Soft switching modulation method and system for minimum current stress in full power range

Abstract

The invention discloses a soft switching modulation method and system for minimum current stress in a full power range. The system comprises an expansion phase shift optimization unit, an in-loop direct power control unit and a cooperative control unit. The in-loop direct power control unit is used for obtaining dynamic correction power, the expansion phase shift optimization unit is used for generating a phase shift ratio combination [D1, D2] which simultaneously meets the minimum current stress and the ZVS condition, and the cooperative control unit generates a PWM driving signal according to the generated phase shift ratio combination [D1, D2] to achieve soft switching control. According to the invention, the problem of current stress minimization in a wide voltage range can be effectively solved, the problem of ZVS loss in a light-load working condition can be prevented, and a load / voltage sudden change condition can be coped with in time; through the design of the ZVS boundary guarantee, the method is especially suitable for scenes needing wide voltage range efficient energy transmission, such as new energy grid connection and electric vehicle charging.

Description

Technical Field

[0001] This invention belongs to the field of power electronic converter control technology, specifically relating to a soft-switching modulation method and system with minimum current stress across the entire power range. Background Technology

[0002] Dual active bridge DC-DC converters have become core components of DC microgrids due to their high power density, electrical isolation, and bidirectional energy transfer capabilities. However, traditional modulation strategies based on dual active bridge DC-DC converters have two major drawbacks: 1. Voltage mismatch condition: when the voltage transfer ratio k=V1 / (nV2) is large, the current stress of single phase shift control (SPS) increases sharply, and the soft switching under light load is lost.

[0003] II. Conflict between dynamic response and steady-state performance: Although existing optimization schemes (such as triple phase-shift control) can reduce current stress, the dynamic response delay is obvious.

[0004] In existing technologies, a TPS modulation method is used to control the DAB to achieve adaptive charging and discharging. This method includes: adding the output of the outermost bus voltage loop to the charging (battery) current setting as the setting for the total battery current loop; providing battery current loops and battery voltage loops arranged in parallel; comparing the output values ​​of the battery current loop and the battery voltage loop, and using the output value of the loop with the larger output value as the power setting; adding the power setting to the power feedback to obtain the per-unit power; inputting the per-unit power to the TPS modulation unit to output each relative phase shift angle, and controlling the DAB hardware circuit by controlling each relative phase shift angle.

[0005] However, these existing technical solutions, which use loop competition control, do not solve the problem of current stress optimization under voltage mismatch, and the control becomes unstable when k>2.5.

[0006] Current research has employed a KTT optimization strategy, which achieves minimum current stress, but without dynamic power correction, the output voltage overshoots high during load surges. Given this technical challenge, there is an urgent need for a modulation method that simultaneously ensures minimum current stress, zero-switching (ZVS) across the entire power range, and fast dynamic response. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a soft-switching modulation method and system for minimizing current stress across the full power range of a DAB converter. By performing segmented shift optimization for dynamic power correction and employing ZVS boundary protection design, it effectively solves the following problems: minimizing current stress over a wide voltage range; ZVS loss under light load conditions; and dynamic response delay during load / voltage abrupt changes.

[0008] This invention is achieved by adopting the following technical solution: A soft-switching modulation method with minimum current stress across the entire power range, the modulation steps of which mainly include: Step 1: Utilize the input voltage V1, output voltage V2, and output current. i 0 Combined with reference voltage V 2ref Capacitor voltage change rate dV 2 / d t, calculate the dynamic correction power p and per-unit power p 1:

[0009] Where η is the initial value of efficiency. p o This refers to the output power. Step 2, utilizing voltage transfer ratio k Per-unit power p 1. The calculated combination of displacement ratios that simultaneously satisfies the minimum current stress and ZVS condition is obtained. D 1, D 2], where, D Compared to the original side H bridge being moved inward, 1 D 2 is the bridge displacement comparison;

[0010] in: k = V 1 / ( nV 2), n For transformer turns ratio; P n As a standardization reference value, f For frequency; L It is an inductor; Step 3, based on the shift ratio combination obtained in Step 2 [ D 1, D [2] Generate PWM drive signals to achieve soft switching control.

[0011] At time t1, the corresponding DAB converter switch S2 is off and S4 is on. At this time, the current is negative, and the transformer primary current flows through the diode. VD 1. VD 4. Secondary current flows through the diode VD 7. VD 6. The primary-side H-bridge output voltage becomes V 1. Secondary edge is - V 2. The voltage across the equivalent inductor remains the same. V 1+n V 2. The current is:

[0012] in, i L (t1) represents the inductor current at time t1.

[0013] At time t3, corresponding to the DAB converter switches S6 and S7 being turned off and S5 and S8 being turned on, the current is positive. The primary current of the transformer forms a loop through S1 and S4, and the primary H-bridge output voltage is... V 1. The secondary current of the transformer passes through the diode. VD 5. VD 8. The secondary output voltage becomes V 2. The voltage across the equivalent inductor becomes V 1-n V 2. The inductor current is:

[0014] in, i L (t3) represents the inductor current at time t3.

[0015] Furthermore, the ZVS conditions described in step two include: When the converter operates at 0≤ D 1≤ D In 2≤1 mode, i L (t1)≤0 i L (t3)≥0 Achieve ZVS for all switching transistors, i.e.

[0016] When the converter operates at 0≤ D 2≤ D In 1≤1 mode, i L (t1)≥0 i L (t3)≤0 Achieve ZVS for all switching transistors, i.e.

[0017] Furthermore, the above method also includes a protection mechanism: when D 1>0.95 or D When 2>0.95, pulse blocking is triggered to prevent pulse overlap and shoot-through of different bridge arm switches due to overmodulation.

[0018] To achieve the above method, this invention designs a corresponding soft-switching modulation system with minimum current stress across the entire power range, including an extended phase-shift optimization unit, an in-loop direct power control unit, and a cooperative control unit; The extended phase-shifting optimization unit is used to utilize per-unit power p 1 and voltage transfer ratio k Generate a shift ratio combination that simultaneously satisfies the minimum current stress and ZVS condition. D 1, D 2], of which D Compared to the original side H bridge being moved inward, 1 D 2 is the bridge displacement comparison; The in-loop direct power control unit is used to utilize real-time sampling of the input voltage. V 1. Output voltage V 2. Output current i 0. Reference voltage V 2ref and capacitor voltage change rate dV 2 / d The dynamic correction power is calculated by t. p and per-unit power p 1.

[0019] The collaborative control unit is used to receive D 1 and D 2. Generate PWM drive signals using DSP.

[0020] Furthermore, the extended phase-shifting optimization unit performs the following phase shifts at different power levels: When the converter operates at 0≤ D 1≤ D In the 2≤1 mode, the power range at the moment of maximum current is used as the objective function, and the KTT condition method is used to determine the power range at this moment, i.e., when (2k-2) / k² < p When 1≤1, calculate:

[0021] When the converter operates at 0≤ D 2≤ D In the 1≤1 mode, the power range at the moment of maximum current is used as the objective function, and the KTT condition method is used to determine the power range at this moment, i.e., when (2 k -2) / (3 k -2)²≤ p 1≤(2 k -2) / k When 2, calculate:

[0022] In order to seek pWhen the power is less than the lower limit of the above power range, the optimal shift ratio combination minimizes the current stress. Taking the first current overlap at times t1 and t3 as the objective function, the power range at this point is calculated, i.e., when 0 ≤ p 1≤(2 k -2) / (3 k When -2)², calculate:

[0023]

[0024] Furthermore, the in-loop direct power control unit includes a capacitor current prediction component, which calculates:

[0025] in: i c For capacitor current, K p This is the proportionality coefficient. K i The integral coefficient; Furthermore, the collaborative control unit is equipped with a dynamic emergency module, which is used for simplified emergency relocation processing; specifically, when the input voltage suddenly changes |d V When 1 / dt|>10V / ms, a simplified shift ratio is used: .

[0026] Furthermore, the collaborative control unit is equipped with a hysteresis switching module, which is used to set a power deviation threshold of ±5% to prevent frequent switching between steady-state and dynamic modes.

[0027] Furthermore, the soft-switching modulation system with minimum current stress across the entire power range is also designed with a light-load optimization unit. When the dual active bridge (DAB) converter is in a low-power transmission scenario, it forces control: segmented optimal phase shift angle. D 1 ≥ 0.7, switching frequency f{sw} ≥ 15kHz. Here, the low-power transmission scenario refers to: dynamic power... p The scenario when <0.2.

[0028] Furthermore, the dual active bridge converter using the above method and system can achieve full-load ZVS across the entire power range.

[0029] The beneficial effects of this invention are as follows: This invention can generate a power source that simultaneously satisfies the minimum current stress and ZVS conditions by modifying dynamic power in a piecewise phase-shift optimization manner. D 1 and D2. Provided to the collaborative control unit, the PWM drive signal is generated by the DSP, which can prevent the loss of ZVS under light load conditions and respond to load / voltage change situations in a timely manner; the overall solution can improve power density and reduce switching losses; this invention is particularly suitable for scenarios that require high-efficiency energy transmission with a wide voltage range, such as new energy grid connection and electric vehicle charging. Attached Figure Description

[0030] Figure 1 The converter modulation strategy of this invention.

[0031] Figure 2 This is a block diagram of the DAB converter and system control in this invention. Detailed Implementation

[0032] Example 1 like Figure 1-2 As shown, the present invention designs a soft-switching modulation system with minimum current stress across the entire power range, including an extended phase-shift optimization unit, an in-loop direct power control unit, and a cooperative control unit; The extended phase-shifting optimization unit is used to utilize per-unit power p 1 and voltage transfer ratio k Generate a shift ratio combination that simultaneously satisfies the minimum current stress and ZVS condition. D 1, D 2], of which D Compared to the original side H bridge being moved inward, 1 D 2 is the bridge displacement comparison; The in-loop direct power control unit is used to utilize real-time sampling of the input voltage. V 1. Output voltage V 2. Output current i 0. Reference voltage V 2ref and capacitor voltage change rate dV 2 / d The dynamic correction power is calculated by t. p and per-unit power p 1: The collaborative control unit is used to receive D 1 and D 2. Generate PWM drive signals using DSP.

[0033] Furthermore, the extended phase-shifting optimization unit performs the following phase shifts at different power levels: When the converter operates at 0≤ D 1≤ D In the 2≤1 mode, the power range at the moment of maximum current is used as the objective function, and the KTT condition method is used to determine the power range at this moment, i.e., when (2k-2) / k² < p When 1≤1, calculate:

[0034] When the converter operates at 0≤ D 2≤ D In the 1≤1 mode, the power range at the moment of maximum current is used as the objective function, and the KTT condition method is used to determine the power range at this moment, i.e., when (2 k -2) / (3 k -2)²≤ p 1≤(2 k -2) / k When 2, calculate:

[0035] In order to seek p When the power is less than the lower limit of the above power range, the optimal shift ratio combination minimizes the current stress. Taking the first current overlap at times t1 and t3 as the objective function, the power range at this point is calculated, i.e., when 0 ≤ p 1≤(2 k -2) / (3 k When -2)², calculate:

[0036]

[0037] Furthermore, the in-loop direct power control unit includes a capacitor current prediction component, which calculates:

[0038] in: i c For capacitor current, K p This is the proportionality coefficient. K i The integral coefficient; Furthermore, the collaborative control unit is equipped with a dynamic emergency module, which is used for simplified emergency relocation processing; specifically, when the input voltage suddenly changes |d V When 1 / dt|>10V / ms, a simplified shift ratio is used: .

[0039] Furthermore, the collaborative control unit is equipped with a hysteresis switching module, which is used to set a power deviation threshold of ±5% to prevent frequent switching between steady-state and dynamic modes.

[0040] Furthermore, the soft-switching modulation system with minimum current stress across the entire power range is also designed with a light-load optimization unit. When the dual active bridge (DAB) converter is in a low-power transmission scenario, it forces control: segmented optimal phase shift angle. D1 ≥ 0.7, switching frequency f{sw} ≥ 15kHz. Here, the low-power transmission scenario refers to: dynamic power... p The scenario when <0.2.

[0041] Figure 2 shows the system configuration of the dual active bridge DC-DC converter. V 1. V 2 represents the DC voltage across the converter. C 1. C 2 is the DC-side support capacitor, L is the series inductor, T is the high-frequency transformer with a turns ratio of n:1, the converter's operating frequency is f, and S1-S8 are the switching transistors of the H-bridge.

[0042] The modulation method of the present invention is implemented using the above system as follows: Step S1, parameter initialization: Set the transformer turns ratio n and the initial efficiency value η; Step S2, the sampling circuit acquires signals: the voltage sensor samples the input voltage. V 1. Output voltage V 2; The current sensor samples the inductor current. i L Output current i 0; Step S3, calculate the voltage transfer ratio k = V 1 / n V 2; Step S4, set the reference voltage V 2ref And the sampled in step S2 V The difference between two values ​​is calculated, and the result is input to the PI controller to obtain the capacitor current. i c Combined with output current i 0 and reference voltage V 2ref Calculate output power p 0, further obtaining the dynamically standardized transmission power. p = p 0 / η; Step S5, based on the voltage transfer ratio k Per-unit power p 1. Calculate the optimal phase shift ratio and select the extended phase shift control mode; Step S6, Pulse generation: Based on the shift ratio D 1 and D 2. Output 8 PWM signals that meet the ZVS condition to the H bridge.

[0043] Calculated using the above steps p 1. and determine pThe shift ratio is further calculated in the interval where 1 is located. D 1 and D 2. It can significantly reduce current stress and achieve ZVS for the switching transistor.

[0044] Example 2 Based on the design of Embodiment 1, when the input voltage changes rapidly, the dynamic response module is activated, enabling the voltage to quickly recover and stabilize.

[0045]

[0046] In summary, any other corresponding modulation methods that can be devised by those skilled in the art after reading this invention document without creative mental effort based on the technical solutions and concepts of this invention are all within the scope of protection of this invention.

Claims

1. A soft-switching modulation method with minimum current stress across the entire power range, characterized in that, The modulation steps mainly include: S1 utilizes the input voltage V1, output voltage V2, and output current. i 0 Combined with reference voltage V 2ref Capacitor voltage change rate dV 2 / d t, calculate the dynamic correction power p : Where η is the initial value of efficiency. p 0 represents output power; When the load (|d) i When 0 / dt|) changes abruptly, the phase shift angle is increased. D Temporarily enhance power transmission; cancel the correction after steady-state recovery. S2, utilizing voltage transfer ratio k Per-unit power p 1. The calculated combination of displacement ratios that simultaneously satisfies the minimum current stress and ZVS condition is obtained. D 1, D 2], where, D Compared to the original side H bridge being moved inward, 1 D 2 is the bridge displacement comparison; in: k = V 1 / ( nV 2), n For transformer turns ratio; p n As a standardized baseline value, f For frequency; L It is an inductor; S3, based on the shift ratio combination obtained in step S2 [ D 1, D [2] Generate PWM drive signals to achieve soft switching control.

2. The soft-switching modulation method with minimum current stress across the entire power range according to claim 1, characterized in that, The dynamic correction power p The calculation includes: when the load (|d i When 0 / dt|) changes abruptly, the phase shift angle is increased. D The power transmission is temporarily boosted, and the correction is canceled after steady-state recovery.

3. The soft-switching modulation method with minimum current stress across the entire power range according to claim 1, characterized in that, The ZVS conditions mentioned in step S2 include: When the converter operates at 0≤ D 1≤ D In 2≤1 mode, i L (t1)≤0, i L (t1) represents the inductor current at time t1; i L (t3)≥0, i L (t3) represents the inductor current at time t3; Achieve ZVS for all switching transistors, i.e. When the converter operates at 0≤ D 1≤ D In 2≤1 mode, i L (t1)≥0 i L (t3)≤0 Achieve ZVS for all switching transistors, i.e. Where: at time t1, the corresponding DAB converter switch transistor S 2. Close. S 4. When the diode is turned on, the current is negative, and the primary current of the transformer flows through the diode. VD 1. VD 4. Secondary current flows through the diode VD 7. VD 6. The primary-side H-bridge output voltage becomes V 1. Secondary edge is - V 2. The voltage across the equivalent inductor remains the same. V 1+n V 2. The current is: At time t3, the corresponding DAB converter switch S 6. S 7. Turn off S 5. S 8. When the circuit is turned on, the current is positive, and the primary current of the transformer flows through... S 1. S The primary-side H-bridge output voltage is 4-way circuit. V 1. The transformer secondary current flows through the diode. VD 5. VD 8. The secondary output voltage becomes V 2. The voltage across the equivalent inductor becomes V 1-n V 2. The inductor current is: .

4. The soft-switching modulation method with minimum current stress across the entire power range according to claim 1, characterized in that, The method also includes a protection mechanism: when D 1>0.95 or D When 2>0.95, pulse blocking is triggered to prevent pulse overlap and shoot-through of different bridge arm switches due to overmodulation.

5. A soft-switching modulation system based on the soft-switching modulation method for minimum current stress across the full power range as described in any one of claims 1-4, characterized in that: This includes an extended phase-shifting optimization unit, an in-loop direct power control unit, and a cooperative control unit; The extended phase-shifting optimization unit is used to utilize per-unit power p 1 and voltage transfer ratio k Generate a shift ratio combination that simultaneously satisfies the minimum current stress and ZVS condition. D 1, D 2], of which D Compared to the original side H bridge being moved inward, 1 D 2 is the bridge displacement comparison; The in-loop direct power control unit is used to utilize real-time sampling of the input voltage. V 1. Output voltage V 2. Output current i 0. Reference voltage V 2ref and capacitor voltage change rate dV 2 / d The dynamic correction power is calculated by t. p and per-unit power p 1; The collaborative control unit is used to receive D 1 and D 2. Generate PWM drive signals using DSP.

6. The soft-switching modulation system with minimum current stress across the entire power range according to claim 5, characterized in that: The extended phase-shifting optimization unit shifts the phase at different power levels as follows: When 0≤ p When 1≤(2k-2) / (3k-2)², calculate: When (2k-2) / (3k-2)²≤ p When 1≤(2k-2) / k², calculate: When (2k-2) / k² < p When 1 ≤ 1, calculate: 。 7. The soft-switching modulation system with minimum current stress across the entire power range according to claim 5, characterized in that: The extended move-first unit is equipped with a KTT solver, and the per-unit power... p 1 and voltage transfer ratio k The result was obtained after calculation by the KTT solver. D 1 and D 2.

8. The soft-switching modulation system with minimum current stress across the entire power range according to claim 5, characterized in that: The in-loop direct power control unit includes a capacitor current prediction component, which calculates: in: i c For capacitor current, K p This is the proportionality coefficient. K i is the integral coefficient.

9. The soft-switching modulation system with minimum current stress across the entire power range according to claim 5, characterized in that: The collaborative control unit is equipped with a dynamic emergency module, which responds to sudden changes in input voltage |d V When 1 / dt|>10V / ms, a simplified shift ratio is used: The dynamic emergency module enables simplified mobile emergency response.

10. The soft-switching modulation system with minimum current stress across the entire power range according to claim 5, characterized in that: The collaborative control unit is equipped with a hysteresis switching module, which is used to set a power deviation threshold of ±5% to prevent frequent switching between steady-state and dynamic modes.

11. The soft-switching modulation system with minimum current stress across the entire power range according to claim 5, characterized in that: The system is also equipped with a light-load optimization unit, which forces the DAB converter to achieve segmented optimal phase shift angles when operating in low-power transmission scenarios. D 1≥0.7, switching frequency f{sw}≥15kHz; wherein, the low-power transmission scenario refers to: dynamic power p The scenario when <0.

2.

12. A dual active bridge converter, characterized in that... The system or method described in any one of claims 1-9 is applied, and full-load ZVS is achieved across the full power range.

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