A switching loss optimization control method and system for an energy storage DC converter

Abstract

The application discloses a kind of switch loss optimization control method and system of energy storage DC converter. Including: first, the voltage / current of battery side and bus side of energy storage DC converter is obtained;Then, the voltage ratio of energy storage DC converter two sides is obtained according to battery side voltage and bus side voltage;Then, control power is obtained according to battery side voltage / current and bus side voltage / current;Then, the working mode of double active bridge circuit is determined using the control power of energy storage DC converter;Finally, according to the working mode of double active bridge circuit, the actual power size of double active bridge circuit is adjusted, and the switch loss optimization of energy storage DC converter is completed.When the battery side voltage, bus side voltage and load power of the circuit change, the control power of the controller of the application can continuously change, smooth transition between each working mode is realized, and the output signal and power gain are basically linear, which can improve the dynamic response speed.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion technology, specifically to a method and system for optimizing the switching losses of an energy storage DC-DC converter. Background Technology

[0002] In recent years, energy storage systems have become a hot topic in the field of power electronics, with wide applications in microgrids, electric vehicle charging, and outdoor mobile power supplies. Among the many power electronic DC-DC converter topologies, the dual active bridge (DAB) circuit, due to its wide gain range, electrical isolation, bidirectional energy flow, symmetrical structure, and flexible control, is well-suited to the main application requirements of energy storage systems and is a research hotspot in related fields.

[0003] Currently, phase-shift control is commonly used in the control methods of dual active bridge circuits. By adjusting multiple degrees of freedom in triple phase-shift control, current stress is reduced and soft switching is achieved. In efficiency optimization analysis, the Lagrange multiplier method is often used to calculate the case where the effective value of the inductor current is minimized. However, the optimal solution obtained by this approach may have phase shift jumps under different operating conditions, and it increases control complexity and affects dynamic performance.

[0004] To reduce the complexity of control systems and improve the practicality of dual active bridge circuit control methods, existing technologies, such as the Chinese patent with publication number CN107968571A, disclose a triple phase-shift control method that achieves the optimal solution for current stress through a single control loop. Another example is the Chinese patent with publication number CN113364298A, which utilizes a resonant dual active bridge topology, combining frequency modulation control and single phase-shift control to achieve soft switching across the entire power range. The Chinese patent with publication number CN118473227A optimizes current stress individually based on different operating power levels and achieves continuous control of the system.

[0005] While the aforementioned patents optimize the current stress of dual active bridge circuits or broaden their soft-switching range and reduce control complexity, they often fail to consider circuit turn-off losses. In low-voltage user energy storage scenarios, due to the large current on the low-voltage side, the losses caused by device turn-off account for a much larger proportion than reactive circulating current and hard turn-on, thus the relevant control methods still have shortcomings. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a control method and system for optimizing the efficiency of a dual active bridge converter across the entire power range. This invention combines triple phase-shift control and frequency modulation control to optimize switching losses and reactive circulating current across the bidirectional full power range.

[0007] The technical solution of this invention is:

[0008] I. A method for optimizing the switching losses of an energy storage DC-DC converter

[0009] Step 1: Obtain the battery-side voltage / current and bus-side voltage / current of the energy storage DC-DC converter;

[0010] Step 2: Calculate the voltage ratio on both sides of the energy storage DC-DC converter based on the battery side voltage and the bus side voltage;

[0011] Step 3: Calculate the control power P based on the battery side voltage / current and the bus side voltage / current. * ;

[0012] Step 4: Utilize the control power P of the energy storage DC-DC converter * Determine the operating modes of the dual active bridge circuit;

[0013] Step 5: Adjust the actual power of the dual active bridge circuit according to its operating mode to optimize the switching losses of the energy storage DC-DC converter.

[0014] The voltage ratio m across the energy storage DC-DC converter satisfies the following formula:

[0015] When nV bat <V bus hour

[0016] When nV bat >V bus hour

[0017] Among them, V bat V is the battery-side voltage. bus denoted as the bus-side voltage, and n is the turns ratio of the secondary to the primary side of the isolation transformer T in the energy storage DC converter.

[0018] The operating modes of the dual active bridge circuit include a first mode, a second mode, a third mode, and a fourth mode, and the specific determination method is as follows:

[0019] Based on the current control power P * The corresponding outward phase shift angle, bridge arm midpoint voltage duty cycle k, switching frequency, power flow direction, and power magnitude are calculated. The bridge arm midpoint voltage duty cycle k is the duty cycle at the lower voltage side between the battery side and the bus side of the transformer.

[0020] If the power of the current dual active bridge circuit is less than the first preset power, the operating mode of the dual active bridge circuit is the first mode;

[0021] If the absolute value of the current outward phase shift angle |D|>k*(1-m) / 2 and the duty cycle k of the bridge arm midpoint voltage is less than the preset maximum duty cycle k max At that time, the operating mode of the dual active bridge circuit is the second mode;

[0022] If the current duty cycle k at the midpoint of the bridge arm is equal to the preset maximum duty cycle k max And the switching frequency is less than the preset maximum switching frequency f max At that time, the operating mode of the dual active bridge circuit is the third mode;

[0023] If the current switching frequency is equal to the preset minimum switching frequency f min At that time, the operating mode of the dual active bridge circuit is the fourth mode.

[0024] When the operating mode of the dual active bridge circuit is the first mode, the duty cycle k of the bridge arm midpoint voltage is equal to the preset minimum duty cycle k. min Switching frequency f s Equal to the preset maximum switching frequency f max The actual power of the dual active bridge circuit can be adjusted by changing the external phase angle D.

[0025] When the operating mode of the dual active bridge circuit is the second mode, the switching frequency f s Equal to the preset maximum switching frequency f max The actual power of the dual active bridge circuit and the outward phase shift angle are adjusted by regulating the duty cycle k of the midpoint voltage of the bridge arm, ultimately enabling the dual active bridge circuit to operate in a soft-switching state.

[0026] When the operating mode of the dual active bridge circuit is the third mode, the duty cycle k of the current bridge arm midpoint voltage is equal to the preset maximum duty cycle k. max By adjusting the switching frequency f s To adjust the power level.

[0027] When the operating mode of the dual active bridge circuit is the fourth mode, the switching frequency f s Equal to the preset minimum switching frequency f min The actual power of the dual active bridge circuit can be adjusted by adjusting the external phase shift angle D until full load is achieved.

[0028] The formulas for the inner phase shift angle d1 on the battery side and the inner phase shift angle d2 on the bus side are as follows:

[0029] When nV bat >V bus hour

[0030] When nV bat <V bus hour

[0031] Where m is the voltage ratio across the energy storage DC-DC converter, V bat V is the battery-side voltage. bus denoted as the bus-side voltage, and n is the turns ratio of the secondary to the primary side of the isolation transformer T in the energy storage DC converter.

[0032] II. A Switching Loss Optimization Control System for Energy Storage DC-DC Converters

[0033] The voltage and current acquisition unit is used to acquire the battery-side voltage / current and bus-side voltage / current of the energy storage DC converter;

[0034] The voltage ratio calculation unit is used to calculate the voltage ratio on both sides of the energy storage DC-DC converter based on the battery side voltage and the bus side voltage.

[0035] The control power calculation unit is used to calculate the control power P based on the battery-side voltage / current and the bus-side voltage / current. * ;

[0036] The operating mode determination unit is used to utilize the control power P of the energy storage DC-DC converter. * Determine the operating modes of the dual active bridge circuit;

[0037] The power regulation unit adjusts the actual power of the dual active bridge circuit according to its operating mode.

[0038] Compared with the prior art, the beneficial effects of the present invention include:

[0039] (1) It realizes continuous control of the dual active bridge converter in the bidirectional full power range;

[0040] (2) Combining triple phase-shift control and frequency modulation control reduces turn-off losses and improves circuit efficiency;

[0041] (3) The controlled object is simplified, and a single controller is used for different working conditions, which is suitable for engineering practice;

[0042] (4) Power linearization processing speeds up the loop speed and improves dynamic performance. Attached Figure Description

[0043] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0044] Figure 1 The circuit topology of the energy storage DC-DC converter provided by the present invention is shown.

[0045] Figure 2 A control block diagram of the control method provided by the present invention.

[0046] Figure 3 This is a schematic diagram illustrating the changes in each degree of freedom under different modes in the control method provided by the present invention.

[0047] Figure 4 The switching timing and key waveform diagrams for mode one of the embodiments provided by the present invention.

[0048] Figure 5 The switching timing and key waveform diagrams for Mode 2 of the embodiment provided by the present invention.

[0049] Figure 6 The switching timing and key waveform diagrams for mode three of the embodiment provided by the present invention.

[0050] Figure 7 The switching timing and key waveform diagrams of mode four in the embodiment of the present invention are shown. Detailed Implementation

[0051] Embodiments of the present invention are described in detail below, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The described embodiments are intended only to facilitate the understanding of the present invention, and are not intended to limit it in any way.

[0052] In the following description, a "circuit" refers to a conductive loop consisting of at least one element or sub-circuit connected by an electrical or electromagnetic link. When an element or circuit is said to be "coupled to" or "connected to" another element, or when an element / circuit is said to be "coupled at" or "connected at" two nodes, it can be directly coupled to or connected to the other element, or there may be intermediate elements. The connection between elements can be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly connected to" another element, it means that there are no intermediate elements between them.

[0053] One embodiment of the present invention provides an energy storage DC-DC converter, the circuit topology of which adopts a dual active bridge converter, as shown in the figure below. Figure 1 As shown. The dual active bridge circuit includes a battery-side voltage regulator capacitor C. bat Bus-side voltage regulator capacitor C bus The circuit includes a battery-side H-bridge circuit with switching transistors S1 to S4, a bus-side H-bridge circuit with switching transistors S5 to S8, a high-frequency isolation transformer T with a turns ratio of 1:n, and a resonant inductor L. r and resonant capacitor C r .

[0054] For each H-bridge circuit, the upper and lower switches are complementary in conduction. When one control signal is determined, the other control signal in the same bridge arm is also uniquely determined. Specifically, the signals of switches S1 and S2 are complementary, the signals of switches S3 and S4 are complementary, the signals of switches S5 and S6 are complementary, and the signals of switches S7 and S8 are complementary.

[0055] The inner phase shift angle on the battery side is defined as d1, and the inner phase shift angle on the bus side is defined as d2, with values ​​ranging from [0,1]. In fundamental frequency analysis, these values ​​are used to adjust the midpoint voltage v of the battery-side bridge arm. ab and the voltage at the midpoint of the bridge arm on the bus side cd The duty cycle. When the inner phase shift angle is 0, the corresponding bridge arm midpoint voltage duty cycle is 1; when the inner phase shift angle is 1, the corresponding bridge arm midpoint voltage duty cycle is 0, meaning there is no conduction moment.

[0056] Specify the voltage v at the midpoint of the bridge arm ab and v cd The voltage phase angle difference is the outward phase shift angle D, when the voltage at the midpoint of the battery-side bridge arm is v ab Lagging behind the midpoint voltage v of the bus-side bridge arm cd When the outward phase angle D is positive, power flows from the battery side to the bus side, and the system is in a discharging state; when the voltage at the midpoint of the battery side bridge arm is v... ab Leading the voltage at the midpoint of the bridge arm on the bus side. cd When the outward phase angle D is negative, power flows from the bus side to the battery side, and the device is in charging mode.

[0057] The switching frequency f of all 8 switching transistors in the dual active bridge circuit s At the same time, they are completely identical and change simultaneously in frequency modulation control mode, at which point neither the inner nor outer phase shift angles change.

[0058] Since the circuit operates similarly when transmitting power in the forward direction and in the reverse direction, this invention only describes the situation when power flows from the battery side to the bus side, i.e., in the discharge state.

[0059] To clearly demonstrate the optimization of switching losses by this invention, this embodiment selects a case where the voltage difference between the two sides after voltage conversion is large. In existing dual active bridge circuit control technology, the turn-off current is very large under this condition, and the loss caused by the turn-off of low-voltage side devices accounts for a much larger proportion than the reactive circulating current and hard turn-on. The efficiency optimization of the control method proposed in this invention is more obvious in this embodiment.

[0060] The control block diagram used in this embodiment is as follows: Figure 2As shown, the system includes a voltage difference comparator, a voltage PI controller, a current difference comparator, a current PI controller, a phase shift angle calculation module, and a drive signal generation module connected in sequence. The outer voltage loop controls the battery voltage and bus voltage based on the charging / discharging state. The outer voltage loop outputs a current reference value I through PI control. * Current loop control object selection Figure 1 Battery voltage I bat The current loop outputs a control signal P through PI control. * Then, the inner phase shift angles d1 and d2 and the outer phase shift angle D corresponding to the current power are obtained through the phase shift angle calculation module, and the corresponding switching frequency f is determined. s Finally, the control signal is generated through the drive signal generation module.

[0061] Specifically, the following steps are included:

[0062] Step 1: Collect and acquire the battery-side voltage / current and bus-side voltage / current of the energy storage DC-DC converter;

[0063] Step 2: Calculate the voltage ratio on both sides of the energy storage DC-DC converter based on the battery side voltage and the bus side voltage;

[0064] The voltage ratio m across the energy storage DC-DC converter satisfies the following formula:

[0065] When nV bat <V bus hour

[0066] When nV bat >V bus hour

[0067] Among them, V bat V is the battery-side voltage. bus denoted as the bus-side voltage, and n is the turns ratio of the secondary to the primary side of the isolation transformer T in the energy storage DC converter.

[0068] In this invention, the inner and outer phase shift angles and switching frequency during circuit operation are determined based on the controller output signal. To facilitate control freedom, a variable k is introduced to represent the duty cycle of the bridge arm midpoint voltage. Fundamental matching is performed based on the calculated voltage ratio to reduce reactive circulating current. Let the inner phase shift angle on the battery side be d1 and the inner phase shift angle on the bus side be d2. The corresponding calculation formulas are as follows:

[0069] When nV bat >V bus hour

[0070] When nV bat <Vbus hour

[0071] Where m is the voltage ratio across the energy storage DC-DC converter, V bat V is the battery-side voltage. bus denoted as the bus-side voltage, and n is the turns ratio of the secondary to the primary side of the isolation transformer T in the energy storage DC converter.

[0072] Step 3: Calculate the control power P based on the battery side voltage / current and the bus side voltage / current. * ;

[0073] Step 4: Utilize the control power P of the energy storage DC-DC converter * Determine the operating modes of the dual active bridge circuit;

[0074] The operating modes of the dual active bridge circuit include the first mode, the second mode, the third mode, and the fourth mode. The specific determination method is as follows:

[0075] Based on the current control power P * The corresponding external phase shift angle, bridge arm midpoint voltage duty cycle k, switching frequency, power flow direction, and power magnitude are calculated. The bridge arm midpoint voltage duty cycle k is the duty cycle of the lower voltage side between the battery side and the bus side of the transformer, that is, the duty cycle of the higher voltage side is k*m.

[0076] If the power of the current dual active bridge circuit is less than the first preset power (which is equal to the circuit power corresponding to the external phase shift angle being k*(1-m) / 2), the operating mode of the dual active bridge circuit is the first mode;

[0077] If the absolute value of the current outward phase shift angle |D|>k*(1-m) / 2 and the duty cycle k of the bridge arm midpoint voltage is less than the preset maximum duty cycle k max At that time, the operating mode of the dual active bridge circuit is the second mode;

[0078] If the current duty cycle k at the midpoint of the bridge arm is equal to the preset maximum duty cycle k max And the switching frequency is less than the preset maximum switching frequency f max At that time, the operating mode of the dual active bridge circuit is the third mode;

[0079] If the current switching frequency is equal to the preset minimum switching frequency f min At that time, the operating mode of the dual active bridge circuit is the fourth mode.

[0080] Step 5: Based on the operating mode of the dual active bridge circuit, adjust the actual power of the dual active bridge circuit to optimize the switching loss of the energy storage DC-DC converter. Specifically, this effectively reduces the turn-off loss of the switching transistors in the dual active bridge circuit across the entire power range.

[0081] This invention divides the circuit operation into four modes based on the controller's output signal; therefore, the circuit's operating mode is related to the actual power. Modes one and four control only the sign and magnitude of the outward phase shift angle; mode two controls only the inward phase shift angle, but to ensure soft switching, the outward phase shift angle follows the change in the inward phase shift angle; mode three adjusts only the switching frequency, such as... Figure 3 As shown.

[0082] Specifically:

[0083] When the dual active bridge circuit operates in the first mode, i.e., the power is close to zero, to ensure continuous positive and negative current, the duty cycle k of the midpoint voltage of the bridge arm is equal to the preset minimum duty cycle k. min Switching frequency f s Equal to the preset maximum switching frequency f max The actual power of the dual active bridge circuit is affected by adjusting the external phase shift angle D. At this time, the switching sequence of each switch transistor and the midpoint voltage v of the bridge arm are also affected. ab and v cd Inductor current waveform as follows Figure 4 As shown.

[0084] When the dual active bridge circuit operates in the second mode, the six switching transistors in the circuit can achieve soft switching. In this state, further increasing the outward phase angle will increase turn-off losses but not decrease turn-on losses. Therefore, the outward phase angle should be stopped. The outward phase angle D is equal to k*(1-m) / 2, and the switching frequency f... s Equal to the preset maximum switching frequency f max The actual power of the dual active bridge circuit and the external phase shift angle are adjusted by regulating the duty cycle k of the bridge arm midpoint voltage. The external phase shift angle is changed due to the adjustment of the voltage duty cycle k, ultimately allowing the dual active bridge circuit to continue operating in soft-switching mode. At this time, the switching sequence of each switch transistor and the bridge arm midpoint voltage v... ab and v cd Inductor current waveform as follows Figure 5 As shown.

[0085] When the dual active bridge circuit is operating in the third mode, the circuit power cannot be increased by further increasing k. The duty cycle k of the current bridge arm midpoint voltage is equal to the preset maximum duty cycle k. max This determines the outward phase angle D, i.e., D = k max *(1-m) / 2, by adjusting the switching frequency f s To adjust the power output. At this time, the switching sequence of each switching transistor and the midpoint voltage V of the bridge arm... ab and v cd Inductor current waveform as follows Figure 6 As shown.

[0086] When the dual active bridge circuit operates in the fourth mode, a noticeable resonance occurs in the current waveform when the switching frequency decreases to near the resonant frequency, and the turn-off current of the switching transistor decreases significantly. However, further reducing the frequency will lead to entering the resonant state, changing the circuit's operating state. Switching frequency f s Equal to the preset minimum switching frequency f min The actual power of the dual active bridge circuit is adjusted by changing the external phase shift angle D until full load is reached. At this point, all switches in the circuit can achieve soft switching with a small turn-off current. The switching sequence of each switch and the midpoint voltage v of the bridge arm are then determined. ab and v cd Inductor current waveform as follows Figure 7 As shown.

[0087] When the battery-side voltage, bus-side voltage, and load power of the circuit change, the controller's output signal can change continuously, achieving a smooth transition between various operating modes. Moreover, the output signal is basically linear with the power gain, which can improve the dynamic response speed.

[0088] This invention also proposes a switching loss optimization control system for an energy storage DC-DC converter, the system comprising:

[0089] The voltage and current acquisition unit is used to acquire the battery-side voltage / current and bus-side voltage / current of the energy storage DC converter;

[0090] The voltage ratio calculation unit is used to calculate the voltage ratio on both sides of the energy storage DC-DC converter based on the battery side voltage and the bus side voltage.

[0091] The control power calculation unit is used to calculate the control power P based on the battery-side voltage / current and the bus-side voltage / current. * ;

[0092] The operating mode determination unit is used to utilize the control power P of the energy storage DC-DC converter. * Determine the operating modes of the dual active bridge circuit;

[0093] The power regulation unit adjusts the actual power of the dual active bridge circuit according to its operating mode.

[0094] In some embodiments, the circuit operates differently from that in this embodiment, therefore the boundaries and key waveforms of each operating mode differ. However, the control methods described in this invention are essentially the same as those in other embodiments and all fall within the scope of protection of this invention.

[0095] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for optimizing the switching loss control of an energy storage DC converter, characterized in that, The method comprises the following steps: Step 1: obtaining the battery-side voltage / current and bus-side voltage / current of the energy storage DC converter; Step 2: calculating the voltage ratio of the two sides of the energy storage DC converter according to the battery-side voltage and the bus-side voltage; Step 3: Calculate the control power P from the battery-side voltage / current and the bus-side voltage / current * ; Step 4: Control power P with energy storage DC converter * determining an operating mode of the dual active bridge circuit; Step 5: adjusting the actual power size of the dual-active-bridge circuit according to the working mode of the dual-active-bridge circuit, and completing the switching loss optimization of the energy storage DC converter; The working mode of the dual-active-bridge circuit comprises a first mode, a second mode, a third mode and a fourth mode, and the specific judgment mode is as follows: According to the current control power P * The corresponding phase angle, bridge arm midpoint voltage duty cycle k, switching frequency and power flow direction, power size are calculated, and the bridge arm midpoint voltage duty cycle k is the duty cycle at the lower voltage side of the battery side and the bus side of the transformer. If the power size of the current dual-active-bridge circuit is less than a first preset power, the working mode of the dual-active-bridge circuit is the first mode; If the absolute value of the current export phase angle |D| is greater than k*(1-m) / 2 and the bridge arm midpoint voltage duty cycle k is less than the preset maximum duty cycle k max , the working mode of the dual active bridge circuit is the second mode. The voltage ratio m of the two sides of the energy storage DC converter satisfies the following formula: wherein, Vbat is the battery-side voltage, Vbus is the bus-side voltage, and n is the turns ratio of the secondary to primary of the isolation transformer T in the energy storage DC converter. If the current bridge arm midpoint voltage duty ratio k is equal to the preset maximum duty ratio k max and the switching frequency is less than the preset maximum switching frequency f max , the working mode of the dual active bridge circuit is the third mode. If the current switching frequency is equal to the preset minimum switching frequency f min When the current switching frequency is equal to the preset minimum switching frequency f min the working mode of the dual active bridge circuit is the fourth mode.

2. The switching loss optimization control method of energy storage DC converter according to claim 1, characterized in that, When the working mode of the dual active bridge circuit is the first mode, the bridge arm midpoint voltage duty ratio k is equal to a preset minimum duty ratio k min , the switching frequency f s is equal to a preset maximum switching frequency f max , and the actual power size of the dual active bridge circuit is adjusted by adjusting the outward phase angle D.

3. The switching loss optimization control method of energy storage DC converter according to claim 1, characterized in that, The working mode of the dual active bridge circuit is the second mode, and the switching frequency f s is equal to the preset maximum switching frequency f max . The actual power size and the outward moving phase angle of the dual active bridge circuit are adjusted by adjusting the bridge arm midpoint voltage duty cycle k, so that the dual active bridge circuit finally works in a soft switching state.

4. The switching loss optimization control method of energy storage DC converter according to claim 1, characterized in that, When the working mode of the double active bridge circuit is the third mode, the current bridge arm midpoint voltage duty ratio k is equal to a preset maximum duty ratio k max , and the power size is adjusted by adjusting the switching frequency f s .

5. The switching loss optimization control method of energy storage DC converter according to claim 1, wherein, When the working mode of the dual active bridge circuit is the fourth mode, the switching frequency f s is equal to the preset minimum switching frequency f min , the actual power size of the dual active bridge circuit is adjusted by adjusting the outward phase angle D until full load is reached.

6. The switching loss optimization control method of energy storage DC converter according to claim 1, wherein, The battery-side internal phase shift angle d1 and the bus-side internal phase shift angle d2 satisfy the following formula: Wherein, m is the voltage ratio of the energy storage DC converter, Vb is the battery side voltage, Vg is the bus side voltage, and n is the turns ratio of the secondary side to the primary side of the isolation transformer T in the energy storage DC converter.

7. A switching loss optimization control system for an energy storage DC converter, the system comprising: a controller configured to: determine a switching frequency for a switching device of the energy storage DC converter; and adjust the switching frequency based on a comparison of the switching frequency to a threshold value. It comprises: A voltage and current acquisition unit configured to acquire the battery-side voltage / current and bus-side voltage / current of the energy storage DC converter; A voltage ratio calculation unit configured to calculate the voltage ratio of the two sides of the energy storage DC converter according to the battery-side voltage and the bus-side voltage; a control power calculation unit configured to calculate a control power P based on the battery-side voltage / current and the bus-side voltage / current * ; The working mode judging unit is configured to utilize the control power P of the energy storage DC converter * determine the working mode of the dual active bridge circuit; A power adjustment unit configured to adjust the actual power size of the dual-active-bridge circuit according to the working mode of the dual-active-bridge circuit; The working mode of the dual-active-bridge circuit comprises a first mode, a second mode, a third mode and a fourth mode, and the specific judgment mode is as follows: According to the current control power P * The corresponding phase angle, bridge arm midpoint voltage duty cycle k, switching frequency and power flow direction, power size are calculated, and the bridge arm midpoint voltage duty cycle k is the duty cycle at the lower voltage side of the battery side and the bus side of the transformer. If the power size of the current dual-active-bridge circuit is less than a first preset power, the working mode of the dual-active-bridge circuit is the first mode; If the absolute value of the current export phase angle |D| is greater than k*(1-m) / 2 and the bridge arm midpoint voltage duty cycle k is less than the preset maximum duty cycle k max , the working mode of the dual active bridge circuit is the second mode. The voltage ratio m of the two sides of the energy storage DC converter satisfies the following formula: wherein, Vbat is the battery-side voltage, Vbus is the bus-side voltage, and n is the turns ratio of the secondary to primary of the isolation transformer T in the energy storage DC converter; If the current bridge arm midpoint voltage duty ratio k is equal to the preset maximum duty ratio k max and the switching frequency is less than the preset maximum switching frequency f max , the working mode of the dual active bridge circuit is the third mode. If the current switching frequency is equal to the preset minimum switching frequency f min When the current switching frequency is equal to the preset minimum switching frequency f min the working mode of the dual active bridge circuit is the fourth mode.

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