SVG-based special dynamic reactive power compensation system for animal husbandry

Abstract

The invention is applicable to the technical field of reactive power compensation devices, and provides an SVG-based special dynamic reactive power compensation system for animal husbandry, which comprises a strategy confirmation module, a strategy verification module and an SVG + FC reactive power compensation verification module, and is characterized in that the strategy confirmation module adopts a theoretical analysis method and starts from mathematical modeling and instantaneous power theory of a three-phase asynchronous motor; based on the principle of series reactive compensation, the reactive compensation principle of the asynchronous motor is analyzed, the control strategy of reactive compensation is determined, the strategy verification module carries out dynamic simulation analysis by building an SVG simulation model under Simulink, the effectiveness of the control strategy is verified, and the control strategy is used for controlling the reactive compensation of the asynchronous motor. The SVG + FC reactive power compensation verification module obtains voltage and current of a power supply system and a load side of a farm through experiments, and then verifies an SVG + FC reactive power compensation scheme through a time domain and frequency domain analysis method. And dynamically adjusting the compensation stiffness of the SVG special for animal husbandry according to the power grid operation state and the load change.

Description

Technical Field

[0001] The invention relates to the technical field of reactive power compensation devices, and more specifically to a dynamic reactive power compensation system for animal husbandry based on SVG. Background Art

[0002] The power system in the intelligent livestock breeding scenario often has problems such as insufficient reactive power and voltage fluctuations due to factors such as load changes and equipment aging, which affect the normal operation of power equipment and the stability of agricultural and animal husbandry production. The power grid in the livestock breeding scenario has different stiffness characteristics. Therefore, the SVG sold on the market cannot fully adapt to the stiffness changes of the power grid in the livestock breeding scenario. This may cause the SVG compensation device to be poorly matched with the power grid during operation, affecting the compensation effect. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention aims to provide a dynamic reactive power compensation system for animal husbandry based on SVG.

[0004] To achieve the above object, the present invention provides the following technical solutions: The SVG-based livestock-specific dynamic reactive power compensation system includes a strategy confirmation module, a strategy verification module, and an SVG+FC reactive power compensation verification module; The strategy confirmation model adopts the method of theoretical analysis, starting from the mathematical modeling of three-phase asynchronous motors and the theory of instantaneous power, and based on the principle of series reactive power compensation, analyzes the reactive power compensation principle of asynchronous motors and determines the control strategy of reactive power compensation; The strategy verification module builds an SVG simulation model under Simulink and conducts dynamic simulation analysis to verify the effectiveness of the control strategy; The SVG+FC reactive power compensation verification module obtains the voltage and current of the farm power supply system and the load side through experiments, and then performs time domain and frequency domain analysis methods to verify the SVG+FC reactive power compensation scheme.

[0005] The present invention is further configured as follows: the SVG control strategy adopts a direct current control method, the SVG is connected to the system, and the nature and size of the reactive power output from the SVG are determined by controlling the amplitude and phase of the SVG output current. SVG , the reactive power output by SVG is offset by the reactive power of system load. s (system) = Q L (Load)-Q SVG = constant value (or 0); The power factor can be kept constant and the voltage hardly fluctuates. The most important thing is to accurately calculate the instantaneous reactive current in the load. The three-phase current and voltage of the collected agricultural and animal husbandry equipment are calculated after operation to obtain the reactive power to be compensated. The computer sends a trigger pulse, which is transmitted to the pulse amplification unit. After amplification, the IGBT is triggered to obtain the compensated reactive current.

[0006] The present invention is further configured as follows: the working principle of the SVG under direct current control can be derived from Formula 1: i S =i L +i C , that is, the power supply current i S is the load current i L and compensation current i C The phase sum; Assuming the load current i L Contains fundamental positive sequence current (including fundamental positive sequence reactive current i Lfq+ and fundamental positive sequence active current i Lfp+ )、fundamental negative sequence current i Lf- and harmonic current i Lh , as shown in Formula 2: L =i Lfp +i Lfq +i Lf- +i Lh ; In order to prevent the power supply current from containing fundamental positive sequence reactive power and fundamental negative sequence current, it is necessary to S Control SVG output current i C Satisfies formula 3: i C =-(i Lfp +i Lf- ); In this way, the power supply current only contains fundamental positive sequence active power and harmonic current, as shown in Formula 4: S =i Lfp +i Lh ; To achieve the compensation purpose, the key is to control the SVG output current i C Satisfy formula 3; From the description of the working principle of SVG, it can be seen that if SVG is to suppress load harmonics on the basis of reactive power compensation, it is only necessary to make SVG output the corresponding harmonic current. Therefore, in this sense, SVG can achieve the dual goals of compensating reactive current and harmonic current at the same time.

[0007] The present invention is further configured as follows: the SVG+FC reactive power compensation scheme assumes that the load consumes inductive reactive power (which is the case for general industrial users) Q L At this time, SVG is controlled to generate capacitive reactive power, and Q SVG =QL , so that during load fluctuations, it can be guaranteed that: Q S =Q SVG -Q L =0, at this time the power factor meets the standard, and because the SVG responds very quickly, it can achieve the purpose of controlling voltage flicker and fluctuation; If it is necessary to provide inductive reactive power to a complex compensation object such as a power grid, the SVG can be controlled to generate inductive reactive power and obtain Q SVG =Q C , so that during load fluctuations, it can still be guaranteed that: Q S =Q SVG -Q C =0.

[0008] The advantages of the present invention are: First, the present invention realizes an adaptive stiffness compensation strategy for power facilities in breeding plants through an SVG reactive compensation device, dynamically adjusts the compensation stiffness of the livestock-specific SVG according to the operating status of the power grid and load changes, and focuses on studying the SPWM inverter control technology, the dynamic performance of the reactive compensation controller, and the dynamic adjustment performance under three-phase imbalance conditions, so as to improve the power factor of the power system, stabilize the voltage, and reduce harmonic interference, thereby improving the operating efficiency and stability of the power system in agricultural and animal husbandry scenarios, and solving the problems of poor adjustment performance, serious harmonics, and short life of traditional reactive compensation controllers. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a block diagram of a dynamic reactive power compensation system for livestock based on SVG according to the present invention; Figure 2 This is a diagram of the SVG control system of the present invention; Figure 3 The working principle diagram of the static VAR generator controlled by direct current of the present invention; Figure 4 This is a system diagram of the present invention with an SVG reactive power compensation device. DETAILED DESCRIPTION

[0010] See also Figure 1-4 , the present invention provides the following technical solutions: Specifically refers to the SVG-based livestock-specific dynamic reactive power compensation system, including 1) Using the method of theoretical analysis, starting from the mathematical modeling of three-phase asynchronous motors and the theory of instantaneous power, based on the principle of series reactive power compensation, the reactive power compensation principle of asynchronous motors is analyzed to determine the control strategy of reactive power compensation; The stator-rotor mutual inductance of a three-phase asynchronous motor is a time-varying parameter, so the flux linkage and voltage are both nonlinear equations. In order to simplify the solution and achieve decoupling in control, it is necessary to establish the corresponding coordinate system transformation, that is, the Clark transformation and Park transformation need to go through the Clark and Park transformations.

[0011] Traditional power theory is defined based on the average power value within a cycle, but this situation is only applicable when the voltage and current are sinusoidal waves. Instantaneous power can break through the power limitation within a cycle and can be applicable to any non-sinusoidal wave and any transition process.

[0012] According to the principle of electromechanics and the definition of instantaneous power, the rotating orthogonal dq coordinate system is rotated synchronously with the three-phase voltage synthesis voltage vector. The initial synthesis voltage vector phase is set to zero, and the d-axis is made to coincide with the synthesis voltage vector. Then the current component in the d-axis direction is the active current component, and the current component in the q-axis direction is the reactive current component. The goal of reactive compensation is to make the reactive component of the current, i.e., the q-axis component, zero. By setting the q-axis current to 0, the deviation between the q-axis current obtained by the feedback link and the target value is subjected to PID operation. The output of the PID controller is the reactive component of the voltage, and the active component of the voltage, that is, the given value of the d-axis voltage component, is also zero. Then, by performing inverse coordinate transformation, the modulation signal of the SPWM control can be obtained, and reactive compensation for the motor can be performed.

[0013] In conjunction with the instruction manual Figure 2 SVG control strategy adopts direct current control method. SVG is connected to the system. The nature and size of reactive power output from SVG are determined by controlling the amplitude and phase of SVG output current. SVG , the reactive power output by SVG is offset by the reactive power of system load. s (system) = Q L (Load)-Q SVG = constant value (or 0), the power factor can be kept constant and the voltage hardly fluctuates. The most important thing is to accurately calculate the instantaneous reactive current in the load. The three-phase current and voltage of the collected agricultural and animal husbandry equipment are calculated to obtain the reactive power to be compensated. The computer sends a trigger pulse, which is transmitted to the pulse amplification unit. After amplification, the IGBT is triggered to obtain the compensated reactive current.

[0014] SVG consists of three basic functional modules: detection module, control operation module and compensation output module. Its working principle is to use the external CT to detect the current information of the system, and then analyze the current current information such as PF, S, Q, etc. through the control chip; then the controller gives the compensation drive signal, and finally the inverter circuit composed of the power electronic inverter circuit sends out the compensation current. The SVG static VAR generator uses a self-commutated bridge circuit composed of turn-off power electronic devices (IGBT), which is connected to the power grid in parallel through a reactor. It properly adjusts the amplitude and phase of the output voltage on the AC side of the bridge circuit, or directly controls the current on its AC side, quickly absorbs or sends out the required reactive power, and achieves the purpose of fast dynamic reactive adjustment. As an active compensation device, it can not only track the impact current of the impact load, but also track and compensate the harmonic current.

[0015] 2) By building an SVG simulation model under Simulink, dynamic simulation analysis is performed to verify the effectiveness of the control strategy.

[0016] In conjunction with the instruction manual Figure 3 It can be seen that the working principle of the active filter type SVG using direct current control is shown in the figure. Formula 1 can be obtained: i S =i L +i C , that is, the power supply current i S is the load current i L and compensation current i C The phase sum.

[0017] Assuming the load current i L Contains fundamental positive sequence current (including fundamental positive sequence reactive current i Lfq+ and fundamental positive sequence active current i Lfp+ )、fundamental negative sequence current i Lf- and harmonic current i Lh , as shown in Formula 2: L =i Lfp +i Lfq +i Lf- +i Lh .

[0018] In order to prevent the power supply current from containing fundamental positive sequence reactive power and fundamental negative sequence current, it is necessary to S Control SVG output current i C Satisfies formula 3: i C =-(i Lfp +i Lf- ).

[0019] In this way, the power supply current only contains fundamental positive sequence active power and harmonic current, as shown in Formula 4: S =i Lfp +iLh .

[0020] Therefore, in order to achieve the purpose of compensation, the key is to control the SVG output current i C Satisfies formula 3.

[0021] From the above description of the working principle of SVG, it can be seen that if SVG is to suppress load harmonics on the basis of reactive power compensation, it is only necessary to make SVG output the corresponding harmonic current. Therefore, in this sense, SVG can achieve the dual goals of compensating reactive current and harmonic current at the same time.

[0022] 3) The voltage and current of the farm power supply system and load side are obtained through experiments, and then time domain and frequency domain analysis methods are used to verify the SVG+FC reactive power compensation scheme.

[0023] In conjunction with the instruction manual Figure 4 SVG+FC reactive power compensation scheme assumes that the load consumes inductive reactive power (this is the case for general industrial users) Q L At this time, SVG is controlled to generate capacitive reactive power, and Q SVG =Q L , so that during load fluctuations, it can be guaranteed that: Q S =Q SVG -Q L =0, at this time the power factor meets the standard, and because the SVG responds very quickly, it can achieve the purpose of controlling voltage flicker and fluctuation.

[0024] If it is necessary to provide inductive reactive power to a complex compensation object such as a power grid, the SVG can be controlled to generate inductive reactive power and obtain Q SVG =Q C , so that during load fluctuations, it can still be guaranteed that: Q S =Q SVG -Q C =0.

Claims

1. SVG-based livestock-specific dynamic reactive power compensation system, including strategy confirmation module, strategy verification module and SVG+FC reactive power compensation verification module; The strategy confirmation model adopts the method of theoretical analysis, starting from the mathematical modeling of three-phase asynchronous motors and the theory of instantaneous power, and based on the principle of series reactive power compensation, analyzes the reactive power compensation principle of asynchronous motors and determines the control strategy of reactive power compensation; The strategy verification module builds an SVG simulation model under Simulink and conducts dynamic simulation analysis to verify the effectiveness of the control strategy; The SVG+FC reactive power compensation verification module obtains the voltage and current of the farm power supply system and the load side through experiments, and then performs time domain and frequency domain analysis methods to verify the SVG+FC reactive power compensation scheme.

2. The SVG-based livestock-specific dynamic reactive power compensation system according to claim 1 is characterized in that: The SVG control strategy adopts a direct current control method. The SVG is connected to the system and the nature and size of the reactive power output from the SVG are determined by controlling the amplitude and phase of the SVG output current. SVG , the reactive power output by SVG is offset by the reactive power of system load. s (system) = Q L (Load)-Q SVG = a constant value (or 0).

3. The SVG-based livestock-specific dynamic reactive power compensation system according to claim 2 is characterized in that: The power factor can be kept constant and the voltage hardly fluctuates. The most important thing is to accurately calculate the instantaneous reactive current in the load. The three-phase current and voltage of the collected agricultural and animal husbandry equipment are calculated to obtain the reactive power to be compensated. The computer sends a trigger pulse, which is transmitted to the pulse amplification unit. After amplification, the IGBT is triggered to obtain the compensated reactive current.

4. The SVG-based livestock-specific dynamic reactive power compensation system according to claim 3 is characterized in that: The SVG working principle of direct current control can be derived from Formula 1: S =i L +i C , that is, the power supply current i S is the load current i L and compensation current i C The phase sum; Assuming the load current i L Contains fundamental positive sequence current (including fundamental positive sequence reactive current i Lfq+ and fundamental positive sequence active current i Lfp+ )、fundamental negative sequence current i Lf- and harmonic current i Lh , as shown in Formula 2: L =i Lfp +i Lfq +i Lf- +i Lh ; In order to prevent the power supply current from containing fundamental positive sequence reactive power and fundamental negative sequence current, it is necessary to S Control SVG output current i C Satisfies formula 3: i C =-(i Lfp +i Lf- ); In this way, the power supply current only contains fundamental positive sequence active power and harmonic current, as shown in Formula 4: S =i Lfp +i Lh ; To achieve the compensation purpose, the key is to control the SVG output current i C Satisfies formula 3.

5. The SVG-based livestock-specific dynamic reactive power compensation system according to claim 4 is characterized in that: It can be seen from the description of the working principle of SVG that if SVG is to suppress load harmonics on the basis of reactive power compensation, it is only necessary to make SVG output corresponding harmonic current. Therefore, in this sense, SVG can achieve the dual goals of compensating reactive current and harmonic current at the same time.

6. The SVG-based livestock-specific dynamic reactive power compensation system according to claim 5 is characterized in that: The SVG+FC reactive power compensation scheme assumes that the load consumes inductive reactive power (which is the case for most industrial users). L At this time, SVG is controlled to generate capacitive reactive power, and Q SVG =Q L , so that during load fluctuations, it can be guaranteed that: Q S =Q SVG -Q L =0, at this time the power factor meets the standard, and because the SVG responds very quickly, it can achieve the purpose of controlling voltage flicker and fluctuation; If it is necessary to provide inductive reactive power to a complex compensation object such as a power grid, the SVG can be controlled to generate inductive reactive power and obtain Q SVG =Q C , so that during load fluctuations, it can still be guaranteed that: Q S =Q SVG -Q C =0.

Images