A photovoltaic energy storage cooperative network control method to suppress photovoltaic power fluctuations

Abstract

The present invention discloses a photovoltaic-storage collaborative networking control method for suppressing photovoltaic power fluctuations, including the following steps: S1, obtaining the current photovoltaic system output power, DC bus voltage and grid frequency data; S2, regularly measuring the real-time maximum available photovoltaic output power through the disturbance observation method, and controlling the photovoltaic reference voltage through the slope limit controller to suppress photovoltaic power fluctuations; thereby reducing the power fluctuation of the energy storage system; S3, adjusting the output of the energy storage system using voltage and current dual closed-loop control and DC bus voltage deviation feedforward control; S4, realizing control of the entire photovoltaic storage system based on the photovoltaic system, energy storage system and inverter networking control. The present invention adopts the above-mentioned photovoltaic-storage collaborative networking control method for suppressing photovoltaic power fluctuations, which solves the technical problems of large energy storage power fluctuations and slow response in the photovoltaic storage system energy storage in the prior art, ensures the energy storage operation efficiency and improves the reliability of the photovoltaic storage inverter.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic energy storage system collaborative networking control, and in particular to a photovoltaic energy storage collaborative networking control method for suppressing photovoltaic power fluctuations. Background Art

[0002] Renewable energy is gradually replacing traditional fossil energy, and the scale of new energy power generation in new power systems is rapidly expanding. The large-scale integration of new energy represented by photovoltaics has caused the power system to gradually shift from a system dominated by synchronous machines to a system dominated by power electronics. In order to cope with the problems such as low inertia caused by large-scale integration of photovoltaics and provide the necessary frequency support for the power grid, network control has been widely used due to its unique advantages.

[0003] In addition, photovoltaic systems are easily affected by environmental changes, and their output power has a large uncertainty. Therefore, a battery energy storage system (BESS) is usually used to suppress the power fluctuations of the photovoltaic system (PVS) and provide additional energy for frequency support. However, in this case, the fluctuations of photovoltaic power can be directly transmitted to the energy storage system through the DC bus, and the operating state of the photovoltaic system will directly affect the operating efficiency and life cycle of the energy storage system. On the one hand, the inherent characteristics of the photovoltaic system and its control will introduce power fluctuations in the system; on the other hand, disturbances in the system, such as changes in photovoltaic power or sudden changes in grid-side load, will cause the DC bus voltage to drop or even trigger protection, causing large fluctuations in the power in the system.

[0004] However, in the current research technology, the fluctuation of energy storage power in the photovoltaic and energy storage shared DC bus system has not been analyzed in essence. The existing photovoltaic and energy storage control technology has a poor effect on suppressing energy storage power fluctuations, which affects the operating efficiency of the energy storage system and endangers the service life of the battery. In addition, the energy storage system cannot respond quickly to grid disturbances and cannot maintain system power balance in time, resulting in reduced grid stability and even triggering protection to paralyze the photovoltaic and energy storage system.

[0005] In view of the above technical defects, a solution is now proposed. The present invention proposes a photovoltaic storage converter control method for suppressing energy storage power fluctuations, which can quickly respond to power grid disturbances while suppressing energy storage power fluctuations. This control method can not only ensure the operating efficiency of the energy storage system and extend the service life of the battery, but also respond to the power changes of the system in a timely manner and improve the stability of the power grid. Summary of the invention

[0006] The purpose of the present invention is to provide a photovoltaic energy storage cooperative network control method for suppressing photovoltaic power fluctuations.

[0007] To achieve the above object, the present invention provides a photovoltaic energy storage cooperative network control method for suppressing photovoltaic power fluctuations, comprising the following steps:

[0008] S1, obtaining the current photovoltaic system output power, DC bus voltage and energy storage battery current;

[0009] S2, regularly measuring the real-time maximum available photovoltaic output power through the perturbation observation method, and controlling the photovoltaic reference voltage through the slope limit controller to suppress photovoltaic power fluctuations; thereby reducing the power fluctuations of the energy storage system;

[0010] S3, using voltage and current double closed-loop control and DC bus voltage deviation feedforward control to adjust the output of the energy storage system and improve the response speed of the energy storage system;

[0011] S4: Control the entire photovoltaic storage system by building a network based on the photovoltaic system, energy storage system and inverter.

[0012] Preferably, in step S2,

[0013] S2.1, measure the voltage and current of the photovoltaic cell terminals and calculate the photovoltaic output power;

[0014] S2.2, calculate the increment of photovoltaic output power to photovoltaic voltage;

[0015] S2.3. Determine the increment of the photovoltaic output power to the voltage. If the increment of the photovoltaic output power to the photovoltaic output voltage is greater than 0, the current photovoltaic working point is on the left side of the maximum power point, and the photovoltaic cell working voltage needs to be increased; if the increment of the photovoltaic output power to the photovoltaic output voltage is less than 0, the current photovoltaic working point is on the right side of the maximum power, and the photovoltaic cell working voltage value should be reduced. When the increment of the photovoltaic output power to the photovoltaic output voltage is equal to 0, the photovoltaic maximum power point is reached;

[0016] S2.4. When changing the photovoltaic output voltage reference value, the slope limit controller is used to limit the rising rate of the photovoltaic output voltage, thereby reducing the fluctuation of the photovoltaic output power caused by the photovoltaic reference voltage step and the overshoot of the proportional-integral controller, thereby reducing the power fluctuation of the energy storage system.

[0017] Preferably, in step S3,

[0018] S3.1, use voltage and current double closed loop to control the energy storage system;

[0019] S3.2, the DC bus voltage deviation is obtained by subtracting the reference voltage from the measured DC bus voltage real-time voltage, and the normalized coefficient K d, get the feedforward duty cycle signal, add the feedforward duty cycle signal to the voltage and current dual closed-loop control output duty cycle signal of the energy storage system, control the energy storage system, and directly introduce the power fluctuations of the photovoltaic system and the energy storage system into the energy storage control using the DC bus voltage. It can respond to the power changes of the system in time and improve the stability of the operation of the entire photovoltaic storage grid-connected system.

[0020] Preferably, in step S4,

[0021] S4.1. The photovoltaic system adopts maximum power point tracking control (MPPT);

[0022] S4.2, the energy storage system adopts constant DC bus voltage control, and adjusts the DC bus voltage through voltage and current double closed-loop control and DC bus voltage deviation feedforward control;

[0023] S4.3. The control of the inverter adopts the virtual synchronous generator control technology (VSG) in the grid control. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flow chart of a photovoltaic-storage collaborative network control method for suppressing photovoltaic power fluctuations according to the present invention;

[0025] Figure 2 A photovoltaic system control block diagram of a photovoltaic storage cooperative network control method for suppressing photovoltaic power fluctuations according to the present invention, taking into account a slope limiting controller;

[0026] Figure 3 A DC bus voltage feedforward control diagram of an energy storage system of a photovoltaic-storage cooperative grid control method for suppressing photovoltaic power fluctuations according to the present invention;

[0027] Figure 4 An active control loop diagram of a photovoltaic-storage cooperative network control method for suppressing photovoltaic power fluctuations according to the present invention;

[0028] Figure 5 A reactive control loop diagram of a photovoltaic-storage cooperative network control method for suppressing photovoltaic power fluctuations according to the present invention;

[0029] Figure 6 This is a control scheme experimental result diagram of a photovoltaic energy storage collaborative network control method for suppressing photovoltaic power fluctuations of the present invention;

[0030] Figure 7 This is a diagram showing the experimental results of a control scheme of a photovoltaic-storage collaborative networking control method for suppressing photovoltaic power fluctuations according to the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0032] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0033] Embodiment 1

[0034] like Figure 1-7 As shown, the following steps are included:

[0035] In step 1, the current photovoltaic system output power, DC bus voltage and energy storage battery current are obtained;

[0036] In step 2, the real-time maximum available photovoltaic output power is measured regularly by the disturbance observation method, and the photovoltaic reference voltage is controlled by the slope limit controller to suppress the photovoltaic power fluctuation; thereby reducing the power fluctuation of the energy storage system; specifically, the following steps are included:

[0037] 2.1. Measure the voltage and current of the photovoltaic cell terminals and calculate the photovoltaic output power;

[0038] 2.2. Calculate the increment of photovoltaic power to photovoltaic voltage;

[0039] 2.3. Determine the increment of power to voltage. If the increment of power to voltage is greater than 0, the current photovoltaic working point is on the left side of the maximum power point, and the photovoltaic cell working voltage needs to be increased; if the increment of power to voltage is less than 0, the current photovoltaic working point is on the right side of the maximum power, and the photovoltaic cell working voltage value should be reduced. When the increment of power to voltage is equal to 0, the photovoltaic maximum power point is reached.

[0040] 2.4. When changing the reference value of the photovoltaic output voltage, the slope limit controller is used to limit the rising rate of the photovoltaic voltage, reducing the fluctuation of the photovoltaic output power caused by the photovoltaic reference voltage step and the overshoot of the proportional controller. This reduces the power fluctuation of the energy storage system, improves the operating efficiency of the energy storage system, and extends the service life of the energy storage system.

[0041] In step 3, the output of the energy storage system is adjusted by using the voltage-current dual closed-loop control and the DC bus voltage deviation feedforward control to improve the response speed of the energy storage system; specifically, the following steps are included:

[0042] 3.1. Use voltage and current double closed loop to control the energy storage system, as shown in the attached Figure 4 shown.

[0043] 3.2. The DC bus voltage deviation is obtained by subtracting the reference voltage from the measured DC bus voltage real-time voltage, and then normalized by the coefficient K. d, get the feedforward duty cycle signal, add the feedforward duty cycle signal to the energy storage voltage and current double closed-loop control output duty cycle signal, and control the energy storage system. Directly introducing the DC bus voltage into the energy storage control can respond to the power changes of the system in time and improve the stability of the power grid.

[0044] In step 4, the photovoltaic system, energy storage system and inverter are controlled accordingly to achieve the coordinated network control of the entire photovoltaic storage system. The control method adopted by photovoltaic, energy storage and inverter specifically includes the following steps:

[0045] 4.1. The photovoltaic system adopts maximum power point tracking control (MPPT), such as Figure 2 As shown. pv and i pv Respectively represent the voltage and current of the photovoltaic module. pvref It is the photovoltaic reference voltage generated by the photovoltaic maximum power tracking technology. PI represents the proportional integral controller and PWM is the modulation module.

[0046] 4.2. Energy storage uses constant DC bus voltage control, and adjusts the DC bus voltage through voltage and current double closed-loop control and DC bus voltage deviation feedforward control. The control box is as shown in the attached Figure 3 As shown, where v dcref and v dc Represent the reference value and actual value of the DC bus voltage respectively, i dc Indicates the actual value of the energy storage current.

[0047] 4.3. The control of the inverter adopts the virtual synchronous generator control technology (VSG) in the grid control, such as Figure 4 and Figure 5 As shown. The active power reference P ref and reactive power reference value Q set Given by the superior dispatcher. n and ω represent the rated angular frequency and actual angular frequency of the power grid respectively. p Represent the moment of inertia and damping coefficient respectively. θ is the grid voltage phase angle. In the reactive loop, V n and V o Respectively represent the rated phase voltage amplitude of the power grid and the actual output phase voltage amplitude of the power grid. q Represent the proportional coefficient and reactive droop coefficient respectively. Using virtual synchronous generator control as the grid control can improve the system inertia and damping characteristics. By simulating the main body model, active frequency regulation and reactive voltage regulation of the synchronous generator, the grid-connected inverter can be compared with the traditional synchronous generator in terms of operation mechanism and external characteristics. When the grid suffers from faults or interference, it can provide inertia support power to ensure the frequency stability of the grid.

[0048] The photovoltaic irradiation intensity is set to 1000W / m 2 , the ambient temperature is 25℃, and the state of charge of the battery in the energy storage system is set to 50%. The experimental results of the system using traditional photovoltaic energy storage control are as follows Figure 6 (a). When the photovoltaic reference voltage v pvref When a voltage disturbance occurs in each MPPT cycle, the PI controller will pv Quickly adjust to v pvref , resulting in PV voltage overshoot.

[0049] Therefore, the photovoltaic power P pv The output power fluctuates at the beginning of each MPPT cycle. In addition, since the photovoltaic system and the energy storage system are coupled together on the DC bus, the photovoltaic power fluctuation will flow directly into the energy storage system through the DC bus, resulting in energy storage power spikes. Figure 6 (b) It can be seen that after adopting the improved control proposed by the present invention, the fluctuation of photovoltaic power and energy storage power is effectively suppressed. The photovoltaic power fluctuation is reduced from 110W to less than 5W. Correspondingly, the energy storage power fluctuation is also significantly reduced. Figure 6 (c) is the steady-state waveform of the voltage and current output by the VSG controlled inverter, which proves that the virtual synchronous generator control is not affected by the proposed control.

[0050] See also Figure 7 As shown in the figure, in order to verify the control performance of the DC bus voltage feedforward control, at t = 1s, the irradiation intensity suddenly increases from 1000W / m 2 Reduced to 700W / m 2 It can be seen that the proposed feedforward control based on DC bus voltage can reduce the transient response time from 130ms to 100ms. At the same time, compared with the traditional control method, the DC bus voltage overshoot value is reduced from 6V to 2V.

[0051] Therefore, the present invention adopts the above-mentioned photovoltaic storage collaborative networking control method for suppressing photovoltaic power fluctuations. This control solves the technical problems of large energy storage power fluctuations and slow response in the photovoltaic storage system energy storage in the prior art; it solves the problem of low inertia of the power grid caused by large-scale photovoltaic integration, and can provide certain frequency support for the power grid; it solves the problems of short energy storage life and low efficiency caused by output power fluctuations, extends the service life of energy storage, reduces the risk of fault accidents, ensures the energy storage operation efficiency, and improves the reliability of the photovoltaic storage inverter.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A photovoltaic energy storage cooperative network control method for suppressing photovoltaic power fluctuations, characterized in that: The following steps are involved: S1, obtaining the current photovoltaic system output power, DC bus voltage and energy storage battery current; S2, regularly measuring the real-time maximum available photovoltaic output power through the perturbation observation method, and controlling the photovoltaic reference voltage through the slope limit controller to suppress photovoltaic power fluctuations; thereby reducing the power fluctuations of the energy storage system; S2.1, measure the voltage and current of the photovoltaic cell terminals and calculate the photovoltaic output power; S2.2, calculate the increment of photovoltaic output power to photovoltaic voltage; S2.

3. Determine the increment of the photovoltaic output power to the voltage. If the increment of the photovoltaic output power to the photovoltaic output voltage is greater than 0, the current photovoltaic working point is on the left side of the maximum power point, and the photovoltaic cell working voltage needs to be increased; if the increment of the photovoltaic output power to the photovoltaic output voltage is less than 0, the current photovoltaic working point is on the right side of the maximum power, and the photovoltaic cell working voltage value should be reduced. When the increment of the photovoltaic output power to the photovoltaic output voltage is equal to 0, the photovoltaic maximum power point is reached; S2.4, when changing the photovoltaic output voltage reference value, the slope limit controller is used to limit the rising rate of the photovoltaic output voltage, thereby reducing the fluctuation of the photovoltaic output power caused by the photovoltaic reference voltage step and the overshoot of the proportional integral controller, thereby reducing the power fluctuation of the energy storage system; S3, using voltage and current double closed-loop control and DC bus voltage deviation feedforward control to adjust the output of the energy storage system and improve the response speed of the energy storage system; In step S3, S3.1, use voltage and current double closed loop to control the energy storage system; S3.2, the DC bus voltage deviation is obtained by subtracting the reference voltage from the measured DC bus voltage real-time voltage, and the normalized coefficient K d , get the feedforward duty cycle signal, add the feedforward duty cycle signal to the voltage and current dual closed-loop control output duty cycle signal of the energy storage system, control the energy storage system, and directly introduce the power fluctuation of the photovoltaic system and the energy storage system into the energy storage control by using the DC bus voltage, so as to respond to the power change of the system in time and improve the stability of the operation of the entire photovoltaic storage grid-connected system; S4: Control the entire photovoltaic storage system by building a network based on the photovoltaic system, energy storage system and inverter.

2. A photovoltaic energy storage cooperative network control method for suppressing photovoltaic power fluctuations according to claim 1, characterized in that: In step S4, S4.

1. The photovoltaic system adopts maximum power point tracking control (MPPT); S4.2, the energy storage system adopts constant DC bus voltage control, and adjusts the DC bus voltage through voltage and current double closed-loop control and DC bus voltage deviation feedforward control; S4.

3. The control of the inverter adopts the virtual synchronous generator control technology (VSG) in the grid control.

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