CN105553274B - A kind of bidirectional DC-DC converter electric current critical continuous mode unified control method - Google Patents

Abstract

The invention discloses a current critical continuous and unified control method of a bidirectional DC-DC converter, relates to a current critical continuous and unified control method of a dual active bridge bidirectional DC-DC converter, and belongs to the field of power electronics. The control method disclosed by the invention controls the voltage of the primary side and the secondary side of the transformer and the phase difference between them, so that the converter can work continuously at the critical limit of the transformer current, and reduce the circulating current and conduction loss of the converter. In addition, through the boundary conditions and control conditions, the transformer current can be in a critical continuous mode, so that the reactive power loss of the circuit is reduced, the current stress of the switch tube and the circulation loss of the converter are reduced, and the efficiency and reliability of the converter can be improved. . The invention can also greatly reduce the complexity of the control unit and realize real-time control. The invention can be applied in the direction of high-frequency isolation switching power supply.

Description

A Continuous and Unified Control Method for Current Criticality of Bidirectional DC-DC Converter

technical field

The invention relates to a current critical continuous and unified control method of a bidirectional DC-DC converter, in particular to a current critical continuous and unified control method of a dual active bridge bidirectional DC-DC converter, belonging to a high-frequency isolated switching power supply in the field of power electronics direction.

Background technique

With the development of power electronics technology, the demand for bidirectional, high-frequency isolation, and high-efficiency converters is gradually increasing, especially in various power supply systems such as solid-state transformers including energy storage units, high-voltage direct current transmission, and micro-grids. These systems require the converter to have the characteristics of bidirectional controllable power flow due to the need for energy control of charging and discharging the energy storage unit. In addition, high transfer efficiency can improve the power density of the entire conversion device, increase reliability, and save costs, so it becomes another important indicator. For the aforementioned applications, the dual active bridge bidirectional DC-DC converter has been extensively studied because of its broad application prospects.

The topology diagram of a common type of bidirectional DC-DC converter is shown in Figure 1. The topology is a symmetrical structure. Both the primary side and the secondary side of the transformer are full bridge circuits composed of switching tubes. The two The two full bridge circuits are connected by a high frequency transformer. This type of converter contains three control variables, including the voltage v _AB between the center points of the two bridge arms of the primary full-bridge circuit, and the voltage v _CD between the center points of the two bridge arms of the secondary full-bridge circuit , and the heading angle between v _AB and v _CD . The duty cycle of the voltage v _AB can be adjusted by controlling the drive signal of the primary side switch tube; the duty cycle of the voltage v _CD can be adjusted by controlling the drive signal of the secondary side switch tube; by adjusting the primary side and the secondary side switch The phase difference between the tube signals can realize the control of the direction angle between v _AB and v _CD . At present, the control methods for dual active bridge bidirectional DC-DC converters can be divided into two categories: a) traditional single-direction control strategy, b) direction-shift plus PWM control strategy. Among them, the direction shift plus PWM control strategy can be a control strategy with two control degrees of freedom and a control strategy with three control degrees of freedom.

The article 'Abidirectional DC-DC converter for an energy storage system with galvanic isolation' published in IEEE Transaction on power electronics [Journal of Power Electronics] in 2007 uses a traditional one-way control strategy. This control strategy enables bidirectional flow control of power. However, when the voltage of the energy storage side fluctuates, its soft switching condition will not be satisfied, and the circulation loss and conduction loss will increase. The article "Extended-phase-shift control of isolated bidirectional dc-dc converter for power distribution in microgrid" published in IEEE Transaction on power electronics [Journal of Power Electronics] in 2012 not only controls the shift angle between two active bridges , also controls the steering angle between the two arms of each active bridge. This method is summarized as a direction-shifting plus PWM control method with two degrees of freedom. This method can effectively reduce reactive power loss and circulation loss, but introduces another control degree of freedom, which increases the complexity of control, making this control method difficult to calculate in real time. The "Stability analysis of isolated bidirectional dual active full-bridge dc-dc converter with triple phase shift control" published in IEEE Transaction on powerelectronics [Journal of Power Electronics] in 2012 belongs to the shift plus PWM control with three control degrees of freedom. This method can further reduce the reactive power loss and circulation loss of the converter, and make the converter work in the optimal state of the full-range input. However, the control unit contains three degrees of freedom, making it difficult for the control unit to be calculated uniformly and in real time. Moreover, the switching of the working area of the converter increases the complexity of the control.

Contents of the invention

In order to overcome the above-mentioned commonly used dual active bridge bidirectional DC-DC converter controller design complex, reduce reactive power loss and conduction loss and other related problems, the present invention discloses a bidirectional DC-DC converter current critical continuous The unified control method, the technical problem to be solved is to provide a dual active bridge bidirectional DC-DC converter current critical continuous unified control method for the topology of commonly used types of bidirectional DC-DC converters, reducing the reactive power of the circuit Loss, reduce the current stress of the switch tube and the circulation loss of the converter, improve the efficiency and reliability of the converter; at the same time, it can greatly reduce the complexity of the control unit.

The purpose of the present invention is achieved through the following technical solutions.

A commonly used type of dual active bridge bidirectional DC-DC converter contains three control variables, including the voltage v _AB between the center points of the two bridge arms of the full bridge circuit on the primary side, and the center point of the two bridge arms of the full bridge circuit on the secondary side. The voltage v _CD between the points, and the shift angle between the transformer primary voltage v _AB and the transformer secondary voltage v _CD . The present invention discloses a bidirectional DC-DC converter current critical continuous unified control method, which uses the difference between the given v _ref of the output voltage of the secondary side and the actual output sampling value V ₂ of the secondary side as the voltage controller The input of the controller, the output of the controller is used to adjust the shift angle control signal between the primary side voltage v _AB of the transformer and the secondary side voltage v _CD of the transformer According to the steering angle control signal Boundary conditions and control conditions between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD can obtain the control signal d ₁ for controlling the transformer primary side voltage v _AB and the control signal for controlling the transformer secondary side voltage v _CD d ₂ . Through the boundary conditions and control conditions described above, the transformer current can be in a critical continuous mode. According to the steering angle control signal Control signal d ₁ and control signal d ₂ , the drive generation unit generates the corresponding switch tube drive control signal, thereby controlling the primary side voltage v _AB of the converter and the secondary side voltage v _CD of the transformer, as well as the primary side voltage v _AB of the transformer and the transformer The shift angle Φ between the secondary side voltage v _CD . The boundary conditions and control conditions can make the transformer current in a critical continuous mode, so that the converter has a larger duty cycle and a smaller steering angle under the same output power. The reactive power loss of the circuit is reduced, the current stress of the switch tube and the circulation loss of the converter are reduced, thereby improving the efficiency and reliability of the converter.

The controller can realize the control of the bidirectional DC-DC converter through only one voltage controller, which can reduce the complexity of the control unit. The voltage controller is preferably a proportional-integral PI controller.

The boundary conditions according to the steering angle control signal The size can be divided into boundary conditions (a) and boundary conditions (b):

When moving to the angle control signal When it is greater than or equal to zero, use boundary condition (a) as shown in formula (1),

When moving to the angle control signal When is less than zero, use boundary condition (b) as shown in formula (2),

Among them, V ₁ and V ₂ are the active bridge DC voltages to the primary side and the secondary side of the converter respectively; n is the transformation ratio 1:n from the primary side to the secondary side of the transformer.

The control conditions are shown in formula (3).

nV ₁ d ₁ =V ₂ d ₂ (3)

The converter is a bidirectional topology, and the primary side and the secondary side can be interchanged.

A bidirectional DC-DC converter current critical continuous unified control method disclosed by the present invention comprises the following steps,

Step 1. Determine the given DC output voltage V _ref on the secondary side of the converter;

Step 2: Sampling the DC voltages of the active bridge on the primary side and the secondary side of the converter, which are denoted as V ₁ and V ₂ respectively. Calculate the difference between the output voltage given value _Vref and _V2 , said difference is used as the input of the output voltage regulator. The output of the voltage regulator is used as a steering angle control signal between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD

Step 3. Control the signal according to the steering angle Boundary conditions and control conditions between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD The control signal d ₁ for controlling the transformer primary side voltage v _AB and the control signal d of the transformer secondary side voltage v _CD can be obtained ₂ . Through the boundary conditions and control conditions described above, the transformer current can be in a critical continuous mode.

Step 3.1, giving the boundary conditions for solving the control signal d ₁ or the control signal d ₂ .

When moving to the angle control signal When it is greater than or equal to zero, the control signal d ₁ is obtained by using the boundary condition (a) as shown in formula (1).

When moving to the angle control signal When it is less than zero, use the boundary condition (b) as shown in formula (2) to obtain the control signal d ₂ .

Among them, V ₁ and V ₂ are the sampling values of the DC voltage of the active bridge on the primary side and the secondary side of the converter respectively, and n is the transformation ratio 1:n of the primary side to the secondary side of the transformer.

Step 3.2, giving control conditions as shown in formula (3).

nV ₁ d ₁ =V ₂ d ₂ (3)

When moving to the angle control signal When greater than or equal to zero, according to the value of the control signal d ₁ obtained in step 3.1, use formula (3) to solve d ₂ ; when moving to the angle control signal When it is less than zero, use the formula (3) to solve _d1 according to the value of the control signal _d2 obtained in step 3.1;

Step 4. Control the signal according to the direction of movement Boundary conditions and control conditions between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD can be used to control the control signal d ₁ of the transformer primary side voltage v _AB and the control signal d of the transformer secondary side voltage v _{CD 2} . By driving the generation unit, the drive signal of the corresponding switch tube is generated, thereby controlling the relationship between the primary side voltage v _AB of the converter and the transformer secondary side voltage v _CD and the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD The steering angle Φ makes the converter have a larger duty cycle and a smaller steering angle under the same output power. The reactive power loss of the circuit is reduced, the current stress of the switch tube and the circulation loss of the converter are reduced, thereby improving the efficiency and reliability of the converter.

The generation of the driving signal of the switching tube in step 4 depends on the specific topology of the bidirectional DC-DC converter.

The generation of the driving signal of the switching tube described in step 4 is aimed at the commonly used bidirectional dual active bridge DC-DC converter, which includes eight switching tube driving control signals, which are respectively marked as: S ₁ , S ₂ , S ₃ , S ₄ , _S5 , _S6 , _S7 , _S8 . The characteristics of the eight switch tube drive signals are: all drive signals are 50% square wave signals; S ₁ and S ₂ are complementary, S ₃ and S ₄ are complementary, S ₅ and S ₆ are complementary, S ₇ and S ₈ is complementary; the time of S ₁ leading S ₃ is controlled by d ₁ , the time of S ₅ leading S ₇ is controlled by d ₂ , and the phase difference between S ₁ and S ₅ is determined by control.

The converter is a bidirectional topology, and the primary side and the secondary side can be interchanged.

Beneficial effect:

1. The present invention discloses a bidirectional DC-DC converter current critical continuous unified control method, which can adjust the voltage v _AB between the center points of the two bridge arms of the primary side full bridge circuit by controlling the drive signal of the primary side switch tube ; By controlling the driving signal of the secondary side switch tube, the voltage v _CD between the center points of the two bridge arms of the secondary side full bridge circuit can be adjusted; by adjusting the phase difference between the primary side and the secondary side switch tube signals, it can be realized Control of the heading angle between v _AB and v _CD . Through the aforementioned control, the length of the interval in which the transformer current is zero when the converter is working is very short, which is critically continuous, and the circulation loss and conduction loss are reduced.

2. Through a bidirectional DC-DC converter current critical continuous unified control method disclosed in the present invention, only one controller can be used to adjust the voltage v _AB between the center points of the two bridge arms of the full bridge circuit on the primary side, and the two Unified control of the voltage v _CD between the center points of the two bridge arms of the secondary side full bridge circuit and the steering angle between v _AB and v _CD . The method does not need to store the control data in the look-up table in advance, can realize real-time control, and the control loop is simple and reliable.

3. Through a bidirectional DC-DC converter current critical continuous unified control method disclosed in the present invention, the reactive power loss of the circuit is reduced, the current stress of the switch tube and the circulation loss of the converter are reduced, thereby improving the converter's performance. efficiency and reliability.

Description of drawings

Fig. 1 is the schematic structural diagram of the dual active bridge bidirectional DC-DC converter circuit of the present embodiment;

FIG. 2 is a block diagram of a unified control method for current critical continuity in this embodiment;

Figure 3 is the main waveform diagram of this example.

Detailed ways

The present invention will be described in detail below in conjunction with accompanying drawing and embodiment, also described the technical problem and beneficial effect that the technical solution of the present invention solves simultaneously, it should be pointed out that described embodiment is only intended to facilitate the understanding of the present invention, and It has no limiting effect on it.

Example 1:

Taking the control of a bidirectional DC-DC converter of a commonly used type as an example to illustrate the realizability and beneficial effects of a current critical continuous unified control method for a bidirectional DC-DC converter disclosed in the present invention.

A common type of dual active bridge bidirectional DC-DC converter is shown in Figure 1. As shown in the figure, the converter is a bidirectional dual active bridge DC-DC converter, the primary side is an active full bridge circuit, and the secondary side is also an active full bridge circuit. Points A and B are the respective midpoints of the two bridge arms of the primary side active bridge; C and D points are the respective midpoints of the two bridge arms of the secondary side active bridge; v _AB is point A and point B The voltage difference between; v _CD is the voltage difference between C and D points. i _p and i _s are the currents of the transformer primary side and secondary side of the converter. V ₁ is the DC voltage of the primary side; V ₂ is the DC voltage of the secondary side.

The control block diagram adopted in this embodiment is shown in FIG. 2 . With reference to FIG. 2, a current critical continuous and unified control method for a bidirectional DC-DC converter disclosed in this embodiment includes the following steps,

Step 1. Determine the given DC output voltage V _ref on the secondary side of the converter;

Step 2: Sampling the DC voltages of the active bridge on the primary side and the secondary side of the converter, which are denoted as V ₁ and V ₂ respectively. Calculate the difference between the output voltage given value _Vref and _V2 , said difference is used as the input of the output voltage regulator. The output of the voltage controller is used as a steering angle control signal between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD Among them, the output of the controller needs positive and negative limit.

Step 3. Control the signal according to the steering angle Boundary conditions and control conditions between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD The control signal d ₁ for controlling the transformer primary side voltage v _AB and the control signal d of the transformer secondary side voltage v _CD can be obtained ₂ . Through the boundary conditions and control conditions described above, the transformer current can be in a critical continuous mode.

Step 3.1, giving the boundary conditions for solving the control signal d ₁ or the control signal d ₂ .

When moving to the angle control signal When it is greater than or equal to zero, the control signal d ₁ is obtained by using the boundary condition (a) as shown in formula (1).

When moving to the angle control signal When it is less than zero, use the boundary condition (b) as shown in formula (2) to obtain the control signal d ₂ .

Among them, V ₁ and V ₂ are the active bridge DC voltages of the primary side and the secondary side of the converter respectively, and n is the transformation ratio 1:n of the primary side to the secondary side of the transformer.

Step 3.2, giving control conditions as shown in formula (3).

nV ₁ d ₁ =V ₂ d ₂ (3)

When moving to the angle control signal When greater than or equal to zero, according to the value of the control signal d ₁ obtained in step 3.1, use formula (3) to solve d ₂ ; when moving to the angle control signal When it is less than zero, use the formula (3) to solve _d1 according to the value of the control signal _d2 obtained in step 3.1;

Step 4. Control the signal according to the direction of movement Boundary conditions and control conditions between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD The control signal d ₁ for controlling the transformer primary side voltage v _AB and the control signal d of the transformer secondary side voltage v _CD can be obtained ₂ Generate the driving signal of the switch tube, thereby controlling the primary side voltage v _AB of the converter and the transformer secondary side voltage v _CD and the shift angle Φ between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD , so that The transformer current is in a critical continuous state, which reduces the reactive power loss of the circuit, the current stress of the switch tube and the circulation loss of the converter, thereby improving the efficiency and reliability of the converter.

The control method described in this embodiment and its circuit topology working process are as follows:

After the converter starts to work on power, for the V ₂ voltage regulator, when the secondary side voltage is lower than the given V _ref of the voltage, the power of the converter is transferred from the V ₁ side to the V ₂ side. The digital controller (DSP TMS320F28335) samples the DC voltage on the _V2 side through the sensor as feedback. Pass the value of V _ref -V ₂ through the digital PI regulator and limiter, the output value As a direction control signal between two active bridges, the value of this direction control signal is positive. Get output control value Then, use the boundary condition (a) to calculate the moving control signal between the two bridge arms of the active bridge on the V ₂ side, which is denoted as d ₁ . Boundary condition (a) can be expressed as: n is the transformation ratio (1:n) of the primary side of the transformer to the secondary side. After d ₁ is calculated, the relational expression: nV ₁ d ₁ =V ₂ d ₂ can be used to calculate the direction-moving control signal d ₂ between the two bridge arms of the active bridge on the V ₁ side. The boundary condition (a) in this control method can ensure that the transformer current is critically continuous (the waveforms are shown as i _p and _is in Figure 3), and under the same power condition, the peak value and effective value of the current are small, reducing Small loss and high efficiency.

When the secondary side voltage is higher than the given V _ref of voltage, the power of the converter is transferred from the V ₂ side to the V ₁ side. The digital controller (DSP TMS320F28335) samples the DC voltage on the _V2 side through the sensor as feedback. Pass the value of V _ref -V ₂ through the digital PI regulator and limiter, the output value As a direction control signal between two active bridges. At this time, the value of the moving direction control signal is a negative value. Get output control value Afterwards, use the boundary condition (b) to calculate the direction-moving control signal between the two bridge arms of the active bridge on the V ₁ side, which is denoted as d ₂ . Among them, the boundary condition (b) can be expressed as: n is the transformation ratio (1:n) of the primary side of the transformer to the secondary side. After d ₂ is calculated, the relational expression: nV ₁ d ₁ =V ₂ d ₂ can be used to calculate the direction-moving control signal d ₁ between the two bridge arms of the active bridge on the V ₂ side. The boundary condition (a) in this control method can ensure that the transformer current is critically continuous. Under the same power condition, the peak value and effective value of the current are small, which reduces loss and improves efficiency.

Drive generation unit obtained by the aforementioned method The three control variables d ₁ and d ₂ generate corresponding driving signals, including S ₁ , S ₂ , S ₃ , S ₄ , S ₅ , S ₆ , S ₇ , and S ₈ . The timing diagram of the drive signal and the relevant circuit waveform are shown in Figure 3. The timing description of the eight driving signals is as follows: all driving signals are 50% square wave signals; S ₁ and S ₂ are complementary, S ₃ and S ₄ are complementary, S ₅ and S ₆ are complementary, S ₇ and S ₈ Complementary; the time of S ₁ leading S ₃ is controlled by d ₁ , the time of S ₅ leading S ₇ is controlled by d ₂ , and the phase difference between S ₁ and S ₅ is controlled by control.

use d ₁ and d ₂ control eight driving signals, which can control the transformer primary side winding voltage v _ab , the secondary side winding voltage v _cd , and the phase difference between v _ab and v _cd . Realize the power control of the converter. When the output power needs to be increased, the output of the DC terminal voltage controller on the V ₂ side will increase, thereby increasing the phase shift angle between v _ab and v _cd , and increasing the output power; when the output power decreases, the output of the DC terminal voltage controller on the V ₂ side Will decrease, thereby reducing the phase shift angle between v _ab and v _cd , reducing the output power. With only one controller, multivariable control of power can be realized, simplifying the design process. In addition, the control method can ensure that the transformer winding current remains critically continuous under different loads. At the same time, the converter has no reactive power loss under any load.

The specific description above is to further describe the purpose, technical solution and beneficial effect of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not used to limit the protection scope of the present invention. , Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. A bidirectional DC-DC converter current critical continuous unified control method is characterized in that: by using the given v _ref of the output voltage of the secondary side and the output voltage sampling value _V of the actual secondary side difference as The input of the voltage controller, the output of the controller is used to adjust the steering angle control signal between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD According to the steering angle control signal Boundary conditions and control conditions between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD , the control signal d ₁ of the transformer primary side voltage v _AB and the control signal d ₂ of the transformer secondary side voltage v _CD can be obtained; Through the boundary conditions and control conditions, the transformer current can be in a critical continuous mode; according to the direction angle control signal The control signal d ₁ and the control signal d ₂ , the drive generation unit generates the corresponding switching tube drive control signal, thereby controlling the primary side voltage v _AB of the transformer and the secondary side voltage v _CD of the transformer, as well as the primary side voltage v _AB of the transformer and the secondary side voltage of the transformer The shift angle Φ between the secondary side voltage v _CD ; the boundary conditions and control conditions can make the transformer current in a critical continuous mode, so that the reactive power loss of the circuit is reduced, the current stress of the switch tube and the circulation loss of the converter Reduced, so that the efficiency and reliability of the converter can be improved. 2. A kind of bidirectional DC-DC converter current critical continuous unified control method according to claim 1, it is characterized in that: described controller only can realize to described bidirectional DC-DC through a voltage controller The control of the converter can reduce the complexity of the control unit; the voltage controller is a proportional-integral PI controller. 3. A kind of bidirectional DC-DC converter current critical continuous unified control method according to claim 1 or 2, it is characterized in that: described boundary condition is controlled according to the direction angle control signal The size can be divided into two types: boundary condition (a) and boundary condition (b); When moving to the angle control signal When it is greater than or equal to zero, use boundary condition (a) as shown in formula (1), When moving to the angle control signal When is less than zero, use boundary condition (b) as shown in formula (2), Among them, V ₁ and V ₂ are the sampling values of the DC voltage of the active bridge on the primary side and the secondary side of the converter respectively; n is the transformation ratio 1:n from the primary side to the secondary side of the transformer. 4 . The current critical continuous and unified control method of a bidirectional DC-DC converter according to claim 3 , wherein the converter has a bidirectional topological structure, and the primary side and the secondary side can be interchanged. 5. A bidirectional DC-DC converter current critical continuous unified control method is characterized in that: comprising the following steps, Step 1. Determine the given DC output voltage V _ref on the secondary side of the converter; Step 2, sampling the active bridge DC voltages on the primary side and the secondary side of the converter, which are respectively denoted as V ₁ and V ₂ ; calculating the difference between the output voltage given value V _ref and V ₂ , the difference The value is used as the input of the output voltage regulator; the output of the voltage regulator is used as the steering angle control signal between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD Step 3. Control the signal according to the steering angle Boundary conditions and control conditions between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD The control signal d ₁ for controlling the transformer primary side voltage v _AB and the control signal d of the transformer secondary side voltage v _CD can be obtained ₂ ; the transformer current can be in a critical continuous mode through the boundary conditions and control conditions; Step 3.1, providing boundary conditions for solving the control signal d ₁ or the control signal d ₂ ; When moving to the angle control signal When is greater than or equal to zero, the control signal d ₁ is obtained by using the boundary condition (a) as shown in formula (1); When moving to the angle control signal When is less than zero, use the boundary condition (b) as shown in the formula (2) to obtain the control signal d ₂ ; Among them, V ₁ and V ₂ are the sampling values of the DC voltage of the active bridge on the primary side and the secondary side of the converter respectively, and n is the transformation ratio 1:n from the primary side to the secondary side of the transformer; Step 3.2, provide control conditions as shown in formula (3); nV ₁ d ₁ =V ₂ d ₂ (3) When moving to the angle control signal When greater than or equal to zero, according to the value of the control signal d ₁ obtained in step 3.1, use formula (3) to solve d ₂ ; when moving to the angle control signal When it is less than zero, use the formula (3) to solve _d1 according to the value of the control signal _d2 obtained in step 3.1; Step 4. Control the signal according to the direction of movement Boundary conditions and control conditions between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD The control signal d ₁ for controlling the transformer primary side voltage v _AB and the control signal d of the transformer secondary side voltage v _CD can be obtained ₂ ; Generate the corresponding switch tube drive signal through the drive unit, thereby controlling the primary side voltage v _AB of the transformer and the transformer secondary side voltage v _CD and the shift between the transformer primary side voltage v _AB and the transformer secondary side voltage v _CD The angle Φ makes the transformer current in a critical continuous mode, which reduces the reactive power loss of the circuit, the current stress of the switch tube and the circulation loss of the converter, thereby improving the efficiency and reliability of the converter. 6. A kind of bidirectional DC-DC converter current critical continuum unified control method according to claim 5, it is characterized in that: the drive signal of generation switching tube described in step 4 is decided according to specific bidirectional DC-DC converter topology . 7. A kind of bidirectional DC-DC converter current critical continuous unified control method according to claim 5, it is characterized in that: the drive signal of generation switching tube described in step 4, for commonly used bidirectional dual active bridge DC- DC converter, which includes eight switch tube drive control signals, respectively marked as: S ₁ , S ₂ , S ₃ , S ₄ , S ₅ , S ₆ , S ₇ , S ₈ ; the eight switch tube drive The characteristics of the signal are: all driving signals are 50% square wave signals; S ₁ and S ₂ are complementary, S ₃ and S ₄ are complementary, S ₅ and S ₆ are complementary, S ₇ and S ₈ are complementary; S ₁ is ahead of S The time of ₃ is controlled by d ₁ , the time of S ₅ ahead of S ₇ is controlled by d ₂ , and the phase difference between S ₁ and S ₅ is controlled by control.