CN204290321U - Micro-capacitance sensor voltage perturbation control system - Google Patents

Abstract

The utility model provides a kind of micro-capacitance sensor voltage perturbation control system, and this system comprises: energy-storage units, power converter cells, coordinate transform and active power calculate unit, power controller, voltage controller, adaptive slicer, current controller, PWM generator; Adaptive slicer, the reactive current reference value exported for the active current reference value that exports power controller and voltage controller carries out amplitude limit, exports meritorious reference current and idle reference current; PWM generator, produces PWM waveform for carrying out PWM to voltage control signal, inputs in power converter cells.The utility model to solve in prior art voltage frequent fluctuation and reactive power in micro-capacitance sensor to be difficult to optimize the technical problem of distributing, and reaches the voltage fluctuation effectively suppressing micro-capacitance sensor, ensures the technique effect that voltage stabilization runs.

Description

Micro-grid voltage perturbation control system

Technical Field

The utility model relates to a little electric wire netting technical field, in particular to little electric wire netting voltage perturbation control system.

Background

In recent years, with the rapid development of micro-grids, micro-grids formed by wind power generation and solar power generation gradually become the mainstream of new energy power supply. Because wind power generation and photovoltaic power generation have the characteristics of randomness, volatility and intermittence, frequent fluctuation of voltage in a micro-grid formed by wind and photovoltaic power generation often occurs, voltage perturbation is caused, and the voltage stability of the micro-grid is seriously influenced. In order to solve the above problems, a large-scale energy storage device is connected to the microgrid to stabilize the voltage and frequency in the microgrid. By introducing a large-scale energy storage technology, the operation characteristic of an intermittent power supply can be effectively improved in real time, and the regulation and control capability of a micro-grid is improved, so that the operation stability and reliability of the micro-grid are improved, and the grid-connection capability of the micro-grid is also improved.

At present, a novel energy storage technology represented by electrochemical energy storage is developed into research and application of a large-capacity and large-scale energy storage system from small capacity and small scale, the problem of large-scale new energy grid connection can be solved through research on a wind-solar energy storage combined power generation system in a micro-grid, and research on a plurality of related problems including panoramic monitoring and operation and maintenance technologies of the combined power generation system can be developed depending on the energy storage system of a wind-solar energy storage demonstration power station.

However, an effective solution is not proposed at present how to fully utilize a large-scale energy storage device to participate in perturbation control of the voltage of the microgrid and optimize and schedule power distribution in the microgrid.

SUMMERY OF THE UTILITY MODEL

The embodiment of the utility model provides a little electric wire netting voltage perturbation control system to voltage frequently fluctuates and reactive power is difficult to optimize the technical problem who distributes among the solution prior art little electric wire netting. The system comprises:

the device comprises an energy storage unit, a converter unit, a coordinate conversion and active power calculation unit, a power controller, a voltage controller, a self-adaptive amplitude limiter, a current controller and a Pulse Width Modulation (PWM) generator;

the energy storage unit is used for supplying power to the micro-grid;

the converter unit is connected with the output end of the energy storage unit and used for adjusting the output current of the energy storage unit to meet the reactive current requirement of the microgrid;

the input end of the coordinate transformation and active power calculation unit is connected with the output end of the converter unit, and is used for converting variables on an ABC coordinate system output by the converter unit into variables on a rotating coordinate system dq, wherein the output end of the coordinate transformation and active power calculation unit comprises: an active current feedback output terminal, a reactive current feedback output terminal and an active power output terminal;

the input end of the power controller is connected with the active power reference value and is connected with the active power output end of the coordinate transformation and active power calculation unit, and the output end of the power controller comprises: an active current reference value output end;

the input end of the voltage controller is connected with the microgrid voltage and the microgrid voltage reference value, and the output end of the voltage controller comprises: a reactive current reference value output end;

the input end of the self-adaptive amplitude limiter is connected with the active current reference value output end of the power controller and the reactive current reference value output end of the voltage controller, and the self-adaptive amplitude limiter is used for carrying out amplitude limiting on the active current reference value output by the power controller and the reactive current reference value output by the voltage controller and outputting active reference current and reactive reference current;

the input end of the current controller is connected with the output end of the adaptive amplitude limiter, and is connected with the active current feedback output end and the reactive current feedback output end of the coordinate transformation and active power calculation unit, so that the active current and the reactive current of the microgrid can be regulated, the active current and the reactive current can track the active reference current and the reactive reference current, and the output end of the current controller outputs a voltage control signal;

and the PWM generator is connected with the output end of the current controller and used for carrying out PWM modulation on the voltage control signal to generate a PWM waveform, and the PWM waveform is input into the converter unit.

In one embodiment, the adaptive slicer comprises: active current amplitude limiting circuit, idle current amplitude limiting circuit, first square processing circuit, second square processing circuit, accumulation circuit, square processing circuit, the minimum circuit of asking, wherein:

the input end of the active current amplitude limiting circuit is connected with the active current reference value output end of the power controller, and the output end of the active current amplitude limiting circuit is connected with the first input end of the minimum value calculating circuit;

the input end of the reactive current amplitude limiting circuit is connected with the reactive current reference value output end of the voltage controller, and the output end of the reactive current amplitude limiting circuit is the reactive reference current output end of the self-adaptive amplitude limiter;

the input of the first square processing circuit is a reference current amplitude limiting value output by the converter unit, and the output end of the first square processing circuit is connected with the positive value input end of the accumulation circuit;

the input end of the second square processing circuit is connected with the reactive current reference value output end of the voltage controller, and the output end of the second square processing circuit is connected with the negative value input end of the accumulation circuit;

the output end of the accumulation circuit is connected with the input end of the squaring processing circuit, and the output end of the squaring processing circuit is connected with the second output end of the minimum value calculating circuit;

and the output end of the minimum value calculating circuit is the active reference current output end of the self-adaptive amplitude limiter.

In one embodiment, the converter unit includes: the three-phase converter is used for converting the energy of the energy storage unit into energy required to be compensated during the perturbation of the voltage of the microgrid;

and the filtering reactance is connected with the three-phase converter and is used for filtering out higher harmonics generated when the direct current power in the energy storage unit is converted into the alternating current reactive power of the micro-grid.

In one embodiment, the three-phase converter includes: for converting the dc power into the ac power under the PWM control.

In one embodiment, a first PI regulator is arranged in the power controller, and the first PI regulator is used for inputting a power set value required to be compensated by active power output by the three-phase converter into the microgrid;

and a second PI regulator is arranged in the voltage controller and used for inputting a voltage perturbation set value required by reactive power output by the three-phase converter and compensated into the microgrid.

In one embodiment, the PWM generator is further configured to interlock, electrically isolate, and power amplify two driving signals on the same bridge arm of the main circuit.

In one embodiment, the three-phase converter is composed of 6 fully-controlled switching devices.

In one embodiment, a PI regulator is provided in the power controller and the voltage controller for performing PI regulation.

In one embodiment, the PWM generator is a model SKYPER32 PWM generator.

The embodiment of the utility model provides an in, a little electric wire netting voltage perturbation control system is provided, when frequent fluctuation appears in little electric wire netting voltage, through voltage and the electric current in the detection little electric wire netting, applied voltage control perturbation device for energy conversion among the extensive energy storage unit stabilizes the reactive current among the little electric wire netting, makes transient voltage can resume normal level, simultaneously through adding the self-adaptation amplitude limiter, makes little electric wire netting voltage can be when fluctuating on a large scale, stabilizes at normal level sooner, thereby has guaranteed the safe and reliable operation of little electric wire netting, the utility model provides a little electric wire netting in the prior art voltage frequent fluctuation and reactive power be difficult to optimize the technical problem of distribution, reached the voltage fluctuation of effectively restraining the little electric wire netting, guaranteed the technological effect of voltage steady operation.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:

fig. 1 is a schematic structural diagram of a microgrid voltage perturbation control system according to an embodiment of the present invention;

fig. 2 is a circuit diagram of a converter unit according to an embodiment of the present invention;

fig. 3 is a circuit diagram of an adaptive slicer according to an embodiment of the present invention;

fig. 4 is a schematic diagram of an output reference current trajectory of an adaptive limiter according to an embodiment of the present invention;

fig. 5 is a schematic diagram of an output power curve of the voltage perturbation device when the voltage on the network side drops according to the embodiment of the present invention;

fig. 6 is a block diagram of converter unit inner loop current control according to an embodiment of the present invention;

fig. 7 is an overall architecture diagram of a control system of an embodiment of the present invention;

fig. 8 is a schematic diagram of a microgrid with a voltage perturbation device according to an embodiment of the present invention;

fig. 9 is a schematic diagram of a phase voltage waveform output by the voltage perturbation device according to the embodiment of the present invention;

fig. 10 is a schematic diagram of a phase current waveform output by the voltage perturbation device according to the embodiment of the present invention;

fig. 11 is a schematic diagram of a voltage amplitude fluctuation waveform of the microgrid before compensation according to an embodiment of the present invention;

fig. 12 is a schematic diagram of a compensated voltage amplitude fluctuation waveform of the microgrid according to an embodiment of the present invention;

fig. 13 is a schematic diagram of an active power waveform output by the voltage perturbation device according to the embodiment of the present invention;

fig. 14 is a schematic diagram of a reactive power waveform output by the voltage perturbation device according to the embodiment of the present invention;

fig. 15 is a schematic circuit diagram of the hardware of the voltage perturbation device according to the embodiment of the present invention;

fig. 16 is a flowchart of a microgrid voltage perturbation control method according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the following embodiments and accompanying drawings. The exemplary embodiments and descriptions of the present invention are provided to explain the present invention, but not to limit the present invention.

In this example, there is provided a microgrid voltage perturbation control system, as shown in fig. 1, comprising: the system comprises an energy storage unit, a converter unit, a coordinate transformation and active power calculation unit, a power controller, a voltage controller, an adaptive amplitude limiter, a current controller and a PWM generator, wherein the functions of the energy storage unit, the converter unit, the coordinate transformation and active power calculation unit, the power controller, the voltage controller, the adaptive amplitude limiter, the current controller and the PWM generator are explained below;

1) the energy storage unit is used for supplying power to the micro-grid;

2) the converter unit is connected with the output end of the energy storage unit and used for adjusting the output current of the energy storage unit to meet the reactive current requirement of the microgrid;

3) and the input end of the coordinate transformation and active power calculation unit is connected with the output end of the converter unit and is used for converting the variable on the ABC coordinate system output by the converter unit into the variable on the rotating coordinate system dq, wherein the output end of the coordinate transformation and active power calculation unit comprises: an active current feedback output terminal, a reactive current feedback output terminal and an active power output terminal;

4) and the input end of the power controller is connected with the active power reference value and is connected with the active power output end of the coordinate transformation and active power calculation unit, and the output end of the power controller comprises: an active current reference value output end;

5) voltage controller, the input links to each other with little electric wire netting voltage and little electric wire netting voltage reference value, and the output includes: a reactive current reference value output end;

6) the input end of the self-adaptive amplitude limiter is connected with the active current reference value output end of the power controller and the reactive current reference value output end of the voltage controller, and the self-adaptive amplitude limiter is used for carrying out amplitude limiting on the active current reference value output by the power controller and the reactive current reference value output by the voltage controller and outputting active reference current and reactive reference current;

7) the input end of the current controller is connected with the output end of the adaptive amplitude limiter, and is connected with the active current feedback output end and the reactive current feedback output end of the coordinate transformation and active power calculation unit, so that the active current and the reactive current of the microgrid can be regulated, the active current and the reactive current can track the active reference current and the reactive reference current, and the output end of the current controller outputs a voltage control signal;

8) and the PWM generator is connected with the output end of the current controller and used for carrying out PWM modulation on the voltage control signal to generate a PWM waveform, and the PWM waveform is input into the converter unit.

In this example, a micro-grid voltage perturbation control system is provided, when the voltage in the micro-grid fluctuates frequently, through detecting the voltage and current in the micro-grid, a voltage control perturbation device is applied, so that the energy in the large-scale energy storage unit is converted into the reactive current in the stable micro-grid, the transient voltage can be recovered to the normal level, and meanwhile, through adding the self-adaptive amplitude limiter, the micro-grid voltage can be stabilized at the normal level more quickly when fluctuating on a large scale, thereby the safe and reliable operation of the micro-grid is ensured, the utility model solves the technical problems that the voltage in the micro-grid fluctuates frequently and the reactive power in the prior art are difficult to optimize and distribute, and achieves the technical effects of effectively inhibiting the voltage fluctuation of the micro-grid and ensuring the stable operation of the voltage.

The specific functions and operation principles of the above-mentioned several components are described below with reference to fig. 1:

1) large Scale energy storage cell (i.e., energy storage cell as described above)

The large-scale energy storage unit in the microgrid mainly comprises a plurality of groups of batteries of various types, stores the energy of wind energy and solar energy in the batteries and is used for supplying power to the microgrid and stabilizing the voltage.

2) Converter unit

The converter unit can be composed of a three-phase power electronic converter and a filter reactance, a self-phase-conversion bridge circuit is connected with a micro-grid through a series reactance by adopting the basic principle of a synchronous compensator, and the alternating-current side current of the self-phase-conversion bridge circuit is properly adjusted according to the instruction of the voltage and the active power of the micro-grid so as to meet the reactive current requirement of the micro-grid, realize the purpose of dynamic reactive compensation and finally realize the rapid stabilization of the voltage. Specifically, the three-phase converter in the converter unit converts the energy of the large-scale energy storage unit into the energy required for compensation during perturbation of the voltage of the microgrid, and the filter reactance in the converter unit is used for filtering out higher harmonics generated when the direct-current power in the energy storage unit is converted into the alternating-current reactive power of the microgrid.

Specifically, the converter may have a structure as shown in fig. 2, and includes a dc capacitor C, IGBT, a filter inductor L, a resistor R, and the like, the controller inputs an inductive or capacitive reactive current to the system through a three-phase converter including 6 fully-controlled switching devices according to a voltage fluctuation condition of the microgrid, and the dc power may be converted into ac power more quickly through the 6 fully-controlled switching devices IGBT provided in the three-phase converter under the PWM control method.

By U_ARepresenting the converter output voltage u_Aa、u_AbAnd u_AcSpace vector of in U_SRepresenting microgrid voltage u_Sa、u_Sb、u_ScThe space vector of (2).

The relationship between the converter output voltage and the dc-side voltage is then:

$\left\{\begin{array}{c}{u}_{\mathrm{Aa}}={\mathrm{MU}}_{\mathrm{dc}}\sin (\mathrm{\ωt}-\mathrm{\δ})\\ u_{\mathrm{Ab}}={\mathrm{MU}}_{\mathrm{dc}}\sin (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3}-\mathrm{\δ})\\ u_{\mathrm{Ac}}={\mathrm{MU}}_{\mathrm{dc}}\sin (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3}-\mathrm{\δ})\end{array}\right.$ (formula 1)

Wherein M is a proportionality coefficient, U_dcIs a DC side voltage, delta is U_AAnd U_SThe included angles between the two parts are all controllable.

From the converter cell schematic of fig. 2, it can be derived:

$\left\{\begin{array}{c}{u}_{\mathrm{Aa}}={\mathrm{Ri}}_a+L\frac{{\mathrm{di}}_a}{\mathrm{dt}}+u_{\mathrm{Sa}}\\ u_{\mathrm{Ab}}={\mathrm{Ri}}_b+L\frac{{\mathrm{di}}_b}{\mathrm{dt}}+u_{\mathrm{Sb}}\\ u_{\mathrm{Ac}}={\mathrm{Ri}}_c+L\frac{{\mathrm{di}}_c}{\mathrm{dt}}+u_{\mathrm{Sc}}\end{array}\right.$ (formula 2)

Substituting equation 1 into equation 2 yields:

$\left\{\begin{array}{c}L\frac{{\mathrm{di}}_a}{\mathrm{dt}}={\mathrm{MU}}_{\mathrm{dc}}\sin (\mathrm{\ωt}-\mathrm{\δ})-u_{\mathrm{Sa}}-{\mathrm{Ri}}_a\\ L\frac{{\mathrm{di}}_b}{\mathrm{dt}}={\mathrm{MU}}_{\mathrm{dc}}\sin (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3}-\mathrm{\δ})-u_{\mathrm{Sb}}-{\mathrm{Ri}}_b\\ L\frac{{\mathrm{di}}_C}{\mathrm{dt}}={\mathrm{MU}}_{\mathrm{dc}}\sin (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3}-\mathrm{\δ})-u_{\mathrm{Sc}}-{\mathrm{Ri}}_C\end{array}\right.$ (formula 3)

The direct current side voltage equation can be obtained from the energy relation:

$\frac{d}{\mathrm{dt}}\left(\frac{1}{2}{\mathrm{CU}}_{\mathrm{dc}}^2\right)=-[u_{\mathrm{Aa}}{i}_a+u_{\mathrm{Ab}}{i}_b+u_{\mathrm{Ac}}{i}_c]$ (formula 4)

Substituting equation 1 into equation 4 and simplifying to obtain:

$\frac{{\mathrm{dU}}_{\mathrm{dc}}}{\mathrm{dt}}=-\frac{M}{C}[i_a\sin (\mathrm{\ωt}-\mathrm{\δ})+i_b\sin (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3}-\mathrm{\δ})+i_C\sin (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3}-\mathrm{\δ})$ (formula 5)

Further, a mathematical model of the main circuit unit under the ABC coordinate system can be obtained:

$\left\{\begin{array}{c}L\frac{{\mathrm{di}}_a}{\mathrm{dt}}={\mathrm{MU}}_{\mathrm{dc}}\sin (\mathrm{\ωt}-\mathrm{\δ})-u_{\mathrm{Sa}}-{\mathrm{Ri}}_a\\ L\frac{{\mathrm{di}}_b}{\mathrm{dt}}={\mathrm{MU}}_{\mathrm{dc}}\sin (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3}-\mathrm{\δ})-u_{\mathrm{Sb}}-{\mathrm{Ri}}_b\\ L\frac{{\mathrm{di}}_c}{\mathrm{dt}}={\mathrm{MU}}_{\mathrm{dc}}\sin (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3}-\mathrm{\δ})-u_{\mathrm{Sc}}-{\mathrm{Ri}}_c\\ \frac{d{U}_{\mathrm{dc}}}{\mathrm{dt}}=-\frac{M}{C}[i_a\sin (\mathrm{\ωt}-\mathrm{\δ})+i_b\sin (\mathrm{\ωt}-\frac{2\mathrm{\π}}{3}-\mathrm{\δ})+i_c\sin (\mathrm{\ωt}+\frac{2\mathrm{\π}}{3}-\mathrm{\δ})\end{array}\right.$ (formula 6)

3) Coordinate transformation and active power calculation unit

By analyzing the formula 6, the change rule of each variable of the converter unit can be known, the coefficient in the formula 6 changes along with time, and the difficulty in analysis and solution is high, so that the ABC/dq conversion is applied to convert the variable on the ABC coordinate system to the variable on the rotating coordinate system dq. Assuming three-phase balance, and taking the direction of the d axis to be consistent with the direction of the voltage space vector US of the microgrid, the mathematical model after dq coordinate transformation is as follows:

$\frac{d}{\mathrm{dt}}\left[\begin{array}{c}{i}_d\\ i_q\\ U_{\mathrm{dc}}\end{array}\right]=\left[\begin{array}{ccc}-\frac{R}{L}& -\mathrm{\ω}& \frac{M}{L}\sin \mathrm{\δ}\\ -\mathrm{\ω}& -\frac{R}{L}& \frac{M}{L}\cos \mathrm{\δ}\\ -\frac{M}{C}\sin \mathrm{\δ}& -\frac{M}{C}\sin \mathrm{\δ}& 0\end{array}\right]\left[\begin{array}{c}{i}_d\\ i_q\\ U_{\mathrm{dc}}\end{array}\right]+\frac{1}{L}\left[\begin{array}{c}-U_m\\ 0\\ 0\end{array}\right]$ (formula 7)

Wherein i_dRepresenting the d-axis current in the dq coordinate system (active current feedback of the inner loop current controller), i_qRepresenting the q-axis current in the dq coordinate system (reactive current feedback of the inner loop current controller), U_mRepresenting the microgrid phase voltage amplitude.

Since equation 7 is a constant coefficient differential equation set, it is convenient to analyze and solve each variable of the coordinate transformation and active power calculation unit, and the equivalent voltage of the unit after dq transformation is a dc voltage, which is:

$\left\{\begin{array}{c}{v}_d=M\sin \mathrm{\δ}\\ v_q=M\cos \mathrm{\δ}\end{array}\right.$ (formula 8)

Therefore, the relationship between the cell voltages and currents on the dq coordinate axis is:

$L\frac{d}{\mathrm{dt}}\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]=\left[\begin{array}{cc}-R& \mathrm{\ωL}\\ -\mathrm{\ωL}& -R\end{array}\right]\left[\begin{array}{c}{i}_q\\ i_q\end{array}\right]+\left[\begin{array}{c}{v}_d-U_m\\ v_q\end{array}\right]$ (formula 9)

According to the instantaneous power theory, the active power P output by the available unit is as follows:

$P=\frac{3}{2}(U_{\mathrm{Sd}}{i}_d+U_{\mathrm{Sq}}{i}_q)=\frac{3}{2}{U}_m{i}_d$ (formula 10)

Thus, the cell outputs a d-axis current i_dOutputting q-axis current i as active current feedback of the inner loop current controller_qAnd the active power P is output as the reactive current feedback of the inner loop current controller and is used as the active power feedback of the outer loop power controller.

4) Adaptive amplitude limiter

When the voltage of the microgrid fluctuates, in order to realize the rapid recovery of the transient voltage supporting capability and reduce the constraint of a conventional control method on the output reference current amplitude limiting value of the power outer loop controller, a self-adaptive amplitude limiter is provided, the structural diagram of which is shown in fig. 3, the self-adaptive amplitude limiter can dynamically adjust the amplitude limiting value of the active reference current according to the reactive reference current output by the power outer loop controller when the voltage of the microgrid fluctuates and even when the voltage of the microgrid fails, so that the output reactive reference current is maximized, and finally, the stability of the voltage of the microgrid can be recovered more rapidly.

As shown in fig. 3, the adaptive slicer may include: active current amplitude limiting circuit, idle current amplitude limiting circuit, first square processing circuit, second square processing circuit, first accumulation circuit, square processing circuit, the minimum circuit of asking, wherein: the input end of the active current amplitude limiting circuit is connected with the active current reference value output end of the power controller, and the output end of the active current amplitude limiting circuit is connected with the first input end of the minimum value calculating circuit; the input end of the reactive current amplitude limiting circuit is connected with the reactive current reference value output end of the voltage controller, and the output end of the reactive current amplitude limiting circuit is the reactive reference current output end of the self-adaptive amplitude limiter; the input of the first square processing circuit is a reference current amplitude limiting value output by the converter unit, and the output end of the first square processing circuit is connected with the positive value input end of the first accumulation circuit; the input end of the second square processing circuit is connected with the reactive current reference value output end of the voltage controller, and the output end of the second square processing circuit is connected with the negative value input end of the first accumulation circuit; the output end of the first accumulation circuit is connected with the input end of the square-opening processing circuit, and the output end of the square-opening processing circuit is connected with the second output end of the minimum value calculating circuit; the output end of the minimum value calculating circuit is an active reference current output end of the self-adaptive amplitude limiter.

In order to prevent system overcurrent, the current reference value is usually limited in the outer loop power controller, and the maximum current output by the converter is generally 1.5 times of the rated current, that is, the limitation condition of the current reference value output by the converter is as follows:

$i_{\lim }^{*}=1.5i_e$ (formula 11)

Wherein,representing the reference current limit value, i, of the converter output_eRepresenting rated value of AC current on micro-grid side, reference current limiting valueIncluding active reference current clipping valuesAnd reactive reference current clipping valueThe relationship between the two satisfies:

$i_{\lim }^{*}=\sqrt{i_{\mathrm{d\; lim}}^{*2}+i_{\mathrm{qlim}}^{*2}}$ (formula 12)

The working principle of the adaptive amplitude limiter is shown in fig. 3, and can be obtained from fig. 3Andthe output range of (d) is:

$i_q^{*}=\left\{\begin{array}{cc}{i}_{q1}^{*},& -i_{\lim }^{*}<i_{q1}^{*}<i_{\lim }^{*}\\ i_{\lim }^{*},& i_{q1}^{*}\&GreaterEqual;i_{\lim }^{*}\\ -i_{\lim }^{*},& i_{q1}^{*}\&le;-i_{\lim }^{*}\end{array}\right.$ (formula 13)

$i_d^{*}=\left\{\begin{array}{cc}{i}_{d1}^{*},& i_{\mathrm{dlim}}^{*}<i_{d1}^{*}\&le;\sqrt{i_{\lim }^{*2}-i_{q1}^{*2}}\\ \sqrt{i_{\lim }^{*2}-i_{q1}^{*2}},& \sqrt{i_{\lim }^{*2}-i_{q1}^{*2}}<i_{d1}^{*}<i_{\lim }^{*}\\ i_{\lim }^{*},& i_{d1}^{*}\&GreaterEqual;i_{\lim }^{*}\\ i_{\mathrm{dlim}}^{*},& i_{d1}^{*}\&le;i_{\mathrm{dlim}}^{*}\end{array}\right.$ (formula 14)

As can be seen from the above equations 13 and 14, in the case of the microgrid voltage drop, the reference current trace output by the adaptive limiter is as shown in fig. 4. At the initial operating point D, the reference current output by the adaptive amplitude limiter is the same as the reference current output by the outer loop controller, namelyAndwhen the voltage of the microgrid drops slightly, the reference current output by the outer ring controller is still within the semicircle of fig. 4, the system reaches a new stable operation point M, but when the voltage of the microgrid drops greatly, the active and reactive reference currents output by the outer ring controller are increased greatly, and when the reference current drops greatlyIncrease to its clipping conditionThen, from equation 13 and equation 14, we can obtain: active reference current output by self-adaptive amplitude limiterBecome intoThe reference current trajectory thus reaches point a and can rotate clockwise along a semicircle of the current control range, as shown in fig. 4. According to different voltage reduction degrees of the microgrid, the reference current vector can stably operate after reaching the point B or continuously rotate to the point C. When the reference current vector moves to point C, at this timePower factor angle of converter outputIs composed ofThus, the converter outputs only reactive power.

Fig. 5 shows the power curve of the converter output when the microgrid voltage drops. Hypothesis systemStarting to operate stably at point Z, the microgrid voltage drops suddenly, changing the operating point to point F in fig. 5. When the conventional control method is adopted, the reactive reference current output by the outer ring controller is limited, and the reactive reference current output by the outer ring controller is limitedMaximum value ofAfter the transient state, the system stably operates at the point M, and the voltage of the micro-grid at the moment is U₁. After the self-adaptive amplitude limiter is adopted, the output reactive reference current can be directly maximizedAfter the transient state, the system is transited to the N point for stable operation, and the voltage of the micro-grid is U at the moment₂. As shown in fig. 5, the adaptive amplitude limiter can increase the capability of the converter to output reactive power, which is more beneficial to the recovery of the microgrid voltage and better than the conventional control method.

5) Current controller and PWM generator

The current controller mainly regulates active current and reactive current, and the purpose of current inner loop control is to make the output current i of the main circuit unit_d、i_qCan track its reference value, thereby enabling the microgrid voltage U_SStabilizes at a desired constant value and outputs a PWM control signal. As can be seen from equation 9: i.e. i_d、i_qCan be composed of v_d、v_qControl regulation, but with coupling between the d-axis and q-axis of the converter voltage and current quantities, i_dWill cause v to be changed_qAnd i_qWith consequent changes and vice versa. The coupled loops cannot be analyzed separately and therefore need to be decoupled. Adding a feedforward compensation term omega Li to the output value of the PI controller of the current inner loop_d、ωLi_qA specific control block diagram is shown in fig. 6.

The transfer function of the converter output voltage in fig. 6 is:

$\left\{\begin{array}{c}{v}_d=(K_P+\frac{K_I}{s})(i_d^{*}-i_d)-\mathrm{\&omega;}{\mathrm{Li}}_q+U_m\\ v_q=(K_P+\frac{K_I}{s})(i_q^{*}-i_q)+\mathrm{\&omega;}{\mathrm{Li}}_d\end{array}\right.$ (formula 15)

Wherein, K_PAnd K_ISubstituting equation 15 into equation 9 for the proportional coefficient and integral coefficient of the PI controller, respectively, can obtain:

$L\frac{d}{\mathrm{dt}}\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]=\left[\begin{array}{cc}R+K_P+\frac{K_I}{s}& 0\\ 0& R+K_P+\frac{K_I}{s}\end{array}\right]\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]+(K_P+\frac{K_I}{s})\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]$ (formula 16)

The off-diagonal element is 0, so that after feedforward compensation is added to the PI output of the current inner loop, decoupling control is realized on d and q axis variables, and the final output v of the current controller_d、v_qFor PWM generator receiving control signal v output by current controller_d、v_qAnd PWM modulation is carried out to generate a PWM waveform.

The PWM generator is not only used for generating PWM modulation waveforms, but also used for carrying out interlocking, electrical isolation and power amplification on two paths of driving signals on the same bridge arm of the main circuit, so that the frequency and the voltage amplitude of the output fundamental wave are the same as those of the micro-grid.

6) Voltage controller and power controller

The voltage controller and the power controller are both external loop controllers, which can also be called as an active power controller and a voltage controller, and the power controller and the voltage controller are both provided with PI (proportional integral) regulators for PI regulation.

Wherein the active power controller outputs the given value of the active current through PI regulationRegulating the output active power of the converter, comparing the given value of the active power with the output active power value of the converter, and generating a d-axis current reference value through PI regulationTo stabilize the active power voltage output by the converter.Satisfies the following conditions:

$i_{d1}^{*}=(K_{\mathrm{dP}}+\frac{K_{\mathrm{dI}}}{s})(P^{*}-P)$ (formula 17)

Wherein, K_dPAnd K_dIProportional coefficient and integral coefficient of d-axis PI controller respectively.

A voltage controller for outputting the given value of the reactive current by PI regulationAnd adjusting the output reactive power of the converter so as to adjust the fluctuation of the voltage of the microgrid. The micro-grid voltage perturbation control link is realized by micro-grid voltage U_SAnd its reference valueGenerating a q-axis current reference valueTo control the microgrid voltage and prevent perturbation of the microgrid voltage, wherein,the requirements are satisfied:

$i_{q1}^{*}=(K_{\mathrm{qP}}+\frac{K_{\mathrm{qI}}}{s})(U_S^{*}-U_S)$ (formula 18)

Wherein, K_qPAnd K_qIRespectively, a proportionality coefficient and an integral coefficient of the q-axis PI controller.

That is, the PI regulator provided in the power controller can input the active power output by the converter to the microgrid according to a power set value to be compensated, and maintain the active power balance in the microgrid, and the PI regulator provided in the voltage controller can input the reactive power output by the converter to the microgrid according to a voltage perturbation set value to be compensated, and maintain the voltage stability in the microgrid.

In this example, when the voltage in the microgrid fluctuates frequently, the microgrid voltage is detected by the voltage transformer, and the voltage effective value and the amplitude value are calculated to form the control of the microgrid voltage fluctuation. The output current of the converter is detected through a current transformer, then the ABC/dq coordinate transformation is utilized to convert the three-phase current into a direct current variable synchronously rotating at the fundamental wave frequency of a microgrid, the direct current variable is compared with active and reactive reference currents obtained by an outer ring voltage/power controller, the reference value of the reactive current is output to the maximum extent through the optimization of an adaptive amplitude limiter, meanwhile, the corresponding current reference value of the active power is obtained, then, two-phase voltage is obtained through the control of the inner ring current, the power electronic main circuit is controlled to output the corresponding alternating current voltage through a PWM generator, and the voltage on the direct current side of the power electronic main circuit is the voltage output by a large-scale energy storage device. The reactive compensation amount of the micro-grid is regulated and controlled through energy conversion in the large-scale energy storage device, and the effect of stabilizing the voltage of the micro-grid is further achieved.

The operation and effect of the microgrid voltage perturbation control system are described below with a simulation example of microgrid voltage perturbation control, fig. 7 is a general architecture diagram of the control system, fig. 8 is a microgrid structure diagram with a voltage perturbation device, and when a fan in fig. 8 is suddenly incorporated into a microgrid or a short circuit occurs in a load, the microgrid voltage fluctuation is caused. In this example, the simulated AC power source used a three-phase AC programmable power model with a line voltage of 0.4kV and a frequency of 50 Hz. During simulation, the voltage of the microgrid fluctuates: the rise at 0.2s is 1.06 times the nominal value, the fall at 0.3s is 0.94 times the nominal value, and the return to the nominal value at 0.4s is shown in figures 9 to 14, where the abscissa represents time in s and the ordinate represents the rise with respect to the nominal value.

Fig. 9 and 10 show phase voltage waveforms and phase current waveforms correspondingly output by the voltage perturbation device when the voltage of the power grid fluctuates, and as can be seen from fig. 10, the voltage perturbation device does not consume active power or reactive power under normal conditions, the current is substantially zero, when the voltage of the microgrid fluctuates, the voltage perturbation device can rapidly generate reactive current, the flow direction of the reactive current changes around 0.3s, and the current phase can be rapidly and smoothly transited, so that the impact is very small.

Fig. 11 and 12 show the power grid voltage amplitude waveforms before and after compensation, and it can be seen from fig. 12 that the variation amplitude of the voltage amplitude after compensation is greatly reduced compared with the variation amplitude of the voltage amplitude before compensation, and the rated voltage can be basically maintained unchanged after compensation. Fig. 13 and 14 are the active power and the reactive power of voltage perturbation device, and active power reduces active output at the reactive sudden change and under the effect of self-adaptation amplitude limiter, and then makes the reactive power maximize of output, and after the grid voltage takes place to fluctuate, voltage perturbation device reacts rapidly, produces corresponding reactive power to make little grid voltage fluctuation ability resume the rated value fast.

As shown in fig. 15, which is a working schematic diagram of a voltage perturbation system, the system uses a TMS320F28335 Digital Signal processor as a core control unit, and has an a/D sampling module, a main program module, a serial communication module, a PWM generation module, etc., when the system works, a sampling conditioning circuit converts three-phase voltage and current analog signals in a microgrid into Digital signals which can be accepted by a DSP (Digital Signal processing), and then sends the Digital signals to an I/O pin of the DSP, the DSP samples, filters and corrects the input signals to obtain values corresponding to the analog signals, and a system control program calculates corresponding control quantities according to the sampling results and control methods and outputs the corresponding control quantities. After receiving the output of the outer loop control and the output of the inner loop controller, the FPGA (Field-Programmable Gate Array) generates a PWM pulse signal, which further controls the output of the driving circuit, so that the main circuit outputs, controls the voltage fluctuation in the microgrid, and makes the voltage of the microgrid operate stably. Specifically, AD7656 can be adopted for A/D, TMS320F28335 can be adopted for DSP, IS61LV51216-12T can be adopted for RAM, XC6SLX45-3CSG324I can be adopted for FPGA, and SKYPER32 can be adopted for PWM.

In this example, the method for controlling the microgrid voltage perturbation based on the voltage perturbation system can be as shown in fig. 16, and comprises the following steps:

step 1601: detecting three-phase current output by the converter unit;

step 1602: converting the three-phase current into a direct current variable synchronously rotating at the fundamental wave frequency of the microgrid;

step 1603: acquiring an active current reference value output by a power controller and a reactive power reference value output by a voltage controller;

step 1604: comparing the direct current variable with the active current reference value and the reactive power reference value to obtain a comparison result;

step 1605: optimizing the comparison result through a self-adaptive amplitude limiter, and outputting active reference current and reactive reference current to the maximum extent;

step 1606: controlling the active reference current and the reactive reference current output to the maximum extent by the self-adaptive amplitude limiter through a current controller to obtain two-phase voltage control signals;

step 1607: and performing PWM modulation on the two-phase voltage control signal to obtain a PWM waveform, and inputting the PWM waveform into the converter unit.

In a specific implementation, in step 1605, the following clipping conditions may be used for optimization:

$\sqrt{i_{\mathrm{dlim}}^{*2}+i_{\mathrm{qlim}}^{*2}}=1.5i_e$

wherein,representing the active reference current clipping value,the reactive reference current amplitude limiting value is represented, the reactive reference current output by the self-adaptive amplitude limiter to the maximum extent is represented, and ie represents a rated value of alternating current on the side of the microgrid;

the active reference current and the reactive reference current which are output to the maximum extent are as follows:

$i_d^{*}=\left\{\begin{array}{cc}{i}_{d1}^{*},& i_{\mathrm{dlim}}^{*}<i_{d1}^{*}\&le;\sqrt{i_{\lim }^{*2}-i_{q1}^{*2}}\\ \sqrt{i_{\lim }^{*2}-i_{q1}^{*2}},& \sqrt{i_{\lim }^{*2}-i_{q1}^{*2}}<i_{d1}^{*}<i_{\lim }^{*}\\ i_{\lim }^{*},& i_{d1}^{*}\&GreaterEqual;i_{\lim }^{*}\\ i_{\mathrm{dlim}}^{*},& i_{d1}^{*}\&le;i_{\mathrm{dlim}}^{*}\end{array}\right.$

$i_q^{*}=\left\{\begin{array}{cc}{i}_{q1}^{*},& -i_{\lim }^{*}<i_{q1}^{*}<i_{\lim }^{*}\\ i_{\lim }^{*},& i_{q1}^{*}\&GreaterEqual;i_{\lim }^{*}\\ -i_{\lim }^{*},& i_{q1}^{*}\&le;-i_{\lim }^{*}\end{array}\right.$

wherein,represents the active current reference value output by the power controller,representing the reactive power reference value output by the voltage controller.

The dc variable synchronously rotating at the frequency of the fundamental wave of the microgrid in the step 1602 may include: the active current feedback, the reactive current feedback, and the active power, specifically, the current controller controls the active reference current and the reactive reference current output by the adaptive limiter to the maximum extent to obtain a two-phase voltage control signal, which may include:

the two-phase voltage control signal is obtained according to the following transfer function:

$\left\{\begin{array}{c}{v}_d=(K_P+\frac{K_I}{s})(i_d^{*}-i_d)-\mathrm{\&omega;}{\mathrm{Li}}_q+U_m\\ v_q=(K_P+\frac{K_I}{s})(i_q^{*}-i_q)+\mathrm{\&omega;}{\mathrm{Li}}_d\end{array}\right.$

wherein v is_dAnd v_qRepresenting a two-phase voltage control signal, K_PIndicating the proportionality coefficient, K, of the PI controller_IRepresenting the integral coefficient of the PI controller, i_dRepresenting active current feedback, i_qRepresenting reactive current feedback, L representing the inductance of the inductor, omega representing the angular frequency of the microgrid voltage, U_mRepresenting the magnitude of the microgrid phase voltage and s representing a complex variable.

In the above embodiment, considering that frequent voltage fluctuation (i.e., voltage perturbation) often occurs in the existing microgrid formed by wind power generation and solar power generation, so that the microgrid cannot operate independently and cannot be incorporated into a large power grid to operate, a large-scale energy storage device is added into the microgrid to form wind, photovoltaic and energy storage integration, and energy in the large-scale energy storage device is converted into reactive energy required in the microgrid in real time according to voltage fluctuation margin and frequency in the microgrid through the voltage perturbation device and a control method, so that voltage stability and safe and reliable operation of the microgrid are ensured. Furthermore, a self-adaptive amplitude limiter is embedded in the power electronic device to form a micro-grid voltage perturbation control device, the self-adaptive amplitude limiter can generate voltage fluctuation in the micro-grid, even voltage drop occurs during fault, under the support of a large-scale energy storage device, the amplitude limiting value of active reference current is dynamically adjusted according to reactive reference current output by a power outer loop controller, the output reactive reference current is maximized, and finally the stability of grid side voltage can be recovered more quickly, so that the voltage perturbation in the micro-grid is effectively controlled.

From the above description, it can be seen that the embodiments of the present invention achieve the following technical effects: the utility model provides a little electric wire netting voltage perturbation control system, when frequent fluctuation appears in little electric wire netting voltage, through voltage and the electric current in the detection little electric wire netting, applied voltage control perturbation device for energy conversion among the extensive energy storage unit stabilizes the reactive current among the little electric wire netting, makes transient state voltage can resume normal level, simultaneously through adding the self-adaptation amplitude limiter, makes little electric wire netting voltage can be when fluctuating on a large scale, stabilizes at normal level sooner, thereby has guaranteed the safe and reliable operation of little electric wire netting, the utility model provides a little electric wire netting frequent fluctuation of voltage and reactive power are difficult to optimize the technical problem of distribution among the prior art, reached the voltage fluctuation of effectively restraining little electric wire netting, guaranteed the technological effect of voltage steady operation.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not intended to limit the present invention, and it will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. A microgrid voltage perturbation control system, comprising: the device comprises an energy storage unit, a converter unit, a coordinate conversion and active power calculation unit, a power controller, a voltage controller, a self-adaptive amplitude limiter, a current controller and a PWM generator;

the energy storage unit is used for supplying power to the micro-grid;

the converter unit is connected with the output end of the energy storage unit and used for adjusting the output current of the energy storage unit to meet the reactive current requirement of the microgrid;

the input end of the coordinate transformation and active power calculation unit is connected with the output end of the converter unit, and is used for converting variables on an ABC coordinate system output by the converter unit into variables on a rotating coordinate system dq, wherein the output end of the coordinate transformation and active power calculation unit comprises: an active current feedback output terminal, a reactive current feedback output terminal and an active power output terminal;

the input end of the power controller is connected with the active power reference value and is connected with the active power output end of the coordinate transformation and active power calculation unit, and the output end of the power controller comprises: an active current reference value output end;

the input end of the voltage controller is connected with the microgrid voltage and the microgrid voltage reference value, and the output end of the voltage controller comprises: a reactive current reference value output end;

the input end of the self-adaptive amplitude limiter is connected with the active current reference value output end of the power controller and the reactive current reference value output end of the voltage controller, and the self-adaptive amplitude limiter is used for carrying out amplitude limiting on the active current reference value output by the power controller and the reactive current reference value output by the voltage controller and outputting active reference current and reactive reference current;

the input end of the current controller is connected with the output end of the adaptive amplitude limiter, and is connected with the active current feedback output end and the reactive current feedback output end of the coordinate transformation and active power calculation unit, so that the active current and the reactive current of the microgrid can be regulated, the active current and the reactive current can track the active reference current and the reactive reference current, and the output end of the current controller outputs a voltage control signal;

and the PWM generator is connected with the output end of the current controller and used for carrying out PWM modulation on the voltage control signal to generate a PWM waveform, and the PWM waveform is input into the converter unit.

2. The microgrid voltage perturbation control system of claim 1, wherein the adaptive limiter comprises: active current amplitude limiting circuit, idle current amplitude limiting circuit, first square processing circuit, second square processing circuit, accumulation circuit, square processing circuit, the minimum circuit of asking, wherein:

the input end of the active current amplitude limiting circuit is connected with the active current reference value output end of the power controller, and the output end of the active current amplitude limiting circuit is connected with the first input end of the minimum value calculating circuit;

the input end of the reactive current amplitude limiting circuit is connected with the reactive current reference value output end of the voltage controller, and the output end of the reactive current amplitude limiting circuit is the reactive reference current output end of the self-adaptive amplitude limiter;

the input of the first square processing circuit is a reference current amplitude limiting value output by the converter unit, and the output end of the first square processing circuit is connected with the positive value input end of the accumulation circuit;

the input end of the second square processing circuit is connected with the reactive current reference value output end of the voltage controller, and the output end of the second square processing circuit is connected with the negative value input end of the accumulation circuit;

the output end of the accumulation circuit is connected with the input end of the squaring processing circuit, and the output end of the squaring processing circuit is connected with the second output end of the minimum value calculating circuit;

and the output end of the minimum value calculating circuit is the active reference current output end of the self-adaptive amplitude limiter.

3. The microgrid voltage perturbation control system of claim 1 wherein the converter unit comprises:

the three-phase converter is used for converting the energy of the energy storage unit into energy required to be compensated during the perturbation of the voltage of the microgrid;

and the filtering reactance is connected with the three-phase converter and is used for filtering out higher harmonics generated when the direct current power in the energy storage unit is converted into the alternating current reactive power of the micro-grid.

4. The microgrid voltage perturbation control system of claim 3 wherein the three-phase inverter comprises: for converting the dc power into the ac power under the PWM control.

5. The microgrid voltage perturbation control system of claim 3, wherein:

the power controller is internally provided with a first PI regulator, and the first PI regulator is used for inputting a power set value required to be compensated by active power output by the three-phase converter into the microgrid;

and a second PI regulator is arranged in the voltage controller and used for inputting a voltage perturbation set value required by reactive power output by the three-phase converter and compensated into the microgrid.

6. The microgrid voltage perturbation control system of claim 1 wherein the PWM generator is further configured to interlock, electrically isolate and power amplify two drive signals on the same leg of the main circuit.