Virtual inertia control method for reverse power supply of optical storage charging station matched with electric vehicle

Abstract

The invention discloses a virtual inertia control method for reverse power supply of an optical storage and charging integrated power station in cooperation with an electric vehicle, and the method comprises the steps: firstly calculating the virtual capacitance of an energy storage system and photovoltaic power generation in the optical storage and charging integrated power station, thereby determining the virtual inertia in a DC distribution network; carrying out additional flexible PV-SOC virtual inertia control on the DC power distribution network according to the monitored power vacancy of the DC power distribution network to obtain a U-I droop control strategy of the additional flexible PV-SOC virtual inertia control, and forwarding the U-I droop control strategy to a DC / DC converter; then a constant-voltage double-closed-loop control system is built when the electric vehicle is connected, reverse power supply is conducted on the direct-current power distribution network through a DC / DC converter, the functions of enhancing system inertia and stabilizing bus voltage fluctuation are achieved, and stable operation of the system is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid safety and stability control, and more specifically, relates to a virtual inertia control method for a photovoltaic storage and charging integrated power station in conjunction with reverse power supply of an electric vehicle. Background Art

[0002] With the massive increase in DC sources and loads such as distributed energy, energy storage, and electric vehicles, the traditional AC power grid is increasingly unable to absorb large-scale distributed energy, and the DC distribution network has become an important development direction for future urban distribution networks. However, the proportion of new energy generation and electronic equipment in the DC distribution network is high, and the system's capacitive inertia is much smaller than the mechanical inertia of the synchronous generator in the AC distribution network. The DC bus voltage is easily affected by power fluctuations and fluctuates violently, which seriously affects the power quality of the system.

[0003] At present, the DC distribution network mainly uses droop control to coordinate multi-terminal converters to jointly control the bus voltage and distribute power according to the predetermined droop coefficient. It is not flexible enough to face special working conditions such as power mutation. It is difficult to effectively smooth the bus voltage fluctuations with inherent DC capacitors alone. The introduction of virtual inertia control can better improve the voltage quality of the system. Although the current mainstream virtual inertia control method has smoothed the voltage fluctuations to a certain extent and improved the stability of the DC distribution network system, it still has a series of shortcomings such as complex control methods and long transient response time.

[0004] The integrated photovoltaic power station consists of photovoltaic devices, energy storage devices and electric vehicle charging facilities. It can use energy storage to improve the absorption rate of photovoltaic power generation and smooth the power impact caused by the randomness of electric vehicle charging, thereby effectively improving the comprehensive utilization efficiency of energy. It is an important component of the future DC distribution network. When the DC distribution network suffers power shocks and the bus voltage fluctuates violently, the charging station can use photovoltaic storage devices and electric vehicles to transmit power to the distribution network to improve the power supply capacity of the system. At present, there is little research on the support of photovoltaic integrated power station and electric vehicle reverse power supply for the voltage stability of the DC distribution network. If a virtual inertia control method for photovoltaic integrated power station with electric vehicle reverse power supply can be designed, it will be able to further enhance the system inertia and smooth the bus voltage fluctuations. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a virtual inertia control method for a photovoltaic storage and charging integrated power station in conjunction with reverse power supply of an electric vehicle. By detecting changes in bus voltage, the DC / DC converter can be flexibly controlled to reversely supply power to the DC distribution network.

[0006] To achieve the above-mentioned purpose of the invention, the present invention provides a virtual inertia control method for a photovoltaic storage and charging integrated power station in cooperation with an electric vehicle for reverse power supply, characterized in that it comprises the following steps:

[0007] (1) Calculate the virtual capacitance C of the energy storage system in the integrated photovoltaic power station vb ;

[0008] (2) Calculate the virtual capacitance C of photovoltaic power generation in the integrated photovoltaic storage and charging power station vpv ;

[0009] (3) Real-time monitoring of the bus voltage u of the DC distribution network dc , when the bus voltage u dc Calculate the power shortage ΔP of the DC distribution network when a drop occurs;

[0010] (4) Perform additional flexible PV-SOC virtual inertia control on the DC distribution network according to the power deficit ΔP, obtain the UI droop control strategy of the additional flexible PV-SOC virtual inertia control and forward it to the DC / DC converter;

[0011] (5) Build a constant pressure dual closed-loop control system when connected to an electric vehicle;

[0012] (6) Introducing virtual inertia G′ into the constant pressure double closed-loop control system vir (s), and then sent to the DC / DC converter;

[0013] (7) Based on the UI droop control strategy, the electric vehicle supplies reverse power to the DC distribution network through the DC / DC converter under a constant voltage dual closed-loop control system.

[0014] The object of the invention of the present invention is achieved in this way:

[0015] The present invention discloses a virtual inertia control method for a photovoltaic-storage-charging integrated power station in cooperation with reverse power supply of an electric vehicle. The method comprises the following steps: firstly, the virtual capacitance of an energy storage system and photovoltaic power generation in the photovoltaic-storage-charging integrated power station is calculated, so as to determine the virtual inertia in a DC distribution network; then, the DC distribution network is additionally subjected to flexible PV-SOC virtual inertia control according to the power shortage of the DC distribution network obtained by monitoring, so as to obtain a UI droop control strategy for the additional flexible PV-SOC virtual inertia control and forward it to a DC / DC converter; then, a constant-voltage dual closed-loop control system is constructed when the electric vehicle is connected, and reverse power is supplied to the DC distribution network through a DC / DC converter, so as to enhance the system inertia and smooth the bus voltage fluctuation, thereby realizing the stable operation of the system.

[0016] At the same time, the virtual inertia control method of the photovoltaic storage and charging integrated power station in cooperation with the reverse power supply of the electric vehicle of the present invention also has the following beneficial effects:

[0017] (1) Energy storage can be used to increase the absorption rate of photovoltaic power generation and mitigate the power impact caused by the randomness of electric vehicle charging, thereby effectively improving the comprehensive utilization efficiency of energy;

[0018] (2) The coordinated control between the energy storage power supply at the charging station and the reverse charging of electric vehicles can automatically stabilize the bus voltage of the distribution network and improve the power quality of the system;

[0019] (3) Electric vehicles are used to reverse charge the DC distribution network, thereby providing virtual inertia to the DC distribution network and improving the voltage stability of the DC distribution network. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of a virtual inertia control method of a photovoltaic storage and charging integrated power station in cooperation with an electric vehicle for reverse power supply;

[0021] Figure 2 is a schematic diagram of the DC distribution network system structure;

[0022] Figure 3 It is the virtual inertia analysis diagram of DC distribution network;

[0023] Figure 4 It is an additional flexible PV-SOC virtual inertia control diagram;

[0024] Figure 5 This is the structure diagram of the electric vehicle access to the DC distribution network system;

[0025] Figure 6 It is a block diagram of the constant pressure control structure including virtual inertia;

[0026] Figure 7 It is the load impact diagram under the additional flexible PV-SOC virtual inertia control;

[0027] Figure 8 It is the load impact diagram under the control of the virtual inertia of electric vehicles; DETAILED DESCRIPTION

[0028] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0029] Example

[0030] In this embodiment, Figure 2This is a schematic diagram of the DC distribution network system structure. When the system is operating normally, the photovoltaic power generation system of the power station directly charges the energy storage system, and the energy storage system supplies power to electric vehicles while reserving a certain amount of energy. When the system is underpowered, the photovoltaic storage device is connected to the DC distribution network to provide energy to the grid in reverse. When the system continues to have a power shortage, V2G technology is used to connect electric vehicles to the grid to alleviate the severe drop in bus voltage caused by the system power shortage.

[0031] Next, we will describe in detail a virtual inertia control method of a photovoltaic storage and charging integrated power station in cooperation with an electric vehicle for reverse power supply. Figure 1 As shown, the following steps are included:

[0032] like Figure 3 As shown in Figure 2, the virtual inertia in the DC distribution network includes the virtual capacitor C of the energy storage system. vb and the virtual capacitor C of photovoltaic power generation vpv , the specific calculation process is as follows:

[0033] (1) Calculate the virtual capacitance C of the energy storage system in the integrated photovoltaic power station vb ;

[0034] (1.1) Calculate the total capacitance energy W of the DC distribution network e :

[0035]

[0036] Where, C is the bus capacitance of the DC distribution network;

[0037] (1.2) Calculate the state of charge Soc of the battery in the energy storage system:

[0038]

[0039] Among them, Q r is the remaining capacity of the battery, Q N is the rated capacity of the battery;

[0040] (1.3) Calculate the initial state of charge of the battery as Soc0:

[0041]

[0042] Among them, Q r0 is the initial remaining capacity of the battery;

[0043] (1.4) Calculate the initial battery energy W of the battery b0 :

[0044] W b0 =Q r0 Ubat =Soc0Q N U bat

[0045] Among them, U bat is the output voltage of the battery;

[0046] (1.5) Calculate the change in the battery's state of charge δ Soc :

[0047]

[0048] ∫i b (t)dt=Q N δ Soc =∫Q N d(δ Soc )

[0049] Among them, i b is the current size during the constant voltage discharge process of the battery;

[0050] (1.6) Calculate the change in battery charge and discharge energy ΔW b :

[0051] ΔW b =∫U bat i b (t)dt

[0052] Replace ∫i in step (1.5) b Substituting (t)dt into the above formula, we can get:

[0053] ΔW b =∫U bat Q N d(δ Soc )

[0054] (1.7) Let the battery charge and discharge energy change equal to the DC distribution network energy change, and then calculate the virtual capacitance C of the energy storage system vb :

[0055]

[0056] Among them, K vb It is the ratio of the SOC change rate to the DC bus voltage change rate, specifically:

[0057]

[0058] Among them, Δu dc is the DC bus voltage change;

[0059] (2) Calculate the virtual capacitance C of photovoltaic power generation in the integrated photovoltaic storage and charging power station vpv;

[0060] (2.1) Based on the charging and discharging equation of the capacitor, the additional inertia current provided by the virtual capacitor is expressed as:

[0061]

[0062] Among them, u dcref is the reference value of bus voltage, i out is the output current of the DC / DC converter, i dc is the bus current of the DC distribution network;

[0063] (2.2), virtual capacitor C vpv for:

[0064]

[0065] Among them, K vpv is the compensation coefficient of the virtual capacitor.

[0066] When the DC bus voltage fluctuates, the virtual capacitor C vpv Compensation is performed flexibly according to the voltage drop speed.

[0067] (3) Real-time monitoring of the bus voltage u of the DC distribution network dc , when the bus voltage u dc Calculate the power shortage ΔP of the DC distribution network when a drop occurs;

[0068] ΔP=ΔP1+ΔP2

[0069]

[0070] Among them, ΔP is the grid access power provided by photovoltaic power generation to the DC distribution network, and ΔP2 is the grid access power provided by the energy storage system to the DC distribution network.

[0071] In this embodiment, the photovoltaic ΔP1 is directly connected to the DC grid and the energy storage system ΔP2 feeds back energy to the grid to supplement the power shortage ΔP of the grid.

[0072] (4) According to the power shortage ΔP, the DC distribution network is additionally subjected to flexible PV-SOC virtual inertia control, and the UI droop control strategy of additional flexible PV-SOC virtual inertia control is obtained:

[0073]

[0074] Among them, i dcref is the bus current reference value, u dc_N is the bus voltage rating, T is the time constant, s is the Laplace complex variable, and D is the duty cycle.

[0075] The UI droop control strategy is forwarded to the DC / DC converter;

[0076] According to the above virtual inertia control method, the above Figure 4 The additional flexible PV-SOC virtual inertia control block diagram shown in Figure 4 It can be seen that the DC / DC converter adopts voltage-current dual-loop control, which can make the actual value track the reference value and eliminate the steady-state error; among them, G v is the transfer function of voltage PI control, G i is the transfer function of current PI control, and its expressions are:

[0077]

[0078] in, is the proportional control coefficient, is the integral control coefficient;

[0079] (5) Build a constant pressure dual closed-loop control system when connected to an electric vehicle, such as Figure 5 As shown;

[0080] (5.1) Electric vehicles use a constant voltage discharge method. It is assumed that the output voltage of the electric vehicle remains unchanged. Therefore, the input voltage u of the DC / DC converter is measured. 01 , measure the electric vehicle constant voltage output voltage u ev1 , measuring the transmission line resistance R1 and inductance L1 of the electric vehicle, the input current i of the DC / DC converter can be calculated 01 :

[0081]

[0082] Where s is the Laplace complex variable;

[0083] (5.2) Calculate the power P1=u input from the electric vehicle to the DC distribution network 01 i 01 ;

[0084] (5.3) Build a constant pressure dual closed-loop control system when connected to electric vehicles:

[0085]

[0086] Among them, G′ v (s) is the PI control function of the voltage outer loop, k' pv , k′ iv are the proportional control coefficient and integral control coefficient of the voltage outer loop control respectively; G′ i (s) is the PI control function of the current inner loop, k' pi , k′ii They are the proportional control coefficient and the integral control coefficient of the current inner loop control respectively;

[0087] (6) Introducing virtual inertia G′ into the constant pressure double closed-loop control system vir (s), and then sent to the DC / DC converter to obtain Figure 6 The constant pressure control structure with virtual inertia shown;

[0088] Among them, the virtual inertia G′ vir (s) is expressed as:

[0089]

[0090] Where T' is the inertia time constant and K' is the virtual inertia coefficient; the system inertia is increased by changing K'.

[0091] In this embodiment, after the constant pressure double closed-loop control system introduces virtual inertia, the unit step response curve of the constant pressure control system is as follows: Figure 7 As shown in Figure 2, when K' is in the range of 0.4-0.8, the DC distribution network system containing electric vehicles can operate stably and provide virtual inertia for the system to ensure bus voltage stability.

[0092] (7) Based on the UI droop control strategy, the electric vehicle supplies reverse power to the DC distribution network through the DC / DC converter under a constant voltage dual closed-loop control system.

[0093] In this embodiment, Figure 8 is the load impact under the virtual inertia control of electric vehicles, Figure 8 It can be seen that after the sudden load increase at t=1s and t=2s, the speed and amplitude of the bus voltage drop are improved, and the system enhances the system stability under severe load shock.

[0094] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A virtual inertia control method for a photovoltaic storage and charging integrated power station in conjunction with reverse power supply of an electric vehicle, characterized in that: The following steps are involved: (1) Calculate the virtual capacitance C of the energy storage system in the integrated photovoltaic power station vb ; (2) Calculate the virtual capacitance C of photovoltaic power generation in the integrated photovoltaic storage and charging power station vpv ; (3) Real-time monitoring of the bus voltage u of the DC distribution network dc , when the bus voltage u dc Calculate the power shortage ΔP of the DC distribution network when a drop occurs; (4) Perform additional flexible PV-SOC virtual inertia control on the DC distribution network according to the power deficit ΔP, obtain the UI droop control strategy of the additional flexible PV-SOC virtual inertia control and forward it to the DC / DC converter; (5) Build a constant pressure dual closed-loop control system when connected to an electric vehicle; (6) Introducing virtual inertia G' into the constant pressure double closed-loop control system vir (s), and then sent to the DC / DC converter; (7) Based on the UI droop control strategy, the electric vehicle supplies reverse power to the DC distribution network through the DC / DC converter under a constant voltage dual closed-loop control system.

2. According to claim 1, a virtual inertia control method for a photovoltaic storage and charging integrated power station in cooperation with reverse power supply of an electric vehicle is characterized in that: The virtual capacitor C vb The calculation method is: (2.1) Calculate the total capacitance energy W of the DC distribution network e : Where, C is the bus capacitance of the DC distribution network; (2.2) Calculate the state of charge Soc of the battery in the energy storage system: Among them, Q r is the remaining capacity of the battery, Q N is the rated capacity of the battery; (2.3) Calculate the initial state of charge Soc0 of the battery as: Among them, Q r0 is the initial remaining capacity of the battery; (2.4) Calculate the initial battery energy W of the battery b0 : W b0 =Q r0 U bat =Soc0Q N U bat Among them, U bat is the output voltage of the battery; (2.5) Calculate the change in the battery's state of charge δ Soc : ∫i b (t)dt=Q N δ Soc =∫Q N d(δ Soc ) Among them, i b is the current size during the constant voltage discharge process of the battery; (2.6) Calculate the change in battery charge and discharge energy ΔW b : ΔW b =∫U bat i b (t)dt Substituting (2.5) into the equation, we can obtain: ΔW b =∫U bat Q N d(δ Soc ) (2.7) Let the battery charge and discharge energy change equal to the DC distribution network energy change, and then calculate the virtual capacitance C of the energy storage system vb : Among them, K vb It is the ratio of the SOC change rate to the DC bus voltage change rate, specifically: Among them, Δu dc is the DC bus voltage change.

3. According to claim 1, a virtual inertia control method for a photovoltaic storage and charging integrated power station in cooperation with reverse power supply of an electric vehicle is characterized in that: The virtual capacitor C vpv The calculation method is: Among them, K vpv is the compensation coefficient of the virtual capacitor.

4. According to claim 1, a virtual inertia control method for a photovoltaic storage and charging integrated power station in cooperation with reverse power supply of an electric vehicle is characterized in that: The calculation method of the power shortage ΔP of the DC distribution network is: ΔP=ΔP1+ΔP2 Among them, ΔP is the grid access power provided by photovoltaic power generation to the DC distribution network, and ΔP2 is the grid access power provided by the energy storage system to the DC distribution network.

5. According to claim 1, a virtual inertia control method for a photovoltaic storage and charging integrated power station in cooperation with reverse power supply of an electric vehicle is characterized in that: The UI droop control strategy of the additional flexible PV-SOC virtual inertia control is: Among them, i dcref is the bus current reference value, u dc_N is the bus voltage rating, T is the time constant, s is the Laplace complex variable, and D is the duty cycle.

6. According to claim 1, a virtual inertia control method for a photovoltaic storage and charging integrated power station in cooperation with reverse power supply of an electric vehicle is characterized in that: The constant pressure double closed-loop control system when connecting to the electric vehicle in step (5) is: (6.1) Measure the input voltage u of the DC / DC converter 01 , measure the electric vehicle constant voltage output voltage u ev1 , measure the transmission line resistance R1 and inductance L1 of the electric vehicle, and calculate the input current i of the DC / DC converter 01 : Where s is the Laplace complex variable; (6.2) Calculate the power P1=u input from the electric vehicle to the DC distribution network 01 i 01 ; (6.3) Build a constant pressure dual closed-loop control system when connected to an electric vehicle: Among them, G' v (s) is the PI control function of the voltage outer loop, k' pv , k' iv are the proportional control coefficient and integral control coefficient of the voltage outer loop control respectively; G i '(s) is the PI control function of the current inner loop, k' pi , k' ii They are respectively the proportional control coefficient and the integral control coefficient of the current inner loop control;.

7. According to claim 1, a virtual inertia control method for a photovoltaic storage and charging integrated power station in cooperation with reverse power supply of an electric vehicle is characterized in that: The virtual inertia G' introduced in the constant pressure double closed-loop control system vir (s) is: Where T' is the inertia time constant and K' is the virtual inertia coefficient; the system inertia is increased by changing K'.

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