CN-117220288-B - Self-adaptive alternating current fractional order filter

CN117220288BCN 117220288 BCN117220288 BCN 117220288BCN-117220288-B

Abstract

The invention discloses a self-adaptive alternating current fractional order filter, which relates to the technical field of electric energy quality and comprises a controllable fractional order capacitor and a harmonic inductor L r which are connected in series, wherein the fractional order filter is connected between an alternating current bus and the ground and is in parallel connection with a load R o , and the controllable fractional order capacitor comprises an output capacitor C r , an output inductance L f , The switching tube S a 、S b 、S c 、S d and the energy storage capacitor C d are formed, the switching tube S a is connected with the switching tube S b in series, the switching tube S c is connected with the switching tube S d in series and respectively connected with two ends of the energy storage capacitor C d in parallel, a connection point of the switching tube S c and the switching tube S d is connected to one end of the output capacitor C r through the output inductor L f , and a connection point of the switching tube S a and the switching tube S b is directly connected to the other end of the capacitor C r . according to the invention, the filter with the controllable fractional order capacitor is constructed, so that zero impedance of subharmonic waves with specific frequency is obtained, and the suppression of low-frequency harmonic current is realized.

Inventors

HE LIANGZONG
LIN ZHILE
ZHOU HONGYAN
CHENG BING
LUO HUAGENG

Assignees

厦门大学

Dates

Publication Date: 20260512
Application Date: 20230921

Claims (5)

1. The self-adaptive alternating current fractional order filter is characterized by comprising a controllable fractional order capacitor and a harmonic inductor L r which are connected in series, wherein the fractional order filter is connected between an alternating current bus and the ground and is in parallel connection with a load R o ; The controllable fractional order capacitor comprises an output capacitor C r , an output inductor L f , a first switching tube S a , a second switching tube S b , Third switching tube S c , The switching device comprises a fourth switching tube S d and an energy storage capacitor C d , wherein the first switching tube S a is connected in series with a second switching tube S b , the third switching tube S c is connected in series with the fourth switching tube S d and is respectively connected in parallel with two ends of the energy storage capacitor C d , the connection point of the third switching tube S c and the fourth switching tube S d is connected to one end of an output capacitor C r through an output inductor L f , and the connection point of the first switching tube S a and the second switching tube S b is directly connected to the other end of the capacitor C r ; The voltage of the controllable fractional order capacitor is controlled by adopting a voltage closed loop, and the voltage is specifically as follows; Carrying out harmonic detection on the bus current I bus , and separating fundamental wave current and harmonic current to obtain a harmonic amplitude I har , a harmonic frequency f har and a harmonic phase theta har at the moment; Obtaining an amplitude U har of the harmonic modulation voltage based on the harmonic amplitude I har and the harmonic frequency f har ; The normalized harmonic current enters an integral delay link to obtain the frequency and the phase of the harmonic modulation voltage, and the frequency and the phase of the harmonic modulation voltage are combined with the amplitude U har of the harmonic modulation voltage to obtain the harmonic modulation voltage; Superposing the harmonic modulation suppression voltage and the alternating current power supply voltage u s to obtain a reference voltage u cr-ref of the output capacitor C r ; After the reference voltage u cr-ref is subtracted from the output capacitor voltage ucr, the input controller performs voltage closed-loop control, and the output driving signal controls the on/off of the first switching tube S a , the second switching tube S b , the third switching tube S c and the fourth switching tube S d .
2. The adaptive ac fractional order filter of claim 1 wherein the amplitude U har of the suppressed harmonic modulation voltage is derived based on the harmonic amplitude I har and the harmonic frequency f har , in particular as follows: U har ＝2πf har L r I har Where f har denotes the harmonic frequency, L r denotes the resonant inductance, and I har the harmonic amplitude.
3. The adaptive ac fractional order filter of claim 1, wherein the frequency and phase of the harmonic-wave-suppressed modulated voltage obtained by introducing the normalized harmonic-wave current into the integral delay section is combined with the amplitude U har of the harmonic-wave-suppressed modulated voltage to obtain the harmonic-wave-suppressed modulated voltage, specifically as follows: Where u har denotes a harmonic modulation suppression voltage, f har denotes a harmonic frequency, and θ har denotes a harmonic phase.
4. The adaptive ac fractional order filter of claim 3 wherein the harmonic-rejection modulated voltage is superimposed on the ac supply voltage u s to obtain a reference voltage u cr-ref for the output capacitor C r , as follows:
5. The adaptive ac fractional order filter of claim 1, wherein the driving signals controlling the first switching tube S a and the fourth switching tube S d are the same, the driving signals controlling the second switching tube S b and the third switching tube S c are the same, and the driving signals controlling the first switching tube S a and the fourth switching tube S d are opposite to the driving signals controlling the second switching tube S b and the third switching tube S c .

Description

Self-adaptive alternating current fractional order filter Technical Field The invention relates to the technical field of electric energy quality, in particular to a self-adaptive alternating current fractional order filter. Background In recent years, smart micro-grids rapidly develop, and various novel power electronic converters and loads are applied to the micro-grids, wherein some nonlinear loads can introduce low-order harmonics, particularly five-order and seven-order current harmonics, in the grids. The low-frequency harmonic distortion is one of the most main electric energy quality problems in a modern intelligent power grid, and can increase the iron core loss and the temperature rise of equipment such as a transformer, a motor and the like, shorten the service life, cause phenomena such as overvoltage, overcurrent and instability of a system, influence the safety and stability of the system, interfere the normal work of a protection device and a measuring instrument, cause misoperation or refusal, cause low-power factors, reduce the efficiency and increase the line loss. In order to better compensate the harmonic wave and the reactive power of which the size and the frequency are changed, so that the power distribution system is more in line with the design of a harmonic environment, an active filter is widely applied as a novel power electronic device for dynamically restraining the harmonic wave and compensating the reactive power, and the derived hybrid active power filter is one of hot spots in current research. For example, the harmonic suppression effect of the filter is enhanced by adding a notch link and adjusting the parameters of the filter, so that the effective suppression of higher harmonics is realized. The passive decoupling capacitor can be split into an active capacitor and a passive decoupling capacitor which are connected in series, so that stable power supply voltage is provided for a load, pulsating power can be absorbed, and harmonic current is restrained. In order to solve the above-mentioned power quality problem, researches on low-frequency harmonic suppression technology have been pursued. Traditionally, passive filters are used to compensate for reactive power and eliminate harmonic currents. For example, a pulse width modulation inverter with an LC filter drives an induction motor to reduce high-frequency noise and harmonic waves output by the induction motor, a wave trap and an LCL filter are combined to realize current harmonic wave filtering and reduce alternating-current capacitance voltage fluctuation, and then a voltage reducing circuit is designed to solve the problem of transformer saturation in a weak power grid, but the compensation capacity and the center frequency of a passive filter are not adjustable generally, and the passive filter cannot adapt to flexible and changeable application scenes. In addition, the parameters of the passive device can change with time due to aging, and the passive device is influenced by the scale of the distributed micro-source and the load type, and non-integer subharmonics such as inter-harmonics and the like can also exist in the micro-grid. There are parameter offsets in various applications of power electronics, such as interleaved boost converters, electromagnetic interference filters, modular multilevel converters, wireless energy transfer, etc. Meanwhile, the variable capacitor, the variable inductor and the high-power factor circuit can adaptively adjust the inductance or the capacitance value meeting the requirement according to different load conditions and harmonic interference frequencies through a plurality of variable units. However, these methods of compensating for parameter errors have the problems of 1) variable capacitance or inductance can only be adjusted to reactance without taking other parasitic parameters such as resistance into account, 2) voltage stress of the switching device will be greatly increased in order to obtain a larger adjustable range, 3) error compensation of device parameters requires higher control accuracy and calculation capability, and 4) such circuits are in the filter main loop, meaning larger capacity and circuit loss. Disclosure of Invention In view of the above problems, the invention provides a self-adaptive alternating current fractional order filter, which is insensitive to device parameters and can maintain good harmonic suppression capability in a certain error range by constructing a filter with controllable fractional order capacitance to obtain zero impedance of subharmonics of specific frequency and realize suppression of low-frequency harmonic current, and enabling the resonant frequency and minimum impedance of the filter to be adjustable so as to suppress current harmonics with random fluctuation of frequency and amplitude. The technical scheme adopted by the invention for solving the technical problems is as follows: The self-adaptive alternating current fraction