Mixed type triple frequency harmonic filter based on symmetrical component method
Technical field
The present invention relates to a kind of mixed type triple frequency harmonic filter, belong to the electrical engineering technical field based on symmetrical component method.
Background technology
Continuous development along with power electronic technology; the extensive use of various power electronic equipments in electric power system; make the quality of power supply of electric power system be subjected to various pollutions; particularly in recent years; gaseous discharge lamp; metal halid lamp; the controllable silicon light modulation lamp; the fluorescent lamps of employing electric ballast etc. are in factory; residential building; hotel's commercial building; a large amount of employings in the office building; its triple-frequency harmonics that produces in three phase and four wire circuit system pollutes the very serious degree that arrived; it causes power quality obviously to descend; the grid power loss increases; shortened equipment life; the ground protection malfunction; distant control function is not normal; capacitor damages; transformer overload; center line hyper-base ripple electric current; cause the electric equipment life-span greatly to shorten; electrical network is overheated, but even fire hazard.
Because it is serious day by day that the triple-frequency harmonics of three-phase four-wire system electrical network pollutes, and country also increases triple-frequency harmonics pollution control need for equipment day by day to the continuing to increase of the dynamics of building " green electrical network ".Present triple-frequency harmonics controlling device mainly contains two big classes: passive three wave arrestment devices and passive triple-frequency harmonics filter.
At present both at home and abroad the solution for the neutral line triple harmonic current of three-phase four-wire system 380V distribution system has:
1, with ABB AB is the triple-frequency harmonics trap scheme of representative, its principle is to seal in a resonance point at power supply fundamental frequency place on the neutral line, be similar to the trap circuit of shunt-resonant circuit, its impedance at the fundamental frequency place is approximately zero, and the impedance at the third harmonic frequencies place is about 2 ohm.In the ordinary course of things, it will cooperate the passive triple frequency harmonic filter of domestic and international manufacturer production to work together, just can obtain apparent in view effect.Because it is connected on the neutral line, therefore,, center line is disconnected, and power consumption equipment is caused significant impact if device breaks down.In addition, the valuable product of this solution, required expense are too high, are difficult to obtain practical application.
2, with the NOKIA capacitor be the passive triple frequency harmonic filter scheme of representative, because the triple-frequency harmonics impedance loop in the three-phase four-wire system distribution system is very low, when distribution transformer is Y/ Δ connection, be about about 0.1 ohm, when distribution transformer is the Y/Y connection for being about 2 ohm; And the internal resistance of passive triple frequency harmonic filter also is about about 0.1 ohm; Therefore, the connection of the filter effect of passive triple frequency harmonic filter and distribution transformer has direct relation.Distribution transformer can cause the triple harmonic current on the zero line to become big when being Y/ Δ connection; Can cause the third harmonic voltage on the zero line to increase when distribution transformer is the Y/Y connection, the voltage on the center line causes serious threat can for people's the security of the lives and property sometimes.Passive triple frequency harmonic filter can be obtained filter effect preferably when distribution transformer is the Y/Y connection, and the filter effect of passive triple frequency harmonic filter is on duty mutually when distribution transformer is Y/ Δ connection.Must just can make passive triple frequency harmonic filter obtain filter effect preferably to the distribution transformer that the Y/Y connection was transformed or be replaced by to the distribution transformer of Y/ Δ connection, but this to consume great amount of manpower and material resources, is actually infeasible scheme.
Above-mentioned these two kinds of schemes are owing to all be to be made of reactor, capacitor, resistor, present the purpose that Low ESR or high impedance reach filtering by the harmonic wave to some number of times, therefore all have some problems of passive filter:
(1) filter effect to harmonic current is subjected to the influence of power system impedance big;
(2) it is bad mains frequency to be offset the situation filter effect that harmonious wavy condition often changes;
(3) harmonic current that other non-linear loads produced that is connected in the same electrical network might flow into this filter, thereby causes overload;
(4) serial or parallel connection resonance may take place in the system impedance of electrical network and passive filter under some frequency.
In order to overcome the above-mentioned defective of passive filter, many researchers have done very many work, such as, by Zhu of Tsing-Hua University from the east of etc. the active and passive combined power filter with both that constitutes of proposition, above-mentioned problem and defective have been solved objectively, triple harmonic current has also been obtained filter effect preferably, but its main circuit is by 3 single tuning passive filters, 9 single tuning passive filters and high pass filter are formed, the main circuit structure complexity, increased the cost of triple-frequency harmonics filter virtually, also increase the volume of filter and the complexity of control, brought difficulty for the application and the marketing of filter.In addition, the main circuit structure of this device also causes filter that the harmonic wave amplification takes place at some frequency place easily.
Summary of the invention
The objective of the invention is to provide a kind of modularized design can be parallel extended, the mixed type triple frequency harmonic filter based on symmetrical component method of independent control.
Technical scheme of the present invention comprises: PWM controller and the single-phase PWM current transformer, line voltage genlock control circuit and the overvoltage that link with this PWM controller, under-voltage, overcurrent and short trouble detect and protective circuit, and the DC power supply that links to each other with single-phase PWM current transformer DC side and be connected the 380V distribution system and the single-phase PWM current transformer between passive link and be used for the high pass filter of filtering high order harmonic component; The single-phase PWM current transformer provides output current i
NoDetection signal give the PWM controller, and and reference current i
L3Compare, be used for hysteresis current control to the single-phase PWM current transformer, the inverter pulse-width control signal that produces is through drive circuit, after shaping, amplification, isolation, drive corresponding M OSFET or IGBT constant power device on the inverter, make the triple harmonic current of single-phase PWM current transformer center line carry out tracking Control, make the variation of the current following instruction current of inverter output, and the triple harmonic current of center line is fed back in the three-phase current by passive link, the triple harmonic current of filtering center line.
Described PWM current transformer (Pulse Width Modulation Converter) is by single-phase IGBT full-bridge module and the electrochemical capacitor C that is attached thereto
dForming, do not use filter inductance here, mainly is because the inductance in the passive link has played the effect of filtering and restriction IGBT current increases speed.
The described passive link that links to each other with the 380V distribution system is the reactive power compensator that neutral line tap is arranged or the passive filter of one group of wye connection, it can not only provide suitable idle to system, path is provided can also for the tertiary current of the zero sequence in the three-phase current; And can also further eliminate the harmonic current of the non-zero sequence of some number of times under passive link 2 condition that is passive filters, as 5 times, 7 inferior, but this will see the structure of passive filter.
Described PWM controller is made up of microcontroller (CPU) and the program storage that is attached thereto respectively, data storage, analog/digital signal conversion circuit, PWM control output, photoelectricity isolation and coupling circuit.
Described high pass filter is used for the higher harmonic current component on the filtering three-phase phase line and the neutral line, and it comprises switch ripple that the power switch IGBT action of PWM current transformer causes and the higher harmonic current component that DC power supply absorbed.
Described line voltage genlock control circuit: the voltage e in the three-phase alternating current
aThrough phase-locked loop pll electrical network phase voltage phase angle is become digital signal by analog signal conversion.Described phase-locked loop pll is made up of low pass filter, phase-locked loop, divider circuit and buffer circuit, find out zero crossing as benchmark in the A phase voltage by negative change timing, and electrical network phase voltage phase angle become digital signal by analog signal conversion, control usefulness for control circuit.
Described overvoltage, under-voltage, overcurrent and short trouble detect with protective circuit to be made up of circuit such as current sensor, voltage sensor, transistor, operational amplifier, comparator, voltage references.
Described DC power supply is used for providing a DC power supply to the PWM current transformer, offsets triple-frequency harmonics zero-sequence current on the center line so that the PWM current transformer can produce a suitable current according to the control command of PWM controller.
The present invention is by the detection to the total current that flows through on the neutral line, and method delay time respectively 120 electrical degrees and 240 electrical degrees by time-delay, and construct a virtual three-phase current with these three amounts, utilize symmetrical component method to extract the component of triple harmonic current on the neutral line that needs compensation then, control PWM current transformer provides the corresponding compensation amount, the component of triple harmonic current on the compensation neutral line, and eliminate the component of the triple harmonic current of phase line in A, B, the C three-phase, thereby reach the purpose of eliminating triple harmonic current.In general, for the three-phase four-wire system of three-phase imbalance, the electric current on the center line also includes the harmonic component of fundametal compoment and other number of times except triple-frequency harmonics; The benefit of this method is that it can extract the triple-frequency harmonics current signal of preface component in addition from current in middle wire, and no matter load is a three-phase imbalance.
Description of drawings
Fig. 1 is a principle of the invention block diagram;
Fig. 2 is a PWM controller principle block diagram;
Fig. 3 is a single-phase PWM current transformer theory diagram;
Fig. 4 is passive link theory diagram;
Fig. 5 is the high pass filter theory diagram;
Fig. 6 is a line voltage genlock schematic block circuit diagram;
Fig. 7 decides deviation band mode schematic diagram for what adopt hysteresis current control;
Embodiment
As Fig. 1, the PWM current transformer that comprises the PWM controller, links to each other respectively with this PWM controller, line voltage genlock control circuit, overvoltage, under-voltage, overcurrent and short trouble detect and protective circuit; The passive link that connects power distribution network and PWM current transformer, the passive high three-way filter that is provided with in order to eliminate high order harmonic component, and the DC power supply of DC power supply is provided for the single-phase PWM current transformer.Here PWM is the abbreviation of pulse-width modulation.
Line voltage genlock control circuit provides the real time data of a series of representative line voltage phase angle for the PWM controller.Electrical network A phase voltage (e
a) obtain electrical network A phase voltage (e through low pass filter, phase-locked loop circuit, frequency divider and latch
a) 10 bit digital phase angle (Q
9, Q
8, Q
7, Q
6, Q
5, Q
4, Q
3, Q
2, Q
1, Q
0), also be that binary number 0000000000~1111111111 is represented electrical network A phase voltage (e
a) 0 °~360 ° of phase angles, the digitized electrical network phase voltage phase angle signal that the PWM controller at first provides according to line voltage genlock control circuit 5, and obtain current signal i on the center line load side in the mode of interrupting with deciding angle
Lo(by analog to digital converter ADC) is designated as the current value under this angle to this current signal and these data deposited in CPU (or DSP) internal memory of representing angle information.Fabricate three-phase current signal with the method for time-delay simultaneously, and obtain the triple-frequency harmonics component i of current in middle wire with symmetrical component method
o, and this current i
oAs control single-phase PWM current transformer reference current; And and the output current i that provides of PWM current transformer
NoCompare, be used for hysteresis current control to the PWM current transformer, make the triple harmonic current of PWM current transformer center line carry out tracking Control, and the triple harmonic current of center line is fed back in the three-phase current, so just realized the purpose of the triple harmonic current of filtering center line by passive link.
Overvoltage, under-voltage, overcurrent and short trouble detect with protective circuit by detection of grid phase voltage (e
a, e
b, e
c), electrical network phase current (i
Sa, i
Sb, i
Sc), three-phase load electric current (i
La, i
Lb, i
Lc), center line load side current i
Lo, center line grid side current i
So, and dc voltage U
DcAnd electric current I
Dc, export various guard signals and give the PWM controller, export with the pwm signal that blocks on the single-phase PWM current transformer, and carry out the corresponding protection action by the PWM controller.
Passive link couples together PWM current transformer and three-phase four-wire system power distribution network, and it can be the reactive power compensator of a wye connection, also can be the passive filtration unit of a wye connection.
Passive high three-way filter is connected between the three-phase four-wire system power distribution network and the neutral line, is provided with in order to eliminate high order harmonic component.
DC power supply is to provide DC power supply to the PWM current transformer.This power supply can common AC transformer add the rectification circuit composition, also forms with the Switching Power Supply that adopts soft switch technique.
Described PWM current transformer is by single-phase IGBT full-bridge module and the electrochemical capacitor C that is attached thereto
dForm, as shown in Figure 2.Here not using filter inductance, mainly is because the inductance in the passive link has played the effect of filtering and restriction IGBT current increases speed.The PWM current transformer provides the neutral line required triple harmonic current by passive link under the control of PWM controller.Thereby realize the purpose of triple harmonic current on the filtering neutral line.The direct voltage of PWM current transformer is (U just
Dc) promptly be the output voltage of DC power supply; Its output current i
NoIt is exactly the triple harmonic current of wanting the neutral line of filtering.
Described PWM controller 3 is isolated with coupling circuit and is formed by microprocessor CPU or DSP and the program storage that is attached thereto respectively, data storage, A/D conversion circuit, PWM control output photoelectricity, as shown in Figure 3.In described PWM controller, microprocessor CPU or DSP are as core devices, the directly work of control A/D conversion circuit, its working procedure is stored in the program storage, microprocessor CPU or DSP detect neutral line load side current i by A/D conversion circuit under the commander of software program
LoAnd the output current i of single-phase PWM current transformer
No, and calculate triple harmonic current component i on the center line by aforesaid method
oBe used to carry out digitized PWM control; Its data storage is used for store data and parameter, the single-phase PWM drive signal of microprocessor CPU or DSP output by PWM control output photoelectricity isolate carry out electrical isolation with coupling circuit and amplify after be used for driving the IGBT device of the single-phase IGBT full-bridge module of single-phase PWM current transformer.
As Fig. 4, the passive link 2 that links to each other with 380V three-phase four-wire system distribution system and PWM current transformer is the passive filter that the neutral point tap is arranged or reactive power compensators of one group of wye connection, it can not only provide suitable idle, the harmonic current of eliminating a part of non-zero sequence to system, can also extract the triple harmonic current of zero sequence from A, B, C three-phase current.
As Fig. 5 because the structure of high pass filter, make it can absorb on most of phase line and center line on higher harmonic current.These higher harmonic currents may be produce by non-linear load or produced by PWM current transformer and DC power supply.
Described overvoltage, under-voltage, overcurrent and short trouble detect with protective circuit 6 to be made up of voltage sensor, current sensor, transistor switching circuit, operational amplifier, comparator etc.It has functions such as over-voltage protecting function, under-voltage protection function, short-circuit protection function.
As Fig. 6, described line voltage genlock control circuit, electrical network A phase voltage (e
a) at first pass through the low pass filter filters out high-frequency interferencing signal, obtain clean electrical network A phase voltage signal, obtain and A phase voltage (e through after the shaping
a) relevant its frequency of representative and the square-wave signal (U of phase place
i), to send in the phase-locked loop, phase-locked loop pll passes through square-wave signal (U
i) carry out bit comparison mutually with the output square-wave signal of frequency divider, export of the input of corresponding pulse signal as frequency divider, 10 bit digital output signals of frequency divider are represented electrical network A phase voltage (e by output after the 10 bit data latches
a) digital signal of phase angle.
The PWM controller at first reads in the digitized electrical network phase voltage phase angle signal that line voltage genlock control circuit provides, and passes through the secondary current signal i of the current transformer on analog to digital converter ADC sampling and the conversion center line load side then
Lo, and this current signal is designated as current value under this angle; Then, the current i on the center line load side regularly constantly
LoCarry out sample conversion.And these data are deposited in CPU (or DSP) internal memory of representing angle information.Simultaneously these data obtain i through after 120 ° and 240 ° of time-delays respectively
L120And i
L240, and with these three current signal i
Lo, i
L120, i
L240Constitute virtual three-phase current signal, so just can obtain the triple-frequency harmonics component i of current in middle wire with symmetrical component method
o, and this current i
oAs control PWM current transformer reference current.
Described control circuit is by detecting the current i on the neutral line load side
Lo, through obtaining the current i on the neutral line load side after 14 analog to digital converter ADC samplings and the conversion
LoDigital value.And being rising edge by pulse in the output square-wave signal of the frequency divider in the line voltage genlock control circuit, the enabling signal of analog to digital converter ADC provides; Analog to digital converter ADC finishes conversion back and provides one to convert signal for microcontroller (CPU or DSP), reads data in the ADC by CPU or DSP, and deposits in and represent electrical network A phase voltage (e
a) in the data space of phase angle.This data space is the 1K byte, and the address is that (XXXXXX0000000000 is a data neutral line load side current i to XXXXXX0000000000~XXXXXX1111111111
LoThe data memory addresses scope of being preserved), the mode of The data circulation covering constantly refreshes current data i
LoThe hexagonal angle of delaying time respectively obtains i
L120, the time-delay 240 ° of angles obtain i
L240, construct a virtual three-phase current with these three electric currents, and utilize symmetrical component method just can obtain the third-harmonic component i of center line
o, 3 times neutral line triple harmonic current component 3
Io
The actual calculation process is as follows: the current electrical network A phase voltage (e of representative
a) the phase angle digital value is designated as α (binary system), the digital value of time-delay hexagonal angle is 01010101 (binary system), the digital value at 240 ° of angles of time-delay is 10101010 (binary systems), the pairing data memory space of the data address of delaying time so behind the hexagonal angle can be calculated as follows: earlier current angle [alpha] is added binary number 0101010101, obtain β ', again β ' and binary number 0000001111111111 are done and computing, and then add binary number XXXXXX0000000000, (its content is designated as i to obtain actual 120 ° of pairing address β of time-delay
L120); In like manner, can obtain delaying time that (its content is designated as i to 240 ° of pairing address γ
L240); 3i like this
o=i
Lo+ i
L120+ i
L240
What the PWM control method here adopted hysteresis current control decides deviation band mode, as shown in Figure 7, and here i
oAs reference instruction offset current (being reference current), i
NoAs actual offset current, deviation band (being the dead band) is Δ I, and when in a single day actual offset current bumps against on the deviation band, power switch is action just, force actual offset current to change in the opposite direction, actual offset current is constantly changed in reference value and the determined zone of deviation band.Thereby reached the purpose of the triple harmonic current on the filtering center line.