TWI673931B - Micro-grid, energy storage system and voltage compensation method - Google Patents

Abstract

A voltage compensation method is used to compensate the normalized voltage of a microgrid. The steps are described below. First, the normalized voltage of the microgrid is monitored. Next, it is determined whether the normalized voltage of the microgrid exceeds a specific range. Then, when the normalized voltage of the microgrid exceeds the specific range, a compensated virtual work is provided to the microgrid through a converter according to the normalized voltage of the microgrid. In this way, the voltage compensation method can improve the system stability and security of the microgrid.

Description

Microgrid, energy storage system and voltage compensation method

The invention relates to a micro-grid technology, and in particular to a micro-grid, an energy storage system and a voltage compensation method for compensating the normalized voltage of the micro-grid by using the virtual work of the energy storage system.

In order to reduce the greenhouse effect caused by the consumption of fossil fuels, countries around the world are actively developing renewable energy sources. For example, solar energy systems and wind turbine systems are common renewable energy applications. However, whether it is a solar system or a wind turbine system, there is a problem that the output energy is not stable. Simply put, the increase of a large amount of renewable energy will cause voltage changes at the distribution end. Therefore, in power supply and microgrid applications, it is necessary to match energy storage systems for effective power management and regulation.

Generally speaking, a micro-grid is a combination of city power, energy storage systems, decentralized power sources (ie, renewable energy), and loads. Under normal circumstances, the power used by the load is provided by the city power and decentralized energy, and the energy storage system acts as a buffer to stabilize the supply and demand of electricity. When the voltage of the microgrid is abnormal (for example, the load has an abnormally large amount of power consumption), in the case of no matching voltage compensation strategy, the distributed power will be merged with the microgrid to ensure the safety of system equipment.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of the specification of decentralized power supply decomposing in the IEEE 1547A standard specification. In Figure 1, the horizontal axis represents the normalized voltage of the microgrid (in units of The voltage of the grid is divided by the rated voltage of the mains), and the vertical axis represents the frequency of the power signal of the microgrid (in Hz). In FIG. 1, according to the normalized voltage and frequency of the power signal of the microgrid, several regions R1, R2, and R3 can be defined. When the state of the microgrid falls in the region R1, there is no need to disconnect the distributed power from the microgrid. When the state of the microgrid falls in the region R2, the distributed power needs to be merged from the microgrid within 2 seconds. In addition, when the state of the microgrid falls in the region R3, it is necessary to disperse the distributed power from the microgrid within 1 second.

In the prior art, methods for voltage compensation of a micro-grid include manual control of a transformer, tap changer of a transformer, capacitor parallel and static synchronous compensation (STATCOM), and other methods. However, the above voltage compensation method has disadvantages such as insufficient voltage compensation accuracy, only one-way compensation, and time consumption.

Based on at least one embodiment of the present invention, the present invention provides a microgrid, an energy storage system, and a voltage compensation method, which can automatically and bidirectionally compensate the normalized voltage of the microgrid, and can have higher voltage compensation accuracy.

Based on at least one embodiment of the present invention, the present invention provides a microgrid, energy storage system, and voltage compensation method, which can reduce the probability of decoupling of distributed power sources, and can increase the system stability and security of the microgrid.

An embodiment of the present invention provides a voltage compensation method for compensating a normalized voltage of a microgrid. The steps are described below. First, the normalized voltage of the microgrid is monitored. Next, it is determined whether the normalized voltage of the microgrid exceeds a specific range. Then, in the positive of the microgrid When the regulated voltage exceeds the specific range, a compensated virtual work is provided to the microgrid through a converter according to the normalized voltage of the microgrid.

An embodiment of the present invention provides an energy storage system. The energy storage system includes a voltage measurement unit, a control unit, and a converter. The voltage measurement unit is used to measure the voltage of the micro-grid. The control unit is electrically connected to the voltage measurement unit, and is configured to calculate the normalized voltage of the microgrid according to the measured voltage of the microgrid, and determine the microgrid. Whether the normalized voltage exceeds a certain range. The converter is electrically connected to the control unit, and when the normalized voltage of the microgrid exceeds the specific range, the control unit controls the microgrid according to the normalized voltage of the microgrid The converter provides compensated virtual work to the microgrid.

An embodiment of the present invention provides a microgrid. The microgrid includes an energy storage system, a distributed power source, and a load. The energy storage system is connected in parallel to the city power, the distributed power source is connected in parallel to the energy storage system, and the load is connected in parallel to the distributed power source, wherein the energy storage system is used to execute the voltage compensation method.

Optionally, the converter is designed to only use a specific percentage of rated power as the virtual work for compensation.

Optionally, the specific ratio is 50%.

Optionally, when the normalized voltage of the microgrid exceeds the specific range, and the normalized voltage of the microgrid is not less than or equal to 0.9pu or greater than or equal to 1.1pu, the The virtual work system has a linear relationship with the normalized voltage of the microgrid. When the normalized voltage of the microgrid is less than or equal to 0.9 pu or greater than or equal to 1.1 pu, the virtual work used as compensation is the rated power of the specific ratio.

Optionally, the specific range is 0.95pu to 1.05pu

Optionally, the distributed power source is a power source of renewable energy.

In summary, the embodiments of the present invention provide a microgrid, an energy storage system, and a voltage compensation method, which have high voltage compensation accuracy, a bidirectional compensation function, and an automatic compensation function. In addition, the microgrid, energy storage system, and voltage compensation method can also increase the system stability and security of the microgrid.

In order to further understand the features and technical contents of the present invention, please refer to the following detailed description and accompanying drawings of the present invention, but these descriptions and attached drawings are only used to illustrate the present invention, not the right to the present invention. No limitation on scope.

1‧‧‧ mains

2‧‧‧ Microgrid

21‧‧‧ Energy Storage System

22‧‧‧ Distributed Power

23‧‧‧Load

3‧‧‧Voltage measurement unit

4‧‧‧Control unit

5‧‧‧ converter

501‧‧‧Power Switching Element

502‧‧‧RLC filter circuit

503‧‧‧Feedback Current Gain

504‧‧‧Feedback Voltage Gain

505‧‧‧Phase Locked Loop

506‧‧‧Parker Converter

507‧‧‧Parker Inverter

508‧‧‧Sine wave pulse width modulator

509, 510‧‧‧ proportional integral controller

511, 512‧‧‧ Subtractors

513‧‧‧ Adder

514‧‧‧Current Sensing Module

Id_cmd, Iq_cmd‧‧‧Current control signal

R1 ~ R3‧‧‧ area

S11 ~ S13‧‧‧‧steps

Vdc‧‧‧DC voltage

Vcontrol‧‧‧Control reference voltage

In order to more clearly explain the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the present invention. For those of ordinary skill in the art, other embodiments may be obtained based on these drawings without paying creative labor.

Figure 1 is a schematic diagram of the decentralized power supply decompression specification in the IEEE 1547A standard specification.

FIG. 2 is a block diagram of a microgrid according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of a voltage compensation curve according to an embodiment of the present invention.

FIG. 4A is a block diagram of an energy storage system according to an embodiment of the present invention.

FIG. 4B is a block diagram of a converter according to an embodiment of the present invention.

FIG. 5 is a flowchart of a voltage compensation method according to an embodiment of the present invention.

FIG. 6A is a schematic diagram of a normalized voltage curve of a microgrid without voltage compensation.

FIG. 6B is a schematic diagram of a normalized voltage curve and a compensated virtual work current curve of a micro-grid using the voltage compensation method of the embodiment of the present invention for voltage compensation.

Embodiments of the present invention provide a microgrid, an energy storage system, and a voltage compensation method capable of using the virtual work of a converter of an energy storage system to compensate for the voltage of a microgrid. The microgrid includes an energy storage system, and the energy storage system includes Converter, and the energy storage system is used to perform the voltage compensation method. The energy storage system monitors the normalized voltage of the microgrid, and when the normalized voltage exceeds a specific range (for example, a specific range from 0.95pu to 1.05pu), the converter in the energy storage system will provide virtual work to Micro-grid to compensate for the normalized voltage of the micro-grid (or nodes of decentralized power).

According to this, the decentralized power supply in the microgrid can be continuously operated without being disconnected from the microgrid. In addition, when the failure of the microgrid causes the normalized voltage to deviate too much from the standard value, or the failure of the microgrid lasts too long, the distributed power will still be merged with the microgrid. At this time, even if the virtual work is used for compensation, the normalized voltage of the microgrid cannot be stabilized. Therefore, it is a better method to dissolve the distributed power source and the microgrid.

Optionally, the aforementioned specific range can be adjusted according to the actual situation, and the converter can be designed to only take out a part of the rated power for virtual work (for example, can only take up to 50% of the rated power for virtual work) To ensure that the converter still has a margin for outputting real power.

First, please refer to FIG. 2, which is a schematic block diagram of a microgrid according to an embodiment of the present invention. The microgrid 2 includes an energy storage system 21, a distributed power source 22, and a load 23, of which the city power 1, the energy storage system 21, the distributed power source 22, and the load 23 are connected in parallel with each other. The power signal used by the microgrid 2 is AC, without loss of generality In the case of three-phase AC, the rated voltage may be 110 volts or 220 volts, and the standard frequency of the power signal is 60 Hz. However, the above is merely an example, and the present invention is not limited thereto.

The commercial power 1 is used to provide power to the load 23 in the microgrid 2 and to store electrical energy in the energy storage system 21 during charging of the energy storage system 21. Without loss of generality, the power signal of the mains is 110 volts or 220 volts 60Hz three-phase alternating current, but the present invention is not limited thereto. The energy storage system 21 acts as a buffer for energy to stabilize the supply and demand of electricity, and can store and release electrical energy during charging and discharging, respectively. The distributed power source 22 is used to provide power to the load 23, and the power generated by the distributed power source 22 is not as stable as the city power 1. The distributed power source 22 may be a source of renewable energy, such as a solar system or a wind turbine system. The invention is not limited to this. The load 23 may be various devices that require power consumption, such as electrical appliances, computers, lamps, or display devices, and the present invention is not limited thereto.

In this embodiment, the energy storage system 21 can also monitor the normalized voltage of the microgrid 2. When the microgrid 2 fails or is abnormal, causing the normalized voltage to drop or rise, the energy storage system 21 can decide whether to reduce the virtual power of its converter based on whether the microgrid 2's normalized voltage falls outside a specific range. Provided to the microgrid 2 to compensate for the normalized voltage of the microgrid 2 (or the node of the decentralized power supply). The converter of the energy storage system 21 determines how much virtual work to output to the microgrid according to the normalized voltage of the microgrid 2. Grid 2. In this way, when the normalized voltage of the microgrid 2 does not deviate too much from the standard value (that is, 1pu) or when the time of abnormal microgrid failure is not long, the distributed power source 22 does not merge from the microgrid 2.

For example, the specific range may be 0.95pu to 1.05pu. When the normalized voltage of the microgrid 2 is 1.02pu, the energy storage system 21 does not use the virtual work of the converter to compensate. However, when the normalized voltage of microgrid 2 is equal to or greater than 1.05pu, the energy storage system 21 compensates by generating negative virtual work through the converter, and when the normalized voltage of microgrid 2 is less than or equal to 0.95pu, The energy storage system 21 compensates by generating positive virtual work through the converter.

In addition, in order to ensure the margin of the converter, the converter can only take out 50% of the rated power for virtual work at most, and a linear relationship exists between the virtual work to be compensated and the normalized voltage of the microgrid 2. For example, when the normalized voltage of microgrid 2 is equal to 0.95pu, the converter provides 10% positive virtual work to compensate the normalized voltage of microgrid 2 and when the normalized voltage of microgrid 2 is equal to or less than 0.9pu The converter provides 50% of positive and virtual work to compensate for the normalized voltage of microgrid 2. Similarly, when the normalized voltage of microgrid 2 is equal to 1.05pu, the converter provides 10% negative virtual work to compensate the normalized voltage of microgrid 2 and when the normalized voltage of microgrid 2 is equal to or greater than 1.1pu At this time, the converter provides 50% of negative virtual work to compensate the normalized voltage of microgrid 2.

Furthermore, as described above, when the normalized voltage of the microgrid 2 deviates too much from the standard value or when the abnormal time of the microgrid 2 is abnormal for a long time, the distributed power source 21 will be merged from the microgrid 2. For example, the normalized voltage of microgrid 2 is 1.5pu. Although the converter tries to provide 50% negative virtual work to compensate the normalized voltage of microgrid 2, it is still not easy to pull the normalized voltage of microgrid 2 to around 1pu. Therefore, at this time, the distributed power source 21 must be disconnected from the microgrid 2.

Next, please refer to FIG. 3, which is a schematic diagram of a voltage compensation curve according to an embodiment of the present invention. When the normalized voltage of the microgrid 2 is between A2pu and A1pu, there is no need to compensate the normalized voltage of the microgrid 2. When the normalized voltage of microgrid 2 is equal to A1pu, the converter outputs a negative virtual work of D2 kVar, and when the normalized voltage of microgrid 2 is greater than or equal to 1.1pu, the converter outputs D4 kVar (kVar) negative virtual work. When the normalized voltage of microgrid 2 is between A1pu and 1.1pu, the negative virtual work to be output by the converter can be calculated according to a linear relationship. Similarly, when the normalized voltage of microgrid 2 is equal to A2pu, the converter outputs D1 kVar of positive and virtual work, and when the normalized voltage of microgrid 2 is greater than or equal to 0.9pu, the converter outputs D3 kVar of positive and virtual work. When the normalized voltage of microgrid 2 is between A2pu and 0.9pu, the positive and virtual work to be output by the converter can be calculated according to a linear relationship.

Please note here that although the voltage compensation curve of FIG. 3 shows a linear relationship between the virtual work to be compensated and the normalized voltage of the microgrid 2, the present invention is not limited by the voltage compensation curve of FIG. 3. In other words, in other embodiments, a non-linear relationship may also be present between the virtual work to be compensated and the normalized voltage of the microgrid 2. In addition, in general, it can be designed that A1 is equal to A2, D1 is equal to D2, and D3 is equal to D4. However, the present invention may not be limited thereto. For example, A1 may not be equal to A2, D1 may not be equal to D2, and D3 may not be equal to D4.

Next, one of the implementations of the energy storage system 21 is further explained, and the implementations described below are not intended to limit the present invention. Please refer to FIG. 2 and FIG. 4A at the same time. FIG. 4A is a block diagram of an energy storage system according to an embodiment of the present invention. The energy storage system 21 includes a voltage measurement unit 3, a control unit 4 and a converter 5, wherein the voltage measurement unit 3 is electrically connected (parallel) to the microgrid 2 and the control unit 4 is electrically connected to the voltage measurement The unit 3 and the converter 5 are electrically connected to the control unit 4.

The voltage measurement unit 3 is used to measure the voltage of the microgrid 2. The control unit 4 receives the voltage measured by the voltage measurement unit 3 and calculates the normalized voltage of the micro-grid 2. Next, the control unit 4 determines a current control signal based on the normalized voltage of the microgrid 2. The converter 5 receives the current control signal to generate a compensated virtual work current to output the corresponding virtual work to compensate the normalized voltage of the micro-grid 2 so as to reduce the probability of decentralization of the distributed power source 22.

Next, one implementation manner of the converter 5 is further described, and the implementation manners described below are not intended to limit the present invention. Please refer to FIG. 4B, which is a block diagram of a converter according to an embodiment of the present invention. The converter 5 includes an energy storage element (for outputting a DC voltage Vdc), a power switching element 501, an RLC filter circuit 502, a feedback current gain 503, a feedback voltage gain 504, a phase-locked loop 505, and a Parker converter 506. Parker inverse converter 507, sine wave pulse width modulator 508, proportional-integral controller (PI controller for short) 509, 510, subtractor 511, 512, adder 513, and current sensing module Group 514.

The power switching element 501 is electrically connected to the feedback current gain device 503 through the current sensing module 514, and is directly electrically connected to the RLC filter circuit 502. The feedback voltage gain device 504 is electrically connected to the RLC filter circuit 502 and the phase-locked loop 505. And the RLC filter circuit 502 is electrically connected (parallel) to the microgrid. The phase-locked loop 505 is electrically connected to the Parker converter 506 and the Parker inverse converter 507, and the Parker converter 506 is electrically connected to the feedback current gain device 503 and the subtractors 511 and 512. The subtractors 511 and 512 are electrically connected to the proportional integral controllers 509 and 510, respectively. The proportional and integral controllers 509 and 510 are electrically connected to the adder 513 and the Parker inverse converter 507, and the adder 513 is also electrically connected to the Parker inverse converter. 507. The sine wave pulse width modulator 508 is electrically connected to the Parker inverse converter 507 and the power switching element 501.

The power switching element 501 receives the DC voltage Vdc output from the energy storage element and a plurality of pulse width modulation signals output from the sine wave pulse width modulator 508, and generates a three-phase current according to the plurality of pulse width modulation signals. The current passes through three current sensors in the current sensing module 514 and can sense a three-phase current signal. The feedback current gain amplifier 503 amplifies the three-phase current signal and outputs it to the Parker converter 506. The RLC filter circuit 502 receives the three-phase current and performs filtering, and outputs the three-phase current for the virtual power compensation to the micro-grid. The feedback voltage gain unit 504 captures the single-phase voltage of the micro-grid and outputs a single-phase signal to the phase-locked loop 505. The phase-locked loop 505 obtains the reference phase θ according to the single-phase voltage signal, and outputs the reference phase θ to the Parker inverse converter 507 and the Parker converter 506.

The Parker converter 506 converts the amplified three-phase current signal into a straight axis and a quadrature axis (DQ) signal according to the reference phase θ. The subtractor 511 subtracts the quadrature axis signal from the Parker converter 506 from the current control signal Iq_cmd from the control unit, and the subtractor 512 subtracts the current control signal Id_cmd from the control unit from the Parker converter 506. Straight axis signal. The proportional-integral controllers 509 and 510 are used to perform proportional-integral operations on the outputs of the subtractors 512 and 511, respectively. The adder 513 is used to add the output of the proportional-integral controller 509 to the control reference voltage Vcontrol. Then, the Parker inverter 507 is connected Receives two control signals (which can form quadrature and straight axis signals) output by the adder 513 and the proportional-integral controller 510, and converts this DQ signal into a three-phase control signal according to the reference phase θ.

The sine wave pulse width modulator 508 receives the three-phase control signal output by the Parker inverse converter 507, and generates a plurality of pulse width modulation signals to the power switching element 501 according to the three-phase control signal, so that the power switching element 501 can generate The corresponding three-phase current is supplied to the RLC filter circuit 502. In FIG. 4B, the power switching element 501 has a total of six power switches and six three-phase control signals to control the six power switches to generate corresponding three-phase currents to the RLC filter circuit 502. In this way, through the control unit to generate the corresponding current control signals Id_cmd, Iq_cmd, the converter 5 can generate corresponding virtual work to compensate the microgrid. Please note here that the current control signals Id_cmd and Iq_cmd are determined based on the voltage compensation curve and the normalized voltage of the microgrid. According to the voltage compensation curve of Figure 3 in this case, the normalized voltage in the microgrid exceeds a certain range, When 1.1pu is less than or equal to 0.9pu and 0.9pu is greater than or equal to the current, the current control signals Id_cmd and Iq_cmd have a linear relationship with the normalized voltage of the microgrid.

Next, please refer to FIG. 5, which is a flowchart of a voltage compensation method according to an embodiment of the present invention. The voltage compensation method may be executed by a converter in the energy storage system 21 of FIG. 2. In step S11, the voltage of the microgrid is measured through the voltage measurement unit of the energy storage system, and the normalized voltage of the microgrid is calculated through the control unit of the energy storage system, so as to monitor the normalized voltage of the microgrid. In step S12, the control unit of the energy storage system determines whether the normalized voltage of the microgrid exceeds a specific range, such as a range of 0.95pu to 1.05pu. If the normalized voltage of the microgrid exceeds a specific range, step S13 is performed, and if the normalized voltage of the microgrid does not exceed a specific range, step S11 is continuously performed. In step S13, the control unit of the energy storage system generates a current control signal to the converter of the energy storage system according to the normalized voltage of the microgrid, and the converter of the energy storage system accordingly generates a corresponding compensated virtual work current to the micro-grid. The grid, so that the converter can provide virtual work to the microgrid to compensate for the normalized voltage according to the normalized voltage.

Next, the efficiency that can be achieved by the voltage compensation method of one embodiment of the present invention is further described. Please refer to FIG. 6A and FIG. 6B. FIG. 6A is a schematic diagram of a normalized voltage curve of a microgrid without voltage compensation, and FIG. 6B is a normalized voltage curve of a microgrid using a voltage compensation method according to an embodiment of the present invention. Schematic diagram of the curve with compensated virtual work current. As shown in FIG. 6A, when an abnormality occurs in the microgrid, the normalized voltage of the microgrid may run to 1.1pu or 0.88pu, and the distributed power will be merged from the microgrid. In Figure 6B, when the microgrid is abnormal, since the converter will provide compensated virtual work current to the microgrid, the normalized voltage of the microgrid can be less than 1.1pu or greater than 0.88pu without decentralizing the distributed power supply. Power Grid Merger.

In summary, the microgrid, energy storage system, and voltage compensation method provided by the embodiments of the present invention can use the virtual work of the energy storage system to compensate for the normalized voltage of the microgrid to reduce the dispersal of the energy elements from the microgrid. Probability, it can increase the system stability and security of the microgrid. Furthermore, since the microgrid, energy storage system, and voltage compensation method provided in the embodiments of the present invention, when the normalized voltage of the microgrid exceeds a specific range, the number of virtual work compensation micro The normalized voltage of the power grid, therefore, the microgrid, energy storage system, and voltage compensation method provided by the embodiments of the present invention have high voltage compensation accuracy, two-way compensation function, and automatic compensation function.

The above description is only an embodiment of the present invention, and is not intended to limit the patent scope of the present invention.

Claims (8)

A voltage compensation method for compensating a normalized voltage of a micro-grid, the micro-grid including an energy storage system, a distributed power source, and a load connected in parallel with a city power source and in parallel with each other, the voltage compensation method includes: monitoring all locations of the micro-grid The normalized voltage; determining whether the normalized voltage of the microgrid exceeds a specific range; and when the normalized voltage of the microgrid exceeds the specific range, through a converter of the energy storage system Providing compensated virtual work to the microgrid according to the normalized voltage of the microgrid; wherein the normalized voltage in the microgrid exceeds the specific range, and the normalization of the microgrid When the voltage is not less than or equal to 0.9 pu or greater than or equal to 1.1 pu, the virtual work system used for compensation has a linear relationship with the normalized voltage of the microgrid; when the normalized voltage of the microgrid is less than or equal to When 0.9 pu or 1.1 pu or more, the virtual power used for compensation is the rated power of the specific ratio. The voltage compensation method according to item 1 of the claim, wherein the converter is designed to take at most a specific percentage of rated power as the virtual work for compensation. The voltage compensation method according to item 2 of the claim, wherein the specific ratio is 50%. The voltage compensation method according to claim 1, wherein the specific range is 0.95pu to 1.05pu. An energy storage system includes: a voltage measurement unit for measuring the voltage of a micro-grid; A control unit, electrically connected to the voltage measurement unit, for calculating the normalized voltage of the microgrid based on the measured voltage of the microgrid, and judging the normalization of the microgrid Whether the voltage exceeds a specific range; a converter is electrically connected to the control unit, wherein when the normalized voltage of the microgrid exceeds the specific range, the control unit is based on the normal of the microgrid The variable voltage controls the converter to provide compensated virtual work to the microgrid; wherein the energy storage system, city power is in parallel with the decentralized power source and load of the microgrid; wherein, in the microgrid, the When the normalized voltage exceeds the specific range, and the normalized voltage of the microgrid is not less than or equal to 0.9pu or 1.1pu or more, the virtual work system for compensation and the regularity of the microgrid The normalized voltage has a linear relationship; when the normalized voltage of the microgrid is less than or equal to 0.9pu or greater than or equal to 1.1pu, the virtual work used as compensation is the rated power of the specific ratio. The energy storage system according to item 5 of the claim, wherein the converter is designed to take at most a specific percentage of rated power as the virtual work for compensation. A micro-grid includes: an energy storage system connected in parallel to a city power supply; a decentralized power supply connected in parallel to the energy storage system; and a load connected in parallel to the decentralized power supply; wherein the energy storage system is used to execute the first to The voltage compensation method described in one of 4 items. The microgrid according to item 7 of the claim, wherein the distributed power source is a power source for renewable energy.