Grid-connected control method of energy storage converter based on droop control

Abstract

The application discloses a grid-connected control method of an energy storage converter based on droop control. The method first obtains the grid voltage phase by using a phase-locked loop, and realizes grid connection of the converter through current control, then starts a droop control loop and gives the voltage and frequency as the voltage loop setting, and finally switches the phase-locked loop output electric angle to the frequency setting integrator output. The method does not need a pre-synchronization process, is suitable for single-converter grid-connected control or multi-converter grid-connected control, and can avoid problems such as control lag caused by breaker closing delay.

Description

Technical Field

[0001] This invention relates to the field of energy storage converter control technology, and in particular to a grid-connected control method for energy storage converters based on droop control. Background Technology

[0002] With economic development and social progress, energy demand is increasing daily. However, the intermittent and fluctuating nature of traditional fossil fuels, leading to grid connection and consumption difficulties, is becoming increasingly prominent, severely restricting the development of renewable energy power generation. This presents a significant opportunity for energy storage technology. Droop control, by simulating the power frequency characteristics of generator sets, enables distributed power sources to jointly maintain system frequency and voltage stability, achieving interconnection-free control of active and reactive power. It is suitable for peer-to-peer control modes in microgrids and can avoid the adverse effects on system performance that might result from a single main control unit failure.

[0003] Droop control is essentially voltage control. When a converter is connected to the grid or put into parallel operation, if its frequency, phase, or voltage amplitude is inconsistent with other systems or the main grid, forced parallel connection or grid connection will cause a large inrush current, leading to an accident. Therefore, droop control must first perform synchronization control before grid connection. When the grid voltage amplitude and phase are detected to reach the threshold, the closing operation is performed after pre-synchronization. This method requires that there be a filter capacitor on the AC side of the energy storage converter; otherwise, AC synchronization control cannot be completed. Secondly, after pre-synchronization is completed, the closing command is issued. Due to the certain delay in the actual circuit breaker closing, the pre-synchronization control cannot be accurately stopped, causing a control delay. Therefore, it is necessary to propose a reliable and effective grid connection control method to ensure that the energy storage converter can be connected to the grid quickly and without impact. Summary of the Invention

[0004] The purpose of this invention is to provide a grid-connected control method for energy storage converters based on droop control.

[0005] Therefore, the technical solution of the present invention is as follows:

[0006] A grid-connected control method for an energy storage converter based on droop control, including...

[0007] Collect grid voltage and current;

[0008] The phase-locked loop (PLL) control module is activated, using the grid voltage as the input to the PLL. The PLL then calculates the grid angle θ. g It is used to realize coordinate transformation and control of voltage and current;

[0009] Close the grid-side circuit breaker to connect the converter to the power grid;

[0010] The grid-side three-phase current i a i bi c Perform coordinate transformation to obtain the dq axis components i d and i q Set both dq axis currents to 0, and start the grid-side current controller to control the grid-side current.

[0011] After a period of delay, once the grid-connected operation has stabilized, the voltage loop will be given u. dref and u qref The actual voltage dq-axis components u are given respectively. d and u q This ensures that the voltage loop output is 0.

[0012] Start the droop controller and use its output voltage as the voltage loop setpoint. Using the phase before the switching moment as the initial phase, integrate the output frequency to obtain the control angle θ. c The grid connection of the energy storage converter was completed.

[0013] Furthermore, after the droop control is activated, the phase-locked loop outputs an angle θ. g As an initial phase, it serves as a phase reference for phase generation.

[0014] Furthermore, the droop control controls the active and reactive power output of the converter by adjusting the voltage frequency and amplitude, respectively. The droop control expression is as follows:

[0015]

[0016] In the formula, ω* and U* are the given values ​​of the inverter output angular frequency and voltage amplitude, P and Q are the actual active and reactive power output of the inverter, P0 and Q0 are the rated active and reactive power output of the inverter, ω0 and U0 are the rated angular frequency and voltage amplitude of the inverter, and k p and k q These are the active and reactive power droop coefficients, respectively.

[0017] Compared with existing technologies, this grid-connected control method for energy storage converters based on droop control can directly achieve grid connection of the converter without the need for a grid connection pre-synchronization process. This method is applicable to grid connection control of a single converter or multiple converters, and can avoid problems such as control lag caused by circuit breaker closing delay. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the energy storage converter topology.

[0019] Figure 2 The flowchart of the grid-connected control method for energy storage converters based on droop control provided by the present invention is shown.

[0020] Figure 3 The grid-connected control principle diagram provided for this invention.

[0021] Figure 4 This is a schematic diagram of a phase-locked loop (PLL) control principle.

[0022] Figure 5 This is a schematic diagram of the droop controller. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention.

[0024] Energy storage converter topology as follows Figure 1 As shown, the AC side circuit breaker is used to disconnect the energy storage converter from the power grid, and the controller collects the grid voltage and current to realize converter control.

[0025] This invention provides a grid-connected control method for energy storage converters based on droop control, the control flow of which is as follows: Figure 2 As shown, this includes the steps to get into character:

[0026] The controller collects grid voltage and current to achieve converter control;

[0027] First, start the phase-locked loop (PLL) control module. The PLL control principle is as follows: Figure 4 As shown, the grid voltage is used as the input to the phase-locked loop (PLL), and the grid angle θ is calculated through the PLL. g It is used to realize coordinate transformation and control of voltage and current;

[0028] Then close the grid-side circuit breaker to connect the converter to the power grid;

[0029] The grid angle θ is output via a phase-locked loop. g The grid-side three-phase current i a i b i c Perform coordinate transformation to obtain the dq axis components i d and i q Set both dq-axis current setpoints to 0, and start the grid-side current controller for grid-side current control, such as... Figure 3 As shown, the difference between the dq axis current setpoint and the feedback current is calculated, and then the error is passed through the PI controller to output the control voltage.

[0030] After a period of delay, once the grid-connected operation has stabilized, the voltage loop will be given u. dref and u qref The actual voltage dq-axis components u are given respectively. d and u q This ensures that the voltage loop output is 0.

[0031] Then activate the droop controller, as follows: Figure 3-5 As shown, Figure 3The selector switches are all set to "2", and their output voltage is used as the voltage loop reference. The phase before the switching is taken as the initial phase, and the phase-locked loop output angle θ is set. g As the initial phase reference, the control angle θ is obtained by integrating the output frequency. c The grid connection of the energy storage converter was completed.

Claims

1. A grid-connected control method for an energy storage converter based on droop control, characterized in that, include Collect grid voltage and current; The phase-locked loop (PLL) control module is activated, using the grid voltage as the input to the PLL. The PLL then calculates the grid angle θ. g It is used to realize coordinate transformation and control of voltage and current; Close the grid-side circuit breaker to connect the converter to the power grid; The grid-side three-phase current i a i b i c Perform coordinate transformation to obtain the dq axis components i d and i q Set both dq axis currents to 0, and start the grid-side current controller to control the grid-side current. After a period of delay, once the grid-connected operation has stabilized, the voltage loop will be given u. dref and u qref The actual voltage dq-axis components u are given respectively. d and u q This ensures that the voltage loop output is 0. Start the droop controller and use its output voltage as the voltage loop setpoint. Using the phase before the switching moment as the initial phase, integrate the output frequency to obtain the control angle θ. c The grid connection of the energy storage converter was completed.

2. The grid-connected control method for energy storage converters based on droop control according to claim 1, characterized in that, After the droop control is activated, the phase-locked loop will output angle θ. g As an initial phase, it serves as a phase reference for phase generation.

3. The grid-connected control method for energy storage converters based on droop control according to claim 2, characterized in that, The droop control regulates the active and reactive power output of the converter by adjusting the voltage frequency and amplitude, respectively. The droop control expression is: In the formula, ω* and U* are the given values ​​of the inverter output angular frequency and voltage amplitude, P and Q are the actual active and reactive power output of the inverter, P0 and Q0 are the rated active and reactive power output of the inverter, ω0 and U0 are the rated angular frequency and voltage amplitude of the inverter, and k p and k q These are the active and reactive power droop coefficients, respectively.

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