Self-adaptive virtual inertia control method and device for energy storage DAB converter

Abstract

The invention discloses a self-adaptive virtual inertia control method and device for an energy storage DAB converter, relates to the field of converter control, and comprises three parts of current feedforward control based on low-pass filtering, voltage compensation control and virtual capacitor Cv parameter self-adaption. Wherein current feed-forward compensation in a low-pass filtering mode is added in a loop causing initial voltage abrupt change so as to improve initial drop of bus voltage, steady-state voltage compensation is added in a droop link so as to realize zero-difference adjustment of the bus voltage, and a function is constructed according to bus voltage deviation and change rate so as to realize self-adaptive adjustment of the virtual capacitor Cv. According to the control method provided by the invention, the bus voltage fluctuation can be effectively inhibited, the voltage steady-state error is reduced, and the supporting capability of the energy storage unit on the bus voltage is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of control of converters, in particular to a kind of energy storage DAB converter adaptive virtual inertia control method and device. BACKGROUND

[0002] DC microgrid containing DC charging station access is an effective carrier to realize photovoltaic, wind power and other new energy networking and electric vehicle fast charging, and has practical application value.However, compared with the rich rotating inertia unit in alternating current large power grid, DC microgrid adopts a large number of power electronic converters, lacks the inertia support of rotating motor, and shows the characteristics of low inertia and weak damping.Under the conditions of new energy output fluctuation, electric vehicle load switching and the like, system power imbalance occurs, bus voltage out-of-limit is easy to occur, and problems such as system power quality and stability are affected.

[0003] The application of energy storage unit to the above-mentioned virtual inertia control method can provide inertia and damping for the system to a certain extent, reduce bus voltage fluctuation, but there are differences in dynamic response performance among different control methods.At the same time, as the main inertia source of DC microgrid, the energy storage unit needs to reduce the steady-state deviation of bus voltage as much as possible while slowing down the change of bus voltage and improving the dynamic response of bus voltage, so as to ensure the power quality of DC microgrid system.In addition, the virtual inertia parameters used in most virtual inertia controls remain fixed, resulting in insufficient control flexibility and affecting the dynamic response of bus voltage. SUMMARY

[0004] The present application aims to provide a kind of energy storage DAB converter adaptive virtual inertia control method and device, to realize the steady-state voltage of DC microgrid without difference control, and inhibit the bus voltage fluctuation when load mutation, improve the dynamic response of DC bus.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0006] The first aspect of the present application provides a kind of energy storage DAB converter adaptive virtual inertia control method, comprising the following steps:

[0007] S1, collect DC microgrid bus voltage u dc , calculate the voltage no difference adjustment compensation item Δu of energy storage DAB converter, to steady-state compensation for droop link in virtual inertia control;

[0008] S2, sample DC bus voltage change rate And combine DC bus voltage fluctuation value Δu dc , to input function adaptive adjustment virtual capacitance parameter C v In virtual inertia control;

[0009] S3, sampling the input voltage U of the energy storage DAB converter i , and superimposing a low-pass filter to calculate the current feedforward compensation term G iff , which is superimposed to the current inner loop of the virtual inertia control, so as to improve the initial voltage mutation;

[0010] S4, the adaptive virtual inertia control method first obtains the output reference current value i set by the voltage-current droop, then outputs the reference voltage value u dcref by the virtual synchronous generator-like control link, and finally generates a PWM modulation signal through the voltage-current double closed loop to drive the converter switch tube to act.

[0011] Further, the voltage zero-error regulation compensation term Δu of step S1 is determined by the following formula:

[0012] Δu=G vc (u n -u dc )

[0013]

[0014] Wherein, u n represents the rated voltage 400V, G vc represents the compensation coefficient, k vcp represents the compensation proportional coefficient, k vci represents the compensation integral coefficient, and s represents the Laplace operator.

[0015] Further, in step S2, the virtual capacitor adaptive function can be represented by the following formula:

[0016]

[0017] Wherein u t represents the fluctuation threshold of the bus voltage, k c1 and k c2 are adjustment coefficients, C v0 is the initial virtual capacitor coefficient of the system, and the theoretical adjustment range of C v is [C v0 -k c2 , C v0 +k c1 ].

[0018] Further, in step S3, the current feedforward compensation term G iff can be represented as:

[0019]

[0020] Wherein, T and T2 are the time constants of the two loop low-pass filters constructed to cause voltage mutation; G iodA small signal transfer function representing the transformer output current and the phase shift ratio, G i A current inner loop PI controller, G iod A current inner loop PI controller, G i Can be represented by the following formula:

[0021]

[0022] Where n represents the turns ratio of the transformer primary and secondary, U i represents the input voltage, D1 represents the phase shift ratio, f represents the switching frequency, L represents the auxiliary inductance value, k ip represents the current inner loop proportional coefficient, k ii represents the current inner loop integral coefficient.

[0023] Further, in step S4, the expression of the virtual inertia control virtual synchronous machine control link is as follows:

[0024]

[0025] Where u dcref is the virtual synchronous machine control output voltage reference value; i dc is the output current, i d is the damping current; considering the voltage-current droop characteristics of the DC microgrid and the linear characteristics of the damping current-voltage, it can be represented as:

[0026]

[0027] Where u n represents the bus rated voltage, kd is the damping coefficient, k droop is the droop coefficient, the voltage zero difference regulation compensation term Δu is introduced, and the expression of the virtual synchronous machine control is as follows:

[0028]

[0029] Further, in step S4, the voltage and current double closed loop specific implementation process includes: the virtual synchronous machine link output voltage reference u dcref is subtracted from the actual sampling bus voltage value u dc , to obtain the voltage error, and then through the voltage outer loop PI controller, the current inner loop current reference i dcref is obtained after limiting. k vp is the proportional coefficient of the PI controller, k vi is the integral coefficient of the PI controller; similarly, the current inner loop reference i dcref is obtained after limiting after passing through the current inner loop PI controller.

[0030] The second aspect of the present application provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor implements the method described above when executing the computer program.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] The present application aims at the problem of bus voltage fluctuation caused by low inertia of a direct current micro-grid system, and proposes a virtual synchronous machine-like control method based on current feedforward and voltage compensation for an energy storage unit in a direct current charging station. In view of the problem of voltage mutation of the traditional virtual synchronous machine-like control when the system power is unbalanced, a low-pass form of current feedforward is proposed to improve the voltage mutation and improve the dynamic response capability of the energy storage unit. Meanwhile, in view of the problem of steady-state error of bus voltage of the virtual synchronous machine-like control, the droop link is improved, and a voltage compensation link is added to reduce the steady-state error of bus voltage. Finally, the virtual capacitor parameters are adaptively adjusted to adapt to different fluctuation conditions of the direct current bus voltage, and the control flexibility is enhanced. Through the research and improvement of the virtual quantity control method of the energy storage DAB converter, the inertia level of the energy storage unit is further improved, and the bus voltage support capability is enhanced. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The figure is a structure diagram of a direct current micro-grid system comprising a direct current charging station according to an embodiment of the present application;

[0034] Figure 2 The figure is a control system block diagram of an energy storage DAB converter according to an embodiment of the present application;

[0035] Figure 3 The figure is a comparison diagram of a traditional virtual synchronous machine-like control and a waveform of the present application, wherein, Figure 3 (a) is a comparison diagram of voltage simulation waveforms of the control system respectively adopting a traditional virtual synchronous machine-like control and the control system of the present application under frequent fluctuation of load power, Figure 3 (b) is a comparison diagram of power simulation waveforms of the control system respectively adopting a traditional virtual synchronous machine-like control and the control system of the present application under frequent fluctuation of load power;

[0036] Figure 4 The figure is a schematic diagram of experimental waveforms of the control method according to an embodiment of the present application, wherein Figure 4 (a) is a schematic diagram of experimental waveforms of system voltage when the control method according to an embodiment of the present application is adopted; Figure 4 (b) is a schematic diagram of experimental waveforms of power when the control method according to an embodiment of the present application is adopted. DETAILED DESCRIPTION

[0037] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments and drawings. Herein, the illustrative embodiments of the present application and their descriptions are used to explain the present application but not as a limitation of the present application.

[0038] It should also be noted that, in order not to obscure the present application due to unnecessary details, only the structures and / or processing steps closely related to the solutions according to the present application are shown in the drawings, and other details not closely related to the present application are omitted.

[0039] It should be emphasized that the term "comprises / comprising" as used herein is used to indicate the presence of a feature, element or step, but not the exclusion of one or more other features, elements or steps.

[0040] It should be emphasized here that the step labels mentioned below are not a limitation of the order of the steps, but it should be understood that the steps can be performed in the order mentioned in the embodiments, or in an order different from the embodiments, or several steps are performed simultaneously.

[0041] The specific implementation process is as follows:

[0042] Reference Figure 1 The embodiment includes a DC micro-grid system structure of a DC charging station, which comprises a new energy unit (including a wind power generation unit and a photovoltaic power generation unit, etc.), an AC / DC load, a grid-connected converter and a DC charging station. Each unit is connected to a DC bus through a power electronic converter.

[0043] Reference Figure 2 The embodiment is a kind of energy storage DAB converter adaptive virtual inertia control system block diagram, based on traditional virtual synchronous machine control loop, current feedforward compensation link is added in current inner loop, voltage zero error regulation compensation item link is added in droop link, and C v Parameter is adjusted adaptively based on bus voltage change rate and fluctuation value, so as to respectively improve the initial voltage mutation of AVSG control, eliminate bus voltage steady-state error and improve voltage dynamic response.

[0044] The adaptive virtual inertia control method of the energy storage DAB converter of the present application is as follows:

[0045] S1, the DC micro-grid bus voltage u dc is collected, and the voltage zero error regulation compensation term Δu of the energy storage DAB converter is calculated, so as to compensate the droop link in the virtual inertia control. The voltage zero error regulation compensation term Δu is determined by the following formula:

[0046] Δu=G vc (u n -udc )

[0047]

[0048] Among them, u n Indicates a rated voltage of 400V, G vc k represents the compensation coefficient. vcp k represents the compensation ratio coefficient. vci Let represent the compensation integral coefficient, and s represent the Laplace operator.

[0049] S2, Rate of change of DC bus voltage And combined with the DC bus voltage fluctuation value Δu dc Using this as input, the constructor adaptively adjusts the virtual capacitor parameter C in the virtual inertia control. v The virtual capacitance adaptive function can be expressed by the following equation:

[0050]

[0051] Where u t k represents the fluctuation threshold of the bus voltage. c1 and k c2 To adjust the coefficient, C v0 C represents the initial virtual capacitance coefficient of the system. v The theoretical adjustment range is [C v0 -k c2 C v0 +k c1 ].

[0052] S3, Input voltage U of the sampling energy storage DAB converter i The current feedforward compensation term G is calculated by superimposing a low-pass filter. iff This is superimposed on the inner current loop of the virtual inertia control to mitigate initial voltage spikes. Current feedforward compensation term G iff It can be represented as:

[0053]

[0054] Where T and T2 are the time constants of the two loop low-pass filters that cause voltage jumps, respectively; G iod G represents the small-signal transfer function of the converter output current compared to the shift. i This indicates a current inner-loop PI controller. G iod With G i It can be expressed by the following formula:

[0055]

[0056] Where n represents the turns ratio of the primary and secondary sides of the transformer, U irepresents input voltage, D1 represents phase-shift ratio, f represents switching frequency, L represents auxiliary inductance value, k ip represents current inner loop proportional coefficient, k ii represents current inner loop integral coefficient.

[0057] S4, the adaptive virtual inertia control method first obtains output current reference i set through voltage-current droop, and then outputs reference voltage value u dcref through the virtual synchronous generator control link. The expression of the virtual synchronous generator control link in the virtual inertia control is as follows:

[0058]

[0059] wherein, u dcref is the output voltage reference value of the virtual synchronous generator control; i dc is output current, i d is damping current; considering the voltage-current droop characteristics and the damping current-voltage linear characteristics of the DC microgrid, it can be expressed as:

[0060]

[0061] wherein, u n represents bus rated voltage, k d is damping coefficient, k droop is droop coefficient. The expression of the virtual synchronous generator control is as follows by introducing voltage zero-error regulation compensation term Δu:

[0062]

[0063] S5, the output reference voltage value u dcref of the virtual synchronous generator link is subtracted from the actual sampling bus voltage value u dc , to obtain voltage error, and then through the voltage outer loop PI controller, after limiting, the current inner loop current reference i dcref is obtained. k vp is the proportional coefficient of the PI controller, k vi is the integral coefficient of the PI controller; similarly, the current inner loop reference i dcref is obtained through the current inner loop PI controller, and then through limiting, the turn-on and turn-off of the single-phase shift control phase-shift ratio control switching tubes S1-S8 can be obtained.

[0064] Table 1 simulation data of example 1

[0065]

[0066] Figure 3 (a) and Figure 3(b) are respectively the system voltage and power simulation comparison waveforms when the traditional virtual synchronous generator control and the control method of the embodiment of the present application are respectively used under frequent fluctuations of load power. Figure 3 (a) shows that when the traditional virtual synchronous generator control algorithm is used, the system voltage cannot return to the rated value after suffering load disturbance, there is a steady-state error in the voltage, and the voltage fluctuation amplitude is large, while the control algorithm of the embodiment of the present application eliminates the steady-state error of the bus voltage, and the voltage fluctuation amplitude is small. Figure 3 (b) shows that when suffering load disturbance, the control power response speed of the embodiment of the present application is fast, which can effectively and quickly support the bus voltage.

[0067] Figure 4 (a) and Figure 4 (b) are respectively the system voltage and power experimental waveforms when the control method of the embodiment of the present application is used under load removal and load sudden increase. Figure 4 (a) shows that when the control method of the embodiment of the present application is used, the bus voltage of the system can be smoothly restored to the rated value after suffering load disturbance, and the bus voltage fluctuation amplitude is small.

[0068] Those of ordinary skill in the art should understand that the exemplary components, systems and methods described in conjunction with the embodiments disclosed herein can be implemented in hardware, software, or a combination of both. Whether the implementation is in hardware or software depends on the specific application and design constraints imposed on the overall system. Skilled artisans can use various methods to implement the described functions in each specific application, but such implementation should not be considered to be beyond the scope of the present application. When implemented in hardware, it can be, for example, an electronic circuit, an application specific integrated circuit (ASIC), appropriate firmware, a plug-in, a functional card, etc. When implemented in software, the elements of the present application are program or code segments used to perform the required tasks. The program or code segments can be stored in a machine-readable medium or transmitted through a data signal carried in a carrier wave in a transmission medium or communication link.

[0069] It should be noted that the present application is not limited to the specific configurations and processes described above and shown in the drawings. For the sake of brevity, detailed descriptions of well-known methods are omitted. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present application is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between steps, after understanding the spirit of the present application.

[0070] Features described and / or illustrated with respect to one implementation can be used in the same manner or in a similar manner in one or more other implementations and / or in combination with or in place of features of other implementations.

[0071] The above descriptions are only the preferred embodiment of the application, not intended to limit the application. The application can be variously changed and modified by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall fall within the protection scope of the application.

Claims

1. A method for adaptive virtual inertia control of an energy storage DAB converter, characterized in that, The method comprises the following steps: S1, collect DC microgrid bus voltage u dc , calculate the voltage zero-error regulation compensation term Δu of the energy storage DAB converter, so as to perform steady-state compensation on the droop link in the virtual inertia control; S2, sampling the direct current bus voltage rate of change And combined with the direct current bus voltage fluctuation value Δu dc , the constructor is constructed with this as input to adaptively adjust the virtual capacitance parameter C in virtual inertia control v ; S3, sampling the input voltage U of the energy storage DAB converter i and superimposing a low-pass filter to calculate a current feedforward compensation term G iff superimposed to the current inner loop of the virtual inertia control, so as to improve the initial voltage mutation; S4, the adaptive virtual inertia control method first obtains the output reference current value i through the voltage-current droop set , then outputs the reference voltage value u through the virtual synchronous generator control link dcref , and finally generates a PWM modulation signal through a voltage-current double closed loop to drive the operation of the converter switch tube.

2. The adaptive virtual inertia control method of an energy storage DAB converter according to claim 1, characterized in that, The voltage zero-error compensation term Δu of step S1 is determined by the following formula: Δu = G vc (u n -u dc ) where u n represents a rated voltage 400 V, G vc represents a compensation coefficient, k vcp represents a compensation proportional coefficient, k vci represents a compensation integral coefficient, s represents a Laplace operator.

3. The adaptive virtual inertia control method of an energy storage DAB converter according to claim 1, wherein, In step S2, the virtual capacitance adaptive function can be expressed by the following formula: Among them, u t k represents the fluctuation threshold of the bus voltage. c1 and k c2 To adjust the coefficient, C v0 C represents the initial virtual capacitance coefficient of the system. v The theoretical adjustment range is [C v0 -k c2 C v0 +k c1 ].

4. The adaptive virtual inertia control method of an energy storage DAB converter according to claim 1, wherein, In step S3, the current feedforward compensation term G iff may be expressed as: where T and T2 are time constants of the two loop low pass filters configured to create a voltage step; G iod G represents a small signal transfer function of the converter output current versus the phase shift, i G represents a current inner loop PI controller, iod G represents a voltage outer loop PI controller, i G can be represented by the following equation: Wherein, n represents the transformer primary and secondary winding ratio, U i represents the input voltage, D1 represents the phase shift ratio, f represents the switching frequency, L represents the auxiliary inductance value, k ip represents the current inner loop proportional coefficient, k ii represents the current inner loop integral coefficient.

5. The adaptive virtual inertia control method of an energy storage DAB converter according to claim 1, wherein, In step S4, the expression of the virtual inertia control virtual synchronous machine control link is as follows: wherein u dcref is a virtual synchronous machine-like control output voltage reference value; i dc is an output current, i d is a damping current; considering the voltage-current droop characteristic and the damping current-voltage linear characteristic of the DC microgrid, it can be expressed as: wherein u n represents the bus voltage rating, k d is a damping coefficient, k droop is a droop coefficient, the expression of the voltage-difference-free regulation compensation term Δu is as follows:

6. The adaptive virtual inertia control method of an energy storage DAB converter according to claim 1, wherein, In step S4, the specific implementation process of the voltage and current double closed loop includes: the virtual synchronous machine-like link outputs a voltage reference u dcref Subtracting the actual sampling bus voltage value u dc , to obtain a voltage error, and then outputting a current inner loop current reference i dcref , k vp is the proportional coefficient of the PI controller, k vi is the integral coefficient of the PI controller; similarly, the current inner loop reference i dcref After passing through the current inner loop PI controller, a single-phase-shift control phase shift ratio is obtained after limiting. 7.An electronic device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein, The processor implements the method of any one of claims 1 to 6 when executing the computer program.

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