KR102186503B1 - The distributed energy resouce system connected to the power distribution network - Google Patents

Abstract

The present invention relates to a distributed power supply system linked to a distribution system, comprising: a distributed power supply generating power; A load receiving power from the distributed power supply or distribution system; And a grid-connecting device for linking or blocking the distributed power system to a distribution system, wherein the distributed power supply includes a power generation unit for generating DC power using new renewable energy; A power conversion device for converting the DC power into AC power; A harmonic phase shifting unit for outputting a phase shift of at least one harmonic component of the power conversion device; A switch for transferring or blocking AC power input through the harmonic phase shifting unit to the load and the grid connection device under control of a control unit; A first detection unit for detecting harmonics of the power conversion device; A second detection unit for detecting harmonics of the distribution system; A third detection unit detecting voltage, current, and frequency at the output terminal of the switch; And a control unit determining a phase of a harmonic component of the power conversion device that minimizes the harmonic component of the distribution system, and controlling the harmonic phase shifting unit based thereon, wherein the control unit is based on information provided from the third detection unit. Accordingly, when it is determined that it is separated from the distribution system, the switch is cut off, and the control unit monitors the impedance change amount for at least two harmonic components according to the information provided from the third detection unit, and the impedance change amount is If the reference value is exceeded during the reference time, it is determined to be separated from the distribution system. According to the present invention, it is possible to stably manage harmonics of a distribution system to which distributed power is connected, and to detect that the distributed power is separated from the distribution system, thereby reducing the risk of an accident.

Description

The distributed energy resouce system connected to the power distribution network}

The present invention relates to a distributed power system linked to a distribution system, and more specifically, to safeguard the harmonic level in a distribution system to which distributed power sources such as power generation facilities using renewable energy are connected, and the connection with the distribution system is blocked. It relates to a distributed power system linked to a distribution system that prevents the risk of accidents due to the operation of the distributed power supply.

Distributed power sources are generally connected to the distribution system through a grid connection device having a structure of a circuit breaker, and are connected together at all times. If an accident such as a ground fault or short circuit occurs on the distribution system side while operating in connection, the system connection device is opened to separate the distribution system from the distributed power supply, and accordingly, overcurrent generated in the distribution system does not flow, thereby protecting the distributed power supply.

In the case of operation in connection with the distribution system, power outages due to harmonics increase due to the recent rapid increase in nonlinear loads such as semiconductor application devices and the expansion of the supply of devices sensitive to electrical quality, whereas failures due to harmonics are difficult to determine the cause and systematic blackout statistics management. It became difficult. When harmonic current flows through the system, the voltage waveform of the system may be distorted, which causes a line power failure. Therefore, management of the harmonics of the distribution system is required to improve the supply reliability of the distribution system and provide high-quality power service.

On the other hand, when it is separated from the distribution system due to a power outage, etc., only the distributed power supply is connected to the load to supply power. In this case, it may be difficult to supply stable power because frequency and voltage fluctuate according to the power and load generated by the distributed power supply. In addition, if the system maintenance personnel are electrocuted or reconnected to the distribution system in the future, short circuits and damage to adjacent facilities may occur due to the phase difference between the voltages on both sides. Therefore, it is necessary to prevent the risk of an accident due to the operation of the distributed power source separated from the distribution system.

We propose a distributed power system connected to the distribution system.

A distributed power supply system connected to a distribution system, comprising: a distributed power supply generating power; And a grid-connecting device for linking or blocking the distributed power system to a distribution system, wherein the distributed power supply includes a power generation unit that generates DC power using new renewable energy; A power conversion device for converting the DC power into AC power; A harmonic phase shifting unit for outputting a phase shift of at least one harmonic component of the power conversion device; A switch for transferring or blocking AC power input through the harmonic phase shifting unit to the grid-connected device under control of a control unit; A first detection unit detecting harmonics of the power conversion device; A second detection unit for detecting harmonics of the distribution system; A third detection unit detecting voltage, current, and frequency at the output terminal of the switch; And a control unit determining a phase of a harmonic component of the power conversion device that minimizes the harmonic component of the distribution system, and controlling the harmonic phase shifting unit based thereon, wherein the control unit is based on information provided from the third detection unit. Accordingly, when it is determined that it is separated from the distribution system, the switch is cut off, and the control unit monitors the impedance change amount for at least two harmonic components according to the information provided from the third detection unit, and the impedance change amount is If the reference value is exceeded during the reference time, it is determined to be separated from the distribution system.

The harmonic phase shifting unit shifts the phase of the third harmonic component, and the control unit monitors an impedance change amount for the fifth and seventh harmonic components.

The control unit opens the switch when the harmonic distortion rate of the distribution system exceeds a reference value by more than a reference time.

The control unit opens the switch when the impedance change amounts for the fifth harmonic component and the seventh harmonic component exceed respective reference values for each reference time.

According to the present invention, it is possible to stably manage the harmonic level of a distribution system to which distributed power is connected.

In addition, when the level of harmonics exceeds the reference value due to the distributed power source, the level of harmonics of the distribution system can be stably managed by blocking the distributed power source from the distribution system.

In addition, when the connection with the distributed power source is blocked due to an accident in the distribution system, it can be detected by a simple method.

In addition, it is possible to eliminate the risk of accidents by preventing the operation of the distributed power source whose connection is blocked.

1 shows a distributed power system connected to a distribution system according to an embodiment of the present invention.

The terms used in the present specification are for describing exemplary embodiments and are not intended to suggest the present invention. In this specification, the singular form also includes the plural form unless specifically stated in the phrase. As used in the specification, “comprises” and/or “comprising” do not exclude the presence or addition of one or more other elements other than the mentioned elements. Throughout the specification, the same reference numerals refer to the same elements, and “and/or” includes each and all combinations of one or more of the mentioned elements. Although "first", "second", and the like are used to describe various elements, it goes without saying that these elements are not limited by these terms. These terms are only used to distinguish one component from another component. Therefore, it goes without saying that the first component mentioned below may be the second component within the technical idea of the present invention. In addition, terms such as "... unit" and "module" described in the specification mean units that process at least one function or operation, which may be implemented as hardware or software, or as a combination of hardware and software. .

Hereinafter, the present invention will be described in more detail with reference to the drawings. The embodiments introduced below are provided as examples in order to sufficiently convey the spirit of the present invention to those of ordinary skill in the art to which the present invention pertains.

1 shows a distributed power system connected to a distribution system according to an embodiment of the present invention.

Referring to FIG. 1, a distributed power supply system according to an embodiment of the present invention includes a distributed power supply 110, a grid connection device 120, and a distribution system 130.

The distributed power supply 110 is connected to the distribution system 130 through the grid connection device 120. The grid connection device 120 connects or blocks the distributed power supply 110 to the distribution system 130. When the distributed power supply 110 generates more than the power required by the load (not shown), excess power provided to the load and remaining power is provided to the distribution system 130 through the grid connection device 120. However, when the distributed power supply 110 fails to generate the power required by the load, the load receives power from the distribution system 130. On the other hand, when an accident such as a power failure occurs in the distribution system 130, the system connection device 120 separates the distributed power supply 110 from the distribution system 130 to prevent the spread of the accident.

In general, when the distributed power supply supplies power to the distribution system, harmonics are introduced into the distribution system due to the nonlinear characteristics of the distributed power supply, deteriorating the power quality. However, even if the distributed power supply 110 according to an embodiment of the present invention is operated in connection with the distribution system 130, it is possible to stabilize the harmonic level of the distribution system 130.

To this end, the distributed power supply 110 includes a power generation unit 1102, a power conversion device 1104, a harmonic phase shift unit 1106, a switch 1108, a first detection unit 1110, a second detection unit 1112, and a third It includes a detection unit 1114 and a control unit 1116.

The power generation unit 1102 generates DC power. The power generation unit 1102 may use new and renewable energy. In this case, the power generation unit 1102 may include a solar panel or a wind turbine. The power generation unit 1102 may non-linearly change a power-voltage curve and a current-voltage curve according to external environments such as solar radiation, temperature, and wind speed. To this end, the power generation unit 1102 may further include a DC-DC converter that supplies constant DC power to the inverter.

The power conversion device 1104 converts DC power generated by the power generation unit 1102 into AC power. Since the power conversion device 1104 needs to be connected to the wiring system 130, it generates AC power synchronized with the phase of the wiring system 130. The power conversion device 1104 may include an inverter. The inverter may be composed of a semiconductor switching device having nonlinear characteristics. In this case, the power conversion device 1104 generates harmonics due to nonlinear characteristics. As the semiconductor switching device, an Insulated Gated Bipolar Transistor (IGBT) may be used. The semiconductor switching device may be switched by a PWM (Pulse Width Modulation) control method. The output stage of the power conversion device 1104 contains a harmonic component generated by PWM switching. As a result, the waveform output from the power conversion device 1140 has a distorted sinusoidal shape. This distorted sine wave includes a fundamental wave, which is a sine wave of the fundamental frequency, and a harmonic wave, which is a sine wave of an integer multiple of the fundamental frequency. The ratio of the harmonic frequency to the fundamental frequency is the order of the harmonic. That is, the nth harmonic (n is a natural number greater than or equal to 2) means a sine wave having a frequency n times the fundamental wave.

The harmonic phase shifting unit 1106 shifts and outputs the phase of at least one harmonic component included in the AC current input from the power conversion device 1104 under the control of the control unit 1116. The harmonic phase shifting unit 1106 receives information on a phase shift object and a phase shift degree from the control unit 1116 and performs a phase shift on a corresponding harmonic component. The harmonic phase shifting unit 1106 may selectively shift a phase of a specific frequency component. To this end, the harmonic phase shifting unit 1106 may include at least one phase shifting unit (not shown). Each phase shifting unit may shift the phase of the harmonic component of the corresponding order by the indicated amount.

The harmonic phase shifting unit 1106 is a filter (not shown) that outputs a waveform by removing a specific harmonic component from the current waveform input from the power converter 1104, and a phase shifting that selects only a specific harmonic component and shifts the phase to output it. A unit (not shown) and a synthesizer (not shown) for synthesizing and outputting the output of the filter (not shown) and the output of the shifting unit (not shown) may be included. The filter (not shown) outputs a component that does not need a phase shift, and the shifting unit (not shown) shifts the phase of a harmonic component that needs a phase shift and outputs it. The synthesizer (not shown) synthesizes and outputs the output component without phase shift and the output component by shifting the phase.

The switch 1108 is opened when a failure of the distribution system 130 or the distributed power supply 110 occurs. Specifically, the switch 1108 is turned on and off under the control of the controller 1116 to provide or cut off AC power to the power line connected to the grid connection device 120. For example, when a problem occurs in the distribution system 130 and the system connection device 120 operates and is separated from the distribution system 130, the switch 1108 is turned off according to the instruction of the control unit 1116, and the system connection device ( Do not provide power to the power line connected to 120). Therefore, it is possible to prevent the system maintenance personnel from electric shock during work.

The first detection unit 1110 detects harmonics of the power conversion device 1104. Specifically, the first detection unit 1110 may detect a harmonic component of the order indicated by the control unit 1116 and provide it to the control unit 1116. For example, the first detection unit 1110 may detect the magnitude and phase of the third harmonic current commanded from the control unit 1116.

The second detection unit 1112 detects harmonics of the distribution system 130. Specifically, the second detection unit 1112 may detect a harmonic component of the order indicated by the control unit 1116 and provide it to the control unit 1116. For example, the second detection unit 1112 may detect the magnitude and phase of the third harmonic current commanded from the control unit 1116.

The control unit 1116 acquires the harmonic components detected by the first detection unit 1110 and the second detection unit 1112, and as a result of combining them, the power that can minimize the harmonic component of the distribution system 130 The amount of phase shift of the harmonics of the converter 1104 is determined. As the harmonic component of the power conversion device 1104 flows into the distribution system 130, it affects the harmonic component of the distribution system 130. Therefore, the power conversion device 1104 does not simply block the inflow of the harmonic component into the distribution system 130, but the inflow of the harmonic component of the power converter 1104 phase-shifted by actively using this Control so as to reduce the harmonic component of (130).

For example, when the third harmonic component of the power conversion device 1104 flows into the distribution system 130, the control unit 1116 minimizes the corresponding third harmonic component of the distribution system 130 Is determined, and the harmonic phase shifting unit 1106 is instructed to shift to the corresponding phase and output.

The control unit 1116 checks the harmonic distortion factor (THD) of the distribution system 130, and when the harmonic distortion factor exceeds the first reference value during the first reference time, the switch 1108 is opened to disperse the dispersion. The power supply 110 may be cut off from the distribution system 130. The harmonic distortion factor refers to the ratio of the sum of the effective values of all harmonic components up to a specific order to the effective value of the basic component. The harmonic distortion factor of the distribution system 130 may be managed by the power supplier. The customer using the distributed power supply 110 may be required to be a value lower than this value, and in this case, the value requested by the power supplier may be set as the first reference value. Even if the harmonic phase shifting unit 1106 performs the harmonic phase shifting operation under the control of the controller 1116, if the harmonic distortion factor exceeds the reference value for more than a reference time, the distribution of the distributed power supply 110 is cut off according to the selection. Harmonic safety of the system 130 is secured.

Conventionally, by disposing a passive or active filter at the output terminal of the inverter of the distributed power supply 110 to manage the harmonic level of the distribution system 130, the harmonics generated from the inverter are simply removed and provided to the distribution system 130. However, according to an embodiment of the present invention, instead of simply removing the harmonics generated from the inverter, the harmonics of the distribution system 130 are minimized by actively using them. Therefore, compared to the method of applying a conventional filter, it is more suitable for the ultimate purpose of power management of stabilizing the harmonics of the distribution system 130. In addition, by applying a simple method of selecting some of the harmonic components flowing into the distribution system 130 from the distributed power supply 110 and shifting only the phase, it can be implemented easily and at a lower cost.

Meanwhile, when the distributed power supply 110 according to an embodiment of the present invention is separated from the distribution system 130, it is possible to detect this and eliminate the risk of an accident caused by the independent operation of the distributed power supply 110. When an accident such as a power outage occurs on the distribution system 130 side and the system connection device 120 operates and is separated from the distribution system 130, whether the distributed power supply 110 is separated from the distribution system 130 by itself It is provided with a means to confirm. To this end, the distributed power supply 110 includes a third detection unit 1114.

The third detection unit 1114 detects voltage, current, and frequency at the output terminal of the switch 1108 and provides the detection to the control unit 1116.

The control unit 1116 checks whether to separate from the distribution system 130 through the information provided from the third detection unit 1114. The controller 1116 may monitor the voltage, current, and frequency provided from the third detection unit 1114 and detect sudden changes thereof. The distributed power supply 110 may drive a load located between the switch 1108 and the grid connection device 120. In this case, when the power system 130 is separated from the power system 130, when the equilibrium state between the power generation output and the load collapses, a change in voltage or frequency occurs. Accordingly, when the voltage or frequency change amount exceeds the second reference value during the second reference time, it may be determined to be separated from the power system 130.

When the distribution system 130 is separated, the system circuit constant, the distribution state of harmonics, the way the harmonics flow, and the like are changed. When the power system 130 is separated from the power system 130, when the balance between the power generation output and the load collapses, the voltage or frequency fluctuates, but if the power generation output and the load are in a balanced state, the voltage or frequency fluctuation is small and thus it is difficult to detect. However, even if the power generation output and the load are in equilibrium, the harmonics are variable and therefore detectable. Accordingly, the controller 1116 may monitor impedance values for at least two harmonic components at the output terminal of the switch 1108. When the connection with the distribution system 130 is disconnected, the impedance value for the harmonic component is greatly increased. In order to prevent malfunction due to noise, the controller 1116 monitors the impedance change for at least two harmonic components based on the detected voltage and current values, and the amount of impedance change for each harmonic component exceeds the reference value for a predetermined reference time, respectively. If so, it is determined that it is separated from the power system 130. At least two harmonic components have a size to some extent, but it is appropriate to select a harmonic component of a relatively high frequency that is liable to fluctuate due to instantaneous separation. For example, it is possible to check whether the separation from the power system is performed by monitoring the amount of change in impedance for the fifth harmonic component and the seventh harmonic component.

As a result, the distributed power supply 110 according to an embodiment of the present invention can check whether the power system 130 is separated from the power system 130 not only when the power generation output and the load are in an unbalanced state, but also when a balanced state is achieved. In addition, since a separate signal is not injected into the power system 130, there is no effect on the power system 130, and power quality can be maintained.

When disconnection from the power system 130 is sensed, the control unit 1116 may open the switch 1108 to block power supply to the power line connected to the system linkage device 120.

The steps of a method or algorithm described in connection with an embodiment of the present invention may be implemented directly in hardware, implemented as a software module executed by hardware, or a combination thereof. Software modules include Random Access Memory (RAM), Read Only Memory (ROM), Erasable Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), Flash Memory, hard disk, removable disk, CD-ROM, or It may reside on any type of computer-readable recording medium well known in the art to which the present invention pertains.

In the above, embodiments of the present invention have been described with reference to the accompanying drawings, but those of ordinary skill in the art to which the present invention pertains can be implemented in other specific forms without changing the technical spirit or essential features. You can understand. Therefore, the embodiments described above are illustrative in all respects, and should be understood as non-limiting.

110: distributed power supply 120: grid-connected device
130: distribution system 1102: power generation department
1104: power converter 1106: harmonic phase shift unit
1108: switch 1110: first detection unit
1112: second detection unit 1114: third detection unit
1116: control unit

Claims (4)

In the distributed power system connected to the distribution system,
Distributed power generating power; And a grid-connecting device for linking or blocking the distributed power supply to a distribution system, and
The distributed power supply is
A power generation unit that generates DC power using renewable energy;
A power conversion device for converting the DC power into AC power;
A harmonic phase shifting unit for outputting a phase shift of at least one harmonic component of the power conversion device;
A switch for transferring or blocking AC power input through the harmonic phase shifting unit to the grid-connected device under control of a control unit;
A first detection unit for detecting harmonics of the power conversion device;
A second detection unit for detecting harmonics of the distribution system;
A third detection unit detecting voltage, current, and frequency at the output terminal of the switch; And
Including; a control unit for determining the phase of the harmonic component of the power conversion device that minimizes the harmonic component of the distribution system and controlling the harmonic phase shifting unit based thereon,
When it is determined that the distributed power supply is separated from the distribution system according to the information provided from the third detection unit, the control unit cuts off the switch,
The control unit monitors the impedance change amount for at least two harmonic components according to the information provided from the third detection unit, and determines that the impedance change amount is separated from the distribution system when both of the impedance changes exceed a reference value for each reference time. and,
The control unit opens the switch when the harmonic distortion rate of the distribution system exceeds a reference value for a reference time or more. The method of claim 1,
The harmonic phase shifting unit shifts the phase of the third harmonic component,
The control unit is a distributed power supply system that monitors the amount of change in impedance for the fifth harmonic component and the seventh harmonic component. delete The method of claim 2, wherein the control unit
Distributed power supply system for opening the switch when the impedance change amount for the fifth harmonic component and the seventh harmonic component exceeds each reference value for each reference time.

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