Guard power supply module control method based on dual active bridge converter

Abstract

The invention relates to the technical field of direct-current power supply systems, in particular to a guard power supply module control method based on a dual-active bridge converter. The method comprises the following steps: taking a discharge mode as an initial mode, monitoring direct current bus side voltage feedback V1, and calculating a phase shift angle phi; judging whether an instruction for starting a charging path is received or not; if an instruction of starting a charging path is received, converting into a charging mode, monitoring voltage feedback V2 at the side of the storage battery pack, and realizing switching between the two working modes by controlling a phase shift angle phi; judging whether the voltage of the direct current bus side is higher than the voltage feedback V1 of the direct current bus side in the discharging mode or not during the starting period of the charging path; if the voltage is higher than V1, the charging path is kept in an open state; and if the voltage is lower than V1, closing the charging path and converting into a discharging mode. The problems that in the prior art, the working mode switching is slow, especially when the power grid voltage suddenly drops or rises, the system response is not timely, and the efficiency is low under the light load or heavy load condition are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current power supply systems, and in particular to a control method for a guard power supply module based on a dual active bridge converter. Background Art

[0002] In the DC power supply system for electric power, the wiring method is based on the safety and reliability of the battery pack. In the event of an accident on the grid side, the battery pack provides stable power for the DC load. If the battery fails or the battery power supply circuit fails, it will cause the DC bus to lose voltage, thus affecting the safe operation of the power system. Therefore, the reliable operation of the battery pack will be the last line of defense in the entire DC system. By introducing the guardian power supply solution, the battery life can be extended, the reliability can be increased, and the maintenance cost can be reduced.

[0003] A guard power supply is a power supply device installed between the DC bus and the battery pack in the power system. At present, most existing guard power supply systems use two unidirectional DC-DC converters or ordinary bidirectional DC-DC converters. When two unidirectional DC-DC converters are used, one is used to charge the battery from the grid and the other is used to supply power from the battery to the load. Although this method can optimize the charging and discharging processes respectively, the system cannot flexibly respond to changes in the grid and load in some cases. In addition, when switching from charging mode to discharging mode or vice versa, there may be a delay in the system, resulting in untimely response, especially when the grid voltage suddenly drops or rises. On the other hand, when using ordinary bidirectional DC-DC converters, the efficiency is often low under light or heavy load conditions, especially when the load changes rapidly, the system may have voltage fluctuations or stability problems, resulting in energy waste and heating problems. Due to the slow switching of the working mode, the system may experience a period of instability when switching from charging mode to discharging mode, which further exacerbates the efficiency problem. In addition, fluctuations in grid voltage or differences in grid standards in different countries may also cause the power supply system to fail to work properly. In order to ensure the reliability and robustness of the power supply system, it needs to be able to operate normally over a wide input voltage range. Summary of the invention

[0004] The purpose of the present invention is to provide a guard power module control method based on a dual active bridge converter to solve the problems of slow working mode switching in the prior art, especially the untimely system response when the grid voltage suddenly drops or rises, and low efficiency under light or heavy load conditions.

[0005] To achieve the above object, a control method for a guard power module based on a dual active bridge converter is provided. Based on an isolated dual active bridge DC-DC converter, a fast switching between two working modes is achieved by adjusting the phase shift angle φ of the converter. The two working modes include a charging mode and a discharging mode. The method comprises the following steps:

[0006] Step 1: Take the discharge mode as the initial mode, open the discharge path and close the charging path by default, set the voltage reference Vref, monitor the DC bus side voltage feedback V1 at the same time, and calculate the phase shift angle φ;

[0007] Step 2: Determine whether an instruction to start the charging path is received;

[0008] Step 3: If an instruction to start the charging path is received, the charging mode is switched to start the charging path, the voltage feedback V2 on the battery pack side is monitored, the phase shift angle φ is recalculated according to the voltage reference Vref, and the switching between the two working modes is achieved by controlling the phase shift angle φ, and then the process goes to step 4;

[0009] If no instruction to start the charging path is received, the discharge mode is maintained and the process returns to step 1;

[0010] Step 4: During the period when the charging path is turned on, determine whether the voltage on the DC bus side is higher than the DC bus side voltage feedback V1 in the discharge mode;

[0011] If it is higher than V1, the charging path is kept open;

[0012] If it is lower than V1, the charging path is closed, the discharging path is opened, the mode is switched to the discharging mode, and the process returns to step 1.

[0013] As a further improvement of the technical solution, in the step 1, the voltage error obtained by subtracting the voltage reference Vref from the DC bus side voltage feedback V1 is outputted by the output voltage controller as a relative phase shift angle φ of the voltage waveforms of the two full-bridge inverters, and the limit range of the phase shift angle φ is -π / 2 to 0;

[0014] In step three, the voltage error obtained by subtracting the voltage reference Vref from the battery pack side voltage feedback V2 is output by the output voltage controller as the relative phase shift angle φ of the voltage waveforms of the two full-bridge inverters. The limit range of the phase shift angle φ of the next cycle is 0 to -π / 2.

[0015] As a further improvement of the technical solution, the isolated dual active bridge DC-DC converter includes a primary side full bridge, a secondary side full bridge, an inductor Lr and a transformer Tr.

[0016] As a further improvement of the present technical solution, the primary side full bridge includes a switch tube Q1, a switch tube Q2, a switch tube Q3 and a switch tube Q4, the source of the switch tube Q1 is connected to the drain of the switch tube Q2, the source of the switch tube Q3 is connected to the drain of the switch tube Q4, the source of the switch tube Q1 is connected to one end of the inductor Lr, the other end of the inductor Lr is connected to the same-name end of the primary side winding of the transformer Tr, and the opposite-name end of the primary side winding of the transformer Tr is connected to the source of the switch tube Q3.

[0017] As a further improvement of the technical solution, the switch tube Q1 and the switch tube Q2 respectively receive complementary drive signals, the duty cycle of the drive signal is 0.5, a dead time is set between the switch tube Q1 and the switch tube Q2, and the midpoint of the bridge arm formed by the switch tube Q1 and the switch tube Q2 is the endpoint A;

[0018] The switch tube Q3 and the switch tube Q4 receive complementary drive signals respectively, the duty cycle of the drive signal is 0.5, a dead time is set between the switch tube Q3 and the switch tube Q4, and the midpoint of the bridge arm formed by the switch tube Q3 and the switch tube Q4 is the endpoint B.

[0019] As a further improvement of the present technical solution, the primary side full-bridge circuit controls the voltage difference Vab between the midpoint endpoint A and the endpoint B of the two bridge arms by adjusting the phase difference between the switch tube Q1 and the switch tube Q3 and between the switch tube Q2 and the switch tube Q4, and the voltage difference Vab corresponds to an adjustable duty cycle D1.

[0020] As a further improvement of the present technical solution, the secondary side full bridge includes a switch tube Q5, a switch tube Q6, a switch tube Q7 and a switch tube Q8, the source of the switch tube Q5 is connected to the drain of the switch tube Q6, the source of the switch tube Q7 is connected to the drain of the switch tube Q8, the drain of the switch tube Q5 is connected to the drain of the switch tube Q7, the source of the switch tube Q6 is connected to the source of the switch tube Q8, the source of the switch tube Q5 is connected to the same-name end of the secondary winding of the transformer Tr, and the opposite-name end of the secondary winding of the transformer Tr is connected to the source of the switch tube Q7.

[0021] As a further improvement of the technical solution, the switch tube Q5 and the switch tube Q6 respectively receive complementary drive signals, the duty cycle of the drive signal is 0.5, a dead time is set between the switch tube Q5 and the switch tube Q6, and the midpoint of the bridge arm formed by the switch tube Q5 and the switch tube Q6 is the endpoint C;

[0022] The switch tube Q7 and the switch tube Q8 receive complementary drive signals respectively, the duty cycle of the drive signal is 0.5, a dead time is set between the switch tube Q7 and the switch tube Q8, and the midpoint of the bridge arm formed by the switch tube Q7 and the switch tube Q8 is the endpoint D.

[0023] As a further improvement of the present technical solution, the secondary side full-bridge circuit controls the voltage difference Vcd between the midpoint endpoint C and the endpoint D of the two bridge arms by adjusting the phase difference between the switch tube Q5 and the switch tube Q7 and between the switch tube Q6 and the switch tube Q8, and the voltage difference Vcd corresponds to an adjustable duty cycle D2.

[0024] As a further improvement of the technical solution, the relationship between the duty cycle D1, the duty cycle D2 and the phase shift angle φ is as follows:

[0025] The range of the phase shift angle φ is determined to be -π / 2≤φ≤π / 2;

[0026] Sample the primary voltage Vin and the secondary voltage Vo, and calculate the gain M, which is defined as M = (nVin) / Vo, where n is the transformer ratio;

[0027] Determine the M value. If M is less than or equal to 1, the module load is light.

[0028]

[0029] If M is less than or equal to 1, the module load is heavy, then

[0030]

[0031] If M is greater than 1, the module load is light, then

[0032]

[0033] If M is greater than 1, the module load is heavy, then

[0034]

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. In the control method of the guard power module based on the dual active bridge converter, by calculating the voltage error between the DC bus side voltage feedback V1, the battery side voltage feedback V2 and the set voltage reference Vref, the output voltage controller outputs the relative phase shift angle φ of the voltage waveform of the two full-bridge inverters, and adjusts the phase shift angle φ according to the voltage error, so as to realize the rapid switching between the charging mode and the discharging mode, and significantly improve the response speed of the system. In particular, when the grid voltage suddenly drops or rises, it can respond quickly to ensure the stable operation of the power system.

[0037] 2. In the control method of the guardian power module based on the dual active bridge converter, based on the isolated dual active bridge DC-DC converter, the direction and amount of energy flow can be controlled by adjusting the phase difference between the primary side full bridge and the secondary side full bridge drive signal. Even under light load or heavy load conditions, it can maintain a high conversion efficiency and can quickly respond to changes in the load. When the load suddenly increases or decreases, the converter can quickly adjust the phase difference to maintain the stability of the output voltage, reduce energy waste and heat problems, and improve the reliability and stability of the system.

[0038] 3. In the control method of the guardian power module based on the dual active bridge converter, based on the isolated dual active bridge DC-DC converter, this converter has the characteristics of a wide input voltage range and can work normally within a wider input voltage range, which enhances the robustness and applicability of the system and enables it to be used under different power grid standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the structure of the present invention in the system;

[0040] Figure 2 Schematic diagram of the circuit topology of the dual active bridge converter in the present invention;

[0041] Figure 3 is an example of dual active bridge control parameters in the present invention;

[0042] Figure 4 It is a closed-loop control block diagram of the present invention;

[0043] Figure 5 The graphs of the duty ratios D1 and D2 in the first and second modes of the present invention as a function of the phase shift angle φ_s are shown;

[0044] Figure 6 The graphs of the duty ratios D1 and D2 changing with the phase shift angle φ_s in the third and fourth modes of the present invention are as follows;

[0045] Figure 7 This is a flow chart of the dynamic adjustment of duty cycles D1 and D2 in the present invention. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the 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.

[0047] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0048] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0049] See also Figure 1-Figure 7 As shown, the purpose of this embodiment is to provide a control method for a guard power module based on a dual active bridge converter, based on an isolated dual active bridge DC-DC converter, by adjusting the phase shift angle φ of the converter to achieve rapid switching between two working modes, the two working modes include a charging mode and a discharging mode, and the method includes the following steps:

[0050] Step 1: Take the discharge mode as the initial mode, open the discharge path and close the charging path by default, set the voltage reference Vref, monitor the DC bus side voltage feedback V1 at the same time, and calculate the phase shift angle φ;

[0051] Step 2: Determine whether an instruction to start the charging path is received;

[0052] Step 3: If an instruction to start the charging path is received, the charging mode is switched to start the charging path, the voltage feedback V2 on the battery pack side is monitored, the phase shift angle φ is recalculated according to the voltage reference Vref, and the switching between the two working modes is achieved by controlling the phase shift angle φ, and then the process goes to step 4;

[0053] If no instruction to start the charging path is received, the discharge mode is maintained and the process returns to step 1;

[0054] When the converter works in charging mode, the phase shift angle φ is set to a positive value (φ>0), which means that the primary side full bridge is ahead of the secondary side full bridge, thereby realizing forward power transmission, that is, energy flows from the DC bus side to the battery pack side. On the contrary, when the converter needs to work in discharge mode, the phase shift angle φ is set to a negative value (φ<0), at which time the secondary side full bridge is ahead of the primary side full bridge, realizing reverse power transmission, that is, energy flows from the battery pack side to the DC bus side.

[0055] Since the working modes of forward power and reverse power are symmetrical, the same calculation formula can be applied by taking the absolute value of the phase shift angle φ when calculating the control parameters under reverse power (discharge mode). This means that no matter whether the converter is operating in charging mode or discharge mode, the calculation logic used is the same, except that the direction of the phase shift angle needs to be considered opposite in discharge mode. Therefore, the above calculation formula for the phase shift angle φ is also applicable to the reverse power case, and it is only necessary to adjust the sign of the phase shift angle φ according to the actual working mode.

[0056] For example, the phase shift angle calculation method described in step 1 and step 3 can remain unchanged for reverse power, but it should be noted that the phase shift angle φ output in the discharge mode should be negative to reflect the change in the direction of energy flow. In this way, we ensure smooth switching between the two working modes and the high efficiency and stability of the system in the entire operating range.

[0057] Step 4: During the period when the charging path is turned on, determine whether the voltage on the DC bus side is higher than the DC bus side voltage feedback V1 in the discharge mode;

[0058] If it is higher than V1, the charging path is kept open;

[0059] If it is lower than V1, the charging path is closed, the discharging path is opened, the mode is switched to the discharging mode, and the process returns to step 1.

[0060] In step 1, the voltage error obtained by subtracting the voltage reference Vref from the DC bus side voltage feedback V1 is output by the output voltage controller as the relative phase shift angle φ of the voltage waveforms of the two full-bridge inverters. The limit range of the phase shift angle φ is -π / 2 to 0.

[0061] In step three, the voltage error obtained by subtracting the voltage reference Vref from the battery pack side voltage feedback V2 is output by the output voltage controller as the relative phase shift angle φ of the voltage waveforms of the two full-bridge inverters. The phase shift angle φ of the next cycle is limited to 0 to -π / 2.

[0062] The above phase shift angle φ refers to the phase difference of the drive signal between the primary side full bridge and the secondary side full bridge. By adjusting this angle, it is possible to control whether the energy flows from the primary side to the secondary side or from the secondary side to the primary side, thereby achieving bidirectional energy transmission.

[0063] As shown in Figure 1, the protection power module based on the dual active bridge converter includes a battery protection device and a battery pack. The battery protection device is connected to the battery pack, which is connected to the DC bus. The battery pack is connected to the DC bus through a nuclear capacity anti-reverse device. The DC bus is connected to a charging device, which is connected to an AC power supply.

[0064] The battery protection device comprises a fuse and a dual active bridge converter, the fuse is connected to the battery pack, and the dual active bridge converter is connected to the DC bus.

[0065] The DC bus is equipped with a monitoring device for monitoring the voltage, current, temperature and other related parameters of the DC bus. The battery pack is connected to a battery inspection instrument for monitoring and evaluating the health status and performance of the battery.

[0066] like Figure 2 As shown, the isolated dual active bridge DC-DC converter includes a primary side full bridge, a secondary side full bridge, an inductor Lr and a transformer Tr;

[0067] The primary side full bridge includes switch tubes Q1, Q2, Q3 and Q4. The source of switch tube Q1 is connected to the drain of switch tube Q2, the source of switch tube Q3 is connected to the drain of switch tube Q4, the source of switch tube Q1 is connected to one end of inductor Lr, the other end of inductor Lr is connected to the same-name end of the primary side winding of transformer Tr, and the opposite-name end of the primary side winding of transformer Tr is connected to the source of switch tube Q3.

[0068] The secondary side full bridge includes switch tube Q5, switch tube Q6, switch tube Q7 and switch tube Q8. The source of switch tube Q5 is connected to the drain of switch tube Q6, the source of switch tube Q7 is connected to the drain of switch tube Q8, the drain of switch tube Q5 is connected to the drain of switch tube Q7, the source of switch tube Q6 is connected to the source of switch tube Q8, the source of switch tube Q5 is connected to the same-name end of the secondary side winding of transformer Tr, and the opposite-name end of the secondary side winding of transformer Tr is connected to the source of switch tube Q7.

[0069] The midpoint of the bridge arm formed by the switch tube Q1 and the switch tube Q2 is end point A, the midpoint of the bridge arm formed by the switch tube Q3 and the switch tube Q4 is end point B, the midpoint of the bridge arm formed by the switch tube Q5 and the switch tube Q6 is end point C, and the midpoint of the bridge arm formed by the switch tube Q7 and the switch tube Q8 is end point D.

[0070] The switch tube Q1 and the switch tube Q2 receive complementary drive signals respectively, the duty cycle of the drive signal is 0.5, and a dead time is set between the switch tube Q1 and the switch tube Q2. The switch tube Q3 and the switch tube Q4 receive complementary drive signals respectively, the duty cycle of the drive signal is 0.5, and a dead time is set between the switch tube Q3 and the switch tube Q4. The primary side full bridge circuit controls the voltage difference Vab between the midpoint endpoint A and the endpoint B of the two bridge arms by adjusting the phase difference between the switch tube Q1 and the switch tube Q3 and the switch tube Q2 and the switch tube Q4. The voltage difference Vab corresponds to an adjustable duty cycle D1.

[0071] The switch tube Q5 and the switch tube Q6 receive complementary drive signals respectively, the duty cycle of the drive signal is 0.5, and a dead time is set between the switch tube Q5 and the switch tube Q6. The switch tube Q7 and the switch tube Q8 receive complementary drive signals respectively, the duty cycle of the drive signal is 0.5, and a dead time is set between the switch tube Q7 and the switch tube Q8. The secondary side full bridge circuit controls the voltage difference Vcd between the midpoint endpoint C and the endpoint D of the two bridge arms by adjusting the phase difference between the switch tube Q5 and the switch tube Q7 and the switch tube Q6 and the switch tube Q8. The voltage difference Vcd corresponds to an adjustable duty cycle D2.

[0072] To prevent shoot-through, a dead time is set between the drive signals of adjacent switches. This means that for a period of time, all switches are off to prevent the current loop from passing through the entire full bridge. The duty cycles D1 and D2 correspond to the output voltage differences Vab and Vcd of the primary and secondary full bridges, respectively. These two duty cycles can be adjusted independently as needed to meet specific application requirements.

[0073] The drain of switch tube Q1 and the drain of switch tube Q3 are connected to the positive electrode of the voltage input terminal and the positive electrode of capacitor Cin, the source of switch tube Q2 and the source of switch tube Q4 are connected to the negative electrode of the voltage input terminal and the negative electrode of capacitor Cin, the drain of switch tube Q5 and the drain of switch tube Q7 are connected to the positive electrode of the voltage output terminal and the positive electrode of capacitor Co, and the source of switch tube Q6 and the source of switch tube Q8 are connected to the negative electrode of the voltage output terminal and the negative electrode of capacitor Co. Vin and Vo are the DC bus voltage and the battery pack voltage respectively, and the equivalent voltage gain of the converter is defined as M=Vin / (nVo), where n is the turns ratio of the transformer.

[0074] like Figure 3As shown in the figure, the switching cycle Ts refers to the time required for the switch device to be turned on and turned on again, that is, a complete switching cycle. During this cycle, the switch tube performs switching operations according to a specific drive signal. The duty cycle described above is the ratio of the switch tube conduction time during the switching cycle to the entire switching cycle. The voltage errors Vab and Vcd marked in the figure refer to the differences between the DC bus side voltage and the battery pack side voltage mentioned above. These errors are used to control the output voltage controller, thereby adjusting the phase shift angle φ and the duty cycles D1 and D2.

[0075] In addition, the relationship between the duty cycle D1 and the duty cycle D2 and the phase shift angle φ is as follows:

[0076] The range of the phase shift angle φ is determined to be -π / 2≤φ≤π / 2;

[0077] Sample the primary voltage Vin and the secondary voltage Vo, and calculate the gain M, which is defined as M = (nVin) / Vo, where n is the transformer ratio;

[0078] Determine the M value. If M is less than or equal to 1, the module load is light.

[0079]

[0080] If M is less than or equal to 1, the module load is heavy, then

[0081]

[0082] If M is greater than 1, the module load is light, then

[0083]

[0084] If M is greater than 1, the module load is heavy, then

[0085]

[0086] like Figure 5 and Figure 6 As shown, the modulation strategy proposed above can accurately obtain the calculation results in the entire definition domain.

[0087] In summary, the relationship between the duty cycle D1, D2 and the shift angle φ is as follows: Figure 7As shown, first, determine that the range of the phase shift angle φ is -π / 2≤φ≤π / 2. Next, sample the input voltage Vin and the output voltage Vo, and calculate the gain M. Then, determine whether the gain M is less than or equal to 1. If M≤1, the duty cycles D1 and D2 are calculated by the following formulas: D1=min(1,D1_Mode1,D1_Mode2) and D2=min(1,D1_Mode1 / M). If M>1, the duty cycles D1 and D2 are calculated by the following formulas: D1=min(1,M*D2_Mode3) and D2=min(1,D2_Mode3,D2_Mode4). Finally, D1 and D2 calculated according to the above conditions are returned to the system or the next stage for processing. This strategy ensures that under different gain conditions, the duty cycles D1 and D2 can be adaptively adjusted to achieve the desired control effect.

[0088] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A control method for a guard power module based on a dual active bridge converter, characterized in that: Based on an isolated dual active bridge DC-DC converter, a fast switch between two working modes is achieved by adjusting the phase shift angle φ of the converter. The two working modes include a charging mode and a discharging mode. Specifically, the following steps are included: Step 1: Take the discharge mode as the initial mode, open the discharge path and close the charging path by default, set the voltage reference Vref, monitor the DC bus side voltage feedback V1 at the same time, and calculate the phase shift angle φ; Step 2: Determine whether an instruction to start a charging path is received; Step 3: If an instruction to start the charging path is received, the charging mode is switched to start the charging path, the voltage feedback V2 on the battery pack side is monitored, the phase shift angle φ is recalculated according to the voltage reference Vref, and the switching between the two working modes is achieved by controlling the phase shift angle φ, and then the process goes to step 4; If no instruction to start the charging path is received, the discharge mode is maintained and the process returns to step 1; Step 4: During the period when the charging path is turned on, determine whether the voltage on the DC bus side is higher than the DC bus side voltage feedback V1 in the discharge mode; If it is higher than V1, the charging path is kept open; If it is lower than V1, the charging path is closed, the discharging path is opened, the mode is switched to the discharging mode, and the process returns to step 1.

2. The method for controlling a guard power module based on a dual active bridge converter according to claim 1, characterized in that: In the step 1, the voltage error obtained by subtracting the voltage reference Vref from the DC bus side voltage feedback V1 is outputted by the output voltage controller as a relative phase shift angle φ of the voltage waveforms of the two full-bridge inverters, and the limit range of the phase shift angle φ is -π / 2 to 0; In step three, the voltage error obtained by subtracting the voltage reference Vref from the battery pack side voltage feedback V2 is output by the output voltage controller as the relative phase shift angle φ of the voltage waveforms of the two full-bridge inverters. The limit range of the phase shift angle φ of the next cycle is 0 to -π / 2.

3. The method for controlling a guard power module based on a dual active bridge converter according to claim 1, characterized in that: The isolated dual active bridge DC-DC converter comprises a primary side full bridge, a secondary side full bridge, an inductor Lr and a transformer Tr.

4. The method for controlling a guard power module based on a dual active bridge converter according to claim 3 is characterized in that: The primary side full bridge includes a switch tube Q1, a switch tube Q2, a switch tube Q3 and a switch tube Q4, the source of the switch tube Q1 is connected to the drain of the switch tube Q2, the source of the switch tube Q3 is connected to the drain of the switch tube Q4, the source of the switch tube Q1 is connected to one end of the inductor Lr, the other end of the inductor Lr is connected to the same-name end of the primary side winding of the transformer Tr, and the opposite-name end of the primary side winding of the transformer Tr is connected to the source of the switch tube Q3.

5. The method for controlling a guard power module based on a dual active bridge converter according to claim 4 is characterized in that: The switch tube Q1 and the switch tube Q2 receive complementary drive signals respectively, the duty cycle of the drive signal is 0.5, a dead time is set between the switch tube Q1 and the switch tube Q2, and the midpoint of the bridge arm formed by the switch tube Q1 and the switch tube Q2 is the endpoint A; The switch tube Q3 and the switch tube Q4 receive complementary drive signals respectively, the duty cycle of the drive signal is 0.5, a dead time is set between the switch tube Q3 and the switch tube Q4, and the midpoint of the bridge arm formed by the switch tube Q3 and the switch tube Q4 is the endpoint B.

6. The method for controlling a guard power module based on a dual active bridge converter according to claim 5, characterized in that: The primary side full bridge circuit controls the voltage difference Vab between the midpoint endpoint A and the endpoint B of the two bridge arms by adjusting the phase difference between the switch tube Q1 and the switch tube Q3 and the switch tube Q2 and the switch tube Q4. The voltage difference Vab corresponds to an adjustable duty cycle D1.

7. The method for controlling a guard power module based on a dual active bridge converter according to claim 6, characterized in that: The secondary side full bridge includes a switch tube Q5, a switch tube Q6, a switch tube Q7 and a switch tube Q8. The source of the switch tube Q5 is connected to the drain of the switch tube Q6, the source of the switch tube Q7 is connected to the drain of the switch tube Q8, the drain of the switch tube Q5 is connected to the drain of the switch tube Q7, the source of the switch tube Q6 is connected to the source of the switch tube Q8, the source of the switch tube Q5 is connected to the same-name end of the secondary side winding of the transformer Tr, and the opposite-name end of the secondary side winding of the transformer Tr is connected to the source of the switch tube Q7.

8. The method for controlling a guard power module based on a dual active bridge converter according to claim 7, characterized in that: The switch tube Q5 and the switch tube Q6 receive complementary drive signals respectively, the duty cycle of the drive signal is 0.5, a dead time is set between the switch tube Q5 and the switch tube Q6, and the midpoint of the bridge arm formed by the switch tube Q5 and the switch tube Q6 is the endpoint C; The switch tube Q7 and the switch tube Q8 receive complementary drive signals respectively, the duty cycle of the drive signal is 0.5, a dead time is set between the switch tube Q7 and the switch tube Q8, and the midpoint of the bridge arm formed by the switch tube Q7 and the switch tube Q8 is the endpoint D.

9. The method for controlling a guard power module based on a dual active bridge converter according to claim 8, characterized in that: The secondary side full bridge circuit controls the voltage difference Vcd between the midpoint endpoint C and the endpoint D of the two bridge arms by adjusting the phase difference between the switch tube Q5 and the switch tube Q7 and the switch tube Q6 and the switch tube Q8. The voltage difference Vcd corresponds to an adjustable duty cycle D2.

10. The method for controlling a guard power module based on a dual active bridge converter according to claim 9, characterized in that: The relationship between the duty cycle D1 and the duty cycle D2 and the phase shift angle φ is as follows: The range of the phase shift angle φ is determined to be -π / 2≤φ≤π / 2; Sample the primary voltage Vin and the secondary voltage Vo, and calculate the gain M, which is defined as M = (nVin) / Vo, where n is the transformer ratio; Determine the M value. If M is less than or equal to 1, the module load is light. If M is less than or equal to 1, the module load is heavy, then If M is greater than 1, the module load is light, then If M is greater than 1, the module load is heavy, then

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