CN106772114A - A kind of multiple access voltage class method of testing of low-voltage ride-through detection equipment - Google Patents

Abstract

The present invention relates to a kind of multiple access voltage class method of testing of low-voltage ride-through detection equipment, including：Addition constraints；Obtain the reactor inductance value under various boundary conditions.The present invention is solved to large-scale photovoltaic power station and net unit carries out integrated testability, and the problem that different voltage class are accessed, by the method increase the detection level and utilization rate of photovoltaic low-voltage ride-through detection equipment, testing cost is reduced, being that grid-connected detection business offers convenience.The technological gap of the association area to the multiple access voltage class adaptability of photovoltaic generation low-voltage ride-through detection equipment is filled up.

Description

A kind of multiple access voltage class method of testing of low-voltage ride-through detection equipment

Technical field

The present invention relates to new energy detection technique field, and in particular to a kind of multiple access voltage class method of testing of low-voltage ride-through detection equipment.

Background technology

Photovoltaic generation is accessed and will bring many adverse effects to the safe and stable operation of power network as a kind of fluctuation, randomness, intermittent very strong brute supply type, scale, is mainly shown as stabilization of power grids problem and power quality problem：When power network occurs large disturbances, if photovoltaic plant does not possess low voltage ride-through capability, it will cause large area off-grid, so as to bring secondary pulse to power network, the transient stability of power network is influenceed.After photovoltaic plant accesses power network, influence, including voltage deviation, variation in voltage, harmonic effects will be produced on the quality of power supply of power network, power network can be made to face compared with test.According to GB《Photo-voltaic power generation station accesses power system technology regulation》The requirement of (GB/T 19964-2012), high-power photovoltaic synchronization inverter must have low voltage ride-through capability (Low Voltage Ride Through, LVRT).Photovoltaic DC-to-AC converter off-grid, photovoltaic plant are only just allowed after grid voltage sags are less than regulation curve should possess the low voltage ride-through capability of reference picture 2.

In face of the situation of photovoltaic generation fast development, in order to solve the technical barrier that China's photovoltaic generation scale is accessed, power network safety operation is ensured, need the research carried out towards Large Copacity photovoltaic low voltage crossing detection technique badly.

Low-voltage ride-through detection equipment is fallen using impedance partial pressure simulation low voltage crossing power network, and falling for different voltage class is realized by adjusting reactor parameter and partial pressure.As shown in figure 3, it is short-circuit reactance device that wherein Xsr is current-limiting reactor, Xsc, the different voltage magnitudes for falling point A by putting into the different reactance values of Xsr and Xsc to reach fall major loop, to realize the unit under test i.e. detection of low voltage ride through of photovoltaic inverter.In the circuit, CB3 divisions are used to control drop-out time.

Test series connection accesses tested photovoltaic plant, and when equipment is operated in bypass condition, CB2 closures, CB1, CB3 and CB4 disconnect, photovoltaic cells normal power generation；When equipment is operated in trystate, close CB1, CB4, disconnects CB2, by current-limiting reactor Xsr inputs, then closes CB3, and by short-circuit reactance Xsc inputs, the voltage of test point is changed into the partial pressure of current-limiting reactor and short-circuit reactance, realizes the function that analog voltage falls.

Nowadays, some areas Net Frame of Electric Network is comparatively weak, and when power system accident or disturbance cause grid voltage sags, photovoltaic plant is it is ensured that not off-grid operation, support that electric network fault recovers function and is particularly important, Site Detection is to ensure the necessary realization rate for possessing above-mentioned functions.Because the actual condition of some regional application circumstances brings challenge for realizing the Site Detection of standard requirement, grid-connected photovoltaic power station 35kV is accessed and deposited with 10kV, the electric network composition of access point, electric network impedance are widely different, and system design compliance is higher.

Use reactor general to a set of testing equipment of 10kV power networks for the photovoltaic low voltage crossing mobile detecting system of capital equipment, the a set of testing equipment of 35kV power networks, or in detecting system break-up device with same complete equipment (such as breaker), reactor uses 10kV set of device, 35kV set of device, both can not be compatible.

At present, pertinent literature and patent not yet study the multiple access voltage class adaptive testing method of photovoltaic generation low-voltage ride-through detection equipment.

The content of the invention

In order to make up above-mentioned blank, the present invention proposes a kind of multiple access voltage class method of testing of low-voltage ride-through detection equipment, meet demand of the current main flow photovoltaic electric station grid connection to the 1.5MW detectabilities of low voltage crossing test platform, solve to large-scale photovoltaic power station and net unit carries out integrated testability, and the problem that different voltage class are accessed.

The purpose of the present invention is realized using following technical proposals：

A kind of multiple access voltage class method of testing of low-voltage ride-through detection equipment, methods described includes：Addition constraints, obtains the reactor inductance value under various boundary conditions；Wherein, the constraints includes：

Condition 1：During input current-limiting reactor, it is ensured that inverter measured point voltage is reduced to more than 90%；

Condition 2：According to examination criteria so that capacity of short circuit is more than 3 times of tested inverter capacity when unloaded；

Condition 3：Main transformer capacity of the system short circuit capacity less than photovoltaic plant is set, less than 20MVA；

Condition 4：According to examination criteria so that low voltage crossing detection meets 20% Voltage Drop value, it is 1 to fall a short circuit and current-limiting reactor ratio at this：4；

Condition 5：According to the otherness of different photovoltaic plant electric network impedances, 35kV electric network impedances scope as 0.5~10 Europe is set, 10kV electric network impedances scope is 0~5 Europe.

Preferably, the reactor inductance value obtained under various boundary conditions includes：Define current-limiting reactor inductance value L₁, short-circuit reactance device inductance value L₂, major network voltage U₁, fall a voltage U₂, major network and the voltage drop Δ u between falling a little fall an inflow current I^*, inverter active power P₂；Acquisition meets the reactor inductance value of the constraints.

Further, when constraints 1 is met, a voltage d-q coordinate is fallen in conversion, and d is real axis, and q is the imaginary axis, then described to fall a voltage U₂Expression formula be：

In formula (1), u₂To fall a voltage dynamic value,To fall component of a voltage on real axis, j is imaginary number, for idle calculating；To fall component of a voltage in the imaginary axis；

The expression formula of the major network and the voltage drop Δ u between falling a little is：

It is described to fall an inflow current I^*Expression formula be：

In formula (3), u₁It is major network voltage dynamic value, x is impedance of the major network between falling a little；

According to falling a voltage U₂With fall an inflow current I^*Obtain to regard and carry power S₂；Its expression formula is：

In formula (4), P₂It is photovoltaic DC-to-AC converter active power, Q₂It is the reactive power of photovoltaic DC-to-AC converter；

Convolution (1)~formula (5), the impedance x according to major network between falling a little obtains current-limiting reactor inductance value L₁, then：

X=2 π fL₁ (6)

In formula (6), f is 50Hz, represents system frequency；L₁It is current limliting reactor inductance value.

Further, due to photovoltaic DC-to-AC converter only active power of output, then by the reactive power Q of photovoltaic DC-to-AC converter₂Zero setting, obtains the maximum induction value under 35kV and 10k inverter powers, and its expression formula is：

(7)

u₂=0.9u₁

Respectively by photovoltaic DC-to-AC converter active-power P₂With line voltage U₁Substitution formula (7), completes the acquisition of maximum induction value under 35kV and 10k inverter powers.

Further, when constraints 2 is met, system short circuit capacity obtains the minimum inductance value under 35kV and 10k inverter powers more than 3 times of inverter capacity, and its expression formula is：

u₁*u₁/2πf(L₁+L₂) ＞ P₂*3 (8)。

Further, when constraints 3 is met, system short circuit capacity is less than main transformer capacity 20MW, obtains the maximum induction value under 35kV and 10k inverter powers, and its expression formula is：

u₁*u₁/2πf(L₁+L₂) ＜ 20MW (9).

Further, according to constraints 1~3, reactor inductance value restriction range is determined：10kV:0~160mH；35kV：240mH~1.97H.

Preferably, according to constraints 4, build using 20mH and combined as minimum inductance value cell, by five tandem compounds of 20mH, 20mH, 40mH, 80mH, 80mH, short-circuit reactance device is by tetra- tandem compounds of 20mH, 40mH, 80mH, 80mH for current-limiting reactor.

Compared with immediate prior art, the beneficial effect that the present invention reaches is：

The proposition of this method meets demand of the current main-stream photovoltaic electric station grid connection to the 1.5MW detectabilities of low voltage crossing test platform, solve to large-scale photovoltaic power station and net unit carries out integrated testability, and the problem that different voltage class are accessed, fill up the technological gap of the association area to the multiple access voltage class adaptability of photovoltaic generation low-voltage ride-through detection equipment；

The detection level and utilization rate of photovoltaic low-voltage ride-through detection equipment are improve, and compatibility is strong；It is that grid-connected detection business brings great convenience while testing cost is reduced.

Brief description of the drawings

A kind of multiple access voltage class method of testing flow chart of low-voltage ride-through detection equipment that Fig. 1 is provided for the present invention；

The photovoltaic low voltage ride-through capability requirement schematic diagram that Fig. 2 is provided for background technology；

The low-voltage ride-through detection equipment schematic diagram that Fig. 3 is provided for background technology；

The low-voltage ride-through detection equipment circuit diagram that Fig. 4 is provided for the present invention；

The disconnecting switch disjunction schematic diagram of the reactor switching that Fig. 5 is provided for the present invention.

Specific embodiment

Specific embodiment of the invention is described in further detail below in conjunction with the accompanying drawings：

By analysis voltage grade photovoltaic plant characteristic, at present the country main flow photovoltaic electric station grid connection unit be two 500kW photovoltaic DC-to-AC converters carried out through three-winding transformer it is grid-connected, grid-connected cell capability is generally 1MW, group string data photovoltaic DC-to-AC converter composition is single and net unit is not more than 1.5MW, therefore low voltage crossing test platform need to possess 1.5MW detectabilities, so as to large-scale photovoltaic power station, simultaneously net unit carries out integrated testability, the main grid-connected voltage grade of photovoltaic plant is 10kV or 35kV, and test platform must is fulfilled for different voltage class and accesses problem.Photovoltaic plant main transformer capacity is typically about 20MVA, and low voltage ride through system simulating grid outage capacity when being tested is not to be exceeded 20MVA.

It is low to wear the calculating that test system key parameter essentially consists in reactor inductance value, and the parameter of reactor directly determines that can low voltage ride through system realize different voltage class, the testing requirement in the power station of different electric network impedance scopes, in the case of identical reactor parameter constant, due to electric network impedance partial pressure, certain influence is produced on Voltage Drop depth.For example 10kV photovoltaic plants electric network impedance is substantially in 1 Europe or so, and 35kV photovoltaic plants electric network impedance is substantially in 3 Europe or so.

As shown in figure 1, a kind of multiple access voltage class method of testing of low-voltage ride-through detection equipment, methods described includes：Addition constraints, obtains the reactor inductance value under various boundary conditions；Wherein, the constraints includes：

Condition 1：During input current-limiting reactor, it is ensured that inverter measured point voltage is reduced to more than 90%, it is ensured that inverter normally runs；

Condition 2：According to examination criteria so that capacity of short circuit is more than 3 times of tested inverter capacity when unloaded；

Condition 3：Main transformer capacity of the system short circuit capacity less than photovoltaic plant is set, less than 20MVA；

Condition 4：According to examination criteria so that low voltage crossing detection meets 20% Voltage Drop value, it is 1 to fall a short circuit and current-limiting reactor ratio at this：4；

Condition 5：According to the otherness of different photovoltaic plant electric network impedances, 35kV electric network impedances scope as 0.5~10 Europe is set, 10kV electric network impedances scope is 0~5 Europe, and most photovoltaic plant electric network impedances can be covered substantially.

Included according to constraints calculating reactance device inductance value：Define current-limiting reactor inductance value L₁, short-circuit reactance device inductance value L₂, major network voltage U₁, fall a voltage U₂, major network and the voltage drop Δ u between falling a little fall an inflow current I^*, inverter power P；Acquisition meets the reactor inductance value of the constraints.

When constraints 1 is met, a voltage d-q coordinate is fallen in conversion, and d is real axis, and q is the imaginary axis, then described to fall a voltage U₂Expression formula be：

In formula (1), u₂To fall a voltage dynamic value,To fall component of a voltage on real axis, j is imaginary number, for idle calculating；To fall component of a voltage in the imaginary axis；

The expression formula of the major network and the voltage drop Δ u between falling a little is：

It is described to fall an inflow current I^*Expression formula be：

In formula (3), u₁It is major network voltage dynamic value, x is impedance of the major network between falling a little；

According to falling a voltage U₂With fall an inflow current I^*Obtain to regard and carry power S₂；Its expression formula is：

In formula (4), P₂It is photovoltaic DC-to-AC converter active power, Q₂It is the reactive power of photovoltaic DC-to-AC converter；

Convolution (1)~formula (5), the impedance x according to major network between falling a little obtains current-limiting reactor inductance value L₁, then：

X=2 π fL₁ (6)

In formula (6), f is 50Hz, represents system frequency；L₁It is current limliting reactor inductance value.

Due to photovoltaic DC-to-AC converter only active power of output, then by the reactive power Q of photovoltaic DC-to-AC converter₂Zero setting, obtains the maximum induction value under 35kV and 10k inverter powers, and its expression formula is：

(7)

u₂=0.9u₁

Respectively by photovoltaic DC-to-AC converter active-power P₂With line voltage U₁Substitution formula (7), completes the acquisition of maximum induction value under 35kV and 10k inverter powers.

When constraints 2 is met, system short circuit capacity obtains the minimum inductance value under 35kV and 10k inverter powers more than 3 times of inverter capacity, and its expression formula is：

u₁*u₁/2πf(L₁+L₂) ＞ P₂*3 (8)。

When constraints 3 is met, system short circuit capacity is less than main transformer capacity 20MW, obtains the maximum induction value under 35kV and 10k inverter powers, and its expression formula is：

u₁*u₁/2πf(L₁+L₂) ＜ 20MW (9).

According to constraints 1~3, reactor inductance value restriction range is determined：10kV:0~160mH；35kV：240mH~1.97H.

According to constraints 4, design is combined using 20mH as minimum inductance value cell, and, by five tandem compounds of 20mH, 20mH, 40mH, 80mH, 80mH, short-circuit reactance device is by tetra- tandem compounds of 20mH, 40mH, 80mH, 80mH for current-limiting reactor；The combination of different induction value input and corresponding Voltage Drop percentage are as shown in the table：

The low test system of wearing of table 1 falls depth combination

As shown above, optimization reactor inductance value proportioning, design current-limiting reactor is 12 kinds of different value combinations, the 11 kinds of different value combinations of short-circuit reactance device, 132 kinds are fallen combination altogether, upper table mark dash area is the distribution that falls for meeting 35kV Voltage Drops, italicized item be meet 10kV Voltage Drops fall distribution, other are that be computed invalid falls distribution.Therefore can realize meeting high-precision Voltage Drop by putting into different induction value.

35kV falls point curve and amounts to 77 points (not worn including 0), is distributed in 20%~90%, and distributed point meets relevant criterion requirement, and adapts to various electric network impedance types in 0.5~10 Europe.

10kV falls point curve and amounts to 28 points (not worn including 0), is distributed in 20%~90%, and distributed point meets the requirement of coherent detection standard, and adapts to various electric network impedance types in 0~5 Europe.

As shown in figure 4, reactor permutation and combination is shown in figure, and connected mode during all reactors input.The combination of some reactors can be selected to be put into operation to access according to depth combination table is fallen in actual motion, requirement is passed through to adapt to multi-voltage grade electrical network low voltage.

As shown in figure 5, reactor switching can realize reactor Free Switching by the way of disconnecting switch disjunction by disconnecting switch QS1~QS10 in figure, to reach the effect of different induction value proportioning in table 1.

Embodiment：

This method can be applied to develop High aititude low voltage crossing transportable test panel platform, complete state the Yellow River, Qinghai Hainan water power, Hi-Tech Wealth's photovoltaic plant, Dunhuang, Gansu Province just too, in wide core photovoltaic plant, the promise of Tibet Shigatse District power, Shannan Prefecture Poly assist multiple scenes such as prosperous photovoltaic plant to complete grid-connected test jobs.

Finally it should be noted that：Above example is only used to illustrate the technical scheme of the application rather than the limitation to its protection domain, although being described in detail to the application with reference to above-described embodiment, those of ordinary skill in the art should be understood：Those skilled in the art still can carry out a variety of changes, modification or equivalent after reading the application to the specific embodiment applied, these changes, modification or equivalent, and it is within the pending right of its application.

Claims (8)

1. a kind of multiple access voltage class method of testing of low-voltage ride-through detection equipment, it is characterised in that methods described bag Include：Addition constraints, obtains the reactor inductance value under various boundary conditions；Wherein, the constraints includes：

Condition 1：During input current-limiting reactor, it is ensured that inverter measured point voltage is reduced to more than 90%；

Condition 2：According to examination criteria so that capacity of short circuit is more than 3 times of tested inverter capacity when unloaded；

Condition 3：Main transformer capacity of the system short circuit capacity less than photovoltaic plant is set, less than 20MVA；

Condition 4：According to examination criteria so that low voltage crossing detection meet 20% Voltage Drop value, this fall it is a little short Road and current-limiting reactor ratio are 1：4；

Condition 5：According to the otherness of different photovoltaic plant electric network impedances, it is 0.5~10 to set 35kV electric network impedance scopes Europe, 10kV electric network impedances scope is 0~5 Europe.

2. the method for claim 1, it is characterised in that the reactor inductance under the acquisition various boundary conditions Value includes：Define current-limiting reactor inductance value L₁, short-circuit reactance device inductance value L₂, major network voltage U₁, fall a voltage U₂, Major network and the voltage drop Δ u between falling a little, fall an inflow current I^*, inverter active power P₂；Obtain and meet described The reactor inductance value of constraints.

3. a voltage is fallen in method as claimed in claim 2, it is characterised in that when constraints 1 is met, conversion D-q coordinates, d is real axis, and q is the imaginary axis, then described to fall a voltage U₂Expression formula be：

$U_2=u_{2}cos\∂-{\mathrm{ju}}_{2}sin\∂---\left(1\right)$

In formula (1), u₂To fall a voltage dynamic value,To fall component of a voltage on real axis, j is void Number, for idle calculating；To fall component of a voltage in the imaginary axis；

The expression formula of the major network and the voltage drop Δ u between falling a little is：

$\mathrm{\Δ}u=U_1-U_2=u_1-u_{2}cos\∂+{\mathrm{ju}}_{2}sin\∂---\left(2\right)$

It is described to fall an inflow current I^*Expression formula be：

$I^{*}=\frac{\mathrm{\Δ}u}{jx}=U_1-U_2=\frac{u_1-u_{2}cos\∂+{\mathrm{ju}}_{2}sin\∂}{jx}=\frac{u_{2}sin\∂-j(u_1-u_{2}cos\∂)}{x}---\left(3\right)$

In formula (3), u₁It is major network voltage dynamic value, x is impedance of the major network between falling a little；

According to falling a voltage U₂With fall an inflow current I^*Obtain to regard and carry power S₂；Its expression formula is：

$\begin{array}{c}{S}_2=P_2+Q_2=U_2*I^{*}=\left(u_2\cos \∂-{\mathrm{ju}}_2\sin \∂\right)*\frac{u_2\sin \∂+j\left(u_1-u_2\cos \∂\right)}{x}\\ =\frac{1}{x}\[{u_2}^2\cos \∂\sin \∂+u_2\sin \∂\left(u_1-u_2\cos \∂\right)+j\left({u_2}^2\cos \∂\left(u_1-u_2\cos \∂\right)-u_2{\sin }^2\∂\right)\]\end{array}---\left(4\right)$

In formula (4), P₂It is photovoltaic DC-to-AC converter active power, Q₂It is the reactive power of photovoltaic DC-to-AC converter；

$\begin{array}{c}{P}_2=\frac{u_1{u}_{2}sin\∂}{x}\\ Q_2=\frac{u_1{u}_2\cos \∂-u_2}{x}\end{array}---\left(5\right)$

Convolution (1)~formula (5), the impedance x according to major network between falling a little obtains current-limiting reactor inductance value L₁, Then：

X=2 π fL₁ (6)

In formula (6), f is 50Hz, represents system frequency；L₁It is current limliting reactor inductance value.

4. method as claimed in claim 2 or claim 3, it is characterised in that due to photovoltaic DC-to-AC converter only active power of output, then By the reactive power Q of photovoltaic DC-to-AC converter₂Zero setting, obtains the maximum induction value under 35kV and 10k inverter powers, its expression Formula is：

$Q_2=\frac{u_1{u}_{2}cos\∂-u_2}{x}=0$

$\begin{array}{c}{u}_1{u}_2\cos \∂-u_2=0\\ u_2=0.9u_1\end{array}---\left(7\right)$

$0.9{u_1}^{2}cos\∂-0.81{u_1}^2=0$

$cos\∂=0.9$

Respectively by photovoltaic DC-to-AC converter active-power P₂With line voltage U₁Substitution formula (7), completes 35kV and 10k inverters The acquisition of maximum induction value under power.

5. method as claimed in claim 2 or claim 3, it is characterised in that when constraints 2 is met, system short circuit capacity More than 3 times of inverter capacity, the minimum inductance value under 35kV and 10k inverter powers is obtained, its expression formula is：

u₁*u₁/2πf(L₁+L₂) ＞ P₂*3 (8)。

6. method as claimed in claim 2 or claim 3, it is characterised in that when constraints 3 is met, system short circuit capacity Less than main transformer capacity 20MW, the maximum induction value under 35kV and 10k inverter powers is obtained, its expression formula is：

u₁*u₁/2πf(L₁+L₂) ＜ 20MW (9).

7. the method for claim 1, it is characterised in that according to constraints 1~3, determine reactor inductance value Restriction range：10kV:0~160mH；35kV：240mH~1.97H.

8. the method for claim 1, it is characterised in that according to constraints 4, design is using 20mH as minimum Inductance value cell combine, current-limiting reactor by five tandem compounds of 20mH, 20mH, 40mH, 80mH, 80mH, Short-circuit reactance device is by tetra- tandem compounds of 20mH, 40mH, 80mH, 80mH.