Voltage Dynamic Support Capacity Evaluation Method for Grid-Forming Converter Grid-Connected Equipment

Abstract

The present invention discloses a method for evaluating the voltage dynamic support ability of a grid-forming converter grid-connected device. First, the voltage amplitude and phase angle of the port of the grid-forming converter grid-connected device, the voltage amplitude and phase angle of the grid connection point, and the grid connection impedance of the grid-forming converter grid-connected device are obtained; then, according to the reactive power outer loop control strategy of the grid-forming converter grid-connected device, the corresponding calculation formula for the evaluation index of the voltage dynamic support ability of the grid-forming converter grid-connected device is selected, and based on the obtained data, the evaluation index of the voltage dynamic support ability of the grid-forming converter grid-connected device is calculated in real time. Compared with the short-circuit ratio index for evaluating the strength of the traditional evaluation system, the voltage dynamic support ability evaluation index of the present invention can accurately evaluate the voltage support ability of the grid-forming converter grid-connected device, and can quantitatively analyze the influence of the reactive power control parameters of the grid-forming converter grid-connected device on the voltage support ability, which is of great significance for improving the voltage support ability of the grid-forming converter grid-connected device and ensuring the safe and stable operation of the power system.

Description

Technical Field

[0001] The present invention belongs to the technical field of equipment evaluation for use with a power supply or a similar power supply system, and specifically relates to a method for evaluating the voltage dynamic support capability of a grid-connected converter device. Background Art

[0002] At present, new energy sources such as wind energy and solar energy have been developed and utilized on a large scale. New energy generators and energy storage rely on key power electronic devices such as inverters to be connected to the grid. The inverter not only realizes the conversion of direct current generated by new energy power generation and alternating current in the grid, but also effectively regulates the quality of electric energy and tracks the maximum power point, helping new energy to smoothly connect to the grid.

[0003] Different from the large capacity, high inertia and strong frequency regulation capability of traditional synchronous machines, the grid-side converters of a large number of existing wind power, photovoltaic and other new energy generators and energy storage devices almost all adopt grid-following control, and rarely have active support functions, lack inertial response and frequency / voltage control capabilities. As the proportion of new energy in the power system continues to increase, the strength of the power grid has also decreased, which has brought challenges to the voltage stability and reliability of the power grid.

[0004] Deploying phase regulators can improve the short-circuit ratio of renewable energy stations, but the current phase regulators have limited inertia support capabilities and do not have frequency regulation capabilities. As the proportion of renewable energy power generation continues to increase, inertia support and frequency stability issues will gradually become more prominent.

[0005] The emergence of grid-connected converters provides a new solution. By simulating the characteristics of synchronous motors, grid-connected converters can be used as equivalent voltage sources after being connected to the grid, effectively providing voltage and frequency support for the system, while enhancing the inertia and damping characteristics of the grid, thereby improving the stability of the grid.

[0006] As a traditional voltage support capability evaluation index, short-circuit ratio is not suitable for new power systems containing power electronic equipment. Therefore, it is necessary to study the voltage support capability evaluation method of the whole process of new energy grid-connected systems containing grid-connected converters. According to the evaluation index, the control parameters of the grid-connected converters are adjusted to promote the construction of a more stable, reliable and sustainable power system. Summary of the invention

[0007] In order to solve the problem of the current lack of voltage support capability evaluation indicators for grid-connected converter equipment, the purpose of the present invention is to propose a voltage dynamic support capability evaluation method suitable for grid-connected converter equipment. The present invention is based on the control strategy of the reactive outer loop of the grid-connected converter equipment, and adjusts the traditional short-circuit ratio indicator, thereby solving the problem that the traditional short-circuit ratio indicator is not suitable for the new power system, and improving the voltage support capability of the grid-connected converter equipment.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for evaluating the voltage dynamic support capability of a grid-connected converter device, comprising the following steps:

[0010] Step 1: Real-time acquisition of dynamic data of the voltage amplitude and phase angle of the grid-connected device port of the grid-connected converter, the voltage amplitude and phase angle of the grid-connected point, and the grid-connected impedance of the grid-connected device of the grid-connected converter;

[0011] Step 2: Determine whether the reactive power outer loop control strategy of the grid-connected equipment of the grid-connected converter is reactive power-voltage droop control. If so, the evaluation index of the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter is The calculation formula is as follows, and jump to step 5. After executing step 5, the evaluation method ends, otherwise proceed to step 3;

[0012]

[0013] Where: , E 0 is the rated voltage of the grid-connected equipment of the grid-connected converter, Q ref is the reactive power output value expected by the grid-connected equipment of the grid-connected converter, K is the reactive power-voltage droop coefficient, Q S The reactive power provided by the grid-connected equipment to the system, U PCC is the voltage amplitude at the grid connection point, E is the port voltage amplitude of the grid-connected device of the grid-connected converter, θ is the voltage phase angle at the grid connection point, is the port voltage phase angle of the grid-connected device of the grid-connected converter, x 2 The grid impedance of the grid-connected equipment of the grid-connected converter;

[0014] Step 3: Determine whether the reactive power outer loop control strategy of the grid-connected equipment of the grid-connected converter is voltage PI control, that is, perform proportional and integral operations on the difference between the voltage reference value and the actual value of the grid-connected point to obtain the grid-connected equipment voltage of the grid-connected converter; if so, the grid-connected equipment voltage dynamic support capability evaluation index of the grid-connected converter is The calculation formula is as follows, and jump to step 6. After executing step 6, the evaluation method ends, otherwise proceed to step 4;

[0015]

[0016] Where: , U ref is the rated output voltage of the grid-connected equipment of the grid-connected converter, k p is the proportional coefficient of the grid-connected equipment voltage PI control of the grid-connected converter, k i It is the integral coefficient of the grid-connected equipment voltage PI control of the grid converter;

[0017] Step 4: When the grid-connected equipment of the grid-connected converter does not consider reactive external loop control, it is assumed that the reference voltage of the grid-connected converter equipment is constant, and the evaluation index of the voltage dynamic support capability of the grid-connected converter equipment is The calculation formula is as follows, and jump to step 7. After executing step 7, the evaluation method ends;

[0018]

[0019] Where: , E 0 The rated voltage of the grid-connected equipment of the grid-connected converter;

[0020] Step 5: Substitute the dynamic data obtained in real time in step 1 into the voltage dynamic support capability evaluation index generated in step 2, and obtain the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter at any time by comparing the absolute value of the index; the larger the absolute value of the index, the stronger the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter;

[0021] Step 6: Substitute the dynamic data acquired in real time in step 1 into the voltage dynamic support capability evaluation index generated in step 3, and obtain the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter at any time by comparing the absolute value of the index; the larger the absolute value of the index, the stronger the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter;

[0022] Step 7: Substitute the dynamic data obtained in real time in step 1 into the voltage dynamic support capability evaluation index generated in step 4, and obtain the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter at any moment by comparing the absolute value of the index; the larger the absolute value of the index, the stronger the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter.

[0023] In the steps 2, 3 and 4, the reactive power equation of the grid-connected device output based on the grid-connected device is , combined with the specific control logic of the grid-connected equipment of the grid-connected converter, the voltage support capability evaluation index of the grid-connected converter equipment is obtained. The proposed index not only reflects the support capability of the grid-connected converter equipment to cope with voltage changes, but also shows the influence of the reactive outer loop control parameters of the grid-connected converter equipment on the support capability, which plays a guiding role in improving the voltage support capability of the grid-connected converter equipment.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The method of the present invention obtains various dynamic data in real time during the whole operation process of the grid-connected equipment of the grid-connected converter, and measures the voltage dynamic support capability of the grid-connected converter equipment in the whole process through the corresponding voltage dynamic support capability evaluation index. Compared with the traditional short-circuit ratio index, the present invention effectively solves the problem that the traditional short-circuit ratio is not suitable for the new power system, and can measure the voltage support capability of the whole process. The present invention combines the reactive outer loop control strategy of the grid-connected converter equipment to evaluate the voltage support capability of the grid-connected converter equipment in real time. The corresponding voltage dynamic support capability evaluation index can reflect the influence of controllable parameters on the voltage support capability of the grid-connected converter equipment, which is of great significance in guiding the parameter design of the grid-connected converter equipment and ensuring the safe and stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flow chart of the method of the present invention.

[0027] Figure 2 It is a new energy transmission system topology including grid-connected converter equipment.

[0028] Figure 3a The grid-connected equipment of the grid-connected converter adopts the reactive power-voltage droop control strategy; Figure 3b The grid-connected device of the grid-connected converter adopts the voltage PI control strategy.

[0029] Figure 4a It is the comparison curve of voltage support capability evaluation index under different droop coefficients in reactive power-voltage droop control mode; Figure 4b It is a comparison curve of the voltage support capacity of the grid-connected point with different droop coefficients under the reactive power-voltage droop control mode.

[0030] Figure 5a It is the comparison curve of voltage support capability evaluation index under different grid-connected impedances in reactive power-voltage droop control mode; Figure 5b It is a comparison curve of the voltage support capacity of the grid point with different grid-connected impedances under the reactive power-voltage droop control mode.

[0031] Figure 6a It is the comparison curve of voltage support capability evaluation index under different proportional coefficients in voltage PI control mode; Figure 6b It is a comparison curve of the voltage support capacity of the grid-connected point with different proportional coefficients under the voltage PI control mode.

[0032] Figure 7a It is the comparison curve of voltage support capability evaluation index under different integral coefficients in voltage PI control mode; Figure 7bIt is a comparison curve of the voltage support capacity of the grid-connected point with different integral coefficients under the voltage PI control mode.

[0033] Figure 8a It is the comparison curve of voltage support capability evaluation index under different grid impedances when the reactive external loop is not considered; Figure 8b It is a comparison curve of the voltage support capacity of the grid point with different grid impedances when the reactive external loop is not considered. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0035] like Figure 1 As shown, the present invention is a method for evaluating the voltage dynamic support capability of a grid-connected converter device, which includes the following steps:

[0036] Step 1: Real-time acquisition of dynamic data of the voltage amplitude and phase angle of the grid-connected device port of the grid-connected converter, the voltage amplitude and phase angle of the grid-connected point, and the grid-connected impedance of the grid-connected device of the grid-connected converter;

[0037] Step 2: Determine whether the reactive power outer loop control strategy of the grid-connected equipment of the grid-connected converter is reactive power-voltage droop control. If so, the evaluation index of the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter is The calculation formula is as follows, and jump to step 5. After executing step 5, the evaluation method ends, otherwise proceed to step 3;

[0038]

[0039] Where: , E 0 is the rated voltage of the grid-connected equipment of the grid-connected converter, Q ref is the reactive power output value expected by the grid-connected equipment of the grid-connected converter, K is the reactive power-voltage droop coefficient, Q S The reactive power provided by the grid-connected equipment to the system, U PCC is the voltage amplitude at the grid connection point, E is the port voltage amplitude of the grid-connected device of the grid-connected converter, θ is the voltage phase angle at the grid connection point, is the port voltage phase angle of the grid-connected device of the grid-connected converter, x 2 The grid impedance of the grid-connected equipment of the grid-connected converter;

[0040] Step 3: Determine whether the reactive power outer loop control strategy of the grid-connected equipment of the grid-connected converter is voltage PI control, that is, perform proportional and integral operations on the difference between the voltage reference value and the actual value of the grid-connected point to obtain the grid-connected equipment voltage of the grid-connected converter; if so, the grid-connected equipment voltage dynamic support capability evaluation index of the grid-connected converter is The calculation formula is as follows, and jump to step 6. After executing step 6, the evaluation method ends, otherwise proceed to step 4;

[0041]

[0042] Where: , U ref is the rated output voltage of the grid-connected equipment of the grid-connected converter, k p is the proportional coefficient of the grid-connected equipment voltage PI control of the grid-connected converter, k i It is the integral coefficient of the grid-connected equipment voltage PI control of the grid converter;

[0043] Step 4: When the grid-connected equipment of the grid-connected converter does not consider reactive external loop control, it is assumed that the reference voltage of the grid-connected converter equipment is constant, and the evaluation index of the voltage dynamic support capability of the grid-connected converter equipment is The calculation formula is as follows, and jump to step 7. After executing step 7, the evaluation method ends;

[0044]

[0045] Where: , E 0 The rated voltage of the grid-connected equipment of the grid-connected converter;

[0046] Step 5: Substitute the dynamic data obtained in real time in step 1 into the voltage dynamic support capability evaluation index generated in step 2, and obtain the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter at any time by comparing the absolute value of the index; the larger the absolute value of the index, the stronger the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter;

[0047] Step 6: Substitute the dynamic data acquired in real time in step 1 into the voltage dynamic support capability evaluation index generated in step 3, and obtain the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter at any time by comparing the absolute value of the index; the larger the absolute value of the index, the stronger the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter;

[0048] Step 7: Substitute the dynamic data obtained in real time in step 1 into the voltage dynamic support capability evaluation index generated in step 4, and obtain the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter at any moment by comparing the absolute value of the index; the larger the absolute value of the index, the stronger the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter. Example

[0049] In order to verify the correctness of the method of the present invention, a simulation platform is built as follows Figure 2 The new energy grid-connected converter and grid-connected equipment transmission system topology shown in the figure was simulated and verified according to the following parameters:

[0050] The actual output of the grid-connected new energy unit is 30MW; the actual output of the grid-connected equipment of the grid-connected converter is 50MW; the receiving end is the infinite grid. The disturbance is a 5% drop in system voltage for 0.18 seconds.

[0051] If the grid-connected equipment of the grid-connected converter adopts reactive power-voltage droop control, the control logic is as follows Figure 3a As shown. For the cases where the reactive power-voltage droop coefficient K is 0.1, 0.3, and 0.5, simulation analysis is performed, and the impact of the reactive power-voltage droop coefficient on the voltage support capacity is shown as follows Figure 4a and Figure 4b shown. Figure 4a This is a comparison curve of voltage support capability evaluation index under different droop coefficients. When the droop coefficient increases, the voltage support capability evaluation index The decrease in absolute value indicates that the voltage support capability decreases. Figure 4b The comparison curve of the voltage support capacity of the grid connection point with different droop coefficients can be seen from the figure: when the droop coefficient increases, the voltage drop increases, which verifies Figure 4a Evaluation indicators of medium voltage support capability The absolute value decreases.

[0052] If the grid-connected equipment of the grid-connected converter adopts reactive power-voltage droop control, simulation analysis is performed for the cases where the grid impedance is 0.01Ω, 0.03Ω, and 0.05Ω. The influence of the grid impedance on the voltage support capacity is as follows: Figure 5a and Figure 5b shown. Figure 5a This is a comparison curve of voltage support capability evaluation index under different grid-connected impedances. When the grid-connected impedance increases, the voltage support capability evaluation index The decrease in absolute value indicates that the voltage support capability decreases. Figure 5b This is a comparison curve of the voltage support capacity of the grid point with different grid impedances. It can be seen from the figure that when the grid impedance increases, the voltage drop increases, which verifies Figure 5a Evaluation indicators of medium voltage support capability The absolute value decreases.

[0053] If the grid-connected equipment of the grid-connected converter adopts voltage PI control, the control logic is as follows Figure 3b As shown. For the proportionality coefficient k p The simulation analysis is carried out for the cases of 0.1, 0.3, and 0.5. The influence of the proportional coefficient on the voltage support capability is as follows Figure 6a and Figure 6b shown. Figure 6a This is a comparison curve of voltage support capability evaluation index under different proportional coefficients. When the proportional coefficient decreases, the voltage support capability evaluation index The decrease in absolute value indicates that the voltage support capability decreases. Figure 6bThe comparison curve of the voltage support capacity of the grid connection point with different proportional coefficients can be seen from the figure: when the proportional coefficient decreases, the voltage change amplitude increases, which verifies Figure 6a Evaluation indicators of medium voltage support capability The absolute value decreases.

[0054] If the grid-connected equipment of the grid-connected converter adopts voltage PI control, for the integral coefficient k i The simulation analysis is carried out for the cases of 0.01, 0.05 and 0.1. The influence of the integral coefficient on the voltage support capability is as follows Figure 7a and Figure 7b shown. Figure 7a The comparison curve of voltage support capability evaluation index under different integral coefficients. When the integral coefficient increases, the voltage support capability evaluation index during the fault process The decrease in absolute value indicates that the voltage support capability decreases. Figure 7b The curves are compared for the voltage support capacity of the grid connection point with different integral coefficients. It can be seen from the figure that during the fault process, when the integral coefficient increases, the voltage drop increases, which verifies Figure 7a Evaluation indicators of medium voltage support capability In addition, after the fault ends, as the integral coefficient increases, the voltage support capability evaluation index The absolute value also increases, even exceeding the steady-state value. Figure 7b It can be seen that the voltage amplitude of the corresponding grid-connected point increases, overvoltage occurs, and the larger the integral coefficient, the more obvious the overvoltage phenomenon.

[0055] If the grid-connected equipment of the grid-connected converter does not adopt reactive power external loop control, it is considered that E=E 0 The simulation analysis is carried out for the cases where the grid impedance is 0.03Ω, 0.04Ω, and 0.05Ω, and the influence of the grid impedance on the voltage support capacity is Figure 8a and Figure 8b shown. Figure 8a This is a comparison curve of voltage support capability evaluation index under different grid-connected impedances. When the grid-connected impedance increases, the voltage support capability evaluation index The decrease in absolute value indicates that the voltage support capability decreases. Figure 8b This is a comparison curve of the voltage support capacity of the grid point with different grid impedances. It can be seen from the figure that when the grid impedance increases, the voltage drop increases, which verifies Figure 8a Evaluation indicators of medium voltage support capability The absolute value decreases.

[0056] The above simulation verification proves that the voltage support capability evaluation method proposed in the present invention can evaluate the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter, and can serve as a supporting basis for the design of grid-connected parameters.

Claims

1. A method for evaluating the voltage dynamic support capability of a grid-connected converter device, characterized in that: The following steps are involved: Step 1: Real-time acquisition of dynamic data of the voltage amplitude and phase angle of the grid-connected device port of the grid-connected converter, the voltage amplitude and phase angle of the grid-connected point, and the grid-connected impedance of the grid-connected device of the grid-connected converter; Step 2: Determine whether the reactive power outer loop control strategy of the grid-connected equipment of the grid-connected converter is reactive power-voltage droop control. If so, the evaluation index of the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter is The calculation formula is as follows, and jump to step 5. After executing step 5, the evaluation method ends, otherwise proceed to step 3; Where: , E0 is the rated voltage of the grid-connected equipment of the grid-connected converter, Q ref is the reactive power output value expected by the grid-connected equipment of the grid-connected converter, K is the reactive power-voltage droop coefficient, Q S The reactive power provided by the grid-connected equipment to the system, U PCC is the voltage amplitude at the grid connection point, E is the port voltage amplitude of the grid-connected device of the grid-connected converter, θ is the voltage phase angle at the grid connection point, is the port voltage phase angle of the grid-connected device of the grid-connected converter, x2 is the grid-connected impedance of the grid-connected device of the grid-connected converter; Step 3: Determine whether the reactive power outer loop control strategy of the grid-connected equipment of the grid-connected converter is voltage PI control, that is, perform proportional and integral operations on the difference between the voltage reference value and the actual value of the grid-connected point to obtain the grid-connected equipment voltage of the grid-connected converter; if so, the grid-connected equipment voltage dynamic support capability evaluation index of the grid-connected converter is The calculation formula is as follows, and jump to step 6. After executing step 6, the evaluation method ends, otherwise proceed to step 4; Where: , U ref is the rated output voltage of the grid-connected equipment of the grid-connected converter, k p is the proportional coefficient of the grid-connected equipment voltage PI control of the grid-connected converter, k i It is the integral coefficient of the grid-connected equipment voltage PI control of the grid converter; Step 4: When the grid-connected equipment of the grid-connected converter does not consider reactive external loop control, it is assumed that the reference voltage of the grid-connected converter equipment is constant, and the evaluation index of the voltage dynamic support capability of the grid-connected converter equipment is The calculation formula is as follows, and jump to step 7. After executing step 7, the evaluation method ends; Where: , E0 is the rated voltage of the grid-connected equipment of the grid-connected converter; Step 5: Substitute the dynamic data obtained in real time in step 1 into the voltage dynamic support capability evaluation index generated in step 2, and obtain the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter at any time by comparing the absolute value of the index; the larger the absolute value of the index, the stronger the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter; Step 6: Substitute the dynamic data acquired in real time in step 1 into the voltage dynamic support capability evaluation index generated in step 3, and obtain the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter at any time by comparing the absolute value of the index; the larger the absolute value of the index, the stronger the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter; Step 7: Substitute the dynamic data obtained in real time in step 1 into the voltage dynamic support capability evaluation index generated in step 4, and obtain the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter at any moment by comparing the absolute value of the index; the larger the absolute value of the index, the stronger the voltage dynamic support capability of the grid-connected equipment of the grid-connected converter.

2. A method for evaluating the voltage dynamic support capability of a grid-connected converter device according to claim 1, characterized in that: In the steps 2, 3 and 4, the reactive power equation of the grid-connected device output based on the grid-connected device is ,Combined with the specific control strategy of the grid-connected equipment of the grid-connected converter, the voltage support capability evaluation index of the grid-connected equipment of the grid-connected converter is obtained.

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