CN110912173B - VSC direct-current power grid control method - Google Patents

Abstract

The invention relates to a control method of a VSC direct current power grid, which defines that a first-stage control is the control adopted by the outermost converter station in the VSC direct current power grid, defines that a second-stage control is the converter station connected with the first-stage converter station through a high-voltage direct current line, the alternating current side of the converter station in the second-stage control is connected with a weak alternating current power grid, the first-stage control uses direct current voltage control and adopts a feedforward double-closed loop decoupling control strategy to control, and the converter station in the second-stage control controls the flow direction of power and the balance of alternating current voltage through the feedforward decoupling control strategy and the phasing angle control. The control method can enable the weak alternating current system in the VSC direct current power grid to stably operate. The weak alternating current system applying the control strategy can stably connect a power feeding station and a power receiving station in the direct current system at the same time, and the alternating current system can carry a certain amount of alternating current load. The hierarchical control strategy provides a solution for multi-converter station control of a direct current power grid.

Description

A VSC DC power grid control method

Technical field

The invention belongs to the field of parallel operation of AC and DC systems, the field of power grid planning, and the field of power system simulation, and relates to a DC power grid, especially a DC power grid based on a voltage source converter station and a hybrid connection of AC and DC systems in the power grid.

Background technique

With the improvement of application technology of power electronic components, DC transmission and DC grid have become important supplements to AC grid. DC transmission has been operating successfully in China for many years, transporting excess power from the central and western regions to the eastern coastal areas. At the same time, UHV DC transmission is working together with UHV AC transmission to continuously transport wind power and solar power from the west and north to the load center in the east, making an important contribution to the country's energy conservation and emission reduction.

In urban distribution networks, due to limited space, most power transmission uses cables as media. In longer-distance AC cable transmission, DC transmission is more economical, and DC transmission takes up less space than AC transmission. The DC grid of voltage source converter (VSC) has great advantages in integrating wind energy and solar energy. It can smoothly connect wind energy and solar power generation and independently control active and reactive power. In view of this, the VSC-based DC grid can serve as an important part of the energy Internet.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a new VSC DC power grid control method, which can improve the control stability of the system in a DC power grid containing a lot of VSC, especially improve the direct current control method relying on VSC inverter. Stability of powered weak AC systems.

The technical solutions adopted by the present invention to solve the technical problems are:

A VSC DC power grid control method defines the first-level control as the control adopted by the outermost converter station in the VSC DC power grid, and defines the second-level control as the commutation connected to the first-level converter station through a high-voltage DC line. Station, the AC side of the converter station in the second-level control is connected to the weak AC power grid. The first-level control uses DC voltage control and adopts a feedforward double closed-loop decoupling control strategy for control. In the second-level control, the converter station The flow direction of power and the balance of AC voltage are controlled through feedforward decoupling control strategy and phase angle control.

Moreover, in the first level control, the DC voltage controls the input parameters to the inner loop through the outer loop PI control. The active and reactive parameters are decoupled in the inner loop to obtain the decoupled control signal. The matrix is calculated through dq->abc, The parameters in the rotating rectangular coordinate system are converted into coordinate parameters of the three-phase AC system. Through these parameters, the converter station outputs a given DC side voltage for DC voltage control.

Moreover, in the second level control, the active power input parameters to the inner loop control through the outer loop PI control, and the active and reactive parameters are decoupled in the inner loop to obtain the decoupled control signal, and the matrix is calculated through dq->abc, The parameters in the rotating rectangular coordinate system are converted into coordinate parameters of the three-phase AC system. Through these parameters, the converter station outputs a given active power for power control.

Moreover, in the fixed phase angle control, the converter station generates a three-phase AC control signal corresponding to the phase angle signal through the given phase angle and signal generating device. Through this signal, the converter station can output the given phase angle. voltage to control the phase angle of the weak AC power grid.

Moreover, in a DC power grid with a weak AC system, the shortest path connecting the converter station to the strong power grid is selected, and the converter is defined according to the number n of converter stations between a certain converter station and the AC strong power grid. The control level of the station is n+1 level control.

Moreover, the third-level converter station is connected to the second-level control converter station through the weak AC power grid.

The advantages and positive effects of the present invention are:

1. This control method can make the weak AC system in the VSC DC grid operate stably. The weak AC system applying this control strategy can stably connect the feeding power station and the power receiving station in the DC system at the same time, and the AC system can carry a certain amount of AC load. This hierarchical control strategy provides a solution for multi-converter station control of DC power grids.

2. This control method can stabilize the AC voltage of the weak AC system connected to the feed power station faster, reduce the stable equilibrium time of the system, and make the entire DC transmission network have better dynamic stability. The converter station that transmits electric energy to the weak AC grid is called a "feeding power station", and the converter station that absorbs electric energy from the weak AC grid is called a "power receiving station". For an AC weak grid in a DC grid, setting the control mode and control scheme of the converter station connected to the weak grid based on the distinction between the feeding power station and the power receiving station can increase the stability of the system.

3. Using this control method, when the power of the weak AC system in the DC grid increases, the power of the weak AC grid voltage control station can be reliably reversed, allowing the DC grid to provide more active power to the weak AC system. The DC grid can ensure reliable operation of the intermediate weak AC system when the power changes, and the balancing station can accurately and timely meet the power changes and stability requirements of the intermediate weak AC system.

Description of the drawings

Figure 1 is a control principle diagram of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and through specific examples. The following examples are only descriptive, not restrictive, and cannot be used to limit the scope of protection of the present invention.

A VSC DC power grid control method. The control system includes converter stations VSC1, VSC2, VSC3, VSC4, AC strong power grid, weak AC power grid, filters in the weak AC power grid, DC transmission lines, decoupling control strategies, and phase angles. control (fixed δ), active power control (P), AC voltage control (U _rms ) and upper-layer hierarchical control strategy. The AC power grid exchanges energy with the DC grid through converter stations VSC1 and VSC4. The DC grid contains a weak AC grid, which exchanges energy with the DC grid through VSC2 and VSC3. The converter station is controlled through the decoupling control strategy. The decoupling control strategy, active power control and phase angle control control the trigger pulses of the converter station, and the upper layer hierarchical control controls the amount of the decoupling control strategy.

Converter station VSC1 and converter station VSC4 are directly connected to the AC strong power grid, so VSC1 and VSC4 belong to the first level of control. VSC2 is connected to VSC1 through a DC cable. The other side of VSC2 is connected to the AC weak power grid, so VSC2 and The shortest path to connect the AC strong power grid is to connect to the strong power grid through VSC1, that is, the control level of VSC2 is the second level. Similarly, the control level of VSC3 is also the second level.

Power flows from VSC1 to VSC2, and then from VSC3 to VSC4. The weak grid load between VSC2 and VSC3 consumes a small part of the AC power, and at the same time, the AC weak grid inputs power to VSC3.

AC is an AC strong power grid. AC inputs AC power to the converter station VSC1. The converter station VSC1 performs switching control through the signal sent by the PWM signal generator. The trigger angle of the PWM signal generator comes from "dq->abc" Calculation matrix, dq parameters come from the improved feedforward decoupling control, the outer loop voltage PI control and the control signal taken from the AC AC grid are output to the improved feedforward decoupling control for calculation, the measured DC voltage value and the given The DC voltage value is compared and output to the PI controller of the outer loop voltage controller.

VSC1 converts AC AC power into DC power through the first stage of DC voltage control, and then transmits it to VSC2. VSC2 adopts constant active power control. The DC current is input to VSC2. The converter station VSC2 uses the signal sent by the PWM signal generator. For switching control, the trigger angle of the PWM signal generator comes from the calculation matrix of "dq->abc", the dq parameter comes from the improved feedforward decoupling control, the outer loop active PI control and the measurement signal taken from the AC AC power grid. It is output to the improved feedforward decoupling control for calculation, the measured active power value is compared with the given active power value, and then output to the PI controller of the outer loop voltage controller. VSC2 converts DC power into AC power and outputs it to the weak AC system through constant active power control.

VSC3 and weak AC system vector, VSC3 performs switch control operations through PWM control signals, converts the power of the weak AC system into DC power and transmits it to the DC power grid. The PWM control signal of VSC3 comes from the sine signal generator, and the sine signal generator The signal comes from the fixed phase angle δ control and the given constant voltage control. The signal of the constant voltage control comes from the difference between the given voltage value and the voltage measurement value.

VSC4 converts DC power into AC power and delivers it to the AC power grid. VSC4 performs switching control through the signal sent by the PWM signal generator. The trigger angle of the PWM signal generator comes from the calculation matrix of "dq->abc", and the dq parameter comes from With the improved feedforward decoupling control, the outer loop voltage PI control and the control signal taken from the AC grid are output to the improved feedforward decoupling control for calculation, and the measured DC voltage value is compared with the given DC voltage value. , output to the PI controller of the outer loop voltage controller.

Converter station VSC2 controls the AC voltage, and converter station VSC3 controls the active power. VSC2 uses fixed phase angle control to generate starting pulses to trigger the switch of the transistor. VSC1 and VSC4 use constant DC voltage control to control the first-level DC of the entire DC grid. voltage to ensure the power transmission of AC strong power grid and DC power grid, and control the triggering pulse of the converter station through a feedforward decoupling control strategy.

What is described above is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the invention, and these all belong to the scope of the present invention. protected range.

Claims (1)

1. A VSC DC power grid control method, characterized in that: the control system includes converter stations VSC1, VSC2, VSC3, VSC4, AC strong power grid, weak AC power grid, filters in the weak AC power grid, DC transmission lines, solution Coupling control strategy, phase angle control, active power control, AC voltage control and upper layer hierarchical control strategy. The AC strong grid AC exchanges energy with the DC grid through the converter stations VSC1 and VSC4. The DC grid contains a weak AC grid, which The weak AC grid exchanges energy with the DC grid through VSC2 and VSC3. The converter station is controlled through the decoupling control strategy. The decoupling control strategy, active power control and phase angle control control the trigger pulse for the converter station, and the upper layer hierarchical control provides solution Coupling control strategy control quantity; Converter station VSC1 and converter station VSC4 are directly connected to the AC strong power grid. VSC1 and VSC4 belong to the first level of control. VSC2 is connected to VSC1 through a DC cable. The other side of VSC2 is connected to the AC weak power grid. The control level of VSC2 is the third level. Level two, the control level of VSC3 is also level two; Power flows from VSC1 to VSC2, and then from VSC3 to VSC4. The weak grid load between VSC2 and VSC3 consumes a small part of the AC power, and at the same time, the AC weak grid inputs power to VSC3; AC is an AC strong power grid. AC inputs AC power to the converter station VSC1. The converter station VSC1 performs switching control through the signal sent by the PWM signal generator. The trigger angle of the PWM signal generator comes from "dq->abc" Calculation matrix, dq parameters come from the improved feedforward decoupling control, the outer loop voltage PI control and the control signal taken from the AC AC grid are output to the improved feedforward decoupling control for calculation, the measured DC voltage value and the given The DC voltage value is compared and output to the PI controller of the outer loop voltage controller; VSC1 converts AC AC power into DC power through the first stage of DC voltage control, and then transmits it to VSC2. VSC2 adopts constant active power control. The DC current is input to VSC2. The converter station VSC2 uses the signal sent by the PWM signal generator. For switching control, the trigger angle of the PWM signal generator comes from the calculation matrix of dq->abc, the dq parameter comes from the improved feedforward decoupling control, the outer loop active PI control and the measurement signal taken from the AC AC grid are output to The improved feedforward decoupling control performs calculations, compares the measured active power value with the given active power value, and outputs it to the PI controller of the outer loop voltage controller. VSC2 converts DC power into AC power through constant active power control. Output to weak AC system; VSC3 and weak AC system vector, VSC3 performs switch control operations through PWM control signals, converts the power of the weak AC system into DC power and transmits it to the DC power grid. The PWM control signal of VSC3 comes from the sine signal generator, and the sine signal generator The signal comes from the fixed phase angle δ control and the given constant voltage control. The signal of the constant voltage control comes from the difference between the given voltage value and the voltage measurement value; VSC4 converts DC power into AC power and transmits it to the AC power grid AC. VSC4 performs switching control through the signal sent by the PWM signal generator. The trigger angle of the PWM signal generator comes from the calculation matrix of dq->abc, and the dq parameter comes from the improvement of The feedforward decoupling control, the outer loop voltage PI control and the control signal taken from the AC AC grid are output to the improved feedforward decoupling control for calculation, the measured DC voltage value is compared with the given DC voltage value, and the output PI controller to the outer loop voltage controller; Converter station VSC2 controls the AC voltage, and converter station VSC3 controls the active power. VSC2 uses fixed phase angle control to generate starting pulses to trigger the switch of the transistor. VSC1 and VSC4 use constant DC voltage control to control the first-level DC of the entire DC grid. voltage to ensure the power transmission of AC strong grid and DC grid, and control the converter station triggering pulse through feedforward decoupling control strategy; The first-level control is defined as the control adopted by the outermost converter station in the VSC DC grid. The second-level control is defined as the converter station connected to the first-level converter station through high-voltage DC lines. The second-level control The AC side of the converter station is connected to a weak AC power grid. The first level of control uses DC voltage control and a feedforward double closed-loop decoupling control strategy. In the second level of control, the converter station uses a feedforward decoupling control strategy and Phase angle control is used to control the flow of power and the balance of AC voltage; In the first level of control, the DC voltage controls the input parameters to the inner loop through the outer loop PI control. The active and reactive parameters are decoupled in the inner loop to obtain the decoupled control signal. The rotation is calculated through the dq->abc matrix. The parameters in the rectangular coordinate system are converted into coordinate parameters of the three-phase AC system. Through these parameters, the converter station outputs a given DC side voltage for DC voltage control; In the second level control, the active power inputs parameters to the inner loop through PI control in the outer loop. The active and reactive parameters are decoupled in the inner loop to obtain a decoupled control signal. The rotation is calculated through the dq->abc matrix. The parameters in the rectangular coordinate system are converted into coordinate parameters of the three-phase AC system. Through these parameters, the converter station outputs a given active power for power control; In fixed phase angle control, the converter station generates a three-phase AC control signal corresponding to the phase angle signal through a given phase angle and a signal generating device. Through this signal, the converter station can output a voltage of a given phase angle. , perform phase angle control of weak AC power grid; In a DC power grid with a weak AC system, select the shortest path connecting a converter station to the strong power grid, and define the number of converter stations based on the number n of converter stations between a certain converter station and the AC strong power grid. The control level is n+1 level control; The third-level converter station is connected to the second-level control converter station through the weak AC power grid.