CN104732113A - Harmonic source injection based method of estimating installed capacity of parallel APF (active power filter) - Google Patents

Abstract

The invention relates to a harmonic source injection based method of estimating installed capacity of a parallel APF (active power filter). The method is provided by considering a load harmonic difference before and after compensation caused by system impedance. The method includes: establishing system side and load side Thevenin equivalent models from a point to be accessed, of the APF; solving system side and load side Thevenin equivalent parameters by means of a harmonic source injection method; calculating the capacity of the parallel APF through the models and the parameters. The method is low in implementing cost, has low error and has great field applicability.

Description

A kind of parallel connection type APF installed capacity predictor method injected based on harmonic source

Technical field

The present invention relates to a kind of parallel connection type APF installed capacity predictor method, especially relate to a kind of parallel connection type APF installed capacity predictor method injected based on harmonic source.

Background technology

Increasing along with power electronic equipment in electrical network and nonlinear-load, the harmonic pollution of electric system is day by day serious.Harmonic wave not only affects the normal work of electrical equipment, and the safety and economic operation of returning electrical network brings hidden danger.Active Power Filter-APF (APF) is the effective means solving Harmonious Waves in Power Systems pollution, applies more and more extensive in electric system.

In actual field, APF capacity is determined most important.Existing parallel connection type APF Capacity Selection, usually electrical network is used as infinitely great power supply, Load harmonic is used as constant harmonic current source, and Load harmonic electric current measurement obtained is directly as the reference of parallel connection type APF capacity.In fact, the selection of system impedance on APF capacity of electrical network has impact, directly often makes APF Capacity Selection less than normal as APF capacity in Load harmonic electric current, thus harmonic compensation is fallen flat.Therefore, the installed capacity how simply estimating parallel connection type APF is efficiently urgent problem.

Summary of the invention

The present invention mainly solves the technical matters existing for prior art; Provide that a kind of cost is low and error is less, there is the parallel connection type APF installed capacity predictor method injected based on harmonic source of stronger practical.

Above-mentioned technical matters of the present invention is mainly solved by following technical proposals:

Based on the parallel connection type APF installed capacity predictor method that harmonic source injects, it is characterized in that, set up the Thevenin's equivalence model of system side and load side from APF point to be accessed, described model is defined as follows:

Inject nth harmonic to PCC point, and each each harmonic injected is separate, PCC place is APF point to be accessed, wherein n be more than or equal to 2 positive integer, the n-th subharmonic current of injection is then the Thevenin's equivalence model of the n-th subharmonic comprises:

Harmonic wave system side Thevenin's equivalence model: the equivalent electromotive force of system side system side equivalent impedance Z _sn; Load side Thevenin's equivalence model: the equivalent electromotive force of load side system side equivalent impedance Z _ln, the voltage at PCC point place is the harmonic current injected to PCC point is

The voltage at PCC point place is and the fling-cut switch in cross-over connection current perturbation source and current perturbation source is K between system side and load side;

$\left\{\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{Sn}}=({\stackrel{\·}{I}}_{\mathrm{Ln}}-{\stackrel{\·}{I}}_{\mathrm{Rn}})Z_{\mathrm{Sn}}+{\stackrel{\·}{U}}_{\mathrm{PCCn}}\\ {\stackrel{\·}{U}}_{\mathrm{PCCn}}={\stackrel{\·}{I}}_{\mathrm{Ln}}{Z}_{\mathrm{Ln}}+{\stackrel{\·}{U}}_{\mathrm{Lh}}\end{array}\right.$ Formula one

Then amount to be asked is and the action of current perturbation source once can obtain two equations, then disturbing source at least action can solve amount to be asked twice

At above-mentioned a kind of parallel connection type APF installed capacity predictor method injected based on harmonic source, if the individual different harmonic current value of n is injected in current perturbation source, then, as n=2, can uniquely solve amount to be asked as n>2, amount to be asked can be gone out by 2n equation Optimization Solution

As shown in Figure 4, be the schematic diagram of APF bucking-out system harmonic wave, K is the fling-cut switch of APF; After then APF compensates, and APF electric current is:

$\stackrel{\·}{I_{\mathrm{Cn}}}=\stackrel{\·}{I_{\mathrm{Ln}}}=\frac{\stackrel{\·}{U_{\mathrm{Sn}}}-\stackrel{\·}{U_{\mathrm{Ln}}}}{Z_{\mathrm{Ln}}}$ Formula two.

Therefore, tool of the present invention has the following advantages: realize that cost is low and error is less, has stronger practical.

Accompanying drawing explanation

Fig. 1 is the parallel connection type APF installed capacity predictor method process flow diagram injected based on harmonic source;

Fig. 2 is the Thevenin's equivalence illustraton of model of system side and load side;

Fig. 3 is the Thevenin's equivalence parametric solution schematic diagram of system side based on harmonic source injection method and load side.

Fig. 4 is the schematic diagram of APF bucking-out system harmonic wave.

Embodiment

Below by embodiment, and by reference to the accompanying drawings, technical scheme of the present invention is described in further detail.

Embodiment:

Below in conjunction with the drawings and specific embodiments, the present invention will be further described.

As shown in Figure 1, the parallel connection type APF installed capacity predictor method injected based on harmonic source is: the Thevenin's equivalence model setting up system side and load side; Utilize the Thevenin's equivalence parameter of harmonic source injection method solving system side and load side; Thevenin's equivalence model and parameter is utilized to calculate parallel connection type APF installed capacity.

As shown in Figure 2, be the Thevenin's equivalence illustraton of model of system side and load side, because hypothesis each harmonic is separate, so what provide in figure is the Thevenin's equivalence model of the n-th subharmonic.PCC place is APF point to be accessed, and system side Thevenin's equivalence model is: the equivalent electromotive force of system side system side equivalent impedance Z _sn.Load side Thevenin's equivalence model is: the equivalent electromotive force of load side system side equivalent impedance Z _ln.The voltage at PCC point place is

As shown in Figure 3, for based on the system side of harmonic source injection method and the Thevenin's equivalence parametric solution schematic diagram of load side.The harmonic current that current perturbation source is injected to PCC point is the fling-cut switch in current perturbation source is K.Particular/special requirement is not had to the capacity in current perturbation source, but in reality, its capacity is more close to load capacity, and result is more accurate.Then can be established an equation group (1) by Fig. 3, wherein, all can measure, be known quantity.Then amount to be asked is

$\left\{\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{Sn}}=({\stackrel{\·}{I}}_{\mathrm{Ln}}-{\stackrel{\·}{I}}_{\mathrm{Rn}})Z_{\mathrm{Sn}}+{\stackrel{\·}{U}}_{\mathrm{PCCn}}\\ {\stackrel{\·}{U}}_{\mathrm{PCCn}}={\stackrel{\·}{I}}_{\mathrm{Ln}}{Z}_{\mathrm{Ln}}+{\stackrel{\·}{U}}_{\mathrm{Lh}}\end{array}\right.$ (1)

Because amount to be asked is four, and the action of current perturbation source once can obtain two equations, so disturbing source at least action twice (current perturbation source inject two different ) amount to be asked can be solved if n (n>2) individual different harmonic current value is injected in current perturbation source, then can go out amount to be asked by 2n equation Optimization Solution

As shown in Figure 4, be the schematic diagram of APF bucking-out system harmonic wave, K is the fling-cut switch of APF.Before APF compensates, system harmonics electric current is:

$\stackrel{\·}{I_{\mathrm{Cn}}}=\stackrel{\·}{I_{\mathrm{Ln}}}=\frac{\stackrel{\·}{U_{\mathrm{Sn}}}-\stackrel{\·}{U_{\mathrm{Ln}}}}{{Z_{\mathrm{Sn}}+Z}_{\mathrm{Ln}}}$ (2)

If the Compensation Objectives of APF is: be standard sine wave by compensation point system side current compensation.After then APF compensates, and APF electric current is:

$\stackrel{\·}{I_{\mathrm{Cn}}}=\stackrel{\·}{I_{\mathrm{Ln}}}=\frac{\stackrel{\·}{U_{\mathrm{Sn}}}-\stackrel{\·}{U_{\mathrm{Ln}}}}{Z_{\mathrm{Ln}}}$ (3)

Traditional APF capacity predictor method utilizes the Load harmonic electric current directly measuring and obtain and formula (2) to estimate APF capacity, but due to the impact of system impedance, the APF capacity of reality is formula (3).Visible, it is less than normal that traditional APF capacity predictor method (formula 2) estimates the capacity obtained, and after adopting harmonic source injection method to try to achieve the Thevenin's equivalence parameter of system side and load side, can more accurately estimate APF installed capacity according to formula (3).

Specific embodiment described herein is only to the explanation for example of the present invention's spirit.Those skilled in the art can make various amendment or supplement or adopt similar mode to substitute to described specific embodiment, but can't depart from spirit of the present invention or surmount the scope that appended claims defines.

Claims (2)

1., based on the parallel connection type APF installed capacity predictor method that harmonic source injects, it is characterized in that, set up the Thevenin's equivalence model of system side and load side from APF point to be accessed, described model is defined as follows:

Inject nth harmonic to PCC point, and each each harmonic injected is separate, PCC place is APF point to be accessed, wherein n be more than or equal to 2 positive integer, the n-th subharmonic current of injection is then the Thevenin's equivalence model of the n-th subharmonic comprises:

Harmonic wave system side Thevenin's equivalence model: the equivalent electromotive force of system side system side equivalent impedance Z _sn; Load side Thevenin's equivalence model: the equivalent electromotive force of load side system side equivalent impedance Z _ln, the voltage at PCC point place is the harmonic current injected to PCC point is

The voltage at PCC point place is and the fling-cut switch in cross-over connection current perturbation source and current perturbation source is K between system side and load side;

$\left\{\begin{array}{c}{\stackrel{.}{U}}_{\mathrm{Sn}}=({\stackrel{.}{I}}_{\mathrm{Ln}}-{\stackrel{.}{I}}_{\mathrm{Rn}})Z_{\mathrm{Sn}}+{\stackrel{.}{U}}_{\mathrm{PCCn}}\\ {\stackrel{.}{U}}_{\mathrm{PCCn}}={\stackrel{.}{I}}_{\mathrm{Ln}}{Z}_{\mathrm{Ln}}+{\stackrel{.}{U}}_{\mathrm{Lh}}\end{array}\right.$ Formula one

Then amount to be asked is z _sn, z _ln, and the action of current perturbation source once can obtain two equations, then disturbing source at least action can solve amount to be asked twice z _sn, z _ln.

2. a kind of parallel connection type APF installed capacity predictor method injected based on harmonic source according to claim 1, is characterized in that, if the individual different harmonic current value of n is injected in current perturbation source, then, as n=2, uniquely solves amount to be asked z _sn, z _ln, as n>2, go out amount to be asked by 2n equation Optimization Solution z _sn, z _ln;

Definition K is the fling-cut switch of APF; After then APF compensates, and APF electric current is: $\stackrel{.}{I_{\mathrm{Cn}}}=\stackrel{.}{I_{\mathrm{Ln}}}=\frac{\stackrel{.}{U_{\mathrm{Sn}}}-\stackrel{.}{U_{\mathrm{Ln}}}}{Z_{\mathrm{Ln}}}$ Formula two.