Power optimization method of hybrid energy storage device

Abstract

The invention belongs to the technical field of energy storage control, and discloses a power optimization method for a hybrid energy storage device, and the method specifically comprises the following steps: collecting a difference value between a rated voltage UN and an actual voltage udc of a DC bus in real time, inputting the difference value into a voltage loop PI controller, and outputting a current difference value delta I of the DC bus; tracking current reference values Ibref and ISCref of the storage battery and the super capacitor corresponding to the current difference value delta I based on the VSG controller, and calculating a difference value delta Ib and a difference value delta ISC between the current reference values of the storage battery and the super capacitor and the actual current value; the two current loop PI controllers are respectively used as the input of the first current loop PI controller and the input of the second current loop PI controller, the first current loop PI controller and the second current loop PI controller respectively output PWM pulse signals for controlling the first bidirectional DC / DC converter and the second bidirectional DC / DC converter, and the first bidirectional DC / DC converter and the second bidirectional DC / DC converter are respectively used for controlling the storage battery and the super capacitor. And designing an extended state observer to estimate and calculate the disturbance quantity, compensating the estimated disturbance to a control strategy of the VSG, enhancing the anti-disturbance capability of the VSG, and maintaining the stable operation of the power distribution network.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage control, and more specifically, the present invention relates to a power optimization method for a hybrid energy storage device. Background Art

[0002] Microgrids usually contain renewable energy generation units (such as solar photovoltaic, wind power) and traditional power generation sources. Due to the intermittent and uncertain nature of renewable energy, the energy supply of microgrids is prone to fluctuations. Hybrid energy storage systems use fast-response supercapacitors or flywheel energy storage to cope with short-term power fluctuations, while using battery energy storage systems to store and release energy to balance long-term energy supply and demand, thereby significantly enhancing the energy reliability and stability of microgrids.

[0003] In microgrids, hybrid energy storage systems can participate in peak-shaving and valley-filling operations, that is, charging during low-demand periods and discharging during peak hours, reducing dependence on external power grids and reducing electricity costs. In practical applications, due to the performance differences and uncertainties of hybrid energy storage devices, its control strategy is difficult to achieve the ideal distribution effect. If state-balanced control is used, it is necessary to monitor the status information of each energy storage unit in real time, and the investment cost is too high. Summary of the invention

[0004] The present invention provides a power optimization method for a hybrid energy storage device, aiming to improve the above-mentioned problem.

[0005] The present invention is implemented as follows: a power optimization method for a hybrid energy storage device, the method is specifically as follows:

[0006] (1) Real-time acquisition of the rated voltage U of the DC bus N and the actual voltage u dc The difference is input into the voltage loop PI controller, and the voltage loop PI controller outputs the current difference ΔI of the DC bus;

[0007] (2) Based on the VSG controller tracking the battery current reference value I corresponding to the current difference ΔI bref , the current reference value of the supercapacitor I SCref , and calculate the battery current reference value I bref The actual current value i b The difference ΔI b , the current reference value of the supercapacitor I SCref The actual current value i SC The difference ΔI SC ;

[0008] (3) The difference ΔI b , difference ΔI SCAs inputs of a first current loop PI controller and a second current loop PI controller, respectively, the first current loop PI controller and the second current loop PI controller respectively output PWM pulse signals for controlling a first bidirectional DC / DC converter and a second bidirectional DC / DC converter;

[0009] The bidirectional DC / DC converter and the second bidirectional DC / DC converter are used for controlling the battery and the supercapacitor respectively.

[0010] Furthermore, after step (1), the method further includes:

[0011] The current difference ΔI is input into the low-pass filter and the high-pass filter respectively, and the low-frequency current difference ΔI is output through the low-pass filter and the high-pass filter. 1 , high frequency current difference ΔI 2 ;

[0012] The low frequency current difference ΔI 1 , high frequency current difference ΔI 2 As the current difference ΔI, they are input into the VSG controller, and the VSG controller calculates the low-frequency current difference ΔI 1 The corresponding battery current reference value I bref And the high-frequency current difference ΔI 2 The corresponding supercapacitor current reference value I SCref .

[0013] Furthermore, the VSG controller converts the low-frequency current difference ΔI 1 As the current difference ΔI, calculate the angular frequency Δω and angular frequency ω corresponding to the current difference ΔI, then input the angular frequency ω into the voltage balance mathematical model to calculate the corresponding battery current reference value I bref ;

[0014] The high-frequency current difference ΔI 2 As the current difference ΔI, calculate the angular frequency Δω and angular frequency ω corresponding to the current difference ΔI, and then input the angular frequency ω into the voltage balance mathematical model to calculate the corresponding supercapacitor current reference value I SCref .

[0015] Furthermore, the calculation of the angular frequency Δω and the angular frequency ω corresponding to the current difference ΔI is:

[0016]

[0017] Δω=ω-ω N ;

[0018] Where D is the damping coefficient, ω, ω Nare the angular frequency and rated angular frequency of the synchronous motor respectively, Δω is the angular frequency difference of the synchronous motor, J is the rotor moment of inertia, and ΔI′ is the correction value of the current difference ΔI.

[0019] Furthermore, the voltage balance mathematical model is as follows:

[0020]

[0021] Eu dc =I ref R a ;

[0022] Where, is the angular frequency of the synchronous motor, is the magnetic flux, E is the electromotive force, R a is the armature resistance, u dc is the actual value of the DC bus voltage.

[0023] Furthermore, the correction value ΔI′ of the current difference ΔI is calculated based on the extended state observer, and the calculation formula is as follows:

[0024]

[0025] Where e is the tracking error of the extended observer, z 1 is the load disturbance, z 2 is the load disturbance after the expansion of the extended state observer, β 1 , β 2 are the correction gains of the extended state observer, b and δ are the tracking factor and filtering factor of the extended state observer respectively;

[0026] The estimated value of the second load disturbance is calculated As the correction value ΔI′ of the current difference ΔI, s is a differential operator.

[0027] Furthermore, the expression of the fal(e,b,δ) function is as follows:

[0028]

[0029] Among them, e is the tracking error of the extended observer, b and δ are the tracking factor and filtering factor of the extended state observer respectively.

[0030] The power optimization configuration strategy of the hybrid energy storage system provided by the present invention first designs a new VSG control model to solve the problem of lack of inertia characteristics of power electronic converters in microgrids. In addition, considering the randomness and volatility of renewable energy power generation in microgrids, an extended state observer is designed in the upper-level control strategy to estimate and calculate the disturbance, and the estimated disturbance is compensated to the control strategy of VSG, thereby enhancing the anti-disturbance capability of VSG and maintaining the stable operation of the distribution network.

[0031] In addition, the present invention combines VSG control and an extended state observer, and utilizes the advantages of VSG's rapid response to enable the control system to respond more quickly to changes in grid demand. When power demand is high, the rapid response characteristics of supercapacitors are used to meet instantaneous power demand, and batteries are used to respond to system demand during periods of low power demand. At the same time, taking into account the randomness and volatility of distributed power sources and load power changes in actual projects, the state observer is combined to provide more accurate system status information, providing more reliable data support for predictive control, without the need to monitor the status information of each energy storage unit, and greatly reducing controllable costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of a control model of a control method for a hybrid energy storage device provided by an embodiment of the present invention;

[0033] Figure 2 A schematic diagram of a control model for a VSG controller and an extended state observer provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The specific implementation modes of the present invention are further explained in detail below by describing the embodiments with reference to the accompanying drawings, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0035] The hybrid energy storage device comprises a battery and a super capacitor, and the battery and the super capacitor are connected to the DC bus through a first bidirectional DC / DC converter and a second bidirectional DC / DC converter respectively.

[0036] Figure 1 The control model of the control method of the hybrid energy storage device provided by the embodiment of the present invention is as follows:

[0037] (1) Real-time acquisition of the rated voltage U of the DC bus N and the actual voltage u dc The difference is input into the voltage loop PI controller, and the voltage loop PI controller outputs the current difference ΔI of the DC bus;

[0038] (2) Based on the VSG controller tracking the battery current reference value I corresponding to the current difference ΔIbref , the current reference value of the supercapacitor I SCref , and calculate the battery current reference value I bref The actual current value i b The difference ΔI b , the current reference value of the supercapacitor I SCref The actual current value i SC The difference ΔI SC ;

[0039] (3) The difference ΔI b , difference ΔI SC They serve as inputs of the first current loop PI controller and the second current loop PI controller respectively. The first current loop PI controller and the second current loop PI controller respectively output PWM pulse signals for controlling the first bidirectional DC / DC converter and the second bidirectional DC / DC converter. The bidirectional DC / DC converter and the second bidirectional DC / DC converter are respectively used for controlling the battery and the supercapacitor.

[0040] In the control of the hybrid energy storage device, not only the stability of the control voltage and frequency is considered, but also the distribution control of high frequency and low frequency is required. Since the supercapacitor has a high power density, the supercapacitor is used for high frequency control, and the battery is used for low frequency control. The current difference ΔI is input into the low-pass filter and the high-pass filter respectively, and the low-frequency current difference ΔI is output through the low-pass filter and the high-pass filter. 1 and high frequency current difference ΔI 2 Low frequency current difference ΔI 1 , high frequency current difference ΔI 2 As the current difference ΔI, it is input into the VSG controller and the extended state observer to act on the battery and the supercapacitor respectively.

[0041] ω c is the cut-off frequency, which defines the frequency point at which the filter starts to attenuate from allowing the signal to pass. In the discrete domain, s=jω is a complex frequency variable, j is an imaginary unit, It is a low-pass filter, which aims to transmit the low-frequency signal to the battery control terminal. It is a high-pass filter, which aims to transmit the high-frequency signal to the supercapacitor control end. bref and i b is the battery current reference value and actual value, I SCref and i SC are the reference value and actual value of the supercapacitor current, PWM is the pulse width modulator, and outputs the trigger pulse of the converter.

[0042] Traditional power grids contain a large number of synchronous motors, and the entire distribution network has sufficient inertia characteristics to cope with power fluctuations within the grid. With the development of new energy generation and power electronic devices, microgrids no longer contain synchronous motors. Since the bidirectional DC / DC converter connected to the energy storage device can perform bidirectional power transmission, it is considered to introduce inertia characteristics similar to those of synchronous motors into the energy storage converter.

[0043] The inertia response equation of the synchronous motor is as follows:

[0044]

[0045] Where D is the damping coefficient, ω, ω N are the angular frequency and rated angular frequency of the synchronous motor respectively, J is the rotor moment of inertia, T m 、T e are mechanical torque and electromagnetic torque respectively, and ΔT is the torque difference.

[0046] The current balance equation in the bidirectional DC / DC converter of the energy storage system is as follows:

[0047]

[0048] In the formula, C dc is the DC capacitance, u dc and U N are the DC bus voltage and rated voltage respectively, G dc is the DC capacitance admittance, i dc and i out They are the output currents at the back end and front end of the bidirectional DC / DC converter of the energy storage system, and ΔI is the current difference.

[0049] By analogy with equation (1) and equation (2), it can be seen that the two sets of formulas are highly similar in composition. By analogy with torque T and current i, that is, let ΔT = ΔI, simulate equation (1) and introduce the inertia characteristics similar to those of synchronous motors in the control of bidirectional DC / DC converters. Specifically, Figure 1 As shown in the VSG module. Figure 1 In the VSG module, the first half is bus voltage control, and the second half is VSG control. N and u dc is the rated value and actual value of the DC bus voltage. PI is a proportional integral controller. The DC bus voltage is output as the DC bus voltage difference Δu after the differential link. dc , and then the output is the current difference ΔI through the PI link. In the continuous domain, s is the differential operator.

[0050] In the embodiment of the present invention, the VSG controller uses formula (3) and formula (4) to calculate the angular frequency Δω and angular frequency ω corresponding to the current difference ΔI, and then inputs the angular frequency ω into the voltage balance mathematical model expressed by formula (5) and formula (6) to calculate the current reference value corresponding to the current difference ΔI. 1 As the current difference ΔI, the corresponding battery current reference value I is calculated based on formulas (3) to (6): bref , the high frequency current difference ΔI 2 As the current difference ΔI, the corresponding supercapacitor current reference value I is calculated based on formulas (3) to (6): SCref , based on formulas (3) to (6), are as follows:

[0051]

[0052] Δω=ω-ω N (4)

[0053]

[0054] Eu dc =I ref R a (6)

[0055] Where D is the damping coefficient, ω, ω N are the angular frequency and rated angular frequency of the synchronous motor respectively, Δω is the angular frequency difference of the synchronous motor, J is the rotor moment of inertia, is the magnetic flux, E is the electromotive force, R a is the armature resistance, u dc is the actual value of the DC bus voltage, and the current difference ΔI is the low-frequency current difference ΔI 1 When the current control loop input reference current I ref Indicates the battery current reference value I bref , the current difference ΔI is the high-frequency current difference ΔI 2 When the current control loop input reference current I ref Indicates the current reference value I of the supercapacitor SCref , ΔI′ is the correction value of the current difference ΔI.

[0056] Since renewable energy generation in microgrids is random and volatile, it is considered to introduce an extended state observer into the upper-level control strategy to estimate and calculate the disturbance, and to compensate the estimated disturbance into the control strategy of the VSG controller to enhance the anti-disturbance capability of the VSG controller.

[0057] Model a first-order nonlinear system including a perturbation:

[0058]

[0059] Where y(t) is the output, x(t) is the state variable, f(x,ω(t),t) is the disturbance action, ω(t) is the real-time disturbance action, a is the compensation factor, and u(t) is the input.

[0060] According to formula (7), the disturbance is expanded into the next new variable x 2 , and changes over time:

[0061]

[0062] At this time, the extended state observer can be expressed as:

[0063]

[0064] Where Z represents the observer load disturbance estimate, B=(1 0), U is a constant (representing proportional control), and K 1 and K 2 is the proportionality coefficient, b 0 is a constant, x 1 Represents a state variable.

[0065] Expanding formula (9) yields:

[0066]

[0067] When the system is stable, Δω=ω-ω N =0, formula (1) can be expressed as:

[0068]

[0069] Let x 1 =ω, substituting the VSG model expressed by equation (1) into equation (8), we can obtain:

[0070]

[0071] When ΔT = ΔI, equation (12) can be expressed as:

[0072]

[0073] This design introduces the fal function for convergence tracking. The fal function is a function used to describe the reliability of the system and can be used to measure the reliability level of the system. Combining equations (10) and (13), we can get:

[0074]

[0075] Where e is the tracking error of the extended observer, z 1 is the load disturbance, z 2 is the load disturbance after the expansion of the extended state observer, β 1 , β 2 are the correction gains of the extended state observer, b and δ are the tracking factor and filtering factor of the extended state observer respectively. The estimated value of the second load disturbance calculated based on formula (14) is As the correction value ΔI′ of the current difference ΔI, formula (3) is introduced to convert the estimated value of the first load disturbance calculated based on formula (14) into As the input in the next iteration, it is used to update the tracking error e of the extended observer. s is a differential operator, such as Figure 2 shown.

[0076] The present invention introduces the fal function for convergence tracking. The fal function is a function used to describe the reliability of a system and can be used to measure the reliability level of the system. The specific expression of fal(e, b, δ) is as follows:

[0077]

[0078] The power optimization configuration strategy of the hybrid energy storage system provided by the present invention designs a new VSG control model, improves the inertia characteristics of the system, designs an extended state observer to estimate and calculate the disturbance, compensates the estimated disturbance into the control strategy of the VSG, and enhances the anti-disturbance ability of the VSG.

[0079] The present invention has been described exemplarily. Obviously, the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A power optimization method for a hybrid energy storage device, characterized in that: The method is specifically as follows: (1) Real-time acquisition of the rated voltage U of the DC bus N and the actual voltage u dc The difference is input into the voltage loop PI controller, and the voltage loop PI controller outputs the current difference ΔI of the DC bus; (2) Based on the VSG controller tracking the battery current reference value I corresponding to the current difference ΔI bref , the current reference value of the supercapacitor I SCref , and calculate the battery current reference value I bref The actual current value i b The difference ΔI b , the current reference value of the supercapacitor I SCref The actual current value i SC The difference ΔI SC ; (3) The difference ΔI b , difference ΔI SC As inputs of a first current loop PI controller and a second current loop PI controller, respectively, the first current loop PI controller and the second current loop PI controller respectively output PWM pulse signals for controlling a first bidirectional DC / DC converter and a second bidirectional DC / DC converter; The bidirectional DC / DC converter and the second bidirectional DC / DC converter are used for controlling the battery and the supercapacitor respectively.

2. The power optimization method of the hybrid energy storage device according to claim 1, characterized in that: After step (1), the method further includes: The current difference ΔI is input into a low-pass filter and a high-pass filter respectively, and a low-frequency current difference ΔI1 and a high-frequency current difference ΔI2 are outputted through the low-pass filter and the high-pass filter; The low-frequency current difference ΔI1 and the high-frequency current difference ΔI2 are input into the VSG controller as the current difference ΔI respectively. The VSG controller calculates the battery current reference value I corresponding to the low-frequency current difference ΔI1. bref And the current reference value I of the supercapacitor corresponding to the high-frequency current difference ΔI2 SCref .

3. The power optimization method of the hybrid energy storage device according to claim 2, characterized in that: The VSG controller uses the low-frequency current difference ΔI1 as the current difference ΔI, calculates the angular frequency Δω and angular frequency ω corresponding to the current current difference ΔI, and then inputs the angular frequency ω into the voltage balance mathematical model to calculate the corresponding battery current reference value I bref .

4. The power optimization method of the hybrid energy storage device according to claim 2, characterized in that: The high-frequency current difference ΔI2 is used as the current difference ΔI, and the angular frequency Δω and angular frequency ω corresponding to the current difference ΔI are calculated. Then the angular frequency ω is input into the voltage balance mathematical model to calculate the corresponding supercapacitor current reference value I SCref .

5. The power optimization method of the hybrid energy storage device according to claim 3 or 4, characterized in that: Calculation of the angular frequency Δω and angular frequency ω corresponding to the current difference ΔI: Give = oh-oh N ; Where D is the damping coefficient, ω, ω N are the angular frequency and rated angular frequency of the synchronous motor respectively, Δω is the angular frequency difference of the synchronous motor, J is the rotor moment of inertia, and ΔI′ is the correction value of the current difference ΔI.

6. The power optimization method of the hybrid energy storage device according to claim 3 or 4, characterized in that: The voltage balance mathematical model is as follows: E-u dc =I ref R a ; Where, is the angular frequency of the synchronous motor, is the magnetic flux, E is the electromotive force, R a is the armature resistance, u dc is the actual value of the DC bus voltage.

7. The power optimization method of the hybrid energy storage device according to claim 5, characterized in that: The correction value ΔI′ of the current difference ΔI is calculated based on the extended state observer, and its calculation formula is as follows: Among them, e is the tracking error of the extended observer, z1 is the load disturbance, z2 is the load disturbance after the expansion of the extended state observer, β1 and β2 are the correction gains of the extended state observer, b and δ are the tracking factor and filtering factor of the extended state observer respectively; The estimated value of the second load disturbance is calculated As the correction value ΔI′ of the current difference ΔI, s is a differential operator.

8. The power optimization method of the hybrid energy storage device according to claim 7, characterized in that: The expression of the fal(e,b,δ) function is as follows: Among them, e is the tracking error of the extended observer, b and δ are the tracking factor and filtering factor of the extended state observer respectively.

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