CN104764965A - Voltage sag generating device based on magnetic controllable reactor (MCR) - Google Patents

Abstract

The invention discloses an MCR-based grid voltage sag generating device, which includes: a fixed reactor, a magnetron reactor, a photovoltaic power station and a control system; the magnetron reactor is connected in parallel with the photovoltaic power station and then connected with the fixed reactance connected in series to the busbar of a known voltage level power supply; the voltage of the known voltage level power supply is denoted as U _N ; one end of the control system is connected to the incoming line of the photovoltaic power station, and the other end is connected to the magnetically controlled reactor connected. In the device disclosed in the present invention, the voltage value at the inlet of the photovoltaic power station is detected in real time through the magnetic control reactor, and the reactance value of the magnetic control reactor is controlled so that the voltage value of the incoming line of the photovoltaic power station is within the U _N Change between 10% and 90% of the grid voltage to simulate the grid voltage sag when the grid fails, so as to test the low voltage ride-through capability of the photovoltaic power station grid-connected; in addition, based on the realization of the magnetic control reactor, its inductance value can be achieved Continuous stepless adjustment can more accurately test the low voltage ride-through capability of photovoltaic power plants connected to the grid.

Description

A voltage sag generating device based on a magnetron reactor (MCR)

technical field

The invention relates to a voltage sag test device in the technical field of new energy distributed power generation connected to a grid, in particular to a voltage sag generating device based on a magnetron reactor (MCR).

Background technique

At present, photovoltaic power generation has become an important form of development and utilization of solar energy resources. The connection of large-scale photovoltaic power stations will have a profound impact on the safe and stable operation of the power grid, especially when the power grid is faulty, the sudden disconnection of photovoltaic power stations will further deteriorate the operation of the power grid. , with more serious consequences.

At the end of 2010, the State Grid Corporation of China issued the "Technical Regulations for Connecting Photovoltaic Power Stations to the Grid", which clearly stated that "photovoltaic power stations should have a certain ability to withstand abnormal voltages, so as to avoid disconnection when the grid voltage is abnormal, causing loss of grid power."

Therefore, in the case of a grid fault, in order to prevent the photovoltaic power plant from suddenly going off the grid and further deteriorating the operating state of the grid, a device that can test its low voltage ride-through capability is needed; however, there is no related research in the prior art plan.

Contents of the invention

The purpose of the present invention is to provide an MCR-based power grid voltage sag generating device, which can simulate the state of grid voltage sag when the grid fails, to accurately test the low voltage ride-through capability of photovoltaic power plants when they are connected to the grid.

The purpose of the present invention is achieved through the following technical solutions:

An MCR-based power grid voltage sag generating device, the device includes: a fixed reactor, a magnetic control reactor MRC, a photovoltaic power station and a control system;

Wherein, after the magnetic control reactor is connected in parallel with the photovoltaic power station, it is connected in series with the fixed reactor to the bus bar of a known voltage level power supply; the voltage of the known voltage level power supply is denoted as U _N ;

One end of the control system is connected to the inlet of the photovoltaic power station, and the other end is connected to the magnetron reactor; it is used to detect the voltage value at the inlet of the photovoltaic power station in real time, and thereby control the magnetron reactor The reactance value of the photovoltaic power station makes the incoming line voltage value of the photovoltaic power station vary between 10% and 90% of the U _N to simulate the grid voltage sag when the power grid fails, so as to test the low voltage ride-through ability of the photovoltaic power plant grid-connected .

Further, the rated voltage of the fixed reactor is the same as the voltage of the known voltage level power supply, and its inductance value is L, then the rated current flowing through each phase of the fixed reactor is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}}<span\; class="notranslate">\; ;</span>$

Among them, f is the system frequency.

Further, the rated voltage of the magnetic control reactor is the same as the voltage of the known voltage level power supply, and its inductance value is Then the maximum allowable current flowing through each phase of the magnetic control reactor is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; MCR</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 9</span>}}\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$

Among them, L is the inductance value of the fixed reactor;

When the magnetron reactor is At this time, the current flowing through the magnetic control reactor is the largest, expressed as:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 9</span>}}\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$

Among them, L _S is the system impedance, and its calculation formula is: S _d is the short-circuit capacity of the busbar.

Further, the magnetic control reactor includes reactor windings and rectification circuits connected to each other;

The reactor winding includes two iron cores, each of which is provided with two sets of coils, the upper and lower sets of coils in one iron core are denoted as coil L _A and coil L _C , The upper and lower groups of coils are recorded as coil L _B and coil L _D ; among them, the outlet end of coil L _A is connected to the inlet end of coil L _D , the outlet end of coil L _B is connected to the inlet end of coil L _C , and the same Thyristors VT1 and VT2 are also provided between the upper and lower coils of the iron core; after the upper and lower coils of different iron cores are cross-connected, freewheeling diodes are arranged across the cross terminals.

Further, the control system detects the voltage value at the inlet of the photovoltaic power station in real time, and controls the reactance value of the magnetron reactor so that the voltage value of the incoming line of the photovoltaic power station is between 10% and 90% of the _U Variations include:

The control system detects the voltage value at the inlet of the photovoltaic power station in real time, and then compares the detection result with the set voltage value, and controls the magnetron reactor according to the comparison result until the voltage value at the inlet of the photovoltaic power station matches the set voltage value. The given voltage value is equal;

Among them, if the detected voltage value is smaller than the set voltage value, the control system increases the firing angle of the thyristors VT1 and VT2 in the magnetron reactor; when the firing angle increases, the conduction angle of VT1 and VT2 decreases, The DC current of the coil decreases, the saturation of the iron core decreases, and the reactance value of the magnetron reactor increases;

If the detected voltage value is larger than the set voltage value, the control system will reduce the firing angle of the thyristors VT1 and VT2 in the magnetron reactor; if the firing angle decreases, the conduction angle of VT1 and VT2 will increase, causing the coil As the DC current increases, the saturation of the iron core increases, and the reactance value of the magnetron reactor decreases.

Further, the minimum short-circuit capacity of the photovoltaic grid-connected point is:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>\frac{{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span>}$

Among them, L is the inductance value of the fixed reactor, L _S is the system impedance;

The capacity of the photovoltaic power station is more than 10 times smaller than the minimum short-circuit capacity of the photovoltaic grid-connected point.

It can be seen from the above-mentioned technical solution provided by the present invention that by using the control system to detect the incoming line voltage in real time, and then controlling the reactance value of the magnetic control reactor, the incoming line voltage value of the photovoltaic power station is within 10%-10% of the system nominal voltage. Change between 90% to simulate the grid voltage sag when the grid fails; this scheme is based on the realization of the magnetic control reactor, so the inductance value of the reactor can be continuously adjusted steplessly, which can more accurately test the grid connection of photovoltaic power plants low voltage ride through capability.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For Those of ordinary skill in the art can also obtain other drawings based on these drawings on the premise of not paying creative work.

FIG. 1 is a schematic structural diagram of an MCR-based power grid voltage sag generating device provided by an embodiment of the present invention;

Fig. 2 is a schematic structural diagram of a magnetron reactor provided by an embodiment of the present invention;

Fig. 3 is a flow chart of determining reactor parameters in a grid voltage sag generating device and performing grid fault simulation provided by an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Fig. 1 is a schematic structural diagram of an MCR-based grid voltage sag generating device provided by an embodiment of the present invention. As shown in Figure 1, the device mainly includes: fixed reactor L1, magnetron reactor (MCR) L2, photovoltaic power station and control system.

Wherein, after the magnetic control reactor is connected in parallel with the photovoltaic power station, it is connected in series with the fixed reactor to the bus bar of the known voltage level power supply; the voltage of the known voltage level power supply is denoted as _UN ; the control system One end is connected to the inlet of the photovoltaic power station, and the other end is connected to the magnetron reactor.

The device can also include three circuit breakers K1, K2, and K3. Before the power supply is not supplied, the circuit breakers K1, K2, and K3 are all in the opening state. After the power supply is supplied, K2 is closed, and K1 and K3 are disconnected. Photovoltaic power station bypass power supply.

In the embodiment of the present invention, in order to test the low-voltage ride-through capability when the photovoltaic power station is connected to the grid, the circuit breakers K1 and K3 are closed, and K2 is opened. At this time, the control system detects the voltage value at the inlet of the photovoltaic power station (as shown in the test point in Figure 1) in real time, and controls the reactance value of the magnetic control reactor so that the voltage value of the incoming line of the photovoltaic power station is within the specified range. The change between 10% and 90% of U _N is used to simulate the grid voltage sag when the grid fails, so as to accurately test the low voltage ride-through capability of the photovoltaic power station.

Since the fixed reactor must bear up to 90% of the rated voltage in this device, a shunt reactor with a higher rated voltage should be selected. The basic characteristics and parameters of the shunt reactor can be found in the national standard "Reactor" (GB 10229). In this embodiment, the rated voltage of the fixed reactor is the same as the voltage of the known voltage level power supply, and its inductance value is preset as L, then the rated current flowing through each phase of the fixed reactor is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}}<span\; class="notranslate">\; ;</span>$

Among them, f is the system frequency.

In order to make the incoming line voltage of the photovoltaic power station vary between 10% and 90% of the rated voltage, the voltage shared by the magnetron reactor should be able to vary between 10% and 90%, so the inductance value of the magnetron reactor should be in At the same time, assuming that the rated voltage of the magnetic control reactor is the same as the voltage of the known voltage level power supply, the maximum allowable current flowing through each phase of the magnetic control reactor is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; MCR</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 9</span>}}\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$

Among them, L is the inductance value of the fixed reactor;

When the magnetron reactor is At this time, the current flowing through the magnetic control reactor is the largest, expressed as:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 9</span>}}\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$

Among them, L _S is the system impedance, and its calculation formula is: S _d is the short-circuit capacity of the busbar.

In the embodiment of the present invention, the rated current of the fixed reactor and the maximum allowable current of the magnetron reactor should be greater than I _max , if the rated current of any reactor is less than the maximum current, the inductance value L of the fixed reactor should be reset .

When the parameters of the fixed reactor and the magnetron reactor are determined, the minimum short-circuit capacity of the photovoltaic grid-connected point (such as the photovoltaic grid-connected point in Figure 1) can be calculated, expressed as:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>\frac{{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$

Among them, L is the inductance value of the fixed reactor, L _S is the system impedance;

Since the incoming line voltage will be unstable when the photovoltaic power station is connected to the grid, the capacity of the photovoltaic power station should be more than 10 times smaller than the minimum short-circuit capacity of the photovoltaic power station to minimize the impact of the photovoltaic power station’s grid connection on the incoming line voltage.

In addition, the above solution of the embodiment of the present invention is realized based on a magnetic control reactor, the wiring of the magnetic control reactor is simple, and the reactance value can be continuously and steplessly adjustable. Therefore, the low-voltage ride-through capability of grid-connected photovoltaic power plants can be tested more accurately. Its structural schematic diagram is shown in Figure 2, mainly including: interconnected reactor windings and rectifier circuits;

The reactor winding includes two iron cores, each of which is provided with two sets of coils, the upper and lower sets of coils in one iron core are denoted as coil L _A and coil L _C , The upper and lower groups of coils are recorded as coil L _B and coil L _D ; among them, the outlet end of coil L _A is connected to the inlet end of coil L _D , the outlet end of coil L _B is connected to the inlet end of coil L _C , and the same Thyristors VT1 and VT2 are also provided between the upper and lower coils of the iron core; after the upper and lower coils of different iron cores are cross-connected, freewheeling diodes are arranged across the cross terminals.

When the power supply is in the positive half cycle, the thyristor VT1 bears the forward voltage, and VT2 bears the reverse voltage. If VT1 is triggered to conduct, the power supply provides DC control voltage and current to the circuit. Similarly, if VT2 is triggered to turn on during the negative half cycle of the power supply, it will also generate DC control voltage and current, and the direction of the control current is the same as when VT1 is turned on. In a power frequency cycle of the power supply, the turn-on of the thyristors VT1 and VT2 plays the role of full-wave rectification, and the freewheeling diode plays the role of freewheeling. Changing the firing angle of VT1 and VT2 can change the size of the control current, thereby changing the saturation of the reactor core, and adjusting the reactance value of the reactor smoothly and continuously.

The corresponding relationship between the magnetic permeability L-μ of the iron core magnetic circuit of the magnetron reactor is calculated according to the following formula:

in $R_0=\frac{l_0}{{\mathrm{\&mu;\&mu;}}_0{S}_0}$

Where: ψ, - Flux linkage, the unit is magnetic flux (Weber); I is the DC excitation current _; W is the number of turns; _μ is the relative magnetic permeability ^; circuit length (centimeter); S ₀ is the magnetic circuit cross section (square centimeter); R ₀ -magnetic resistance.

The above is the main composition structure of the device provided by the present invention, and the working process thereof will be described in detail below in conjunction with accompanying drawing 3 .

As shown in Figure 3, first of all, it is necessary to determine the rated voltage and inductance of the fixed reactor and the magnetic control reactor, and then determine whether the maximum current flowing through the two reactors is less than its rated current (these two steps have been carried out earlier detailed description, so no more details); if yes, proceed to the next step; otherwise, it is necessary to re-determine the rated voltage and inductance of the fixed reactor and the magnetron reactor.

Then, set the voltage value at the inlet of the photovoltaic power station (as shown in the test point in Figure 1), and the control system detects the voltage value at the inlet of the photovoltaic power station in real time, and then compares the detection result with the set voltage value , according to the comparison result, the magnetron reactor is controlled until the voltage value at the inlet of the photovoltaic power station is equal to the set voltage value.

Among them, if the detected voltage value is smaller than the set voltage value, the control system increases the firing angle of the thyristors VT1 and VT2 in the magnetron reactor; when the firing angle increases, the conduction angle of VT1 and VT2 decreases, The DC current of the coil decreases, the saturation of the iron core decreases, and the reactance value of the magnetron reactor increases;

If the detected voltage value is larger than the set voltage value, the control system will reduce the firing angle of the thyristors VT1 and VT2 in the magnetron reactor; if the firing angle decreases, the conduction angle of VT1 and VT2 will increase, causing the coil As the DC current increases, the saturation of the iron core increases, and the reactance value of the magnetron reactor decreases.

In the above process of adjusting the thyristor, the corresponding DC excitation current I can be calculated from the inductance value of the magnetron reactor, and the firing angle α of the thyristor can be calculated from the DC excitation current I to adjust it.

For ease of understanding, a specific example is used below for illustration; it should be noted that the numerical values used in the following examples are only examples, and users can make corresponding changes according to actual needs.

In this example, the power supply voltage U _N is set to 35kV, and the short-circuit capacity S _d of the busbar is 600MVA, then the system impedance L _S is:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 35</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 600</span>}}\mathrm{<span\; class="notranslate">\; \&Omega;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2.04</span>}\mathrm{<span\; class="notranslate">\; \&Omega;</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2.04</span>}}{\mathrm{<span\; class="notranslate">\; 314</span>}}\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 6.5</span>}\mathrm{<span\; class="notranslate">\; mH</span>}<span\; class="notranslate">\; ;</span>$

The rated voltage of the fixed reactor is selected as the system nominal voltage 35kV, and the inductance L is 300mH, so the rated current flowing through one phase of the reactor is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 35000</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 50</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 0.3</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 214.4</span>}\mathrm{<span\; class="notranslate">\; A</span>}$

In order to make the voltage shared by the magnetron reactor vary between 10% and 90%, the inductance value of the magnetron reactor needs to be within between. The rated voltage of the magnetic control reactor is selected as the nominal voltage of the power grid 35kV, so the maximum allowable current flowing through each phase of the magnetic control reactor is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; MCR</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 35000</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 50</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 0.033</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1949.2</span>}\mathrm{<span\; class="notranslate">\; A</span>}$

When the inductance value of the magnetic control reactor is 33.3mH, the current of the line is the largest, and the current at this time is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 35000</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 50</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 0.3398</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 189.3</span>}\mathrm{<span\; class="notranslate">\; A</span>}$

The rated current of the above-mentioned fixed reactor and the maximum allowable current of the magnetic control reactor are both greater than the maximum current flowing through the line, so the selection of the reactor is successful. At this time, the minimum short-circuit capacity of the photovoltaic grid-connected point is:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 35</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 50</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 0.3065</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 12.72</span>}\mathrm{<span\; class="notranslate">\; MVA</span>}$

Since the grid-connected photovoltaic power station will lead to unstable incoming line voltage, the capacity of the photovoltaic power station is more than 10 times smaller than the minimum short-circuit capacity of the photovoltaic grid-connected point, so as to minimize the impact of photovoltaic power station grid-connected on the incoming line voltage. Therefore, The capacity of the photovoltaic power station that can be selected in this example is about 1MVA.

Afterwards, the low-voltage ride-through capability of the photovoltaic power plant can be tested in the manner shown in Figure 3 .

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person familiar with the technical field can easily conceive of changes or changes within the technical scope disclosed in the present invention. Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (6)

1. An MCR-based grid voltage sag generating device, characterized in that the device comprises: a fixed reactor, a magnetron reactor MRC, a photovoltaic power station and a control system; Wherein, after the magnetic control reactor is connected in parallel with the photovoltaic power station, it is connected in series with the fixed reactor to the bus bar of a known voltage level power supply; the voltage of the known voltage level power supply is denoted as U _N ; One end of the control system is connected to the inlet of the photovoltaic power station, and the other end is connected to the magnetron reactor; it is used to detect the voltage value at the inlet of the photovoltaic power station in real time, and thereby control the magnetron reactor The reactance value of the photovoltaic power station makes the incoming line voltage value of the photovoltaic power station vary between 10% and 90% of the U _N to simulate the grid voltage sag when the power grid fails, so as to test the low voltage ride-through ability of the photovoltaic power plant grid-connected . 2. The device according to claim 1, wherein the rated voltage of the fixed reactor is the same as the voltage of the known voltage level power supply, and its inductance value is L, then every The rated current of the phase is: ${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;fL</span>}}<span\; class="notranslate">\; ;</span>$ Among them, f is the system frequency. 3. The device according to claim 1, wherein the rated voltage of the magnetron reactor is the same as the voltage of the known voltage level power supply, and its inductance value is Then the maximum allowable current flowing through each phase of the magnetic control reactor is: ${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; MCR</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 9</span>}}\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$ Among them, L is the inductance value of the fixed reactor; When the magnetron reactor is At this time, the current flowing through the magnetic control reactor is the largest, expressed as: ${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 9</span>}}\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$ Among them, L _S is the system impedance, and its calculation formula is: S _d is the short-circuit capacity of the busbar. 4. The device according to claim 1 or 3, wherein the magnetron reactor comprises a reactor winding and a rectifier circuit connected to each other; The reactor winding includes two iron cores, each of which is provided with two sets of coils, the upper and lower sets of coils in one iron core are denoted as coil L _A and coil L _C , The upper and lower groups of coils are recorded as coil L _B and coil L _D ; among them, the outlet end of coil L _A is connected to the inlet end of coil L _D , the outlet end of coil L _B is connected to the inlet end of coil L _C , and the same Thyristors VT1 and VT2 are also provided between the upper and lower coils of the iron core; after the upper and lower coils of different iron cores are cross-connected, freewheeling diodes are arranged across the cross terminals. 5. The device according to claim 1, characterized in that the control system detects the voltage value at the inlet of the photovoltaic power station in real time, and controls the reactance value of the magnetic control reactor so that the voltage value of the incoming line of the photovoltaic power station Variations between 10% and 90% of the _UN include: The control system detects the voltage value at the inlet of the photovoltaic power station in real time, and then compares the detection result with the set voltage value, and controls the magnetron reactor according to the comparison result until the voltage value at the inlet of the photovoltaic power station matches the set voltage value. The given voltage value is equal; Among them, if the detected voltage value is smaller than the set voltage value, the control system increases the firing angle of the thyristors VT1 and VT2 in the magnetron reactor; when the firing angle increases, the conduction angle of VT1 and VT2 decreases, The DC current of the coil decreases, the saturation of the iron core decreases, and the reactance value of the magnetron reactor increases; If the detected voltage value is larger than the set voltage value, the control system will reduce the firing angle of the thyristors VT1 and VT2 in the magnetron reactor; if the firing angle decreases, the conduction angle of VT1 and VT2 will increase, causing the coil As the DC current increases, the saturation of the iron core increases, and the reactance value of the magnetron reactor decreases. 6. The device according to claim 1, wherein the minimum short-circuit capacity of the photovoltaic grid-connected point is: ${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; =</span>\frac{{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span>}$ Among them, L is the inductance value of the fixed reactor, L _S is the system impedance; The capacity of the photovoltaic power station is more than 10 times smaller than the minimum short-circuit capacity of the photovoltaic grid-connected point.