A method and apparatus for controlling the voltage regulation gain of an active power filter (APF)

Abstract

The application discloses a voltage regulation gain control method and device of an active filter (APF), and comprises the following steps: in the operation process of the APF, a gain monitor and a gain optimizer are used to monitor the state of an APF voltage regulator respectively; the gain monitor detects the oscillation of the voltage regulator through filtering, level detection and pulse discrimination on the voltage regulation output of the APF, and the gain of the APF voltage regulator is adjusted until the oscillation disappears; the gain optimizer optimizes the gain of the APF voltage regulator according to the short-circuit capacity before the gain adjustment, so that the gain monitor adjusts according to the gain, and the gain optimizer uses the slope compensation coefficient mode to keep the gain calculation unchanged under different slopes, and still uses the calculation method in linear relationship with the short-circuit capacity to calculate the gain. The application can realize the optimization of the gain calculated by the short-circuit capacity, and the gain calculated in the slope mode is suitable for the control under different slopes, can effectively and accurately control the oscillation of the APF, and optimizes the control parameters of the APF.

Description

Technical Field

[0001] This invention relates to the control of power equipment, and in particular to a method and apparatus for voltage regulation gain control of an active power filter (APF). Background Technology

[0002] Active power filters (APFs) use power electronic converters to compensate for harmonic currents. Compared with passive filters, they have advantages such as better real-time compensation, faster dynamic response, and less likelihood of resonance with the power grid. They are applied in LCC-HVDC converter station scenarios to replace fixed harmonic compensation devices or work in conjunction with fixed harmonic compensation devices to dynamically filter harmonics in the converter station in real time, and to provide dynamic reactive power compensation for the converter station. They can simultaneously solve problems such as frequent switching of high-voltage filters and frequent switching of low-voltage reactors caused by power fluctuations in the converter station and AC system voltage fluctuations.

[0003] An APF (Automatic Power Regulator) possesses voltage control capabilities. In practical engineering applications, to ensure stable control of high-voltage, high-capacity APFs, the gain of its voltage regulator often needs to be optimized based on weaker system short-circuit capacities or the most severe anticipated fault conditions to ensure a fast and stable response under these operating conditions. However, when APFs are applied to converter stations with large-scale renewable energy integration, the system short-circuit capacity varies greatly. If the APF voltage regulator gain remains constant, the APF response will become very slow when the system short-circuit capacity becomes very large. However, the system's fundamental reactive power voltage control requirements always necessitate that the APF have fast response characteristics across all variations in system short-circuit capacity. Therefore, the APF voltage regulator gain needs to be appropriately adjusted for different system short-circuit capacities to achieve optimal response characteristics. In existing technologies, the APF voltage regulator gain cannot be appropriately adjusted for different system short-circuit capacities. Summary of the Invention

[0004] In view of this, the present invention provides a voltage regulation gain control method and apparatus for an active power filter (APF) to solve the problem that the gain of the APF voltage regulator cannot be properly adjusted when the system short-circuit capacity is different.

[0005] To address the above problems, this invention provides a voltage regulation gain control method for an active power filter (APF), comprising:

[0006] During the operation of the APF, a gain monitor and a gain optimizer are used to monitor the status of the APF voltage regulator.

[0007] The gain monitor determines the oscillation of the voltage regulator by filtering, level detection, and pulse discrimination of the APF voltage regulation output. It then adjusts the gain of the APF voltage regulator by using a slope compensation coefficient until the oscillation disappears.

[0008] Before the gain adjustment, the gain optimizer optimizes the gain of the APF voltage regulator based on the short-circuit capacity, so that the gain monitor adjusts according to this gain.

[0009] The gain optimizer uses a slope compensation coefficient to keep the gain calculation constant under different slopes, and the gain can still be calculated using a calculation method that is linearly related to the short-circuit capacity.

[0010] Preferably, the gain K of the APF voltage regulator is adjusted using a slope compensation coefficient. G ,include:

[0011] Using formula Determine the gain K G

[0012] Where S is the system short-circuit capacity, S min K is the minimum short-circuit capacity of the system. min K represents the APF voltage regulator gain value corresponding to the system's minimum short-circuit capacity. slope This is the slope compensation coefficient;

[0013] Where U is the rated voltage of the APF voltage control point, sl ope is the slope, representing the ratio of voltage fluctuation to capacitance fluctuation when the system load changes, and S is the system short-circuit capacity.

[0014] Preferably, during the process of determining the oscillation of the voltage regulator, the filtering process includes:

[0015] A bandpass filter is used, and the center frequency is tuned to the frequency value of the APF voltage controller in unstable mode to distinguish oscillations caused by excessive APF voltage regulator gain.

[0016] Preferably, during the process of determining the oscillation of the voltage regulator, the process of level detection and pulse identification includes:

[0017] By comparing the output of the DC blocking function with a preset value, a pulse signal is output that confirms the presence of oscillation.

[0018] If the number of pulse signals exceeds the threshold, the gain of the APF voltage controller is reduced until the oscillation disappears.

[0019] Preferably, the gain optimizer optimizes the gain of the APF voltage regulator based on the short-circuit capacity before the gain adjustment, including:

[0020] The calculated value of the short-circuit capacity after the reactive power output of the APF changes is used by the gain monitor to adjust the gain of the APF voltage regulator. The calculated value is the average value of multiple step changes.

[0021] Embodiments of the present invention also provide a voltage regulation gain control device for an active power filter (APF), which has a processor for executing the above-described method steps. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating the principle of an embodiment;

[0023] Figure 2 This is a flowchart of an embodiment;

[0024] Figure 3 This is a flowchart of the gain control in the embodiment;

[0025] Figure 4 This is a schematic diagram illustrating the principle of slope control in the embodiment. Detailed Implementation

[0026] To clearly illustrate the solutions in this invention, preferred embodiments are given below and described in detail with reference to the accompanying drawings.

[0027] The flowchart of the embodiments of the present invention can be referred to. Figure 2 This includes the following steps:

[0028] S11: During the operation of the APF, a gain monitor and a gain optimizer are used to monitor the status of the APF voltage regulator, respectively.

[0029] S12: The gain monitor determines the oscillation of the voltage regulator by filtering, level detection, and pulse discrimination of the voltage regulation output of the APF, and adjusts the gain of the APF voltage regulator by using a slope compensation coefficient until the oscillation disappears;

[0030] S13: Before the gain adjustment, the gain optimizer optimizes the gain of the APF voltage regulator according to the short-circuit capacity, so that the gain monitor adjusts according to this gain.

[0031] The gain optimizer uses a slope compensation coefficient to keep the gain calculation constant under different slopes, and the gain can still be calculated using a calculation method that is linearly related to the short-circuit capacity.

[0032] Through the above steps, the present invention can achieve gain optimization using short-circuit capacity and gain calculated in the form of slope, applicable to control under different slopes, and can effectively and accurately control the oscillation of APF power and optimize APF control parameters.

[0033] In the embodiments, the principle of the voltage regulation gain control method of the active filter (APF) of the present invention is as follows: Figure 1 As shown, it consists of an APF voltage regulator, a gain monitor, and a gain optimizer. The gain monitor is used to monitor for continuous oscillations caused by excessive gain of the APF voltage regulator; the gain optimizer is activated at an appropriate time to obtain the optimal gain of the APF voltage regulator.

[0034] Specifically, during APF operation, the gain monitor continuously monitors the output of the APF voltage regulator to check for persistent oscillations caused by excessive gain in the APF voltage regulator. Such oscillations occur when the system short-circuit capacity decreases while the APF voltage regulator remains operating at high gain. If the gain monitor detects oscillations in the APF voltage regulator output, it reduces the APF voltage regulator gain until the oscillations disappear.

[0035] The gain optimizer is activated at an appropriate time during the operation of the APF voltage regulator, such as when certain triggering conditions are met, for example:

[0036] 1) After system transient fault recovery; 2) After gain control action; 3) After voltage negative sequence content reaches the set value and recovers; 4) After APF shutdown and restart, wait for a period of time, such as 10 hours; 5) Manual start-up.

[0037] The following conditions must be met simultaneously for gain optimization to start: 1) The system voltage is within a reasonable range (0.95pu-1.05pu); 2) The system frequency is within a reasonable range (49.5Hz-50.5Hz); 3) The negative sequence content of the system voltage is within the normal range (less than 2%).

[0038] The process of determining the gain in this invention includes: applying a short-term voltage step to the reference voltage of the APF voltage regulator; calculating the system short-circuit capacity by monitoring the reactive power change of the APF voltage regulator and the system voltage change; compensating the gain optimizer algorithm for the presence of other voltage regulation devices in the system to ensure that the gain optimizer calculation is correct; and finally determining the optimal gain of the APF voltage regulator based on the system short-circuit capacity.

[0039] The gain monitor consists of a filtering stage, a level detection stage, a pulse discrimination stage, and a gain control stage, such as... Figure 3As shown. Gain monitoring is completed through the following four steps. Each step is explained in detail below:

[0040] The filtering stage includes step S101, which distinguishes between oscillations caused by excessive gain of the APF voltage regulator and oscillations caused by other reasons.

[0041] The filtering stage uses a bandpass filter, and its transfer function formula 1 is as follows:

[0042]

[0043] In the formula, ω0 is the center angular frequency of the bandpass filter, Q is the quality factor of the bandpass filter, the larger the Q value, the narrower the bandwidth of the bandpass filter, and A(ω0) is the gain of the bandpass filter at the center angular frequency.

[0044] The center frequency is tuned to the frequency value of the APF voltage regulator in unstable mode, generally between 5Hz and 50Hz, to distinguish between oscillations caused by excessive APF voltage regulator gain and oscillations caused by other reasons, so that the gain monitor only responds to oscillations caused by excessive gain, and does not cause the APF gain to decrease due to other system instability.

[0045] Step S102: The level detection circuit compares the output of the filtering circuit with a preset value to determine whether there is oscillation;

[0046] The level detection stage consists of a DC blocking stage and a comparison stage. The DC blocking stage is used to avoid the influence of the DC component after a voltage step on the level detection stage. The transfer function formula 2 for the DC blocking stage is as follows:

[0047]

[0048] T1 is the DC blocking time constant.

[0049] The comparison stage compares the output of the DC blocking stage with a preset small value (e.g., 0.01 pu) to determine if oscillation exists. If the output of the DC blocking stage is greater than the preset level value, it outputs 1; if the output of the filtering stage is less than the preset level value, it outputs 0.

[0050] Step S103: The pulse discrimination step is used to eliminate certain erroneous pulses emitted by the level detection step. If a sudden step change occurs in the system voltage, causing a sudden change in the output of the APF voltage regulator, the level detection step will output a pulse. The pulse discrimination step adds a set time interval. If the pulse still exists after the time interval, it is considered that oscillation has indeed occurred, thus avoiding unnecessary reduction in the gain of the APF voltage regulator. Specifically, the pulse discrimination step performs zero-crossing judgment on the output of the level detection step and continuously records the time of N consecutive zero-crossings, such as 5 (or more) times. It compares the 5 zero-crossing times with a set time. If all 5 zero-crossing times meet the condition (less than the set time), it is judged that oscillation has occurred and outputs 1; if the 5 zero-crossing times do not meet the condition (less than the set time), it outputs 0.

[0051] Step S104: The gain control circuit continuously adjusts the gain of the APF voltage regulator based on the pulse emitted by the pulse discrimination circuit to eliminate system oscillations caused by excessive APF voltage regulator gain until the oscillations disappear. Specifically, the gain control circuit determines whether to reduce the APF voltage regulator gain based on the output of the pulse discrimination circuit. If the pulse discrimination circuit outputs 1, the gain of the APF voltage regulator is linearly reduced until the oscillations disappear; if the pulse discrimination circuit outputs 0, the current gain is maintained.

[0052] In the gain control process described above, the gain optimizer also participates in gain control. The gain optimizer consists of two parts: a pulse generation stage and a measurement and calculation stage. The pulse generation stage determines the activation conditions of the gain optimizer and, upon meeting these conditions, issues a voltage step pulse to initiate measurement. In practical applications, the gain optimizer typically activates once every few tens of hours in steady state, or once after a system transient occurs. Activation requires certain system conditions to be met, such as a system voltage within the range of 0.95 pu to 1.05 pu, a system frequency within the range of 49.5 Hz to 50.5 Hz, and a negative sequence voltage content below 2%. The measurement and calculation stage calculates the system short-circuit capacity based on the reactive power change and voltage change of the APF (Average Power Regulator), and optimizes the gain value of the APF voltage regulator based on the short-circuit capacity.

[0053] Specifically, the pulse generation stage includes gain optimization trigger conditions and gain optimization start conditions. These are designed to ensure that short-circuit capacity calculations are performed when the system needs to adjust the gain, while minimizing the number of short-circuit capacity calculations and reducing the impact on the system. The gain optimization trigger condition is activated when one of the following conditions is met: 1) after a system transient fault is recovered; 2) after gain control is activated; 3) after the negative voltage sequence reaches a set value and recovers; 4) after the APF is restarted from a shutdown, for a period of time; 5) manual startup. The gain optimization start condition is activated when the following conditions are met simultaneously: 1) the system voltage is within a reasonable range (0.95 pu-1.05 pu); 2) the system frequency is within a reasonable range (49.5 Hz-50.5 Hz); 3) the negative voltage sequence is within a normal range (less than 2%). When one or more of the gain optimization trigger conditions are met, and the gain optimization start condition is also met, the pulse generation stage will emit a small voltage step pulse (0.002 pu or less) to the target voltage value, causing a small voltage step in the target voltage value. After the pulse generation stage generates a voltage step pulse, it measures the APF voltage change ΔUsvc and the reactive power change ΔQsvc, calculates the system short-circuit capacity S according to the following formula, and linearly adjusts the gain K of the APF voltage regulator. G .

[0054]

[0055]

[0056] Where: S is the system short-circuit capacity, ΔQ SVC Let ΔU be the change in reactive power of APF. SVC U represents the change in APF voltage. PCC The rated voltage at the point of common coupling. min K is the minimum short-circuit capacity of the system. min Kslope is the APF voltage regulator gain value corresponding to the minimum short-circuit capacity of the system, and Kslope is the slope compensation coefficient.

[0057] With a fixed slope, the gain and system short-circuit capacity are approximately linearly related. A larger short-circuit capacity corresponds to a larger gain, resulting in better regulation. Conversely, a smaller short-circuit capacity corresponds to a smaller gain, preventing APF regulation oscillations caused by excessive gain. However, with the addition of a slope, the relationship between gain and system short-circuit capacity is no longer linear. Under the same short-circuit capacity, a larger slope can lead to instability in APF regulation. This invention addresses this by adding a slope compensation coefficient, ensuring that the gain calculation still follows a linear relationship based on changes in short-circuit capacity, thus guaranteeing accurate gain calculation.

[0058] The slope compensation coefficient Kslope here enables the gain to be automatically corrected under different slopes, achieving more accurate gain compensation.

[0059] See Figure 4 , Figure 4 The diagram shows that the system has two system load lines, namely system load line A and system load line B.

[0060] U1 is the initial operating point; U3 is the voltage without APF (Dynamic Var Compensator) regulation when the system load line changes from system-load line A to system-load line B due to system changes; U2 is the voltage after regulation by APF (Dynamic Var Compensator) according to the APF slope regulation characteristics when the system load line changes from system-load line A to system-load line B due to system changes.

[0061] The currents corresponding to U1 and U3 can be understood as the initial current IQR. Without APF regulation, there is no reactive power regulation, and the system voltage changes from U1 to U3. The current IC1 corresponding to U2 is the current after APF regulation. The APF current becomes (IC1-IQR), which regulates the system voltage from U3 to U2.

[0062] IC represents capacitive current, and IL represents inductive current.

[0063] The voltage U' at any point on the system load line A: U' = U1 - I × X L I represents the compensation current, and the impedance value is X. L ΔI is (IC1-IQR), positive for inductive compensation IL, negative for capacitive compensation IC;

[0064] Wherein, impedance X L The calculation is as follows:

[0065] Let the system short-circuit capacity be S, then the impedance value is X. L (U is the rated voltage of the APF voltage control point);

[0066] When the system voltage changes, the system load line changes from system load line A to system load line B. The voltage first jumps from U1 to U3, and after APF compensation, the voltage is compensated back to the U2 position point.

[0067] When the slope is zero, the voltage at point U1 is the same as the voltage at point U2, and the voltage that APF needs to compensate for is ΔU = U. 13 When the slope is not zero, the voltage at point U1 is different from the voltage at point U2. After compensation, the system voltage returns to U1. 2， The voltage that the APF needs to compensate for is ΔU = U 23 However, the voltage difference detected by the APF is still U. 13U 13 >U 23 If U 13 The control is based on the voltage difference. When the slope is large, it may cause control instability. In the case of gain control, the voltage deviation needs to be compensated to obtain stable control characteristics.

[0068] The embodiments of the present invention innovatively introduce the definition of slope;

[0069] After eliminating parameter ΔI, the following is obtained

[0070] also, It can be deduced S represents the system short-circuit capacity.

[0071] therefore

[0072] Thus, U is obtained 23 with U 13 The relationship is

[0073]

[0074] (When slope = 0, Kslope = 1)

[0075] Based on the above formula, it can be concluded that when using an APF and compensating through a voltage controller, accurate compensation can be achieved, thereby preventing sudden oscillations in the system to the greatest extent.

[0076] Embodiments of the present invention also provide an apparatus that employs a computer device and has a processor. When the code is running, the above-described method flow can be implemented to control the APF to compensate the power grid.

[0077] Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention for the solutions described in the various embodiments of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of controlling voltage regulation gain of an active power filter (APF), characterized by, include: During the operation of the APF, a gain monitor and a gain optimizer are used to monitor the status of the APF voltage regulator. The gain monitor determines the oscillation of the voltage regulator by filtering, level detection, and pulse discrimination of the APF voltage regulation output. It then adjusts the gain of the APF voltage regulator by using a slope compensation coefficient until the oscillation disappears. The gain optimizer optimizes the gain of the APF voltage regulator according to the short-circuit capacity before the gain adjustment, and the gain monitor adjusts the gain of the APF voltage regulator in a manner of slope compensation coefficient according to the gain comprising: using the formula determining the gain Wherein, S is the system short-circuit capacity, Smin is the minimum short-circuit capacity of the system, K is the APF voltage regulator gain value corresponding to the minimum short-circuit capacity of the system, slope K is the slope compensation coefficient; where U is the rated voltage of the APF voltage control point, slope is the slope indicating the ratio of voltage fluctuation to capacitance fluctuation when the system load changes, and S is the system short-circuit capacity.

2. The voltage regulation gain control method of claim 1, wherein, During the process of determining the oscillation of the voltage regulator, the filtering process includes: A bandpass filter is used, and the center frequency is tuned to the frequency value of the APF voltage controller in unstable mode to distinguish oscillations caused by excessive APF voltage regulator gain.

3. The voltage regulation gain control method of claim 1, wherein, During the process of determining the oscillation of the voltage regulator, the level detection and pulse identification process includes: By comparing the output of the DC blocking function with a preset value, a pulse signal is output that confirms the presence of oscillation. If the number of pulse signals exceeds the threshold, the gain of the APF voltage controller is reduced until the oscillation disappears.

4. The voltage regulation gain control method of claim 1, wherein, The gain optimizer optimizes the gain of the APF voltage regulator based on the short-circuit capacity before the gain adjustment, including: The calculated value of the short-circuit capacity after the reactive power output of the APF changes is used by the gain monitor to adjust the gain of the APF voltage regulator. The calculated value is the average value of multiple step changes.

5. A voltage regulation gain control device for an active power filter (APF), comprising a processor for executing the method steps of any one of claims 1 to 4.

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