CN100347925C - Electric network power oscillation inhibitor based on photovoltaic battery - Google Patents

Abstract

The grid power oscillation suppressor based on photovoltaic cells belongs to the technical field of grid power oscillation suppression. It is characterized in that it is a device based on photovoltaic cells to suppress grid power oscillations. It converts solar energy into electrical energy through solar panels and outputs DC voltage. , and then invert the direct current into alternating current and send it to the power grid. It can send active power to the power grid and dynamically adjust the power grid. During normal operation, part of the active power is sent to the grid; when power oscillation occurs in the grid, the active and reactive power output by the grid power oscillation suppressor is adjusted according to the control law, so that the grid can be restored to stability as soon as possible; using clean Renewable energy - solar energy dynamically regulates the power of the grid and partially supplies power, which suppresses the power oscillation of the grid, improves the stability of the grid, and increases the damping of the system.

Description

Grid Power Oscillation Suppressor Based on Photovoltaic Cells

technical field

A grid power oscillation suppressor based on photovoltaic cells belongs to the technical field of grid power oscillation suppression.

Background technique

In order to optimize the allocation of resources on a larger scale, improve the economic efficiency of the power grid, and improve the efficiency of accident support, my country's electric power is developing towards a large-scale network. The strategic pattern of "west-to-east power transmission, north-south mutual supply, and national networking" is gradually taking shape. However, With the increasing size of the power grid and the increasingly complex structure, the operation stability of the power grid is very important, especially for weakly interconnected AC power grids and AC-DC interconnected power grids, the problem of power oscillation is particularly prominent, which directly threatens the security and stability of the power grid Therefore, scholars at home and abroad have done a lot of research on it;

The problem of power oscillation is usually the problem of insufficient system oscillation damping. At present, the main methods are to use the power system stabilizer (PSS) to control the excitation of the generator to improve the damping of system oscillation, and to use additional stabilization signals to modulate high-voltage direct current (HVDC ) converter control for power transmission and flexible power transmission device (such as controllable series compensation, static var compensator, etc.) Regulating reactive power is also affected by factors such as generator terminal voltage limitation, while using additional stable signals to modulate HVDC power transmission converter control Since the HVDC system is embedded in a large AC and DC system, the active power to be regulated is still flow in the system, the active power of the entire system does not increase or decrease, which means that active power regulation only has an effect on the corresponding subsystems, but has no effect on the entire system, and for traditional HVDC converters, its response The speed is slow, and the purpose of dynamic adjustment cannot be achieved. In addition, the adjustment of its reactive power can only be unidirectionally adjusted within a small range. Therefore, its control effect is greatly affected, which is not as good as PSS; flexible power transmission Methods such as device control cannot adjust the active power of the entire system, and its control effect is not as good as that of PSS;

Therefore, if the power supply outside the entire AC-DC system can be used for power regulation, the effect of suppressing power oscillation will be more significant; Solar energy is directly converted into electrical energy, and the DC voltage is output. The DC power is converted into AC power through the photovoltaic inverter and sent to the grid. The photovoltaic inverter is composed of voltage source type devices that can be quickly turned off. Sending active power to the grid can also perform large-scale two-way reactive power regulation on the system; during normal operation, the grid power oscillation suppressor based on photovoltaic cells outputs part of the active power; when the grid oscillates, adjust its active power and reactive power output, improve the stability and damping of the power grid, and help the power grid to restore stability as soon as possible;

The designed power grid power oscillation suppressor based on photovoltaic cells uses clean and renewable energy - solar energy to suppress power oscillations; at present, people only use photovoltaic cells for power generation, and no one thinks of using them to suppress The power oscillation of the system, and the harm of the power oscillation to the power grid is huge, and the suppression of the power oscillation is very urgent and important to the power grid, especially the large-scale power grid. Therefore, the present invention is a brand new concept and subject.

Contents of the invention

The purpose of the present invention is to provide a grid power oscillation suppressor based on photovoltaic cells.

The present invention is characterized in that:

The suppressor is a grid power oscillation suppressor that converts solar energy into direct current, and then uses a photovoltaic inverter to convert the direct current into alternating current and sends it to the grid. The suppressor includes photovoltaic panels, photovoltaic inverters, filters transformers, grid-connected transformers, voltage transformers, current transformers and controllers, of which:

Photovoltaic panels, which convert solar energy into direct current;

A photovoltaic inverter, the DC bus of the inverter is connected to the DC output terminal of the photovoltaic cell panel;

A filter, the input end of the filter is connected to the output end of the photovoltaic inverter, and the other end of the filter is connected to one end of the following grid-connected transformer;

A grid-connected transformer, the input end of the transformer is connected to the corresponding output end of the filter, and the output end of the transformer is connected to the grid;

The voltage transformer, that is, PT, its input terminal is connected to the filter and the connection terminal of the grid-connected transformer, and its output terminal is connected to the corresponding input port of the following controller;

The current transformer, that is, CT, the connection line between the filter and the grid-connected transformer passes through the CT, and its output terminal is connected to the corresponding input port of the following controller;

The controller is a digital control circuit, using any one of a digital signal processor, a single-chip microcomputer, and a computer; the controller follows the following steps to realize that the active power to the grid is between zero and the maximum output power of the photovoltaic panel. The adjustment of the reactive power of the grid is adjusted bidirectionally in the way of exporting to the grid or absorbing from the grid. The specific adjustment steps are as follows:

Step 1. Initialization, that is, set the following parameters in the controller, and all power and voltage parameters use standard per unit values:

The initial value of the output active power P _sc0 of the power oscillation suppressor;

The grid voltage RMS initial value V _m0 of the power oscillation suppressor;

The initial values u _rq0 and u _rd0 of the q-axis and d-axis components of the grid-connected inverter output voltage of the power oscillation suppressor in the dq coordinate system;

Reactive power adjustment coefficient k ₁ and active power adjustment coefficient k ₂ , 0<k ₁ <100000, 0<k ₂ <100000, are set by the operator according to the grid operation status;

The control coefficients k _p1 and k _i1 of the first PI controller, 0<k _p1 <1000, 0<k _i1 <1000, are set by the operator according to the operation status of the grid;

The control coefficients k _p2 and k _i2 of the second PI controller, 0<k _p2 <1000, 0<k _i2 <1000, are set by the operator according to the operation status of the grid;

Adjust reactive power and/or active power according to the operating conditions of the power grid;

By changing the q-axis and d-axis components of the grid-connected inverter output voltage in the d-q coordinate system, the purpose of adjusting its output active power and reactive power is achieved;

Step 2. Grid reactive power adjustment is performed in the following steps:

Step 21. Calculate the input value μ _PIS1 of PI control by the first adder according to the following formula: μ _PIS1 =V _m0 -V _m -k ₁ Δω,

Among them, V _m is the effective value of the grid voltage, which is input to the controller after being measured by the voltage transformer;

Δω is the angular velocity variation of the grid generator, which is calculated from the frequency f of the grid voltage measured by the following formula: Δω=2π(ff ₀ ), where f ₀ is 50 or 60Hz;

Step 22. The first PI controller performs control operation after receiving the output of the first adder, and outputs the corresponding control quantity μ _PIC1 , the calculation formula is as follows: μ _PIC1 = k _p1 μ _PIS1 + k _i1 ∫ _{μ PIS1} dt , where k _p1 and k _i1 are the control coefficients of the first PI controller;

Step 23. Use the first comparator to calculate the d-axis component u _rd of the output voltage of the grid-connected inverter in the dq coordinate system according to the following formula, u _rd = u _rd0 -μ _PIC1 ;

Step 3. Grid active power regulation is performed in the following steps:

Step 31. Calculate the input value μ _PIS2 of PI control by the second adder according to the following formula: μ _PIS2 =P _sc0 -P _sc +k ₂ Δω,

Among them, P _sc is the output active power of the power oscillation suppressor, the three-phase voltage u _a , u _b and u _c of the power grid measured by the voltage transformer and the three-phase current i _a , i _b and i _c measured by the current transformer are input The calculation formula for the controller is as follows: P _sc ＝ u _a i _a + u _b i _b + u _c i _c ;

Step 32. The second PI controller performs a control operation after receiving the output of the second adder, and outputs the corresponding control quantity μ _PIC2 , the calculation formula is as follows: μ _PIC2 =k _p2 μ _PIS2 +k _i2 ∫μ _PIS2 dt , where k _p2 and k _i2 are the control coefficients of the second PI controller;

Step 33. Use the second comparator to calculate the q-axis component u _rq of the output voltage of the grid-connected inverter in the dq coordinate system according to the following formula, u _rq = u _rq0 -μ _PIC2 ;

Step 4. Transform from d-q to abc coordinates:

Calculate the components u _rq and u _rd in the dq coordinate system obtained from the above calculation according to the following dq to abc coordinate transformation formula to obtain the output three-phase voltage u _at , u _bt and u _ct of the grid-connected inverter:

$\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; at</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; bt</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; ct</span>}}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; rd</span>}}\\ {\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="u\; rq\; u"\; filenames="C20061001111300132.png,C20061001111300141.png"\; state="\{\{state\}\}">u</figure-callout></span><figure-callout\; id="0"\; label="u\; rq\; u"\; filenames="C20061001111300132.png,C20061001111300141.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; rq</span>}}& \\ {}_{}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\end{array}\right]$

Among them, u ₀ is the zero-sequence voltage of the power grid, which is calculated by the following formula: ${\mathrm{<figure-callout\; id="0"\; label="u"\; filenames="C20061001111300132.png,C20061001111300141.png"\; state="\{\{state\}\}">u</figure-callout>}}_0=\frac{1}{3}(u_a+u_b+u_c).$

The control law of the PI controller is a proportional-integral-derivative (PID) control method.

The purpose of adjusting the output active power and reactive power of the grid-connected inverter is achieved by changing the amplitude and phase angle of the output voltage of the grid-connected inverter.

The angular velocity variation Δω of the power grid generator is sent to the controller after the rotational speed n is measured by the generator rotational speed sensor and calculated by the following formula: $\mathrm{\&Delta;\&omega;}=2\mathrm{\&pi;}(\frac{2\mathrm{no}{p}_f}{60}-f_0),$ Among them, p _f is the number of pole pairs of the generator rotor.

The active power P _sc output by the power oscillation suppressor is calculated by the two-table method.

The DC bus of the inverter is connected in parallel with a braking resistor branch, the braking resistor branch is connected in series with a braking resistor and a braking resistor switch, the control terminal of the braking resistor switch is connected to the controller The braking resistor switch control signal output terminal is connected.

The power grid power oscillation suppressor based on photovoltaic cells proposed by the present invention uses solar energy to dynamically adjust grid power to achieve the function of suppressing power oscillation; photovoltaic cells, that is, solar cells, directly convert solar energy into electrical energy, output DC voltage, and pass through photovoltaic inverters. The inverter converts DC power into AC power and transmits it to the grid. The photovoltaic inverter is composed of voltage source type devices that can be quickly turned off. Power regulation; during normal operation, the grid power oscillation suppressor based on photovoltaic cells sends part of the active power to the grid; when power oscillation occurs in the grid, quickly adjust its output active power and reactive power, improve system damping, and improve grid stability sex.

The designed grid power oscillation suppressor based on photovoltaic cells utilizes clean and renewable energy - solar energy to suppress power oscillations;

Its characteristics are as follows:

1. Utilize clean and renewable energy - solar energy to regulate active power to the grid;

2. Through the dynamic adjustment of active and reactive power, it can suppress the power oscillation of the power grid and improve the stability and damping of the power grid;

Description of drawings

Fig. 1. Hardware schematic of photovoltaic cell-based grid power oscillation suppressor.

Fig. 2. Control law diagram of grid power oscillation suppressor based on photovoltaic cells.

Figure 3. Program flow chart of photovoltaic cell-based grid power oscillation suppressor.

Figure 4. Application example diagram of grid power oscillation suppressor based on photovoltaic cells.

Figure 5. Simulation results of an application example of a grid power oscillation suppressor based on photovoltaic cells Figure 1.

Fig. 6. Simulation results of the application example of grid power oscillation suppressor based on photovoltaic cells Fig. 2.

Fig. 7. Hardware schematic diagram of grid power oscillation suppressor with braking resistor branch based on photovoltaic cells.

Detailed ways

The grid power oscillation suppressor 8 based on photovoltaic cells is shown in the virtual frame of Fig. 1, which consists of a photovoltaic cell panel 1, a photovoltaic inverter 2, a filter 3, a grid-connected transformer 4, a controller 5, a voltage transformer 6, and a current mutual inductance Device 7 and other components, the following describes each component in detail:

1 is a photovoltaic panel, which can be composed of multiple photovoltaic cells, convert solar energy into electrical energy, and output DC voltage;

The second is a photovoltaic inverter, which converts DC power into AC power and transmits it to the grid. The inverter is composed of voltage source type devices that can be quickly turned off, and it has fast active and reactive power adjustment capabilities;

The third is the filter, which filters out the high-frequency harmonics output by the photovoltaic inverter, so that the voltage waveform output by the inverter is basically consistent with the grid voltage waveform after being filtered;

4 is a grid-connected transformer, which connects the AC output from the inverter to the grid after being filtered;

5 is the controller, which is responsible for data sampling, processing and control, etc., and adjusts active power and/or reactive power according to the conditions of solar energy and power grid;

The control law is included in the controller 5, which calculates and processes the relevant signals such as voltage and current collected by the controller 5, and the final result directly controls the inverter 2 through the controller 5, which can be as shown in Figure 2 The proportional-integral (PI) shown can also be a proportional-integral-derivative (PID) control method or other control methods. According to the control law, the active power P _sc and reactive power Q _sc output by the inverter are adjusted to suppress the power of the grid Oscillation, the adjusted active power can be adjusted from zero to the maximum output value of the above-mentioned photovoltaic cells, and the adjusted reactive power can be output to or absorbed from the grid, that is, two-way adjustment of reactive power; in addition, according to grid power oscillation For the situation, the switching of the braking resistor branch is controlled by the controller;

6 is a voltage transformer, which measures the grid voltage and sends it to the controller;

7 is a current transformer, which measures the grid current and sends it to the controller;

9 represents the grid;

Fig. 7 is a schematic diagram of the hardware with braking resistor branch 8, the braking resistor branch is controlled by the controller, and switching can be performed at any time according to the needs to suppress the power oscillation of the power grid, which can be composed of braking resistors and electronic switches;

In the appendix, the single-unit infinite system is taken as an example to illustrate the working principle of the grid power oscillation suppressor based on photovoltaic cells, and a digital simulation is performed to show its working effect.

Claims (3)

1. based on the electric network power oscillation inhibitor of photovoltaic cell, it is characterized in that, this inhibitor is a kind of conversion of solar energy to be become direct current, with photovoltaic DC-to-AC converter dc inverter is become the electric network power oscillation inhibitor of giving electrical network of alternating current again, described inhibitor contains photovoltaic battery panel, photovoltaic DC-to-AC converter, filter, the transformer that is incorporated into the power networks, voltage transformer, current transformer and controller, wherein:

Photovoltaic battery panel becomes direct current to conversion of solar energy;

Photovoltaic DC-to-AC converter, the dc bus of this inverter links to each other with the dc output end of described photovoltaic battery panel;

Filter, the input of this filter links to each other with the output of photovoltaic DC-to-AC converter, and the other end of this filter links to each other with an end of the following transformer that is incorporated into the power networks;

The transformer that is incorporated into the power networks, the input of this transformer links to each other with the corresponding output of described filter, and the output of this transformer links to each other with electrical network;

Voltage transformer, i.e. PT, its input links to each other with the transformer link that is incorporated into the power networks with filter, and its output links to each other with the corresponding input port of following controller;

Current transformer, i.e. CT, above-mentioned filter passes CT with the transformer connecting line that is incorporated into the power networks, and its output links to each other with the corresponding input port of following controller;

Controller is a kind of digital control circuit, adopts any in digital signal processor, single-chip microcomputer, the computer; This controller realizes the active power of electrical network according to the following steps from zero to the adjusting the described photovoltaic battery panel peak power output, and by to electrical network output or the mode bidirectional modulation that absorbs from electrical network, concrete regulating step is as follows to the reactive power of electrical network:

Following parameter is promptly set in step 1. initialization in this controller, all power and voltage parameter adopt per unit value:

The active power of output initial value P of power oscillation inhibitor _Sc0

The line voltage effective value initial value V of power oscillation inhibitor _M0

Q axle and the d axle component initial value u of the combining inverter output voltage of power oscillation inhibitor under the d-q coordinate system _Rq0And u _Rd0

Reactive power adjustment factor k ₁With active power adjustment factor k ₂, 0＜k ₁＜100000,0＜k ₂＜100000, set by the operation of power networks situation by the operator;

The one PI controller control coefrficient k _P1And k _I1, 0＜k _P1＜1000,0＜k _I1＜1000, set by the operation of power networks situation by the operator;

The 2nd PI controller control coefrficient k _P2And k _I2, 0＜k _P2＜1000,0＜k _I2＜1000, set by the operation of power networks situation by the operator;

According to the operation of power networks situation, carry out reactive power and/or active power and regulate;

Reach the purpose of regulating its active power of output and reactive power by changing the q axle and the d axle component of combining inverter output voltage under the d-q coordinate system;

Step 2. power system reactive power is regulated according to the following steps and is carried out:

Step 21. is calculated as follows the input value μ of PI control by first adder _PIS1: μ _PIS1=V _M0-V _m-k ₁Δ ω,

Wherein, V _mBe the line voltage effective value, record this controller of back input by voltage transformer;

Δ ω is a grid generator angular velocity varies amount, is calculated through following formula by the frequency f of measuring line voltage: Δ ω=2 π (f-f ₀), wherein, f ₀Be 50 or 60Hz;

Step 22. a PI controller is controlled computing after the output that receives described first adder, output control corresponding amount μ _PIC1, computing formula is as follows: μ _PIC1=k _P1μ _PIS1+ k _I1∫ μ _PIS1Dt, wherein, k _P1And k _I1It is the control coefrficient of a PI controller;

Step 23. is calculated the d axle component u of combining inverter output voltage under the d-q coordinate system as follows by first comparator _Rd, u _Rd=u _Rd0-μ _PIC1

Step 3. electric network active power adjustments is carried out according to the following steps:

Step 31. is calculated as follows the input value μ of PI control by second adder _PIS2: μ _PIS2=P _Sc0-P _Sc+ k ₂Δ ω,

Wherein, P _ScBe the power oscillation inhibitor active power of output, record electrical network three-phase voltage u by voltage transformer _a, u _bAnd u _cAnd current transformer records three-phase current i _a, i _bAnd i _cAfter input to controller and calculate, computing formula is as follows: P _Sc=u _ai _a+ u _bi _b+ u _ci _c

Step 32. the 2nd PI controller is controlled computing after the output that receives described second adder, output control corresponding amount μ _PIC2, computing formula is as follows: μ _PIC2=k _P2μ _PIS2+ k _I2∫ μ _PIS2Dt, wherein, k _P2And k _I2It is the control coefrficient of the 2nd PI controller;

Step 33. is calculated the q axle component u of combining inverter output voltage under the d-q coordinate system as follows by second comparator _Rq, u _Rq=u _Rq0-μ _PIC2

Step 4. arrives the abc coordinate transform by d-q:

Component u under the d-q coordinate system that aforementioned calculation is obtained _RqAnd u _RdCalculate combining inverter output three-phase voltage u by following d-q to abc coordinate transform formula _At, u _BtAnd u _Ct:

$\left[\begin{array}{c}{u}_{\mathrm{at}}\\ u_{\mathrm{bt}}\\ u_{\mathrm{ct}}\end{array}\right]=\left[\begin{array}{ccc}\cos \mathrm{\&theta;}& -\sin \mathrm{\&theta;}& 1\\ \cos (\mathrm{\&theta;}-\frac{2\mathrm{\&pi;}}{3})& -\sin (\mathrm{\&theta;}-\frac{2\mathrm{\&pi;}}{3})& 1\\ \cos (\mathrm{\&theta;}+\frac{2\mathrm{\&pi;}}{3})& -\sin (\mathrm{\&theta;}+\frac{2\mathrm{\&pi;}}{3})& 1\end{array}\right]\left[\begin{array}{c}{u}_{\mathrm{rd}}\\ u_{\mathrm{rq}}\\ u_0\end{array}\right]$

Wherein, u ₀Be the electrical network residual voltage, calculate through following formula: $u_0=\frac{1}{3}(u_a+u_b+u_c).$

2. the electric network power oscillation inhibitor based on photovoltaic cell according to claim 1 is characterized in that: the control law of described PI controller is proportion integration differentiation (PID) control mode.

3. the electric network power oscillation inhibitor based on photovoltaic cell according to claim 1, it is characterized in that: a brake resistance branch road in the parallel connection of described inverter dc bus, this brake resistance props up the route brake resistance and brake resistance switch serial connection forms, and the control end of described brake resistance switch links to each other with the brake resistance switch controlling signal output of described controller.

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