JP6354092B2 - AC power supply device and isolated operation detection method - Google Patents

Description

  The present invention relates to an AC power supply device and an isolated operation detection method, and more particularly to an AC power supply device capable of interconnecting operation with a commercial power supply and an isolated operation detection method thereof.

  In recent years, an AC power supply device that outputs electric power generated using a solar battery panel or the like as an AC power supply has been popularized. Such an AC power supply device covers a part of electric power used in a home or the like in connection with a commercial power supply supplied from a power plant or the like. This AC power supply device stops the output of the connected power generation equipment, etc. when the commercial system power supply is stopped for inspection or when the commercial system power supply is temporarily disconnected due to a power failure or the like Is required. In such a case, if the power supply to the line load is not stopped, the power is supplied from the AC power supply to the commercial system power supply even though the power supply is originally stopped on the commercial system power supply side. This is because the safety cannot be secured. Therefore, Patent Document 1 discloses a method of detecting an isolated operation in which the commercial power supply is disconnected and the AC power supply device operates independently.

  Patent Document 1 discloses an isolated operation detection method. In Patent Document 1, in response to the fact that the power signal of the system power supply satisfies a certain condition, reactive power is injected in a direction that promotes the frequency change of the power supply signal, and the single operation is performed based on the frequency change of the power supply signal at that time. It is to detect.

Japanese Patent No. 4,835,587

  However, the method disclosed in Patent Document 1 has a problem in that frequency fluctuation due to temporary disturbance of the system is erroneously detected as an isolated operation.

  One aspect of the AC power supply device according to the present invention is an inverter that generates an AC power signal from a DC power signal and outputs the AC power signal to a system wiring to which a commercial system power is transmitted, and a control unit that controls the inverter And the control unit has an isolated operation detection unit that detects that the commercial system power supply is disconnected and is in an isolated operation, and the isolated operation detection unit becomes the isolated operation. An isolated operation determination process is performed to determine the isolated operation after it is determined that there is a possibility of the isolated operation in the isolated operation possibility determination process. In the isolated operation determination process, the latest frequency indicating the latest frequency of the power signal transmitted to the system wiring is stored in the first buffer, and the frequency of the power signal in the past is stored. A polarity value indicating the change polarity of the latest frequency is accumulated in the second buffer, and the frequency of the power supply signal is monotonously increased based on the latest frequency and the polarity value accumulated in a preset determination period. The single operation is detected in response to a monotonous decrease and the amount of change in the frequency of the power signal is outside a preset frequency change threshold range.

  One aspect of the islanding detection method according to the present invention is an inverter that generates an AC power signal from a DC power signal and outputs the AC power signal to a system wiring to which a commercial system power is transmitted, and controls the inverter. A control unit that detects that the commercial system power supply is disconnected, and an independent operation detection method for an AC power supply apparatus that determines the possibility of the isolated operation. After determining that there is a possibility of the isolated operation in the isolated operation possibility determining process, the isolated operation determining process for determining the isolated operation is performed. The latest frequency information indicating the latest frequency of the power signal transmitted to the system wiring is accumulated and the latest frequency from the frequency of the power signal in the past is stored. Information on the polarity value indicating the change polarity is accumulated, and based on the latest frequency and the polarity value accumulated within a preset determination period, the frequency of the power signal is monotonously increased or monotonically decreased and the power signal The single operation is detected in response to the frequency change amount being outside the preset frequency change threshold range.

  The AC power supply apparatus and its isolated operation detection method according to the present invention accumulates the frequency history of the power signal for a certain period after it is determined that there is a possibility of isolated operation, and based on the history, the power supply When the frequency of the signal monotonously increases or monotonously decreases and the amount of change in the frequency is outside the preset frequency change threshold range, it is detected that the AC power supply device is operating alone. As a result, the AC power supply device and the islanding operation detection method detect the islanding operation based on the tendency of the frequency change before the amount of change in the frequency of the power signal reaches the amount of change generally defined as islanding operation. can do.

  According to the present invention, it is possible to shorten the time required for detecting an isolated operation while preventing erroneous detection.

1 is a block diagram of an AC power supply device according to a first exemplary embodiment; It is a figure explaining the calculation method of the newest frequency used in the isolated operation detection method in the alternating current power supply device concerning Embodiment 1, a past frequency, and a frequency deviation. It is a figure explaining the update timing of the frequency of the power signal in the isolated operation detection method in the alternating current power supply device concerning Embodiment 1. FIG. 3 is a flowchart for explaining an isolated operation detection method in the AC power supply apparatus according to the first exemplary embodiment;

Embodiment 1
Embodiments of the present invention will be described below with reference to the drawings. The AC power supply device 1 according to the first exemplary embodiment is independent of the interconnection operation state in which the electric power generated at a power plant or the like operates in conjunction with the commercial grid power supply SPS that supplies the consumer with the commercial grid power supply SPS. And a single operation state that operates in the same manner. In addition, the AC power supply device 1 according to the first embodiment performs an isolated operation detection for detecting a state in which the commercial power supply is disconnected during operation in the interconnected operation state and has become an isolated operation state. Below, especially the independent operation detection method of the alternating current power supply device 1 concerning Embodiment 1 is demonstrated.

  FIG. 1 shows a block diagram of an AC power supply device 1 according to the first exemplary embodiment. In the example shown in FIG. 1, the commercial power supply SPS and the load to be supplied with power are shown so that the usage form of the AC power supply device 1 can be understood. The load is, for example, an electric appliance used at home.

  As shown in FIG. 1, the AC power supply 1 according to the first embodiment includes a PCS (Power Conditioner System) 10, and a PV (Photo Voltaics) and a storage battery BAT are connected to the PCS 10. Note that the AC power supply device 1 may be connected to another power generation source such as a wind power generator instead of PV.

  The PCS 10 includes a control unit (for example, energy management unit 11), a DC / DC converter 12, a DC / AC inverter 13, a DC / DC converter 14, and a switch SW1. The energy management unit 11 includes an arithmetic device such as a CPU (Central Processing Unit), for example, and controls the DC / DC converter 12, the DC / DC converter 14, and the DC / AC inverter 13. Moreover, the energy management part 11 has the independent operation detection part 11a. A detailed description of the isolated operation detection unit 11a will be described later.

  The DC / DC converter 12 converts the voltage level of the DC voltage of the electric power generated by the solar battery panel PV and outputs it to the DC / AC inverter 13. The DC / DC converter 14 converts the voltage level of the direct current voltage of the power stored in the battery BAT and outputs it to the DC / AC inverter 13. The DC / AC inverter 13 converts the DC power provided by the DC / DC converter 12 into AC power and outputs the AC power to the system wiring to which power from the commercial system power supply SPS is supplied. That is, the DC / AC inverter 13 generates an AC power signal from the DC power signal, and outputs the generated AC power signal to the system wiring to which the power from the commercial system power supply SPS is supplied. The switch SW1 is provided between the DC / AC inverter 13 and the system wiring, and an open / close state is controlled based on a switch control signal output from the energy management unit 11.

  The power signal monitoring unit 31 monitors the voltage and current of the power signal transmitted to the system wiring, and outputs the monitored voltage and current values to the energy management unit 11 as the monitor signal S1. In addition, the power signal which mixed the signal of the electric power supplied from the commercial system power supply SPS and the output from PCS10 is transmitted to a system connection point.

  Then, operation | movement of the independent operation | movement detection part 11a of the energy management part 11 is demonstrated. The isolated operation detection unit 11a detects that the AC power supply device 1 has shifted to the isolated operation state based on a change in the frequency of the power signal transmitted to the system wiring. In order to detect the frequency change of the power signal, the isolated operation detection unit 11a uses the latest frequency, the past frequency, and the frequency deviation calculated from the moving average value of the frequencies. Therefore, before describing the specific operation of the isolated operation detection unit 11a, a method of calculating the latest frequency, the past frequency, and the frequency deviation used in the isolated operation detection process will be described. FIG. 2 is a diagram for explaining a calculation method of the latest frequency, the past frequency, and the frequency deviation used in the isolated operation detection method in the AC power supply according to the first embodiment.

  As shown in FIG. 2, the frequency of the power supply signal is held at a constant cycle (for example, a cycle of 5 msec) set independently of the frequency of the power supply signal. In FIG. 2, the frequency information of the held power signal is indicated by C-3 to Cm (m is an integer indicating the frequency information number).

  The isolated operation detection unit 11a uses the twice moving average value of the frequency obtained every half cycle from the frequency detection unit as the latest frequency.

  The isolated operation detection unit 11a uses, as the past frequency, a moving average value for 80 msec before a certain period (for example, 200 msec before) from the latest frequency. Further, the isolated operation detection unit 11a uses a value obtained by subtracting the past frequency from the latest frequency as the frequency deviation. The energy management unit 11 uses the frequency deviation.

  The frequency information Cm described above is accumulated based on the system frequency information updated every half cycle of the power supply signal. FIG. 3 is a diagram for explaining the update timing of the frequency of the power signal in the isolated operation detection method in the AC power supply according to the first embodiment.

  As shown in FIG. 3, the system frequency information is updated every half cycle of the power signal. The cycle of the power signal is a cycle determined based on voltage or current information detected by the power signal monitor 31. In the AC power supply device 1, the zero cross point of the power signal is detected based on the voltage information included in the monitor signal S 1 output from the power signal monitor unit 31, the half cycle of the power signal is detected based on the interval of the zero cross point, and the power source Get the frequency of the signal. The period and frequency of the power signal can also be calculated using, for example, Fourier transform processing.

  On the other hand, the frequency information Cm used for calculating the moving average or the like is updated at a constant cycle independent of the cycle of the power supply signal. FIG. 3 shows an example in which a power signal of about 50 Hz is monitored and frequency information is updated every 5 msec. Therefore, in FIG. 3, the frequency information Cm is updated twice during one cycle of the power signal. Moreover, in FIG. 3, the energy management part 11 showed the example which calculates the past frequency information from the frequency information Cm for 80 msec, for example.

  Next, a specific isolated operation detection process of the isolated operation detection unit 11a will be described. FIG. 4 illustrates an isolated operation detection process of the AC power supply apparatus 1 according to the first embodiment. The isolated operation detection unit 11a is provided with a detection period flag FDTM as a flag necessary for processing, and a first buffer BUF_A and a second buffer BUF_B as buffers for holding values necessary for processing. In FIG. 4, i is shown as a value indicating the number of a buffer necessary for processing. This i is given 0 as an initial value when the AC power supply device 1 is started.

  As illustrated in FIG. 4, the isolated operation detection unit 11 a performs the isolated operation detection process of steps S <b> 11 to S <b> 28 for each half cycle of the power signal (step S <b> 10). In the isolated operation detection process, first, it is confirmed whether or not the period detection flag FDTM is valid (for example, 1) (step S11). In step S11, when the period detection flag FDTM is invalid (for example, 0), the independent operation possibility determination process in steps S12 to S13 is performed. On the other hand, if the period detection flag FDTM is valid in step S11, the single operation determination process in steps S15 to S28 is performed. In addition, step S19-step S21 are the processes performed also in an independent driving possibility determination process.

  In the isolated operation possibility determination process, first, a frequency deviation is calculated (step S12). Then, it is determined whether or not the frequency deviation is outside the detection start threshold range (step S13). As the detection start threshold range, for example, a range where the absolute value of the frequency deviation does not exceed 0.1 Hz can be set as the detection start threshold range.

  In step S13, when the absolute value of the frequency deviation is within the detection start threshold range, the isolated operation detection unit 11a determines that the AC power supply device 1 is not in the isolated operation state (step S19), and i Is initialized to zero (step S20), and the detection period flag FDTM is invalidated (step S21).

  On the other hand, if the absolute value of the frequency deviation is outside the detection start threshold range in step S13 (YES branch in step S13), the isolated operation detection unit 11a initializes i to zero (step S14). The independent operation determination process is started.

  In the isolated operation determination process, first, the detection period flag FDTM is set to a valid state (for example, 1) (step S15). Subsequently, the isolated operation detection unit 11a holds the latest frequency calculated at that time in the first buffer BUF_A [0] (step S16). Further, the isolated operation detection unit 11a holds the frequency change polarity indicating the frequency change polarity in the second buffer BUF_B [0] (step S17). In step S17, 1 is held in the second buffer BUF_B [0] if the frequency deviation is a positive value, and 0 is held in the second buffer BUF_B [0] if the frequency deviation is a negative value. . Then, the isolated operation detection unit 11a increases the count value i by one (step S18).

  After the period detection flag FDTM becomes valid in step S15, the isolated operation detection unit 11a performs the processing after step S22 every time the isolated operation detection process is activated based on the determination in step S11.

  In step S22, the latest frequency calculated at the time when the detection process is started is held in the first buffer BUF_A [i]. In step S23, the frequency change amount is calculated, and the frequency change polarity is held in the second buffer BUF_B [i] (step S23). Here, the frequency change amount is a value obtained by subtracting the latest frequency in the last isolated operation detection process from the latest frequency at the present time. In step S23, if the frequency change amount is a positive value, 1 is held in the second buffer BUF_B [i], and if the frequency change amount is a negative value, 0 is stored in the second buffer BUF_B [i]. Hold on.

  Subsequently, the isolated operation detection unit 11a determines whether or not the count value i is equal to or greater than a preset determination period value N (step S24). Although this determination period value N can be set to an arbitrary value, in the present embodiment, it is set to 7 (for example, the number of buffers to be accumulated is 8). Note that the determination period value N is preferably matched to a frequency fluctuation period due to an expected temporary system disturbance.

  If the count value i is smaller than the determination period value N in step S24 (NO branch of step S24), the isolated operation detection unit 11a increments the count value i by 1 and ends the isolated operation detection process once ( Step S28). That is, the isolated operation detection unit 11a stores the latest frequency newly calculated in the first buffer BUF_A and newly calculated in the second buffer BUF_B until the count value i reaches the determination period value N. Accumulate frequency change polarity values.

  On the other hand, when it is determined in step S24 that the count value i has reached the determination period value N (YES in step S24), the isolated operation detection unit 11a refers to the value of the second buffer BUF_B [i]. Then, it is determined whether the frequency change during the determination period is monotonously increasing or monotonically decreasing (step S25). For example, when the frequency change during the determination period is monotonically increasing, the value obtained by integrating the second buffer BUF_B [0] to the second buffer BUF_B [N] is N + 1. When the frequency change during the determination period is monotonously decreasing, the value obtained by integrating the second buffer BUF_B [0] from the second buffer BUF_B [0] is 0.

  When the frequency change during the determination period is not monotonously increasing or decreasing in the determination process of step S25 (NO branch of step S25), the single operation detection unit 11a determines that the AC power supply device 1 is not in the single operation state. (Step S19), i is initialized to zero (step S20), and the detection period flag FDTM is invalidated (step S21).

  When the frequency change during the determination period in the determination process in step S25 is monotonically increasing or decreasing (YES in step S25), the frequency increase or decrease during the determination period with reference to the first buffer BUF_A It is determined whether the amount is outside the frequency change threshold range (step S26). Here, the frequency change threshold range is preferably set to about 0.2 Hz so as not to erroneously detect an isolated operation due to a gradual change in frequency (for example, ± 2 Hz / second) due to an expected temporary system disturbance. . Further, the amount of increase or decrease of the frequency is changed from the latest frequency stored in the first buffer BUF_A [0] in which the value is first held to the second buffer BUF_A [N] in which the value is finally held. It is calculated as the absolute value of the value obtained by subtracting the latest stored frequency.

  And in step S26, when the amount of increase or decrease in frequency is equal to or greater than the frequency change threshold range, the isolated operation detection unit 11a enters the isolated operation detection state (step S27). On the other hand, if the increase or decrease in the frequency is smaller than the frequency change threshold range in step S26, the isolated operation detection unit 11a determines that the AC power supply device 1 is not in the isolated operation state (step S19), i Is initialized to zero (step S20), and the detection period flag FDTM is invalidated (step S21).

  When the isolated operation is detected by the above operation, the energy management unit 11 switches the logic level of the switch control signal to open the switch SW1 (off state). Thereby, the AC power supply device 1 can stop the output in response to the detection of the single operation.

  From the above description, in the AC power supply device 1 according to the first exemplary embodiment, the isolated operation determination process is started based on the frequency history information after the frequency change of the power supply signal becomes larger than a certain level, The isolated operation can be detected in response to the change in the power signal during the isolated operation determination process being performed showing a change exceeding a certain condition. In particular, in the AC power supply device 1 according to the first exemplary embodiment, the sign of the isolated operation is determined at an early stage based on the frequency deviation, and the fineness of the power signal in a short period after it is determined that there is a possibility of the isolated operation. An isolated operation can be detected based on a simple frequency change.

  By such multiple determination processing, the AC power supply device 1 according to the first exemplary embodiment can prevent erroneous detection of isolated operation. Further, in the AC power supply device 1 according to the first exemplary embodiment, since the isolated operation can be determined based on the frequency change of the power supply signal in a short period, it is possible to shorten the time until the operation is determined to be in the isolated operation state.

  The PCS needs to be disconnected from the system instantaneously (for example, within 0.2 seconds) after shifting to the single operation state, and when the frequency fluctuates temporarily due to system disturbance (for example, 3 cycles of 0.8 Hz increase) It is necessary to continue the interconnected operation without considering it as an operation state. In the AC power supply device 1 according to the first exemplary embodiment, when the frequency of the power signal is 50 Hz and the determination engine value N is 7, the isolated operation can be detected in about 0.08 seconds. Further, when the frequency of the power supply signal is 60 Hz under the same conditions, the isolated operation can be detected in about 0.07 seconds.

  Further, the isolated operation detection method in the AC power supply device 1 according to the first embodiment can be combined with the isolated operation detection method of the frequency feedback method with step injection. As described above, when combined with the frequency feedback type isolated operation detection method with step injection, the isolated operation can be detected with higher accuracy and at higher speed.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.

1 AC power supply 10 PCS for PV
11 Energy Management Unit 11a Independent Operation Detection Unit 12, 14 DC / DC Converter 13 DC / AC Inverter 20 BAT PCS
SW1 switch S1 monitor signal PV solar panel BAT battery SPS commercial power supply CB breaker

Claims (9)

An inverter that generates an AC power signal from a DC power signal and outputs the AC power signal to a system wiring to which power from a commercial power supply is supplied;
A control unit for controlling the inverter,
The controller is
Having an isolated operation detection unit for detecting that the commercial system power supply is in an isolated operation in a disconnected state;
The isolated operation detection unit
Performing an isolated operation possibility determination process for determining the possibility of the isolated operation,
In the single operation possibility determination process, after it is determined that there is a possibility of the single operation, the single operation determination process for determining the single operation is performed,
In the isolated operation determination process,
The latest frequency indicating the latest frequency of the power signal transmitted to the system wiring is stored in the first buffer, and the polarity value indicating the change polarity of the latest frequency from the frequency of the power signal in the past is set to the second value. Accumulate in the buffer,
Based on the latest frequency and the polarity value accumulated within a predetermined determination period, the frequency of the power signal monotonously increases or decreases monotonically and the amount of change in the frequency of the power signal exceeds the frequency change threshold range. In response to this, an AC power supply device that detects the single operation.   The AC power supply device according to claim 1, wherein the control unit disconnects the output of the inverter from the commercial power supply in response to detecting the isolated operation.   The AC power supply apparatus according to claim 1 or 2, wherein the isolated operation detection unit performs the isolated operation possibility determination process or the isolated operation determination process every half cycle of the power signal.   4. The AC power supply device according to claim 1, wherein the isolated operation detection unit calculates the latest frequency at a constant cycle set independently of the frequency of the power signal. 5.   In the second buffer, a frequency deviation indicating a difference between a past frequency indicating the frequency of the power supply signal a certain period before the latest frequency and the latest frequency is first accumulated as the polarity value, and a period before and after. 5. The AC power supply apparatus according to claim 1, wherein a frequency change polarity value indicating the difference between the latest frequencies calculated in step S <b> 1 is accumulated as the polarity value after the frequency deviation.   In the isolated operation possibility determination process, in response to a frequency deviation indicating a difference between the past frequency indicating the frequency of the power supply signal and a latest period before the latest frequency being equal to or greater than a detection start threshold range. The AC power supply device according to any one of claims 1 to 5, wherein it is determined that there is a possibility of the independent operation.   The AC power supply apparatus according to claim 6, wherein the detection start threshold range is set to a range of −0.1 Hz to 0.1 Hz.   The AC power supply apparatus according to any one of claims 1 to 7, wherein the frequency change threshold range is set in a range of -0.2 Hz to 0.2 Hz. In an independent operation in which an AC power signal is generated from a DC power signal and the AC power signal is output to a system wiring to which a commercial system power is transmitted, and the inverter is controlled and the commercial system power is disconnected. A control unit for detecting that there is a single operation detection method in an AC power supply device,
Performing an isolated operation possibility determination process for determining the possibility of the isolated operation,
In the single operation possibility determination process, after it is determined that there is a possibility of the single operation, the single operation determination process for determining the single operation is performed,
In the isolated operation determination process,
Accumulating the latest frequency information indicating the latest frequency of the power signal transmitted to the system wiring, and storing information on the polarity value indicating the change polarity of the latest frequency from the frequency of the power signal in the past,
Based on the latest frequency and the polarity value accumulated within a preset determination period, the frequency of the power supply signal monotonously increases or decreases monotonically and the amount of change in the frequency of the power supply signal falls outside the frequency change threshold range. A single operation detection method in an AC power supply device that detects that the single operation is performed according to the above.

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