient shift is D int The calculation formula is: ， Among them, the function v and function λ The expression for 0 is as follows: in, D 1 is the shift phase of the first half switching cycle, D 2 is the shift phase ratio of the half switching cycle after the change.

2. A DC bias suppression method for a dual active bridge converter as claimed in claim 1, characterized in that: In step S1, the distribution coefficient p The expression is: ， N tr is the transformer primary-to-secondary turns ratio, L ' s is the secondary leakage inductance equivalent to the primary side, U p is the primary voltage, U s is the secondary voltage, L p is the primary side leakage inductance.

3. A DC bias suppression method for a dual active bridge converter as claimed in claim 2, characterized in that: In step S1, the phase shift angle before the change is φ 1 is divided into two parts, pφ 1 is assigned to the switch of the primary side, and the angle (1- p ) φ 1 is assigned to the switch on the secondary side, and the original secondary side shifts phase to the left and right directions respectively, among which the phase shift angle before the change is φ 1 is equal to D 1 T , T is half a switching cycle.

4. A DC bias suppression method for a dual active bridge converter as claimed in claim 3, characterized in that: In step S3, the transient phase shift angle φ int Divide into two parts, pφ int Assigned to the switch of the primary side, the angle (1- p ) φ int The switches assigned to the secondary side shift the phase of the original secondary side to the left and right directions respectively, where the transient phase shift angle φ int equal D int T .

5. A DC bias suppression method for a dual active bridge converter as claimed in claim 4, characterized in that: Also included, according to the distribution coefficient p or transient shift D int The output PWM signal drives the switches in the dual active bridge converter.

6. A DC bias suppression method for a dual active bridge converter as claimed in claim 5, characterized in that: Also included is that the duty cycle of the PWM signal is 0.

5.

7. A dual active bridge converter, characterized in that: A DC bias suppression method for a dual active bridge converter as described in any one of claims 1 to 6, comprising a primary H-bridge, a secondary H-bridge, a transformer, multiple inductors and multiple resistors, wherein the first input terminal and the second input terminal of the primary bridge are connected in parallel with the primary voltage, the first output terminal, the first resistor, the first inductor, the primary winding of the transformer, and the second output terminal of the primary H-bridge are connected in sequence, the first input terminal, the second resistor, the second inductor, the secondary winding of the transformer, and the second input terminal of the secondary H-bridge are connected in sequence, and the first output terminal and the second output terminal of the secondary H-bridge are connected in parallel with the secondary voltage.

8. A dual active bridge converter as claimed in claim 7, characterized in that: According to the distribution coefficient p or transient shift D int Generates PWM signals to the switches of the dual active bridge converter.

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