Reactive Power Compensation Control Strategy Based on an Energy Unidirectional Flow Controllable Converter

Abstract

The present invention relates to a reactive compensation control strategy based on a controllable converter with unidirectional energy flow, which specifically includes the following steps: first, judging whether to connect to an LC series filter circuit according to the load in the power grid, then completing the voltage loop design, and using a single-cycle control method to improve the modulation wave by injecting odd harmonics according to the reactive power required by the converter to adjust the AC side input current sampling signal output. In addition to not changing the advantages of single-cycle control that do not require the use of a phase-locked loop and the AC side does not require the use of a voltage sensor, the input current and the AC side fundamental voltage are kept as close to the same polarity as possible, thereby achieving the purpose of suppressing possible distortion of the input current at the common coupling point. Compared with the traditional SPWM (SVPWM) modulation method, the method provided by the present invention has the advantages of simple implementation, fast dynamic response, strong robustness, low cost, and high power factor.

Description

Technical Field

[0001] The present invention belongs to the field of dynamic reactive power compensation control technology in power quality control technology, and in particular relates to a reactive power compensation control strategy based on a controllable converter with unidirectional energy flow. Background Art

[0002] Amidst increasingly severe grid pollution, research on harmonic suppression and reactive power compensation has garnered widespread attention. Simultaneously, power quality control devices based on power electronics, such as static VAR compensators (SVCs), static VAR generators (SVGs), active power filters (APFs), and universal power quality controllers (UPQCs), are gaining increasing application. These power quality control devices are widely recognized for their ability to improve the power factor of power supply systems and loads, reduce equipment capacity, minimize power losses, stabilize the voltage at the receiving end and on the grid, and effectively enhance and improve the quality of supplied power. Research into the fundamental theories and key technologies involved in power quality control devices has become one of the most sought-after research areas in electrical engineering.

[0003] In many practical industrial applications, electrical energy does not need to be transmitted in both directions. In these cases, the preferred solution is to use a controllable converter with unidirectional energy transmission, such as the front-end converter for energy-saving speed-regulating power supplies for fans and pump motors, communications power supplies, power switching power supplies, and electric vehicle charging power supplies. Compared with controllable converters with bidirectional energy transmission, controllable converters with unidirectional energy transmission can use fewer fully controlled components, have higher system stability, relatively simple control circuits, and relatively low manufacturing costs, demonstrating significant application advantages. Considering these factors, in recent years, an increasing number of research teams have begun to explore and study the possibility of integrating reactive power compensation and harmonic suppression functions with controllable converters with unidirectional energy transmission.

[0004] However, current distortion, which causes unidirectional energy transmission, limits the ability of controllable converters to provide power quality management. Clearly, finding a way to reduce or completely eliminate input current distortion in such converters is an effective way to improve their power quality management capabilities.

[0005] The single-cycle control method is a nonlinear large-signal PWM control theory and an analog PWM control technique. This control method controls the duty cycle so that the average value of the switching variable in each switching cycle is strictly equal to or proportional to the control reference. The average input current tracks the reference current and is not constrained by the load current. Even large harmonics in the load current do not distort the input current. Single-cycle control does not require a phase-locked loop (PLL), a multiplier, or input voltage sampling. This feature eliminates the need for AC voltage sensors in power electronic converters using this control technique, reducing the cost and complexity of the overall control circuit.

[0006] Therefore, it is very necessary to propose a reactive power compensation control strategy for a controllable converter with unidirectional energy flow based on single-cycle control. Summary of the Invention

[0007] To achieve the above-mentioned object, the present invention provides a reactive power compensation control strategy based on a unidirectional energy flow controllable converter, wherein the unidirectional energy flow controllable converter includes a single-phase unidirectional energy flow controllable converter, and the single-phase unidirectional energy flow controllable converter includes a single-phase bridgeless converter based on an LC series filter circuit, a single-phase VIENNA converter based on an LC series filter circuit, and a single-phase diode H-bridge converter based on an LC series filter circuit;

[0008] The steps of the reactive power compensation control strategy based on a unidirectional energy flow controllable converter of the present invention are as follows:

[0009] (1) When the power grid contains inductive or capacitive loads, a control signal is given to connect the LC series filter circuit. When the power grid contains only resistive loads, a control signal is given to disconnect the LC series filter circuit.

[0010] (2) Sampling the DC side voltage of the single-phase energy unidirectional flow controllable converter to obtain the DC voltage signal U dc ;

[0011] (3) The reference signal U of the DC voltage signal * dc The DC voltage signal U sampled in step (2) dc Subtract and get the input signal ΔU of the voltage regulator. Send the input signal ΔU to the voltage regulator to get the output u of the voltage regulator. m ;

[0012] (4) According to the single-cycle control principle, the output u of the voltage regulator m for

[0013]

[0014] where R s R is the current sampling resistor on the AC side of the single-phase energy unidirectional flow controllable converter, e is the equivalent resistance of the single-phase energy unidirectional flow controllable converter, u m is a positive number;

[0015] (5) The output u of the voltage regulator in step (4) is m Send it to the carrier generation module to generate an amplitude of u m triangle wave;

[0016] (6) The AC side current sampling resistor R of the controllable converter through the single-phase energy unidirectional flow s The AC side input current i of the single-phase energy unidirectional flow controllable converter s Sampling is performed to obtain the single-phase AC input current sampling signal R s i s ;

[0017] (7) The single-phase AC input current sampling signal R in step (6) s i s Send it to the absolute value module to get the absolute value signal |R s i s |;

[0018] (8) According to the reactive power required by the single-phase energy unidirectional flow controllable converter, the corresponding odd harmonics are injected into the absolute value signal |R s i s |Adjustment is performed, and the modulation wave adjustment signal Δx is

[0019] △x=|Qsin((2n+1)ωt+α)|n=1,2,3..N

[0020] Where Q is a real number, n is a positive integer, ω is the angular frequency, t is the time, and α is a specific angle;

[0021] (9) The final modulated wave signal is |R s i s +△x|;

[0022] (10) The final modulated wave signal |R s i s +△x| and the carrier exchange signals through the comparator to generate a PWM signal, which in turn controls the on and off of the switching devices of the single-phase energy unidirectional flow controllable converter.

[0023] This invention proposes a reactive power compensation control strategy for a controllable converter with unidirectional energy flow. This strategy utilizes a single-cycle control method, eliminates the need for a phase-locked loop (PLL), AC-side voltage sensors, and additional current sensors, resulting in low implementation costs. Compared to traditional SPWM (SVPWM) modulation, this method offers advantages such as simple implementation, fast dynamic response, strong robustness, low cost, and high converter power factor.

[0024] The following is a detailed description with reference to the accompanying drawings in conjunction with embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 System structure diagram and control strategy block diagram for reactive power compensation of energy unidirectional flow controllable converter;

[0026] Figure 2 A single-phase bridgeless converter based on an LC series filter circuit in an embodiment of the present invention;

[0027] Figure 3 It is a single-phase VIENNA converter based on LC series filter circuit;

[0028] Figure 4 It is a single-phase diode H-bridge converter based on LC series filter circuit;

[0029] Figure 5 The AC side input voltage and input current waveforms of a single-phase bridgeless converter based on an LC series filter circuit when only single-cycle control is used and the third harmonic is not injected into the modulation wave;

[0030] Figure 6 The THD of the AC side input current of a single-phase bridgeless converter based on an LC series filter circuit is calculated when only single-cycle control is used and the third harmonic is not injected into the modulation wave.

[0031] Figure 7 To adopt the proposed control strategy, after the third harmonic is injected into the modulation wave, the AC side input voltage and input current waveforms of the single-phase bridgeless converter based on the LC series filter circuit are shown;

[0032] Figure 8 In order to adopt the proposed control strategy, the AC side input current THD of the single-phase bridgeless converter based on the LC series filter circuit is calculated after the third harmonic is injected into the modulation wave. DETAILED DESCRIPTION

[0033] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings to fully understand the purpose, features and effects of the present invention. This embodiment provides a detailed implementation and specific operation process, but the scope of protection of the present invention is not limited to this embodiment.

[0034] The technical solution adopted by the present invention is as follows Figure 1 As shown, Figure 2 Taking the single-phase bridgeless converter based on the LC series filter circuit as an example, the steps of the reactive power compensation control strategy based on the controllable converter with unidirectional energy flow of the present invention are as follows:

[0035] (1) When the power grid contains inductive or capacitive loads, a control signal is given to connect the LC series filter circuit. When the power grid contains only resistive loads, a control signal is given to disconnect the LC series filter circuit.

[0036] (2) Sampling the DC side voltage of the single-phase bridgeless converter based on the LC series filter circuit to obtain the DC voltage signal U dc ;

[0037] (3) The reference signal U of the DC voltage signal* dc The DC voltage signal U sampled in step (2) dc Subtract and get the input signal ΔU of the voltage regulator. Send the input signal ΔU to the voltage regulator to get the output u of the voltage regulator. m ;

[0038] (4) According to the single-cycle control principle, the output u of the voltage regulator m for

[0039]

[0040] where R s R is the current sampling resistor on the AC side of the single-phase bridgeless converter based on the LC series filter circuit. e is the equivalent resistance of the single-phase bridgeless converter based on the LC series filter circuit, u m is a positive number;

[0041] (5) The output u of the voltage regulator in step (4) is m Send it to the carrier generation module to generate an amplitude of u m triangle wave;

[0042] (6) The AC side current sampling resistor R of the single-phase bridgeless converter based on the LC series filter circuit s The AC side input current i of the single-phase bridgeless converter based on the LC series filter circuit is s Sampling is performed to obtain the single-phase AC input current sampling signal R s i s ;

[0043] (7) The single-phase AC input current sampling signal R in step (6) s i s Send it to the absolute value module to get the absolute value signal |R s i s |;

[0044] (8) According to the reactive power required by the single-phase bridgeless converter based on the LC series filter circuit, the third harmonic is injected into the absolute value signal |R s i s |Adjustment is performed, and the modulation wave adjustment signal Δx is

[0045] △x=|20sin(3ωt+180°)|

[0046] Where ω is the angular frequency and t is the time;

[0047] (9) The final modulated wave signal is |R s i s +△x|;

[0048] (10) The final modulated wave signal |R s i s +△x| and the carrier are exchanged with each other through a comparator to generate a PWM signal, which in turn controls the on and off of the switching devices of the single-phase bridgeless converter based on the LC series filter circuit.

[0049] Example: Simulation results analysis.

[0050] A single-phase bridgeless converter model based on LC series filter circuit was built in Matlab / Simulink, and its control strategy was simulated.

[0051] Take the case of a grid containing resistive and inductive loads as an example. Figure 5 、 Figure 6 They are respectively the AC side input voltage, input current waveform and AC side input current THD of the single-phase bridgeless converter based on LC series filter circuit when only single cycle control is adopted and the third harmonic is not injected into the modulation wave. Figure 7 、 Figure 8 The AC side input voltage, input current waveform and AC side input current THD of the single-phase bridgeless converter based on the LC series filter circuit are respectively shown after the third harmonic is injected into the modulation wave by adopting the proposed control strategy. It can be seen that when only single-cycle control is adopted and the third harmonic is not injected into the modulation wave, the input current distortion of the single-phase bridgeless converter based on the LC series filter circuit is serious, and the current THD is 5.28%, while the national standard requires the current THD to be 5%. After the third harmonic is injected into the modulation wave, the input current distortion of the single-phase bridgeless converter based on the LC series filter circuit is improved, and the input current THD is only 3.69%, which is within the range required by the national standard, proving the effectiveness of the reactive power compensation control strategy based on the energy unidirectional flow controllable converter provided by the present invention.

[0052] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the concept and scope of the present invention. Without departing from the design of the present invention, various modifications and improvements made to the technical solution of the present invention by engineers and technicians in this field should fall within the scope of protection of the present invention.

Claims

1. A reactive power compensation control strategy based on a unidirectional energy flow controllable converter, wherein the unidirectional energy flow controllable converter includes a single-phase unidirectional energy flow controllable converter, wherein the single-phase unidirectional energy flow controllable converter includes a single-phase bridgeless converter based on an LC series filter circuit, a single-phase Vienna converter based on an LC series filter circuit, and a single-phase diode H-bridge converter based on an LC series filter circuit. It is characterized in that A reactive power compensation control strategy based on a unidirectional energy flow controllable converter has the following steps: (1) When the power grid contains inductive or capacitive loads, a control signal is given to connect the LC series filter circuit. When the power grid contains only resistive loads, a control signal is given to disconnect the LC series filter circuit. (2) Sampling the DC side voltage of the single-phase energy unidirectional flow controllable converter to obtain the DC voltage signal U dc ; (3) The reference signal U of the DC voltage signal * dc The DC voltage signal U sampled in step (2) dc Subtract and get the input signal ΔU of the voltage regulator. Send the input signal ΔU to the voltage regulator to get the output u of the voltage regulator. m ; (4) According to the single-cycle control principle, the output u of the voltage regulator m for where R s R is the current sampling resistor on the AC side of the single-phase energy unidirectional flow controllable converter, e is the equivalent resistance of the single-phase energy unidirectional flow controllable converter, u m is a positive number; (5) The output u of the voltage regulator in step (4) is m Send it to the carrier generation module to generate an amplitude of u m triangle wave; (6) The AC side current sampling resistor R of the controllable converter through the single-phase energy unidirectional flow s The AC side input current i of the single-phase energy unidirectional flow controllable converter s Sampling is performed to obtain the single-phase AC input current sampling signal R s i s ; (7) The single-phase AC input current sampling signal R in step (6) s i s Send it to the absolute value module to get the absolute value signal |R s i s |; (8) According to the reactive power required by the single-phase energy unidirectional flow controllable converter, the corresponding odd harmonics are injected into the absolute value signal |R s i s |Adjust the modulation wave to adjust the signal Δx to △x=|Qsin((2n+1)ωt+α)|n=1,2,3..N Where Q is a real number, n is a positive integer, ω is the angular frequency, t is the time, and α is a specific angle; (9) The final modulated wave signal is |R s i s +△x|; (10) The final modulated wave signal |R s i s +△x| and the carrier exchange signals through the comparator to generate a PWM signal, which in turn controls the on and off of the switching devices of the single-phase energy unidirectional flow controllable converter.

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