A preset time feedback controller, control system and control method of a dual active bridge circuit

Abstract

The present invention discloses a preset time feedback controller of a dual active bridge circuit in the field of power electronics technology, comprising: a time conversion law for inputting a preset time t p , output scale transformation coefficient m ( t ); time scale transformation law, used to input the scale transformation coefficient m ( t ), System Error e ( t ), output scale error signal Z ( t ), the system error e ( t ) is the sampling signal of the output voltage x ( t ) and the expected voltage x d The difference between the input and output voltages; feedback control law, used to input and output voltage sampling signals x ( t ), output scale transformation coefficient m ( t ), the rate of change of the time scale transformation coefficient, and the output scale error signal Z ( t ), System Error e ( t ), the expected voltage change rate and non-negative parameters α , output control signal u ( t ) The dual active bridge circuit is controlled by a PWM modulator and a driving circuit. The present invention transforms and reduces the time stability analysis of the output voltage error of the dual active bridge circuit, and uses the design concept of feedback control to realize a preset time feedback controller of the dual active bridge circuit.

Description

Technical Field

[0001] The invention relates to the technical field of electronics and electrical engineering, and in particular to a control system of a dual active bridge circuit. Background Art

[0002] In the dual active bridge charging and discharging circuit, in order to ensure the steady-state performance and transient performance of the output bus voltage when the battery is discharged, the controller of the dual active bridge charging and discharging circuit must be designed to form a closed-loop control, thereby generating a pulse width modulation signal (PWM) or a phase shift control signal to form an equivalent duty cycle, which is used to control the on and off of the switch tube in the dual active bridge circuit. The dual active bridge circuit usually adopts a traditional PID controller, that is, the deviation between the desired voltage and the output voltage is proportional, integral and differential operations to generate a control signal. The dual active bridge circuit used in energy storage power equipment is used as a charging and discharging circuit for energy storage batteries. Its low-voltage side is connected to the battery and the high-voltage side is connected to the bus. When the bus voltage drops, the dual active bridge circuit is required to quickly track the bus voltage set value through the discharge control of the battery. However, the traditional PID controller cannot accurately predict the response time of the output voltage of the dual active bridge circuit, that is, the dual active bridge circuit based on the traditional PID controller cannot ensure that the response time of the bus voltage can meet the requirements of stable operation of energy storage power equipment.

[0003] In addition, since traditional PID control is a linear control strategy based on classical control theory, after its control parameters are adjusted, they generally do not change with the real-time status of the control system. However, the dual active bridge circuit is a typical switching nonlinear system. The dead time of the switching device, load disturbance and nonlinear load will deteriorate the quality of the output voltage waveform. Therefore, it is difficult to meet the steady-state performance and dynamic performance of the inverter using traditional linear control methods, which is particularly prominent in the battery discharge condition in the energy storage system. This puts high demands on the adjustment of PID control parameters, resulting in a long development cycle and increased development costs. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a preset time feedback controller, a control system and a control method for a dual active bridge circuit, which transforms and reduces the time stability analysis of the output voltage error of the dual active bridge circuit, and uses the design concept of feedback control to realize the preset time feedback controller of the dual active bridge circuit.

[0005] The object of the present invention is achieved in this way: a preset time feedback controller of a dual active bridge circuit, comprising:

[0006] Time conversion law, used to enter the preset time t p , output scale transformation coefficient μ ( t );

[0007] Time scale transformation law, used to input the scale transformation coefficient μ ( t ), System Error e ( t ), output scale error signal Z ( t ), the system error e ( t ) is the sampling signal of the output voltage x ( t ) and the expected voltage x d The difference between

[0008] Feedback control law, used to input and output voltage sampling signals x ( t ), output scale transformation coefficient μ ( t ), the rate of change of the time scale transformation coefficient , output scale error signal Z ( t ), System Error e ( t ), the expected voltage change rate and non-negative parameters α , output control signal u ( t ) The dual active bridge circuit is controlled via a PWM modulator and a drive circuit.

[0009] Furthermore, the time conversion law adopts the following formula:

[0010]

[0011] in, t p For preset time, μ ( t ) is the time scale transformation coefficient.

[0012] Furthermore, the time scale transformation law adopts the following formula:

[0013] Z ( t )= μ ( t ) e ( t )

[0014] in, Z ( t ) is the scale error signal, e ( t ) is the systematic error.

[0015] Furthermore, the feedback control law adopts the following formula:

[0016]

[0017] in, f s is the switching frequency, N is the transformer turns ratio, V bat is the battery voltage, L s is the resonant inductor, D is the duty cycle, R out is the output impedance, C 2 is the output capacitor, V bus is the bus voltage, P 0 is the output power.

[0018] A preset time feedback control system of a dual active bridge circuit, comprising a preset time feedback controller of the dual active bridge circuit, a PWM modulator, a driving circuit, a dual active bridge circuit and a conditioning circuit;

[0019] The output end of the dual active bridge circuit is connected to the input end of the sampling and conditioning circuit, the output end of the sampling and conditioning circuit is connected to the input end of the preset time feedback controller of the dual active bridge circuit, the output end of the preset time feedback controller of the dual active bridge circuit is connected to the input end of the PWM modulator, the output end of the PWM modulator is connected to the input end of the driving circuit, and the output end of the driving circuit is used to control the on and off of the switch tube of the dual active bridge circuit.

[0020] A preset time feedback control method for a dual active bridge circuit, using the above control system, comprises the following steps:

[0021] Step 1) Set the preset time t p Perform time conversion to obtain the scale transformation coefficient μ ( t ),

[0022] Step 2) Scale the transformation coefficients μ ( t ) and the sampling signal of the output voltage x ( t ), expected voltage x d Systematic error caused by difference e ( t ) performs time scale transformation and outputs scale error signal Z ( t);

[0023] Step 3) The sampling signal of the output voltage x ( t ), output scale transformation coefficient μ ( t ), the rate of change of the time scale transformation coefficient , output scale error signal Z ( t ), System Error e ( t ), the expected voltage change rate , non-negative parameters α Perform feedback control and output control signal u ( t );

[0024] Step 4) Control signal u ( t ) as the modulation signal of the PWM modulator, the PWM modulator generates a pulse control signal v duty , and then generate a driving signal after passing through the driving circuit v dr , used to control the on and off of the switch tube in the dual active bridge circuit, thereby achieving bus voltage V bus stability.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention adopts a combination of time transformation law, time scale conversion law and feedback control law, and can preset the response time of the output voltage of the dual active bridge circuit, which is beneficial to improving the controllability and rapid responsiveness of the dual active bridge circuit. The invented controller simplifies the system control structure while ensuring the tracking performance of the system, making the controller easy to implement in practical applications, shortening the development cycle to reduce development costs; applying the present invention to energy storage power equipment can ensure the rapidity of the dual active bridge circuit to establish or maintain the bus voltage, thereby meeting the requirements for stable operation of the energy storage power equipment; from the perspective of the design of the control strategy, the invented preset time feedback controller also includes the dynamic form of the system, which ensures the control accuracy of the control system and improves the robustness of the energy storage power equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0027] Figure 1 It is a schematic diagram of the control system in the present invention.

[0028] Figure 2 It is a schematic diagram of the hardware structure of the application circuit in the control system of the present invention.

[0029] Figure 3 Schematic diagram of the controller in the present invention.

[0030] Figure 4 This is a flow chart of the feedback control law calculation subroutine implemented in the present invention.

[0031] Figure 5 is a voltage simulation waveform according to an embodiment of the present invention.

[0032] Figure 6 4 is a duty cycle simulation waveform of an embodiment of the present invention.

[0033] in, Figure 1 Symbolic names in:

[0034] .

[0035] Figure 2 Symbolic names in:

[0036] .

[0037] Other Figure 1 Description of symbols in .

[0038] Figure 3 , Figure 4 Symbol name reference in Figure 1 . DETAILED DESCRIPTION

[0039] 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.

[0040] like Figure 1 and Figure 2 As shown, a preset time feedback control system of a dual active bridge circuit comprises:

[0041] The dual active bridge circuit 1, the sampling and conditioning circuit 2, the preset time feedback controller 3, the PWM modulator 4 and the driving circuit 5, wherein the PWM modulator 4 and the preset time feedback controller 3 can be implemented by a digital controller. The dual active bridge circuit includes a battery voltage source V bat , bus voltageV bus , eight power switch tubes Q1~Q8, resonant inductor L s ,capacitance C 1 ~C 3 And transformer T r1 ;capacitance C 1 The voltage across the battery is the battery voltage V bat ,capacitance C 2 The voltage across the two ends is the bus voltage V bus . Bus voltage V bus After sampling and conditioning circuit 2, the bus voltage sampling signal is obtained U bus (i.e. expected voltage x d ), as the input signal of the preset time feedback controller 3, is sent to the program processing unit of the digital control chip, that is, the preset time feedback controller 3, and the operation of the control strategy composed of the time conversion law, the time scale transformation law and the feedback control law is completed in the preset time feedback controller 3 to obtain the control signal u ( t ), control signal u ( t ) as a modulation wave and compared with the carrier signal in the PWM modulator 4 to generate a duty cycle signal v duty The signal is output by the PWM modulator 4 to the drive circuit 5, and the drive circuit outputs a pulse control signal v dr The switch tubes Q1 to Q8 in the dual active bridge circuit 1 are acted on, thereby realizing the control function of the preset time feedback controller of the battery discharge in the dual active bridge circuit 1; the switch tubes Q1 to Q8 in the dual active bridge circuit 1 are driven by the signal v dr Under the control of the inductor, the energy flow is controlled by controlling the phase shift angle of the switch tube corresponding to each switching cycle. L s1 ,capacitance C 2 After filtering, the output bus voltage V bus .

[0042] like Figure 3 The preset time feedback controller of the dual active bridge shown in the figure is composed of three parts: time conversion law, time scale transformation law and feedback control law; the preset timet p sent to the time conversion law, which outputs the scale conversion coefficient μ ( t ), the scale transformation coefficient μ ( t ) is sent to the time scale transformation law, the time scale transformation coefficient μ ( t ) and its rate of change Sent to the feedback control law; the bus voltage of the dual active bridge circuit V bus The sampling signal of the output voltage is obtained through the sampling and conditioning circuit U bus (ie output voltage x ( t )), the sampling signal of the output voltage x ( t ) and the expected voltage change rate Sent to the feedback control law, the sampling signal of the output voltage x ( t ) and the desired voltage x d The difference e ( t ) are sent to the time scale transformation law and the feedback control law as system errors; the time scale transformation coefficient μ ( t ) and the systematic error e ( t ) Output scale error signal after time scale transformation law Z ( t ), and the scale error signal Z ( t ) is used to obtain the scale error signal change rate by taking the first-order derivative , the scale error signal Z ( t ) is sent to the feedback control law; non-negative parameter α Send to feedback control law; select appropriate Lyapunov function V ( t )=1 / 2 z 2 ( t ), design the feedback control law so that the derived Lyapunov function satisfies ;in c For any parameter greater than zero, the specific mathematical model of the feedback control law can be obtained, and the system error will be t p The control output signal is generated by the feedback control law. u (t ).

[0043] like Figure 2 As shown, the control signal output by the feedback control law is u ( t ) as the modulation signal of the PWM modulator, the pulse control signal generated by the PWM modulator v duty , and then generate a driving signal after passing through the driving circuit v dr , used to control the on and off of the switch tube in the dual active bridge circuit, thereby achieving bus voltage V bus stability.

[0044] The following is a further explanation of the theoretical derivation process of controller design and stability analysis.

[0045] The design of the controller needs to utilize the structural characteristics of the dual active bridge dynamic equation. Therefore, the small signal modeling method is first used to establish a small signal model of the duty cycle to the bus voltage when the battery is discharged, and the small signal model is Laplace transformed to obtain a continuous mathematical model.

[0046] System Duty Cycle d ( s ) to bus voltage V bus The transfer function between is:

[0047] (1)

[0048] In the above formula, f s is the switching frequency, N is the transformer turns ratio, V bat is the battery voltage, L s is the resonant inductor, D is the duty cycle, R out is the output impedance, C 2 is the output capacitor, V bus is the bus voltage, P 0 is the output power.

[0049] Solve the inverse Laplace transform of the above transfer function to obtain the continuous mathematical model of the dual active bridge circuit

[0050] (2)

[0051] in, .

[0052] Defining state variables x ( t )= V bus ( t ).definition u ( t )= d ( t ) is the control input, and the mathematical model of the full-bridge circuit can be summarized as:

[0053] (3)

[0054] This model is only used as a controlled object in simulation.

[0055] From the mathematical model in (2), it can be seen that the controlled object is a first-order system, and the controller can be directly designed by the preset time feedback control method; the invented preset time feedback controller consists of three parts: time conversion law, time scale transformation law and feedback control law to ensure the rapid convergence of the dual active bridge circuit system; the main control goal of the dual active bridge circuit system is to make the circuit bus voltage V bus ( t ) tracks to the expected value, and defines the sampling signal of the output voltage as x ( t ), the expected voltage is x d , the output error of the system is as follows:

[0056] e ( t )= x ( t )- x d (4)

[0057] In the above formula, e ( t ) is the output error of the system.

[0058] Before designing the controller, the time conversion law is introduced in the following form:

[0059] (5)

[0060] In the above formula, t p For preset time, μ ( t ) is the time scale transformation coefficient.

[0061] The time scale conversion coefficient μ ( t) is sent to the time scale transformation law, and the system error of the system is calculated by using the time transformation law. e ( t ) is scaled to obtain:

[0062] Z ( t )= μ ( t ) e ( t ) (6)

[0063] In the above formula, Z ( t ) is the scale error signal.

[0064] Solve the first-order derivative of the scale error signal, which has the following form:

[0065] (7)

[0066] In the above formula, is the rate of change of the scale error signal, is the rate of change of the scale transformation coefficient, is the rate of change of system error.

[0067] Select the Lyapunov function:

[0068] (8)

[0069] Designing the controller u ( t ) so that the derived Lyapunov function satisfies ,in c Assuming any parameter greater than zero, the dual active bridge circuit under the controller can meet the preset time stability condition, and the output error of the system will be zero at the set time. V ( t ) has the following first-order derivative form:

[0070] (9)

[0071] Designing the system controller u ( t )for:

[0072] (10)

[0073] In the above formula, a is the non-negative parameter to be designed. Substituting the controller (10) into (9) yields:

[0074] (11)

[0075] In the above formula, is a positive constant, the system error will be t p The internal time is zero, completing the design requirements of the preset time feedback controller of the dual active bridge circuit system.

[0076] Regarding the method of setting the design parameters: Using Matlab software, the parameters of the preset time feedback controller of the designed dual active bridge circuit are set and the performance simulation is performed. Design a simulation program to determine the initial conditions of the dual active bridge circuit x (0), set the design parameters a , t p , until the dual active bridge output voltage x ( t ) has good tracking performance and fast response.

[0077] The control program consists of a main program module and a feedback control law calculation subprogram module. Figure 3 and Figure 4 The writing methods of the main program and the feedback control law calculation subroutine are explained respectively.

[0078] Combination Figure 4 In the main program, the design parameters are first adjusted according to the set values ​​in the simulation. a,t p Assignment, for output voltage x ( t ) to sample and set the expected voltage x d . Determine the sampling period. When the sampling time is up, call the preset time feedback control law calculation subroutine to calculate the control signal u ( t ), the control signal u ( t ) is sent to the PWM modulator, and then sampled, calculated and output in a cycle.

[0079] Combination Figure 3 The preset time controller calculation subroutine first calculates the time scale conversion coefficient according to formula (5): μ ( t ), according to formula (6), the system output error e ( t ) performs time scale transformation and outputs scale error signal Z ( t ), the output voltage x ( t ), expected voltage change rate x d , System output error e ( t), time scale variation coefficient μ ( t ) and its rate of change , scale error signal Z ( t ), non-negative parameters a The control signal is sent to the feedback control law and is calculated according to formula (10) u ( t ).

[0080] A specific embodiment of the present invention is as follows:

[0081] The main parameters of the dual active bridge circuit system are as follows: Under the condition of battery discharge, the given bus voltage is the expected voltage x d =400V, transformer turns ratio (battery side winding / bus side winding) N=0.125, switching frequency 40kHz, resonant inductor L s1 = 0.00000066H, output power 5kW. The specific parameters of the dynamic system are: k 1 =23.86, k 2 =32, T=0.64.

[0082] The time conversion law, time scale transformation law and feedback control law in the controller are obtained using equations (5), (6) and (10) respectively. a= 0.002, respectively preset time t p =0.5s, t p =1s and t p =2s when the simulation waveform is as follows Figure 5-6 As shown, Figure 5 is the output voltage of the dual active bridge, Figure 6 is the equivalent duty cycle; Figure 5 It can be seen that the output voltage of the dual active bridge circuit is established within the above preset time, thereby verifying the effectiveness of the present invention.

[0083] From the above description, it can be seen that the preset time feedback controller of the dual active bridge circuit of the invention has the following advantages:

[0084] (1) The design structure is simple, the control accuracy is high, and the tracking response speed is fast. The preset time control strategy can establish the output voltage time of the dual active bridge circuit at the preset time, which helps to improve the rapid response of the system;

[0085] (2) The preset time feedback controller of the circuit system is designed using the state feedback control strategy. This simplifies the structure of the dual active bridge circuit controller while ensuring the tracking performance of the system, making the controller easy to implement in practical applications.

[0086] (3) From the perspective of control strategy design, the controller design adopted includes dynamic form, which ensures the control accuracy of the control system;

[0087] (4) In addition to being used in energy storage power equipment, the present invention can also be used in bidirectional energy storage charging and discharging circuits such as Buck-Boost and CLLC to achieve high reliability.

[0088] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A preset time feedback controller for a dual active bridge circuit, characterized in that: include: Time conversion law, used to enter the preset time t p , output scale transformation coefficient μ(t); The time scale transformation law is used to input the scale transformation coefficient μ(t), the system error e(t), and output the scale error signal Z(t). The system error e(t) is the sampling signal x(t) of the output voltage and the expected voltage x d The difference between Feedback control law, which is used to input the sampling signal x(t) of the output voltage, the scaling coefficient μ(t), and the rate of change of the scaling coefficient , scale error signal Z(t), system error e(t), expected voltage change rate And non-negative parameter α, the output control signal u(t) controls the dual active bridge circuit through the PWM modulator and the drive circuit, and the feedback control law adopts the following formula: ； ； ； ； Among them, f s is the switching frequency, N is the transformer turns ratio, V bat is the battery voltage, L s is the resonant inductor, D is the duty cycle, R out is the output impedance, C2 is the output capacitance, V bus is the bus voltage, and P0 is the output power.

2. The preset time feedback controller of the dual active bridge circuit according to claim 1, characterized in that: The time conversion law adopts the following formula: ； Among them, t p is the preset time, μ(t) is the scale transformation coefficient.

3. A preset time feedback controller for a dual active bridge circuit according to claim 1 or 2, characterized in that: The time scale transformation law adopts the following formula: Z(t)=μ(t)e(t); Among them, Z(t) is the scale error signal and e(t) is the system error.

4. A preset time feedback control system for a dual active bridge circuit, characterized in that: A preset time feedback controller, a PWM modulator, a drive circuit, a dual active bridge circuit and a sampling conditioning circuit comprising the dual active bridge circuit according to any one of claims 1 to 3; The output end of the dual active bridge circuit is connected to the input end of the sampling and conditioning circuit, the output end of the sampling and conditioning circuit is connected to the input end of the preset time feedback controller of the dual active bridge circuit, the output end of the preset time feedback controller of the dual active bridge circuit is connected to the input end of the PWM modulator, the output end of the PWM modulator is connected to the input end of the driving circuit, and the output end of the driving circuit is used to control the on and off of the switch tube of the dual active bridge circuit.

5. A preset time feedback control method for a dual active bridge circuit, using the control system of claim 4, characterized in that: The following steps are involved: Step 1) Set the preset time t p Perform time conversion to obtain the scale transformation coefficient μ(t), Step 2) The scale transformation coefficient μ(t) is combined with the sampled signal x(t) of the output voltage and the expected voltage x d The system error e(t) formed by the difference is transformed into a time scale and the scale error signal Z(t) is output; Step 3) The sampling signal x(t) of the output voltage, the scaling coefficient μ(t), and the rate of change of the scaling coefficient , scale error signal Z(t), system error e(t), expected voltage change rate , non-negative parameter α is used for feedback control and the output control signal u(t); Step 4) The control signal u(t) is used as the modulation signal of the PWM modulator, and the PWM modulator generates a pulse control signal v duty , and then generate the driving signal v after passing through the driving circuit dr , used to control the on and off of the switch tube in the dual active bridge circuit, so as to achieve the bus voltage V bus stability.

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