A method and system for adaptively adjusting bus voltage of a supercapacitor energy storage system

Abstract

The present invention discloses a method and system for adaptively regulating the bus voltage of a supercapacitor energy storage system, the method adopts an adaptive control strategy to regulate the bus voltage and / or adopts a set point regulation strategy to regulate the bus voltage; the adaptive control strategy is a dual-loop control strategy using a current inner loop with fixed parameters and an adaptive voltage outer loop, the proportional parameter and integral parameter of the voltage outer loop dynamically change with the terminal voltage of the supercapacitor, and the closed-loop bandwidth of the system is far away from the zero point of the right half plane: the set point regulation strategy is: if the difference between the actual value and the expected value of the current bus voltage is within the allowable error range, no adjustment is made; if it is not within the allowable error range, the prediction error is calculated based on the current difference and using an advance compensator, and the adjustment amount is determined and adjusted using the prediction error. The above method can effectively alleviate the fluctuation effect of the input voltage mutation or load mutation on the output voltage.

Description

Technical Field

[0001] The present invention belongs to the technical field of supercapacitor energy storage systems, and in particular relates to a bus voltage adaptive regulation method and system for a supercapacitor energy storage system. Background Art

[0002] In recent years, fuel reserves and climate change challenges have provided strong impetus for the development of clean transportation systems, renewable energy and smart grids. Supercapacitor energy storage systems are widely used in these fields. In supercapacitor energy storage systems, supercapacitors provide energy to the load through DC-DC converters. Supercapacitor energy storage components have the characteristics of high power density, fast charge and discharge rate, long cycle life and wide operating temperature range. Supercapacitors are more efficient in absorbing feedback energy, and the problem of low energy density can also be solved by connecting components in series and parallel. Due to the above advantages, supercapacitor energy storage systems have received widespread attention.

[0003] Since the terminal voltage of the supercapacitor varies greatly with the capacity and the unknown load will fluctuate randomly, the DC bus voltage will inevitably fluctuate. When the bus voltage is unstable, it will directly affect the normal operation of various loads and pose a serious threat to the reliability and safety of the energy storage system. Since both the input voltage and load conditions are changing, it is of great significance to design an effective supercapacitor DC bus voltage control strategy for such a time-varying system to ensure that the supercapacitor energy storage system maintains a stable DC bus voltage.

[0004] At present, the main technologies in these areas are: (1) The classic fixed-parameter PID control strategy, which can be used to better stabilize the bus voltage when the output voltage quality requirements are not high. However, when the load and input voltage suddenly change, the bus voltage stabilization effect is not good. (2) The sliding film control strategy can adapt to changes in input voltage and other parameters. However, the use of sliding film control will cause the system state to cross the equilibrium point back and forth, which will result in large output voltage ripple. (3) Control strategies based on optimization and data-driven can adapt to changes in system characteristics while reducing voltage ripple. However, both methods require a lot of training time and computation, and are difficult to apply to real-time fields. Summary of the invention

[0005] The purpose of the present invention is to provide a bus voltage adaptive regulation method and system for a supercapacitor energy storage system, which is used to solve the technical problem of output voltage fluctuation under the condition of sudden input voltage or sudden load change. Among them, in view of the problem of sudden input voltage change, the bus voltage adaptive regulation method of the present invention adopts an adaptive control strategy for regulation, wherein the proportional and integral parameters of the voltage outer loop are functions of the supercapacitor terminal voltage, so it can adapt to the characteristics of the supercapacitor terminal voltage changing with time during operation; in view of the problem of sudden load change, the bus voltage adaptive regulation method of the present invention adopts a set point regulation strategy, which quickly adjusts the set value according to the error, and reduces the stabilization time and overshoot of the bus voltage.

[0006] On the one hand, the present invention provides a method for adaptively regulating bus voltage of a supercapacitor energy storage system, which uses an adaptive control strategy to regulate the bus voltage and / or uses a set point regulation strategy to regulate the bus voltage;

[0007] The adaptive control strategy is a dual-loop control strategy that uses a current inner loop with fixed parameters and an adaptive voltage outer loop. The proportional parameter and integral parameter of the current inner loop are fixed values, and the proportional parameter and integral parameter of the voltage outer loop change dynamically with the terminal voltage of the supercapacitor. The closed-loop bandwidth of the system is ω c Far away from the zero point of the right half plane, and the system cutoff frequency ω = ω c When , the amplitude of the system open-loop transfer function is 1;

[0008] The set point adjustment strategy is: if the difference between the actual value and the expected value of the current bus voltage is within the allowable error range, no adjustment is made; if it is not within the allowable error range, the prediction error is calculated based on the current difference and using the lead compensator, and the adjustment amount is determined using the prediction error and adjusted.

[0009] Further optionally, the system corresponds to a closed-loop bandwidth ω c Far away from the zero point of the right half plane and the system cutoff frequency ω=ω c , when the amplitude of the corresponding system open-loop transfer function is 1, determine the proportional parameter and integral parameter of the voltage outer loop; wherein, when the closed-loop system cutoff frequency ω=ω c , when the amplitude of the open-loop transfer function is 1, it is expressed as:

[0010]

[0011] In the formula, K p is the proportional parameter of the voltage outer loop, K i is the integral parameter of the voltage outer loop, s is a complex variable, G is the coefficient related to the load resistance, supercapacitor terminal voltage, and bus voltage, a and b are the closed-loop zeros and poles of the system, ω c is the closed-loop bandwidth.

[0012] Further optionally, the voltage outer loop makes the closed loop bandwidth ω c Away from the zero point of the right half plane, the closed-loop bandwidth ω c satisfy:

[0013]

[0014] Where a is the zero point on the right plane of the system, and x is the parameter to be selected, which represents the degree to which the closed-loop bandwidth is away from the zero point.

[0015] Further optionally, the proportional parameter and integral parameter of the voltage outer loop are expressed as follows:

[0016]

[0017]

[0018] In the formula, K p is the scale parameter, K i is the integration parameter, R L and C f are the values ​​of the load resistor and capacitor, V sc is the terminal voltage of the supercapacitor, L is the inductance of the converter, is the expected value of bus voltage.

[0019] Further optionally, the open-loop transfer function G of the system o (s) is:

[0020]

[0021] in:

[0022]

[0023] In the formula, K p is the scale parameter, K i is the integration parameter, R L and C f are the values ​​of the load resistance and capacitor respectively, s is a complex variable, G is the coefficient related to the load resistance, supercapacitor terminal voltage, and bus voltage, a and b are the closed-loop zeros and poles of the system, V sc is the terminal voltage of the supercapacitor, L is the inductance of the converter, V o is the bus voltage.

[0024] Further optionally, the proportional parameter and the integral parameter of the current inner loop have value ranges of 0.2-0.5 and 150-356 respectively.

[0025] Further optionally, in the set point adjustment strategy, the adjustment amount is determined and adjusted according to the following formula:

[0026]

[0027] In the formula, e min and e max are the upper and lower bounds of the error allowed by the system; is defined as the expected value of the bus voltage, V o ′ is the actual set value of the system input, m is the error proportional factor, e p is the prediction error.

[0028] Further optionally, the prediction error e p As shown below:

[0029]

[0030] In the formula, e p (s) is the prediction error e p The corresponding Laplace transform expression, T m and α m are design parameters, α m Related to the response speed and robustness to noise, T m is the time constant, s is the complex variable in Laplace transform, and e(s) is the Laplace transform expression corresponding to the current bus voltage error e.

[0031] Further optionally, the supercapacitor provides energy to the bus through a DC-DC converter. When energy flows from the supercapacitor to the load, the DC-DC converter operates in a Boost mode. When energy flows from the load to the supercapacitor, the DC-DC converter operates in a Buck mode.

[0032] In a second aspect, the present invention provides a supercapacitor energy storage system, a physical layer and a control layer thereof;

[0033] The physical layer includes an energy supply module and an energy consumption module, wherein the energy supply module includes a super capacitor and a converter, and the energy consumption module is composed of a bus, a traction and a braking load;

[0034] The control layer includes a voltage acquisition unit, a current acquisition unit, and a bus voltage regulation method unit. The voltage acquisition unit and the current acquisition unit respectively acquire voltage signals and current signals, and feed them back to the bus voltage regulation method unit.

[0035] The bus voltage regulation method unit adopts an adaptive control strategy to regulate the bus voltage and / or adopts a set point regulation strategy to regulate the bus voltage;

[0036] The adaptive control strategy is a dual-loop control strategy that uses a fixed-parameter current inner loop and an adaptive voltage outer loop. The proportional parameter and integral parameter of the current inner loop are fixed values, and the proportional parameter and integral parameter of the voltage outer loop change dynamically with the terminal voltage of the supercapacitor. The closed-loop bandwidth of the system is ω c Far away from the zero point of the right half plane, and the system cutoff frequency ω = ω c When , the amplitude of the system open-loop transfer function is 1;

[0037] The set point adjustment strategy is: if the difference between the actual value and the expected value of the current bus voltage is within the allowable error range, no adjustment is made; if it is not within the allowable error range, the prediction error is calculated based on the current difference and using the lead compensator, and the adjustment amount is determined using the prediction error and adjusted.

[0038] Beneficial Effects

[0039] The present invention aims at the problem of sudden change of input voltage. The bus voltage adaptive regulation method of the present invention adopts an adaptive control strategy for regulation, wherein the proportion and integral parameters of the voltage outer loop are functions of the supercapacitor terminal voltage, so it can adapt to the characteristics of the supercapacitor terminal voltage changing with time during operation, and ensure the stability of the bus voltage; in view of the problem of sudden change of load, the bus voltage adaptive regulation method of the present invention adopts a set point regulation strategy, which modifies the set value of the bus voltage according to the trend of the bus voltage error. Therefore, it can adapt to the change of load, improve the dynamic response capability of the system, reduce overshoot and stabilization time. In summary, the method and system provided by the present invention, which takes into account that the terminal voltage of the supercapacitor will change with the running time, and the control system constructed is a time-varying system; taking into account that the load condition is unknown and changes randomly during operation, the control system constructed can adapt to the change of load. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a structural block diagram of the supercapacitor energy storage system of the present invention;

[0041] Figure 2 It is a double-loop control block diagram of the present invention;

[0042] Figure 3 It is a structural block diagram of the control method of the present invention. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to the embodiments.

[0044] like Figure 1As shown, the supercapacitor energy storage system provided by the present invention has a power supply connected to a DC-DC converter to power the DC link. In a supercapacitor tram, traction, braking and other loads obtain energy from the DC link. The fast adaptive bus voltage regulation strategy of the supercapacitor-based energy storage system controls the DC-DC converter by adjusting the duty cycle to ensure that the bus voltage is stable and provides the power required by the load. The DC-DC converter allows bidirectional energy flow: from power supply to load (boost mode) and from load to power supply (buck mode). Figure 1 In the example, for the DC-DC converter, L is the inductor of the converter, S1 and S2 are MOSFETs, and D is the duty cycle of the converter. For the supercapacitor, R sc is the internal resistance of the supercapacitor, C sc is the capacitance value, V sc is the terminal voltage of the supercapacitor, R L and C f are the values ​​of the load resistance and capacitance respectively.

[0045] In order to solve the problem of sudden change in input voltage, the output voltage of the external voltage loop is related to the voltage at the supercapacitor terminal, and the voltage at the supercapacitor terminal changes greatly. Therefore, in order to ensure the stability of the output voltage of the external voltage loop, it is necessary to overcome the problem of sudden change in the voltage at the supercapacitor terminal. Figure 2 As shown, the present invention adopts a dual-loop control scheme, which includes a current inner loop with fixed parameters and an adaptive voltage outer loop. The reasoning process is as follows:

[0046] The output voltage is expressed as follows:

[0047]

[0048] Where V o (s), i sc (s) are the Laplace forms of bus voltage and supercapacitor output current, V o , D, and s are respectively the actual value of the bus voltage, the duty cycle of the converter, and the complex variable in the Laplace transform. From the above, it can be seen that the output voltage will change with the supercapacitor terminal voltage V sc We assume that the inner current loop can achieve a good following effect, so the transfer function of the inner current loop is The controller used in the voltage outer loop is a PI controller, so the open-loop transfer function of the system is G o (s) is:

[0049]

[0050] in:

[0051]

[0052] Therefore, the expression of the closed-loop transfer function is:

[0053]

[0054] In this embodiment, the control of the current inner loop uses a fixed-parameter PI controller, where the proportional parameter K p is 0.25, the integral parameter K i is 166.

[0055] The calculation method of the adaptive voltage controller is to make the voltage outer loop so that the closed-loop bandwidth ω can be c Far away from the zero point of the right half plane, ω c Should be designed to:

[0056]

[0057] Consider x = 10, at ω = ω c When the open-loop transfer function is o (s)|=1, that is:

[0058]

[0059] Substituting formula (5) into formula (6), the simplified expression is:

[0060]

[0061] K p for:

[0062]

[0063] K i for:

[0064]

[0065] The proportional and integral parameters in the adaptive control strategy are functions of the supercapacitor terminal voltage, and can adapt to the characteristics of the supercapacitor terminal voltage changing with time during operation.

[0066] In summary, in order to solve the problem of sudden change in input voltage, the proportional parameter and integral parameter of the current inner loop are fixed values, and the specific values ​​can be adjusted according to the accuracy requirements; the proportional parameter and integral parameter of the voltage outer loop change dynamically with the terminal voltage of the supercapacitor, which is deduced under the requirement of formula (6). To further improve the control effect, the voltage outer loop makes the closed-loop bandwidth ω c Away from the zero point of the right half plane, the proportional and integral parameters of formulas (8) and (9) are deduced.

[0067] In view of the problem of sudden load change, the bus voltage adaptive adjustment method of the present invention can adopt a set point adjustment strategy, which quickly adjusts the set value according to the error to reduce the stabilization time and overshoot of the bus voltage. The specific logic is: by adjusting the set value, it is integrated into the voltage control loop without affecting the original control structure. The set point adaptive adjustment strategy determines whether it is within the allowable range of error by making a difference between the actual value and the expected value of the current bus voltage. If it is within the allowable range of error, the set value is not adjusted. If it is outside the allowable range, the possible future difference is calculated based on the current difference using the lead compensator. The future difference calculated and multiplied by a certain adjustment coefficient is the adjustment value required for the set value. When the bus voltage is less than the expected value, the set point adaptive adjustment strategy will increase the set value, so that the actual output voltage value also increases, speeding up the time to reach the expected value, otherwise it will reduce the set value. It should be understood that the allowable error range is an empirical value set according to the accuracy requirements, and the present invention does not specifically limit this. The expected value of the bus voltage is a set value that meets the application requirements.

[0068] The set point adjustment strategy determines the adjustment amount and makes adjustments according to the following formula:

[0069]

[0070] where m·e p is based on the set point and the prediction error e p The adjustment of m = 0.2 can usually improve the dynamic response of the system. In actual situations, the appropriate value can be found through offline research. min and e max It is the upper and lower bounds of the error allowed by the system, which is an empirical value set according to the accuracy requirements.

[0071] Prediction error p The actual error and a look-ahead compensator, the prediction error is calculated as:

[0072]

[0073] Among them, T m and α m is the parameter that needs to be designed and is related to the system. In most cases, α m Choose between 0.05 and 0.3, and T m When selecting, ensure that the zero point of the compensator matches the main pole of the system.

[0074] According to actual experimental conditions, in the present invention, α mThe best effect is obtained by setting T to 0.05. m For 0.01.m, choose 0.28. e min and e max -1 and 1 respectively.

[0075] Through the above technical solution, when the load fluctuates, the bus voltage value will fluctuate, but the set point adaptive adjustment strategy can quickly adjust the set value according to the error, thereby reducing the stabilization time and overshoot of the bus voltage.

[0076] It should be understood that in some implementations, the bus voltage can be regulated by an adaptive control strategy alone, or by a set point regulation strategy alone; in other implementations, the bus voltage can be regulated by both an adaptive control strategy and a set point regulation strategy.

[0077] Based on the above technical principles, the present invention also provides a supercapacitor energy storage system, its physical layer and control layer;

[0078] The physical layer includes an energy supply module and an energy consumption module. The energy supply module includes a super capacitor and a converter. The energy supply module provides energy to the energy consumption module. In this embodiment, the energy consumption module is composed of a bus and a traction and braking load.

[0079] The control layer includes a voltage acquisition unit, a current acquisition unit, and a bus voltage regulation method unit. The voltage acquisition unit and the current acquisition unit respectively acquire voltage signals and current signals, and feed them back to the bus voltage regulation method unit.

[0080] The bus voltage regulation method unit adopts an adaptive control strategy to regulate the bus voltage and / or adopts a set point regulation strategy to regulate the bus voltage;

[0081] Among them, the technical details of the bus voltage regulation method unit when using an adaptive control strategy to regulate the bus voltage and / or using a set point regulation strategy to regulate the bus voltage are described in reference to the above technical principles, and the present invention will not further describe this.

[0082] It should be emphasized that the examples described in the present invention are illustrative rather than restrictive, and therefore the present invention is not limited to the examples described in the specific embodiments. Any other embodiments derived by those skilled in the art based on the technical solution of the present invention that do not depart from the purpose and scope of the present invention, whether modified or replaced, also fall within the scope of protection of the present invention.

Claims

1. A method for adaptively regulating bus voltage of a supercapacitor energy storage system, characterized in that: Adopting an adaptive control strategy to adjust the bus voltage and / or adopting a set point adjustment strategy to adjust the bus voltage; The adaptive control strategy is a dual-loop control strategy that uses a current inner loop with fixed parameters and an adaptive voltage outer loop. The proportional parameter and integral parameter of the current inner loop are fixed values, and the proportional parameter and integral parameter of the voltage outer loop change dynamically with the terminal voltage of the supercapacitor. The closed-loop bandwidth of the system is ω c Far away from the zero point of the right half plane, and the system cutoff frequency ω = ω c When , the amplitude of the system open-loop transfer function is 1; the set point adjustment strategy is: if the difference between the actual value and the expected value of the current bus voltage is within the allowable error range, no adjustment is made; if it is not within the allowable error range, the prediction error is calculated based on the current difference and using the lead compensator, and the adjustment amount is determined and adjusted using the prediction error; The system corresponds to the closed-loop bandwidth ω c Far away from the zero point of the right half plane and the system cutoff frequency ω=ω c , when the amplitude of the corresponding system open-loop transfer function is 1, determine the proportional parameter and integral parameter of the voltage outer loop; wherein, when the closed-loop system cutoff frequency ω=ω c , when the amplitude of the open-loop transfer function is 1, it is expressed as: In the formula, K p is the proportional parameter of the voltage outer loop, K i is the integral parameter of the voltage outer loop, s is a complex variable, G is the coefficient related to the load resistance, supercapacitor terminal voltage, and bus voltage, a and b are the closed-loop zeros and poles of the system, ω c is the closed-loop bandwidth; The set point adjustment strategy determines the adjustment amount and makes adjustments according to the following formula: In the formula, e min and e max is the upper and lower bounds of the system’s allowed error; V o * is defined as the expected value of the bus voltage, V′ o is the actual set value of the system input, m is the error proportional factor, e p is the prediction error.

2. The bus voltage adaptive regulation method according to claim 1, characterized in that: The voltage outer loop in Boost converter mode makes the closed loop bandwidth ω c Away from the zero point of the right half plane, the closed-loop bandwidth ω c satisfy: Where a is the zero point on the right plane of the system, and x is the parameter to be selected, which represents the degree to which the closed-loop bandwidth is away from the zero point.

3. The bus voltage adaptive regulation method according to claim 2 is characterized in that: The proportional parameter and integral parameter of the voltage outer loop are expressed as follows: In the formula, K p is the scale parameter, K i is the integration parameter, R L and C f are the values ​​of the load resistor and capacitor, V sc is the terminal voltage of the supercapacitor, L is the inductance of the converter, V o * is the expected value of bus voltage.

4. The bus voltage adaptive regulation method according to claim 1, characterized in that: The open-loop transfer function of the system is G o (s) is: in: In the formula, K p is the scale parameter, K i is the integration parameter, R L and C f are the values ​​of the load resistance and capacitor respectively, s is a complex variable, G is the coefficient related to the load resistance, supercapacitor terminal voltage, and bus voltage, a and b are the closed-loop zeros and poles of the system, V sc is the terminal voltage of the supercapacitor, L is the inductance of the converter, V o is the bus voltage.

5. The bus voltage adaptive regulation method according to claim 1, characterized in that: The proportional parameter and integral parameter of the current inner loop have value ranges of 0.2-0.5 and 150-356 respectively.

6. The bus voltage adaptive regulation method according to claim 1, characterized in that: The prediction error e p As shown below: In the formula, e p (s) is the prediction error e p The corresponding Laplace transform expression, T m and α m are design parameters, α m Related to the response speed and robustness to noise, T m is the time constant, s is the complex variable in Laplace transform, and e(s) is the Laplace transform expression corresponding to the current bus voltage error e.

7. The bus voltage adaptive regulation method according to claim 1, characterized in that: The supercapacitor provides energy to the bus through a DC-DC converter. When energy flows from the supercapacitor to the load, the DC-DC converter operates in the Boost mode. When energy flows from the load to the supercapacitor, the DC-DC converter operates in the Buck mode.

8. A supercapacitor energy storage system, characterized in that: The method according to any one of claims 1 to 7, comprising: a physical layer and a control layer; Wherein, the physical layer includes an energy supply module and an energy consumption module, the energy supply module includes a super capacitor and a converter, and the energy supply module provides energy to the energy consumption module; The control layer includes a voltage acquisition unit, a current acquisition unit, and a bus voltage regulation method unit. The voltage acquisition unit and the current acquisition unit respectively acquire voltage signals and current signals, and feed them back to the bus voltage regulation method unit. The bus voltage regulation method unit adopts an adaptive control strategy to regulate the bus voltage and / or adopts a set point regulation strategy to regulate the bus voltage; The adaptive control strategy is a dual-loop control strategy that uses a fixed-parameter current inner loop and an adaptive voltage outer loop. The proportional parameter and integral parameter of the current inner loop are fixed values, and the proportional parameter and integral parameter of the voltage outer loop change dynamically with the terminal voltage of the supercapacitor. The closed-loop bandwidth of the system is ω c Far away from the zero point of the right half plane, and the system cutoff frequency ω=ω c When , the amplitude of the system open-loop transfer function is 1; The set point adjustment strategy is: if the difference between the actual value and the expected value of the current bus voltage is within the allowable error range, no adjustment is made; if it is not within the allowable error range, the prediction error is calculated based on the current difference and using the lead compensator, and the adjustment amount is determined using the prediction error and adjusted.

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