Harmonic suppression and dynamic voltage compensation method based on composite control series filter

Abstract

The invention relates to a harmonic suppression and dynamic voltage compensation method based on a composite control series filter, and belongs to the field of power electronic technology and electric energy quality control. Harmonic current passing through a primary winding of a transformer and a sudden rising or falling signal of power supply voltage are extracted, and after the two signals are controlled and combined into a reference signal, a voltage source inverter (VSI) connected with a secondary side of the transformer in parallel shows a controllable voltage characteristic. The control parameters of the harmonic current can enable the transformer to present relatively large controllable impedance to harmonic waves, so that harmonic wave isolation is realized. In addition, the VSI compensates for the system voltage deviation by detecting the voltage drop. And finally, establishing a simulation model to verify that the series active power filter based on the control strategy can isolate harmonic waves and effectively compensate voltage deviation. Harmonic suppression and dynamic voltage compensation functions can be realized at the same time, and the power quality of a middle-high voltage system is improved.

Description

Technical Field

[0001] This invention relates to the fields of power electronics technology and power quality management, and in particular to a method for harmonic suppression and dynamic voltage compensation based on a composite control series filter. Background Technology

[0002] With the development of the global energy internet and distributed generation technology, power systems face power quality problems such as harmonic pollution and voltage sags / sags. While traditional dynamic voltage restorers (DVRs) can quickly compensate for voltage deviations, they can only regulate load voltage and cannot suppress harmonics generated by nonlinear loads. Parallel active power filters (APFs) are limited by inverter capacity and are difficult to apply to medium- and high-voltage systems, and their filtering effect on voltage-type harmonic loads is limited. Therefore, a new device and method that combines harmonic suppression and voltage compensation is urgently needed. Summary of the Invention

[0003] The purpose of this invention is to provide a harmonic suppression and dynamic voltage compensation method based on a composite-controlled series filter, which overcomes the technical deficiency of existing technologies that cannot simultaneously suppress harmonics and compensate for voltage deviations. This invention utilizes a series active power filter (SAPF) based on a composite control strategy to achieve harmonic suppression and dynamic voltage compensation, thereby improving the power quality of medium- and high-voltage systems.

[0004] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0005] The harmonic suppression and dynamic voltage compensation method based on a composite controlled series filter includes the following steps:

[0006] Step S1: Harmonic current detection and fundamental frequency separation, extracting harmonic components from the grid current to provide a reference signal for harmonic suppression;

[0007] Step S2: Voltage Deviation Detection and Compensation Reference Generation. Detect the deviation between the load voltage and the rated value, and generate a voltage compensation reference signal.

[0008] Step S3: Generate and superimpose composite control signals, combining harmonic control signals with voltage compensation signals to drive the inverter to output controllable voltage;

[0009] Step S4: Inverter drive and compensation execution. Controllable voltage is output through the voltage source inverter VSI to achieve harmonic isolation and voltage compensation.

[0010] The harmonic current detection and fundamental frequency separation described in step S1, extracting harmonic components from the grid current to provide a reference signal for harmonic suppression, specifically involves: based on the transformer equivalent T circuit, the voltage equation can be written as:

[0011]

[0012] Where U1, Z1, and I1 are the primary side voltage, impedance, and current, respectively; U2', Z2', and I2' are the secondary side voltage, impedance, and current referred to the primary side, respectively, Z... m As the excitation impedance, the controllable secondary voltage U2 is connected across the secondary winding and the primary winding, and the current I1 meets the requirements of a series transformer.

[0013] -U′2=k1I1

[0014] Where k1 is a controllable coefficient, and Z is the impedance of the equivalent terminal AX. AX It can be derived from the following formula:

[0015]

[0016] When only harmonic current is detected Harmonic equivalent impedance of the time winding It can be written as:

[0017]

[0018] Therefore, harmonic equivalent impedance The variable is changed by setting a controllable coefficient k1. Furthermore, to ensure stable operation within the system, a larger k1 value results in better system performance. This also improves harmonic isolation performance, enabling the function of the harmonic suppressor.

[0019] Step S2, voltage deviation detection and compensation reference generation, detects the deviation between the load voltage and the rated value, and generates a voltage compensation reference signal; specifically, in the voltage compensation vector, U S U T U L These are the power supply voltage, the voltage at the transformer terminal AX, and the voltage at the load terminal, respectively. The relationship between these three voltages satisfies... To ensure the normal operation of the load, the power supply voltage before normal operation is selected to expand or contract as the compensation reference voltage U. ref Therefore, any voltage deviation can be compensated by the output voltage of the series-connected APF, so the user can always see a nearly continuous and satisfactory voltage waveform on the load side. In this way, a minimal system can be restored. The voltage is as follows:

[0020]

[0021] in, U is the minimum voltage amplitude on the power supply side. L The voltage amplitude on the load side, where α is the phase difference of the system voltage before and after compensation. The maximum compensable phase angle difference α. max for The series active power generated by the APF is:

[0022]

[0023] Among them, I L Generally refers to load current. Given the phase angle between the load voltage and current, suppression and voltage compensation are analyzed based on the harmonic principle.

[0024] Step S3 involves generating and superimposing a composite control signal, combining the harmonic control signal with the voltage compensation signal to drive the inverter to output a controllable voltage. Specifically, the voltage control equation generated by the voltage source inverter (VSI) is as follows:

[0025] U i =k1i h +k2ΔU

[0026] Among them, U i Let i be the voltage at the i-th node (or a certain monitoring point). h ΔU represents the harmonic current, and ΔU represents the voltage deviation.

[0027] According to the superposition theorem, the control strategy proposed in this invention controls the fundamental component and harmonic components separately. Therefore, this series of APFs, based on this control strategy, can exhibit high impedance harmonics to isolate harmonics, and compensate for voltage deviation drops by detecting the voltage and setting a controllable coefficient k2.

[0028] Step S4 describes the inverter drive and compensation execution, which uses a controllable voltage output via VSI to achieve harmonic isolation and voltage compensation, including harmonic current detection and voltage deviation detection methods.

[0029] 1) Harmonic current detection method:

[0030] Assumption via i s Multiplying (t) by cosωt and sinωt, we get the following equation:

[0031]

[0032] Where n is the harmonic order. It is the initial phase angle of the nth harmonic current, I n Let ω be the effective value of the nth harmonic current, t be the angular frequency, and t be the time variable. Through the implementation of the LPF, the RMS value yields the basic active and reactive power. The basic current can then be expressed as follows:

[0033]

[0034] Where i sp (t), i sq(t) is i s (t) The components after coordinate transformation; harmonic currents can be obtained as the basic current through subtraction:

[0035] i h (t)=i s (t)-i sf (t)

[0036] 2) Voltage deviation detection method:

[0037] The virtual current of phase β is obtained by applying the load voltage u L Constructed with a 90° delay, the following formula was obtained after calculation:

[0038]

[0039] Among them, u p u q Let u be the voltage component in the p, q coordinate system; α u β The load voltage components are in the α and β stationary coordinate system. Harmonic voltage components in the p, q coordinate system.

[0040] After the LPF filter removes harmonics, an inverse coordinate transformation can be performed to remove the fundamental components of the load voltage.

[0041]

[0042] Among them, u αf u βf The fundamental voltage components in the α and β coordinate systems after harmonic filtering; This represents the fundamental voltage component in the p, q coordinate system after LPF filtering.

[0043] Similarly, voltage deviation can also be obtained.

[0044] ΔU=U Lref -U Lf =U Lref -U αf

[0045] Among them, U Lref U is the load reference voltage. αf Let be the fundamental voltage of the load voltage fundamental component on the α axis.

[0046] The beneficial effects of this invention are as follows: This invention proposes a harmonic suppression and dynamic voltage compensation control strategy for a SAPF (Active Power Filter). First, the basic principle of harmonic suppression is analyzed: by detecting the harmonic current on the primary side of the transformer, and based on the voltage-current control equation and the T-type equivalent circuit, the primary winding of the transformer presents a high impedance to harmonic components, thereby achieving the function of a harmonic isolator. Simultaneously, the voltage deviation across the load is detected, making the primary winding of the transformer a controllable voltage source to compensate for voltage fluctuations at the load end. Since the voltage deviation is in the fundamental frequency form and does not interfere with harmonic components, the two control modes are superimposed to form a composite control method, enabling the primary side of the transformer to present both high harmonic impedance and function as a controllable fundamental voltage source. Finally, a simulation model is established in Matlab / Simulink software, and the simulation results verify the effectiveness of the proposed control strategy. This invention can simultaneously achieve harmonic suppression and dynamic voltage compensation functions, improving the power quality of medium and high voltage systems. Attached Figure Description

[0047] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate the invention and are used to explain it, but do not constitute an undue limitation of the invention.

[0048] Figure 1 This is a flowchart of the harmonic suppression and dynamic voltage compensation method based on a composite controlled series filter according to the present invention.

[0049] Figure 2 The magnetic coupling circuit of the dual-winding transformer of the present invention;

[0050] Figure 3 This is the equivalent T-type circuit of the present invention;

[0051] Figure 4 This is the voltage compensation vector diagram of the present invention;

[0052] Figure 5 The topology of the SAPF for harmonic suppression and dynamic voltage compensation of the present invention;

[0053] Figure 6 This invention demonstrates the filtering performance under inductive nonlinear loads.

[0054] Figure 7 This invention demonstrates the filtering performance under capacitive nonlinear loads.

[0055] Figure 8 This invention provides voltage deviation compensation performance during power supply expansion.

[0056] Figure 9 This invention provides voltage deviation compensation performance when the power supply droops. Detailed Implementation

[0057] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] See Figures 1 to 9 As shown, the series active power filter (SAPF) control strategy for harmonic suppression and dynamic voltage compensation of this invention extracts the harmonic current and the sudden rise or fall signals of the power supply voltage through the primary winding of the transformer. After controlling and combining these two signals into a reference signal, the voltage source inverter (VSI) connected in parallel with the secondary winding of the transformer will exhibit controllable voltage characteristics. The control parameters of the harmonic current enable the transformer to present a large controllable impedance to harmonics, thereby achieving harmonic isolation. In addition, the VSI compensates for system voltage deviation by detecting voltage drop. Finally, a simulation model is established to verify that the series active power filter based on this control strategy can isolate harmonics and effectively compensate for voltage deviation.

[0059] See Figure 1 As shown, the harmonic suppression and dynamic voltage compensation method based on a composite controlled series filter of the present invention includes:

[0060] Step S1: Harmonic current detection is separated from the fundamental frequency, and harmonic components are extracted from the grid current to provide a reference signal for harmonic suppression;

[0061] Step S2, Voltage Deviation Detection and Compensation Reference Generation: Detect the deviation between the load voltage and the rated value, and generate a voltage compensation reference signal;

[0062] Step S3: Generate and superimpose composite control signals, combining harmonic control signals with voltage compensation signals to drive the inverter to output controllable voltage;

[0063] Step S4: Inverter drive and compensation are executed, and a controllable voltage is output through VSI to achieve harmonic isolation and voltage compensation.

[0064] Preferably, the core of step S1 considers the analysis of system dynamic characteristics, the separation of harmonic current detection from the fundamental frequency, and the extraction of harmonic components from the grid current to provide a reference signal for harmonic suppression. Figure 2 and Figure 3 The diagram shows the magnetic coupling circuit and equivalent T-circuit of a two-winding transformer. According to... Figure 3 The voltage equation for the transformer equivalent circuit T shown can be written as:

[0065]

[0066] Where U1, Z1, and I1 are the primary side voltage, impedance, and current, respectively; U2', Z2', and I2' are the secondary side voltage, impedance, and current referred to the primary side, respectively, Z... m Assuming the excitation impedance is given, and the controllable voltage U2' is connected across the secondary winding and the primary winding, and the current I1 satisfies the requirements of a series transformer:

[0067] -U′2=k1I1 (2) where k1 is a controllable coefficient, and Z is the impedance of the equivalent terminal AX. AX The following can be derived from the formulas (1) and (2):

[0068]

[0069] When only harmonic current is detected Harmonic equivalent impedance of the time winding It can be written as:

[0070]

[0071] Therefore, harmonic equivalent impedance The variable is changed by setting a controllable coefficient k1. Furthermore, to ensure stable operation within the system, a larger k1 value results in better system performance. This also improves harmonic isolation performance, enabling the function of the harmonic suppressor.

[0072] Preferably, the core of step S2 lies in voltage deviation detection and compensation reference generation, detecting the deviation between the load voltage and the rated value, and generating a voltage compensation reference signal. See also Figure 4 The voltage compensation vector diagram shown is shown, where U S U T U L The voltages are the power supply voltage, the voltage at the transformer terminal AX, and the voltage at the load terminal, respectively. The relationship between these three voltages satisfies... To ensure the normal operation of the load, the power supply voltage before normal operation is selected to expand or contract as the compensation reference voltage U. ref Therefore, any voltage deviation can be compensated by the output voltage of the series-connected APF, so the user can always see a nearly continuous and satisfactory voltage waveform on the load side. In this way, a minimal system can be restored. The voltage is as follows:

[0073]

[0074] in, U is the minimum voltage amplitude on the power supply side. L The voltage amplitude on the load side is given, where α is the phase difference of the system voltage before and after compensation. Let be the maximum voltage amplitude of the transformer; then the maximum phase angle difference α to be compensated. max for

[0075] The series active power generated by the APF is

[0076]

[0077] Among them, I L Refers to load current. Given the phase angle between the load voltage and current, suppression and voltage compensation are analyzed based on harmonic principles. Figure 4 The main series APF circuit is given.

[0078] Preferably, the core of step S3 lies in the generation and superposition of composite control signals, combining harmonic control signals with voltage compensation signals to drive the inverter to output a controllable voltage. See also Figure 1 The system control scheme block diagram is shown below. The voltage control equation generated by the voltage source inverter (VSI) is as follows:

[0079] U i =k1i h +k2ΔU (7)

[0080] Among them, U i Let i be the voltage at the i-th node (or a certain monitoring point). h ΔU represents the harmonic current, and ΔU represents the voltage deviation.

[0081] According to the superposition theorem, the proposed control strategy controls the fundamental and harmonic components separately. Therefore, this series of APFs, based on this control strategy, can exhibit high impedance harmonics to isolate them, and compensate for voltage deviation drops by detecting the voltage and setting a controllable coefficient k2.

[0082] Preferably, the core of step S4 lies in the inverter drive and compensation execution, which achieves harmonic isolation and voltage compensation by outputting a controllable voltage through the VSI, specifically including harmonic current detection method and voltage deviation detection method:

[0083] 1) Harmonic current detection method:

[0084] Assumption via i s Multiplying (t) by cosωt and sinωt, we get the following equation:

[0085]

[0086] Where n is the harmonic order. It is the initial phase angle of the nth harmonic current, I nLet ω be the effective value of the nth harmonic current, t be the angular frequency, and t be the time variable. Through the implementation of the LPF, the RMS value yields the basic active and reactive power. The basic current can then be expressed as follows:

[0087]

[0088] Among them, i sp (t), i sq (t) is i s (t) The components after coordinate transformation, harmonic current can be obtained by subtraction, such as... Figure 5 As shown, the basic current in formula (9)

[0089] i h (t)=i s (t)-i sf (t) (9)

[0090] 2) Voltage deviation detection method:

[0091] The virtual current of phase β is constructed by the following formula, with the load voltage Lu delayed by 90°

[13] . After calculation, the following formula is obtained:

[0092]

[0093] Where u p u q Let u be the voltage component in the p, q coordinate system. α u β Let α and β be the load voltage components in the stationary coordinate system. Harmonic voltage components in the p, q coordinate system.

[0094] After the LPF filters out harmonics and performs an inverse coordinate transformation, the fundamental component of the load voltage can be removed.

[0095]

[0096] Similarly, voltage deviation through Figure 5 Available

[0097] ΔU=U Lref -U Lf =U Lref -U αf (12)

[0098] 3) Simulation Analysis

[0099] Operating Condition 1: To verify the effectiveness of the proposed control strategy in a series active filter, a simulation model was established. The filtering effect is as follows: Figure 6 As shown, the total harmonic distortion (THD) is 3.85%. Meanwhile, in Figure 7In this system, when the nonlinear load exhibits voltage-source harmonic characteristics, the THD is 3.21%, and the power supply current is almost sinusoidal. Therefore, this series of active filters can effectively function as harmonic isolators for both voltage-source and current-source harmonic loads.

[0100] Operating Condition 2: When the power supply voltage rises sharply at 1.0s and falls sharply at 2.0s, Figure 8 and Figure 9 Both studies demonstrate that the series-connected APF with fast dynamic response exhibits good voltage deviation compensation performance. Therefore, from Figure 6 , Figure 7 and Figure 8 , Figure 9 It can be seen that the implementation of this control strategy can effectively isolate harmonics and compensate for deviations in system voltage changes.

[0101] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made to the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for harmonic suppression and dynamic voltage compensation based on a composite controlled series filter, characterized in that: Includes the following steps: Step S1: Harmonic current detection and fundamental frequency separation, extracting harmonic components from the grid current to provide a reference signal for harmonic suppression; Step S2: Voltage Deviation Detection and Compensation Reference Generation. Detect the deviation between the load voltage and the rated value, and generate a voltage compensation reference signal. Step S3: Generate and superimpose composite control signals, combining harmonic control signals with voltage compensation signals to drive the inverter to output controllable voltage; Step S4: Inverter drive and compensation execution. Controllable voltage is output through the voltage source inverter VSI to achieve harmonic isolation and voltage compensation.

2. The harmonic suppression and dynamic voltage compensation method based on a composite controlled series filter according to claim 1, characterized in that: Step S1, which involves detecting and separating the harmonic current from the fundamental frequency, extracting the harmonic components from the grid current to provide a reference signal for harmonic suppression, specifically involves: Based on the transformer T-type equivalent circuit, the voltage equation can be written as: Where U1, Z1, and I1 are the primary side voltage, impedance, and current, respectively; U2', Z2', and I2' are the secondary side voltage, impedance, and current referred to the primary side, respectively, Z... m As the excitation impedance, the controllable secondary voltage U2' is connected across the secondary winding and the primary winding current I1, which meets the requirements of a series transformer. -U′2=k1I1 Where k1 is a controllable coefficient, and Z is the impedance of the equivalent terminal AX. AX Derived from the following formula: When only harmonic current is detected Harmonic equivalent impedance of the time winding Written as: Therefore, harmonic equivalent impedance The variable is changed by setting a controllable coefficient k1; in addition, to ensure stable operation, the larger the value of k1 in the system, the better the system performance; harmonic isolation performance, so that the function of harmonic suppressor can be played.

3. The harmonic suppression and dynamic voltage compensation method based on a composite controlled series filter according to claim 1, characterized in that: Step S2, voltage deviation detection and compensation reference generation, detects the deviation between the load voltage and the rated value, and generates a voltage compensation reference signal. Specifically, in the voltage compensation vector, U... S U T U L The voltages are the power supply voltage, the voltage at the transformer terminal AX, and the voltage at the load terminal, respectively. The relationship between these three voltages satisfies... The power supply voltage is selected to expand or contract as the compensation reference voltage U. ref Any voltage deviation can be compensated by the output voltage of the series-connected APF; the voltage is as follows: in, U is the minimum voltage amplitude on the power supply side. L Let be the voltage amplitude on the load side, and α be the phase difference of the system voltage before and after compensation. The maximum voltage amplitude of the transformer; the maximum compensable phase angle difference α. max for: The series active power generated by the APF is: Among them, I L Refers to load current. Given the phase angle between the load voltage and current, suppression and voltage compensation are analyzed based on the harmonic principle.

4. The harmonic suppression and dynamic voltage compensation method based on a composite controlled series filter according to claim 1, characterized in that: Step S3, which involves generating and superimposing a composite control signal, combines the harmonic control signal with the voltage compensation signal to drive the inverter to output a controllable voltage. Specifically: The voltage control equation generated by the voltage source inverter VSI is: You i =k1i h +k2ΔU Among them, U i Let i be the voltage at the i-th node or a certain monitoring point. h Here, ΔU represents the harmonic current, and ΔU represents the voltage deviation. According to the superposition theorem, the APF exhibits high impedance harmonics in order to isolate harmonics, and compensates for voltage deviation drop by detecting voltage and setting a controllable coefficient k2.

5. The harmonic suppression and dynamic voltage compensation method based on a composite controlled series filter according to claim 1, characterized in that: Step S4 describes the inverter drive and compensation execution, which uses a controllable voltage output via VSI to achieve harmonic isolation and voltage compensation, including harmonic current detection and voltage deviation detection methods. 1) Harmonic current detection method: set up via i s Multiplying (t) by cosωt and sinωt, we get the following equation: Where n is the harmonic order. It is the initial phase angle of the nth harmonic current, I n Let ω be the effective value of the nth harmonic current, ω be the angular frequency, and t be the time variable. By implementing the LPF, the RMS value can be obtained as the basic active and reactive power; then, the basic current is expressed as follows: Where i sp (t), i sq (t) is i s (t) The components after coordinate transformation, and the harmonic current are obtained by subtraction to obtain the basic current: i h (t)=i s (t)-i sf (t) 2) Voltage deviation detection method: The virtual current of phase β is obtained by applying the load voltage u L Constructed with a 90° delay, the following formula was obtained after calculation: Among them, u p u q Let u be the voltage component in the p, q coordinate system; α u β The load voltage components are in the α and β stationary coordinate system. Harmonic voltage components in the p, q coordinate system; After the LPF filter removes harmonics, an inverse coordinate transformation can be performed to remove the fundamental components of the load voltage. Among them, u αf u βf The fundamental voltage components in the α and β coordinate systems after harmonic filtering; The fundamental voltage component in the p, q coordinate system after LPF filtering; Similarly, the voltage deviation can be obtained: ΔU=U Lref -U Lf =U Lref -U αf Among them, U Lref U is the load reference voltage. αf Let be the fundamental voltage of the load voltage fundamental component on the α axis.

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