Three-phase dual-active bridge converter and DC bias elimination method thereof

Abstract

The invention discloses a three-phase dual-active bridge converter and a DC bias elimination method thereof, and belongs to the technical field of power electronic converters, and the method comprises the steps: extracting DC bias components of each phase current of a primary side and a secondary side; performing proportional-integral adjustment on the direct-current bias component of each phase of current of the primary side and the secondary side to obtain the variable quantity of the duty ratio of each phase of bridge arm of the primary side and the secondary side; and adding the variable quantity of the duty ratio of each phase bridge arm of the primary side and the secondary side with the original duty ratio of each phase bridge arm, and modulating to obtain a pulse width modulation signal to be output to a switch in the three-phase dual-active bridge converter. According to the three-phase dual-active bridge converter and the DC bias elimination method thereof, the hardware cost can be saved; direct current bias generated by exciting current of the transformer can be eliminated in real time through closed-loop control, and excessive design and saturation of a magnetic device are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and in particular to a three-phase dual active bridge converter and a DC bias elimination method thereof. Background Art

[0002] The three-phase dual active bridge (DAB3) converter is one of the most promising DC-DC converters for high-power applications. It has advantages such as electrical isolation, bidirectional power transmission, and a wide soft switching range. It is widely used in electric vehicles, new energy power generation and other fields.

[0003] The medium- and high-frequency solid-state transformer based on three-phase dual active bridge significantly reduces the weight and volume of the transformer, but preventing the transformer core from saturating has become one of the key challenges to ensure the safe operation of the solid-state transformer.

[0004] In practical applications, factors such as unequal dead time, drive delay mismatch, deviations in semiconductor device forward characteristics, and DC bus voltage harmonics can cause DC bias in the transformer flux linkage. Because the magnetizing inductance is typically large and the winding resistance is small, the damping effect of the DC bias is weak, causing the bias to gradually accumulate, leading to additional power loss, core saturation, and malfunction of the power electronic converter.

[0005] However, detecting and eliminating DC offset in three-phase dual-active bridge converters is complex. Measuring three-phase flux or current significantly increases the number of sensors required, and the DC flux offset for all phases must be corrected simultaneously. Existing methods for eliminating DC offset often require numerous sensors and complex calculations. Summary of the Invention

[0006] The present invention aims to provide a three-phase dual-active bridge converter and a DC bias elimination method thereof, which only requires two current sensors and is simple to calculate; and can also adapt to bidirectional power transmission conditions.

[0007] To achieve the above object, the technical solution of the present invention is:

[0008] A method for eliminating DC bias of a three-phase dual active bridge converter comprises: step S1, extracting DC bias components of each phase current of the primary side and the secondary side;

[0009] Step S2, performing proportional-integral adjustment on the DC bias components of the primary and secondary phase currents to obtain the duty cycle changes of the primary and secondary phase bridge arms;

[0010] Step S3: Add the change in duty cycle of each phase bridge arm of the primary side and the secondary side to the original duty cycle of each phase bridge arm, modulate the obtained pulse width modulation signal and output it to the switch in the three-phase dual active bridge converter.

[0011] Furthermore, the step S1 includes: step S11, sampling the primary DC bus current i at six sampling moments in one switching cycle T. pDC , where the six sampling moments of the primary side are t1, t1+1 / 6T, t1+1 / 3T, t1+1 / 2T, t1+2 / 3T, and t1+5 / 6T. The value range of the first sampling moment t1 of the primary side is 0 to 1 / 6T;

[0012] Step S12: sampling the secondary DC bus current i at six sampling moments within a switching cycle T. sDC , where the six sampling moments of the secondary side are t2, t2+1 / 6T, t2+1 / 3T, t2+1 / 2T, t2+2 / 3T, and t2+5 / 6T. The value range of the first sampling moment t2 of the secondary side is 0~1 / 6T;

[0013] Step S13 , obtaining the DC bias components of each phase current on the primary side and the secondary side according to the primary DC bus current and the secondary DC bus current at each sampling moment.

[0014] Furthermore, the DC bias component i of the primary first phase current pMA_DC The calculation formula is as follows:

[0015]

[0016] Among them, i pDC (t1) is the primary DC bus current at the first sampling moment, is the primary DC bus current at the fourth sampling moment;

[0017] The DC bias component i of the primary second phase current pMB_DC The calculation formula is as follows:

[0018]

[0019] in, is the primary DC bus current at the second sampling moment, is the primary DC bus current at the fifth sampling moment;

[0020] The DC bias component i of the primary third phase current pMC_DC The calculation formula is as follows:

[0021]

[0022] Among them, is the primary DC bus current at the third sampling moment, is the primary DC bus current at the sixth sampling moment;

[0023] The DC bias component i of the secondary first phase current sMA_DC The calculation formula is as follows:

[0024]

[0025] Among them, i sDC (t2) is the secondary DC bus current at the first sampling moment, is the secondary DC bus current at the fourth sampling moment;

[0026] The DC bias component i of the secondary side second phase current sMB_DC The calculation formula is as follows:

[0027]

[0028] in, is the secondary DC bus current at the second sampling moment, is the secondary DC bus current at the fifth sampling moment;

[0029] The DC bias component i of the secondary third phase current sMC_DC The calculation formula is as follows:

[0030]

[0031] in, is the secondary DC bus current at the third sampling moment, is the secondary DC bus current at the sixth sampling moment.

[0032] Furthermore, the step S2 includes: pMA_DC After comparing with the target value, the change in duty cycle of the primary first phase bridge arm ΔD is obtained through the proportional link and the integral link. pA ; The DC bias component i of the primary second phase current pMB_DC After comparing with the target value, the change in duty cycle of the primary side second phase bridge arm ΔD is obtained through the proportional link and the integral link. pB ; The DC bias component i of the primary third phase current pMC_DC After comparing with the target value, the change in duty cycle of the primary third-phase bridge arm ΔD is obtained through the proportional link and the integral link. pC ; The DC bias component i of the secondary first phase current sMA_DC After comparing with the target value, the change in the duty cycle of the first phase bridge arm of the secondary side ΔD is obtained through the proportional link and the integral link. sA ; The DC bias component i of the secondary side second phase current sMB_DC After comparing with the target value, the change in the duty cycle of the secondary side second phase bridge arm ΔD is obtained through the proportional link and the integral link. sB; The DC bias component i of the secondary third phase current sMC_DC After comparing with the target value, the change in the duty cycle of the secondary side third phase bridge arm ΔD is obtained through the proportional link and the integral link. sC .

[0033] Furthermore, the step S3 includes: changing the duty cycle change ΔD of the primary first phase bridge arm pA The original duty cycle D of the first phase bridge arm of the primary side pA Add, modulate and get the pulse width modulation signal to output to the switch of the first phase bridge arm of the primary side; change the duty cycle of the second phase bridge arm of the primary side ΔD pB The original duty cycle D of the second phase bridge arm of the primary side pB Add, modulate and get the pulse width modulation signal to output to the switch of the second phase bridge arm of the primary side; change the duty cycle of the third phase bridge arm of the primary side ΔD pC The original duty cycle D of the primary third phase bridge arm pC Add, modulate and get the pulse width modulation signal to output to the switch of the third phase bridge arm of the primary side; change the duty cycle of the first phase bridge arm of the secondary side ΔD sA The original duty cycle D of the first phase bridge arm of the secondary side sA Add, modulate and get the pulse width modulation signal to output to the switch of the first phase bridge arm of the secondary side; change the duty cycle of the second phase bridge arm of the secondary side ΔD sB The original duty cycle D of the second phase bridge arm of the secondary side sB Add, modulate and get the pulse width modulation signal to output to the switch of the second phase bridge arm of the secondary side; change the duty cycle of the third phase bridge arm of the secondary side ΔD sC The original duty cycle D of the secondary third phase bridge arm sC The pulse width modulation signal is added and modulated to output to the switch of the third phase bridge arm on the secondary side.

[0034] In a specific embodiment, the original duty cycle D of the primary first phase bridge arm is pA , the original duty cycle D of the second phase bridge arm of the primary side pB , the original duty cycle D of the primary third phase bridge arm pC , the original duty cycle D of the first phase bridge arm of the secondary side sA , the original duty cycle D of the secondary side second phase bridge arm sB , the original duty cycle D of the secondary side third phase bridge arm sC The values are the same.

[0035] In a specific embodiment, the original duty cycle D of the primary first phase bridge arm is pA , the original duty cycle D of the second phase bridge arm of the primary side pB , the original duty cycle D of the primary third phase bridge arm pC , the original duty cycle D of the first phase bridge arm of the secondary side sA, the original duty cycle D of the secondary side second phase bridge arm sB , the original duty cycle D of the secondary side third phase bridge arm sC The value of is 0.5.

[0036] In a specific embodiment, a current sensor is placed at each of the DC bus capacitors on the primary side and the secondary side to detect the DC bus current.

[0037] The present invention also provides a three-phase dual-active bridge converter, which uses the above-mentioned DC bias elimination method for the three-phase dual-active bridge converter, including a primary-side conversion module, a voltage transformation module, a secondary-side conversion module, a primary-side DC bus capacitor and a secondary-side DC bus capacitor. The primary DC voltage, the primary-side conversion module, the voltage transformation module, the secondary-side conversion module, and the secondary-side DC voltage are connected in sequence. The primary DC bus capacitor is connected in parallel between the primary DC voltage and the primary conversion module, and the secondary DC bus capacitor is connected in parallel between the secondary-side conversion module and the secondary-side DC voltage.

[0038] Furthermore, the primary side conversion module includes a primary side first phase bridge arm, a primary side second phase bridge arm, and a primary side third phase bridge arm, and the primary side first phase bridge arm, the primary side second phase bridge arm, and the primary side third phase bridge arm are connected in parallel; the secondary side conversion module includes a secondary side first phase bridge arm, a secondary side second phase bridge arm, and a secondary side third phase bridge arm, and the secondary side first phase bridge arm, the secondary side second phase bridge arm, and the secondary side third phase bridge arm are connected in parallel.

[0039] Beneficial effects: The present invention provides a three-phase dual-active bridge converter and a DC bias elimination method thereof. The DC bus current of the primary and secondary sides is sampled at several specific moments within a cycle through current sensors; the DC bias components of each phase bridge arm are extracted through these sampling points; the DC bias components are then PI-adjusted to obtain the duty cycle of each phase bridge arm, thereby eliminating the DC bias generated by the transformer's excitation current. The present invention can extract the three-phase DC bias components through two current sensors on the primary and secondary sides, which can save hardware costs; the DC bias generated by the transformer's excitation current can be eliminated in real time through closed-loop control, avoiding overdesign and saturation of magnetic devices; and the calculation method of the DC bias component is simple, which can improve the control response speed.

[0040] In order to make the above features and advantages of the present invention more clearly understood, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The diagram is a circuit diagram of a three-phase dual active bridge converter according to the present invention.

[0042] Figure 2 The present invention provides a control block diagram of a method for eliminating DC bias of a three-phase dual active bridge converter.

[0043] Figure 3 Schematic diagram of the six sampling moments of the primary side and the secondary side.

[0044] Figure 4 The experimental waveforms of the primary DC bus current and phase current before and after adopting this method are shown in the figure below: The primary DC voltage is 200V, the secondary DC voltage is 400V, and the power flows from the primary to the secondary.

[0045] Figure 5 The experimental waveforms of the primary DC bus current and phase current before and after adopting this method are shown in the figure below: The primary DC voltage is 200V, the secondary DC voltage is 360V, and the power flows from the primary to the secondary.

[0046] Figure 6 The primary DC voltage is 220V, the secondary DC voltage is 400V, and the power flows from the secondary to the primary. The experimental waveforms of the primary DC bus current and phase current before and after adopting this method are shown. DETAILED DESCRIPTION

[0047] To make the purpose and technical solutions of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] The present application provides a method for eliminating a DC bias of a three-phase dual-active bridge converter, which is applied to a three-phase dual-active bridge converter.

[0049] Figure 1 FIG. 1 is a circuit diagram of a three-phase dual active bridge converter according to the present invention. Figure 1 As shown, the present invention is a three-phase dual active bridge converter comprising a primary side conversion module 1, a voltage transformation module 2 and a secondary side conversion module 3, the primary side DC voltage U p , primary side conversion module 1, transformer module 2, secondary side conversion module 3, secondary side DC voltage U s Connect in sequence.

[0050] Optionally, the three-phase dual active bridge converter of the present invention may further include a capacitor C p , capacitor C p Connected in parallel with the primary DC voltage U p Between the primary side conversion module 1. Among them, the capacitor C p is the primary DC bus capacitance.

[0051] Optionally, the three-phase dual active bridge converter of the present invention may further include a capacitor Cs , capacitor C s Connected in parallel to the secondary side conversion module 3 and the secondary side DC voltage U s Among them, the capacitor C s is the DC bus capacitance on the secondary side.

[0052] Furthermore, the primary side conversion module 1 includes a primary side first phase bridge arm 11, a primary side second phase bridge arm 12, and a primary side third phase bridge arm 13, which are connected in parallel.

[0053] Furthermore, the secondary side conversion module 3 includes a secondary side first phase bridge arm 31, a secondary side second phase bridge arm 32, and a secondary side third phase bridge arm 33, which are connected in parallel.

[0054] Furthermore, the transformer module 2 includes a first phase inductor L ka , the second phase inductance L kb , the third phase inductor L kc , first phase transformer T a , the second phase transformer T b , third phase transformer T c The midpoint of the primary first phase bridge arm 11 passes through the first phase inductor L ka Connect the first phase transformer T a The first end of the primary winding, the midpoint of the primary second phase bridge arm 12 passes through the second phase inductor L kb Connect the second phase transformer T b The first end of the primary winding, the middle point of the primary third phase bridge arm 13 passes through the third phase inductor L kc Connect the third phase transformer T c The first end of the primary winding of the first phase transformer T a The second end of the primary winding and the second phase transformer T b The second end of the primary winding and the third phase transformer T c The second end of the primary winding of the first phase transformer T a The first end of the secondary winding is connected to the midpoint of the bridge arm of the secondary first phase bridge arm 31, and the second phase transformer T b The first end of the secondary winding is connected to the middle point of the bridge arm of the secondary second phase bridge arm 32, and the third phase transformer T c The first end of the secondary winding is connected to the middle point of the bridge arm of the secondary third phase bridge arm 33, and the first phase transformer T a The second end of the secondary winding, the second phase transformer T b The second end of the secondary winding and the third phase transformer T c The second end of the secondary winding is connected.

[0055] Optionally, the primary first phase bridge arm 11 includes a switch Q1 and a switch Q2, and the switch Q1 and the switch Q2 are connected in series.

[0056] Optionally, the primary second phase bridge arm 12 includes a switch Q3 and a switch Q4, and the switch Q3 and the switch Q4 are connected in series.

[0057] Optionally, the primary third-phase bridge arm 13 includes a switch Q5 and a switch Q6, and the switch Q5 and the switch Q6 are connected in series.

[0058] Optionally, the secondary first phase bridge arm 31 includes a switch Q7 and a switch Q8 , and the switch Q7 and the switch Q8 are connected in series.

[0059] Optionally, the secondary side second phase bridge arm 32 includes a switch Q9 and a switch Q10, and the switch Q9 and the switch Q10 are connected in series.

[0060] Optionally, the secondary third phase bridge arm 33 includes a switch Q11 and a switch Q12 , and the switch Q11 and the switch Q12 are connected in series.

[0061] Furthermore, switches Q1 to Q6 form a three-phase full-bridge topology on the primary side; switches Q7 to Q12 form a three-phase full-bridge topology on the secondary side.

[0062] More specifically, N tr Represents the first phase transformer T a , the second phase transformer T b , third phase transformer T c turns ratio.

[0063] More specifically, i pDC Represents the primary DC bus current, i sDC Indicates the secondary DC bus current.

[0064] More specifically, i pa 、i pb 、i pc Represent the phase current of the first phase of the primary side, the phase current of the second phase of the primary side, and the phase current of the third phase of the primary side respectively; i sa 、i sb 、i sc They represent the phase current of the first phase of the secondary side, the phase current of the second phase of the secondary side, and the phase current of the third phase of the secondary side respectively.

[0065] Figure 2 A control block diagram of a method for eliminating DC offset of a three-phase dual active bridge converter according to the present invention is shown. The method for eliminating DC offset of a three-phase dual active bridge converter according to the present invention includes steps S1 to S3.

[0066] Step S1: extracting the DC bias components of the primary and secondary phase currents.

[0067] The DC bias component represents the component of the excitation current DC bias on the primary side or the secondary side.

[0068] Step S2: The DC bias components of the primary and secondary phase currents are adjusted by proportional integral (PI) to obtain the change in duty cycle of the primary and secondary phase bridge arms.

[0069] In step S3, the change in the duty cycle of each phase bridge arm of the primary side and the secondary side is added to the original duty cycle of each phase bridge arm, and a pulse width modulation (PWM) signal is obtained through modulation and output to the switch in the three-phase dual active bridge converter to achieve DC bias elimination.

[0070] Furthermore, the step S1 specifically includes steps S11 to S13.

[0071] Step S11: sampling the primary DC bus current i at six sampling moments within a switching cycle T. pDC , where the six sampling moments of the primary side are t1, t1+1 / 6T, t1+1 / 3T, t1+1 / 2T, t1+2 / 3T, and t1+5 / 6T, and the value range of the first sampling moment t1 of the primary side is 0 to 1 / 6T.

[0072] The first sampling time t1 of the primary side may be any time between 0 and 1 / 6T.

[0073] More specifically, in step S11, the primary DC bus current i at the first sampling moment is obtained. pDC (t1), the primary DC bus current at the second sampling moment Primary DC bus current at the third sampling moment Primary DC bus current at the fourth sampling moment Primary DC bus current at the fifth sampling moment Primary DC bus current at the sixth sampling moment

[0074] Step S12: sampling the secondary DC bus current i at six sampling moments within a switching cycle T. sDC , where the six sampling moments of the secondary side are t2, t2+1 / 6T, t2+1 / 3T, t2+1 / 2T, t2+2 / 3T, and t2+5 / 6T, and the value range of the first sampling moment t2 of the secondary side is 0~1 / 6T.

[0075] The first sampling time t2 of the secondary side is any time within the same 1 / 6T as the first sampling time t1 of the primary side.

[0076] More specifically, in step S12, the secondary DC bus current i at the first sampling moment is obtained.sDC (t2), the secondary DC bus current at the second sampling moment Secondary DC bus current at the third sampling moment Secondary DC bus current at the fourth sampling moment Secondary DC bus current at the fifth sampling moment Secondary DC bus current at the sixth sampling moment

[0077] Figure 3 Six sampling moments of the primary and secondary sides are shown, where is the primary DC bus current i pDC and the secondary DC bus current i sDC The phase angle between.

[0078] Step S13 , obtaining the DC bias components of each phase current on the primary side and the secondary side according to the primary DC bus current and the secondary DC bus current at each sampling moment.

[0079] More specifically, the DC bias component i of the primary first phase current pMA_DC The calculation formula is as follows:

[0080]

[0081] More specifically, the DC bias component of the primary second phase current i pMB_DC The calculation formula is as follows:

[0082]

[0083] More specifically, the DC bias component of the primary third phase current i pMC_DC The calculation formula is as follows:

[0084]

[0085] More specifically, the DC bias component i of the secondary first phase current sMA_DC The calculation formula is as follows:

[0086]

[0087] More specifically, the DC bias component of the secondary second phase current i sMB_DC The calculation formula is as follows:

[0088]

[0089] More specifically, the DC bias component of the secondary third phase current i sMC DC The calculation formula is as follows:

[0090]

[0091] Optionally, in step S1 , the DC bus current may be detected by placing a current sensor near the DC bus capacitors of the primary side and the secondary side respectively.

[0092] Furthermore, the step S2 includes: pMA_DC After comparing with the target value, the change in duty cycle of the primary first phase bridge arm ΔD is obtained through the proportional link and the integral link. pA .

[0093] Optionally, the target value may be 0.

[0094] Furthermore, the step S2 further includes: pMB_DC After comparing with the target value, the change in duty cycle of the primary side second phase bridge arm ΔD is obtained through the proportional link and the integral link. pB .

[0095] Optionally, the target value may be 0.

[0096] Furthermore, the step S2 further includes: pMC_DC After comparing with the target value, the change in duty cycle of the primary third-phase bridge arm ΔD is obtained through the proportional link and the integral link. pC .

[0097] Optionally, the target value may be 0.

[0098] Furthermore, the step S2 includes: sMA_DC After comparing with the target value, the change in the duty cycle of the first phase bridge arm of the secondary side ΔD is obtained through the proportional link and the integral link. sA .

[0099] Optionally, the target value may be 0.

[0100] Furthermore, the step S2 further includes: sMB_DC After comparing with the target value, the change in the duty cycle of the secondary side second phase bridge arm ΔD is obtained through the proportional link and the integral link. sB .

[0101] Optionally, the target value may be 0.

[0102] Furthermore, the step S2 further includes: sMC_DC After comparing with the target value, the change in the duty cycle of the secondary side third phase bridge arm ΔD is obtained through the proportional link and the integral link.sC .

[0103] Optionally, the target value may be 0.

[0104] Furthermore, the step S3 includes: changing the duty cycle change ΔD of the primary first phase bridge arm pA The original duty cycle D of the first phase bridge arm of the primary side pA The pulse width modulation signal is added and modulated to output to the switch of the first phase bridge arm of the primary side.

[0105] Furthermore, the step S3 further includes: changing the duty cycle change ΔD of the primary side second phase bridge arm pB The original duty cycle D of the second phase bridge arm of the primary side pB The pulse width modulation signal is added and modulated to output to the switch of the second phase bridge arm of the primary side.

[0106] Furthermore, the step S3 further includes: changing the duty cycle change ΔD of the primary third phase bridge arm pC The original duty cycle D of the primary third phase bridge arm pC The pulse width modulation signal is added and modulated to output to the switch of the third phase bridge arm of the primary side.

[0107] Furthermore, the step S3 further includes: changing the duty cycle change ΔD of the first phase bridge arm of the secondary side sA The original duty cycle D of the first phase bridge arm of the secondary side sA The pulse width modulation signal is added and modulated to output to the switch of the first phase bridge arm of the secondary side.

[0108] Furthermore, the step S3 further includes: changing the duty cycle change ΔD of the secondary side second phase bridge arm sB The original duty cycle D of the second phase bridge arm of the secondary side sB The pulse width modulation signal is added and modulated to output to the switch of the second phase bridge arm of the secondary side.

[0109] Furthermore, the step S3 further includes: changing the duty cycle change ΔD of the secondary side third phase bridge arm sC The original duty cycle D of the secondary third phase bridge arm sC The pulse width modulation signal is added and modulated to output to the switch of the third phase bridge arm on the secondary side.

[0110] More specifically, the original duty cycle D of the primary first phase bridge arm pA , the original duty cycle D of the second phase bridge arm of the primary side pB , the original duty cycle D of the primary third phase bridge arm pC , the original duty cycle D of the first phase bridge arm of the secondary side sA , the original duty cycle D of the secondary side second phase bridge arm sB, the original duty cycle D of the secondary side third phase bridge arm sC is the steady-state duty cycle.

[0111] Optionally, the original duty cycle D of the primary first phase bridge arm pA , the original duty cycle D of the second phase bridge arm of the primary side pB , the original duty cycle D of the primary third phase bridge arm pC , the original duty cycle D of the first phase bridge arm of the secondary side sA , the original duty cycle D of the secondary side second phase bridge arm sB , the original duty cycle D of the secondary side third phase bridge arm sC The values can be the same.

[0112] In a specific embodiment, the original duty cycle D of the primary first phase bridge arm is pA , the original duty cycle D of the second phase bridge arm of the primary side pB , the original duty cycle D of the primary third phase bridge arm pC , the original duty cycle D of the first phase bridge arm of the secondary side sA , the original duty cycle D of the secondary side second phase bridge arm sB , the original duty cycle D of the secondary side third phase bridge arm sC The value of is 0.5.

[0113] More specifically, the driving signals of the two switches in the same phase bridge arm are complementary.

[0114] As can be seen from the above, the DC offset elimination method of the three-phase dual active bridge converter of the present invention performs closed-loop regulation on the extracted DC offset component, thereby eliminating the DC offset generated by the excitation current.

[0115] Furthermore, the total DC bias can be obtained by adding the DC bias component of the primary side of each phase current to the DC bias component of the secondary side and returning them to the value of the primary side.

[0116] In order to verify the feasibility of the DC bias elimination method of the three-phase dual active bridge converter of the present invention, an experimental verification was carried out on a hardware platform built in the laboratory. The simulation prototype parameters are as follows: primary DC voltage U p is 200V, the secondary DC voltage U s is 400V, the excitation inductance L m is 380uH, leakage inductance L k is 7.9uH, the transformer turns ratio N tr is 0.5, the equivalent resistance R is 60mΩ, and the switching frequency f s The frequency is 20kHz, the rated power P is 4.35kW, the proportional gain Kp of the PI regulator is 0.0251, and the integral gain Ki of the PI regulator is 0.1579. The key waveforms are as follows: Figure 4 、 Figure 5 、 Figure 6 shown.

[0117] During the experiment, the duty cycle error will induce a DC component, where the duty cycle errors of the primary-side bridge arms are D pa_err = +0.2%, D pb_err =0%, D pc_err =0.1%, the duty cycle errors of the secondary bridge arm are D sa_err =0%, D sb_err = +0.2%, D sc_err =0.1%. Figure 4 、 Figure 5 、 Figure 6 As shown, when there is a duty cycle error, at different voltage ratios d=U s / (U p *N tr ) conditions, whether it is forward power transmission or reverse power transmission, the ripple of the phase current and DC bus current will increase, resulting in increased losses. However, once the method proposed in this application is adopted, the current switching ripple can be quickly compensated, achieving three-phase current balance and significantly reducing the bus current ripple. For example Figure 4 The DC bus current ripple dropped from 10.4A to 4.4A, a 57.7% reduction, indicating that the DC bias in the excitation current was completely eliminated. Furthermore, the proposed method also completely eliminated the harsh noise generated by the transformer as it approached saturation.

[0118] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown in sequence as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least some of the steps in the accompanying drawings may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The order of execution of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

[0119] Although the present invention has been disclosed above with reference to the embodiments, they are not intended to limit the present invention. Anyone with ordinary skill in the art may make slight changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope of the appended patent applications.

Claims

1. A method for eliminating DC bias of a three-phase dual active bridge converter, characterized in that: include, Step S1, extracting the DC bias component of each phase current of the primary side and the secondary side; Step S2, performing proportional-integral adjustment on the DC bias components of the primary and secondary phase currents to obtain the duty cycle changes of the primary and secondary phase bridge arms; Step S3: Add the change in duty cycle of each phase bridge arm of the primary side and the secondary side to the original duty cycle of each phase bridge arm, modulate the obtained pulse width modulation signal and output it to the switch in the three-phase dual active bridge converter.

2. A method for eliminating DC bias of a three-phase dual active bridge converter according to claim 1, characterized in that: The step S1 includes: Step S11: sampling the primary DC bus current i at six sampling moments within a switching cycle T. pDC , where the six sampling moments of the primary side are t1, t1+1 / 6T, t1+1 / 3T, t1+1 / 2T, t1+2 / 3T, and t1+5 / 6T. The value range of the first sampling moment t1 of the primary side is 0 to 1 / 6T; Step S12: sampling the secondary DC bus current i at six sampling moments within a switching cycle T. sDC , where the six sampling moments of the secondary side are t2, t2+1 / 6T, t2+1 / 3T, t2+1 / 2T, t2+2 / 3T, and t2+5 / 6T. The value range of the first sampling moment t2 of the secondary side is 0~1 / 6T; Step S13 , obtaining the DC bias components of each phase current on the primary side and the secondary side according to the primary DC bus current and the secondary DC bus current at each sampling moment.

3. The method for eliminating DC bias of a three-phase dual active bridge converter according to claim 2, wherein: The DC bias component i of the primary first phase current pMA_DC The calculation formula is as follows: Among them, i pDC (t1) is the primary DC bus current at the first sampling moment, is the primary DC bus current at the fourth sampling moment; The DC bias component i of the primary second phase current pMB_DC The calculation formula is as follows: in, is the primary DC bus current at the second sampling moment, is the primary DC bus current at the fifth sampling moment; The DC bias component i of the primary third phase current pMC_DC The calculation formula is as follows: in, is the primary DC bus current at the third sampling moment, is the primary DC bus current at the sixth sampling moment; The DC bias component i of the secondary first phase current sMA_DC The calculation formula is as follows: Among them, i sDC (t2) is the secondary DC bus current at the first sampling moment, is the secondary DC bus current at the fourth sampling moment; The DC bias component i of the secondary side second phase current sMB_DC The calculation formula is as follows: in, is the secondary DC bus current at the second sampling moment, is the secondary DC bus current at the fifth sampling moment; The DC bias component i of the secondary third phase current sMC_DC The calculation formula is as follows: in, is the secondary DC bus current at the third sampling moment, is the secondary DC bus current at the sixth sampling moment.

4. A method for eliminating DC bias of a three-phase dual active bridge converter as claimed in claim 3, characterized in that: The step S2 includes: pMA_DC After comparing with the target value, the change in duty cycle of the primary first phase bridge arm ΔD is obtained through the proportional link and the integral link. pA ; The DC bias component i of the primary second phase current pMB_DC After comparing with the target value, the change in duty cycle of the primary side second phase bridge arm ΔD is obtained through the proportional link and the integral link. pB ; The DC bias component i of the primary third phase current pMC_DC After comparing with the target value, the change in duty cycle of the primary third-phase bridge arm ΔD is obtained through the proportional link and the integral link. pC ; The DC bias component i of the secondary first phase current sMA_DC After comparing with the target value, the change in the duty cycle of the first phase bridge arm of the secondary side ΔD is obtained through the proportional link and the integral link. sA ; The DC bias component i of the secondary side second phase current sMB_DC After comparing with the target value, the change in the duty cycle of the secondary side second phase bridge arm ΔD is obtained through the proportional link and the integral link. sB ; The DC bias component i of the secondary third phase current sMC_DC After comparing with the target value, the change in the duty cycle of the secondary side third phase bridge arm ΔD is obtained through the proportional link and the integral link. sC .

5. A method for eliminating DC bias of a three-phase dual active bridge converter as claimed in claim 4, characterized in that: The step S3 includes: changing the duty cycle of the first phase bridge arm of the primary side ΔD pA The original duty cycle D of the first phase bridge arm of the primary side pA The pulse width modulation signal is added and modulated to output to the switch of the first phase bridge arm of the primary side; The change in duty cycle of the second phase bridge arm of the primary side ΔD pB The original duty cycle D of the second phase bridge arm of the primary side pB The pulse width modulation signal is added and modulated to output to the switch of the second phase bridge arm of the primary side; The change in duty cycle of the primary third-phase bridge arm ΔD pC The original duty cycle D of the primary third phase bridge arm pC The pulse width modulation signal is added and modulated to output to the switch of the third phase bridge arm of the primary side; The change in the duty cycle of the first phase bridge arm of the secondary side ΔD sA The original duty cycle D of the first phase bridge arm of the secondary side sA The pulse width modulation signal is added and modulated to output to the switch of the first phase bridge arm of the secondary side; The change in the duty cycle of the second phase bridge arm of the secondary side ΔD sB The original duty cycle D of the second phase bridge arm of the secondary side sB The pulse width modulation signal is added and modulated to output to the switch of the second phase bridge arm of the secondary side; The change in the duty cycle of the secondary third-phase bridge arm ΔD sC The original duty cycle D of the secondary third phase bridge arm sC The pulse width modulation signal is added and modulated to output to the switch of the third phase bridge arm on the secondary side.

6. A method for eliminating DC bias of a three-phase dual active bridge converter as claimed in claim 5, characterized in that: The original duty cycle D of the first phase bridge arm of the primary side pA , the original duty cycle D of the second phase bridge arm of the primary side pB , the original duty cycle D of the primary third phase bridge arm pC , the original duty cycle D of the first phase bridge arm of the secondary side sA , the original duty cycle D of the secondary side second phase bridge arm sB , the original duty cycle D of the secondary side third phase bridge arm sC The values are the same.

7. A method for eliminating DC bias of a three-phase dual active bridge converter according to claim 6, characterized in that: The original duty cycle D of the first phase bridge arm of the primary side pA , the original duty cycle D of the second phase bridge arm of the primary side pB , the original duty cycle D of the primary third phase bridge arm pC , the original duty cycle D of the first phase bridge arm of the secondary side sA , the original duty cycle D of the secondary side second phase bridge arm sB , the original duty cycle D of the secondary side third phase bridge arm sC The value of is 0.

5.

8. The method for eliminating DC bias of a three-phase dual active bridge converter according to claim 2, wherein: The DC bus current is detected by placing a current sensor at the DC bus capacitor on the primary side and the secondary side respectively.

9. A three-phase dual active bridge converter, characterized in that: A method for eliminating DC bias of a three-phase dual-active bridge converter according to any one of claims 1 to 8 is applied, comprising a primary conversion module, a voltage transformation module, a secondary conversion module, a primary DC bus capacitor, and a secondary DC bus capacitor, wherein the primary DC voltage, the primary conversion module, the voltage transformation module, the secondary conversion module, and the secondary DC voltage are connected in sequence, the primary DC bus capacitor is connected in parallel between the primary DC voltage and the primary conversion module, and the secondary DC bus capacitor is connected in parallel between the secondary conversion module and the secondary DC voltage.

10. A three-phase dual active bridge converter as claimed in claim 9, characterized in that: The primary side conversion module includes a primary side first phase bridge arm, a primary side second phase bridge arm, and a primary side third phase bridge arm, wherein the primary side first phase bridge arm, the primary side second phase bridge arm, and the primary side third phase bridge arm are connected in parallel; The secondary side conversion module includes a secondary side first phase bridge arm, a secondary side second phase bridge arm, and a secondary side third phase bridge arm, and the secondary side first phase bridge arm, the secondary side second phase bridge arm, and the secondary side third phase bridge arm are connected in parallel.

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