Overvoltage suppression control method and suppressor

Abstract

The invention discloses an overvoltage suppression control method and suppressor based on instantaneous power, and the method comprises the steps: monitoring the voltage of a feeder line in real time, and starting a voltage source converter when the voltage of the feeder line is detected to be abnormal; converting the three-phase voltage and the three-phase current into alpha-beta coordinate system components through Clark conversion; calculating the oscillation component of the instantaneous real power and the total compensation amount of the instantaneous virtual power, and generating a compensation current instruction based on the oscillation component and the total compensation amount; and performing proportional-integral adjustment on the compensation current deviation to generate a modulation wave, comparing the modulation wave with a triangular carrier to generate a driving signal to output compensation current, and quitting operation when the voltage returns to normal. Meanwhile, the invention provides a suppressor hardware structure for realizing the method. According to the invention, low-amplitude overvoltage and capacitor failure rate can be accurately eliminated, and equipment loss is reduced.

Description

Technical Field

[0001] This invention relates to the field of power system overvoltage protection technology, and in particular to an overvoltage suppression control method and suppressor based on instantaneous power. Background Technology

[0002] With the continuous expansion of the power grid, the demand for reactive power compensation in high-voltage distribution networks is increasing, leading to a significant rise in the number of reactive power compensation capacitor banks. Therefore, the proper configuration and precise setting of parallel capacitor bank protection are crucial. When a capacitor in a line fails, the remaining capacitors may break down, triggering a vicious chain reaction. Given this, timely detection of internal component damage within the capacitors is a key aspect of ensuring their safe operation. Common fault types in parallel compensation capacitors include internal component failures, internal inter-electrode short-circuit faults, and internal or external electrode-to-casing (shell) short-circuit faults.

[0003] The fundamental principle of reactive power compensation in power systems is to achieve regional reactive power balance. Parallel capacitor banks, as commonly used reactive power compensation devices, are widely used in distribution network feeders. However, these parallel capacitor banks frequently fail, leading to increased feeder losses and affecting the reliability and power quality of power supply from the distribution network to users.

[0004] Therefore, in feeder reactive power compensation, there is an urgent need for a device that can reduce the failure rate of feeder reactive power compensation capacitors. Summary of the Invention

[0005] To address the problem that existing surge arresters cannot suppress sustained overvoltages with amplitudes below their operating thresholds, leading to damage to parallel capacitor banks, increased feeder line losses, and decreased power supply reliability, this invention proposes an overvoltage suppressor based on instantaneous power.

[0006] The specific technical solution is as follows: An overvoltage suppression control method, based on instantaneous power theory, includes:

[0007] Real-time monitoring of feeder voltage; when an abnormal feeder voltage is detected, the voltage source converter is activated.

[0008] The three-phase voltage and current are converted into αβ coordinate system components through Clark transformation;

[0009] Calculate the oscillation component of instantaneous real power and the total compensation amount of instantaneous virtual power, and generate a compensation current command based on the oscillation component and the total compensation amount;

[0010] The compensation current deviation is proportional-integral (PI) to generate a modulation wave, which is then compared with a triangular carrier wave to generate a drive signal to output the compensation current. Operation ceases once the voltage returns to normal. By real-time voltage monitoring, Clark transform to separate oscillation power, PI regulation of the deviation current, and comparison with the triangular carrier wave to output the compensation current, and by quickly exiting operation after voltage recovery, the system can accurately suppress low-amplitude sustained overvoltages while reducing equipment losses.

[0011] Furthermore, the command to generate the compensation current includes:

[0012] Calculate the real power current component and the imaginary power current component of the α-axis oscillation;

[0013] Calculate the real power current component and the imaginary power current component of the β-axis oscillation;

[0014] The sum of the negative values ​​of the four current components is used as the command value. By calculating the four current components along the α and β axes and superimposing their negative values, full compensation for harmonics and reactive components is achieved, keeping the power supply current sinusoidal.

[0015] Furthermore, the output compensation current includes:

[0016] Real-time acquisition of actual compensation current value, and calculation of the deviation between actual value and command value;

[0017] The deviation between the actual value and the command value is processed by a proportional-integral controller and a modulation signal is generated.

[0018] The modulated signal is compared with a triangular carrier wave to generate a drive signal. A process of real-time acquisition of current deviation, PI regulation, and generation of the modulated signal is employed to improve the accuracy of the compensation current tracking and reduce harmonic residual rate.

[0019] Furthermore, the generation of the drive signal includes:

[0020] When the modulation signal voltage is greater than the triangular carrier voltage, the upper bridge arm switch of the voltage source converter is turned on.

[0021] When the modulation signal voltage is less than the triangular carrier voltage, the lower bridge arm switch of the voltage source converter is turned on. Clearly define the comparison logic between the modulation wave and the carrier wave to ensure the accuracy of the PWM drive signal and reduce switching losses.

[0022] Furthermore, it also includes DC-side voltage control:

[0023] Detect the deviation between the actual value and the reference value of the DC-side capacitor voltage;

[0024] The deviation between the actual value and the reference value of the DC-side capacitor voltage is converted into an active current regulation quantity through a proportional-integral controller.

[0025] The active power regulation is superimposed on the fundamental active power component of the compensation current command. The active power regulation is generated by the DC voltage deviation and superimposed on the fundamental component to maintain DC side voltage stability and avoid compensation interruption.

[0026] Furthermore, the voltage reference value is greater than three times the peak value of the power supply phase voltage. Limiting the reference voltage to three times the peak value of the power supply phase voltage ensures the rapid tracking capability of the compensation current.

[0027] Furthermore, the Clark transform employs a power-invariant transform matrix:

[0028] A power-invariant Clark transformation matrix is ​​used to ensure energy conservation during coordinate transformation and improve calculation accuracy.

[0029] Furthermore, the calculation of the current components satisfies:

[0030]

[0031] The oscillation power can be separated and accurately compensated at the millisecond level by using a four-component current calculation formula.

[0032] An overvoltage suppressor for implementing an overvoltage suppression control method includes:

[0033] A voltage source converter, wherein the DC side of the voltage source converter is equipped with an energy storage capacitor;

[0034] Controller, the controller includes:

[0035] Voltage detection module: monitors feeder voltage;

[0036] Power processing module: performs Clark transformation and instantaneous power oscillation component separation;

[0037] Current control module: realizes proportional-integral adjustment of deviation current and triangular carrier comparison;

[0038] Switching control module: Starts up when voltage is abnormal and shuts down the converter after voltage recovery. Through the coordinated operation of four modules—voltage monitoring, power processing, current control, and switching control—the control method is implemented in hardware to ensure real-time overvoltage suppression.

[0039] Furthermore, the switching control module is configured to: trigger startup when a component failure, inter-electrode short circuit, or pole-to-shell short circuit is detected in the parallel capacitor bank; and trigger startup when the feeder voltage continuously exceeds 105% of the rated value.

[0040] The above technical solution has the following advantages or technical effects:

[0041] 1. This invention can accurately suppress low-amplitude overvoltages. By separating the oscillating power components through instantaneous power theory and combining the power invariance of Clark transform, it generates compensation current commands in real time, effectively eliminating low-amplitude continuous overvoltages that traditional surge arresters cannot protect against, and reducing capacitor failure rates.

[0042] 2. This invention can significantly reduce equipment losses. It adopts a short-time switching mechanism, which only starts when the voltage is abnormal and exits within 10ms after recovery. Compared with the long-term operation mode of traditional active filters, the equipment losses are lower.

[0043] 3. This invention can improve the accuracy of harmonic compensation. Based on the deviation current PI regulation and triangular carrier comparison, it drives the upper / lower bridge arm of the converter to move accurately, thereby reducing the tracking error of the compensation current and the harmonic distortion rate of the power supply current.

[0044] 4. This invention uses DC-side voltage PI control to superimpose the adjustment amount onto the fundamental active component, maintaining the capacitor voltage fluctuation range; combined with a 3 times peak voltage constraint design, it ensures rapid tracking of the compensation current under all operating conditions. Attached Figure Description

[0045] Figure 1 This is a flowchart of the method of the present invention;

[0046] Figure 2 This is the Clark transformation diagram from the abc coordinate system to the αβ coordinate system of this invention;

[0047] Figure 3 This is the Clark inverse transformation diagram from the αβ coordinate system to the abc coordinate system of this invention;

[0048] Figure 4 This is a schematic diagram of the overvoltage suppressor of the present invention;

[0049] Figure 5 This is a control block diagram of the instantaneous constant power control strategy of the present invention;

[0050] Figure 6 This is a control schematic diagram of the triangular wave comparison method of the present invention;

[0051] Figure 7 This is a schematic diagram of the PI control principle of this invention;

[0052] Figure 8 This is a circuit diagram of the instruction current calculation circuit for the DC-side voltage control stage of the present invention;

[0053] Figure 9 This is the equivalent circuit diagram of the power quality problem in the feeder system of the present invention;

[0054] Figure 10 This is the equivalent circuit diagram of the power quality management of the feeder system of the present invention. Detailed Implementation

[0055] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] Example 1

[0057] like Figure 1 As shown, an overvoltage suppression control method, based on instantaneous power theory, includes:

[0058] Real-time monitoring of feeder voltage; when an abnormal feeder voltage is detected, the voltage source converter is activated.

[0059] The three-phase voltage and current are converted into αβ coordinate system components through Clark transformation;

[0060] Calculate the oscillation component of instantaneous real power and the total compensation amount of instantaneous virtual power, and generate a compensation current command based on the oscillation component and the total compensation amount;

[0061] The proportional-integral adjustment of the compensation current deviation generates a modulation wave, which is then compared with a triangular carrier wave to generate a drive signal to output the compensation current. The operation stops when the voltage returns to normal.

[0062] When the feeder voltage is detected to be continuously exceeding the standard, such as when the parallel capacitor bank experiences component failure, inter-electrode short circuit, or pole-to-casing short circuit, the voltage source converter is activated. This mechanism is designed to handle low-amplitude overvoltages that cannot be suppressed by traditional surge arresters.

[0063] Transform the voltage and current from the abc coordinate system to the αβ0 coordinate system, and define the instantaneous power in the αβ0 coordinate system. Transform the three-phase voltage and current to the αβ0 stationary coordinate system.

[0064] (1) Electrical quantity αβ0 transformation For any three-phase voltage, the Clark transformation and its inverse transformation are as follows:

[0065]

[0066] In the formula: v a v b v c These are the three-phase voltages (a, b, and c) of the three-phase system; v0, v α v β These are the instantaneous voltages in the αβ0 coordinate system, respectively.

[0067] v0, v α v β Transform to v a v b v c Use the following formula:

[0068]

[0069] For any three-phase line current i a i b i c The following formula can be used to transform i0, i α i β :

[0070]

[0071] This formula achieves i a i b i c Swap to i0, i α i β In the commutative expression, i0 is the zero-order component, i α i β These are the α-axis components and the β-axis components, respectively.

[0072]

[0073] One advantage of using the Clark transform is that it separates the zero-sequence component from the abc coordinate system. The α-axis and β-axis components have no effect on the zero-sequence component. In a three-phase three-wire system, the zero-sequence component does not exist, so i0 can be removed from the above equations, simplifying the transformation relationship. If the three-phase voltages are symmetrical in a three-phase four-wire system, there is no zero-sequence voltage, and therefore v0 can also be removed. However, when both zero-sequence voltage and zero-sequence current exist, the complete Clark transform equations should be used.

[0074] If v0 can be removed from the transformation formula, then the Clark transform and its inverse transform become

[0075]

[0076] A similar formula exists for line current. Here, the instantaneous values ​​of phase voltage and line current in the abc stationary coordinate system are transformed to the αβ stationary coordinate system, or vice versa. The three coordinate axes a, b, and c differ spatially by 2π / 3, while the α axis and β axis are orthogonal to each other, and the α axis and a axis are parallel. The coordinate transformations expressed by equations (5) and (6) are as follows: Figure 2 , Figure 3 As shown.

[0077] The Clark forward and inverse transforms used in equations (1) to (4) have the characteristic of constant power. All traditional power definitions have a prerequisite: the system must be in a steady state. However, three-phase instantaneous active power has a clear and universally accepted physical meaning and is applicable to transient processes.

[0078] Three-phase instantaneous active power p 3φ (t) can be calculated using the instantaneous values ​​of phase voltage and line current:

[0079] p 3φ (t)=v a (t)i a (t)+v b (t)i b (t)+v(t)i c (t) (7);

[0080] p 3φ =v a i a +v b i b +v c i c (8);

[0081] In the formula, v a v b and v c i is the instantaneous value of the phase voltage. a i b and i c This represents the instantaneous value of the line current. In a system without a neutral line, v a v b and v c Measurements are taken using a common reference point, generally referred to as the "ground" or "virtual star point." However, this reference point can actually be chosen arbitrarily, and p is calculated using equation (3-7). 3φ (t) The result is the same for any chosen common reference point.

[0082] The quantities in the abc coordinate system in equation (8) are replaced with αβ0 components using equations (2) and (4) to calculate the results.

[0083]

[0084] The power invariance characteristic of the Clark transform is proven in equation (9), and this characteristic will also be utilized in instantaneous power theory. Instantaneous power theory is defined in a three-phase system, which may or may not have a neutral line. The three instantaneous powers, namely instantaneous zero-sequence power p0, instantaneous real power p, and instantaneous imaginary power q, are defined based on the instantaneous phase voltage and instantaneous line current in the αβ0 coordinate system, as shown in the following equation:

[0085]

[0086] In a three-phase ungrounded system, there is no zero-sequence current, i.e., i0 = 0. In this case, only instantaneous power defined on the α and β axes exists, because the product vi00 in equation (3-9) is always equal to zero. Therefore, in a three-phase three-wire system, the real power p representing the total energy flow per unit time can be represented by the α and β components, i.e., p 3φ =p.

[0087] Another approach to introducing instantaneous power theory into a three-phase three-wire system is to utilize the instantaneous voltage vector and instantaneous current vector defined in equations (7) and (8). Since the traditional concept of complex power uses the conjugate of voltage and current phasors, it is only applicable to systems with a fixed grid frequency under steady-state conditions. It is possible to define a new instantaneous complex power using the instantaneous voltage vector and instantaneous current vector. The instantaneous complex power s is defined as the product of the voltage vector e and the conjugate i* of the current vector i, as shown in the following equation:

[0088]

[0089] The instantaneous real power and instantaneous imaginary power defined in equation (9) are a part of the instantaneous complex power s defined in equation (3-11). Since instantaneous voltage and instantaneous current are used, the instantaneous complex power s has no restrictions and is applicable to both steady state and transient state.

[0090] In traditional power theory, reactive power is defined as a component of instantaneous (active) power, except that the average value of this component is zero. In the theory of instantaneous reactive power, virtual power refers to the sum of the products of instantaneous three-phase voltage and certain current components, and these products do not contribute to energy transfer between subsystems at any time. In this theory, the term "instantaneous reactive power" in the context of a three-phase system is used as a synonym for virtual power, and therefore they have the same physical meaning.

[0091] The general equations of instantaneous power theory indicate that if the fundamental frequency of the power system is asymmetrical or contains harmonic voltages, it is impossible to compensate the load current and simultaneously satisfy the following three "optimal" compensation characteristics: (1) the instantaneous active power drawn from the power source is constant; (2) the current drawn from the power source is sinusoidal; and (3) the transmission line loss is minimized and the effective value of the current drawn from the power source is minimized when transmitting the same amount of energy to the load. When the system voltage is symmetrical and sinusoidal, it is possible to simultaneously satisfy the above three optimal compensation characteristics. However, under asymmetrical or non-sinusoidal system voltage conditions, using an overvoltage suppressor to compensate the load current can only guarantee one of the above optimal characteristics.

[0092] A three-phase ungrounded system has no neutral conductor, therefore no zero-sequence current component, and thus the zero-sequence power in such a system is always equal to zero. For example... Figure 4The diagram shows the architecture of an overvoltage suppressor. The electrical quantities input to the control module for calculating instantaneous power are the electrical quantities at the point of common coupling (PCC), namely the phase voltage at PCC and the line current of the nonlinear load to be compensated. The constant instantaneous power control strategy is developed based on instantaneous power theory. According to the concepts of real power and imaginary power, in order to draw constant instantaneous power from the power source, the overvoltage suppressor should be installed as close as possible to the nonlinear load and compensate for the oscillating real power component of the load. When the system uses a three-phase system without a neutral line, the zero-sequence power is equal to zero.

[0093] The overvoltage suppressor should provide the oscillating portion of the instantaneous active current of the load, such as... Figure 5 As shown, the command to generate compensation current includes:

[0094] Calculate the real and imaginary power current components of the α-axis oscillation: the oscillating component of the instantaneous active current on the α-axis. Oscillating component of instantaneous active current on the β axis

[0095] In the calculation formula, the negative sign of the real power is to be consistent with... Figure 4 The current direction used in this system is matched; when the load current and the overvoltage suppressor current flow into the load and overvoltage suppressor, the positive sign is taken, i.e., the "load current convention" is adopted. If the power generated by the current drawn by the overvoltage suppressor is... If the values ​​are exactly equal, then the power system will only provide the actual power for the constant portion of the load. In order to compensate For an oscillating energy flow, the DC energy storage element of the PWM converter must be large enough to prevent large voltage fluctuations. This overvoltage suppressor can further optimize the compensated current, filtering out the portion of the load current that generates virtual power. Therefore, instantaneous reactive current i should also be compensated. αq and i βq :

[0096] Calculate the real and imaginary power current components of the β-axis oscillation: the oscillating component of the instantaneous reactive current on the α-axis. Oscillating component of instantaneous reactive current on the β axis

[0097] What is being compensated is the total virtual power. The reason for using a negative sign is the same as explained above regarding the compensation for oscillation real power. Unlike other methods, compensating for the total virtual power -q does not require any energy storage components.

[0098] The sum of the negative values ​​of the four current components is used as the command value.

[0099] The overvoltage suppressor compensates for both the real and virtual power fluctuations of the load, thus ensuring that only a constant real power is drawn from the power system. (Average actual power of the load). Therefore, from the power flow perspective, the instantaneous power constant control strategy provides optimal compensation, even when the system voltage is non-sinusoidal or asymmetrical.

[0100] When the overvoltage suppressor is in operation, it must continuously draw a small amount of average real power from the power system. This energy is supplied to cover the switching losses and resistive losses of the PWM converter. Otherwise, this energy would be provided by the DC capacitor, which continuously discharges it. This type of overvoltage suppressor power converter is a boost converter; to ensure PWM current control is achieved, its DC voltage must be maintained above the peak value of the AC bus voltage.

[0101] Instantaneous power constant control strategies play a crucial role in active power filter research, as the accuracy and speed of instantaneous power calculation directly impact the performance of active power filters. The inverter main circuit, acting as the "actuator" of the overvoltage suppressor, determines the accuracy of its execution of the compensation current command—that is, the precision with which the compensation current tracks the command current—based on the overall performance of the inverter main circuit and the compensation current control strategy employed. Currently, the main circuit structure of active power filters is relatively mature, and most utilize PWM converters. Therefore, the overvoltage suppressor employs a PWM converter as its main circuit.

[0102] After receiving the command current signal from the detection circuit, the compensation current generating circuit produces the compensation current. The basic principle of compensation current control is to control the switching elements of the main circuit in the compensation current generating circuit based on the relationship between the command signal and the actual compensation current, thereby generating the required PWM waveform. The control result should ensure that the actual compensation current signal can follow the changes of its command signal.

[0103] This invention employs a deviation current triangular carrier comparison method, such as... Figure 6 As shown, this method differs from the ordinary PWM control method using a triangular wave. Instead of directly comparing the command signal with the triangular carrier wave, it compares i... C with i * C deviation Δi C Perform PI adjustment to amplify the Δi C The signal is then compared with a triangular carrier wave to output a PWM signal. This control method outputs a control signal with a frequency equal to the frequency of the triangular carrier wave, which can improve the lifespan of the switching devices and offers good economic performance.

[0104] It also includes DC-side voltage control:

[0105] Detect the deviation between the actual value and the reference value of the DC-side capacitor voltage;

[0106] The deviation between the actual value and the reference value of the DC-side capacitor voltage is converted into an active current regulation quantity through a proportional-integral controller.

[0107] The active power regulation is superimposed on the fundamental active power component of the compensation current command.

[0108] When an overvoltage suppressor fully compensates for harmonics and reactive currents in the power grid, the power supply only outputs active current, while the overvoltage suppressor outputs harmonic current to exchange reactive power with the load. The DC-side capacitor of the overvoltage suppressor should maintain a constant voltage. On one hand, controlling the overvoltage suppressor to output harmonics and reactive current is an inversion process, involving energy exchange between the overvoltage suppressor and the load. On the other hand, when the overvoltage suppressor compensates for harmonic currents, power losses occur during the switching on and off of power devices, requiring a certain amount of active current from the grid. These factors all lead to a decrease in the DC-side capacitor voltage, affecting the compensation performance of the overvoltage suppressor. To maintain a constant DC-side voltage, the three-phase power supply must also replenish active power to the DC-side capacitor of the overvoltage suppressor; this is a rectification process. Instantaneous active and reactive power are composed of DC and AC components, where the AC component is generated by harmonics and the DC component by the fundamental frequency. Let the instantaneous active power output by the power supply be p. s The instantaneous active power and instantaneous reactive power of the overvoltage suppressor are p and i, respectively. q The power loss of the power device is Δp. When the overvoltage suppressor compensates for harmonic currents and reactive currents in the power grid, there is...

[0109]

[0110] From the above equation, we can see that the instantaneous active power p of the overvoltage suppressor consists of the device loss power Δp and the AC component. The composition, Δp, is related to the switching frequency of the power devices. It consumes the energy stored in the DC-side capacitor, causing a decrease in the DC-side capacitor voltage. The AC component indicates that the active filter exchanges active power with the load during operation. In one cycle, The instantaneous value of the DC-side voltage is not zero, and the instantaneous value of the DC-side voltage will fluctuate slightly, but the average value is zero. It will not affect the average voltage on the DC side.

[0111] The output compensation current includes:

[0112] Real-time acquisition of actual compensation current value, and calculation of the deviation between actual value and command value;

[0113] The deviation between the actual value and the command value is processed by a proportional-integral controller and a modulation signal is generated.

[0114] The modulated signal is compared with the triangular carrier wave to generate the driving signal.

[0115] When the overvoltage suppressor is working normally, the compensation current output using the deviation current triangular carrier wave tracks the change of the command current in a sawtooth wave pattern on both sides. Analyzing the compensation current of phase A, neglecting the effect of line resistance, we have...

[0116]

[0117] In the formula, K(n) is the switching function, which can be 1 / 3 or 2 / 3, and di ca / dt represents the rate of change of the compensation current output by the overvoltage suppressor. To ensure performance, it must be greater than or equal to the rate of change of the harmonic current.

[0118] Assuming when i ca >i * ca (i * ca When the current is the commanded value for the A-phase compensation current, the lower switch of the A-phase bridge arm of the overvoltage suppressor should be on, and the upper switch should be off. Taking K(n) = 1 / 3, then:

[0119]

[0120] To ensure the compensation current i ca It has good following ability, at this time i ca To reduce it, then:

[0121]

[0122] Substituting equation (10) into equation (11), we get:

[0123] u dc >3u sa ;

[0124] Generally, the following is taken:

[0125] u dc >3u sam ;

[0126] That is, the DC side voltage value should be more than 3 times the peak value of the power supply phase voltage. On this basis, the larger the DC side voltage, the better the tracking performance of the compensation current generated by the overvoltage suppressor and the better the compensation effect. However, the voltage withstand requirements of the switching devices are also higher. Therefore, it is necessary to take all factors into consideration and select the most suitable value.

[0127] Overvoltage suppressors typically employ a voltage source inverter structure in their main circuit, with capacitors generally used for energy storage on the DC side. When the overvoltage suppressor's compensation current rapidly tracks grid current harmonics or load current harmonics, it absorbs a certain amount of active power from the system and incurs switching losses. This will cause a voltage u across the DC-side capacitor. dc The fluctuations. Due to u dc Fluctuations in voltage can cause overvoltage or undervoltage on the DC side, affecting its normal operation and even jeopardizing the safety of the overvoltage suppressor. Therefore, to ensure its normal operation, it is necessary to control the DC side voltage u. dc Control measures are implemented to keep the voltage essentially constant. To stabilize the voltage across the capacitor, the AC side of the overvoltage suppressor must draw a certain amount of active power from the power supply and transfer it to the DC side. Typically, the deviation between the given DC side voltage reference value and the actual DC side voltage value, after adjustment and calculation, is superimposed on the DC component of the overvoltage suppressor's active current, thereby regulating the capacitor voltage.

[0128] Let the DC side voltage be u. dc The reference value for the DC side voltage is u. * dc The basic relationship is as follows:

[0129]

[0130] In the formula, K p K is the proportional gain of the PI controller. i The integral coefficient of the PI controller, Δu dc This represents the deviation between the DC-side voltage and its reference value.

[0131] Figure 7 In the middle, u dc with u * dc The difference is used to obtain the adjustment signal Δi through a PI controller. p Overlay Figure 8 shown After inverse transformation, the command compensation current will include the fundamental active current component that needs to be compensated, thereby enabling energy exchange between the AC and DC sides of the active filter, and reducing u dc Adjust to the given voltage reference value.

[0132] When the voltage returns to the normal range, the converter is shut down within 10ms.

[0133] Example 2

[0134] like Figure 4 As shown, an overvoltage suppressor is used to implement an overvoltage suppression control method, comprising:

[0135] A voltage source converter, wherein the DC side of the voltage source converter is equipped with an energy storage capacitor;

[0136] Controller, the controller includes:

[0137] Voltage detection module: monitors feeder voltage;

[0138] Power processing module: performs Clark transformation and instantaneous power oscillation component separation;

[0139] Current control module: realizes proportional-integral adjustment of deviation current and triangular carrier comparison;

[0140] Switching control module: Starts up when the voltage is abnormal and shuts down the converter after the voltage is restored.

[0141] The switching control module is configured to: trigger startup when a component failure, inter-electrode short circuit, or pole-to-shell short circuit is detected in the parallel capacitor bank; and trigger startup when the feeder voltage continuously exceeds 105% of the rated value.

[0142] The primary purpose of overvoltage suppressors is to provide overvoltage protection at the transformer on the feeder and at both ends of the line. Traditional overvoltage protection often uses surge arresters, whose main function as overvoltage protection for parallel capacitor banks is to limit reignition overvoltages during circuit breaker switching. However, during capacitor bank switching operations, the amplitude of the closing overvoltage is usually low, generally not exceeding the specified value, so the effect of surge arresters is not significant. The starting voltage of surge arresters is typically very high, and currently, no protective measures are in place for overvoltages occurring on the line with amplitudes lower than the arrester's operating voltage. Such overvoltages are a major cause of capacitor damage. Therefore, overvoltage suppressors are more advantageous for protecting against these voltages.

[0143] Figure 9 This is the equivalent circuit diagram of the power quality problems caused by the feeder system, where the load current i L From the load fundamental current i Lf and load harmonic current i Lh It consists of two parts. Specifically, the nonlinear load draws a fundamental current component i from the feeder system. Sf and a harmonic current component i Sh Harmonic current component i Sh It is composed of harmonic voltage source V Sh Generated. X L Let i be the impedance of the feeder system. If the load harmonic current i Lh When it flows into the power system, it generates an additional harmonic voltage drop, equal to X. L ·i Lh This causes the voltage V at the load terminal to... T It has deteriorated further.

[0144] The main function of an overvoltage suppressor is to compensate for the harmonic current i of the load. Lh This means that the overvoltage suppressor confines the load harmonic current to the load end, preventing its propagation into the feeder system. With proper control, the overvoltage suppressor can exhibit selective compensation characteristics, allowing selection of the compensation response to the power supply current i. sh or load current i Lh Compensation will be provided.

[0145] In feeder systems, such as Figure 10 As shown, the load current i L It contains a large number of harmonic components, and the current i absorbed by the load from the feeder system S Distortion occurs. C To compensate for the current. The load current can be decomposed into the fundamental component i. Lf Harmonic component i Lh And satisfy: i s =i L +i C ;

[0146] The overvoltage suppressor detects the voltage V and current signal i of the compensation object. L The harmonic detection algorithm generates a command signal for the compensation current, which is then used to drive the inverter to output a compensation current i with equal amplitude but opposite direction. C The compensation current cancels out the harmonic and reactive currents in the circuit, and the resulting power supply current is the desired fundamental current. Overvoltage suppressors are power electronic devices with very high real-time requirements. When harmonics are generated in the power grid, the system detects harmonic currents, tracks current, and controls the output to eliminate harmonics and reactive components in the grid. Higher real-time performance is desirable, and theoretically, detection and control should be completed simultaneously.

[0147] Figure 10 This is an equivalent circuit diagram for power quality management in a feeder system. The circuit diagram includes an overvoltage suppressor control system. The overvoltage suppressor control system mainly consists of two modules: a voltage source converter and an overvoltage suppressor controller. The voltage source converter is responsible for power processing to synthesize the compensation current that should be drawn from the feeder system. The overvoltage suppressor controller is responsible for signal processing to determine the instantaneous reference value of the compensation current in real time, and this reference value is continuously transmitted to the voltage source converter.

[0148] The voltage source converter is equipped with a PWM controller, and the overvoltage suppressor controller uses a control algorithm based on instantaneous power theory, operating in a closed-loop manner. The load current i is continuously monitored. L And calculate the compensation current reference value i * CThe instantaneous value of this current reference is used as the input signal for the PWM controller. Ideally, the PWM controller can be considered a linear power amplifier, where the compensation current i... C Accurately track its reference value i * C If the compensation current i C =-i Lh , then i S =i Lf That is, the feeder current contains only the fundamental component, making the power supply current and the power supply voltage in phase with a sine wave, and the power factor is 1.

[0149] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method of overvoltage suppression control, implemented based on instantaneous power theory, characterized by, The method comprises: Real-time monitoring of feeder voltage, starting the voltage source converter when feeder voltage anomaly is detected; Converting three-phase voltage and current into αβ coordinate system components through Clark transformation; Calculating the oscillation component of instantaneous real power and the total compensation of instantaneous reactive power, generating compensation current instruction based on the oscillation component and the total compensation; Proportional integral adjustment of compensation current deviation to generate modulation wave, then comparing with triangular carrier to generate drive signal to output compensation current, and exiting operation when voltage returns to normal.

2. The overvoltage suppression control method of claim 1, wherein The compensation current instruction generation comprises: Calculating α-axis oscillation real power current component and reactive power current component; Calculating β-axis oscillation real power current component and reactive power current component; Summing up the negative values of the four current components as instruction value.

3. The overvoltage suppression control method of claim 1, wherein The compensation current output comprises: Real-time acquisition of compensation current actual value, calculating the deviation of actual value and instruction value; Processing the deviation of actual value and instruction value through proportional integral regulator and generating modulation signal; Comparing the modulation signal with triangular carrier to generate drive signal.

4. The overvoltage suppression control method of claim 3, wherein The drive signal generation comprises: When modulation signal voltage is greater than triangular carrier voltage, turning on the upper bridge arm switch tube of voltage source converter; When modulation signal voltage is less than triangular carrier voltage, turning on the lower bridge arm switch tube of voltage source converter.

5. The overvoltage suppression control method of claim 1, wherein Further comprising DC side voltage control: Detecting the deviation of DC side capacitor voltage actual value and reference value; Converting the deviation of DC side capacitor voltage actual value and reference value into active current regulation amount through proportional integral controller; Superimposing the active regulation amount to the fundamental active component of compensation current instruction.

6. A method of overvoltage suppression control according to claim 5, wherein The voltage reference value is greater than 3 times of the peak value of power supply phase voltage.

7. The overvoltage suppression control method of claim 1, wherein The Clark transformation adopts power invariance transformation matrix:

8. The overvoltage suppression control method of claim 2, wherein The current component calculation satisfies:

9. An overvoltage suppressor for implementing the overvoltage suppression control method according to any one of claims 1 to 8, characterized in that, The method comprises: Voltage source converter, the DC side of the voltage source converter is configured with energy storage capacitor; Controller, the controller comprises: Voltage detection module: monitoring feeder voltage; Power processing module: performing Clark transformation and instantaneous power oscillation component separation; Current control module: realizing deviation current proportional integral adjustment and triangular carrier comparison; Switching control module: starting the converter when voltage anomaly is detected and closing the converter when voltage returns to normal.

10. An overvoltage suppressor as defined in claim 9, wherein The switching control module is configured to trigger start when detecting element failure, inter-pole short circuit or pole-pair shell short circuit of shunt capacitor bank, and trigger start when feeder voltage continuously exceeds rated value 105%.

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