Unbalance control method giving consideration to harmonic compensation and three-phase active power regulation functions

Abstract

An unbalance control method giving consideration to harmonic compensation and three-phase active power regulation functions comprises the following steps that 1, a three-phase four-wire system is decomposed into three independent single-phase power supply systems, and A-phase, B-phase and C-phase fundamental wave active currents are distributed again through a single-phase harmonic detection method; 2, calculating A-phase current ia (t); and step 3, obtaining a sinusoidal signal which has the same frequency and phase as the A-phase power grid voltage and has a peak value of 1 through phase locking, and multiplying the voltage ua (t) by the current ia (t). The method is used for solving the problems that existing electric equipment basically uses uncontrolled bridge rectification, carries a large amount of harmonic waves and is limited in improvement of electric energy quality.

Description

Technical Field

[0001] The invention relates to an unbalanced control method taking into account both harmonic compensation and three-phase active power regulation functions. Background Art

[0002] Most of the loads in my country's power grid are single-phase loads. Due to the uneven spatial distribution of users, the randomness, type and size of the loads are difficult to determine. There are not only a large number of reactive power and harmonics, but also serious imbalance of three-phase loads. Harmonics and reactive power have many hazards: increase line current, accelerate line aging; cause voltage waveform distortion, reduce the power quality of the power grid; may affect or even damage other electrical equipment, etc. They have a certain impact on the stability of the entire power system.

[0003] The power grid generally uses APF to compensate for harmonics and reactive power, but APF is often used in three-phase three-wire systems, and is not applicable to the three-phase four-wire system of the rural power grid. The load of a single user is limited, the number is large and the distribution is scattered, so it is not realistic to use terminal power correction equipment to improve the power quality. As the three-phase load is unbalanced, SVG is usually used to balance the three-phase current. The reactive power and negative sequence current detected by the load are compared with the current generated by SVG in a closed loop, and finally the IGBT is controlled to output a compensation current of equal size and opposite direction. Although this technical solution realizes the regulation of imbalance and compensation of reactive current, it does not compensate for harmonics. However, existing electrical equipment basically uses uncontrolled bridge rectification, which carries a large number of harmonics, so this method has limited effect on improving power quality. Summary of the invention

[0004] The purpose of the present invention is to provide an unbalanced control method that takes into account both harmonic compensation and three-phase active power regulation functions, so as to solve the problem that existing electrical equipment basically uses uncontrolled bridge rectification, has a large amount of harmonics, and has limited effect on improving power quality.

[0005] In order to solve the above problems, the technical solution of the present invention is: An unbalance control method taking into account both harmonic compensation and three-phase active power regulation functions comprises the following steps: Step 1: Decompose the three-phase four-wire system into three independent single-phase power supply systems, and use the single-phase harmonic detection method to redistribute the fundamental active current of phase A, phase B and phase C; Step 2: Calculate the phase A current i a (t); Step 3: Through phase locking, a sinusoidal signal with the same frequency and phase as the A-phase grid voltage and a peak value of 1 is obtained, and the voltage u a (t) and current i a (t) and we can get:

[0006] The DC component is obtained by using a low-pass filter, and then amplified by one time and multiplied by the sinusoidal signal obtained by phase locking to obtain the fundamental active current I pa (t); Step 4: Calculate the fundamental active current I of phase B and phase C according to the above steps pb (t) and I pc (t), and then take the mean value of the three-phase fundamental current amplitude I pave , will I pave As the amplitude of the target current under the grid-side balanced state;

[0007] Step 5: Multiply the amplitude of the target current by the phase of the three-phase voltage to obtain the target current ipav of each phase e _a、ipav e _b and i pave_c . Three-phase current i k (t) is subtracted from the target current to obtain the given current i required for compensation of each phase Tk (t): i Ta (t) = i a (t)-i pave_a ; i Tb (t) = i b (t)-i pave_b ; i Tc (t) = i c (t)-i pave_c ; Step 6: When the regulator balances the three-phase current, the power consumed by the regulator is: w res =U a I Ta +U b I Tb +U c I Tc =U a [ΔI pa (t)+i La (t)]+U b [ΔI pb (t)+i Lb (t)]+U c [ΔI pc (t)+i Lc (t)] =[U a ΔI pa (t)+U b ΔI pb(t)+U c ΔI pc (t)]+[U a i La (t)+U b i Lb (t)+U c i Lc (t)]. =U L [ΔI pa (t)+ΔI pb (t)+ΔI pc (t)]+[U a i La (t)+U b i Lb (t)+U c i Lc (t)] =[U a i La (t)+U b i Lb (t)+U c i Lc (t)]=w apf

[0008] The beneficial effects of the present invention are: it can adjust the three-phase four-wire system with unbalanced load, balance the three-phase current, compensate for reactive power and harmonics, so as to improve the power quality of the system. Using a single-phase harmonic detection algorithm, the fundamental active current of each phase is extracted, and its average is taken as the target value of each phase current when the three phases are balanced. Through the control of the regulator, the grid-side current is redistributed under the condition that the load-side current remains unchanged to achieve a balanced state, eliminate reactive power and harmonics, and reduce the neutral line current. In this way, the three-phase current balance is achieved, the neutral line current is effectively reduced, and reactive power and harmonic currents are compensated at the same time, thereby improving the power quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be further described below in conjunction with the accompanying drawings: Figure 1 Schematic diagram of the current detection algorithm of the three-phase unbalanced regulator of the present invention. DETAILED DESCRIPTION

[0010] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0011] like Figure 1As shown, an unbalanced control method taking into account both harmonic compensation and three-phase active power regulation functions comprises the following steps: Step 1: Decompose the three-phase four-wire system into three independent single-phase power supply systems, and use the single-phase harmonic detection method to redistribute the fundamental active currents of phases A, B, and C to compensate for the reactive, harmonic, and fundamental negative-sequence active currents and balance the grid-side active current.

[0012] Step 2: Since the three phases are independent of each other, the single-phase harmonic detection algorithm is introduced by taking phase A as an example. The current i a (t) Fourier decomposition is as follows:

[0013] Where: n refers to 2...n If the basic active current I of phase A is pa , basic reactive current I qa and harmonic current I ha (t) are respectively expressed as follows: I pa =I1cosφ1; (2) I qa =I1sinφ1 (3) Substituting equations (2), (3) and (4) into equation (1), we can obtain: At this time, the A phase current is decomposed into the fundamental active current I pa (t), reactive current I qa (t) Harmonic current I ha (t). As long as I pa (t), and i a (t) can be subtracted to obtain harmonics and reactive current.

[0014] Assume that the A-phase grid voltage is: e a (t) = U m sinωt (6) U m It refers to the grid voltage amplitude; Step 3: Get a sinusoidal signal with the same frequency and phase as the A-phase grid voltage and a peak value of 1 through phase locking u a (t) = sinωt (7) will u a (t) and current i a (t) and we get: It can be seen from formula (8) that u a (t) is the peak value of e at 1 a (t),u a (t) is multiplied by the A phase current, and the result can be expressed as the sum of the DC component and the AC component. Among them, the DC component is is the fundamental active current amplitude I pa Half of the DC component can be obtained by using a low-pass filter and then amplified by one time to obtain I pa Finally, multiply it by the phase-locked sinusoidal signal sinωt to get the fundamental active current I pa (t).

[0015] Step 4: Similarly, the fundamental active current I of phase B and phase C can be obtained pb (t), I pc (t), take the mean value of the three-phase fundamental current amplitude I pave , which is used as the amplitude of the target current under the grid-side balanced state.

[0016] Step 5: Multiply the amplitude of the target current by the phase of the three-phase voltage to obtain the target current ipav of each phase e _a、ipav e _b and ipav e _c, three-phase current i k (t) is subtracted from the target current to obtain the given current i required for compensation of each phase Tk (t):i Ta (t) = i a (t)-i pave_a

[0017] i Tb (t) = i b (t)-i pave_b (10) i Tc (t) = i c (t)-i pave_c

[0018] Step 6: Ignoring the internal resistance of the DC capacitor and the circuit resistance, when the regulator balances the three-phase current, the power consumed by the regulator is: w res =U a I Ta +U b I Tb +U c I Tc =U a [ΔI pa (t)+i La (t)]+Ub [ΔI pb (t)+i Lb (t)]+U c [ΔI pc (t)+i Lc (t)] =[U a ΔI pa (t)+U b ΔI pb (t)+U c ΔI pc (t)]+[U a i La (t)+U b i Lb (t)+U c i Lc (t)] =U L [ΔI pa (t)+ΔI pb (t)+ΔI pc (t)]+[U a i La (t)+U b i Lb (t)+U c i Lc (t)]=[U a i La (t)+U b i Lb (t)+U c i Lc (t)]=w apf (11) It can be seen from the above formula that under ideal conditions, when the algorithm is used to adjust the fundamental negative-sequence active current and the neutral line zero-sequence current, no active power loss will be generated.

[0020] The contents described in the embodiments of this specification are merely an enumeration of the implementation forms of the inventive concept. The protection scope of the present invention should not be regarded as limited to the specific forms described in the embodiments. The protection scope of the present invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. An unbalanced control method taking into account both harmonic compensation and three-phase active power regulation functions, characterized in that: The steps include: Step 1: Decompose the three-phase four-wire system into three independent single-phase power supply systems, and use the single-phase harmonic detection method to redistribute the fundamental active current of phase A, phase B and phase C; Step 2: Calculate the phase A current i a (t); Step 3: Through phase locking, a sinusoidal signal with the same frequency and phase as the A-phase grid voltage and a peak value of 1 is obtained, and the voltage u a (t) and current i a (t) and we can get: The DC component is obtained by using a low-pass filter, and then amplified by one time and multiplied by the sinusoidal signal obtained by phase locking to obtain the fundamental active current I pa (t); Step 4: Calculate the fundamental active current I of phase B and phase C according to the above steps pb (t) and I pc (t), and then take the mean value of the three-phase fundamental current amplitude I pave , will I pave As the amplitude of the target current under the grid-side balanced state; Step 5: Multiply the amplitude of the target current by the phase of the three-phase voltage to obtain the target current i of each phase pave_a 、i pave_b and i pave_c ; Three-phase current i k (t) is subtracted from the target current to obtain the given current i required for compensation of each phase Tk (t): i Ta (t)=i a (t)-i pave_a ; i Tb (t)=i b (t)-i pave_b ; i Tc (t)=i c (t)-i pave_c ; Step 6: When the regulator balances the three-phase current, the power consumed by the regulator is: w res =U a I Ta +U b I Tb +U c I Tc =U a [ΔI pa (t)+i La (t)]+U b [ΔI pb (t)+i Lb (t)]+U c [ΔI pc (t)+i Lc (t)] =[U a ΔI pa (t)+U b ΔI pb (t)+U c ΔI pc (t)]+[U a i La (t)+U b i Lb (t)+U c i Lc (t)] =U L [ΔI pa (t)+ΔI pb (t)+ΔI pc (t)]+[U a i La (t)+U b i Lb (t)+U c i Lc (t)] =[U a i La (t)+U b i Lb (t)+U c i Lc (t)]=w apf 。 2. The unbalanced control method according to claim 1 that takes into account both harmonic compensation and three-phase active power regulation functions, characterized in that: In step 2, the A phase current i a The calculation method of (t) includes: For phase A current i a (t) Perform Fourier decomposition The basic active current I of phase A pa , basic reactive current I qa and harmonic current I ha (t) are respectively expressed as follows: I pa =I1cosφ1; I qa =I1sinφ1; Then i a The expression of (t) is:

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