Characteristic harmonic compensation method based on improved STATCOM

Abstract

The method comprises the following steps: extracting frequency information of power grid voltage based on a characteristic harmonic compensation method of an improved STATCOM to obtain a reference phase and frequency of h-order harmonic; the load current is converted into a d-q coordinate system through a Cabc-dqh change matrix module and decomposed into a load active current component and a load reactive current component, and then a reference current instruction value is obtained through low-pass filtering; performing low-pass filtering on the active current component and the reactive current component to obtain a system side current component as a reference value; comparing each separated harmonic current component with a reference value, and inputting the current components to a fuzzy PI controller to obtain voltage compensation instructions of the characteristic harmonic waves under a d axis and a q axis respectively; and superposing each compensation instruction and the original reactive compensation and direct-current voltage control instruction of the STATCOM, and then inputting PWM (Pulse Width Modulation) to enable the STATCOM to output current containing a characteristic harmonic compensation component. According to the method, multi-synchronous rotating coordinate system detection and fuzzy PI adaptive control are introduced, and dynamic and accurate compensation of multiple characteristic harmonics is realized on the premise of not changing the main circuit topology of the STATCOM.

Description

Technical Field

[0001] This invention belongs to the field of power system power quality management technology, specifically involving a characteristic harmonic compensation method based on an improved STATCOM, used for the suppression and compensation of characteristic harmonics in high-voltage DC converter stations. Background Technology

[0002] High-voltage direct current (HVDC) transmission systems play a crucial and irreplaceable role in the transmission and distribution of electrical energy in scenarios such as large-capacity transmission, long-distance transmission, and asynchronous grid interconnection. They are a vital supporting technology in modern power systems. However, the core equipment of these systems, converter stations, generate a significant number of characteristic subharmonics during actual operation, commonly including the 5th, 7th, 11th, and 13th harmonics. These harmonics can cause distortion of the grid's bus voltage, posing a serious threat to the safe and stable operation of various devices connected to the grid.

[0003] In traditional harmonic mitigation, the main approach relies on passive filters. While these devices are simple in structure and low in cost, their filtering performance is significantly affected by the system impedance characteristics. Switching passive filters can even cause parallel resonance between the filter and the system background impedance, which can amplify specific harmonic voltages.

[0004] Static Synchronous Compensators (STATCOMs), as flexible AC transmission devices based on fully controlled power devices, are renowned for their rapid reactive power regulation and voltage support capabilities. Their classic control strategies primarily revolve around the fundamental component design, with dynamic reactive power compensation as the core objective. The academic community has made valuable explorations in applying STATCOMs to harmonic suppression, laying the foundation for this research. Building upon this foundation, we further explore a characteristic harmonic compensation method based on an improved STATCOM, aiming to enhance the comprehensive harmonic mitigation performance of STATCOMs under complex power grid conditions. Summary of the Invention

[0005] This invention provides a characteristic harmonic compensation method based on an improved STATCOM. This method introduces multi-synchronous rotating coordinate system detection technology and fuzzy PI adaptive control to achieve dynamic and accurate compensation of multiple characteristic harmonics without changing the STATCOM main circuit topology.

[0006] The technical solution adopted in this invention is as follows: The characteristic harmonic compensation method based on the improved STATCOM is characterized by the following steps: Step 1: Real-time acquisition of three-phase current signals from the power grid system side i abc Load current i Labc Grid voltage U s ; Step 2: Extract the grid voltage U s The frequency information is obtained. h The reference phase and frequency of the subharmonic; the load current i Labc pass C abc-dqh The transformation matrix module is converted to the dq coordinate system and decomposed into the load active current components. i Ldh and load reactive current component i Lqh The reference current command value is then obtained after low-pass filtering. i dhref and i qhref ; Step 3: Extract the three-phase current signal from the power grid system side i abc middle h Sub-characteristic harmonic current and through C abc-dqh The change matrix module obtains the active current component. i dh0 and reactive current components i qh0 The system-side current component is obtained after low-pass filtering. i dh and i qh As a reference value; Step 4: Compare the separated harmonic current components with the reference values ​​and input them to the fuzzy PI controller to obtain the voltage compensation commands Δ for the characteristic harmonics on the d-axis and q-axis, respectively. U dh and Δ U qh ; Step 5: Transfer each voltage compensation command Δ U dh and Δ U qh pass C dqh-abc The inverse transformation matrix is ​​used to transform back to the abc three-phase stationary coordinate system, and the compensation commands for each step are obtained. U href ; Step 6: Send each compensation instruction Uhref Compared to the existing reactive power compensation and DC voltage control commands of STATCOM U ref The superimposed input PWM modulation drives the power switching device of the STATCOM, causing the STATCOM to output a current containing characteristic harmonic compensation components.

[0007] In step 1, the three-phase current signal from the power grid system side is acquired. i abc Three-phase load current i Labc Grid voltage U s ,like Figure 1 As shown.

[0008] In step 2, the h The second harmonics include the 5th, 7th, 11th, and 13th characteristic harmonics. Among them, the 5th and 11th harmonics are negative sequence harmonics, and a negative rotation angle is used for coordinate transformation, i.e., the rotation angle is - ; The 7th and 13th harmonics are positive sequence harmonics, and a positive rotation angle is used for coordinate transformation, i.e., the rotation angle is + ; The h The reference phase and frequency of the subharmonics are extracted from the grid voltage by a phase-locked loop (PLL) to obtain the fundamental phase. θ And obtained through frequency multiplication θ h = h*θ The frequency is f h =h*f 1, of which: θ h This represents the reference phase angle of the h-th harmonic in the synchronous rotating coordinate system. h For harmonic order, f 1 represents the fundamental frequency of the grid voltage.

[0009] In step 2, C abc-dqh The change matrix module is specifically as follows: (1); In formula (1): h For harmonic order, ω ω is the fundamental angular frequency.

[0010] load current i Labc pass C abc-dqh The transformation matrix module transforms the coordinates to the dq coordinate system, resulting in...i Ldh and i Lqh Specifically: (2); In formula (2): , , Indicates load current i Labc The currents in phases a, b, and c respectively.

[0011] Then it passes through a low-pass filter (LPF) to obtain i dhref 、i qhref This is used as a reference for subsequent harmonic compensation.

[0012] In step 3, the three-phase current signal of the power grid system side is extracted. i abc middle h The active and reactive current components of the sub-characteristic harmonic current will pass the system current through the same C abc-dqh The transformation matrix is ​​used to convert to the dq coordinate system of the corresponding harmonic, specifically as follows: (3); In formula (3): express Active current component of subharmonics correspond Subharmonic reactive current component; , , Indicates the three-phase current signal on the power grid system side i abc The currents in phases a, b, and c respectively.

[0013] Then and After filtering out high-frequency fluctuations during the transformation process using a low-pass filter, a current component that can be used for reference is obtained. i dh and i qh .

[0014] In step 4, the separated harmonic current components are compared with reference values, specifically: (4); In equation (4): , These represent the harmonic current errors of the h-th characteristic harmonic on the d-axis and q-axis, respectively. , These represent the reference current commands for the h-th characteristic harmonic on the d-axis and q-axis, respectively. and respectively compared with the corresponding rate of change The input is fed into a fuzzy PI controller to obtain voltage compensation commands for the characteristic harmonics on the d-axis and q-axis, respectively. U dh and U qh ; Among them, the fuzzy PI controller uses harmonic current error e ( t ) and its rate of change ε ( t As input, the proportional gain is output through the fuzzy rule base. K p and integral gain K i Adjustment amount K p , K i This enables adaptive tuning of the controller parameters. Wherein: (5); The final actual parameters of the fuzzy PI controller are: (6); (7); In the formula: K p0 , K i0 The input is the initial value obtained by traditional PI tuning.

[0015] The design principles of the fuzzy rule base are shown in Table 1:

[0016] When error e With error change rate ε When both are large, the output is larger. K p and K i To accelerate response; When error e Smaller error change rate ε When the value is large, the output is small. K p and K i To prevent overshoot; When error e Larger error change rate ε When it is smaller, it mainly increases K i To eliminate steady-state error; When error e With error change rate ε When both are small, the output is smaller. K p and K i In order to maintain stability.

[0017] In step 5 C dqh-abc The inverse transformation matrix is: (8); U dh and U qh pass C dqh-abc The inverse transformation matrix is ​​used to transform back to the abc three-phase stationary coordinate system to obtain the compensation command. U href Specifically: (9); In equation (9): U dh and U qh This indicates voltage compensation commands on the d-axis and q-axis.

[0018] In step 6, the two signals are superimposed and then used to generate a drive pulse through a PWM modulator to control the on and off of the fully controlled power devices in the STATCOM, thereby achieving dynamic compensation for characteristic harmonics while retaining the original dynamic reactive power compensation function of the STATCOM.

[0019] This invention discloses a characteristic harmonic compensation method based on an improved STATCOM, with the following technical advantages: 1) This invention, through innovative upgrades to the control algorithm, enables STATCOM to maintain excellent dynamic reactive power compensation performance while integrating comprehensive suppression capabilities of multiple characteristic harmonics, thereby improving equipment efficiency.

[0020] 2) This invention achieves effective separation of characteristic harmonics by accurately transforming multiple synchronous rotating coordinate systems. Combined with the parameter adaptive characteristics of the fuzzy PI controller, the system can quickly track and accurately compensate for characteristic harmonics of different orders and varying amplitudes, and can adapt to complex power grid operating conditions.

[0021] 3) This invention has a clear structure and a high degree of modularity, allowing it to be seamlessly embedded into existing STATCOM control systems as an independent functional unit. This facilitates technical improvements without requiring large-scale modifications to the main circuit and existing control system, reducing the complexity and cost of engineering applications and improving reliability. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and examples; Figure 1 This is a diagram of the STATCOM system architecture.

[0023] Figure 2 Diagram of the improved STATCOM control strategy.

[0024] Figure 3 This is a structural diagram of a fuzzy PI controller.

[0025] Figure 4 The waveform diagram of the bus current before compensation.

[0026] Figure 5 The waveform of the bus current after compensation.

[0027] Figure 6 A diagram illustrating the proportion of each harmonic before and after compensation. Detailed Implementation

[0028] Example: Figure 1 The diagram shows the basic components upon which this invention is based, as well as the positions of the voltages and currents involved in the structure.

[0029] Figure 2 To improve the STATCOM control strategy diagram, the implementation method of multi-synchronous rotating coordinate system transformation is demonstrated. In actual implementation, based on this principle, the 5th, 7th, 11th, and 13th characteristic harmonics are detected in parallel. The fundamental phase is extracted through a phase-locked loop, and rotating reference phases for each harmonic are generated. The integration relationship between the characteristic harmonic compensation module and the traditional control system is shown. In specific implementation, the harmonic compensation command and the basic control command are superimposed at this stage to form a comprehensive modulation signal.

[0030] Figure 3The diagram shows the structure of the fuzzy PI controller, illustrating its input and output structure. During implementation, the controller parameters were adaptively tuned based on this rule base. When a harmonic current error and its rate of change are detected to be large, the control gain is automatically increased to accelerate the response.

[0031] Figures 4-6 Together they demonstrated the harmonic compensation effect. Figure 4 To compensate for the voltage waveform at the front bus, significant voltage distortion is observed. Figure 5 The voltage waveform after compensation using the method of this invention shows that the voltage sinusoidality is significantly improved. Figure 6 This document compares the harmonic content before and after harmonic compensation. PSCAD simulations verified that after implementing the control strategy of this invention, the 5th harmonic voltage content decreased from 4.82% to 1.45%, the 7th harmonic from 2.13% to 0.89%, the 11th harmonic from 1.67% to 0.72%, and the 13th harmonic from 1.25% to 0.58%, with the total harmonic distortion rate decreasing from 6.35% to 2.81%. Simultaneously, the DC-side voltage fluctuation of the STATCOM remained consistently within ±2% of the rated value, demonstrating that this invention effectively improves the system's harmonic suppression capability while maintaining its original performance.

Claims

1. A characteristic harmonic compensation method based on improved STATCOM, characterized in that... Includes the following steps: Step 1: Real-time acquisition of three-phase current signals from the power grid system side i abc Load current i Labc Grid voltage U s ; Step 2: Extract the grid voltage U s The frequency information is obtained. h The reference phase and frequency of the subharmonic; the load current i Labc pass C abc-dqh The transformation matrix module is converted to the dq coordinate system and decomposed into the load active current components. i Ldh and load reactive current component i Lqh The reference current command value is then obtained after low-pass filtering. i dhref and i qhref ; Step 3: Extract the three-phase current signal from the power grid system side i abc middle h Sub-characteristic harmonic current and through C abc-dqh The change matrix module obtains the active current component. i dh0 and reactive current components i qh0 The system-side current component is obtained after low-pass filtering. i dh and i qh As a reference value; Step 4: Compare the separated harmonic current components with the reference values ​​and input them to the fuzzy PI controller to obtain the voltage compensation commands for the characteristic harmonics on the d-axis and q-axis, respectively. U dh and U qh ; Step 5: Transfer each voltage compensation command U dh and U qh pass C dqh-abc The inverse transformation matrix is ​​used to transform back to the abc three-phase stationary coordinate system, and the compensation commands for each step are obtained. U href ; Step 6: Send each compensation instruction U href Compared to the existing reactive power compensation and DC voltage control commands of STATCOM U ref The superimposed input PWM modulation drives the power switching device of the STATCOM, causing the STATCOM to output a current containing characteristic harmonic compensation components.

2. The characteristic harmonic compensation method based on the improved STATCOM according to claim 1, characterized in that: In step 2, the h The second harmonics include the 5th, 7th, 11th, and 13th characteristic harmonics. Among them, the 5th and 11th harmonics are negative sequence harmonics, and a negative rotation angle is used for coordinate transformation, i.e., the rotation angle is - The 7th and 13th harmonics are positive sequence harmonics, and a positive rotation angle is used for coordinate transformation, i.e., the rotation angle is + .

3. The characteristic harmonic compensation method based on the improved STATCOM according to claim 2, characterized in that: h The reference phase and frequency of the subharmonics are extracted from the grid voltage by a phase-locked loop (PLL) to determine the fundamental phase. θ And obtained through frequency multiplication θ h = h*θ The frequency is f h =h*f 1, of which: θ h This represents the reference phase angle of the h-th harmonic in the synchronous rotating coordinate system. h For harmonic order, f 1 represents the fundamental frequency of the grid voltage.

4. The characteristic harmonic compensation method based on the improved STATCOM according to claim 3, characterized in that: In step 2, C abc-dqh The change matrix module is specifically as follows: （1）； In formula (1): h For harmonic order, ω The fundamental angular frequency; load current i Labc pass C abc-dqh The transformation matrix module transforms the coordinates to the dq coordinate system, resulting in... i Ldh and i Lqh Specifically: （2）； In formula (2): , , Indicates load current i Labc The currents in phases a, b, and c respectively; After passing through a low-pass filter (LPF), the result is... i dhref 、i qhref This is used as a reference for subsequent harmonic compensation.

5. The characteristic harmonic compensation method based on the improved STATCOM according to claim 4, characterized in that: In step 3, the three-phase current signal of the power grid system side is extracted. i abc middle h The active and reactive current components of the sub-characteristic harmonic current will pass the system current through the same C abc-dqh The transformation matrix is ​​used to convert to the dq coordinate system of the corresponding harmonic, specifically as follows: （3）； In formula (3): express Active current component of subharmonics correspond Subharmonic reactive current component; , , Indicates the three-phase current signal on the power grid system side i abc The currents in phases a, b, and c respectively; Then and After filtering out high-frequency fluctuations during the transformation process using a low-pass filter, a current component that can be used for reference is obtained. i dh and i qh .

6. The characteristic harmonic compensation method based on the improved STATCOM according to claim 5, characterized in that: In step 4, the separated harmonic current components are compared with reference values, specifically: （4）； In equation (4): , These represent the harmonic current errors of the h-th characteristic harmonic on the d-axis and q-axis, respectively. , These represent the reference current commands for the h-th characteristic harmonic on the d-axis and q-axis, respectively. and respectively compared with the corresponding rate of change The input is fed into a fuzzy PI controller to obtain voltage compensation commands for the characteristic harmonics on the d-axis and q-axis, respectively. U dh and U qh .

7. The characteristic harmonic compensation method based on the improved STATCOM according to claim 6, characterized in that: Fuzzy PI controller with harmonic current error e ( t ) and its rate of change ε ( t As input, the proportional gain is output through the fuzzy rule base. K p and integral gain K i Adjustment amount K p , K i This enables adaptive tuning of the controller parameters; where: （5）； The final actual parameters of the fuzzy PI controller are: （6）； （7）； In the formula: K p0 , K i0 The input is the initial value obtained by traditional PI tuning.

8. The characteristic harmonic compensation method based on the improved STATCOM according to claim 6, characterized in that: When error e With error change rate ε When both are large, the output is larger. K p and K i To accelerate response; When error e Smaller error change rate ε When the value is large, the output is small. K p and K i To prevent overshoot; When error e Larger error change rate ε When it is smaller, it mainly increases K i To eliminate steady-state error; When error e With error change rate ε When both are small, the output is smaller. K p and K i In order to maintain stability.

9. The characteristic harmonic compensation method based on the improved STATCOM according to claim 8, characterized in that: In step 5 C dqh-abc The inverse transformation matrix is: （8）； U dh and U qh pass C dqh-abc The inverse transformation matrix is ​​used to transform back to the abc three-phase stationary coordinate system to obtain the compensation command. U href Specifically: （9）； In equation (9): U dh and U qh This indicates voltage compensation commands on the d-axis and q-axis.

10. The characteristic harmonic compensation method based on the improved STATCOM according to claim 9, characterized in that: In step 6, the two signals are superimposed and then used to generate a drive pulse through a PWM modulator to control the on and off of the fully controlled power devices in the STATCOM, thereby achieving dynamic compensation for characteristic harmonics while retaining the original dynamic reactive power compensation function of the STATCOM.

Images