Evaluation method for voltage dynamic support capability of grid-connected converters

Abstract

The present invention discloses a method for evaluating the voltage dynamic support capability of a grid-type converter. First, the inductance from the grid-type converter to the grid connection point and the voltage amplitude and current amplitude of the grid connection point immediately before the disturbance are measured in real time to obtain the reactive loop control parameters of the grid-type converter. Secondly, according to the control logic of the grid-type converter, the voltage dynamic support capability evaluation index formula of the grid-type converter is obtained. Finally, the voltage dynamic support capability index of the grid-type converter is calculated. Compared with the traditional short-circuit ratio index for measuring voltage intensity, the voltage dynamic support capability evaluation index proposed by the present invention can evaluate the voltage support capability of the grid-type converter during the entire disturbance process, and the index reflects the influence of the reactive outer loop control parameters of the grid-type converter on the voltage support capability at different stages of the disturbance. It is of great significance for improving the voltage support capability of the grid-type converter 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 in particular relates to a method for evaluating the dynamic voltage support capability of a grid-type converter. Background Art

[0002] Currently, most renewable energy sources in power systems are connected to the grid via grid-connected converters. However, these converters have significant technical limitations, including insufficient active support capabilities, a lack of system inertia response, and a lack of frequency regulation. As renewable energy penetration continues to increase, grid strength continues to decline, resulting in reduced voltage stability margins and increased power supply reliability risks. To address this technical bottleneck, grid-connected converters simulate the external characteristics of synchronous generators, enabling them to function as an equivalent voltage source. This provides dynamic inertia support and voltage support for the power system, effectively improving grid operational stability.

[0003] Traditional power systems use the short circuit ratio (SCR) to measure system voltage strength. However, with a high proportion of power electronic equipment connected to the grid via transformers, this metric cannot accurately measure the system's voltage support capability. Therefore, it is urgent to establish a dynamic voltage support evaluation method for grid-connected converters. This quantitative analysis, guiding control parameter optimization, will have significant engineering value in building a resilient and sustainable new power system. Summary of the Invention

[0004] In order to solve the problem of the current lack of voltage support capability evaluation indicators for grid-type converters, the purpose of the present invention is to propose a voltage dynamic support capability evaluation method suitable for grid-type converters. The present invention is based on the reactive outer loop control of the grid-type converter, and analyzes the impact of control parameter changes on the stability of the power system through the amplitude characteristic curve of the voltage dynamic support capability indicator, thereby improving the voltage support capability of the grid-type converter and solving the problem of the lack of indicators for measuring the voltage support capability of the grid-type converter.

[0005] In order to achieve the above object, the technical solution adopted in the present invention is:

[0006] A method for evaluating the dynamic voltage support capability of a grid-connected converter includes the following steps:

[0007] Step 1: In a power system containing a grid-type converter, the inductance from the grid-type converter to the grid connection point and the voltage and current amplitudes at the grid connection point immediately before the disturbance are measured in real time to obtain the reactive power outer loop control parameters of the grid-type converter.

[0008] Step 2: Based on the reactive power output equation of the grid-connected converter Reactive outer loop control equation E=kp (Q ref -Q S )+k i ∫(Q ref -Q S )dt+E0 and the circuit equation The evaluation index of voltage dynamic support capability of grid-type converter is obtained for:

[0009]

[0010] Where Q S is the reactive power output by the grid-type converter, U PCC , θ are the voltage amplitude and phase angle of the grid connection point immediately before the disturbance, I o is the output current amplitude of the grid-type converter, α is the voltage phase angle of the grid-type converter, is the power factor angle; E and E0 are the actual value and reference value of the electromotive force of the grid-type converter, respectively. ref is the reactive power reference value output by the grid-connected converter, k p k is the proportional coefficient of the reactive outer loop of the grid-type converter, i is the integral coefficient of the reactive outer loop of the grid-type converter; ΔQ S (s) is the reactive power change of the grid-type converter output, ΔU PCC (s) is the voltage amplitude change at the grid connection point, s is the Laplace operator, I o0 is the output current of the grid-type converter before the disturbance, U PCC0 is the voltage amplitude of the grid-connected point before the disturbance, L2 is the inductance from the grid-connected converter to the grid-connected point;

[0011] Substituting the real-time measured data and the obtained control parameters in step 1 into the voltage dynamic support capability evaluation index of the grid-type converter to obtain the voltage dynamic support capability of the grid-type device;

[0012] Step 3: Measure multiple parameters in real time through step 1 to obtain the voltage dynamic support capability evaluation index during the entire disturbance process, draw the amplitude characteristic curve of the voltage dynamic support capability evaluation index, and obtain the voltage dynamic support capability of the grid-type converter in the dynamic process after the disturbance occurs by comparing the amplitudes of the amplitude characteristic curve of the voltage dynamic support capability evaluation index; the larger the amplitude of the amplitude characteristic curve, the stronger the voltage dynamic support capability of the grid-type converter; by comparing the amplitude characteristic curves of the values ​​of the reactive outer loop control parameters of the grid-type converter, the support stage of the reactive outer loop control parameters of the grid-type converter on the voltage dynamic support capability can be reflected.

[0013] Through simulation verification, the proportional coefficient k of the reactive outer loop of the grid-type converter is pThe impact on the dynamic voltage support capability is mainly reflected in the medium frequency band, that is, the dynamic development process of the disturbance, the proportional coefficient k of the reactive outer loop of the grid-type converter p The smaller the value, the stronger the dynamic voltage support capability of the grid-type converter is; the integral coefficient k of the reactive outer loop of the grid-type converter is i The impact on the dynamic voltage support capability is mainly reflected in the medium and low frequency bands, that is, the steady-state and dynamic recovery process. The integral coefficient k of the reactive outer loop of the grid-type converter is i The larger the inductance L2 is, the stronger the dynamic voltage support capability of the grid-type converter is. The influence of the inductance L2 from the grid-type converter to the grid-connected point on the dynamic voltage support capability is mainly reflected in the high-frequency band, that is, at the moment of disturbance, the smaller the inductance L2 is from the grid-type converter to the grid-connected point, the stronger the dynamic voltage support capability of the grid-type converter is.

[0014] The indicators proposed in the present invention not only reflect the supporting capability of the grid-connected converter equipment to cope with voltage changes, but also demonstrate the influence of the reactive outer loop control parameters of the grid-connected converter equipment on the supporting capability, which plays a guiding role in improving the dynamic voltage supporting capability of the grid-connected converter equipment.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] The method of the present invention can calculate the voltage dynamic support capability of the grid-type converter during the entire disturbance process based on the power system operating parameters and the reactive outer loop control parameters of the grid-type converter. Compared with the traditional voltage strength measurement short-circuit ratio index, the present invention effectively solves the problem that the traditional short-circuit ratio index focuses on the voltage strength of the entire power system and is not suitable for the new power system with power electronics, and can measure the voltage dynamic support capability of the grid-type converter during the disturbance process. In addition, the index proposed in the present invention can reflect the support stage of the reactive outer loop control parameters of the grid-type converter on the voltage support capability. The present invention evaluates the voltage support capability of the grid-type equipment by combining the reactive outer loop control strategy of the grid-type converter. The proposed index can reflect the influence of controllable parameters on the voltage support capability of the grid-type converter, and is of great significance in guiding the parameter design of the grid-type converter and ensuring the safe and stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the method of the present invention.

[0018] Figure 2 It is a new energy transmission system topology containing grid-type converters.

[0019] Figure 3 It is the reactive outer loop control strategy of grid-type converter.

[0020] Figure 4It is a comparison of voltage dynamic support capability evaluation indicators under different proportional coefficients.

[0021] Figure 5 It is a comparison of voltage dynamic support capabilities under different proportional coefficients.

[0022] Figure 6 It is a comparison of voltage dynamic support capability evaluation indicators under different integral coefficients.

[0023] Figure 7 It is a comparison of voltage dynamic support capabilities under different integral coefficients.

[0024] Figure 8 This is a comparison of evaluation indicators of the dynamic voltage support capability of different grid-connected converters under inductance to the grid connection point.

[0025] Figure 9 This is a comparison of the dynamic voltage support capabilities of different grid-connected converters under inductance to the grid connection point. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0027] like Figure 1 As shown, the present invention provides a method for evaluating the dynamic voltage support capability of a grid-type converter, comprising the following steps:

[0028] Step 1: In a power system containing a grid-type converter, the inductance from the grid-type converter to the grid connection point and the voltage and current amplitudes at the grid connection point immediately before the disturbance are measured in real time to obtain the reactive power outer loop control parameters of the grid-type converter.

[0029] Step 2: Based on the reactive power output equation of the grid-connected converter Reactive outer loop control equation E=k p (Q ref -Q S )+k i ∫(Q ref -Q S )dt+E0 and the circuit equation The evaluation index of voltage dynamic support capability of grid-type converter is obtained for:

[0030]

[0031] Where Q S is the reactive power output by the grid-connected converter, U PCC , θ are the voltage amplitude and phase angle of the grid connection point immediately before the disturbance, I o is the output current amplitude of the grid-type converter, α is the voltage phase angle of the grid-type converter, is the power factor angle; E and E0 are the actual value and reference value of the electromotive force of the grid-type converter, respectively. ref is the reactive power reference value output by the grid-connected converter, k p k is the proportional coefficient of the reactive outer loop of the grid-type converter, i is the integral coefficient of the reactive outer loop of the grid-type converter; ΔQ S (s) is the reactive power change of the grid-type converter output, ΔU PCC (s) is the voltage amplitude change at the grid connection point, s is the Laplace operator, I o0 is the output current of the grid-type converter before the disturbance, U PCC0 is the voltage amplitude of the grid-connected point before the disturbance, L2 is the inductance from the grid-connected converter to the grid-connected point;

[0032] According to the reactive power output equation of the grid-type converter Reactive outer loop control equation E=k p (Q ref -Q S )+k i ∫(Q ref -Q S )dt+E0 and the circuit equation The evaluation index of the dynamic voltage support capability of the grid-type converter is obtained. Specifically, it is assumed that the grid-type converter does not output active power, so θ = α, and the influence of resistance is ignored, that is, Linearize and Laplace transform the three equations: ΔQ S (s)=U PCC0 ΔI o (s)+I o0 ΔU PCC (s), L2sΔI o (s)=ΔE(s)-ΔU PCC (s), eliminating ΔI o (s) and ΔE(s), and the evaluation index of the dynamic voltage support capability of the grid-type converter is obtained. This index can reflect the support stage of the reactive outer loop control parameters of the grid-type converter on the dynamic voltage support capability during the whole disturbance process.

[0033] The data measured in real time in step 1 and the control parameters obtained are substituted into the voltage dynamic support capability evaluation index of the grid-type converter to obtain the voltage dynamic support capability of the grid-type device.

[0034] Step 3: Measure multiple parameters in real time through step 1 to obtain the voltage dynamic support capability evaluation index during the entire disturbance process, draw the amplitude characteristic curve of the voltage dynamic support capability evaluation index, and obtain the voltage dynamic support capability of the grid-type converter in the dynamic process after the disturbance occurs by comparing the amplitudes of the amplitude characteristic curve of the voltage dynamic support capability evaluation index; the larger the amplitude of the amplitude characteristic curve, the stronger the voltage dynamic support capability of the grid-type converter; by comparing the amplitude characteristic curves of the values ​​of the reactive outer loop control parameters of the grid-type converter, the support stage of the reactive outer loop control parameters of the grid-type converter on the voltage dynamic support capability can be reflected.

[0035] Example:

[0036] In order to verify the correctness of the voltage dynamic support capability evaluation method for grid-type converters proposed in the present invention, a simulation platform is built as follows: Figure 2 The new energy grid-connected converter transmission system model shown was simulated and verified using the following parameters:

[0037] The actual output of the grid-following new energy generator is 80MW; the actual output of the grid-forming converter is 0MW; the receiving end is the infinite power grid. The system voltage drops by 5% during the disturbance of 12-12.18s.

[0038] Figure 3 The reactive outer loop control strategy of the grid-type converter is constructed, where 1 / s is the integral link and the time domain form is ∫xdt, where x is the integrand. In the present invention, x=k i (Q ref -Q S ). Expressed in equation form: E = k p (Q ref -Q S )+k i ∫(Q ref -Q S )dt+E0.

[0039] In order to verify the influence of the proportional coefficient of the reactive outer loop of the grid-type converter on the dynamic voltage support capability, the proportional coefficient k of the reactive outer loop of the grid-type converter is 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 dynamic voltage support capability is as follows: Figure 4 and Figure 5 shown. Figure 4 It is a comparison of voltage dynamic support capability evaluation indicators under different proportional coefficients. Figure 5 This is a comparison of voltage dynamic support capabilities under different proportional coefficients. Figure 4 It can be seen that the proportional coefficient k of the reactive outer loop of the grid-type converter is pThe impact on the voltage dynamic support capability is mainly reflected in the mid-frequency band, that is, the dynamic development process of the disturbance. p When the mid-frequency band ΔQ decreases, S (s) / ΔU PCC (s) The amplitude increases, and the voltage dynamic support capability is enhanced. Figure 5 The simulation results show that the proportional coefficient k of the reactive outer loop of the grid-type converter is p The voltage drop amplitude is reduced during the disturbance process, and the voltage dynamic support capability of the grid-type converter is enhanced, which proves the rationality of the voltage dynamic support capability index proposed in the present invention.

[0040] In order to verify the influence of the integral coefficient of the reactive outer loop of the grid-type converter on the voltage dynamic support capability, the integral coefficient k of the reactive outer loop of the grid-type converter is i The simulation analysis is carried out for the cases of 0.1, 0.3 and 0.5. The influence of the integral coefficient on the dynamic voltage support capability is as follows: Figure 6 and Figure 7 shown. Figure 6 It is a comparison of voltage dynamic support capability evaluation indicators under different integral coefficients. Figure 7 This is a comparison of the voltage dynamic support capability under different integral coefficients. Figure 6 It can be seen that the integral coefficient k of the reactive outer loop of the grid-type converter is i The impact on the voltage dynamic support capability is mainly reflected in the medium and low frequency bands, that is, the steady state and dynamic recovery process. The larger the integral coefficient, the stronger the voltage dynamic support capability. Figure 7 The simulation results show that the integral coefficient k of the reactive outer loop of the grid-type converter is i Increases, the voltage drop amplitude decreases during the disturbance process, and the voltage dynamic support capability of the grid-type converter is enhanced.

[0041] In order to verify the influence of the inductance from the grid-connected converter to the grid-connected point on the dynamic voltage support capability, a simulation analysis is performed for the cases where the inductance L2 from the grid-connected converter to the grid-connected point is 0.1, 0.3 and 0.5H. The influence of the inductance from the grid-connected converter to the grid-connected point on the dynamic voltage support capability is shown in the following figure. Figure 8 and Figure 9 shown. Figure 8 This is a comparison of evaluation indicators of the dynamic voltage support capability of different grid-connected converters under inductance to the grid connection point. Figure 9 This is a comparison of the voltage dynamic support capability of different grid-connected converters under inductance to the grid connection point. Figure 8 It can be seen that the influence of the inductance from the grid-connected converter to the grid connection point on the dynamic voltage support capability is mainly reflected in the high frequency band, that is, at the moment of disturbance. This shows that the inductance from the grid-connected converter to the grid connection point is the main factor affecting the power distribution at the moment of disturbance. As the inductance from the grid-connected converter to the grid connection point decreases, the disturbance instant ΔQ S(s) / ΔU PCC As the amplitude of (s) increases, the voltage dynamic support capability is enhanced. Figure 9 It can be seen from the simulation results that the inductance from the grid-connected converter to the grid point is reduced, the voltage drop amplitude is reduced during the disturbance process, and the voltage dynamic support capability of the grid-connected converter is enhanced.

[0042] Through analysis Figure 4 and Figure 5 , Figure 6 and Figure 7 , Figure 8 and Figure 9 , which proves that the voltage dynamic support capability evaluation method proposed in the present invention can evaluate the voltage dynamic support capability of the grid-connected converter in the small disturbance dynamic process, and can serve as a supporting basis for the grid-connected parameter design.

Claims

1. A method for evaluating the dynamic voltage support capability of a grid-connected converter, characterized by: The following steps are involved: Step 1: In a power system containing a grid-type converter, the inductance from the grid-type converter to the grid connection point and the voltage and current amplitudes at the grid connection point immediately before the disturbance are measured in real time to obtain the reactive power outer loop control parameters of the grid-type converter. Step 2: Based on the reactive power output equation of the grid-connected converter , reactive outer loop control equation and circuit equations , and obtain the evaluation index of the voltage dynamic support capability of the grid-type converter for: Where, is the reactive power output by the grid-type converter, U PCC 、 are the voltage amplitude and phase angle of the grid connection point immediately before the disturbance, I o is the output current amplitude of the grid-type converter, is the voltage phase angle of the grid-type converter, is the power factor angle; E and E0 are the actual value and reference value of the electromotive force of the grid-type converter respectively. is the reactive power reference value output by the grid-connected converter, k p k is the proportional coefficient of the reactive outer loop of the grid-type converter, i is the integral coefficient of the reactive outer loop of the grid-type converter; is the reactive power change output by the grid-type converter, is the voltage amplitude variation at the grid connection point, s is the Laplace operator, I o0 is the output current of the grid-type converter before the disturbance, U PCC0 is the voltage amplitude of the grid-connected point before the disturbance, L2 is the inductance from the grid-connected converter to the grid-connected point; Substituting the real-time measured data and the obtained control parameters in step 1 into the voltage dynamic support capability evaluation index of the grid-type converter to obtain the voltage dynamic support capability of the grid-type device; Step 3: Measure multiple parameters in real time through step 1 to obtain the voltage dynamic support capability evaluation index during the entire disturbance process, draw the amplitude characteristic curve of the voltage dynamic support capability evaluation index, and obtain the voltage dynamic support capability of the grid-type converter in the dynamic process after the disturbance occurs by comparing the amplitudes of the amplitude characteristic curve of the voltage dynamic support capability evaluation index; the larger the amplitude of the amplitude characteristic curve, the stronger the voltage dynamic support capability of the grid-type converter; by comparing the amplitude characteristic curves of the values ​​of the reactive outer loop control parameters of the grid-type converter, the support stage of the reactive outer loop control parameters of the grid-type converter on the voltage dynamic support capability can be reflected.

2. A method for evaluating the dynamic voltage support capability of a grid-connected converter according to claim 1, characterized in that: Proportional coefficient k of the reactive outer loop of the grid-type converter p The impact on the dynamic voltage support capability is mainly reflected in the medium frequency band, that is, the dynamic development process of the disturbance, the proportional coefficient k of the reactive outer loop of the grid-type converter p The smaller the value, the stronger the dynamic voltage support capability of the grid-type converter is; the integral coefficient k of the reactive outer loop of the grid-type converter is i The impact on the dynamic voltage support capability is mainly reflected in the medium and low frequency bands, that is, the steady-state and dynamic recovery process. The integral coefficient k of the reactive outer loop of the grid-type converter is i The larger the inductance L2 is, the stronger the dynamic voltage support capability of the grid-type converter is. The influence of the inductance L2 from the grid-type converter to the grid-connected point on the dynamic voltage support capability is mainly reflected in the high-frequency band, that is, at the moment of disturbance, the smaller the inductance L2 is from the grid-type converter to the grid-connected point, the stronger the dynamic voltage support capability of the grid-type converter is.

3. The method for evaluating the dynamic voltage support capability of a grid-connected converter according to claim 1, wherein: In the step 2, according to the reactive power output equation of the grid-type converter , reactive outer loop control equation and circuit equations , we get the evaluation index of the voltage dynamic support capability of the grid-type converter, specifically: it is considered that the grid-type converter does not output active power, so , while ignoring the effect of resistance, that is ; Linearize and Laplace transform the three equations: 、 、 , eliminate and , the evaluation index of the dynamic voltage support capability of the grid-type converter is obtained, which can reflect the support stage of the reactive outer loop control parameters of the grid-type converter on the dynamic voltage support capability during the whole disturbance process.

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