KR20070025269A - Islanding detection device using automatic phase-shift method - Google Patents

Abstract

An islanding detection device using an automatic phase-shift method is provided to detect the islanding by converging or diverging the frequency of the voltage at a point of the common coupling. An islanding detection device using an automatic phase-shift method includes a PWM(Pulse Width Modulation) unit, a voltage controller(36), a current controller(34), a sine wavel unit(38), and a PLL(Phase Locked Loop)(60). The PWM unit varies a pulse width according to a magnitude of a sine wave, and delivers the pulse width to an inverter. The voltage controller controls an input terminal voltage of an inverter of a power distribution system at a constant value. The current controller controls an output terminal current of the inverter of the power distribution system at a constant value. The sine wave unit generates a sine wave, which is in-phase with an output current reference value of the power distribution system. The PLL detects the inverter output current and controls the inverter output current to be in-phase with a coupling voltage.

Description

Isolation operation detection device using automatic phase shift method

1 is a view showing the power flow of the grid-tied photovoltaic power generation system (distributed power supply) according to the present invention.

Figure 2 is a block diagram of a grid-tied photovoltaic power generation system (distributed power supply) implemented for the experiment according to the present invention.

3 is an algorithm configuration diagram of an isolated driving detection apparatus using an automatic phase shifting method according to an exemplary embodiment of the present invention.

4 is a simulation result showing the frequency and inverter output current command conversion of the connection point (PCC) by the automatic phase shift method in the isolated operation according to the present invention.

5 is a view showing the characteristics of the automatic phase shift method in the system frequency change and isolated operation according to the present invention.

6 is an experimental result showing that the isolated operation by the automatic phase shift method according to the present invention is detected.

7 is a result of comparing the output current when the system frequency is 60.5Hz in normal operation by the conventional Sandia frequency fluctuation method and the automatic phase shift method according to the present invention.

8 is a view showing the frequency and inverter output current command change of the connection point (PCC) by the Sandia frequency fluctuation method in the isolated operation of the prior art.

9 is a view showing a frequency and inverter output current command change of the connection point (PCC) by the automatic phase shift method in the isolated operation according to the present invention.

*** Explanation of symbols for the main parts of the drawing ***

20: DC-DC converter 30: inverter

32: pulse width modulation (PWM) section 34: current controller

36: voltage controller 38: sinusoidal (sin) portion

60: phase synchronization loop (PLL) section

The present invention relates to an isolated operation detection apparatus and method by an automatic phase shift method.

More specifically, the link point voltage of the distributed power supply is applied by applying the principle that the inverter output current of the grid-connected distributed power supply including the solar power generation system, wind power generation, fuel cell power generation, etc. continues to lag behind or precede the voltage of the connection point. The present invention relates to an isolated operation detecting apparatus and a method by an automatic phase shifting method in which the frequency of the divergence (convergence) is detected.

In general, distributed power supply is introduced into distribution system to perform linkage operation. Voltage or frequency change, harmonic component inflow, power factor reduction, DC component current inflow, isolation operation prevention, system cutoff and reconnection, grounding, transient protection There are several problems to solve. In the case of grid-tied systems, protection technology against power outages and other accidents of the system must be secured. If a ground fault or power failure of the system is not detected by the inverter, personal injury may occur, so protection is essential.

In particular, the technology to be secured for grid linkage of distributed power generation including photovoltaic power generation is anti-islanding control. When a photovoltaic system and other distributed power sources are disconnected from the grid due to power outages or accidents, if the output of the photovoltaic system and the power consumption of the distribution line load are balanced, the system takes over the distribution line load and continues to operate. This phenomenon is called isolated operation. If this condition persists, it may cause safety accidents of the track maintainer and may adversely affect the electrical installation. Therefore, if the power supply is cut off in the system, it must be immediately detected and the power generation stopped.

To detect the isolated operation of grid-connected distributed sources, voltage information at the generation system, the customer, and the point of common coupling (PCC) that the grid is connected to is essential. If the voltage or frequency of the link point is out of the specified allowable range (IEEE929-2000), the method of judging isolated operation is called the manual method. Several active detection methods have been introduced to solve this problem.

Active detection methods developed to date include the frequency bias method, the Sandia frequency variation method, the frequency jump method, and the Sandia voltage variation method. Among them, the Sandia frequency variation method developed by Sandia National Laboratory (SNL) The non-detection zone (NDZ) is relatively effective among the isolated operation detection methods known to date. However, in order to detect the isolated operation, the inverter output current is distorted even in the normal operation state, so the total harmonic distortion (THD) of the current increases and the power factor decreases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. In a steady state, the output current reference value of the distributed power supply is output as a sine wave in phase with the voltage at the linkage point. It is an object of the present invention to provide an isolated operation detection apparatus and method using an automatic phase shifting method that detects isolated operation by causing the PCC frequency of a distributed power source to diverge (converge) by being behind or ahead of a point voltage. There is,

Another object is a new isolated operation detecting device by automatic phase shifting which detects the isolated operation by causing the frequency of the voltage at the common connection point of the distributed power source to diverge (converge). It is an object of the present invention to provide an isolation operation detection device and a method for detecting power generation immediately after isolation operation occurs without distortion of output current.

SUMMARY OF THE INVENTION An object of the present invention as described above is to provide an apparatus and method for detecting an isolated operation of a grid-connected distributed power source including a photovoltaic system, wind power generation, fuel cell generation, and the like. A pulse width modulation (PWM) unit for transmitting to an inverter of a distributed power supply, a voltage controller for constantly controlling the inverter input terminal voltage of the distributed power supply, a current controller for constantly controlling the inverter output terminal current of the distributed power supply, A sinusoidal sin unit for generating a sinusoidal wave in phase with the voltage at the linkage point and a phase synchronous loop for detecting the inverter output current of the distributed power supply to match the phase of the linkage point voltage. There is provided an isolation operation detecting apparatus using an automatic phase shifting method including a PLL) section.

를 더해줌으로써 정상상태에서는

가 영이 되고, 고립운전상태가 되면 가속이득

값에 의해 분산전원의 인버터 출력전류가 연계점의 전압에 비해 계속 뒤지거나 앞서게 하는 원리를 적용하여 분산전원의 연계점 전압의 주파수가 발산(수렴)하게 하여 고립운전상태를 검출하는 자동 위상 이동법을 이용한 고립운전 검출 방법을 제공함으로써 달성된다.On the phase of the inverter output current command value of the distributed power supply

By adding

Is zero, and acceleration gain

The automatic phase shifting method detects the isolated operation state by diverging (converging) the frequency of the link point voltage of the distributed power supply by applying the principle that the inverter output current of the distributed power supply lags or advances with the voltage of the linking point according to the value. It is achieved by providing an isolated operation detection method using a.

Hereinafter, an isolated operation detecting apparatus and method using an automatic phase shifting method according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing the power flow of the grid-tied photovoltaic power generation system (distributed power supply) according to the present invention. In more detail with reference to Figure 1,

Even if the power supply is interrupted in the system, isolated operation may occur because the magnitude and frequency of the point of common coupling (PCC) voltage are maintained by LC resonance in the RLC parallel load expressed by the customer.

라고 하면 계통으로 유입되는 유효전력

, 무효전력

는 식 각각 아래와 같다.Since the output current of the inverter is controlled to match the phase of the PCC voltage detected through the digital PLL, the voltage of the PCC is adjusted.

Speaking of active power flowing into the grid

, Reactive power

Are as follows.

인 상태에서 고립운전이 발생하면 연계점(PCC) 전압의 크기가 변하게 되고,

인 경우에는 주파수가 변한다. 그리고

,

인 경우에는 연계점(PCC) 전압의 크기와 주파수가 그대로 유지된다. 그런데 IEEE929-2000에서 규정하는 계통의 전압, 주파수 허용 변동범위를 적용하면 수동 검출법으로 검출할 수 없는 검출 불능 영역(NDZ : Non Detection Zone)이 나타나게 된다.From the stomach

When isolated operation occurs in the state of, the magnitude of the PCC voltage changes,

If, the frequency changes. And

,

In case of, the magnitude and frequency of the PCC voltage are maintained. However, when the voltage and frequency tolerance range of the system specified by IEEE929-2000 is applied, a non-detection zone (NDZ) that cannot be detected by a manual detection method appears.

Figure 2 is a block diagram of a grid-tied photovoltaic power generation system (distributed power supply) implemented for the experiment according to the present invention. Referring to Figure 2 in more detail,

는 인버터 입력단 전압을 일정하게 제어하기 위한 전압제어기 출력으로서 인버터 전류 지령치의 크기이고,

은 인버터 출력전류의 지령치이다.Shown in Figure 2

Denotes the magnitude of the inverter current command value as a voltage controller output for uniformly controlling the inverter input terminal voltage,

Is the command value of the inverter output current.

The detection device proposed in the present invention solves the problem of increasing the total harmonic distortion factor (THD) by increasing the reference value of the inverter output current with the PCC voltage in a steady state, and inverting the inverter when an isolated operation state occurs. It is a method of detecting isolated operation by causing the frequency of the PCC voltage to diverge (converge) as a result of the output current being lower than or ahead of the reference voltage.

3 is an algorithm configuration diagram of an isolated driving detection apparatus using an automatic phase shifting method according to an exemplary embodiment of the present invention. Referring to Figure 3 in more detail,

이라고 하면

에 의해 인버터 출력 전류지령은 앞서거나 뒤진 전류지령을 내보내게 된다. 이때의

은 다음과 같다.Inverter output command

Speaking of

Inverter output current command causes the current or backward current command to be sent. At this time

Is as follows.

는 연계점의 추정 각주파수이고

은 계통주파수로 고정된 각 주파수이며

는 가속이득이다.here

Is the estimated angular frequency of the junction

Is the frequency fixed at the system frequency

Is acceleration gain.

에 의해 RLC 병렬부하에 나타나는 연계점의 전압은

이며 이때의

는 식 아래와 같다. Inverter output current command when isolated operation occurs

The voltage at the junction point appearing in the RLC parallel load is

Where

Is as shown below.

이면

이고 ,

이면

이므로 연계점(PCC)의 주파수

가 증가(감소)한다. 결국

일 경우 가속이득

에 의하여 주파수는 계속 증가(감소)하므로 변동 한계치를 넘는 순간 인버터를 정지시킨다.

Back side

ego ,

Back side

Frequency of the junction point (PCC)

Increases (decreases) finally

Acceleration gain if

The frequency continues to increase (decrease) so that the inverter is stopped as soon as the variation limit is exceeded.

That is, FIG. 3 is a diagram of generating a current command value for detecting the isolated operation, and the isolated operation is generated so that the PCC voltage frequency is diverged (converged), so that the frequency estimated by the phase locked loop (PLL) is If it is out of the allowable range (59.3 ~ 60.5 [Hz]), it is judged as isolated operation immediately.

When the isolated operation detection method by the automatic phase shift method is explained in more detail,

로 표현되고, 고립운전이 발생하게 되면

에 의하여

이 되어 인버터 출력 지령전류는 연계점(PCC)의 전압보다 위상이 앞서거나 뒤진 전류를 출력하게 된다.Inverter output command current of distributed power supply

When isolated operation occurs

By

As a result, the inverter output command current outputs a current that is out of phase or behind the voltage of the PCC.

에 대하여 RLC 병렬회로 의한 연계점(PCC) 전압

이 된다. Current source when isolated operation occurs

PCC voltage by RLC parallel circuit

Becomes

이다. here

to be.

이므로

이 된다. However, the voltage phase detected at the link point PCC

Because of

Becomes

이 되므로

에 대한 2차방정식으로 나타내면 다음과 같은 식이 된다. therefore

So

The quadratic equation for gives the equation

로 나타내면,this

If expressed as

이 되며,

Will be

이면

이고

이면

가 발산(수렴)되는데 그 방향은

의 부호와 같다. therefore

Back side

ego

Back side

Is diverging (converging)

Same as the sign of.

일때,

이면

되고,

이 되므로

이되어 계속 감소하게 되고, That is, when isolated operation occurs, the initial frequency estimation value

when,

Back side

Become,

So

Will continue to decrease,

되면

되고

이 되므로

되어 계속 증가한다.

When

Being

So

Continues to increase.

Therefore, if isolated frequency occurs and the estimated frequency is lower than the grid frequency, the frequency decreases gradually. If the estimated frequency is larger than the grid frequency, the PCC voltage frequency gradually increases.

EXAMPLE

Simulation and experiment were carried out under the condition that the quality factor was Q = 2.5 in accordance with the isolation operation detection test conditions specified in IEEE929-2000.

Goodness at this time is prescribed | regulated as follows.

로 하면 다음과 같은 부하조건이 나온다.At this time, inverter output of photovoltaic power generation system

If the load condition is as follows.

Resonance Frequency [Hz] C [uF] L [mH] 59.3 272 25.44255 60 274.0336 25.6763 60.5 272 26.48268

,

인 경우 제안된 고립운전 검출법의 우수성과 타당성을 시뮬레이션과 실험을 통해 검증하였다.Under the same load conditions

,

In the case of, the superiority and validity of the proposed isolated operation detection method are verified through simulation and experiment.

4 is a simulation result showing the frequency and inverter output current command conversion of the connection point (PCC) by the automatic phase shift method in the isolated operation according to the present invention. Referring to Figure 4 in more detail,

4 (a) shows the original current command on the right side of the sinusoidal wave after 0.5 seconds, and the actual current command on the left side. In the case of isolated operation, in case of LC load having a frequency higher than the commercial frequency of 60 [Hz], the current command before the phase is outputted. At this time, the frequency continues to increase under the influence of the acceleration gain K, as opposed to the former, and the inverter determines that the operation is isolated and stops generating power.

4B shows the original current command on the left side and the actual current command on the sine wave after 0.5 seconds. In case of LC load with frequency lower than 60 [Hz] which is common frequency during isolated operation, it outputs current command out of phase. At this time, the frequency continues to decrease under the influence of the acceleration gain K, and the inverter of the photovoltaic power generation system judges the isolated operation to stop the power generation.

5 is a view showing the characteristics of the automatic phase shift method in the system frequency change and isolated operation according to the present invention. Referring to Figure 5 in more detail,

If the system frequency is within 59.7 ~ 60.3 [Hz] within the allowable range up to 0.6 seconds, the proposed isolated operation detection algorithm operates stably. Simulation results show that the frequency continues to increase under influence.

6 is an experimental result showing that the isolated operation by the automatic phase shift method according to the present invention is detected. Referring to Figure 6 in more detail,

인 경우과

일때의 각각의 조건에서 연계점의 주파수가 허용 범위를 초과하여 고립운전이 검출됨을 보여주는 실험결과이다.

If and

Experimental results show that isolated operation is detected when the frequency of the link point exceeds the allowable range under each condition.

7 is a result of comparing the output current when the system frequency is 60.5Hz in normal operation by the conventional Sandia frequency fluctuation method and the automatic phase shift method according to the present invention. In more detail with reference to Figure 7,

When the frequency of the system rises to 60.5 [Hz] during normal operation, the isolated operation detection method using the automatic phase shifting method has a distortion in the output current command compared to the Sandia frequency variation method which is the best among the existing isolated operation detection methods. This shows no results.

8 is a view showing the frequency and inverter output current command change of the connection point (PCC) by the Sandia frequency fluctuation method in the isolated operation of the prior art. In more detail with reference to Figure 8,

인 경우과

일때의 각각의 조건에서 샌디아 주파수 변동법은 출력전류

에 고립운전 검출시 왜곡이 나타남을 보여주는 결과이다.

If and

At each condition, the Sandia frequency fluctuation method

The result shows that the distortion appears when the isolated operation is detected.

9 is a view showing a frequency and inverter output current command change of the connection point (PCC) by the automatic phase shift method in the isolated operation according to the present invention. In more detail with reference to Figure 9,

인 경우과

일때의 각각의 조건에서 자동 위상 이동법을 이용한 고립운전 검출법은 출력전류

에 왜곡이 없이 고립운전 검출이 가능함을 보이는 결과이다.

If and

The isolated current detection method using the automatic phase shift method under each condition of

This shows that isolated operation can be detected without distortion.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto and is intended by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalent claims.

As described above, the isolated operation detection apparatus and method by the automatic phase shifting method according to the present invention can be applied to various distributed power generation systems to detect isolated operation, so that it is possible to detect an area that cannot be detected by the conventional method, and thus has high reliability. It is possible to implement the system,

Another effect is that the total harmonic distortion rate of the current (THD: Total Harmonic) is shown because the conventional method shows a distorted waveform instead of the sine wave of the output current in order to detect an isolated operation that may occur even in the normal state instead of the isolated operation. Distortion) is increased and power factor is lowered, but the detection method according to the present invention has a low total harmonic distortion (THD) of the current because the current command value is a sine wave in a steady state. When the power factor is high and an isolated driving state occurs, the voltage frequency of the linking point (PCC) is diverged (converged), so that the isolated operating state can be detected quickly.

Claims (5)

In the device for detecting the isolated operation of the grid-connected distributed power supply, including photovoltaic power generation system, wind power generation, fuel cell power generation, A pulse width modulator (PWM) unit for changing a pulse width according to the amplitude of a sine wave and transferring the pulse width to an inverter of a distributed power supply; A voltage controller for constantly controlling the voltage of the inverter input terminal of the distributed power supply; A current controller for constantly controlling the inverter output stage current of the distributed power supply; A sinusoidal wave unit generating a sinusoidal wave in phase with the voltage at an associated point of the distributed power supply; And A phase synchronizing loop (PLL) unit configured to detect an inverter output current of the distributed power supply and match the phase of the link point voltage; Isolation operation detection apparatus using an automatic phase shift method comprising a. The PLL of claim 1, wherein the PLL unit An isolated phase detection device using an automatic phase shifting method, characterized in that it is determined as an isolated operation when the estimated frequency is outside the allowable range of 59.3 Hz to 60.5 Hz. The PLL of claim 1, wherein the PLL unit Acceleration gain K is multiplied when isolated operation occurs.

The isolated operation detecting device using the automatic phase shifting method according to claim 1, wherein the frequency of the link point voltage diverges (converges) to detect the isolated operation by causing the reference value of the inverter output current to lag behind or precede the voltage. In the method for detecting the isolated operation of the grid-connected distributed power supply, including photovoltaic power generation system, wind power generation, fuel cell power generation, On the phase of the inverter output current command value of the distributed power supply

By adding

Is zero, and acceleration gain

The automatic phase shifting method detects the isolated operation state by diverging (converging) the frequency of the link point voltage of the distributed power supply by applying the principle that the inverter output current of the distributed power supply lags or advances with the voltage of the linking point according to the value. Isolated method detection using the. The method of claim 4, wherein The isolated operation detection method using the automatic phase shift method, characterized in that it is determined as an isolated operation if the estimated frequency of the link point voltage of the distributed power supply falls outside the allowable range of 59.3 Hz to 60.5 Hz.

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