JP3235768B2 - Method of detecting isolated operation of distributed power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a fuel cell power supply,
The present invention relates to an islanding detection method for a plurality of distributed power supplies, such as a solar power supply, which are distributed in a system.

[0002]

2. Description of the Related Art When a switch on the system side is released due to an accident or construction during a system interconnection of a distributed arrangement type power supply (a power failure state), a function for diagnosing abnormal system voltage and frequency normally provided by the distributed arrangement type power supply is provided. Power supply is disconnected from the system. However, when the distributed power supply and its load are matched, that is, when the power flow with the power system is very small, the distributed power supply continues to operate despite opening of the switch. This is called an islanding operation state.
Such a state may cause an unexpected situation such as an electric shock to the security and maintenance of the power system.

One of the methods for detecting the above-mentioned islanding operation state is to apply a constant-period phase fluctuation to an output current command of a current control type inverter and to generate a same-period frequency fluctuation generated in a connection point voltage after a power failure. Has been already proposed to detect islanding by detecting. FIG. 5 shows a conventional example.

In FIG. 5, 1 is a DC power supply such as a fuel cell power supply or a solar power supply, 2 is an inverter, 3 is a reactor, 4 is a current transformer (CT), 5 is a phase comparator 51, a phase adjuster 52 and A PLL (phase locked loop) circuit including a sine wave (sin wave) generator 53 and the like, 6 is a phase shifter, 7 is a divider, 8 is a multiplier, 9A and 9B are adders,
0 is a current regulator (ACR), 11 is pulse width modulation (PW).
M) a signal generator, 12 is a current phase fluctuation command circuit composed of multipliers 121A, 121B, etc., 13 is a frequency / voltage (F / V) converter 131, a commercial frequency removal filter 13
2A, a frequency fluctuation detection circuit including a fluctuation frequency component detection filter 132B, a comparator 133, and the like.

In such a configuration, usually, the voltage Vs at the grid connection point is taken into the PLL circuit 5 to generate a reference sine wave Vref of the inverter. From the Vref and the active power command (P command), an output current command value I ^* of the inverter is obtained via a divider 7, a multiplier 8, and an adder 9A. The difference between the current command value I ^* and the detection value Iist is represented by A
An inverter voltage command is input to the CR 10 to obtain an inverter voltage command, from which a PWM signal generator 11 generates an inverter firing signal, and performs the firing control.

Next, the isolated operation will be described. In the current phase variation command circuit 12, the multiplier 121A multiplies the phase variation frequency component by an appropriate reactive power command (Q command), and the multiplier 121B further performs a reference sine wave Vref.
A current command Iq ^* for causing the reactive power to fluctuate in a constant cycle is generated by a multiplication process with a sine wave having a phase shift of 90 degrees from. The adder 9A adds this Iq ^* and the original current command Ip ^* of the inverter to obtain an output current command value I ^{* of the} inverter.

As a result, the inverter fluctuates the voltage waveform in order to output a current Iq ^* whose phase is earlier or later than the voltage Vs at the system interconnection point, but when the inverter is connected to the power system, The influence does not appear on the grid connection point voltage, and a stable voltage and frequency are maintained. In contrast,
When disconnected from the grid, the output voltage fluctuation of the inverter appears at the interconnection point, and in the case of the current control type inverter, it appears as a frequency fluctuation having the same cycle as the current fluctuation. For example, when the current command is in the advanced phase, the inverter attempts to generate a voltage that is further advanced than the interconnection point voltage generated by the inverter.
The operation shifts to the high frequency side by the operation of the phase adjuster 52 in the LL circuit 5. Conversely, in the case of a delay command, the operation shifts to the lower frequency side.

Therefore, in the example of FIG. 5, a frequency fluctuation detection circuit 13 is provided, the interconnection point voltage is converted to a frequency by an F / V converter 131, a system frequency component is removed by a filter 132A, and a filter 132B To detect only the same frequency component ΔF as the phase variation period, and determine whether or not the detected amount ΔF has exceeded the discrimination level by the comparator 133, and when it exceeds, issue a system disconnection command or an inverter stop command. I have.

[0009]

However, since the amount of frequency fluctuation detected by the conventional method is a minute fluctuation, if there is a frequency fluctuation in the power system in the same cycle as a current command generated by some other factor, erroneous detection is performed. There is a problem that causes. Therefore, an object of the present invention is to prevent an erroneous detection caused by a frequency fluctuation in the same cycle as a current command generated due to some factor, and to reliably detect an islanding operation.

[0010]

According to an aspect of the present invention, a plurality of distributed power supplies are arranged in a system and a current control type power supply for controlling an output current thereof to a desired value. A power conversion device, and a determination circuit that determines a single operation by detecting a frequency variation of the same cycle that occurs at a point of interconnection with the system at the time of a power failure by giving a phase variation of a fixed cycle to the output current command value, A fixed time after the detection of the frequency fluctuation, the phase fluctuation command of the current is fixed to a predetermined value, and when the frequency fluctuation of the interconnection point voltage after the fixing is equal to or less than a certain value, it is determined that the isolated operation is performed. I have.

According to the second aspect of the present invention, a plurality of distributed power sources distributed in a system, a current control type power converter for controlling an output current thereof to a desired value, and a constant period of the output current command value A decision circuit for detecting frequency fluctuations of the same cycle that occur at the interconnection point with the system at the time of a power outage and judging the isolated operation, and for a fixed time after the detection of the frequency fluctuations, It is characterized in that the phase change command is fixed to a predetermined value, and when the frequency change of the interconnection point voltage after fixing becomes a unique rate of change of the distributed arrangement type power supply, the operation is determined to be the isolated operation.

According to the third aspect of the present invention, a plurality of distributed power sources distributed in a system, a current control type power conversion device for controlling an output current thereof to a desired value, and a constant period of the output current command value are provided. A decision circuit for detecting frequency fluctuations of the same cycle that occur at the interconnection point with the system at the time of a power outage and judging the isolated operation, and for a fixed time after the detection of the frequency fluctuations, It is characterized in that the phase variation command is fixed to a predetermined value, and when the frequency of the interconnecting point voltage after fixing reaches a frequency level predicted in a certain period, the operation is determined to be the isolated operation.

[0013]

Function: The current phase fluctuation command, which fluctuates in a constant cycle, is fixed at a constant value for a predetermined time after the frequency fluctuation is detected, and the resulting frequency change of the interconnection point voltage is monitored, thereby enabling independent operation. Make sure that it can be detected.

[0014]

FIG. 1 is a block diagram showing a first embodiment of the present invention, in which a fluctuation / fixed switching circuit 122 is added to a current phase fluctuation command circuit 12 as compared with the conventional example shown in FIG.
A monostable circuit 134,
An exclusive OR circuit (EXOR) 135 and an AND circuit (AND) 136 are added.

In other words, attention is paid to the fact that the frequency fluctuation caused by other factors during the interconnection is not related to the current phase fluctuation given by the inverter. It does not change. On the other hand, if the phase fluctuation is fixed after the interconnection is cut off, the frequency fluctuation amount becomes zero or decreases. Therefore, by determining the presence or absence of the frequency fluctuation after the phase fluctuation is fixed, it is possible to determine the cause of the frequency fluctuation.

Therefore, in this embodiment, when the frequency change is detected by the comparator 133, a signal for fixing the Q command for a fixed time is generated from the monostable circuit 134 to the change / fix switching circuit 122, and the current phase change command is issued. Output via the circuit 12. The output of the monostable circuit 134 and the output of the comparator 133 are input to the EXOR 135. By inputting the output of the EXOR 135 and the output of the monostable circuit 134 to the AND 136, the frequency fluctuation ΔF during the Q command fixed period is reduced. Detect presence / absence.

That is, if the frequency variation ΔF is detected during the fixed period of the Q command, it is determined that the operation has occurred due to other factors during the interconnection, while if the frequency variation ΔF is not detected, it is determined that the operation is the isolated operation. After the system is shut down, a stop command is given to the inverter. Table 1 shows the above relationship.
Shown in

[Table 1]

FIG. 2 is a block diagram showing a second embodiment of the present invention. In place of the EXOR 135 shown in FIG.
7, a comparator 133A and an on-delay timer 138 are provided. When the frequency change is detected by the comparator 133, a signal for fixing the Q command for a fixed time is generated from the monostable circuit 134 to the change / fix switching circuit 122, and is output via the current phase change command circuit 12. Are the same as in FIG.

From the interconnection point voltage Vs, the F / V converter 131
, The commercial frequency component is removed by the commercial frequency removal filter 132A, and the frequency of the interconnection point voltage is detected.
By passing through 37, the rate of change of the frequency is detected. This is supplied to a comparator 133A including a window comparator.
And an on-delay timer 138 that secures a certain period of time to prevent a malfunction, to detect whether or not the rate of change is unique to the inverter.

That is, the frequency variation generated after the system is cut off has a frequency change rate determined by the response characteristic of the inverter, and the frequency response characteristic of the inverter has a constant value due to the characteristic of the phase adjuster 52 in the PLL circuit 5. . By detecting the rate of change in frequency during the fixed period and determining whether or not this is the rate of change unique to the inverter, it is possible to determine the cause of the occurrence of frequency fluctuation.

FIG. 3 is a block diagram showing a third embodiment of the present invention. A comparator 13 for introducing the output of a commercial frequency rejection filter 132A instead of the 1EXOR 135 shown in FIG.
3B. When the frequency fluctuation is detected by the comparator 133, a signal for fixing the Q command to the fluctuation / fixing switching circuit 122 for a fixed time is generated from the monostable circuit 134 and output from the current phase fluctuation command circuit 12. Up to this point, it is the same as FIG. 1 and FIG.

After detecting the frequency of the interconnection point voltage Vs after the command is fixed, the comparator 133B determines whether or not the frequency has reached the frequency predicted in advance. If the frequency has reached the frequency, the inverter stop signal is output. Output. That is, the periodic frequency fluctuation after the system interruption is caused by the periodic fluctuation of the current phase command. If the phase fluctuation command is fixed, the frequency change rate becomes a constant amount determined by the phase command value. Therefore, the isolated operation is detected by detecting the interconnection point frequency after a certain period of time and determining whether or not this is the frequency predicted from the above change rate.

FIG. 4 shows the relationship between the current phase command and the frequency of the interconnection point voltage. FIG. 5A shows the movement of the current phase command, and FIG. 5B shows the frequency change of the interconnection point voltage. In each of the above embodiments, the current fluctuation phase command that fluctuates in a constant cycle is changed for a certain time after the detection of the frequency fluctuation in FIG.
It can be said that it is fixed to an appropriate value as shown in (a), and it is determined whether or not the isolated operation is performed from the resulting frequency change fs of the interconnection point voltage as shown in (b).

[0024]

According to the present invention, it is possible to discriminate between frequency fluctuations caused by other factors during interconnection and frequency fluctuations caused by the current phase command of the inverter, so that reliable islanding detection is possible. The following advantages are obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the present invention.

FIG. 4 is a waveform chart for explaining the operation of FIGS. 1 to 3;

FIG. 5 is a configuration diagram showing a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... Interconnection inverter, 3 ... Reactor, 4 ... Current transformer, 5 ... PLL circuit, 6 ... Phase shifter, 7 ... Divider, 8, 121A, 121B ... Multiplier, 9A, 9B …
Adder, 10: current controller (ACR), 11: pulse width modulation (PWM) circuit, 12: current phase variation command circuit, 1
3: frequency fluctuation detection circuit, 122: fluctuation / fixed switching circuit, 131: frequency / voltage (F / V) converter, 132
A, 132B ... filters, 133, 133A, 133B
.., Comparator 134, monostable circuit 135, exclusive OR circuit (EXOR) 136… AND circuit (AN
D) Circuit, 137: Differentiating circuit, 138: On-delay timer.

Claims (3)

(57) [Claims] 1. A plurality of distributed power supplies distributed in a power system, a current control type power converter for controlling an output current of the power supply to a desired value, and a phase fluctuation of a fixed cycle to an output current command value. A determination circuit that detects frequency fluctuations of the same cycle occurring at an interconnection point with a system at the time of a power outage and determines islanding operation, and for a predetermined time after the detection of the frequency fluctuations, the phase fluctuation command of the current is predetermined. Characterized in that the isolated operation is determined when the frequency variation of the interconnection point voltage after fixing is equal to or less than a certain value. 2. A plurality of distributed power supplies distributed in a system, a current control type power converter for controlling an output current of the power supply to a desired value, and a phase fluctuation of a fixed cycle to an output current command value. A determination circuit that detects frequency fluctuations of the same cycle occurring at an interconnection point with a system at the time of a power outage and determines islanding operation, and for a predetermined time after the detection of the frequency fluctuations, the phase fluctuation command of the current is predetermined. And determining that the isolated operation is performed when the frequency change of the interconnection point voltage after fixing becomes a unique rate of change of the distributed arrangement type power supply. 3. A plurality of distributed power supplies distributed in a system, a current control type power converter for controlling an output current of the power supply to a desired value, and a phase fluctuation of a fixed cycle to an output current command value. A determination circuit that detects frequency fluctuations of the same cycle occurring at an interconnection point with a system at the time of a power outage and determines islanding operation, and for a predetermined time after the detection of the frequency fluctuations, the phase fluctuation command of the current is predetermined. And detecting the isolated operation when the frequency of the fixed interconnection point voltage reaches a frequency level predicted for a certain period of time.