JP2004279321A - Power-measuring device, reverse power flow detector, and interconnected system power generation plant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power-measuring device which increases the accuracy of measurement of effective power using a simple circuit configuration, a reverse power flow detector which increases the accuracy of detection of a reverse power flow using a simple circuit configuration, and to provide an interconnected system power generation plant. <P>SOLUTION: The interconnected system power generation plant 50, connected to a power supply line 24 which connects a load 16 to a commercial power system 21, is interconnected to the commercial system 21 and supplies power to the load 16. In the plant 50, a microcomputer 41 samples the value of AC voltage applied to the load 16, and the value of the alternating current flowing in the supply line 24 between a connection point to which the plant 50 is connected and the commercial system 21, as digital data a plurality of times in a single period of the AC voltage, and multiplies the values of sampled voltage data on the AC voltage with the values of sampled current data, integrates the multiplication results over a single period of the AC voltage, and judges whether or not a reverse power flow into the commercial system 21 is occuring, based on effective power found on the basis of the integration result. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power measurement device for obtaining active power, a reverse power flow detection device, and a grid-connected power generation device.
[0002]
[Prior art]
In recent years, cogeneration systems that use a gas engine to drive a generator and use both generated heat and electric power have become widespread. In this cogeneration system, there is known a cogeneration system that functions as a grid-connected power generation device that connects power generated by a generator to commercial power and supplies the load to a load, thereby achieving efficient energy utilization. And Patent Document 1.).
[0003]
In such a grid-connected power generation device, the generated power is converted into a frequency, a phase, and a voltage corresponding to the commercial power via the inverter device, and the power is connected to the commercial power system to supply the power to the load. .
[0004]
In this grid-connected power generation apparatus, there is known a power generation apparatus in which a load supply power supplied to a load is compared with a generated power to detect a reverse power flow.
[0005]
The load supply power is, for example, an analog first effective current detection circuit that detects an effective value of an alternating current supplied to the load, and an analog first effective current detection circuit that detects the effective value of an alternating voltage applied to the load. A voltage detection circuit, a first multiplier for multiplying an output of the first effective current detection circuit and an output of the first effective voltage detection circuit, and a position of an AC current supplied to the load and an AC voltage applied to the load. An analog first power factor measuring device that measures a power factor based on a phase difference, and a first computing device that calculates active power by multiplying an output of the first multiplier by an output of the first power factor measuring device. Is measured by a power measuring device having:
[0006]
The generated power is, for example, an analog-type second effective current detection circuit that detects an effective value of an alternating current on the output side of the grid-connected power generation device, similarly to the measurement of the load supply power, and a grid-connected power generation device. An analog second effective voltage detection circuit for detecting an effective value of the AC voltage on the output side of the output terminal; a second multiplier for multiplying an output of the second effective current detection circuit and an output of the second effective voltage detection circuit; A second analog power factor measuring device for measuring a power factor based on a phase difference between an AC current on the output side of the grid-connected power generation device and an AC voltage on the output side of the grid-connected power generation device, and a second multiplier Is multiplied by the output of the second power factor measuring device to calculate the active power.
[0007]
[Patent Document 1]
JP 2001-268799 A
[0008]
[Problems to be solved by the invention]
However, the above-described power measurement device requires an effective current detection circuit, an effective voltage detection circuit, a multiplier, a power factor measurement device, an arithmetic unit, and the like, so that the number of components is large and the circuit is complicated. There is. Particularly, in the above-described grid-connected power generation device, since the load supply power and the generated power are detected, there is a problem that a circuit for detecting the reverse power flow becomes complicated.
[0009]
Further, in the above-described power measurement device, the power factor is obtained based on the phase difference between the AC current and the AC voltage, and the active power is obtained by multiplying the effective voltage value, the effective current value, and the power factor. In order to accurately determine the power, the power factor (that is, the phase difference between the AC current and the AC voltage) must be accurately determined. However, when the load suddenly fluctuates or the current waveform is distorted, it is difficult to accurately determine the power factor (phase difference), and there is a problem that the measurement accuracy of the active power is inferior. In particular, in the above-described grid-connected power generation device, when the load suddenly decreases, the power factor on the load side fluctuates and the current waveform is distorted, so that the measurement accuracy of the active power is poor, and the detection accuracy of the reverse power flow is low. There is a problem of inferiority.
[0010]
Therefore, an object of the present invention is to provide a power measuring device that improves the accuracy of measuring the active power with a simple circuit configuration, a reverse power flow detecting device that improves the detection accuracy of a reverse power flow with a simple circuit configuration, and a grid-connected power generation. It is to provide a device.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a sampling means for sampling a value of an AC voltage and a value of an AC current of a line to be measured as digital data a plurality of times within one cycle of the AC voltage, and a value of the voltage sampling data of the AC voltage Multiplying means for multiplying the value of the AC current by the current sampling data corresponding to the value of the voltage sampling data; and integrating means for integrating the multiplication result by the multiplying means over a predetermined cycle of the AC voltage. Power calculating means for obtaining active power based on the result of integration by the integrating means.
[0012]
In this case, the power calculation means may determine the active power by dividing the integration result by the integration means by the number of times of sampling within the predetermined period.
[0013]
Further, the sampling means, the multiplying means, the integrating means, and the power calculating means may be constituted by a microcomputer.
[0014]
A power supply line connecting a commercial power system and a load is connected to a system interconnection power generation device that is connected to the commercial power system and supplies power to a load, and a value of an AC voltage applied to the load, and Sampling means for sampling the value of the AC current of the power supply line between the connection point to which the grid-connected power generation device is connected and the commercial power system as digital data a plurality of times within one cycle of the AC voltage; Multiplying means for multiplying a value of the voltage sampling data of the AC voltage by a value of the current sampling data of the AC current corresponding to the value of the voltage sampling data; and a multiplication result by the multiplying means over a predetermined period of the AC voltage. Integrating means for calculating the active power based on the result of integration by the integrating means; and active power determined by the power calculating means. Zui and, is characterized in that a backward flow determining means for determining whether or not the reverse power flow to the commercial power system.
[0015]
In this case, the power calculation means may determine the active power by dividing the integration result by the integration means by the number of times of sampling within the predetermined period.
[0016]
The reverse power flow determining means may determine that a reverse power flow is occurring in the commercial power system when the active power obtained by the power calculating means has a negative value.
[0017]
Further, the sampling means, the multiplying means, the integrating means, the power calculating means, and the reverse power flow judging means may be constituted by a microcomputer.
[0018]
Further, in a grid-connected power generator connected to a power supply line connecting a commercial power system and a load and supplying power to the load in connection with the commercial power system, a value of an AC voltage applied to the load, Sampling means for sampling an AC current value of a power supply line between a connection point to which the grid-connected power generation device is connected and the commercial power system as digital data a plurality of times within one cycle of the AC voltage; Multiplying means for multiplying the value of the voltage sampling data of the AC voltage by the value of the current sampling data of the AC current corresponding to the value of the voltage sampling data; Integrating means for integrating over the entire range, power calculating means for obtaining active power based on the result of integration by the integrating means, and power calculating means for calculating the active power. Based on the power, it is characterized in that a backward flow determining means for determining whether or not the reverse power flow to the commercial power system.
[0019]
In this case, the power calculation means may determine the active power by dividing the integration result by the integration means by the number of times of sampling within the predetermined period.
[0020]
The reverse power flow determining means may determine that a reverse power flow is occurring in the commercial power system when the active power obtained by the power calculating means has a negative value.
[0021]
Further, the sampling means, the multiplying means, the integrating means, the power calculating means, and the reverse power flow judging means may be constituted by a microcomputer.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0023]
FIG. 1 is a block diagram of a cogeneration system mainly including power supply including a grid-connected power generation device according to an embodiment of the present invention. FIG. 2 is a configuration diagram of a grid-connected power generation device according to an embodiment of the present invention.
[0024]
The cogeneration system 100 is roughly divided into a gas engine 11, a power transmission mechanism 12, an engine controller 13, an exhaust heat utilization unit 14, a distribution board 15, a load 16, and a grid-connected power generator 50. .
[0025]
The grid-connected power generation device 50 includes a power generator 17, an inverter device 18, and a control device 19.
[0026]
The gas engine 11 burns a primary energy source 20 such as city gas under the control of an engine control unit 13 and drives a generator 17 via a power transmission mechanism unit 12 including a timing belt and a pulley. In parallel with this, the gas engine 11 supplies the generated heat as exhaust heat to an exhaust heat utilization unit 14 such as a water heater (not shown).
[0027]
The generator 17 is driven by the gas engine 11 via the power transmission mechanism 12, and generates three-phase AC power.
[0028]
The inverter device 18 converts the AC power supplied from the generator 17 into the same frequency as the commercial power system 21 (for example, 50 Hz or 60 Hz) in accordance with a switching signal supplied from a switching element drive circuit (not shown) in the control device 19. ) To AC power.
[0029]
In this case, the engine control unit 13 sets the number of revolutions of the gas engine 11 in accordance with the amount of power supplied to the load 16. Therefore, a signal corresponding to the number of rotations of the generator 17 or the number of rotations of the gas engine 11 is input to the control device 19 of the grid-connected power generation device 50.
[0030]
In FIG. 2, a commercial power system 21 is connected to loads 16a, 16b, 16c via a power supply line 24 via a connection point breaker 22 and load breakers 23a, 23b, 23c.
[0031]
The grid-connected power generator 50 is connected to a power supply line 24 connecting the commercial power system 21 and the load 16 via a power-generating breaker 25 via a power-generating power supply line 26, and is connected to the commercial power system 21. It is configured to be able to supply power to the load 16 in a system.
[0032]
The commercial power system 21 and the system interconnection generator 50 are, for example, single-phase three-wire 100V / 200V AC power supplies.
[0033]
The power supply lines 24 correspond to the R-phase, O-phase, and T-phases of the commercial power system 21 from three lines of an R-phase power supply line 24a, an O-phase power supply line 24b, and a T-phase power supply line 24c. Become. For example, the voltage between the RO lines is 100 V AC, the voltage between the TO lines is 100 V AC, and the voltage between the RT lines is 200 V AC.
[0034]
The power generation-side power supply lines 26 correspond to the R 'phase, O' phase, and T 'phase of the grid-connected power generation device 50, and correspond to the R' phase power supply lines 26a, the O 'phase power supply lines 26b, and the T' phase. 'Consists of three lines of the phase power supply line 26c. For example, the R'-O 'line voltage is 100V AC, the T'-O' line voltage is 100V AC, and the R'-T 'line voltage is 200V AC.
[0035]
The load 16a is connected to the R-phase power supply line 24a and the O-phase power supply line 24b, and receives an AC voltage of 100V. The load 16b is connected to the O-phase power supply line 24b and the T-phase power supply line 24c, and receives an AC voltage of 100V. The load 16c is connected to the R-phase power supply line 24a and the T-phase power supply line 24c, and is applied with an AC voltage of 200V.
[0036]
The loads 24a and 24b are, for example, electric appliances such as refrigerators. The load 24c is, for example, an electric appliance such as an air conditioner.
[0037]
The breakers 22, 23a, 23b, 23c, 25 are stored in the distribution board 15 (FIG. 1). The interconnection point breaker 22 blocks an overcurrent from the commercial power system 21 to the load 16. The load breakers 23a, 23b, and 23c block overcurrents from the commercial power system 21 or the grid-connected power generator 50 to the loads 16a, 16b, and 16c. The power generation breaker 25 blocks an overcurrent from the grid-connected power generation device 50 to the load 16.
[0038]
The inverter device 18 of the grid-connected power generation device 50 includes a rectifier circuit 31 in which diodes are connected in a three-phase bridge, a smoothing capacitor 32, a booster circuit 33, an inverter circuit 34, and a filter circuit 35.
[0039]
The boosting circuit 33 includes a boosting reactor 33a, a boosting switching element (for example, IGBT) 33b, a backflow prevention diode 33c, and an electrolytic capacitor 33d.
[0040]
The inverter circuit 34 includes switching elements Q1 to Q4 connected in a bridge. The switching elements Q1 to Q4 are, for example, IGBTs.
[0041]
The filter circuit 35 includes current-smoothing reactors 35a and 35b and a capacitor 35c.
[0042]
The power (three-phase AC power) generated by the generator 17 is subjected to AC / DC conversion via a rectifier circuit 31, is smoothed by a smoothing capacitor 32, and is output as DC power. Then, the output DC power is boosted by the booster circuit 33. In the booster circuit 33, boosting is performed by the switching operation of the boosting switching element 33b according to the switching signal output from the switching signal output circuit of the control device 19.
[0043]
The inverter circuit 34 converts the DC power supplied from the generator 17 side to the same frequency (for example, 50 Hz or 60 Hz) as the commercial power system 21 in accordance with the switching signal supplied from the switching element drive circuit in the control device 19. Convert to AC power.
[0044]
When the power converted to AC by the inverter circuit 34 is supplied to the load 16, the power converted to AC by the inverter circuit 34 is supplied to the load 16 a via the filter circuit 35, the power generation breaker and the load breakers 23 a, 23 b, and 23 c. , 16b, 16c. At this time, the AC power output from the inverter circuit 34 passes through the filter circuit 35 to remove harmonic components, and is output as a sine wave AC power from a PWM (Pulse Width Modulation) wave. Here, the output voltage of the inverter circuit 34 is synchronized with the voltage of the commercial power system 21.
[0045]
The control device 19 includes an R-phase power supply line 21 a between one microcomputer (hereinafter referred to as “microcomputer”) 41, a connection point P <b> 1 to which the grid-connected power generation device 50 is connected, and the commercial power system 21. A current sensor (CT) 42 for detecting the AC current IR, and a current for detecting the AC current IT of the T-phase power supply line 24c between the connection point P2 to which the grid-connected power generation device 50 is connected and the commercial power system 21. It includes a sensor 43, a voltage sensor (PT) 44 for detecting a voltage VR between the R and O lines, and a voltage sensor 45 for detecting a voltage VT between the T and O lines. Further, the control device 19 includes a power generation-side current sensor 46 that detects an output current (alternating current) IR ′ of the grid-connected power generation device 50. The power generation side current sensor 46 is provided on the R′-phase power supply line 26a.
[0046]
The voltage sensors 44 and 45 are provided between the filter circuit 35 and the power generation breaker 25. Specifically, one end of the voltage sensor 44 is connected to the R'-phase power supply line 26a, and the other end is connected to the O'-phase power supply line 26b. Further, one end of the voltage sensor 45 is connected to the O′-phase power supply line 26b, and the other end is connected to the T′-phase power supply line 26c. The voltage sensors 44 and 45 detect the R′-O ′ line voltage and the T′-O ′ line voltage which are the output voltages of the grid-connected power generation device 50. Since it can be regarded as having the same phase, the same frequency, and the same voltage, the AC line voltage VR and the TO line voltage VT of the commercial power system 21, that is, the AC voltage applied to the load 16 are substantially detected. It will be. Note that one end of the voltage sensor 44 may be connected to the R-phase power supply line 24a, and the other end may be connected to the O-phase power supply line 24b. Further, one end of the voltage sensor 45 may be connected to the O-phase power supply line 24b, and the other end may be connected to the T-phase power supply line 24c.
[0047]
The microcomputer 41 includes a switching element drive circuit (not shown) that outputs a switching signal to the switching elements Q1 to Q4 of the inverter circuit 34, and a switching signal output circuit (not shown) that outputs a switching signal to the boosting switching element 33b of the booster circuit 33. And
[0048]
The microcomputer 41 captures values detected by the current sensors 42, 43, 46 and the voltage sensors 44, 45.
[0049]
FIG. 3 shows an electric circuit for taking values detected by the current sensor and the voltage sensor into the microcomputer.
[0050]
The values of the currents IR, IT, IR 'detected by the current sensors 42, 43, 46 are converted into voltage signals by current detection circuits 53, 54, 55, respectively, and the A / D input ports 63, 64 of the microcomputer 41. , 65 are applied.
[0051]
The current detection circuit 53 includes resistors R1, R2, R3, R4, a capacitor C1, and diodes D1, D2. The DC voltage Vcc (for example, 5 [V]) is applied to the current detection circuit 53. Then, when the current IR of the power supply line 42a is 0 [A], the values of the resistors R2, R3, R4, etc. are set so that the voltage becomes Vcc / 2 (for example, 2.5 [V]). I have. The current detection circuits 54 and 55 have the same configuration and operate in the same manner as the current detection circuit 53. Therefore, the same reference numerals are given and the description is omitted.
[0052]
The values of the voltages VR and VT detected by the voltage sensors 44 and 45 are converted into voltage signals by the voltage detection circuits 51 and 52, respectively, and applied to the A / D input ports 61 and 62 of the microcomputer 41, respectively.
[0053]
The voltage detection circuit 51 includes resistors R11, R12, R13, R14, capacitors C11, C12, and diodes D11, D12. The DC voltage Vcc (for example, 5 [V]) is applied to the voltage detection circuit 51. Then, the values of the resistors R12, R13, R14 and the like are set so that the voltage Vcc / 2 (for example, 2.5 [V]) when the voltage VR between the R'-O 'lines is 0 [V]. Have been. The voltage detection circuit 52 has the same configuration and operates in the same manner as the voltage detection circuit 51.
[0054]
FIG. 4 shows a voltage waveform of an AC voltage and a current waveform of an AC current taken into the microcomputer 41, for example. FIG. 4A shows a voltage waveform, and FIG. 4B shows a current waveform.
[0055]
As shown in FIG. 4, the microcomputer 41 converts the voltage signals (that is, the values of the AC voltages VR and VT) applied to the A / D input ports 61 and 62 into a predetermined period within one cycle of the AC voltages VR and VT. Sampling is performed a plurality of times at a sampling interval Δt, and the result of the sampling is A / D converted and obtained as digital data.
[0056]
Further, the microcomputer 41 converts the voltage signals applied to the A / D input ports 63, 64, 65 (that is, the values of the AC currents IR, IT, IR ') within one cycle of the AC voltages VR, VT. Sampling is performed a plurality of times at a sampling interval Δt, and the result of the sampling is A / D converted and obtained as digital data.
[0057]
The sampling of the values of the AC voltages VR and VT and the values of the AC currents IR, IT and IR 'are performed synchronously.
[0058]
The microcomputer 41 (FIG. 2) includes a CPU, a ROM, and a RAM (not shown). The CPU performs various calculations, controls input / output of signals, and calculates calculation results to the RAM based on a control program stored in the ROM. Control of the storage of the data.
[0059]
In the present embodiment, the microcomputer 41 determines the active power based on the value of the AC voltage VR and the value of the sampling data of the AC current IR. Further, the microcomputer 41 obtains the active power based on the value of the AC voltage VT and the value of the sampling data of the AC current IT. Further, the microcomputer 41 determines the active power based on the value of the AC voltage VR and the value of the sampling data of the AC current IR ′.
[0060]
Further, the microcomputer 41 detects a reverse power flow to the commercial power system 21 based on the active power obtained based on the values of the sampling data of the AC voltages VR and VT and the AC currents IR and IT.
[0061]
That is, the control device 19 functions as a power measuring device and also functions as a reverse power flow detecting device.
[0062]
Hereinafter, the control operation of the microcomputer 41 for obtaining the active power using the values of the AC voltages VR and VT and the values of the AC currents IR and IT based on the control program of the microcomputer 41 will be described with reference to the flowchart shown in FIG. .
[0063]
First, the microcomputer 41 determines whether or not the grid-connected power generation device 50 is in operation (step S1). That is, the microcomputer 41 does not take in the values of the AC voltages VR and VT and the values of the AC currents IR and IT immediately after the start of the operation.
[0064]
When the grid-connected power generation device 50 is not at the start of operation (Step S1; No), since the microcomputer 41 has taken in the values of the AC voltages VR and VT and the values of the AC currents IR and IT, the A / D conversion ends. It is determined whether or not it has been performed (step S2). If the A / D conversion has not been completed (step S2; No), step S1 is determined again.
[0065]
When the A / D conversion is completed (Step S2; Yes), the microcomputer 41 converts the value of the digital voltage sampling data indicating the value of the AC voltage VR obtained by the A / D conversion into the value of the voltage sampling data. The corresponding AC current IR is multiplied by the value of the current sampling data. Next, the microcomputer 41 integrates the multiplication result (step S3). For example, as shown in FIG. 4, the value Vn of the voltage sampling data is multiplied by the value In of the current sampling data corresponding to the value Vn of the voltage sampling data.
[0066]
Similarly, the microcomputer 41 calculates the value of the digital voltage sampling data indicating the value of the AC voltage VT obtained by the A / D conversion, the value of the current sampling data of the AC current IT corresponding to the value of the voltage sampling data, and Multiply by Next, the microcomputer 41 integrates the multiplication result (step S4).
[0067]
Next, the microcomputer 41 monitors one of the AC voltages VR and VT after starting the integration, and determines whether a predetermined cycle (for example, one cycle) of the AC voltage has elapsed. (Step S5).
[0068]
For example, as shown in FIG. 4, the microcomputer 41 monitors zero cross points X and X 'at which the AC voltage VR or VT switches from a negative value to a positive value. The microcomputer 41 sets XX ′ between the zero-cross points as one cycle. Then, the accumulation is started from the zero cross point X (X ′).
[0069]
That is, in step S5, it is determined whether one cycle set in this way has elapsed.
[0070]
If one cycle has not elapsed (Step S5; No), the microcomputer 41 starts A / D conversion of the R-phase system voltage, that is, the instantaneous value of the AC voltage detected by the voltage sensor 44 (Step S6). Similarly, the microcomputer 41 starts A / D conversion of the T-phase system voltage, that is, the instantaneous value of the AC voltage detected by the voltage sensor 45 (step S7).
[0071]
Further, A / D conversion of the instantaneous value of the R-phase system current, that is, the AC current detected by the current sensor 42 is started (step S8). Similarly, the microcomputer 41 starts A / D conversion of the T-phase system current, that is, the instantaneous value of the AC current detected by the current sensor 43 (step S9). After the processing in step S9, the process returns to the determination in step S1.
[0072]
When the system interconnection power generation device 50 is in operation (Step S1; Yes), the microcomputer 41 proceeds to the process of Step S6.
[0073]
If one cycle has elapsed in step S5, the microcomputer 41 obtains the active power A based on the integration result obtained over one cycle of the AC voltage in step S3 (step S10). Specifically, the active power A is obtained by dividing the integration result obtained in step S3 by the number of times of sampling in one cycle.
[0074]
Further, the microcomputer 41 obtains the active power B based on the integration result obtained over one cycle of the AC voltage in step S4. Specifically, the active power B is obtained by dividing the integration result obtained in step S4 by the number of times of sampling in one cycle.
[0075]
Then, the microcomputer 41 stores the calculated active powers A and B in a RAM (register) (not shown) (step S11).
[0076]
The microcomputer 41 determines whether or not reverse power flows to the commercial power system 21 based on the stored active powers A and B. Specifically, the microcomputer 41 determines whether the active power A or B is a negative value. Then, the microcomputer 41 determines that reverse power flows to the commercial power system 21 when the active power A or B becomes a negative value.
[0077]
Here, when there is no reverse power flow to the commercial power system 21 in the R-phase power supply line 24a, the phase difference between the AC voltage VR and the AC current IR is within 90 °, and the active power A is 0 or positive. Value. Similarly, when there is no reverse power flow to the commercial power system 21 in the T-phase power supply line 24c, since the phase difference between the AC voltage VT and the AC current IT is within 90 °, the active power B is 0 or positive. Is the value of
[0078]
Assuming that the output power of the grid-connected power generation device 50 is 5 [kW] and the power consumption of the load 16 is 7 [kW], the output power of the commercial power system 21 is 2 [kW].
[0079]
In the case of a stable operation state in which the fluctuation of the normal load 16 is small, the grid-connected power generation device 50 is operated while maintaining a constant output power (for example, 5 [kW]), so that no reverse power flow occurs.
[0080]
On the other hand, when the load 16 rapidly decreases, for example, when the power consumption of the load 16 decreases to 4 [kW], and when the output power of the grid-connected power generation device 50 is 5 [kW], the commercial power system 21 A situation where a reverse power flow can occur will occur.
[0081]
When reverse power flows to the commercial power system 21 on the R-phase power supply line 24a, the phase difference between the AC voltage VR and the AC current IR becomes larger than 90 °. Similarly, when reverse power flows to the commercial power system 21 on the T-phase power supply line 24c, the phase difference between the AC voltage VT and the AC current IT becomes larger than 90 °. Then, the active power becomes a negative value.
[0082]
When the reverse power flow occurs as described above, the transition is made such that the phase difference between the AC voltage VR and the AC current IR becomes 180 °. In the process in which the phase difference changes from 90 ° to 180 °, the current waveform of the AC current IR is disturbed, and it is difficult to accurately detect the phase difference between the AC voltage VR and the AC current IR. Similarly, it is difficult to accurately detect the phase difference between the AC voltage VT and the AC current IT.
[0083]
In the present embodiment, the value of the voltage sampling data of the AC voltage sampled as digital data is multiplied by the value of the current sampling data of the AC current, and the multiplication result is integrated over a predetermined period (for example, one period). Since the active powers A and B are obtained by dividing the integration result by the number of times of sampling within a predetermined cycle (for example, one cycle), when the active powers A and B are obtained, the AC voltage VR and the AC current IR are calculated. And the phase difference between the AC voltage VT and the AC current IT need not be detected. Therefore, even when the current waveform is disturbed or the power factor fluctuates (for example, when the load 16 decreases), Active powers A and B can be accurately obtained, and reverse power flow can be accurately detected.
[0084]
Then, even when the load 16 is reduced and the current waveform is disturbed, the active powers A and B can be accurately obtained, so that the phase difference becomes 180 ° and the reverse is performed under the condition that the current waveform is stable. The reverse power flow can be detected more quickly than in the case where it is determined whether or not a power flow is occurring.
[0085]
Further, since the reverse power flow is determined for each cycle of the AC voltage based on the active powers A and B for one cycle of the AC voltage, the reverse power flow can be detected more quickly.
[0086]
As described above, when the reverse power flow to the commercial power system 21 is detected, for example, the power supply from the grid-connected power generation device 50 can be cut off by operating the power-generating breaker 25.
[0087]
Next, a case where active power is obtained based on the values of AC voltages VR and VT detected by voltage sensors 44 and 45 and the value of AC current IR 'detected by current sensor 46 will be described. In this case, the operation is performed in substantially the same manner as the flowchart shown in FIG. 5, and thus the description will be made with reference to FIG.
[0088]
In this case, in step S3 in FIG. 5, the microcomputer 41 indicates digital voltage sampling data indicating the value of the AC voltage VR obtained by the A / D conversion and the value of the AC voltage VT obtained by the A / D conversion. The digital voltage sampling data is added. Then, the voltage addition result is multiplied by the current sampling data of the AC current IR ′ corresponding to the voltage sampling data, and the multiplication result is integrated. It should be noted that digital voltage sampling data indicating the value of the AC voltage VR obtained by the A / D conversion or digital voltage sampling data indicating the value of the AC voltage VT obtained by the A / D conversion is doubled. Then, the calculation result may be multiplied by the current sampling data of the AC current IR ′ corresponding to the voltage sampling data, and the multiplication result may be integrated. Here, the process of step S4 is omitted.
[0089]
In step S8, A / D conversion of the R′-phase AC current, that is, the current value detected by the power generation side current sensor 46 is started. Here, the process of step S9 is omitted.
[0090]
That is, the microcomputer 41 samples the value of the current detected by the power generation-side current sensor 46 and performs A / D conversion, and samples the values of the AC voltages VR and VT detected by the voltage sensors 44 and 45 to perform A / D conversion. / D conversion. Then, the microcomputer 41 adds the digital voltage sampling data indicating the value of the AC voltage VR obtained by the A / D conversion and the digital voltage sampling data indicating the value of the AC voltage VT obtained by the A / D conversion. I do. Then, the voltage sampling data indicating the result of the voltage addition is multiplied by the current sampling data of the AC current IR ′ corresponding to the voltage sampling data, and the multiplication result is integrated over one cycle.
[0091]
In step S10, the active power A 'is obtained by dividing the integration result integrated over one cycle by the number of times of sampling within one cycle. This active power A ′ indicates active power supplied by the grid-connected power generator 50.
[0092]
In step S11, the active power A 'is stored in a RAM (not shown).
[0093]
Through the above operation, the active power A 'supplied by the grid-connected power generation device 50 is obtained.
[0094]
When the active powers A and B on the commercial power system 21 side are positive values, the power supplied from the commercial power system 21 to the load 16 is obtained by adding the active power A and the active power B. The power supplied from the grid-connected power generation device 50 to the load 16 is the active power A ′. Therefore, by adding the active power A, the active power B, and the active power A ′, the power consumed by the entire load 16 can be obtained.
[0095]
As described above, according to the present embodiment, even when the phases of the voltage waveform and the current waveform are shifted (that is, when the power factor is smaller than 1) or when the current waveform is disturbed, the AC current and the AC voltage Since it is not necessary to detect the phase difference of the active power, it is possible to accurately measure the active power.
[0096]
Further, according to the present embodiment, since the active power is obtained by the arithmetic processing based on the control program of the microcomputer 41, the effective current detecting circuit, the effective voltage detecting circuit, the multiplier, the power factor measuring device, the computing device and the like are used. Since no hardware is required, a simple circuit configuration can be achieved.
[0097]
As described above, the present invention has been described based on the above embodiment, but the present invention is not limited to this.
[0098]
For example, in the above-described embodiment, the case where the voltage waveform of the AC voltage is a sine wave is described. However, the present invention is not limited to this. When the voltage waveform and the current waveform are not sine waves, for example, a triangular wave, a sawtooth wave, and a rectangular wave The present invention can be applied to a case where the voltage waveform has periodicity such as a wave and a trapezoidal wave. In this case, similarly to the above-described embodiment, there is an effect that the active power can be accurately measured with a simple circuit configuration, and the detection accuracy of the reverse power flow can be improved.
[0099]
Further, in the above-described embodiment, the case of a system interconnection power generation device including a generator driven by a gas engine in a cogeneration system has been described. However, the present invention is not limited to this, and a prime mover such as a gasoline engine, a diesel engine, etc. It is also possible to apply to a grid-connected power generator having a private power generator that generates electric power by means of power generation, and a grid-connected power generator including a device that converts natural energy into electric power, such as a solar cell or a wind power generator. It is also possible to apply to.
[0100]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the electric power measuring device which concerns on this invention, the measurement accuracy of active power improves with a simple circuit structure. Further, according to the reverse power flow detection device and the system interconnection power generation device according to the present invention, the detection accuracy of the reverse power flow is improved with a simple circuit configuration.
[Brief description of the drawings]
FIG. 1 is a block diagram of a cogeneration system mainly including power supply including a grid-connected power generation device according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of a grid-connected power generation device according to an embodiment of the present invention.
FIG. 3 is an electric circuit diagram showing a configuration for taking values detected by a voltage sensor and a current sensor into a microcomputer.
4A and 4B are waveform diagrams showing a voltage waveform of an AC voltage and a current waveform of an AC current, wherein FIG. 4A is a voltage waveform diagram, and FIG. 4B is a current waveform diagram.
FIG. 5 is a flowchart showing a control operation of the microcomputer.
[Explanation of symbols]
17 generator
19 Control device (power measurement device, reverse power flow detection device)
21 Commercial power system
24 Power supply line (measured line)
26 Power supply line on the power generation side (measured line)
41 microcomputer (sampling means, multiplication means, accumulation means, power calculation means, reverse power flow judgment means)
50 grid-connected power generator

Claims (11)

Sampling means for sampling the value of the AC voltage and the value of the AC current of the measured line as digital data a plurality of times within one cycle of the AC voltage;
Multiplying means for multiplying a value of the voltage sampling data of the AC voltage by a value of the current sampling data of the AC current corresponding to the value of the voltage sampling data;
Integrating means for integrating the result of multiplication by the multiplying means over a predetermined period of the AC voltage;
A power calculating means for obtaining active power based on a result of integration by the integrating means. The power measuring device according to claim 1,
The power measuring device according to claim 1, wherein the power calculating unit obtains the active power by dividing a result of the integration by the integrating unit by the number of times of sampling within the predetermined period. The power measuring device according to claim 1 or 2,
The power measuring device according to claim 1, wherein said sampling means, said multiplying means, said integrating means, and said power calculating means are constituted by a microcomputer. A power supply line connecting the commercial power system and the load is connected to a system interconnection power generation device that is connected to the commercial power system and supplies power to the load.
The value of the AC voltage applied to the load, and the value of the AC current of the power supply line between the connection point to which the grid-connected power generation device is connected and the commercial power system within one cycle of the AC voltage Sampling means for sampling as digital data a plurality of times,
Multiplying means for multiplying a value of the voltage sampling data of the AC voltage by a value of the current sampling data of the AC current corresponding to the value of the voltage sampling data;
Integrating means for integrating the result of multiplication by the multiplying means over a predetermined period of the AC voltage;
Power calculating means for obtaining active power based on the result of integration by the integrating means;
A reverse power flow detecting device comprising: a reverse power flow determining means for determining whether or not reverse power flows to the commercial power system based on the active power obtained by the power calculating means. The reverse power flow detecting device according to claim 4,
The reverse power flow detecting device according to claim 1, wherein the power calculating means obtains the active power by dividing the integration result by the integration means by the number of times of sampling within the predetermined period. The reverse power flow detecting device according to claim 4 or 5,
The reverse power flow detecting device, wherein the reverse power flow determining means determines that reverse power flows in the commercial power system when the active power obtained by the power calculating means has a negative value. The reverse power flow detection device according to any one of claims 4 to 6,
The reverse power flow detecting device according to claim 1, wherein said sampling means, said multiplying means, said integrating means, said power calculating means, and said reverse power flow determining means are constituted by a microcomputer. In a system interconnection power generation device connected to a power supply line connecting a commercial power system and a load, and supplying power to a load in connection with the commercial power system,
The value of the AC voltage applied to the load, and the value of the AC current of the power supply line between the connection point to which the grid-connected power generation device is connected and the commercial power system within one cycle of the AC voltage Sampling means for sampling as digital data a plurality of times,
Multiplying means for multiplying a value of the voltage sampling data of the AC voltage by a value of the current sampling data of the AC current corresponding to the value of the voltage sampling data; and a multiplication result by the multiplying means over a predetermined period of the AC voltage. Integration means for integrating
Power calculating means for obtaining active power based on the result of integration by the integrating means;
A reverse power flow determining means for determining whether or not reverse power flows to the commercial power system based on the active power obtained by the power calculating means; The grid-connected power generator according to claim 8,
The grid-connected power generator according to claim 1, wherein the power calculation unit obtains the active power by dividing the integration result by the integration unit by the number of times of sampling within the predetermined period. The grid-connected power generator according to claim 8 or 9,
The system-interconnected power generator according to claim 1, wherein the reverse power flow determining means determines that reverse power flows to the commercial power system when the active power obtained by the power calculating means has a negative value. The grid-connected power generator according to any one of claims 8 to 10,
The grid-connected power generation device, wherein the sampling unit, the multiplication unit, the integration unit, the power calculation unit, and the reverse power flow determination unit are configured by a microcomputer.

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