CN104505841A - Static synchronous power generator reactive support control method for power grid asymmetric short circuit fault - Google Patents

Abstract

The invention relates to a static synchronous power generator reactive support control method for a power grid asymmetric short circuit fault. Unbalance degree of voltage of a grid-connected point is calculated in real time, negative sequence reactive current is dynamically outputted, and reactive support is performed on one phase or two phases with the short circuit fault; and an instruction current amplitude limiting strategy is adopted, and negative sequence reactive current is ensured to be outputted to the maximum limit along with increasing of degree of asymmetry so that negative sequence current support control at the maximum degree is realized. Problems of overcompensation and overvoltage caused by injection of three-phase symmetric reactive current of an original control strategy can be effectively avoided by the control strategy so that a new solution idea is provided for the asymmetric short circuit fault.

Description

The Static Synchronous generator reactive support and control method of electrical network asymmetry short circuit fault

Technical field

The present invention relates to a kind of Static Synchronous generator negative phase-sequence dynamic reactive support and control strategy under electrical network asymmetry short circuit fault, can realize only carrying out reactive power support to the phase be short-circuited or two phase voltages.

Background technology

In recent years, based on the mature technologies such as high-voltage large-capacity STATCOM and battery energy storage, with the synchronous control mode of advanced person for core, have both the inertia of conventional synchronization generator and synchronous/damping torque characteristic and voltage regulation properties, can exert oneself according to intermittent energy and load variations situation real-time, the public grid-connected point voltage frequency of quick adjustment and amplitude, and then improve its dynamic characteristic, the Static Synchronous generator techniques strengthening also site grid strength is developed rapidly, but when electrical network generation asymmetry short circuit fault, because it still injects three-phase symmetrical reactive current according to the size of grid-connected point voltage positive sequence component, to cause not falling the voltage overcompensation of phase and overvoltage, jeopardize the safe and stable operation of electrical network equally, therefore in the urgent need to the phase-splitting dynamic reactive support and control technology under research electrical network asymmetry short circuit fault.

Patent of the present invention stops synchronous generator (as shown in Figure 1) for H bridge cascade chain type Structural Static, by the optimization to control strategy, can successfully manage under electrical network asymmetry short circuit fault because export three-phase symmetrical dynamic reactive support electric current and cause do not fall the overpressure problems that phase voltage overcompensation causes, for electrical network unsymmetrical short-circuit provides new solution, be conducive to electrical network safe and stable operation under unbalanced fault.

At present, ABB is only had to be proposed Static Synchronous generator (SSG) product abroad, but it does not have the negative phase-sequence dynamic reactive support and control strategy under electrical network asymmetry short circuit fault, and domestic Static Synchronous generator techniques and related control strategies thereof are still in the starting stage.

Summary of the invention

The object of this invention is to provide negative phase-sequence dynamic reactive support and control strategy under a kind of Static Synchronous Generator Network asymmetry short circuit fault, stopping a synchronous generator phase-splitting dynamic reactive support technology difficult problem in order to H bridge cascade chain type Structural Static under solving asymmetry short circuit fault, avoiding the overpressure problems caused because injecting three-phase symmetrical reactive current.

For achieving the above object, the solution of the present invention comprises:

The Static Synchronous generator reactive support and control method of electrical network asymmetry short circuit fault, step is as follows: the uneoupled control 1) carrying out positive sequence active current, positive sequence reactive current, negative phase-sequence active current, negative phase-sequence reactive current; 2) in real time calculate grid-connected point voltage degree of unbalance, ask for negative phase-sequence dynamic support referenced reactive current under asymmetry short circuit fault according to degree of unbalance.

Also comprise step 3) amplitude limit control is carried out to instruction current.

According to degree of unbalance, calculate negative phase-sequence dynamic reactive current-order ---rated current, V _p---line voltage positive sequence component; V _n---line voltage negative sequence component.

Negative phase-sequence dynamic reactive electric current according to $I_p\≤I_e-I_n^{*}=I_e-\sqrt{{\left(I_{\mathrm{nd}\_\mathrm{ref}}^{*}\right)}^2+{\left(I_{\mathrm{nq}\_\mathrm{ref}}^{*}\right)}^2}$ Amplitude limit; ---forward-order current instruction; ---the instruction of positive sequence active current; ---positive sequence referenced reactive current; ---negative current instructions; ---the instruction of negative phase-sequence active current; ---negative phase-sequence referenced reactive current; I _e---rated current.

Under first the present invention eliminates asymmetry short circuit fault by injection residual voltage, the alternate unbalanced power of three-phase that negative sequence voltage and positive sequence reactive current cause; Secondly, detect grid-connected point voltage degree of unbalance in real time, according to degree of unbalance dynamical output negative phase-sequence reactive current, and then realize only to the dynamic reactive support and control falling phase voltage; Finally, according to negative-sequence current size, amplitude limit is carried out to forward-order current, guarantee OPTIMAL REACTIVE POWER support and control under asymmetry short circuit fault.Under the invention solves electrical network asymmetry short circuit fault, H bridge cascade chain type Structural Static stops a synchronous generator phase-splitting dynamic reactive support technology difficult problem, avoids the overpressure problems caused because injecting three-phase symmetrical reactive current.

Accompanying drawing explanation

Fig. 1 is that H bridge cascade chain type Structural Static stops synchronous generator structure chart;

Fig. 2 is H bridge cascade Static Synchronous generator negative phase-sequence dynamic reactive support and control policy construction figure;

Fig. 3 is that positive-negative sequence is separated Decoupling network;

Fig. 4 is active power close loop control block diagram;

Fig. 5 is reactive power closed-loop control block diagram;

Fig. 6 is residual voltage control program.

Embodiment

If normal grid voltage phase voltage peak value is V _t, falling phase voltage peak value is n × V _t(0≤n≤1), with V _tcarry out mark the one as fiducial value, then according to unsymmetrical short-circuit modes such as line voltage single-phase earthing, two phase ground and two-phase phase faults, Static Synchronous generator output voltage under line voltage asymmetry short circuit fault can be obtained respectively and express formula.

Single-phase grounding fault:

According to symmetrical component method, when be short-circuited fault time, if grid-connected point voltage phase place does not change, then can obtain that Static Synchronous generator under single-phase grounding fault exports positive sequence, negative phase-sequence, zero-sequence component amplitude are:

$V_p=\frac{2+n}{3},V_n=V_0=\frac{n-1}{3}$

When can obtain single phase ground fault thus, three-phase voltage expresses formula such as formula 1) shown in:

$v_{\mathrm{abc}}=\frac{(2+n)}{3}\left[\begin{array}{c}\cos \left(\mathrm{\ωt}\right)\\ \cos (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})\\ \cos (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\end{array}\right]+\frac{(n-1)}{3}\left[\begin{array}{c}\cos \left(\mathrm{\ωt}\right)\\ \cos (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\\ \cos (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})\end{array}\right]+\frac{(n-1)}{3}\left[\begin{array}{c}\cos \left(\mathrm{\ωt}\right)\\ \cos \left(\mathrm{\ωt}\right)\\ \cos \left(\mathrm{\ωt}\right)\end{array}\right]---1)$

In formula: V _p---line voltage positive sequence component; V _n---line voltage negative sequence component; V ₀---line voltage zero-sequence component; v _abc---three-phase power grid voltage; N---grid voltage sags amplitude.

Two relative ground circuit faults:

According to symmetrical component method, when be short-circuited fault time, if grid-connected point voltage phase place does not change, then can obtain that Static Synchronous generator under two relative ground circuit faults exports positive sequence, negative phase-sequence, zero-sequence component amplitude are:

$V_p=\frac{1+2\×n}{3},V_n=V_0=\frac{1-n}{3}$

When can obtain two relative ground circuits thus, three-phase voltage expresses formula such as formula 2) shown in:

$v_{\mathrm{abc}}=\frac{(1+2\×n)}{3}\left[\begin{array}{c}\cos \left(\mathrm{\ωt}\right)\\ \cos (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})\\ \cos (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\end{array}\right]+\frac{(1-n)}{3}\left[\begin{array}{c}\cos \left(\mathrm{\ωt}\right)\\ \cos (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\\ \cos (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})\end{array}\right]+\frac{(1-n)}{3}\left[\begin{array}{c}\cos \left(\mathrm{\ωt}\right)\\ \cos \left(\mathrm{\ωt}\right)\\ \cos \left(\mathrm{\ωt}\right)\end{array}\right]---2)$

In formula: V _p---line voltage positive sequence component; V _n---line voltage negative sequence component; V ₀---line voltage zero-sequence component; v _abc---three-phase power grid voltage; N---grid voltage sags amplitude.

Two-phase phase fault:

According to symmetrical component method, when be short-circuited fault time, if grid-connected point voltage phase place does not change, then can obtain that Static Synchronous generator under two-phase phase fault exports positive sequence, negative phase-sequence, zero-sequence component amplitude are:

$V_p=\frac{1+n}{2},V_n=\frac{1-n}{2},V_0=0$

When can obtain two-phase phase fault thus, three-phase voltage expresses formula such as formula 3) shown in:

$v_{\mathrm{abc}}=\frac{(1+n)}{2}\left[\begin{array}{c}\cos \left(\mathrm{\ωt}\right)\\ \cos (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})\\ \cos (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\end{array}\right]+\frac{(1-n)}{2}\left[\begin{array}{c}\cos \left(\mathrm{\ωt}\right)\\ \cos (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3})\\ \cos (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3})\end{array}\right]---3)$

In formula: V _p---line voltage positive sequence component; V _n---line voltage negative sequence component; V ₀---line voltage zero-sequence component; v _abc---three-phase power grid voltage; N---grid voltage sags amplitude.

Accordingly, the present invention is under asymmetry short circuit fault, and negative phase-sequence dynamic reactive support and control strategy is as follows:

the uneoupled control that control strategy realizes positive sequence, negative sequence component is separated by positive-negative sequence;

by formula 1), formula 2), formula 3), according to positive-negative sequence be separated after line voltage positive sequence, negative sequence component size, calculate degree of unbalance in real time;

according to degree of unbalance, by formula 4), by closed-loop control+instruction current Feed-forward Control Strategy, exporting negative phase-sequence dynamic reactive electric current in real time, realizing the support to falling phase voltage.I _efor rated current.

$I_{\mathrm{Nq}\_\mathrm{ref}}=\frac{V_n}{V_p}\×I_e---4)$

Below in conjunction with accompanying drawing, the present invention will be further described in detail.

H bridge cascade chain type Static Synchronous generator under electrical network asymmetry short circuit fault negative phase-sequence dynamic reactive support and control policy control structure block diagram as shown in Figure 2, whole system is separated by positive-negative sequence and phase lock control, negative-sequence current generate, the feedforward of negative phase-sequence instruction current amplitude limit and instruction, residual voltage controls, submodule Pressure and Control etc. are formed.

(1) positive-negative sequence is separated Decoupling network and phase-locked loop

When there is uneven or asymmetry short circuit fault in line voltage, its voltage comprises positive sequence, negative phase-sequence, zero-sequence component simultaneously, first need to be separated positive and negative sequence component by Decoupling network shown in Fig. 3 for this reason, lock positive sequence fundametal compoment phase place on this basis.

(2) power closed-loop control

Power closed-loop control, by accepting host computer or control end power instruction far away, realizes the accurate control to Static Synchronous generator active power, reactive power.For accelerating system response time, the mode adopting power feedforward to be combined with closed-loop control realizes, and power ring adjuster exports as active current, referenced reactive current.According to instantaneous power theory, active power, reactive power value of feedback are respectively:

$P_f=\frac{3}{2}\×V_p\×I_{\mathrm{pd}}$

$Q_f=\frac{3}{2}\×V_p\×I_{\mathrm{pq}}$

In formula: P _f---instantaneous active feeds back; Q _f---instantaneous reactive feeds back; V _p---line voltage positive sequence component; I _pd---positive sequence active current; I _pq---positive sequence reactive current.

Active power, reactive power closed-loop control block diagram are as shown in Figure 4, Figure 5.

(3) negative current instructions generates and current limit

First, detect three-phase power grid voltage in real time, be separated Decoupling network according to positive-negative sequence and obtain negative phase-sequence, positive sequence voltage component respectively, by formula 4) calculate negative phase-sequence dynamic reactive current-order; Secondly, by the separated network of positive-negative sequence shown in Fig. 3, positive-negative sequence separation is carried out to three-phase grid electric current, realize the uneoupled control of positive sequence active current, positive sequence reactive current, negative phase-sequence active current, negative phase-sequence reactive current; Finally, under electrical network asymmetry short circuit fault, for ensureing that negative-sequence current exports, realize the dynamic support to falling phase voltage, need carry out amplitude limit to positive sequence current-order, specific strategy is as follows:

positive sequence current values is calculated, such as formula 5 according to meritorious, the idle instruction current of positive sequence) shown in;

$I_p^{*}=\sqrt{{\left(I_{\mathrm{pd}\_\mathrm{ref}}^{*}\right)}^2+{\left(I_{\mathrm{pq}\_\mathrm{ref}}^{*}\right)}^2}---5)$

negative sequence current value is calculated, such as formula 6 according to meritorious, the idle instruction current of negative phase-sequence) shown in;

$I_n^{*}=\sqrt{{\left(I_{\mathrm{nd}\_\mathrm{ref}}^{*}\right)}^2+{\left(I_{\mathrm{nq}\_\mathrm{ref}}^{*}\right)}^2}---6)$

amplitude limit principle is positive sequence, negative phase-sequence instruction current sum is no more than the Static Synchronous rated current of generator, and under electrical network asymmetry short circuit fault, should be preferential with negative-sequence current output, obtain forward-order current amplitude limit value accordingly such as formula 7) shown in.

$I_p\≤I_e-I_n^{*}=I_e-\sqrt{{\left(I_{\mathrm{nd}\_\mathrm{ref}}^{*}\right)}^2+{\left(I_{\mathrm{nq}\_\mathrm{ref}}^{*}\right)}^2}---7)$

In formula: ---forward-order current instruction; ---the instruction of positive sequence active current; ---positive sequence referenced reactive current; ---negative current instructions; ---the instruction of negative phase-sequence active current; ---negative phase-sequence referenced reactive current; I _e---rated current.

(4) residual voltage controls

The guarantee of residual voltage control program is alternate all presses, and under electrical network asymmetry short circuit fault, still can ensure that H bridge cascade chain type Structural Static stops the equilibrium of direct voltage on synchronous generator three chains, its control structure block diagram as shown in Figure 6.First, calculate three chains DC voltage average value separately, by it after three-phase to two phase inversion, can be calculated residual voltage phase place and amplitude information by pi regulator, this value is residual voltage; Secondly, export meritorious, reactive current and residual voltage controller according to Static Synchronous generator to export and determine residual voltage phase information; Finally using the 0 axle component that residual voltage converts as dq0 → abc, be added to each submodule after 2r → 3s conversion.

Can to realize under electrical network asymmetry short circuit fault only carrying out dynamic reactive support to the voltage that imbalance falls phase by above-mentioned control strategy, effectively prevent the overcompensation overpressure problems that original control strategy causes.Meanwhile, owing to have employed instruction current amplitude limit strategy, can ensure, along with degree of asymmetry increases, to export negative phase-sequence reactive current to greatest extent, to realize maximum negative-sequence current support and control.

Be presented above concrete execution mode, but the present invention is not limited to described execution mode.Basic ideas of the present invention are above-mentioned basic scheme, and for those of ordinary skill in the art, according to instruction of the present invention, designing the model of various distortion, formula, parameter does not need to spend creative work.The change carried out execution mode without departing from the principles and spirit of the present invention, amendment, replacement and modification still fall within the scope of protection of the present invention.

Claims (4)

1. the Static Synchronous generator reactive support and control method of electrical network asymmetry short circuit fault, it is characterized in that, step is as follows: the uneoupled control 1) carrying out positive sequence active current, positive sequence reactive current, negative phase-sequence active current, negative phase-sequence reactive current; 2) in real time calculate grid-connected point voltage degree of unbalance, ask for negative phase-sequence dynamic support referenced reactive current under asymmetry short circuit fault according to degree of unbalance.

2. the Static Synchronous generator reactive support and control method of electrical network asymmetry short circuit fault according to claim 1, is characterized in that, also comprise step 3) amplitude limit control is carried out to instruction current.

3. the Static Synchronous generator reactive support and control method of electrical network asymmetry short circuit fault according to claim 2, is characterized in that, according to degree of unbalance, calculates negative phase-sequence dynamic reactive current-order i _e---rated current, V _p---line voltage positive sequence component; V _n---line voltage negative sequence component.

4. the Static Synchronous generator reactive support and control method of electrical network asymmetry short circuit fault according to claim 3, is characterized in that, negative phase-sequence dynamic reactive electric current according to $I_p\≤I_e-I_n^{*}=I_e-\sqrt{{\left(I_{\mathrm{nd}\_\mathrm{ref}}^{*}\right)}^2+{\left(I_{\mathrm{nq}\_\mathrm{ref}}^{*}\right)}^2}$ Amplitude limit; ---forward-order current instruction; ---the instruction of positive sequence active current; ---positive sequence referenced reactive current; ---negative current instructions; ---the instruction of negative phase-sequence active current; ---negative phase-sequence referenced reactive current; I _e---rated current.