Maximum reactive power compensation tracking system

Abstract

The present invention discloses a maximum reactive power compensation tracking system, wherein the input end of the grid current detector is connected to the grid, and the output end is respectively connected to the load current calculator and the second reactive current detector; the input end of the output current detector is connected to the output current controller, and the output end is respectively connected to the load current calculator and the output current controller; the input end of the first reactive current detector is connected to the load current calculator, and the output end is connected to the output current instruction synthesizer; the input end of the closed-loop controller is connected to the second reactive current detector, and the output end is connected to the output current instruction synthesizer; the input end of the output current controller is connected to the output current instruction synthesizer and the output current detector, and the output end is connected to the grid through the output current detector. Through the technical solution of the present invention, the delay can be reduced, the steady-state compensation effect can be optimally controlled, and the closed-loop control with fast dynamic response and high steady-state accuracy of reactive current on the grid side is realized.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a maximum reactive power compensation tracking system. Background Art

[0002] With the development of modern industrial technology and the rapid electronicization of electrical equipment, the reactive power characteristics in the distribution system have undergone tremendous changes. The reactive power has changed from being stable, slow, and single-inductive to being more impactful, rapid, and both capacitive and inductive may exist in large quantities.

[0003] like Figures 1 to 3 As shown, the existing static var generator (SVG) usually uses an open-loop or closed-loop compensation method to track and compensate the reactive power of the power grid. However, the existing open-loop method will always bring certain errors to the compensation of the power grid and cannot achieve the optimal reactive current compensation. The existing closed-loop method, due to the limitation of the controller algorithm, although the steady-state accuracy is guaranteed, the rapidity of compensation is sacrificed and the same low-latency tracking response as the open-loop method cannot be achieved. Summary of the invention

[0004] In response to at least one of the above problems, the present invention provides a maximum reactive power compensation tracking system, which simultaneously calculates the reactive currents on the grid side and the load side, performs closed-loop control on the grid side reactive current and directly superimposes it with the reactive current on the load side, which is equivalent to utilizing both closed-loop and open-loop control methods. The calculated load reactive current is used for pre-command compensation, and its real-time response speed is exactly the same as that of the open loop, which can minimize the delay caused by anything other than the reactive detection algorithm. The calculated grid reactive current is used for closed-loop control, which can optimize the steady-state compensation effect, give full play to the compensation characteristics of the SVG stepless output, and control the final grid reactive current to the target value, thereby realizing closed-loop control with fast dynamic response and high steady-state accuracy of the grid side reactive current.

[0005] To achieve the above-mentioned purpose, the present invention provides a maximum reactive power compensation tracking system, comprising: a grid current detector for detecting the instantaneous value of grid-side current; an output current detector for obtaining the output current of an output current controller; a load current calculator for calculating the load current through the grid current and the instantaneous value of the output current; a first reactive current detector for calculating the reactive power generated by the load; a second reactive current detector for calculating the reactive current of the grid; an output current instruction synthesizer, a closed-loop controller and the output current controller for synthesizing the reactive current instructions of the two reactive current detectors; the input end of the grid current detector is connected to the grid, and the output end is respectively connected to the load current calculator and the second reactive current detector; the input end of the output current detector is connected to the output current controller, and the output end is respectively connected to the load current calculator and the output current controller; the input end of the first reactive current detector is connected to the load current calculator, and the output end is connected to the output current instruction synthesizer; the input end of the closed-loop controller is connected to the second reactive current detector, and the output end is connected to the output current instruction synthesizer; the input end of the output current controller is connected to the output current instruction synthesizer and the output current detector, and the output end is connected to the grid through the output current detector.

[0006] In the above technical solution, preferably, the output current controller includes an SVG output current controller and an inverter.

[0007] In the above technical solution, preferably, the grid current detector and the output current detector are current transformers or Hall current sensors.

[0008] In the above technical solution, preferably, the first reactive current detector and the second reactive current detector are fast Fourier transformers or inverse Fourier transformers, instantaneous reactive current calculators or reactive current calculators based on time domain transformation.

[0009] In the above technical solution, preferably, the closed-loop controller is a PID controller or a repetitive controller.

[0010] In the above technical solution, preferably, the SVG output current controller adopts a PID output current control mode, a repetitive current control mode or a hysteresis current control mode, and the inverter is a three-level modular SVG, a two-level SVG or a combination of SVG and a capacitor cabinet.

[0011] In the above technical solution, preferably, the output of the output current command synthesizer is the sum of the output of the closed-loop controller and the output of the first reactive current detector.

[0012] The present invention also proposes a maximum reactive power compensation tracking system, which adds a load current detector and deletes the load current calculator on the basis of the maximum reactive power compensation tracking system described in any one of the above technical solutions; the load current detector is connected to the load end for detecting the load end current, and the output end is connected to the input end of the first reactive current detector to output the current detection result; the input end of the grid current detector is connected to the grid, and the output end is connected to the second reactive current detector; the input end of the output current detector is connected to the output current controller, and the output end is feedback connected to the output current controller.

[0013] The present invention also proposes a maximum reactive power compensation tracking system, which adds a load current detector and deletes the output current detector on the basis of the maximum reactive power compensation tracking system described in any one of the above technical solutions; the load current detector is connected to the load end for detecting the load end current, and the output end is connected to the first reactive current detector and the load current calculator; the input end of the load current calculator is respectively connected to the grid current detector and the compliance current detector, and the output end is connected to the output current controller; the output end of the output current controller is connected to the grid.

[0014] In the above technical solution, preferably, the load current calculator is used to calculate the static reactive current by subtracting the output value of the grid current detector from the output value of the load current detector.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: by simultaneously calculating the reactive current magnitudes on the grid side and the load side, the grid side reactive current is closed-loop controlled and then directly superimposed with the load side reactive current, which is equivalent to utilizing both closed-loop and open-loop control methods at the same time, and performing pre-command compensation by using the calculated load reactive current. Its real-time response speed is exactly the same as that of the open-loop, and the delay caused by anything other than the reactive detection algorithm can be minimized. By using the calculated grid reactive current for closed-loop control, the steady-state compensation effect can be optimally controlled, and the compensation characteristics of the SVG stepless output can be fully utilized to control the final grid reactive current to the target value, thereby realizing closed-loop control with fast dynamic response and high steady-state accuracy of the grid side reactive current. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of a working circuit of a static VAR generator according to an embodiment of the prior art;

[0017] Figure 2 It is a schematic diagram of the voltage and current signals of the power grid without using static VAR generator compensation;

[0018] Figure 3The schematic diagram of voltage and current signals of the power grid using static VAR generator compensation;

[0019] Figure 4 A schematic diagram of the connection mode of the maximum reactive current compensation tracking system disclosed in the first embodiment of the present invention;

[0020] Figure 5 A logic diagram of the maximum reactive current compensation tracking system disclosed in the first embodiment of the present invention;

[0021] Figure 6 A schematic diagram of the connection mode of the maximum reactive current compensation tracking system disclosed in the second embodiment of the present invention;

[0022] Figure 7 A schematic diagram of the implementation logic of the maximum reactive current compensation tracking system disclosed in the second embodiment of the present invention;

[0023] Figure 8 A schematic diagram of the connection mode of the maximum reactive current compensation tracking system disclosed in Embodiment 3 of the present invention;

[0024] Fig. 9 This is a logic diagram for realizing the maximum reactive current compensation tracking system disclosed in Embodiment 3 of the present invention.

[0025] In the figure, the corresponding relationship between each component and the reference numeral is as follows:

[0026] 100. Grid current detector, 200. Output current detector, 300. Load current calculator, 400. Output current controller, 401. SVG output current controller, 402. Inverter, 500. Second reactive current detector, 600. Closed-loop controller, 700. Output current command synthesizer, 800. First reactive current detector, 900. Load current detector. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0029] like Figure 1 The working circuit diagram of the existing static VAR generator is shown in FIG. The static VAR generator can be connected between the power grid and the load, or at the end of the load.g Represents the grid current, I p Represents active current, I s Represents the output current of the static VAR generator, I L Indicates the load current, I q Represents the reactive component of the load current. Under ideal conditions, I s =I q , so that there is only active current I on the grid side p .

[0030] When the load is capacitive or inductive, the load current I L There will be a large amount of reactive current components in the power supply, which will affect the power supply quality and safety.

[0031] When the static VAR generator is not turned on, the grid current is exactly the same as the load current, such as Figure 2 shown.

[0032] When the static VAR generator is turned on, it will output a reactive current component equal to the reactive power of the load to the grid, so that there is only active current on the grid side, and the phase difference between the grid current and the grid voltage is 0. Figure 3 shown.

[0033] like Figure 1 The static VAR generator shown generally adopts an open-loop or closed-loop mode. When the open-loop mode is adopted, the static VAR generator directly samples the current of the load, calculates the reactive current of the load, and then allows the static VAR generator to output an equal reactive current. This compensation speed is the fastest, but due to sampling errors, errors in the output current of the device and other factors, the compensation accuracy is not high enough. When the closed-loop mode is adopted, the static VAR generator directly samples the current on the grid side, calculates the reactive current content on the grid side, and controls the reactive current content on the grid side to 0 through algorithms such as PID or repetitive control. However, in this mode, if the load reactive current fluctuates impulsively, the closed-loop control loop bandwidth of PID or repetitive control is limited, and there is a large delay. In order to overcome the above-mentioned defects, the present invention proposes a method such as Figure 4 The maximum reactive current compensation tracking system is shown.

[0034] Embodiment 1:

[0035] like Figure 4 and Figure 5As shown, a maximum reactive power compensation tracking system provided by the present invention includes: a grid current detector 100 for detecting the instantaneous value of grid-side current; an output current detector 200 for obtaining the output current of an output current controller; a load current calculator 300 for calculating the load current through the grid current and the instantaneous value of the output current; a first reactive current detector 800 for calculating the reactive power generated by the load; a second reactive current detector 500 for calculating the reactive current of the grid; an output current instruction synthesizer 700, a closed-loop controller 600 and an output current controller 400 for synthesizing the reactive current instructions of the two reactive current detectors; the input end of the grid current detector 100 is connected to the grid, The output end is respectively connected to the load current calculator 300 and the second reactive current detector 500; the input end of the output current detector 200 is connected to the output current controller 400, and the output end is respectively connected to the load current calculator 300 and the output current controller 400; the input end of the first reactive current detector 800 is connected to the load current calculator 300, and the output end is connected to the output current instruction synthesizer 700; the input end of the closed-loop controller 600 is connected to the second reactive current detector 500, and the output end is connected to the output current instruction synthesizer 700; the input end of the output current controller 400 is connected to the output current instruction synthesizer 700 and the output current detector 200, and the output end is connected to the power grid through the output current detector 200.

[0036] In this embodiment, the input end of the grid current detector 100 is connected to the grid, and the grid current signal is sent to the second reactive current detector 500 and the load current calculator 300; the input end of the output current detector 200 is connected to the output primary line of the output current controller 400 including the static VAR generator, and the detected output current signal is sent to the load current calculator 300 and the output current controller 400; the load current calculator 300 can calculate the real-time load current according to the grid current and the output current signals, and send the real-time load current signal to the first reactive current detector 80 0 calculates the load reactive current, and the load reactive current calculation result is sent to the output current instruction synthesizer 700 as instruction one. The grid reactive current signal detected by the second reactive current detector 500 is passed through the closed-loop controller 600 to obtain instruction two. The output current instruction synthesizer 700 synthesizes instruction one and instruction two to obtain the final device output instruction; the input of the output current controller 400 is the aforementioned final device output instruction, which drives the IGBT power device to be turned on and off according to the real-time output current by adjusting the PWM pulse width, thereby realizing the actual inverter output of the static VAR generator.

[0037] In the above embodiment, preferably, the output current controller 400 includes an SVG output current controller 401 and an inverter 402. The SVG output current controller 401 changes the time and moment of driving the IGBT to turn on and off according to the instruction and the actual SVG output current through a certain algorithm such as PI regulation, repetitive control or hysteresis control, and finally realizes the inversion of the energy on the DC side to the AC grid.

[0038] Specifically, the instruction of the SVG output current controller 401 is the sum of the outputs of the first reactive current detector 800 and the closed-loop controller 600. The output current detector 200 is electrically connected to the inverter 402 and is ultimately connected to the busbar of the power grid. The output of the output current detector 200 is subtracted from the output of the power grid current detector 100 and the result is given to the first reactive current detector 800 for reactive current calculation. The SVG output current controller 401 uses the detection result of the output current detector 200 as feedback and compares it with the instruction to generate a series of pulse signals with varying duty cycles or frequencies. After being amplified by the hardware drive, the signals are electrically connected and transmitted to the inverter 402. Because of these drive pulse signals, the IGBT switching devices of the inverter 402 generate corresponding switching actions, thereby ultimately achieving output current control.

[0039] In the above embodiment, preferably, the grid current detector 100 and the output current detector 200 are current transformers or Hall current sensors.

[0040] In the above embodiment, preferably, the first reactive current detector 800 and the second reactive current detector 500 are fast Fourier transformers or inverse Fourier transformers, instantaneous reactive current calculators or reactive current calculators based on time domain transformation.

[0041] In the above embodiment, preferably, the closed-loop controller 600 is a PID controller or a repetitive controller.

[0042] In the above embodiment, preferably, the output of the output current command synthesizer 700 is the sum of the output of the closed-loop controller 600 and the output of the first reactive current detector 800 .

[0043] In the above embodiment, preferably, the SVG output current controller 401 adopts a PID output current control mode, a repetitive current control mode or a hysteresis current control mode, and the inverter 402 is a three-level modular SVG, a two-level SVG or a combination of an SVG and a capacitor cabinet.

[0044] In the above embodiment, preferably, the output of the output current command synthesizer 700 is the sum of the output of the closed-loop controller 600 and the output of the first reactive current detector 800 .

[0045] Embodiment 2:

[0046] like Figure 6 and Figure 7 As shown, the present invention also proposes a maximum reactive power compensation tracking system. On the basis of the maximum reactive power compensation tracking system of the above-mentioned embodiment one, a load current detector 900 is added and the load current calculator 300 is deleted; the load current detector 900 is connected to the load end for detecting the load end current, and the output end is connected to the input end of the first reactive current detector 800 to output the current detection result; the input end of the grid current detector 100 is connected to the grid, and the output end is connected to the second reactive current detector 500; the input end of the output current detector 200 is connected to the output current controller 400, and the output end is feedback connected to the output current controller 400.

[0047] Embodiment three:

[0048] like Figure 8 and Fig. 9 As shown, the present invention also proposes a maximum reactive power compensation tracking system. On the basis of the maximum reactive power compensation tracking system of the above-mentioned embodiment 1, a load current detector 900 is added and the output current detector 200 is deleted; the load current detector 900 is connected to the load end for detecting the load end current, and the output end is connected to the first reactive current detector 800 and the load current calculator 300; the input end of the load current calculator 300 is respectively connected to the grid current detector 100 and the current detector, and the output end is connected to the output current controller 400; the output end of the output current controller 400 is connected to the grid. The load current calculator 300 is used to calculate the static reactive current by subtracting the output value of the grid current detector 100 from the output value of the load current detector 900.

[0049] In the above embodiment, according to the power supply current I g 、Load current I L and the static VAR generator output current I s , always satisfy I L =I g +I s , the output current of the static VAR generator can be calculated through the load current and the grid current. Fig. 9 In the implementation form, the load current I L Subtract the grid current I g The output current I s , that is, the output of the load current detector 900 minus the output of the grid current detector 100 , is connected to the SVG output current controller 401 .

[0050] Specifically, when the load current I L There is a sudden change, the reactive power of the load I qWhen a mutation occurs, the mutation component is △I q , the mutation component △I q The first reactive current detector 800 will detect the reactive current and transmit it to the SVG controller so that the SVG inverter circuit will immediately output the corresponding reactive component △I qs However, due to the detection error and the existence of the device inverter error, △I qs Not equal to △I q , there is an error. At the same time, the final compensation result is the remaining reactive component △I on the grid side. qg , the grid current detector 100 and the second reactive current detector 500 can detect the remaining reactive component △I on the grid side. qg As feedback, it is transmitted to the closed-loop controller 600. Generally, the instruction of the closed-loop controller 600 is 0, but it can also be a specific value in some cases. At this time, the closed-loop control controller generates another instruction △I through PID control or repeated control. qg1 The instruction transmission superimposes the original instruction to make the SVG inverter circuit immediately output the corresponding reactive component △I qs2 Due to the closed-loop control regulation, after a period of regulation, the command △I qg1 Always make △I qs2 Satisfaction: △I qs2 +△I qs =△I q , so that the reactive current on the grid side is completely offset.

[0051] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A maximum reactive power compensation tracking system for compensating reactive current generated in a power grid, characterized in that: include: A grid current detector for detecting the instantaneous value of grid-side current; An output current detector for obtaining an output current of an output current controller, wherein the output current controller includes an SVG output current controller and an inverter; A load current calculator for calculating the load current from the grid current and the instantaneous value of the output current; A first reactive current detector for calculating the reactive power generated by the load; a second reactive current detector for calculating reactive current of the power grid; An output current command synthesizer, a closed-loop controller and the output current controller for synthesizing reactive current commands of two reactive current detectors; The input end of the grid current detector is connected to the grid, and the output end is respectively connected to the load current calculator and the second reactive current detector; The input end of the output current detector is connected to the output current controller, and the output end is respectively connected to the load current calculator and the output current controller; The input end of the first reactive current detector is connected to the load current calculator, and the output end is connected to the output current instruction synthesizer; The input end of the closed-loop controller is connected to the second reactive current detector, and the output end is connected to the output current command synthesizer; The input end of the output current controller is connected to the output current instruction synthesizer and the output current detector, and the output end is connected to the power grid through the output current detector; The first reactive current detector and the second reactive current detector are fast Fourier transformers or inverse Fourier transformers, instantaneous reactive current calculators or reactive current calculators based on time domain transformation; The output of the output current command synthesizer is the sum of the output of the closed-loop controller and the output of the first reactive current detector.

2. The maximum reactive power compensation tracking system according to claim 1, characterized in that: The grid current detector and the output current detector are current transformers or Hall current sensors.

3. The maximum reactive power compensation tracking system according to claim 1, characterized in that: The closed-loop controller is a PID controller or a repetitive controller.

4. The maximum reactive power compensation tracking system according to claim 1, characterized in that: The SVG output current controller adopts a PID output current control mode, a repetitive current control mode or a hysteresis current control mode, and the inverter is a three-level modular SVG, a two-level SVG or a combination of SVG and a capacitor cabinet.

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