CN1832289A - Neutral harmonic current managing device and control method thereof - Google Patents

Abstract

This invention discloses a neutral line harmonic current management device and its control method, in which, an instruction current operation circuit, a control circuit, a drive circuit, a single phase bridge inverter and a separation transformer are serial between a three-phase four-line power system and a non-linear load and a three phase un-controllable bridge commutation circuit is connected between the single-phase bridge inverter and the non-linear load. Advantages: 1, it's not necessary for the single phase bridge inverter to bear the working frequency of the power system due to the special topological structure of the separation transformer, 2, applying active devices, 3, any new aberration components are not increased in the composition process of the three-phase four-line power system.

Description

Neutral harmonic electric current controlling device and control method thereof

Technical field

The present invention relates to the electric power quality control technology, relate in particular to a kind of efficient, low withstand voltage neutral harmonic electric current controlling device and control method thereof.

Background technology

Mains by harmonics has caused electric network pollution and sinusoidal voltage wave distortion, makes the power supply equipment of electric power system many anomalies and fault occur, and situation is on the rise.In today increasingly mature, be an important topic of current power department for harmonic wave control to Harmonious Waves in Power Systems generation, detection and research on standard thereof.

With regard to the neutral line of distribution system, because the existence of fluorescent lamp, desk lamp with dimmer switch, computer even load, the harmonic wave in the electric power system makes the voltage of electrical network and current waveform distort, and can produce a large amount of odd harmonics, wherein the content of 3 subharmonic is bigger, can reach 40%.In the three-phase distribution circuit, the integer harmonics of 3 on the phase line can stack on the neutral line, makes the current value of the neutral line may surpass electric current on the phase line.

The neutral harmonic electric current that this is very big will produce adverse influence for load.Increasing single-phase load becomes very important to the humorous unbalanced influence that involves between the three-phase that electrical network produces.The accident that neutral line current causes also has report in China.

Therefore, at present just seem extremely important for the improvement of the electric power system neutral harmonic of skyscraper.Especially for as key sectors such as dispatching of power netwoks building, public security control buildings, the reliability of its power supply just requires very high.But these departments itself are again the units that nonlinear-load is concentrated, and therefore just are necessary to carry out the work that neutral harmonic is administered, to prevent the power failure accident.

Traditional neutral harmonic improvement method has passive filter and two kinds of methods of active filter.

1, passive filter method

As tortuous transformer filtering method, this method has following characteristics:

1) harmonic wave cancellation ability depends on the comparison of filter and system impedance size, and general harmonic filtration ability can only reach 50%.

2) owing to want cancellation zero sequence high order harmonic component, volume of transformer is bigger.

3) owing to require filter bigger to impedance of fundamental frequency, harmonic impedance is less, makes the transformer device structure complexity, the manufacturing process complexity; Therefore increased the capacity of system.

2, active filter method

By detecting the electric current on the actual neutral line, the Control current generating means produces an opposite electric current and offsets with it, thereby reaches the purpose of electric current on the compensation neutral line.Compare with passive filter, the active filter method has more advantage:

1) because active filter adopts the closed loop Detection ﹠ Controling, the filter compensation ability is improved greatly, can be up to 80 ~ 95%;

2) control is difficult for causing the filter overload flexibly;

3) power frequency presents high impedance, and harmonic wave presents Low ESR;

4) can not produce voltage disturbance;

5) because active filter adopts the electronic power switch device, consumption active power is very little during harmonic compensation, the efficient height.

Traditional active filter that is applicable to neutral harmonic improvement method is based on the bridge-type voltage source type inverter of three-phase and four-line, and two kinds of four phase current transformers and 3-phase power converters are arranged.Four phase current transformers are to add the 4th pair of brachium pontis on the basis of phase three-wire three bridge-type inverter, are specifically designed to the compensation of neutral current, and required like this power electronic device just increases; And 3-phase power converter with four mutually the difference of current transformer maximum be with three pairs of brachium pontis compensation three-phase currents, the neutral line links to each other with DC side bus mid point provides the neutral line current passage, the sort circuit structure needs 6 electronic power switch devices, and main circuit directly is connected with system, in order to reach compensation effect, dc voltage requires than higher.So just increased the switching loss of power electronic device, and too high du/dt and di/dt make that also the electromagnetic interference of device is more serious.Integrate, adopt the bridge-type voltage source type inverter of three-phase and four-line carry out neutral harmonic improvement have high input, control complexity, poor reliability.

Summary of the invention

The objective of the invention is to overcome the problem and shortage that prior art exists, a kind of neutral harmonic electric current controlling device and control method thereof are provided, thereby pollution is carried out dynamically administering in real time to neutral harmonic, and the neutral current of infield is met the requirements.

The object of the present invention is achieved like this:

1, device

As Fig. 1, this device is made up of three-phase and four-line electric power system 1, instruction current computing circuit 2, control circuit 3, drive circuit 4, single-phase bridge type inverter 5, isolating transformer 6, the uncontrollable bridge rectifier 7 of three-phase, nonlinear load 8;

Its annexation is: between three-phase and four-line electric power system 1 and nonlinear load 8, be in series with instruction current computing circuit 2, control circuit 3, drive circuit 4, single-phase bridge type inverter 5, isolating transformer 6 successively; Between single-phase bridge type inverter 5 and nonlinear load 8, be connected with the uncontrollable bridge rectifier 7 of three-phase.

Described instruction current computing circuit 2 is a kind of modules of gathering the voltage and current signal of three-phase and four-line electric power system 1 and separating harmonic signal, claims that the harmonic signal that separates is an instruction current.

Described control circuit 3 is a kind of drive controlling functional blocks, according to producing corresponding drive signal by instruction current computing circuit 2 gained instruction current control Driver Circuit 4.

Described drive circuit 4 is a kind of drive-pulse generators, and the control of controlled circuit 3 produces required switch drive drive waveform power cell switch closure.

Described single-phase bridge type inverter 5 is a kind of power unit modules, injects the harmonic current of required compensation to three-phase and four-line electric power system 1.

Described isolating transformer 6 is a kind of by three interconnected three-phase transformers of forming of single-phase transformer, plays buffer action.

The uncontrollable bridge rectifier 7 of described three-phase is a kind of rectification modules, provides single-phase bridge type inverter 5 dc voltages, plays through-put power.

The operation principle of this device is:

The electric current of three-phase and four-line electric power system 1 is passed through the command signal that instruction current computing circuit 2 calculates offset current, and this signal produces by control circuit 3 and answers pulse-width modulation (PWM) the signal V of compensation rate _i, obtain drive signal V through drive circuit 4 _OutDirectly pass to the gate pole of single-phase bridge type inverter 5, single-phase bridge type inverter 5 produces offset current and returns bus by isolating transformer 6, thereby reaches the compensation of neutral current.Single-phase bridge type inverter 5 DC side provide power supply by the uncontrollable bridge rectifier 7 of three-phase, and this rectification circuit can not produce additional Zero-pharse harmonic electric current to system.

Single-phase bridge type inverter 5, its output links to each other with three-phase and four-line electric power system 1 by isolating transformer 6.The former limit of isolating transformer 6 is Y ₀Connection, secondary are open-delta connection.Single-phase bridge type inverter 5, DC side provides power supply by the uncontrollable bridge rectifier 7 of three-phase, and this rectification circuit can not produce additional Zero-pharse harmonic electric current to three-phase and four-line electric power system 1, promptly can not produce additional harmonic current on the neutral line.Single-phase bridge type inverter 5 is zero with the instantaneous power of three-phase and four-line electric power system 1 exchange during compensation zero sequence harmonic current.The fluctuation of dc voltage is mainly by the switching loss of switching device, the asymmetric electric current of compensation be connected the inductive energy storage effect and produce, for dc voltage stability at certain level, can realize by selecting suitable electric capacity.

2, control method

As Fig. 1, Fig. 3,

Make i ^* _cBe the neutral line instruction current that should compensate, promptly instruction current computing circuit 2 isolated neutral harmonic electric current from three-phase and four-line electric power system 1 also is the harmonic current that single-phase bridge type inverter 5 must compensate;

i _cBe the single-phase bridge type inverter 5 actual offset currents that produce;

i _eBe error current;

Error current i _e=i ^* _c-i _c, the proportional integral in control circuit 3 (PI) control, the triangular carrier that its output and control circuit 3 produce relatively obtains a kind of igbt (IGBT) gate pole control signal V of single-phase bridge type inverter 5 _iThrough the drive circuit 4 gate electrode drive signals V that gets back _Out, single-phase bridge type inverter 5 sends offset current i under this drive signal control _c, inject electric power system 1 by isolating transformer 6, reach the purpose of compensation neutral harmonic.

The present invention has the following advantages and good effect:

1),, be easy to realize, and cost is low so this apparatus structure is simple because the special topological structure of isolating transformer 6 makes single-phase bridge type inverter 5 need not to bear electric power system 1 power-frequency voltage;

2) adopt active device, compensation effect is good, economic and reliable;

3) do not increase any new allocation of distortion in electric power system 1 compensation process;

4) in time domain, calculate the current compensation component, clear physics conception, fast operation has been realized the compensation compatibility of goals;

5) the automaticity height is easy and simple to handle, is easy to safeguard.

The present invention is applicable to that to low pressure three-phase and four-line electric power system 1---being mainly commerce, building, civilian power system---carry out the improvement of harmonic current on the neutral line.

Description of drawings

Fig. 1 is this apparatus structure block diagram;

Fig. 2 is the control method block diagram;

Fig. 3 is single-phase bridge type inverter and electric power system connection diagram;

Fig. 4 drives the interface circuit of IGBT and control, drive pulse waveform figure for M57962L;

Wherein:

The electric power system of 1-three-phase and four-line; 2-instruction current computing circuit;

The 3-control circuit; The 4-drive circuit;

The 5-single-phase bridge type inverter; The 6-isolating transformer;

The uncontrollable bridge rectifier of 7-three-phase; The 8-nonlinear load.

V _i-IGBT gate pole control signal; V _Out-IGBT gate electrode drive signals

Embodiment

The present invention is further described below in conjunction with drawings and Examples.

1, device

1) drive circuit 4 employing mixing integrated drive electronics M57962L are core devices.

2) the controlled inverter of single-phase full bridge that single-phase bridge type inverter 5 is by 4 switching devices---igbt (IGBT)---forms injects the harmonic current of required compensation to electric power system 1.

3) single-phase bridge type inverter 5 and electric power system 1 connection diagram as shown in Figure 3, establish:

u _a, u _b, u _cBe the three-phase voltage of electric power system 1,

L _SBe the equivalent inductance of system 1,

u _dBe dc voltage,

i _c ^*Be instruction current, i.e. the harmonic current that electric power system 1 must compensate.

Isolating transformer 6 is that 1: 1 single-phase transformer constitutes by three no-load voltage ratios, and its secondary winding order end to end is connected between the bridge circuit of single-phase bridge type inverter 5, and its former limit winding is Y ₀Connection links to each other with electric power system 1.

The fundamental voltage of symmetry is zero after the voltage stack of secondary winding induction, and zero sequence subharmonic voltage and unbalance voltage are non-vanishing in the voltage stack back of secondary winding induction.Like this, be dc voltage u at opening part voltage _dBe mainly zero sequence subharmonic voltage and unbalance voltage, so single-phase bridge type inverter 5 has avoided bearing fundamental voltage, dc voltage u _dCan be very low, thus the loss of switching device can be reduced, and can not increase the electric current that single-phase bridge type inverter 5 bears.

Suppose the three-phase voltage u of system 1 _a, u _b, u _cSymmetry, and transformer is that no-load voltage ratio is 1: 1 a ideal transformer, both ignored the internal resistance and the leakage inductance of transformer, and excitation reactance is infinite, then has:

$i_c^{*}=i_a=i_b=i_c=i_g/3---\left(1\right)$

In fact, transformer can not be ideal, and (1) formula is false at this moment, also contains first-harmonic symmetry current component in every phase current, shown in (2) formula:

i _a＝i ^* _c+I _m?sin(ωt+α)

i _b＝i ^* _c+I _m?sin(ωt+α-2π/3) (2)

i _c＝i ^* _c+I _m?sin(ωt+α+2π/3)

This fundamental current is an excitation current component, and following formula is still set up after the three-phase current addition:

$i_c^{*}=i_g/3.$

Under the ideal transformer situation, the instantaneous power of system and single-phase bridge type inverter 5 exchanges is:

$u_a{i}_a+u_b{i}_b+u_c{i}_c+L_s\frac{{\mathrm{di}}_a}{\mathrm{dt}}{i}_a+L_s\frac{{\mathrm{di}}_b}{\mathrm{dt}}+L_s\frac{{\mathrm{di}}_c}{\mathrm{dt}}{i}_c---\left(3\right)$

When disregarding single-phase bridge type inverter 5 switching device losses, the power of this exchange is mainly cushioned by single-phase bridge type inverter 5 dc bus capacitors equally.By (1) Shi Kede, the three-phase addition result of following formula is 0, can obtain:

${\mathrm{Cu}}_d\frac{{\mathrm{du}}_d}{\mathrm{dt}}=L_s\frac{{\mathrm{di}}_g}{\mathrm{dt}}{i}_g---\left(4\right)$

Can obtain by (4) formula:

$u_d={\stackrel{\‾}{U}}_d+\sqrt{\frac{L_s}{C}}{i}_g---\left(5\right)$

Wherein, U _dBe dc voltage mean value.The permission voltage change ratio is ε, then can in the hope of the dc bus capacitor amount be:

$C=\frac{9L_s}{{\mathrm{\ϵ}}^2{{\stackrel{\‾}{U}}^2}_d}{i}^{2}g\max ---\left(6\right)$

Wherein, i _{G max}For compensating the peak value of current in middle wire.

2, method

Adopt the ring PWM control mode that stagnates to produce the IGBT gate pole control signal V of single-phase bridge type inverter 5 _i

The ring PWM control that stagnates is meant adopts the chain rate that stagnates to produce gate pole control signal pwm pulse than mode.As Fig. 2, the comparator that the proportional integral in the control circuit 3 (PI) is controlled and is connected in thereafter constitutes the comparator with hysteresis characteristic jointly, error current i _eAs the input of comparator, export the break-make of the switching device IGBT that controls single-phase bridge type inverter 5 by it with hysteresis characteristic.By ring width is the gate pole control signal pwm pulse V of the hysteresis comparator generation of 2 Δ I _iGet driving pulse V through drive circuit 4 _OutThe break-make of the power device IGBT of control single-phase bridge type inverter 5, the offset current i that single-phase bridge type inverter 5 produces _cJust at i _c ^*-Δ I and Scope in, the trace command current i of indentation _c ^*2 Δ I are wide for ring width, and then switching frequency is low, but tracking error is big; 2 Δ I are narrow for ring width, and then tracking error is little, but the switching frequency height, even surpass the tolerance frequency scope of switching device IGBT, and switching loss also increases thereupon, may cause burning switching device IGBT, and final ring width 2 Δ I will be determined by the experiment situation.

The ring PWM control that stagnates has following advantage:

1) hardware circuit is simple;

2) belong to real-time control mode, current response is fast.

3, embodiment

380V, a capacity are the low withstand voltage neutral line active filter of 5KVA.

The phase voltage of system is 110V, and harmonic source is the three-phase imbalance load, adopts three single phase rectifier circuits, the big inductance of DC side band; Single-phase bridge type inverter 5 dc bus capacitors are 1000 μ F, and dc voltage is provided through the uncontrollable bridge rectifier 7 of three-phase by step-down transformer.Single-phase bridge type inverter 5 is the single-phase bridge reactive inverters that adopt power model to constitute.Since integrated driving, protection and absorption circuit in the power model, so the whole test device volume is little, simple in structure.Control circuit 3 is a kernel control chip with the digital signal processor DSP chip TMS320LF2407A of company of Texas Instruments (TI), include 16 road A/D and sampling holder and three-phase PWM signal generation circuit, therefore adding some simple ancillary equipment just can realize functional requirement.The outer program data memory RAM of man-machine interface, sheet that comprises the Industrial PC Computer communication.

M57962L drives interface circuit figure such as Fig. 4 of IGBT, the IGBT gate pole control signal V that control circuit 3 sends _iConnect 13 pin of M57962L, V through the Transistor-Transistor Logic level reverse buffer _iWaveform shown in top right plot.The gate pole G of IGBT is through small resistor R _WLink to each other with 5 pin of M57962L, collector electrode C is through fast recovery diode D ₁Link to each other with 1 pin of M57962L, radiation utmost point E links to each other with 4,6 pin of M57962L through two electric capacity of voltage regulation.IGBT gate-drive waveform V _OutCorresponding V _iShown in bottom-right graph, the positive driving voltage of output is+15V about, negative driving voltage is-10V.T wherein _PLHBe service time, t _rBe the collector current rise time, t _PHLBe the turn-off time, t _fIt is collector current fall time.M57962L inside has the saturation detection of moving back and protection link, can respond fast when overcurrent takes place but turn-offs IGBT at a slow speed, and provide fault-signal by optocoupler to control circuit 3, and powerful, versatility is good.

Claims (7)

1, a kind of low withstand voltage neutral harmonic electric current controlling device is characterized in that:

Between three-phase and four-line electric power system (1) and nonlinear load (8), be in series with instruction current computing circuit (2), control circuit (3), drive circuit (4), single-phase bridge type inverter (5), isolating transformer (6) successively; Between single-phase bridge type inverter (5) and nonlinear load (8), be connected with the uncontrollable bridge rectifier of three-phase (7).

2, by the described controlling device of claim 1, it is characterized in that:

Control circuit (3) is a kernel control chip with digital signal processor DSP chip TMS320LF2407A.

3, by the described controlling device of claim 1, it is characterized in that:

It is core devices that drive circuit (4) adopts mixing integrated drive electronics M57962L.

4, by the described controlling device of claim 1, it is characterized in that:

The controlled inverter of single-phase full bridge that single-phase bridge type inverter (5) is made up of 4 switching devices---insulated gate bipolar transistor IGBT---.

5, by the described controlling device of claim 1, it is characterized in that:

Isolating transformer (6) is that 1: 1 single-phase transformer constitutes by three no-load voltage ratios, and its secondary winding order end to end is connected between the bridge circuit of single-phase bridge type inverter (5), and its former limit winding is Y ₀Connection links to each other with three-phase and four-line electric power system (1).

6, a kind of control method of low withstand voltage neutral harmonic electric current controlling device is characterized in that:

Make i ^*The neutral line instruction current of c for compensating; i _cBe the single-phase bridge type inverter 5 actual offset currents that produce; i _eBe error current;

Error current $i_e=i_c^{*}-i_c,$ Proportional integral PI control in control circuit (3), the triangular carrier that its output and control circuit (3) produce relatively obtains the insulated gate bipolar transistor IGBT gate pole control signal (V of a kind of single-phase bridge type inverter (5) _i); Through drive circuit (4) gate electrode drive signals (V that gets back _Out), single-phase bridge type inverter (5) sends offset current i under this drive signal control _c, inject three-phase and four-line electric power system (1) by isolating transformer (6), reach the purpose of compensation neutral harmonic.

7, by the described control method of claim 7, it is characterized in that: adopt the ring PWM control mode that stagnates to produce the IGBT gate pole control signal of single-phase bridge type inverter (5).

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