JP2005094921A - Distributed power generation system and method for preventing its isolated operation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distributed power generation system that is provided with an isolated operation preventing function with which isolated operation is prevented without fail even in high-density linked state and is free from reverse power flows to the system power supply side. <P>SOLUTION: The distributed power generation system that can be linked with a system power supply 30, comprises an underpower relay 5, a passive isolated operation preventing device 6, and an active isolated operation preventing device 7. The distributed power generation system is so constructed that a reverse power flow to the system power supply 30 side is not permitted. The generation output is controlled based on a target value of generated output. This target value is set with a predetermined allowance provided so that power becomes further insufficient relative to a set value of parallel off as a reference value for detecting underpower in the underpower relay. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a distributed power generation system, and more particularly to a distributed power generation system that can be connected to a system power supply and has an isolated operation prevention function that prevents an isolated operation during a system power failure.

In recent years, the development of distributed energy systems aimed at reducing CO ₂ emissions and saving energy has been actively developed and put into practical use. The use of the power generation system is expected to progress rapidly in the future. In particular, gas engine cogeneration systems capable of cogeneration with heat and power are attracting attention because of their high overall energy efficiency because they can effectively use not only electric power but also heat energy generated by the gas engine.

  By the way, the distributed power generation system does not cover all the power demand in the power consumption area alone, but links the system power supply such as commercial AC power supplied by the power company with the system power supply. The type of usage (system interconnection type usage mode) as a grid-connected power generation device that is replenished from the mainstream is mainly used for homes and the like. In the case of such grid connection type usage, it is necessary to establish grid connection functions such as synchronous control with the grid power supply, grid protection coordination, and prevention of isolated operation during grid power failure.

  Here, as a method of the isolated operation prevention function, the system voltage is monitored, a passive method that detects changes that appear during isolated operation due to a system power failure, and a specific fluctuation is given to the output from the grid-connected power generation device side. There are two active methods for detecting changes that occur during islanding. As passive methods, there are methods such as a voltage phase jump detection method, a third harmonic distortion rapid increase detection method, and a frequency change rate detection method (see, for example, Patent Document 1 or 2 below). It may not be detected without appearing. For this reason, it is necessary to use the active method so that the passive method can be complemented and detection is possible even in the reverse power flow balance state. Examples of the active system include a frequency shift system, an active power fluctuation system, a reactive power fluctuation system, and the like (for example, see Patent Documents 3 to 7 below).

On the other hand, in the case of the above grid-connected usage pattern, in the distributed power generation system that does not allow reverse power flow to the grid power supply side, one of the following three methods is currently provided according to the power grid interconnection technical requirement guidelines. Therefore, it is necessary to secure the function for preventing isolated operation. That is, 1) a reverse power relay (RPR) and an underpower relay (UPR) are provided, or 2) a reverse power relay (RPR) and an isolated operation prevention function (one or more of each of an active method and a passive method). Or 3) It is necessary to provide an isolated operation prevention function (one or more of the active method and the passive method).
Japanese Patent No. 3405786 Japanese Patent No. 3022152 JP 11-41820 A JP 09-308112 A JP 09-252540 A JP 09-252541 A Japanese Patent Application Laid-Open No. 08-149841

  By the way, in the case of a residential (household) cogeneration system or the like, there are many cases where the system-connected power generators are densely installed in a relatively small area because there are many cases where they are installed in advance at the time of new construction. There are many cases of high-density interconnection. It has been pointed out that in such a high-density interconnected state, in the active system of the above-described isolated operation prevention function, the same type of fluctuations from the individual grid-connected power generation devices overlap each other and interfere with each other and do not function normally.

  Also, in a distributed power generation system that does not allow reverse power flow to the system power supply side, it is difficult to prevent reverse power flow, particularly in a high-density connection state. In other words, of the above three methods, the isolated operation prevention function alone, or the combined use of the isolated operation prevention function and the reverse power relay allows the reverse power relay to allow a slight reverse power flow for each power generation system. Therefore, there is a possibility that the reverse power flow state and the insufficient power state may be balanced between the plurality of power generation systems, and there is a possibility that the isolated operation state cannot be accurately detected. Furthermore, in the case of a combination of a reverse power relay and an underpower relay, when a photovoltaic power generation system is also installed, power is supplied from the photovoltaic power generation system even when the power supply of the system power is interrupted. There is a problem that it depends on driving detection, and it is difficult to establish an independent driving preventing function that functions independently.

  The present invention has been made in view of the above-mentioned problems, and its purpose is to solve the above problems and to have an isolated operation prevention function that can reliably prevent isolated operations even in a high-density connected state. An object of the present invention is to provide a distributed power generation system that does not allow reverse power flow to the system power supply side.

  In order to achieve this object, the first characteristic configuration of the distributed power generation system according to the present invention is a distributed power generation system that can be interconnected with a system power source, comprising a shortage power relay, a passive islanding prevention device, The system is provided with an active isolated operation prevention device and configured not to allow reverse power flow to the system power supply side. Here, the “reverse power flow” means a power flow from the voltage / current detection point toward the system power supply side for the operation of the underpower relay. Hereinafter, in the description according to the present invention, “reverse power flow” is used in the same meaning.

  In addition to the first feature configuration, the second feature configuration includes a generator that generates DC power, and a power converter that converts the DC power generated by the generator into AC power having a predetermined voltage and frequency. Output control means for controlling the operation of the power converter and interconnection connection with the system power supply, and the insufficient power represented by the difference obtained by subtracting the output power of the power converter from the power consumption of the load is a predetermined solution. Underpower detection means for detecting an underpower detection signal by detecting that the set value is below a set value, and a passive single unit for detecting a change appearing in a system voltage at the time of power outage of the system power supply and outputting a first power outage detection signal An operation detecting means, and an active islanding detecting means for detecting a change appearing at the time of a power failure of the system power supply based on a predetermined characteristic fluctuation given to the output power of the power converter and outputting a second power failure detection signal. And The underpower relay is configured such that, based on the underpower detection signal output by the underpower detection means, the output control means opens a relay that interconnects the power converter and the system power supply. The passive islanding prevention device is a relay in which the output control means interconnects the power converter and the system power supply based on the first power failure detection signal output by the passive islanding detection means. Or at least one of the operation stop of the power converter, and the active islanding prevention device is configured to output the second power failure detection signal output by the active islanding detection means. Based on this, the output control means opens at least one of the relay that interconnects the power converter and the system power supply, or at least one of the operation stop of the power converter. In that it is configured to perform.

  According to the first or second characteristic configuration of the distributed power generation system, since the shortage power relay is provided, in each of the distributed power generation systems, the shortage power amount has a predetermined disconnection set value in the shortage power state. If it falls below, the power generation output of the distributed power generation system stops, so that the reverse power flow to the system power supply side is completely prevented. Therefore, even in a high-density interconnected state, there is no fear of interfering with each other and becoming an equilibrium state, so that the isolated operation preventing function functions normally. In addition, since the isolated operation prevention function has both passive and active methods, it can compensate for the shortcomings of each method and reliably detect a power failure of the system power supply, and can detect the isolated operation state. The state can be stopped.

  In particular, in the case of the second feature configuration, output control means for controlling the opening or shutting down of the relay connected to the grid power supply for the power converter, passive islanding detection means, and active islanding detection The passive and active isolated operation prevention devices are constituted by the means, and the underpower relay is formed by adding the underpower detection means to the same output control means, so that the effect of the first characteristic configuration is achieved. Can do.

  By the way, normally, in the grid interconnection technical requirement guideline, in the single-phase three-wire or three-phase three-wire electric system, the shortage power relay must be installed in each phase. It has a feature that it may be detected in the total power.

  In the third feature configuration, in addition to the first or second feature configuration described above, a power shortage state is established with respect to a set value that is a reference value for detecting power shortage of the power shortage relay. The power generation output is controlled based on the generated power target value set with a predetermined margin.

  The fourth feature configuration includes a heater and a heater control unit that controls the operation of the heater in addition to the third feature configuration, and surplus power is generated with respect to the power generation output of the power generation target value. The heater control unit controls the surplus power to be consumed by the heater.

  According to the third or fourth characteristic configuration of the distributed power generation system, there is a margin so that the insufficient power relay detects a decrease in the insufficient power state and does not interrupt the operation of the distributed power system or the grid connection. Since the power generation output control is performed, it is possible to prevent the power supply from the distributed power generation system from frequently stopping in accordance with the load decrease. In other words, when a power shortage relay is used instead of the reverse power relay, the power supply from the distributed power generation system stops whenever the load falls below the sum of the power generation output and the disconnection set value. Can be prevented. Here, the generated power target value is set to be lower than the power obtained by subtracting the power of the disconnection set value from the load.

  In particular, according to the fourth characteristic configuration, when the power generation output is controlled with the generated power target value of the third characteristic configuration, if the load is further reduced, the possibility that the insufficient power relay operates is increased. By converting the reduced load, that is, the surplus power into heat energy by the consumption of the heater, it is possible to avoid an operation stop state of the distributed power generation system while suppressing unnecessary power consumption.

  The fifth characteristic configuration is that in addition to any one of the first to fourth characteristic configurations, a combined heat and power generator is provided.

  According to the fifth characteristic configuration of the distributed power generation system, not only the distributed power generation system functions as a cogeneration system but also a combined heat and power generator is generated when used in combination with the fourth characteristic configuration. By integrating the heat energy and the heat energy generated by the heater, more efficient use of the heat energy becomes possible.

  In order to achieve this object, the characteristic configuration of the method for preventing isolated operation of a distributed power generation system according to the present invention is that a distributed power generation system that is connected to a system power supply without reverse power flow is connected to a shortage power relay and passive islanding operation. In the state where the occurrence of reverse power flow from the distributed power generation system to the system power supply side when the system power supply is normal is eliminated by a shortage power relay. The operation preventive device and the active isolated operation preventive device detect a power failure of the system power supply to prevent an isolated operation state of the distributed power generation system.

  According to the characteristic configuration of the method for preventing isolated operation of the distributed power generation system described above, a power shortage relay is provided, and in each distributed power generation system, if the power shortage is below a predetermined disconnection set value in a power shortage state, Since the power generation output of the power generation system can be stopped, the reverse power flow to the system power supply side is completely prevented. Therefore, even in a high-density interconnected state, there is no concern of mutual interference and equilibrium, so that the passive and active islanding prevention devices function normally. In addition, since the isolated operation prevention device has both a passive method and an active method, it can compensate for the disadvantages of each method and reliably detect a power failure of the system power supply. Can be prevented.

  An embodiment of a distributed power generation system according to the present invention (hereinafter referred to as “the present invention system” as appropriate) will be described with reference to the drawings.

<First Embodiment>
As shown in FIG. 1, the system 1 of the present invention includes a generator 2 that generates DC power, and an inverter 3 that converts the DC power generated by the generator 2 into AC power having a predetermined voltage and frequency. An example), an output control means 4 for controlling the operation of the inverter 3 and the interconnection connection with the system power supply 30 to be described later, an insufficient power detection means 5, a passive islanding detection means 6, and an active islanding detection means. 7. Further, the system 1 of the present invention has a configuration in which the output of the inverter 3 is connected to the system power supply 30 to supply power to the load 31.

  The generator 2 is not limited to a specific generator as long as it is a generator that generates DC power. For example, in addition to a fuel cell and a solar cell that directly output a DC voltage, a hydropower, wind power, an internal combustion engine, Also included is one that generates DC power by AC / DC conversion of AC power output from a squirrel-cage induction machine, a DC excitation synchronous machine, a permanent magnet synchronous machine, or the like by rotational energy generated by a micro gas turbine or the like. In the case of a fuel cell, an internal combustion engine, or a micro gas turbine, the generator 2 functions as a part of a cogeneration system that generates heat in addition to electric power.

  The inverter 3 is a DC / AC converter 8 that converts DC power into AC power having a predetermined voltage and frequency, and an interconnection that interconnects the AC output of the DC / AC converter 8 and the AC power of the system power supply 30. The relay 9, the current detector 10 that detects the AC current (instantaneous value) output from the DC / AC conversion unit 8 between the DC / AC conversion unit 8 and the interconnection relay 9, and the AC voltage (instantaneous) of the system power supply 30. A voltage detector 11 that detects the value) on the system power supply 30 side of the interconnection relay 9. Further, the DC / AC conversion unit 8 includes a bridge circuit 12 composed of gate elements composed of IGBTs (3-terminal bipolar MOS composite semiconductor elements), and a gate drive unit 13 that drives on / off of each gate element of the bridge circuit 12. The gate drive unit 13 is controlled by the sine wave PWM method and is configured to include a control unit 14 that controls the phase shift amount of the bridge circuit 12. The bridge circuit 12 outputs a 100V single-phase alternating current that is opposite to a single 100V single-phase alternating current, and outputs a 100V / 200V single-phase three-wire sine wave output with the intermediate voltage as a middle line. The same 100V / 200V single-phase three-wire sine wave output is synchronously controlled.

  The underpower detection means 5 constitutes an underpower relay (UPR) together with the output control means 4 and the interconnection relay 9 of the inverter 3, and the system current (instantaneous value) supplied from the system power supply 30 to the load 31 is obtained. Input the detection current of the grid current detector 32 and the detection voltage of the voltage detector 11 (both analog values) to be detected, and the shortage of the generated power supplied from the inverter 3 with respect to the power consumed by the load 31 ( When the power shortage is less than the disconnection set value by comparing the power shortage measurement unit 19 for determining the power shortage) with the power shortage measured by the power shortage measurement unit 19 and the set-off set value (also referred to as a settling value). A power shortage determination unit 20 that outputs the power shortage detection signal Sf to the output control means 4 is provided.

  In the present embodiment, the passive islanding detection means 6 constitutes a voltage phase jump detection type passive islanding prevention device together with the output control means 4, and the detected currents of the current detector 10 and the voltage detector 11. And a detection voltage (both analog values) are respectively input, a phase change detection unit 21 that detects a phase change of the output power of the inverter 3, and a frequency change rate due to the phase change detected by the phase change detection unit 21 is predetermined. When the set value is exceeded, it is determined to be a power failure of the system power supply 30, and the first power failure determination unit 22 that outputs the first power failure detection signal Sj is provided.

  In the present embodiment, the active islanding detection means 7 constitutes a phase shift type active islanding prevention device together with the output control means 4, and includes a phase difference setting unit 23, a phase difference detection unit 24, and a second. The power failure determination unit 25 and a storage unit 26 that stores setting values, detection values, calculations, or determination algorithms used in these units are provided. The phase difference setting unit 23 outputs the system voltage phase of the system power supply 30 and the AC output of the inverter 3 (more specifically, the AC output of the bridge circuit 12) to the control unit 14 of the inverter 3 in accordance with a determination algorithm described later. A set value θs of a phase difference θ (hereinafter referred to as “phase shift amount θ” as appropriate) with respect to the phase of the output current is set, and the set value θs is set at the timing specified by the determination algorithm. Output to. Based on this phase shift amount θ, a phase shift is forcibly applied to the AC output of the inverter 3 to perform isolated operation detection by an active method. The phase difference detection unit 24 inputs the detection current and the detection voltage of the current detector 10 and the voltage detector 11 respectively, and detects the detected value of the phase shift amount θ from the difference between each zero cross point of the input detection current and the detection voltage. θn is detected at a timing defined by the determination algorithm. The second power failure determination unit 25 determines a power failure of the system power supply 30 according to the determination algorithm based on the set value θs and the collected detection value θn, and outputs a second power failure detection signal Sn at the time of power failure determination.

  The phase difference setting unit 23, the phase difference detection unit 24, and the second power failure determination unit 25 of the active isolated operation detecting means 7 are realized by executing arithmetic processing and determination processing described later in software, and the whole For example, it is configured by applying a stored program type computer system such as a microcomputer. Similarly, the phase change detection unit 21 and the first power failure determination unit 22 of the passive islanding detection unit 6, the underpower detection signal Sf of the underpower detection unit 5, and the like are similarly realized by a microcomputer or the like. The detection current and detection voltage (both analog values) of the current detector 10 and the voltage detector 11 are input to the analog port of the microcomputer, converted into a digital signal by the built-in A / D converter, and the phase It is input to the change detection unit 21 and the phase difference detection unit 24. If the microcomputer does not have an analog port, A / D conversion processing may be performed on the current detector 10 and voltage detector 11 side.

  The output control means 4 includes a gate block 15 that controls operation stop of the DC / AC conversion unit 8 and a disconnection control unit 16 that controls opening and closing of the interconnection relay 9. When the gate block 15 receives any one of the power shortage detection signal Sf, the first power failure detection signal Sj, and the second power failure detection signal Sn, the gate block 15 stops operation with respect to the gate drive unit 13 of the DC / AC conversion unit 8. The signal S1 is output, and the operation of the DC / AC converter 8 is stopped. When the disconnection control unit 16 receives any one of the insufficient power detection signal Sf and the second power failure detection signal Sn, the disconnection control unit 16 outputs the disconnection signal S2 to the interconnection relay 9 to open the interconnection relay 9. The interconnection connection between the AC output of the DC / AC conversion unit 8 and the AC power of the system power supply 30 is cut off.

  Hereinafter, the operation of each part of the insufficient power detection unit 5, the passive islanding detection unit 6, and the active islanding detection unit 7, that is, the processing of the islanding operation prevention method of the distributed power generation system according to the present invention will be described. .

  First, the underpower detection means 5 receives the detection current of the system current detector 32 and the detection voltage of the voltage detector 11 as inputs by the underpower measurement unit 19 that detects the system current, and supplies the input to the load 31 from the system power supply 30. The grid power to be calculated is calculated. This system power is power that is supplemented as a shortage of the generated power supplied from the inverter 3 to the load 31, and thus becomes insufficient power in the system 1 of the present invention. The power shortage determining unit 20 sequentially compares the power shortage calculated by the power shortage measuring unit 19 with the set-off set value sequentially in real time, and detects the shortage power below the set-off set value to detect the shortage power. The detection signal Sf is output to the output control means 4. The disconnection set value is set to about 5% of the rated output of the inverter 3. For example, in the case of a 1 kW system, the separation setting value is set to 50 W. Note that the set release value can be changed according to the use environment or the like as appropriate.

  When the output control means 4 receives the insufficient power detection signal Sf, the gate block 15 outputs an operation stop signal S1 to the gate drive unit 13 of the DC / AC conversion unit 8. As a result, the gate drive unit 13 stops the gate drive of the bridge circuit 12 of the DC / AC conversion unit 8, so that the operation of the bridge circuit 12 is stopped and the AC output from the DC / AC conversion unit 8 is stopped. Further, the disconnection control unit 16 outputs the disconnection signal S2 to the interconnection relay 9 to open the interconnection relay 9, and the AC output of the DC / AC conversion unit 8 and the AC power of the system power supply 30 are generated. Since the interconnection connection is cut off, double operation can be prevented.

  Next, the passive islanding detection means 6 will be described. The phase change detection unit 21 receives the detection current (output current of the DC / AC conversion unit 8) and the detection voltage (system voltage) of the current detector 10 and the voltage detector 11, and each of the input detection current and detection voltage is received. The phase difference between the current and voltage in each cycle is detected from the difference between the zero cross points. Since the output of the DC / AC converter 8 is controlled with a power factor = 1 in principle, the phase difference is the same in phase regardless of the impedance of the load 31 when the system power supply is normal and the system power is normal. It becomes. However, when the system power supply 30 fails, the current phase changes (jumps) abruptly according to the impedance of the load 31 at the moment of the power outage, so that the system power outage can be detected by detecting this jump. The first power failure determination unit 22 converts the detected phase difference into a frequency change. For example, when the AC frequency of the system power supply is 60 Hz, the frequency is detected as if it has instantaneously changed to 60 + α (Hz) due to the detection phase difference. Here, α has a positive value for a delayed load and a negative value for a leading load. Next, the first power failure determination unit 22 calculates Δf = | α | / 60 × 100 (%) as the frequency change rate, and when Δf exceeds a predetermined set value, Determine and output the first power failure detection signal Sj. Here, the predetermined set value is in the range of 0.2 to 1.0%. In principle, it can be detected after one cycle (0.0167 seconds) from the system power failure.

  When the output control unit 4 receives the first power failure detection signal Sj, the gate block 15 outputs an operation stop signal S1 to the gate drive unit 13 of the DC / AC conversion unit 8. As a result, the gate drive unit 13 stops the gate drive of the bridge circuit 12 of the DC / AC conversion unit 8, so that the operation of the bridge circuit 12 is stopped and the AC output from the DC / AC conversion unit 8 is stopped. The operation of the DC / AC converter 8 can be stopped within 0.5 seconds after the occurrence of a system power failure.

  Next, the operation of the active islanding detection means 7 will be described with reference to the flowchart shown in FIG. Since the passive islanding detection means 6 cannot detect a phase change when the load impedance is a pure resistance, a system power failure cannot be detected in principle. Therefore, the active islanding detection means 7 complements this. It is means to do. In the present embodiment, the active islanding detection means 7 performs phase shift type active islanding detection. This is because the phase difference is set periodically by the phase difference setting unit 23 to the AC output current of the inverter 3, the phase difference detection unit 24 detects this phase variation, and the second power failure determination unit 25 detects the detected value system. A system power failure is detected by detecting the difference between normal and system power failure. Specifically, it is executed according to the processing procedure and determination algorithm shown in the flowchart of FIG.

  As shown in FIG. 2, the first power failure determination process (# 10 to # 15), the second power failure determination process (# 20 to # 25), the third power failure determination process (# 30 to # 35), and the later It consists of four blocks of processing (# 36, # 37), and the first power failure determination processing (# 10 to # 15) is continued cyclically until the power failure of the system power supply 30 is detected. When a power failure is detected in the determination process (# 10 to # 15) (# 15), the process proceeds to the second power failure determination process (# 20 to # 25) and the second power failure determination process (# 20 to # 25). If a power failure is detected (# 25), the process proceeds to a third power failure determination process (# 30 to # 35), and if a power failure is not detected in the second power failure determination process (# 20 to # 25) (# 25). ), Returning to the first power failure determination processing (# 10 to # 15), and when a power failure is detected in the third power failure determination processing (# 30 to # 35) ( 35), which is the flow to shift to the post-processing (# 36, # 37).

  First, as a pre-process, registration of the threshold value Δθt used in the first to third power failure determination processes is performed in advance. Here, an arbitrary value in the range of 1 ° to 1.4 ° is registered as the threshold Δθt and stored in the storage unit 7. In the present embodiment, through the first to third power failure determination processes, the first set value of the phase difference is fixed at 0 °, the second set value of the phase difference is fixed at 3 °, for example, and the threshold Δθt is also the same value. Is used.

  In the first power failure determination process, the phase of the system voltage of the system power supply 30 is continuously applied to the control unit 14 of the inverter 3 every period (every cycle) during a first period of a predetermined period (eight periods in the present embodiment). And a set value θs of a phase difference θ (hereinafter, appropriately referred to as “phase shift amount θ”) between the output current of the inverter 3 and the AC output of the inverter 3 (more specifically, the AC output of the bridge circuit 12). The phase difference setting unit 23 sets the set value θs to 0 ° of the first set value (# 10), and the set value θs is in the first period of 8 cycles (n = 0 to 7). Synchronously, it is output to the control unit 14 (# 11).

  Next, although not shown in FIG. 2, the control unit 14 controls the gate drive unit 13 so that the phase shift amount θ becomes 0 ° based on the set value θs (= 0 °). Then, the detection current and the detection voltage of the current detector 10 and the voltage detector 11 reflecting the phase control are input to the phase difference detection unit 24. The phase difference detection unit 24 detects the detection value θn of the phase shift amount θ in each cycle n (n = 0 to 7) from the difference between each zero cross point of the input detection current and detection voltage, and temporarily stores it in the storage unit 7. Store (# 11). The progress during the first period is separately monitored by counting up the variable n and determining whether the variable n is 8. In step # 11, eight detection values θn (n = 0 to 7) are acquired, and the first period ends. Next, before shifting to the second period, the phase difference setting unit 23 sets the set value θs to 3 ° which is the second set value (# 12).

  Then, the process proceeds to the second period of the same eight periods as the first period, and the set value θs (= 3 °) is synchronized with the control unit 14 during the second period of eight periods (n = 8 to 15). Is output (# 13). Next, although not shown in FIG. 2, the control unit 14 controls the gate driving unit 13 so that the phase shift amount θ is 3 ° based on the set value θs (= 3 °). Then, the detection current and the detection voltage of the current detector 10 and the voltage detector 11 reflecting the phase control are input to the phase difference detection unit 24. The phase difference detection unit 24 detects the detection value θn of the phase shift amount θ in each cycle n (n = 8 to 15) from the difference between the zero cross points of the input detection current and detection voltage, and temporarily stores them in the storage unit 7. Store (# 13). The progress during the second period is separately monitored by counting up the variable n and determining whether the variable n is 16. In step # 13, eight detection values θn (n = 8 to 15) are acquired, and the second period ends.

  The second power failure determination unit 25 calculates the average value Δθ ave of the difference between the detected values of the first period and the second period of the phase shift amount θ by the following equation 1 (# 14). The detection value θn (n = 0 to 15) is stored in the storage unit 7.

  Instead of using the detected value of the phase shift amount θ in the second period as it is, Δθave is calculated as in step # 14 to obtain the detected value of the phase difference, so that the detected phase fluctuation is caused by a power failure of the system power supply. It is easy to determine whether it is due to the phase control error of the inverter 3. That is, if it is assumed that the phase control error of the inverter 3 occurs in common in the first period and the second period, the phase control error of the inverter 3 is canceled by the difference process of Equation 1, and Δθave Since it becomes equal to the phase difference in the case of no power supply, it is possible to accurately determine the power failure of the system power supply by evaluating Δθave. Furthermore, since Δθave approaches 0 or close to 0 at the time of a power failure of the system power supply without depending on the load impedance, stable power failure determination is possible. In addition, by using detection values for a total of 16 cycles, phase detection errors due to voltage fluctuations and current fluctuations due to instantaneous disturbances can be absorbed, and the possibility of erroneous detection due to the disturbances can be reduced.

  Next, the second power failure determination unit 25 determines the absolute value of the difference between the detected value Δθave of the phase difference and the second set value S (= 3 °), that is, the fluctuation amount of the phase difference that appears at the time of a power failure of the system power supply and the threshold value. The magnitude determination with Δθt is executed in the manner shown in the following equation 2, and the first power failure determination in the first power failure determination processing is performed (# 15). Since the first set value is 0 °, the second set value is equal to the difference between the first set value and the second set value.

  If the inequality shown in Equation 2 is true (YES), that is, if the fluctuation of the phase difference that appears at the time of power failure of the system power supply is greater than or equal to the threshold value, a provisional determination is made that the power supply of the system power supply is lost. The process proceeds to processing (# 20 to # 25).

  In the first power failure determination (# 15), if the inequality shown in Equation 2 is not satisfied (NO), the process returns to step # 10, and the first power failure determination processing (# 10 to # 15) It is repeatedly executed until it is determined.

  When the process proceeds to the second power failure determination process (# 20 to # 25), basically, the same process as the first power failure determination process (# 10 to # 15) is executed.

  In the second power outage determination process (# 25) in the second power outage determination process, if the inequality shown in Equation 2 is true (YES), that is, if the fluctuation of the phase difference that appears at the time of power outage of the system power supply is greater than or equal to the threshold value Then, a temporary determination with a power failure of the system power supply is performed, and the process proceeds to a third power failure determination process (# 30 to # 35). Further, in the second power failure determination (# 25), when the inequality shown in Equation 2 is not satisfied (NO), the process returns to the head (# 10) of the first power failure determination processing, and the first power failure determination processing (# 10). To # 15) are repeated until the power failure of the system power supply is determined again.

  When shifting to the third power failure determination process (# 30 to # 35), basically, the first power failure determination process (# 10 to # 15) and the second power failure determination process (# 20 to # 25) The same process is executed.

  In the second power outage determination process (# 35) in the third power outage determination process, if the inequality shown in Equation 2 is true (YES), that is, if the variation of the phase difference that appears at the time of the power outage of the system power supply is greater than or equal to the threshold value Then, a final determination is made that the system power supply is interrupted, and the process proceeds to post processing (# 36, # 37). Further, in the third power failure determination (# 35), when the inequality shown in Equation 2 is not satisfied (NO), the process returns to the head (# 20) of the second power failure determination processing, and the second power failure determination processing (# 20). To # 25) are repeated until the power failure of the system power supply is determined again.

  When the process proceeds to post-processing, first, the internal state is set to the isolated operation detection state, and the second power failure determination unit 25 outputs the second power failure detection signal Sn to the output control means 4 (# 36). When the output control means 4 receives the second power failure detection signal Sn, the output control means 4 performs an output current immediate stop process on the inverter 3 (# 37). Specifically, the gate block 15 outputs an operation stop signal S <b> 1 to the gate drive unit 13 of the DC / AC conversion unit 8. As a result, the gate drive unit 13 stops the gate drive of the bridge circuit 12 of the DC / AC conversion unit 8, so that the operation of the bridge circuit 12 is stopped and the AC output from the DC / AC conversion unit 8 is stopped. Further, the disconnection control unit 16 outputs the disconnection signal S2 to the interconnection relay 9 to open the interconnection relay 9, and the AC output of the DC / AC conversion unit 8 and the AC power of the system power supply 30 are generated. Since the interconnection connection is cut off, double operation can be prevented.

  Next, the time required for the active islanding detection means 7 to detect the islanding state is examined. As described in detail with reference to FIG. 2, the active type isolated operation detection process by the system 1 of the present invention includes the first power failure determination process (# 10 to # 15) and the second power failure determination process (# 20). To # 25), the third power failure determination process (# 30 to # 35) is a main time consuming element, and each power failure determination process is equally composed of a first period and a second period of 8 cycles. Here, when the frequency of the system power supply is 60 Hz, one cycle is about 0.01667 seconds (1/60 seconds), but the output of the set value θs by the phase difference setting unit 23 and the bridge circuit 12 based on the set value θs. Since the phase difference detection by the phase difference detection unit 24 is completed within one cycle, the time required from the occurrence of a power failure to the detection of the power failure can be calculated by the number of cycles in between.

  The first power failure determination process (first period and second period) is repeatedly executed until the power failure is temporarily determined in the first power failure determination (# 15), and the power failure is temporarily determined in the first power failure determination (# 15). Then, the process of sequentially executing the second power failure determination process and the third power failure determination process is followed. In this case, since a power failure has occurred, the determination of the power failure is naturally made in the second and third power failure determinations (# 25, # 35). The number of cycles required until the final determination of the power failure is made in the third power failure determination (# 35) depends on the timing of the power failure occurring in the first power failure determination processing (the first period and the second period). . In this case, it also depends on the load impedance and the first set value. When the load impedance is resistive and the first set value is 0 °, even if a power failure occurs during the first period of the first power failure determination process, the phase detection value during the first period does not vary. Therefore, a power failure is detected in the subsequent first power failure determination (# 15). If a power outage occurs during the second period of the first power outage determination process, the power outage appears only in some of the detected values in the 8 cycles, so a power outage occurs in the second half of the second period in relation to the threshold value. In such a case, the power failure may not be detected in the subsequent first power failure determination (# 15). In that case, the first power failure determination process (the first period and the second period) will be repeated again. In the first power failure determination process, approximately 8 to 24 cycles are required from the occurrence of a power failure to the detection of the power failure (it may be shorter than 8 cycles), and 40 to 56 cycles are required throughout all the power failure determination processes. Is 60 Hz, a power failure can be detected within a range of 0.667 seconds to 0.933 seconds. As a result, it is possible to satisfy the constraint that the operation time required for preventing the independent operation of the active system in the power system interconnection technical requirement guideline is 0.5 seconds or more and within 1 second.

Second Embodiment
Next, the system 40 of the present invention according to the second embodiment will be described. As shown in FIG. 3, the system 40 of the present invention has, as a basic configuration, the generator 2 that generates DC power and the DC power generated by the generator 2 as a predetermined voltage, as in the first embodiment. Inverter 3 for converting to AC power of frequency, output control means 4 for controlling operation of inverter 3 and interconnection connection with system power supply 30, insufficient power detection means 5, passive islanding detection means 6, active Single operation detection means 7. A duplicate description of the parts common to the first embodiment is omitted.

  The first difference from the first embodiment is that the generator 2 is a cogeneration type generator that generates heat in addition to electric power such as a fuel cell or a micro gas turbine. 2 is provided with a heat exchanger 41 that recovers the exhaust heat of No. 2 and an exhaust heat utilization hot water supply / heating unit 42 for using the exhaust heat recovered by the heat exchanger 41 for hot water supply or heating. Here, the heat exchanger 41 and the exhaust heat utilization hot water supply / heating unit 42 are well-known units used in a general cogeneration system, and detailed description thereof is omitted.

  The second difference is that the generated power target value setting means for setting the generated power target value having a predetermined margin so as to be in a more insufficient power state with respect to the set-off set value used in the insufficient power detection means 5. 18, and the control unit 14 of the DC / AC conversion unit 8 controls the output so that the AC output does not fall below the generated power target value. The third difference is that, as part of the load 31, an electric heater 43 capable of supplying heat to the exhaust heat utilization hot water supply / heating unit 42 is provided, and the output control means 4 controls the heater of the electric heater 43. It is a point provided with a portion 17.

  In the first embodiment, since the insufficient power detection means 5 is always operated in an insufficient power state of 5% or more of the generated power output (rated value), the generated power output and the load are not in the reverse power flow state. Is close to the equilibrium state of 5% of rated output (disconnection set value) or less, even if the system power supply 30 is normal, the isolated operation prevention function is activated and the operation of the DC / AC converter 8 is stopped, and the output As a result, the current is cut off. Therefore, under circumstances such as when the load fluctuation is severe, the emergency stop state of the system 1 of the present invention may frequently occur. Since it is not preferable in terms of power generation efficiency when the generation system is repeatedly started and stopped, it is preferable to prevent this in a power generation system without a reverse power flow. In the second embodiment, due to the second difference, the control unit 14 of the DC / AC conversion unit 8 outputs so that the AC output is maintained at or above the generated power target value set by the generated power target value setting means 18. By controlling, it is avoided that the DC / AC conversion part 8 falls into an operation stop. The generated power target value is set in advance assuming the maximum value of the load fluctuation so that the insufficient power becomes 5% or more of the rated output, for example. As a result, in the second embodiment, the inventive system 40 can operate stably.

  By the way, it is preferable in terms of operation efficiency that the generator 2 is operated at a constant output with the output fixed at, for example, a rated output. Therefore, when the generator 2 is operating at a constant power output, if a load change occurs, the insufficient power will change following the load change. When it is difficult to predict the load fluctuation in advance, there is a possibility that the shortage of power is reduced due to a decrease in the load, and an equilibrium state that is equal to or lower than the set value of the disconnection occurs, causing the DC / AC conversion unit 8 to stop operating. Also, in setting the generated power target value, if an excessive margin is provided with respect to the set-off set value, the insufficient power state is always set higher, so that the system power usage ratio increases, and the distributed power generation system The merit of introduction decreases. Therefore, it is preferable to set the generated power target value with the margin as small as possible, but the risk of load fluctuation increases as described above.

  In the second embodiment, the heater control unit 17 in the output control unit 4 sets the insufficient power calculated by the insufficient power measurement unit 19 of the insufficient power detection unit 5 and the generated power target value setting unit 18 sets the generated power target value. When the shortage power falls below the shortage power set value, the excess power consumed by the electric heater 43 is consumed. The electric heater is controlled to turn on and off. Further, when the output of the electric heater 43 is variable, the output is changed according to the surplus power. Due to such heater control, the shortage power state always has a certain margin with respect to the disconnection set value, so that the system 40 of the present invention can operate stably, and not only consumes the surplus power but also discharges it. Since it can utilize as heat energy in the heat utilization hot water supply / heating unit 42, the overall energy efficiency can be improved.

  Hereinafter, another embodiment will be described.

  <1> In each of the above embodiments, the passive islanding detection means 6 has a voltage phase jump detection type passive islanding detection function, and the active islanding detection means 7 is a phase shift type active islanding operation. Although a configuration having a detection function is adopted, the isolated operation detection method is not limited to the method of the above embodiment in any of the passive method and the active method, and may be replaced with another method. However, other types may be used in combination.

  <2> The disconnection set value used by the insufficient power detection means 5 is not limited to the values exemplified in the above embodiment.

  Further, in the processing flow of the active islanding detection means 7, the processing procedure and the set values and threshold values to be used are not limited to the procedures and values exemplified in the above embodiment. For example, in the first to third power failure determination processes, the first set value is fixed to 0 ° and the second set value S is fixed to 3 °, but may be other than 0 ° and 3 °, respectively. Furthermore, the first to third power failure determination processes may be combined into one time to adjust the number of cycles during the first period and the second period.

  <3> In the second embodiment, the generator 2 is a cogeneration generator that generates heat in addition to electric power, such as a fuel cell or a micro gas turbine, and recovers exhaust heat of the generator 2. Although it was set as the structure provided with the heat exchanger 41 and the waste heat utilization hot water supply heating unit 42 for utilizing the waste heat collect | recovered with the heat exchanger 41 for hot water supply or heating, the generator 2 is not necessarily a cogeneration type. It doesn't matter. In this case, the heat energy output by the electric heater 43 may be used by other than the exhaust heat utilization hot water supply / heating unit 42.

  <4> In the second embodiment, the power generation target value setting unit 18 is provided, and the control unit 14 of the DC / AC conversion unit 8 uses the generated power target value set by the power generation power target value setting unit 18 as the AC output. Although the configuration (second difference) for controlling output so as not to fall below is adopted, only the configuration may be added to the system of the present invention of the first embodiment.

  <5> In the above embodiment, it is assumed that the inverter 3 outputs 100 V / 200 V of a single-phase three-wire sine wave output with a frequency of 60 Hz, but the electrical system, output voltage, and frequency of the AC output of the inverter 3 are The electrical system, output voltage, and frequency of the above embodiment are not limited.

1 is a circuit block diagram showing an embodiment of a distributed power generation system according to the present invention. The flowchart which shows an example of the active islanding detection process of the distributed power generation system which concerns on this invention The circuit block diagram which shows other embodiment of the distributed power generation system which concerns on this invention

Explanation of symbols

1, 40: Distributed generation system according to the present invention 2: Generator 3: Inverter (power converter)
4: Output control means 5: Underpower detection means 6: Passive islanding detection means 7: Active islanding detection means 8: DC / AC conversion unit 9: Interconnection relay 10: Current detector 11: Voltage detector 12 : Bridge circuit 13: Gate drive unit 14: Control unit 15: Gate block 16: Disconnection control unit 17: Heater control unit 18: Generated power target value setting means 19: Underpower measurement unit 20: Underpower determination unit 21: Phase Change detection unit 22: first power failure determination unit 23: phase difference setting unit 24: phase difference detection unit 25: second power failure determination unit 26: storage unit 30: system power supply 31: load 32: system current detector 41: heat exchange Unit 42: Waste heat utilization hot water supply / heating unit 43: Electric heater Sf: Underpower detection signal Sj: First power failure detection signal Sn: Second power failure detection signal S1: Operation stop signal S : Disconnection signal

Claims (6)

A distributed power generation system that can be connected to a grid power source,
A distributed power generation system comprising a power shortage relay, a passive islanding prevention device, and an active islanding prevention device, and configured not to allow reverse power flow to the system power supply side. A generator for generating DC power;
A power converter that converts the DC power generated by the generator into AC power having a predetermined voltage and frequency;
Output control means for controlling the operation of the power converter and the interconnection connection with the system power supply;
Underpower detection means for detecting that the power shortage represented by the difference obtained by subtracting the output power of the power conversion device from the power consumption of the load falls below a predetermined disconnection set value and outputting a power shortage detection signal;
A passive islanding detection means for detecting a change appearing in a system voltage at the time of a power failure of the system power supply and outputting a first power failure detection signal;
An active islanding detection means for detecting a change appearing at the time of a power failure of the system power supply based on a predetermined characteristic variation applied to the output power of the power converter, and outputting a second power failure detection signal;
The underpower relay is configured such that, based on the underpower detection signal output by the underpower detection means, the output control means opens a relay that interconnects the power converter and the system power supply. ,
The passive islanding prevention device is a relay that connects the power converter and the grid power source to the output control unit based on the first power failure detection signal output by the passive islanding detection unit. It is configured to perform at least one of opening or stopping the operation of the power converter,
The active islanding prevention device includes a relay that connects the power converter and the grid power source to the power control unit based on the second power failure detection signal output from the active islanding detection unit. The distributed power generation system according to claim 1, wherein the distributed power generation system is configured to perform at least one of opening and operation stop of the power conversion device.   The generated power output is based on the generated power target value set with a predetermined margin so as to be in a more insufficient power state with respect to the set-off set value which is a reference value for detecting the insufficient power of the insufficient power relay. The distributed power generation system according to claim 1, wherein the power generation system is controlled. A heater and a heater control unit for controlling the operation of the heater;
4. The distributed type according to claim 3, wherein when the surplus power is generated with respect to the power generation output of the generated power target value, the heater control unit controls the surplus power to be consumed by the heater. Power generation system.   The distributed power generation system according to any one of claims 1 to 4, further comprising a cogeneration type generator. A method for preventing isolated operation of a distributed power generation system that is connected to a system power supply without reverse power flow,
The distributed power generation system comprises a shortage relay, a passive islanding prevention device and an active islanding prevention device,
In a state where the occurrence of reverse power flow from the distributed power generation system to the system power supply side at the time of normal operation of the system power supply by an insufficient power relay,
A distributed power generation system isolated by detecting a power failure of the system power supply by the passive islanding prevention device and the active islanding prevention device to prevent an isolated operation state of the distributed generation system Driving prevention method.

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