Method for improving deadbeat predictive control robustness of DAB converter

Abstract

The invention discloses a method for improving deadbeat predictive control robustness of a DAB converter, and belongs to the technical field of converters. The method comprises the following steps: measuring electrical parameters of the dual-active bridge DC-DC converter; designing a super-spiral disturbance observer; discretizing the superhelix disturbance observer; and calculating a control signal u * at the moment k by using output information of the super-spiral disturbance observer, namely a predicted value # imgabs0 # of the output voltage at the moment k + 1 and a predicted value # imgabs1 # of the system lumped disturbance at the moment k + 1, and calculating and constraining a phase shift angle. The invention provides a topological structure for performing disturbance observation and compensation based on the disturbance observer, the disturbance observer adopting the superhelix principle can realize accurate observation and compensation of disturbance, and compared with a traditional disturbance observation algorithm, the disturbance compensation performance is improved, and buffeting is reduced.

Description

Technical Field

[0001] The invention relates to a method for improving the robustness of deadbeat predictive control of a DAB converter, belonging to the technical field of converters. Background Art

[0002] The deadbeat output voltage control of the dual active bridge DC-DC converter (DAB) is extremely sensitive to the accuracy of system parameters. In practical applications, as the environment changes or the components age, the values ​​of the internal high-frequency transformer inductance and DC output capacitor of the DAB converter will undergo non-negligible changes, which may lead to the degradation of control system performance. In addition, potential errors in the measurement and manufacturing process will further affect the accuracy of system parameters, such as steady-state errors, poor dynamic performance, and circulating current problems in the parallel structure, thereby increasing the difficulty of control.

[0003] In some extreme cases, inaccurate parameters may cause system oscillation, seriously threatening the stability of the control system and possibly causing safety hazards such as overvoltage and overcurrent. Especially when the excitation capacity of the high-frequency transformer is limited, inaccurate parameters may cause the high-frequency transformer to saturate, thereby causing unexpected current stress and potential damage to the converter. Therefore, it is crucial to improve the robustness of the deadbeat output voltage control of the dual active bridge DC-DC converter.

[0004] The existing DAB converter deadbeat output voltage control method usually adopts a control strategy that combines the current stress optimal model predictive (MPC) controller and the PI control module to improve the robustness of the system. In this strategy, the MPC controller is only used for the calculation of the outer phase angle, while the PI control module is used for the calculation of the inner phase angle, and the robustness of the system is improved by adjusting the parameters. However, although this method improves the robustness of the system to a certain extent, the introduction of the PI control module may affect the transient control performance and limit the full play of the fast dynamic advantages inherent in the MPC controller.

[0005] Another improvement method is to use parameter identification technology to estimate the transformer leakage inductance online. However, this method is only applicable to the single-phase modulation strategy and cannot be applied to the dual-phase modulation strategy (DPS) with more control freedom. In addition, this method also does not adequately consider the compensation for the mismatch of output capacitor parameters, which limits its effectiveness in practical applications.

[0006] In recent years, model-free predictive control methods have also been applied to the control of DAB converters. Although this method has certain advantages in theory, it is difficult to effectively deploy it in microprocessors due to its heavy computational burden, so it is limited in practical applications. Summary of the invention

[0007] In order to solve the problems existing in the background technology, the present invention provides a method for improving the robustness of the deadbeat predictive control of a DAB converter.

[0008] To achieve the above object, the present invention adopts the following technical solution: a method for improving the robustness of the deadbeat predictive control of a DAB converter, the method comprising the following steps:

[0009] S1: Measure the electrical parameters of the dual active bridge DC-DC converter;

[0010] S2: Design superhelical disturbance observer;

[0011] S201: Input a control signal u, wherein the control signal u is proportional to the output power P n The relationship is u=0.5P n ;

[0012] S202: Obtain the load current I through the current sensor load ;

[0013] S203: Measure the output voltage U through the voltage sensor o ;

[0014] S204: Design of superhelical disturbance observer:

[0015]

[0016] In formula (1):

[0017] Represents the predicted value of the output voltage;

[0018] Represents the output voltage error;

[0019] k 1 and k 2 represents the observer gain that needs to be adjusted;

[0020] b 0 represents a constant;

[0021] sgn(*) represents the sign function;

[0022] C o represents the output capacitance;

[0023] Represents the predicted value of the system lumped disturbance;

[0024] t is the time.

[0025] S3: Discretize the superhelical disturbance observer;

[0026] S301: The predicted value of the output voltage The initial value of and the predicted value of the system lumped disturbance The initial values ​​of are all set to 0;

[0027] S302: Set the control period to T and the control frequency to f s , in each control cycle, the output voltage U at time t = k is obtained respectively o (k) and load current I load (k);

[0028] S303: Calculate the output voltage at time k+1 and the predicted value of the system lumped disturbance, that is, the expression of the discretized super-helical disturbance observer is as follows:

[0029]

[0030] S4: Using the output information of the superhelical perturbation observer, that is, the predicted value of the output voltage at time k+1 And the predicted value of the system lumped disturbance at time k+1 Calculate the control signal u at time k * :

[0031]

[0032] In formula (3):

[0033] f s represents the control frequency;

[0034] b 0 represents a constant;

[0035] U ref Represents voltage given;

[0036] I load (k) represents the load current at time k;

[0037] C o represents the output capacitance;

[0038] S5: Calculate and constrain the phase shift angle.

[0039] S501: According to the minimum current stress double phase shift modulation strategy calculation method, the control signal u at time k is * Modulation is the internal phase shift angle D 1 and the outward phase angle D 2 Then applied to the DAB converter;

[0040] S502: Inner phase shift angle D 1 The output and external phase angle D 2 The following constraints are imposed on the output of to achieve accurate and robust voltage control:

[0041]

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention proposes a topological structure for disturbance observation and compensation based on a disturbance observer. The disturbance observer using the superhelix principle can realize accurate observation and compensation of disturbances. Compared with the traditional disturbance observation algorithm, the disturbance compensation performance is improved and the jitter is reduced. In addition, the observer described in the present invention is designed according to the second-order sliding mode principle, and the sign function is hidden in the integral term, which essentially eliminates the jitter phenomenon, improves the voltage control performance and robustness, and can effectively eliminate the output voltage control error caused by parameter errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a control block diagram of the present invention;

[0045] Figure 2 The figure is a comparison diagram of the output voltage control results of the method of the present invention and the traditional method under the condition of 60% transformer inductance error and sudden change of load resistance, wherein: (a) is the experimental result diagram of the traditional deadbeat method, and (b) is the experimental waveform diagram of the present invention; the three waveforms from top to bottom respectively represent the port voltage of the DAB converter, the port output current and the internal current of the high-frequency transformer, and the load resistance switching occurs at the position where the current waveform increases in step in the figure;

[0046] Figure 3 The experimental performance waveform comparison diagram of the method of the present invention and the traditional method when the output voltage is stepped down from 80V to 60V and the load resistance is maintained at 30Ω when there is a 60% transformer inductance error, wherein: (a) represents the traditional zero-beat method, and (b) represents the method of the present invention. DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0048] The present invention relates to a method for improving the robustness of deadbeat predictive control based on a super-helical disturbance observer, which is used to improve the robustness of deadbeat output voltage control of a dual active bridge DC-DC converter (DAB) against parameter errors and external disturbances.

[0049] The present invention requires that the converter has a current sensor and a voltage sensor to improve the robustness of the deadbeat output voltage control, without the need for additional hardware design, thereby reducing hardware costs.

[0050] The algorithm can be implemented by programming in a digital control chip (DSP) and can be applied to a general dual active bridge DC-DC converter controller, and has extremely high application value and economic value.

[0051] A method for improving the robustness of the deadbeat predictive control of a DAB converter of the present invention comprises the following steps:

[0052] S1: Measure the electrical parameters of the dual active bridge DC-DC converter through offline testing, including the leakage inductance L of the high-frequency transformer r0 , output capacitor C o and the transformer primary-to-secondary turns ratio n;

[0053] S2: Using the port output voltage and load current of the DAB converter under different working conditions, a superhelical disturbance observer is designed based on the voltage and current equations of the DAB converter; the influence of non-ideal factors such as parameter errors and external disturbances in the voltage control process of the DAB converter is observed and suppressed. The superhelical disturbance observer is designed based on the superhelical principle and can achieve finite time observation error convergence. The second-order sliding mode characteristics can significantly suppress the jitter phenomenon caused by the traditional sliding mode structure and achieve the optimal observation effect.

[0054] S201: Input a control signal u, wherein the control signal u is proportional to the output power P n The relationship is u=0.5P n ;

[0055] S202: Obtain the load current I through the current sensor load ;

[0056] S203: Measure the output voltage U through the voltage sensor o ;

[0057] S204: Design of superhelical disturbance observer:

[0058]

[0059] In formula (1):

[0060] Represents the predicted value of the output voltage;

[0061] Represents the output voltage error;

[0062] k 1 and k 2represents the observer gain that needs to be adjusted;

[0063] b 0 Represents a constant related to the electrical parameters, input voltage and control frequency of the DAB converter;

[0064] sgn(*) represents the sign function;

[0065] C o represents the output capacitance;

[0066] Represents the predicted value of the system lumped disturbance;

[0067] t is the time.

[0068] S3: Discretize the superhelical disturbance observer;

[0069] S301: The predicted value of the output voltage The initial value of and the predicted value of the system lumped disturbance The initial values ​​of are all set to 0;

[0070] S302: Set the control period to T and the control frequency to f s , in each control cycle, the output voltage U at time t = k is obtained respectively o (k) and load current I load (k);

[0071] S303: Calculate the output voltage at time k+1 and the predicted value of the system lumped disturbance, that is, the expression of the discretized super-helical disturbance observer is as follows:

[0072]

[0073] S4: Considering the generation of control signal with one-cycle forward prediction delay compensation, the control signal u is predicted one step forward to compensate for the delay in the digital control system. The output information of the super-helical disturbance observer is used, that is, the predicted value of the output voltage at time k+1 And the predicted value of the system lumped disturbance at time k+1 Calculate the control signal u at time k * :

[0074]

[0075] In formula (3):

[0076] f s represents the control frequency;

[0077] b 0 Represents a constant related to the electrical parameters, input voltage and control frequency of the DAB converter;

[0078] U ref Represents voltage given;

[0079] I load (k) represents the load current at time k;

[0080] C o represents the output capacitance;

[0081] S5: Calculate and constrain the phase shift angle.

[0082] S501: In order to realize the control of the DAB converter, according to the existing minimum current stress double phase shift modulation strategy calculation method, the control signal u at time k is * Modulation is the internal phase shift angle D 1 and the outward phase angle D 2 Generally speaking, the actual values ​​of the electrical parameters of the DAB converter during operation may deviate from the above-mentioned measured values.

[0083] S502: In order to prevent damage to the converter, the internal phase shift angle D 1 The output and external phase angle D 2 The following constraints are imposed on the output to limit the output range and achieve accurate and robust voltage control:

[0084]

[0085] The present invention is applied to the dual active bridge DC-DC converter topology, and adopts a dual phase shift strategy (DPS) for control, that is, changing the phase shift angle between different bridge arms in two H bridges and between two different H bridges. The disturbance observer of the present invention is designed according to the discretized current-voltage equation of the dual active bridge DC-DC converter, and the required information is the current current and voltage of the DAB converter. The converter parameters in the expression use the same values ​​as those in the controller. The disturbance observer is designed using the superhelix principle in the second-order sliding mode theory, and the output of the disturbance observer is fed into the main controller to achieve disturbance compensation.

[0086] As attached Figure 3 As shown, although the traditional deadbeat method has faster dynamic performance, the output voltage has a large steady-state error under this condition, and the error is positively correlated with the output power, which is not conducive to practical application. On the other hand, the experimental results of the present invention can completely eliminate the error, have better steady-state and dynamic following performance, and greatly improve the robustness of the system.

[0087] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations within the meaning and range of equivalents of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0088] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for improving the robustness of deadbeat predictive control of a DAB converter, characterized in that: The method comprises the following steps: S1: Measure the electrical parameters of the dual active bridge DC-DC converter; S2: Design superhelical disturbance observer; S3: Discretize the superhelical disturbance observer; S4: Using the output information of the superhelical perturbation observer, that is, the predicted value of the output voltage at time k+1 And the predicted value of the system lumped disturbance at time k+1 Calculate the control signal u at time k * ; In formula (3): f s represents the control frequency; b0 represents a constant; U ref Represents voltage given; I load (k) represents the load current at time k; C o represents the output capacitance; S5: Calculate and constrain the phase shift angle.

2. The method for improving the robustness of the deadbeat predictive control of a DAB converter according to claim 1, characterized in that: The S2 comprises the following steps: S201: Input a control signal u, wherein the control signal u is proportional to the output power P n The relationship is u=0.5P n ; S202: Obtain the load current I through the current sensor load ; S203: Measure the output voltage U through the voltage sensor o ; S204: Design of superhelical disturbance observer: In formula (1): Represents the predicted value of the output voltage; Represents the output voltage error; k1 and k2 represent the observer gains that need to be adjusted; b0 represents a constant; sgn(*) represents the sign function; C o represents the output capacitance; Represents the predicted value of the system lumped disturbance; t is the time.

3. The method for improving the robustness of the deadbeat predictive control of a DAB converter according to claim 2, characterized in that: The S3 comprises the following steps: S301: The predicted value of the output voltage The initial value of and the predicted value of the system lumped disturbance The initial values ​​of are all set to 0; S302: Set the control period to T and the control frequency to f s , in each control cycle, the output voltage U at time t = k is obtained respectively o (k) and load current I load (k); S303: Calculate the output voltage at time k+1 and the predicted value of the system lumped disturbance, that is, the expression of the discretized super-helical disturbance observer is as follows:

4. The method for improving the robustness of the deadbeat predictive control of a DAB converter according to claim 3, characterized in that: The S5 comprises the following steps: S501: According to the minimum current stress double phase shift modulation strategy calculation method, the control signal u at time k is * After being modulated into an inner phase shift angle D1 and an outer phase shift angle D2, it is applied to the DAB converter; S502: Apply the following constraints to the output of the inner phase shift angle D1 and the output of the outer phase shift angle D2 respectively to achieve accurate and robust voltage control:

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