Sliding mode control method and system for dual-active bridge DC-DC converter

Abstract

A sliding mode control method for a dual-active bridge DC-DC converter comprises the following steps: constructing a state space model of a DAB by taking the transmission power of the DAB as a control quantity; constructing a sliding mode surface function by taking the difference value between the expected output voltage of the DAB and the actual output voltage of the DAB as a system error variable; constructing a sliding mode control law according to the state space model of the DAB and a sliding mode surface function; tracking the output voltage of the DAB by using the sliding mode control law to obtain the transmission power of the DAB, and carrying out per-unit processing on the transmission power of the DAB; and solving the phase shift ratio of the DAB according to the per-unit transmission power and the voltage conversion ratio K of the DAB. According to the design, the dynamic response of the system can be remarkably improved, the buffeting phenomenon of a traditional sliding mode is restrained, and the calculated amount is small.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and in particular to a sliding mode control method and system for a dual active bridge DC-DC converter. Background Art

[0002] In order to deal with the disturbance and stability problems caused by random fluctuations in power of distributed power sources and frequent switching of loads on DC microgrids, energy storage units and bidirectional DC-DC converters have become the core equipment of DC microgrid systems. They can effectively smooth power fluctuations, stabilize DC bus voltage, improve power quality, and improve system performance. Dual active bridge DC-DC converters (DAB, all referred to as DABs) have the characteristics of bidirectional energy transfer, symmetrical topology, high power density, easy zero voltage conduction, and electrical isolation. They have attracted extensive attention from scholars at home and abroad and have gradually become the mainstream converters of DC microgrid systems.

[0003] However, the high proportion of new energy access may cause the DC bus voltage of the DC microgrid to fluctuate in a large range, resulting in the mismatch between the DAB input and output voltage, increasing the return power and current stress, and making it difficult for some switch tubes to achieve ZVS. This will increase the loss and reduce the system efficiency, making the dynamic response performance of the system inevitably affected. Therefore, it is necessary to optimize the dynamic response performance of DAB and consider using sliding mode control to optimize the response speed of DAB. However, the traditional sliding mode control strategy is prone to jitter, which affects the system control accuracy and damages the system performance. At the same time, the existing sliding mode control and model predictive control methods have complex parameter design and large calculation amount, which affects the dynamic response performance of the system. Therefore, there is a need for an improved dual active bridge DC-DC converter control strategy that can significantly improve the system dynamic response and significantly suppress the jitter phenomenon of the traditional sliding mode, so as to improve the overall performance of the DC microgrid. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems that the PI control of the dual active bridge DC-DC converter in the prior art has insufficient control accuracy and poor tracking effect, and the sliding mode control has jitter phenomenon, which affects the system stability and has high calculation complexity. A sliding mode control method and system for a dual active bridge DC-DC converter with small calculation amount, which can significantly improve the dynamic response of the system and suppress the jitter phenomenon of the traditional sliding mode is provided.

[0005] To achieve the above objectives, the technical solution of the present invention is:

[0006] A sliding mode control method for a dual active bridge DC-DC converter, the control method comprising the following steps:

[0007] S1. Taking the transmission power of DAB as the control variable, a state space model of DAB is constructed;

[0008] S2, taking the difference between the expected output voltage of DAB and the actual output voltage of DAB as the system error variable, constructing the sliding surface function;

[0009] S3, constructing a sliding mode control law according to the state space model of the DAB and the sliding surface function;

[0010] S4, using the sliding mode control law to track the output voltage of the DAB, obtain the transmission power of the DAB, and normalize the transmission power of the DAB;

[0011] S5. Calculate the phase shift ratio of DAB according to the normalized transmission power and the voltage conversion ratio K of DAB.

[0012] In step S1, the state space model of DAB is:

[0013]

[0014] z=C2V2;

[0015] u=P;

[0016] In the above formula, u is the control quantity; P is the transmission power of DAB; C2 is the capacity of the secondary capacitor; V2 is the output voltage of DAB; is the rate of change of output voltage; I2 is the output current of DAB.

[0017] In step S2, the sliding surface function is:

[0018]

[0019] In the above formula, E is the system error variable, E = V2 ref -V2;V 2ref is the expected value of the output voltage of DAB; V2 is the output voltage of DAB; k1 and k2 are the sliding surface control gains, and both k1 and k2 are greater than zero.

[0020] In step S3, setting the sliding mode control law according to the state space model and sliding surface function of the DAB includes the following steps:

[0021] According to the state space model and sliding surface function of the DAB, the model equivalent part u of the mode control law is obtained. eq ;

[0022] The switching control part u of the module control law is obtained according to the super-helical algorithm sw ;

[0023] According to the model equivalent part u of the modular control law eq , the switching control part of the modular control law sw Get the sliding mode control law u:

[0024] u=u eq +u sw .

[0025] In step S3, the model equivalent part u of the mode control law is obtained according to the state space model and the sliding surface function of the DAB. eq , including the following steps:

[0026] Substitute the state space model of DAB into the sliding surface expression, and differentiate the sliding surface function to obtain the first-order derivative of the sliding surface function:

[0027]

[0028] Let the first-order derivative of the sliding surface function s = 0, and solve the model equivalent part u of the control law eq :

[0029]

[0030] In the above formula, I2 is the output current of DAB; V2 is the output voltage of DAB, C2 is the capacity of the secondary capacitor, z = C2V2; E is the system error variable, E = V2 ref -V2, V 2ref is the expected value of the output voltage of DAB; V1 is the input voltage of DAB; k1 and k2 are the sliding surface control gains; k1 and k2 are both greater than zero.

[0031] In step S3, the switching control part u of the module control law is obtained according to the superhelical algorithm. sw The following steps are involved:

[0032] Combining the superhelical algorithm and the general form of the switching control part of the control law, the switching control part of the control law is obtained. sw :

[0033]

[0034] In the above formula, α and β are superhelical control gains, α<0, β<0; s is the sliding surface function.

[0035] In step S5, the voltage conversion ratio K of the DAB is calculated according to the following formula:

[0036]

[0037] Wherein, V1 is the input voltage of DAB; V2 is the output voltage of DAB; n is the ratio of the number of turns of the primary coil of DAB to the number of turns of the secondary coil.

[0038] A sliding mode control system of a dual active bridge DC-DC converter, the control system comprising:

[0039] The first building module is used to build a state space model of DAB by taking the transmission power of DAB as the control quantity;

[0040] The state space model of the DAB is:

[0041]

[0042] z=C2V2;

[0043] u=P;

[0044] In the above formula, u is the control quantity; P is the transmission power of DAB; C2 is the capacity of the secondary capacitor; V2 is the output voltage of DAB; is the rate of change of output voltage; I2 is the output current of DAB;

[0045] A second construction module is used to construct a sliding surface function by taking the difference between the desired output voltage of the DAB and the actual output voltage of the DAB as a system error variable;

[0046] The sliding surface function is:

[0047]

[0048] In the above formula, E is the system error variable, E = V2 ref -V2;V 2ref is the expected value of the output voltage of DAB; V2 is the output voltage of DAB; k1 and k2 are the control gains of the sliding surface, and both k1 and k2 are greater than zero;

[0049] A third construction module is used to construct a sliding mode control law according to the state space model of the DAB and the sliding surface function;

[0050] The setting of the sliding mode control law according to the state space model and the sliding mode surface function of the DAB comprises:

[0051] According to the state space model and sliding surface function of the DAB, the model equivalent part u of the mode control law is obtained. eq :

[0052]

[0053] In the above formula, I2 is the output current of DAB; V2 is the output voltage of DAB, C2 is the capacity of the secondary capacitor, z = C2V2; E is the system error variable, E = V2 ref -V2, V 2ref is the expected value of the output voltage of DAB; V1 is the input voltage of DAB; k1 and k2 are the control gains of the sliding surface; k1 and k2 are both greater than zero;

[0054] The switching control part u of the module control law is obtained according to the super-helical algorithm sw :

[0055]

[0056] In the above formula, α and β are superhelical control gains, α<0, β<0; s is the sliding surface function;

[0057] According to the model equivalent part u of the modular control law eq , the switching control part of the modular control law sw Get the sliding mode control law u:

[0058]

[0059] In the above formula, u is the sliding mode control law, I2 is the current of the DAB load, C2 is the capacity of the secondary capacitor, V2 is the output voltage of the DAB, z=C2V2, E is the system error variable, k1 and k2 are the sliding surface control gains, k1 and k2 are both greater than zero, α and β are the superhelical control gains, α<0, β<0, and s is the sliding surface function.

[0060] An output module, used for tracking the output voltage of the DAB by using the sliding mode control law, obtaining the transmission power of the DAB, and normalizing the transmission power of the DAB;

[0061] A solution module, used for solving the DAB shift ratio according to the normalized transmission power and the DAB voltage conversion ratio K;

[0062] The calculation formula of the voltage conversion ratio K of the DAB is:

[0063]

[0064] Wherein, V1 is the input voltage of DAB, V2 is the output voltage of DAB, and n is the ratio of the number of turns of the primary coil of DAB to the number of turns of the secondary coil.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] 1. In a sliding mode control method for a dual active bridge DC-DC converter of the present invention, the transmission power of DAB is used as the control quantity to construct a state space model of DAB, and the difference between the expected output voltage of DAB and the actual output voltage of DAB is used as the system error variable to construct a sliding surface function; the model equivalent part of the mode control law is obtained according to the state space model and the sliding surface function of DAB, and the switching control part of the control law is obtained according to the super spiral algorithm, and then the sliding mode control law is obtained. The super spiral sliding mode control in this design is an improved sliding mode control method. By introducing a continuous control law, the super spiral sliding mode control replaces the high-frequency switching term of the system switching control part in the traditional sliding mode control with an integral form, so that the control signal has continuity, and the chattering phenomenon of the traditional sliding mode control is effectively suppressed; at the same time, the design retains the advantages of fast response speed of sliding mode control and strong robustness to parameter changes and external disturbances, significantly improves the dynamic response speed and adjustment accuracy of the system, and can also effectively cope with complex working conditions such as sudden change of input voltage, load change and reference voltage adjustment, and can significantly improve the dynamic performance of DAB when voltage fluctuation occurs in the DC microgrid. Therefore, in this design, the traditional sliding mode control is improved through the super-helical algorithm to effectively suppress the chattering phenomenon. At the same time, the advantages of sliding mode control such as fast response speed and strong robustness to parameter changes and external disturbances are retained, which significantly improves the dynamic performance of DAB when voltage fluctuations occur in the DC microgrid.

[0067] 2. In the sliding mode control method of a dual active bridge DC-DC converter of the present invention, the control quantity of the sliding mode control system is the transmission power of DAB. The input voltage and output voltage of the DAB are tracked by the sliding mode control law, so that the transmission power of DAB can be output, and then the transmission power of DAB is converted into a per-unit value. In addition, the present invention adopts a multi-objective optimization control combined with the optimization of the return power under dual phase shifting, and uses the optimization control mathematical model of the return power, that is, using the voltage conversion ratio k and the per-unit value of the transmission power, that is, the output quantity is the inner and outer phase shifts of the extended phase shift, and the calculation amount is small. Therefore, this design takes the transmission power of DAB as the control quantity, uses the sliding mode control law to track the input voltage and output voltage of DAB, outputs the transmission power of DAB, and then simply standardizes the transmission power into a per-unit value, so that the optimal phase shift can be directly optimized and controlled to output, and the calculation amount is small.

[0068] 3. In the sliding mode control method of a dual active bridge DC-DC converter of the present invention, the transmission power of DAB is used as the control quantity, which is applicable to various phase shifting modes of DAB, such as single phase shifting, extended phase shifting, double phase shifting, etc., and can be changed according to different phase shifting modes, and has strong adaptability. Therefore, this design uses the transmission power of DAB as the control quantity, which can be applicable to various phase shifting modes of DAB, and has strong adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 The present invention is a flowchart of a sliding mode control method for a dual active bridge DC-DC converter provided by an embodiment of the present invention.

[0070] Figure 2 It is a topological structure diagram of a dual active bridge DC-DC converter provided in an embodiment of the present invention.

[0071] Figure 3 4 is a simplified topological diagram of a dual active bridge DC-DC converter provided in an embodiment of the present invention.

[0072] Figure 4 The invention discloses a control flow chart of a dual active bridge DC-DC converter.

[0073] Figure 5 It is a simulation waveform comparison diagram of the super spiral sliding mode control (STSMC) provided by an embodiment of the present invention and the traditional sliding mode control (SMC).

[0074] Figure 6 The present invention provides an embodiment of a super spiral sliding mode control (STSMC) and PI control, traditional sliding mode control (SMC) output voltage experimental waveform comparison diagram when the output voltage reference value changes.

[0075] Figure 7 The present invention provides an embodiment of the present invention providing a comparison diagram of the output voltage experimental waveforms of super spiral sliding mode control (STSMC), PI control and traditional sliding mode control (SMC) when the load changes suddenly.

[0076] Figure 8 The present invention provides an embodiment of the present invention providing a comparison diagram of the output voltage experimental waveforms of super spiral sliding mode control (STSMC), PI control and traditional sliding mode control (SMC) when the input voltage suddenly changes.

[0077] Fig. 9 The present invention is a schematic structural diagram of a sliding mode control system of a dual active bridge DC-DC converter provided in an embodiment of the present invention.

[0078] Fig.10 It is a structural schematic diagram of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0079] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0080] Dual Active Bridge (DAB) DC-DC converter can achieve a wide voltage range, high power density, electrical isolation and bidirectional power transmission. It is a key device for connecting DC buses of different voltage levels or realizing energy exchange between energy storage units and DC buses.

[0081] A sliding mode control method for dual active bridge DC-DC converters, see Figure 1 , Figure 1 1 is a flow chart of a sliding mode control method for a dual active bridge DC-DC converter provided by an embodiment of the present invention, wherein the sliding mode control method comprises steps S1 to S5;

[0082] S1. Taking the transmission power P of DAB as the control quantity, a state space model of DAB is constructed according to the simplified topology diagram of dual active bridge DC-DC converter (DAB, hereinafter referred to as DAB).

[0083] In this embodiment, the dual active bridge DC-DC converter topology is shown in FIG. Figure 2 As shown, the dual active bridge DC-DC converter consists of the primary and secondary side H1 full bridge and H2 full bridge, high frequency transformer T, inductor L (its value L is the sum of all leakage inductances of the transformer), input side DC power supply V1 and output side load R (the voltage on both sides of load R is the output voltage V2), and buffer capacitors C1 and C2. Among them, the switch tubes S1-S4 constitute the primary side H1 bridge of the transformer, and the switch tubes S5-S8 constitute the secondary side H2 bridge; the transformer ratio of the dual active bridge DC-DC converter is n:1 (that is, the ratio of the number of turns of the primary coil of the DAB to the number of turns of the secondary coil), u AB 、u CD are the AC side voltages of bridges H1 and H2, u L is the leakage inductance voltage, i L is the inductor current.

[0084] like Figure 3 As shown, the dual active bridge DC-DC converter topology diagram is simplified to obtain a simplified topology diagram of the dual active bridge DC-DC converter. Figure 3 middle, I ave is the average secondary current of DAB, is the current of the secondary capacitor C2 of DAB, V2 is the output voltage of DAB, and I2 is the output current of DAB.

[0085] In this embodiment, according to the simplified DAB topology diagram, it can be obtained that:

[0086]

[0087] In the above formula, I ave is the average current of the secondary side of DAB; I2 is the output current of DAB; is the current of the secondary capacitor C2 of DAB; V2 is the output voltage of DAB; P is the transmission power of DAB;

[0088] Taking the transmission power P of DAB as the control variable, the state space model of DAB can be simplified as follows:

[0089]

[0090] z=C2V2;

[0091] u=P;

[0092] In the above formula, u is the control quantity; P is the transmission power of DAB; C2 is the capacity of the secondary capacitor of DAB; V2 is the output voltage of DAB; is the rate of change of the output voltage of DAB; I2 is the output current of DAB;

[0093] C2V2 is represented as a whole by z to reduce the complexity and calculation amount of the controller.

[0094] S2. Taking the difference between the expected output voltage of DAB and the actual output voltage of DAB as the system error variable, a sliding surface function is constructed.

[0095] Specifically, the system error variable is first defined, and the difference between the expected output voltage of DAB and the actual output voltage of DAB is taken as the system error variable:

[0096] E=V2 ref -V2;

[0097] In the above formula, E is the system error variable; V 2ref is the expected value of the output voltage of DAB; V2 is the secondary output voltage of DAB;

[0098] The sliding surface of sliding mode control is constructed as follows:

[0099]

[0100] In the above formula, s is the sliding surface function; E is the system error variable; V 2ref is the expected value of the output voltage of DAB; V2 is the output voltage of DAB; k1 and k2 are the sliding surface control gains, and both k1 and k2 are greater than zero.

[0101] In this embodiment, the mode surface control gain is used to control the error convergence speed, and at the same time, an integral term is introduced into the sliding mode surface to eliminate the output voltage steady-state error.

[0102] Let the sliding surface function s = 0, and solve the expression of error e:

[0103]

[0104] In the above formula, c0 is the initial value of the output voltage error in steady state, and e is the base of the natural logarithm.

[0105] When t→∞, V2→V2ref , that is, error E→0. From the above formula, we can see that k1 and k2 are both greater than 0, which allows the error E to converge to 0 in a finite time. The convergence speed depends on the values ​​of k1 and k2. Therefore, it is necessary to set the sliding surface control gains k1 and k2 to be greater than zero.

[0106] S3. Constructing a sliding mode control law according to the state space model of the DAB and the sliding surface function.

[0107] Taking the derivative of the sliding surface function, we get:

[0108]

[0109] Since the output voltage reference value is a fixed value, its derivative is 0. At the same time, the state space model of the DAB is substituted into the above formula to obtain the first-order derivative of the sliding surface function:

[0110]

[0111] E=V2 ref -V2;

[0112] Since sliding mode control generally adopts equivalent sliding mode method, the control law u consists of two parts, namely the model equivalent part and the switching control part:

[0113] u=u eq +u sw ;

[0114] In the above formula, u eq is the equivalent part of the model, which brings the system state to the sliding surface; u sw To switch the control part, ensure that the system state does not leave the sliding surface.

[0115] For the model equivalent part of the sliding mode control law u eq , can be obtained according to the state space model and sliding surface function of the DAB:

[0116] When the system state does not reach the sliding surface, the switching control amount u is ignored. sw The influence of the model equivalent control quantity is the controller input. Let the first-order derivative of the sliding surface function s = 0, solve the control quantity, and obtain the model equivalent control quantity u eq :

[0117]

[0118] E=V2 ref -V2;

[0119] In the above formula, I2 is the output current of DAB; V2 is the output voltage of DAB; C2 is the capacity of the secondary capacitor, z=C2V2; E is the system error variable; V 2ref is the expected value of the output voltage of DAB; V1 is the input voltage of DAB; k1 and k2 are the sliding surface control gains, and both k1 and k2 are greater than zero.

[0120] For the switching control part of the sliding mode control law, sw , the switching control part of the traditional sliding mode control law can be improved and obtained through the super spiral algorithm.

[0121] The traditional switching control part is generally:

[0122] u sw =k s sgn(s);

[0123] Among them, k s is the gain of the switching control part; sgn is the sign function.

[0124] Since the switching control part of the traditional sliding mode control is a sign function and directly acts on the control quantity, when the system state reaches the sliding mode surface, the control signal will begin to have discontinuity, resulting in the generation of chattering. This phenomenon will affect the system control accuracy, increase energy consumption, and damage system performance;

[0125] To eliminate the discontinuity term of the traditional sliding mode control, a higher order sliding mode control, such as super helical sliding mode control, can be used. Replacing the switching control part in the sliding mode control with the super helical algorithm can eliminate the discontinuity term. For this system, the general form of the super helical algorithm is:

[0126]

[0127] It can be seen from the above formula that the super-helical algorithm makes the control signal continuous, thereby suppressing the occurrence of chattering.

[0128] From the above process, it can be seen that the switching control part of the control law is:

[0129]

[0130] Where α and β are superhelical control gains, α<0, β<0; s is the sliding surface function; sgn is the sign function.

[0131] According to the model equivalent part u of the modular control law eq , the switching control part of the modular control law sw Get the sliding mode control law u:

[0132] Based on u=u eq +usw , we can get:

[0133]

[0134] Where E = V2 ref -V2;

[0135] In the above formula, u is the sliding mode control rate; I2 is the current of the DAB load; C2 is the capacity of the secondary capacitor, V2 is the output voltage of the DAB, z = C2V2; E is the system error variable; V 2ref is the expected value of the output voltage of DAB; k1 and k2 are the sliding surface control gains, both of which are greater than zero; α and β are the superhelical control gains, α<0, β<0; s is the sliding surface function.

[0136] In this embodiment, in order to prove the stability of the above sliding mode control law, the Lyapunov function method is used to perform stability analysis:

[0137] The general form of the superhelix algorithm is expressed as Substitute the sliding surface function into the derivative formula We can get:

[0138]

[0139] For the convenience of analysis, the above formula is rewritten as:

[0140]

[0141] In the above formula, λ1=αz, λ2=βz, α and β are superhelical control gains.

[0142] Construct the Lyapunov function V(s):

[0143]

[0144] When the Lyapunov function satisfies the following three conditions a, b, and c, the sliding mode control law is stable:

[0145] a. When s≠0, V(s)>0;

[0146] b. When S→∞, V(s)→∞;

[0147] When c and s≠0,

[0148] According to the formula of Lyapunov function V(s), Lyapunov function V(s) obviously satisfies conditions a and b. Therefore, it is necessary to prove that Lyapunov function V(s) satisfies condition c.

[0149] Proving that the Lyapunov function V(s) satisfies condition c includes the following steps:

[0150] Define the system state variables as:

[0151]

[0152] Since V(s) is differentiable everywhere when the system has not converged to a stable point (s = 0), the state variable ζ is derived using d|s| / dt = ssgn(s):

[0153]

[0154] Simplifying the above system state variables, we get the simplified system state variable equation:

[0155]

[0156] In the above formula,

[0157] Thus we get the quadratic matrix V of the Lyapunov function V(s):

[0158] V=ζ T Pζ;

[0159] In the above formula, P is a real symmetric matrix,

[0160] The simplified system state variable equation Taking the derivative, we get:

[0161]

[0162] In the above formula,

[0163] Use Q to determine whether the Lyapunov function V(s) satisfies condition c:

[0164] When Q is a negative definite matrix, The quadratic matrix is also negative, at this time The system is asymptotically stable;

[0165] If Q is a negative definite matrix, it must satisfy:

[0166]

[0167] It can be seen that if Q is a negative definite matrix, it must satisfy λ1<0, λ2<0;

[0168] Since λ1=αz, λ2=βz, when α<0, β<0, the Lyapunov function V(s) satisfies condition c and the system is asymptotically stable. Therefore, α<0, β<0 are used as constraints for the parameters of the sliding mode control law.

[0169] S4, obtaining the input voltage and output voltage of the DAB, tracking the input voltage and output voltage of the DAB by using the sliding mode control law, obtaining the transmission power of the DAB, and normalizing the transmission power of the DAB;

[0170] Specifically, in step S4, the transmission power of the DAB is normalized according to the following formula:

[0171]

[0172] Where, P is the transmission power of DAB, P N is the reference power, which is the maximum transmission power of the dual active bridge DC-DC converter when single phase shift is adopted. is the normalized transmission power, f s is the frequency.

[0173] S5. According to the normalized transmission power and the voltage conversion ratio K of the DAB, the shift ratio of the DAB is solved, and then the DAB is controlled.

[0174] In this embodiment, when DAB adopts dual phase shift control, solving the phase shift ratio of DAB according to the normalized transmission power and the voltage conversion ratio K of DAB includes the following steps:

[0175] According to the following table, the normalized transmission power, and the DAB voltage conversion ratio K, the corresponding internal shift ratio D is calculated with the goal of optimizing the return power. 1.opt Compared with outward migration 2.opt , and according to the internal shift compared to D 1.opt Compared with outward migration 2.opt Regulate DAB.

[0176]

[0177] The sliding mode control method of the dual active bridge DC-DC converter in the present invention is applicable to various phase shifting modes of DAB, such as single phase shifting, extended phase shifting, double phase shifting, etc., and can be changed according to different phase shifting modes, and has strong adaptability. In addition, it can also be combined with optimization schemes of multiple objectives to evolve into a multi-objective optimization control strategy.

[0178] Taking dual phase shift control as an example, a super spiral sliding mode control method described in the present invention is used in combination with reflux power optimization control to control the dual active bridge DC-DC converter. Figure 4 As shown, the control method of the present invention is verified by a simulation platform:

[0179] First, the circuit simulation parameters and the reflux power optimization controller parameters are set.

[0180] The circuit simulation parameters of the dual active bridge DC-DC converter are shown in Table 1 below:

[0181]

[0182] Table 1: Simulation circuit parameters

[0183] The double phase shift reflux power optimization scheme is adopted to optimize the system reflux power through the reflux power optimization controller: the input is the voltage conversion ratio K, the transmission power per unit value The output is the inner and outer phase shift ratios D1 and D2 of the double phase shift. By sampling and calculating the circuit parameters, the power range is determined, and the optimal phase shift ratio is calculated to control the circuit.

[0184] The specific parameters of the reflux power optimization controller are shown in Table 2 below:

[0185]

[0186] Table 2: Backflow power optimization controller parameters

[0187] In Table 2, D 1.opt and D 2.opt The optimal shift ratio is calculated as follows: This is the minimum reflux power at this time.

[0188] When DAB uses dual phase shift control, the transmission power per unit value And the optimal inner and outer shifts D calculated in Table 2 above 1.opt and D 2.opt .

[0189] For the dual active bridge DC-DC converter super spiral sliding mode control method described in the present invention, the control quantity is the transmission power P, and the transmission power P is normalized to obtain the normalized transmission power The super-helical sliding mode control is used as the output voltage loop to output the normalized transmission power. The normalized transmission power The voltage conversion ratio K of DAB obtained by sampling is input into the reflux power optimization controller together to obtain the optimal inner and outer shift ratios and then control the dual active bridge DC-DC converter circuit.

[0190] After setting the circuit simulation parameters and the reflux power optimization controller parameters, a simulation test was performed. The test results are as follows:

[0191] Figure 5 It is a simulation waveform comparison diagram of the super spiral sliding mode control (STSMC) provided by an embodiment of the present invention and the traditional sliding mode control (SMC). Figure 5 (Left) is the simulation waveform of the traditional sliding mode control (SMC), such as Figure 5 (Left) As shown in the figure, when the output voltage V2 is not close to the reference value 30V, that is, the system is not close to the stable point, the switching control part u of the SMC sw Keep continuous, and when approaching the stable point, due to the switching control part u of the traditional sliding mode control sw Generally u sw =k s sgn(s),u sw Due to the existence of sgn(s), discontinuity begins to appear, causing the control quantity to vibrate, resulting in a larger V2 ripple (0.18V). Figure 5 (Right) is a simulation waveform diagram of the super spiral sliding mode control (STSMC) of the present invention, Figure 5 As shown in (right), since STSMC eliminates the discontinuity term of SMC, the system exhibits continuity whether it is close to the stable point or not, which better solves the jitter phenomenon and also significantly reduces the V2 ripple (0.035V).

[0192] Figure 6 It is a comparison diagram of the output voltage experimental waveforms of super spiral sliding mode control (STSMC), PI control and traditional sliding mode control (SMC) when the output voltage reference value changes (the given value suddenly changes from 30V to 40V) provided by an embodiment of the present invention. Figure 7 An embodiment of the present invention provides a comparison diagram of the output voltage experimental waveforms of super spiral sliding mode control (STSMC), PI control and traditional sliding mode control (SMC) when the load suddenly changes (the output load suddenly changes from 10Ω to 20Ω). Figure 8 The present invention provides an embodiment of the present invention, which provides a comparison diagram of the output voltage experimental waveforms of super spiral sliding mode control (STSMC), PI control and traditional sliding mode control (SMC) when the input voltage suddenly changes (the input voltage suddenly changes from 50V to 60V).

[0193] It can be seen from the above simulation result diagram that the dynamic response time of the traditional sliding mode control and the super-helical control described in the present invention are both within 20ms, and the overshoot is within 1V, which are much smaller than the PI control, and the super-helical sliding mode control described in the present invention can achieve no overshoot.

[0194] In summary, the present invention provides a sliding mode control method for a dual active bridge DC-DC converter, which can achieve fast and smooth switching of the DAB converter when various system operating conditions change, and its output voltage overshoot and response time are significantly smaller than PI control; in addition, the sliding mode control method adopts a super spiral algorithm, which can significantly improve the system dynamic performance when the input voltage changes suddenly, the load changes, and the reference voltage changes compared with traditional PI control and traditional sliding mode control, and can significantly suppress the jitter phenomenon of the traditional sliding mode, thereby solving the dynamic response problem of the dual active bridge DC-DC converter (DAB) in the DC microgrid when the system is disturbed; at the same time, the sliding mode control method can be applied to DAB using single phase shift, extended phase shift, double phase shift and other phase shifting methods, and can also be combined with optimization schemes of multiple objectives to evolve into a multi-objective optimization control strategy.

[0195] According to the above method, this embodiment will be further described from the perspective of the sliding mode control system of the dual active bridge DC-DC converter. The sliding mode control system of the dual active bridge DC-DC converter can be implemented as an independent entity or integrated in an electronic device, such as a terminal.

[0196] like Fig. 9 As shown, a sliding mode control system of a dual active bridge DC-DC converter is provided, the system is used to execute the sliding mode control method of the dual active bridge DC-DC converter in the above embodiment, and the system comprises:

[0197] The first building module is used to build a state space model of DAB by taking the transmission power of DAB as the control variable.

[0198] The state space model of the DAB is:

[0199]

[0200] z=C2V2;

[0201] u=P;

[0202] In the above formula, u is the control quantity, P is the transmission power of DAB, C2 is the capacity of the secondary capacitor, V2 is the load voltage of DAB, V2 is the output voltage of DAB, and I2 is the output current of DAB.

[0203] The second building module is used to build a sliding surface function by taking the difference between the expected output voltage of the DAB and the actual output voltage of the DAB as the system error variable.

[0204] The sliding surface function is:

[0205]

[0206] In the above formula, E is the system error variable, V 2ref is the expected value of the output voltage of DAB, V2 is the output voltage of DAB, k1 and k2 are the sliding surface control gains, and both k1 and k2 are greater than zero.

[0207] The third construction module is used to construct a sliding mode control law according to the state space model of the DAB and the sliding surface function.

[0208] Setting the sliding mode control law according to the state space model and sliding surface function of the DAB includes the following steps:

[0209] According to the state space model and sliding surface function of the DAB, the model equivalent part u of the mode control law is obtained. eq ;

[0210] The switching control part u of the module control law is obtained according to the super-helical algorithm sw ;

[0211] According to the model equivalent part u of the modular control law eq , the switching control part of the modular control law sw Get the sliding mode control law u:

[0212] u=u eq +u sw .

[0213] The model equivalent part u of the mode control law is obtained according to the state space model and sliding surface function of the DAB. eq , including the following steps:

[0214] Substitute the state space model of DAB into the sliding surface expression, and differentiate the sliding surface function to obtain the first-order derivative of the sliding surface function:

[0215]

[0216] Let the first derivative of the sliding surface function be Solve to obtain the model equivalent part u of the control law eq :

[0217]

[0218] E=V2 ref -V2;

[0219] In the above formula, I2 is the output current of DAB, V2 is the output voltage of DAB, C2 is the capacity of the secondary capacitor, z=C2V2, E is the system error variable, V 2ref is the expected value of the output voltage of DAB, V1 is the input voltage of DAB, E is the system error variable, k1 and k2 are the sliding surface control gains, and both k1 and k2 are greater than zero.

[0220] The switching control part u of the module control law is obtained according to the super-helical algorithm sw The following steps are involved:

[0221] Combining the superhelical algorithm and the general form of the switching control part of the control law, the switching control part of the control law is obtained. sw :

[0222]

[0223] Where α and β are superhelical control gains, α<0, β<0, and s is the sliding surface function.

[0224] The output module tracks the output voltage of the DAB by using the sliding mode control law to obtain the transmission power of the DAB and normalizes the transmission power of the DAB.

[0225] The reflux power optimization control module is used to solve the DAB shift ratio according to the normalized transmission power and the DAB voltage conversion ratio K.

[0226] The voltage conversion ratio K of the DAB is calculated according to the following formula:

[0227]

[0228] Wherein, V1 is the input voltage of DAB, V2 is the output voltage of DAB, and n is the ratio of the number of turns of the primary coil of DAB to the number of turns of the secondary coil.

[0229] Also, see Fig.10 , Fig.10 is a schematic diagram of an electronic device provided by an embodiment of the present invention. Fig.10 As shown, the electronic device includes a memory and a processor, the memory is used to store computer program code and transmit the computer program code to the processor; the processor is used to execute the sliding mode control method of the dual active bridge DC-DC converter as described in Example 1 according to the instructions in the computer program code.

[0230] A person of ordinary skill in the art will appreciate that all or part of the steps in the various methods of the above embodiments may be completed by instructions, or by controlling related hardware through instructions. The instructions may be stored in a computer-readable storage medium and loaded and executed by a processor.

[0231] The embodiment of the present invention also provides a storage medium, in which a plurality of instructions are stored, and when the instructions are executed by the processor, the steps of the sliding mode control method of the dual active bridge DC-DC converter provided in the above embodiment can be implemented. Since the instructions stored in the storage medium can execute the steps in the sliding mode control method of the dual active bridge DC-DC converter provided in the embodiment of the present invention, the beneficial effects that can be achieved by the sliding mode control method of any dual active bridge DC-DC converter provided in the embodiment of the present invention can be achieved, as detailed in the above embodiment, which will not be repeated here.

Claims

1. A sliding mode control method for a dual active bridge DC-DC converter, characterized in that: The control method comprises the following steps: S1. Taking the transmission power of DAB as the control variable, a state space model of DAB is constructed; S2, taking the difference between the expected output voltage of DAB and the actual output voltage of DAB as the system error variable, constructing the sliding surface function; S3, constructing a sliding mode control law according to the state space model of the DAB and the sliding surface function; S4, using the sliding mode control law to track the output voltage of the DAB, obtain the transmission power of the DAB, and normalize the transmission power of the DAB; S5. Calculate the phase shift ratio of DAB according to the normalized transmission power and the voltage conversion ratio K of DAB.

2. The sliding mode control method of a dual active bridge DC-DC converter according to claim 1, characterized in that: In step S1, the state space model of DAB is: z=C2V2; u=P; In the above formula, u is the control quantity; P is the transmission power of DAB; C2 is the capacity of the secondary capacitor; V2 is the output voltage of DAB; is the rate of change of output voltage; I2 is the output current of DAB.

3. The sliding mode control method of a dual active bridge DC-DC converter according to claim 2, characterized in that: In step S2, the sliding surface function is: In the above formula, E is the system error variable, E = V 2ref -V2;V 2ref is the expected value of the output voltage of DAB; V2 is the output voltage of DAB; k1 and k2 are the sliding surface control gains, and both k1 and k2 are greater than zero.

4. The sliding mode control method of a dual active bridge DC-DC converter according to claim 3, characterized in that: In step S3, setting the sliding mode control law according to the state space model and sliding surface function of the DAB includes the following steps: According to the state space model and sliding surface function of the DAB, the model equivalent part u of the mode control law is obtained. eq ; The switching control part u of the module control law is obtained according to the super-helical algorithm sw ; According to the model equivalent part u of the modular control law eq , the switching control part of the modular control law sw Get the sliding mode control law u: in=in eq +in sw 。 5. The sliding mode control method of a dual active bridge DC-DC converter according to claim 4, characterized in that: In step S3, the model equivalent part u of the mode control law is obtained according to the state space model and the sliding surface function of the DAB. eq , including the following steps: Substitute the state space model of DAB into the sliding surface expression, and differentiate the sliding surface function to obtain the first-order derivative of the sliding surface function: Let the first derivative of the sliding surface function be Solve to obtain the model equivalent part u of the control law eq : In the above formula, I2 is the output current of DAB; V2 is the output voltage of DAB, C2 is the capacity of the secondary capacitor, z = C2V2; E is the system error variable, E = V 2ref -V2, V 2ref is the expected value of the output voltage of DAB; V1 is the input voltage of DAB; k1 and k2 are the sliding surface control gains; k1 and k2 are both greater than zero.

6. The sliding mode control method of a dual active bridge DC-DC converter according to claim 4, characterized in that: In step S3, the switching control part u of the module control law is obtained according to the superhelical algorithm. sw The following steps are involved: Combining the superhelical algorithm and the general form of the switching control part of the control law, the switching control part u of the control law is obtained. sw : In the above formula, α and β are superhelical control gains, α<0, β<0; s is the sliding surface function.

7. The sliding mode control method of a dual active bridge DC-DC converter according to claim 1, characterized in that: In step S5, the voltage conversion ratio K of the DAB is calculated according to the following formula: Wherein, V1 is the input voltage of DAB; V2 is the output voltage of DAB; n is the ratio of the number of turns of the primary coil of DAB to the number of turns of the secondary coil.

8. A sliding mode control system of a dual active bridge DC-DC converter, characterized in that: The control system comprises: The first building module is used to build a state space model of DAB by taking the transmission power of DAB as the control quantity; A second construction module is used to construct a sliding surface function by taking the difference between the desired output voltage of the DAB and the actual output voltage of the DAB as a system error variable; A third construction module is used to construct a sliding mode control law according to the state space model of the DAB and the sliding surface function; An output module, used for tracking the output voltage of the DAB by using the sliding mode control law, obtaining the transmission power of the DAB, and normalizing the transmission power of the DAB; The solution module is used to solve the DAB shift ratio according to the normalized transmission power and the DAB voltage conversion ratio K.

9. The sliding mode control system of a dual active bridge DC-DC converter according to claim 8, characterized in that: The state space model of the DAB is: z=C2V2; u=P; In the above formula, u is the control quantity; P is the transmission power of DAB; C2 is the capacity of the secondary capacitor; V2 is the output voltage of DAB; is the rate of change of output voltage; I2 is the output current of DAB; The sliding surface function is: In the above formula, E is the system error variable, E = V 2ref -V2;V 2ref is the expected value of the output voltage of DAB; V2 is the output voltage of DAB; k1 and k2 are the control gains of the sliding surface, and both k1 and k2 are greater than zero; The setting of the sliding mode control law according to the state space model and the sliding mode surface function of the DAB comprises: According to the state space model and sliding surface function of the DAB, the model equivalent part u of the mode control law is obtained. eq : In the above formula, I2 is the output current of DAB; V2 is the output voltage of DAB, C2 is the capacity of the secondary capacitor, z = C2V2; E is the system error variable, E = V 2ref -V2, V 2ref is the expected value of the output voltage of DAB; V1 is the input voltage of DAB; k1 and k2 are the control gains of the sliding surface; k1 and k2 are both greater than zero; The switching control part u of the module control law is obtained according to the super-helical algorithm sw : In the above formula, α and β are superhelical control gains, α<0, β<0; s is the sliding surface function; According to the model equivalent part u of the modular control law eq , the switching control part of the modular control law sw Get the sliding mode control law u: In the above formula, u is the sliding mode control law; I2 is the current of the DAB load; C2 is the capacity of the secondary capacitor, V2 is the output voltage of the DAB, z=C2V2; E is the system error variable; k1 and k2 are the sliding surface control gains; k1 and k2 are both greater than zero; α and β are superhelical control gains, α<0, β<0; s is the sliding surface function.

10. The sliding mode control system of a dual active bridge DC-DC converter according to claim 9, characterized in that: The calculation formula of the voltage conversion ratio K of the DAB is: Wherein, V1 is the input voltage of DAB, V2 is the output voltage of DAB, and n is the ratio of the number of turns of the primary coil of DAB to the number of turns of the secondary coil.

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