JP2015210135A - Electric power measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power measurement device capable of measuring electric power with high accuracy even in a situation where the electric power supplied via an electric power line fluctuates severely.SOLUTION: A current transformer 101 outputs an electric current in accordance with the electric current flowing in an electric power line 109. A switching element 102 switches the connection destination of the current transformer 101 to a charging circuit 107 or a measurement circuit 103 under control of an MCU 105. The measurement circuit 103 outputs a voltage corresponding to the output electric current of the current transformer 101. An A/D converter 104 A/D converts the output voltage of the measurement circuit 103. The MCU 105 executes an ordinary measurement or a reference measurement using the A/D converter synchronously with the measurement period. The MCU 105 controls the sampling period of A/D conversion in the ordinary measurement in accordance with the A/D conversion value. When the A/D conversion values of the reference measurement and ordinary measurement are close, the electric power obtained by the reference measurement is made the measured electric power in the ordinary measurement.

Description

  The present invention relates to a power measuring device that measures power supplied through a power line.

  As this type of power measuring device, an analog signal corresponding to the current supplied to the load via the power line is generated, A / D conversion of the analog signal is performed, and the resulting A / D conversion value is used. There is an apparatus for calculating electric power (see, for example, Patent Document 1). Also, in this type of power measuring device, a current corresponding to the current flowing through the power line to be measured is generated by electromagnetic induction, and this current is charged into a capacitor such as a secondary battery or a super capacitor. Some are used as a power source. According to this power measuring apparatus, power measurement can be performed without receiving power supply from a power source such as a commercial power source or a battery.

  Since such a power measuring device uses a capacitor as a power source, it is required to reduce the power consumption during power measurement as much as possible. Therefore, in the conventional power measuring apparatus, as shown in FIG. 8, power is intermittently measured in synchronization with the measurement cycle. As shown in FIG. 8, the measurement cycle includes a measurement period in which the power measurement device samples the current value flowing through the power line and performs power measurement, and a current obtained from electromagnetic induction from the power line without performing power measurement to the capacitor. It consists of a charging period for charging. Here, the measurement cycle is determined by the lower limit value of the current that can be supplied from the current transformer or electromagnetic induction from the power line. Further, in the conventional power measuring device, when the lower limit value of the current that can be supplied from the current transformer or electromagnetic induction from the power line decreases, control is performed to lengthen the charging period and lengthen the measurement cycle.

JP 2012-225767 A

  By the way, the above-described conventional power measuring device has a lower limit value of the current that can be supplied from the current transformer or electromagnetic induction from the power line, and when the measurement cycle is lengthened, when the power fluctuation of the power line is severe, every moment There is a problem that the power that fluctuates cannot be calculated in detail and the power measurement accuracy is reduced. In addition, since the measurement cycle is determined based on the lower limit value of the current that can be supplied from the current transformer or electromagnetic induction from the power line in the conventional power measurement device, in order to obtain the required power measurement accuracy, There was a problem that it was necessary to avoid the installation in the area where the fluctuation was severe, and the installation conditions were limited.

  The present invention has been made in view of the circumstances described above, and provides a power measuring device capable of performing power measurement with high accuracy even in a situation where fluctuations in power supplied via a power line are severe. It is aimed.

  The present invention relates to a power measuring device that generates a current corresponding to a current flowing through a power line to be measured, charges the capacitor, and measures the power supplied from the power line using the capacitor as a power source, at a preset sampling cycle. An A / D converter that A / D-converts a signal indicating a current waveform flowing through the power line synchronously, and calculates the power supplied by the power line based on an A / D conversion value obtained from the A / D converter And a control unit configured to control the sampling period according to the A / D conversion value.

  According to the present invention, since the sampling period of A / D conversion is controlled based on the A / D conversion value obtained from the A / D converter, it is possible to lengthen the measurement period in order to reduce power consumption. This can be avoided, and power can be measured with high accuracy even in a situation where fluctuations in the power supplied via the power line are severe.

It is a block diagram which shows the structure of the electric power measuring apparatus which is one Embodiment of this invention. It is a time chart explaining the normal measurement and reference measurement which are performed in the embodiment. It is a figure which shows the calculation method of the electric power which a power line supplies in the same embodiment. It is a figure which shows the initial setting of the electric power measurement apparatus performed in the embodiment. It is a flowchart which shows the processing content of the main program which MCU in the same embodiment performs. It is a flowchart which shows the processing content of the program of the normal mode and Sleep mode which MCU performs in the same embodiment. It is a flowchart which shows the processing content of the program of the measurement mode which MCU performs in the same embodiment. It is a time chart which shows operation | movement of the conventional electric power measurement apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a power measuring apparatus 100 according to an embodiment of the present invention. The power measuring apparatus 100 includes a current transformer 101, a switching element 102, a measuring circuit 103, an A / D converter 104, an MCU (Micro Controller Unit) 105, a communication circuit 106, and a charging circuit. 107 and a secondary battery 108. In FIG. 1, the circuit related to voltage measurement of the power measuring apparatus 100 is not shown.

  The current transformer 101 is a transformer that outputs a current corresponding to the current flowing through the power line 109. The switching element 102 is a switching element that switches the supply destination of the output current of the current transformer 101 to the measurement circuit 103 or the charging circuit 107 in accordance with a control command from the MCU 105.

  The measurement circuit 103 includes a resistor and the like, and outputs an AC voltage proportional to the AC current supplied from the current transformer 101 via the switching element 102 to the A / D converter 104. The A / D converter 104 samples the AC voltage supplied from the measurement circuit 103 and performs A / D conversion under the control of the MCU 105, and outputs the A / D conversion value obtained as a result to the MCU 105.

  The charging circuit 107 is a circuit that rectifies an alternating current supplied from the current transformer 101 via the switching element 102 to generate a direct current, and charges the secondary battery 108 with the direct current. The measurement circuit 103, the A / D converter 104, the MCU 105, and the communication circuit 106 that constitute the power measurement apparatus 100 operate using the secondary battery 108 as a power source. Note that a supercapacitor may be used as the power source of the power measuring apparatus 100 instead of the secondary battery 108.

  The MCU 105 includes a ROM that stores various programs, a RAM that is used as a work area, and a rewritable nonvolatile memory such as an EEPROM. The MCU 105 controls each unit in the power measurement apparatus 100 by executing a program in the ROM, and calculates a current value flowing through the power line 109 based on the A / D conversion value supplied from the A / D converter 104. The power value is calculated by multiplying the current value by a voltage value obtained from a voltage measurement circuit (not shown), and the power value is output to the communication circuit 106. The communication circuit 106 transmits the power value input from the MCU 105 to a server (not shown). This server is a device that manages power values transmitted from many power measurement devices 100.

The outline of the control of each part in the power measuring apparatus 100 performed by the MCU 105 will be described as follows. First, in synchronization with a preset measurement cycle, the MCU 105 connects the current transformer 101 to the measurement circuit 103 by the switching element 102, and performs A / D conversion of the output voltage of the measurement circuit 103 only for a preset measurement period. The A / D converter 104 is executed. In each measurement cycle, when the measurement period ends, the remaining time is set as the charging period. In this charging period, the current transformer 101 is connected to the charging circuit 107 by the switching element 102, and the charging circuit 107 is charged with the secondary battery 108.
As shown in FIG. 2, the MCU 105 performs normal measurement or reference measurement in each measurement cycle. More specifically, the MCU 105 performs reference measurement in synchronization with a reference measurement cycle that is an integer multiple of the measurement cycle. Then, the MCU 105 performs normal measurement in each measurement cycle in which reference measurement is not performed. The reference measurement period is set by referring to the sampling table stored in the nonvolatile memory. This sampling table will be described later.

  In normal measurement, the MCU 105 causes the A / D converter 104 to perform A / D conversion at a sampling period determined according to the A / D conversion value of the A / D converter 104, and acquires the A / D conversion value. In this normal measurement, the reason for adopting the sampling period determined according to the A / D conversion value of the A / D converter 104 is as follows.

  First, when the amplitude of the A / D conversion value output from the A / D converter 104 is large, the power supplied via the power line 109 is large and the charging current supplied from the charging circuit 107 to the secondary battery 108 is also large. . In such a case, since the lower limit value of the current that can be supplied to each part in the power measuring apparatus 100 by the secondary battery 108 is large, the sampling period of the A / D converter 104 is shortened to consume the A / D converter 104. It is possible to increase power.

  On the other hand, when the amplitude of the A / D conversion value output from the A / D converter 104 is small, the power supplied via the power line 109 is small and the charging current supplied from the charging circuit 107 to the secondary battery 108 is also small. . In such a case, since the lower limit value of the current that the secondary battery 108 can supply to each part in the power measuring apparatus 100 is small, it is difficult to shorten the sampling period of the A / D converter 104.

  Therefore, in this embodiment, the MCU 105 shortens the sampling period in normal measurement when the A / D conversion value of the A / D converter 104 is large, and the A / D conversion value of the A / D converter 104 is small. Controls to increase the sampling period in normal measurement. This control is performed with reference to a sampling table stored in the nonvolatile memory.

  In the reference measurement, the MCU 105 causes the A / D converter 104 to perform A / D conversion at a sampling period employed when the current value that can be supplied from the secondary battery 108 is sufficiently large, and the A / D conversion value. To get. The sampling period in this reference measurement is shorter than the sampling period employed in normal measurement.

  In the present embodiment, the MCU 105 calculates the power transmitted through the power line 109 in each measurement cycle. However, since the normal measurement often has a long sampling cycle, if the power supplied by the power line 109 is obtained using the A / D conversion value obtained in the normal measurement, the power measurement accuracy may be deteriorated. . Therefore, in this embodiment, the power supplied by the power line 109 is calculated by the method shown in FIG.

  First, in this embodiment, when the reference measurement is performed, the MCU 105 calculates the power supplied by the power line 109 using each A / D conversion value obtained in the reference measurement.

Next, when normal measurement is performed, the MCU 105 compares the total value of each A / D conversion value obtained in the normal measurement with the total value of each A / D conversion value obtained in the reference measurement. When comparing the total value, a part of the data at the reference measurement is thinned out in accordance with the sampling of the normal measurement. When the total value of both A / D conversion values coincides within a certain error range, the MCU 105 regards the power calculated in the reference measurement as the power during normal measurement. By handling in this way, at the time of normal measurement, the calculation process for calculating the power from the A / D conversion value becomes unnecessary, and the power consumption of the MCU 105 can be saved while preventing the deterioration of the power measurement accuracy.
The above is the configuration of the power measuring apparatus 100 according to the present embodiment.

Next, the operation of this embodiment will be described. FIG. 4 is a diagram illustrating an initial setting procedure of the power measuring apparatus 100 performed in the present embodiment. This initial setting is performed before the power measuring apparatus 100 is shipped. First, known AC power is transmitted to the power line 109 to which the current transformer 101 is connected. Then, the connection destination of the current transformer 101 is set to the measurement circuit 103 by the switching element 102, and an A / D conversion value obtained from the A / D converter 104 at this time is acquired. Next, in the state where the same AC power is transmitted via the power line 109, the switching element 102 sets the connection destination of the current transformer 101 as the charging circuit 107, and at this time, the current value supplied from the charging circuit 107 to the secondary battery 108 And obtaining the optimum sampling period, reference measurement period, and measurement period in the normal measurement based on the current value. Various kinds of power transmitted through the power line 109 are changed, and such processing is repeated, and the representative value of the A / D conversion value of the A / D converter 104 in each processing, the optimum sampling cycle, the reference measurement cycle, and Create a sampling table that correlates the measurement cycle and write it to the non-volatile memory. Although various aspects can be considered as to how to determine the representative value of the A / D conversion value of the A / D converter 104, for example, the effective value of the A / D conversion value within a predetermined time may be used as the representative value. Good.
The above is the initial setting of the power measuring apparatus 100.

  Next, the measurement operation of the power measuring apparatus 100 will be described. When the power measuring device 100 is installed on the power line 109 to be measured and the current transformer 101 is connected to the power line 109, a current corresponding to the current of the power line 109 flows to the current transformer 101. Here, in the initial state, the switching element 102 connects the current transformer 101 to the charging circuit 107. For this reason, the charging circuit 107 receives a supply of current from the current transformer 101 and causes a charging current to flow through the secondary battery 108. As a result, the charging voltage of the secondary battery 108 (that is, the power supply voltage of the power measuring device 100) rises. Thereby, the MCU 105 starts executing the main program shown in FIG.

  The MCU 105 resets the program counter (step S101), executes the initial processing program stored at a predetermined address in the ROM, and sets various control registers, timers, and the like in the RAM (step S102). Next, the MCU 105 reads the sampling table from the nonvolatile memory and stores it in the RAM (step S103).

  Next, the MCU 105 performs reference measurement (step S104). More specifically, the MCU 105 gives a control command to the switching element 102 and switches the connection destination of the current transformer 101 from the charging circuit 107 to the measuring circuit 103. Then, the MCU 105 sets the sampling period of the A / D converter 104 to the sampling period for reference measurement, causes the A / D converter 104 to perform A / D conversion of the output voltage of the measurement circuit 103 a predetermined number of times, An A / D conversion value is acquired. Then, the power supplied by the power line 109 is calculated using the predetermined number of acquired A / D conversion values.

  Next, the MCU 105 obtains, for example, an effective value within a predetermined period obtained from the predetermined number of A / D conversion values acquired at step S104, and from the sampling table in the RAM, the sampling period and reference measurement associated with this effective value. Read cycle and measurement cycle. Each read cycle is initialized as a normal measurement sampling cycle, a reference measurement cycle, and a measurement cycle (step S105).

  Next, the MCU 105 executes processing in the normal mode (step S106). Then, the MCU 105 determines whether or not a RESET operation has been performed during the processing in the normal mode (step S107). If the determination result is “YES”, the MCU 105 repeats the processing of steps S101 to S106. On the other hand, if the determination result in step S107 is “NO”, the MCU 105 continues the process in the normal mode (step S106). Note that the RESET operation is specifically pressing of a RESET button provided on the casing of the power measuring apparatus 100 or receiving a RESET signal from the server.

  FIG. 6A is a flowchart showing the processing contents of the normal mode program executed in step S106 of FIG. In this normal mode program, the MCU 105 first proceeds to a transition process to the sleep mode shown in FIG. 6B (step S201). In this transition process, first, a control command is given to the switching element 102, and the connection destination of the current transformer 101 is switched from the measurement circuit 103 to the charging circuit 107 (step S211). Next, the MCU 105 cuts off the power supply from the secondary battery 108 to the measurement circuit 103 (step S212). This process may be executed when the power consumption of the measurement circuit 103 is large, and does not necessarily need to be executed otherwise. Next, the MCU 105 switches the clock supplied from the clock generator (not shown) to the MCU 105 from the main clock having a high frequency to the sub clock having a low frequency, and shifts to the sleep mode (step S213). In the sleep mode, the MCU 105 waits for an interval interrupt from the timer to occur.

  When the timer value reaches the timer compare value preset in the compare register, a timer interval interrupt is generated. Thereby, the MCU 105 proceeds to the process of step S202 of FIG. 6A, returns the clock of the clock generator from the sub clock to the main clock, and executes the process of the measurement mode. When the measurement mode processing ends, the MCU 105 writes the measurement cycle obtained in the measurement mode processing as a timer compare value in the compare register and starts the timer (step S203). Then, the process returns to step S201. Therefore, in the normal mode, the processes in steps S201 to S203 are repeated at the measurement cycle set as the timer compare value in step S202.

  FIG. 7 is a flowchart showing the processing contents of the measurement mode program executed in step S202 of FIG. This measurement mode program is started once every measurement cycle. First, the MCU 105 gives a control command to the switching element 102, and switches the connection destination of the current transformer 101 from the charging circuit 107 to the measuring circuit 103 (step S301). Next, the MCU 105 determines whether or not the current measurement cycle is a measurement cycle for performing reference measurement (step S302). If this determination is “NO”, the flow proceeds to step S 311 to determine whether the current measurement cycle is a measurement cycle in which normal measurement is performed. If the determination result is “NO”, the measurement mode process is terminated, and the process returns to step S203 in FIG.

  On the other hand, if the current measurement cycle is a measurement cycle for performing normal measurement, the determination result in step S311 is “YES”, and the flow proceeds to step S312. Next, in step S312, the MCU 105 sets a sampling period for normal measurement (in this example, the sampling period initially set in step S105 in FIG. 5) in the A / D converter 104. In step S313, the MCU 105 performs normal measurement by causing the A / D converter 104 to perform A / D conversion of the output voltage of the measurement circuit 103. Next, in step S314, the MCU 105 determines the total value of the A / D conversion values obtained in the immediately preceding reference measurement (or the reference measurement performed in step S104 of the main program when the measurement mode program is executed first). Is compared with the total value of the A / D conversion values obtained by the normal measurement in step S313, and it is determined whether or not the total values of both A / D conversion values match.

  If the total value of the two A / D conversion values coincides within a certain error range, the MCU 105 performs the immediately preceding reference measurement (when the program in the measurement mode is executed first, in step S104 of the main program). The power value calculated in the reference measurement) is used as the measured power in the normal measurement in step S313 (step S315). Then, the measurement mode process ends, and the process returns to step S203 in FIG.

  On the other hand, when the total value of both A / D conversion values does not match within a certain error range in step S314, the MCU 105 sets the mismatch FLAG set in the RAM to “1”, and the reference measurement cycle. The measurement cycle is overwritten on (step S316). Then, the measurement mode process ends, and the process returns to step S203 in FIG.

  In the measurement cycle in which the reference measurement is to be performed, in the measurement mode program, when the process proceeds to step S302 via step S301, the determination result in step S302 is “YES”, and the process proceeds to step S321. Next, in step S321, the MCU 105 sets the reference measurement sampling period in the A / D converter 104, and causes the A / D converter 104 to perform A / D conversion of the output voltage of the measurement circuit 103. The reference measurement is performed by Then, the power supplied from the power line 109 is calculated using the A / D conversion value obtained from the A / D converter 104. Next, proceeding to step S322, the MCU 105 obtains an effective value of the A / D conversion value acquired in the reference measurement of step S321, and in the sampling table in the RAM, the sampling period and reference measurement period associated with this effective value. And read the measurement cycle. Then, each read cycle is reset as a normal measurement sampling cycle, a reference measurement cycle, and a measurement cycle.

  Next, the MCU 105 determines whether or not the mismatch FLAG is “1” (step S323). If the determination result is “NO”, the MCU 105 ends the measurement mode process and returns to step S203 in FIG. On the other hand, if the determination result of step S323 is “YES”, the process proceeds to step S324. In this step S324, the MCU 105 uses the average value of the power obtained in the previous reference measurement (step S104 or step S321) and the current reference measurement (step S321) as the measured power, and the mismatch FLAG is “0”. And Then, the measurement mode process ends, and the process returns to step S203 in FIG.

  Thereafter, when the measurement mode program is activated again, in the process of step S314, the A / D conversion value obtained by the reference measurement in step S321 is the same as the A / D conversion value obtained in the normal measurement (step S313). It becomes the object of comparison. Further, the power obtained by the reference measurement in step S321 is used as the power calculated by the reference measurement in step S315.

  In the measurement mode processing described above, the situation in which the A / D conversion value in the normal measurement (step S313) and the A / D conversion value obtained by the immediately preceding reference measurement match within a certain error range continues. If so, the processing from step S311 to S315 is repeated until the reference period set based on the sampling table is reached. In this case, the determination result in step S302 is “YES”, and when the process proceeds to step S323 via steps S321 and S322, the determination result is “NO”. Therefore, in this case, reference measurement is performed in synchronization with the reference measurement period defined in the sampling table, and the measured power is updated each time this reference measurement is performed.

  On the other hand, if the A / D conversion value in the normal measurement (step S313) and the A / D conversion value obtained by the immediately preceding reference measurement do not match within a certain error range, the mismatch FLAG is “1”. And the measurement cycle is overwritten on the reference measurement cycle (step S316). Therefore, when the program in the measurement mode of FIG. 7 is started in the next measurement cycle, the measurement cycle is set to the reference measurement cycle by the process of step S316, and the determination result in step S302 is “YES”. Reference measurement is executed (step S321). Since the determination result in step S323 is “YES”, the average value of the power obtained by the current reference measurement and the power obtained by the previous reference measurement is set as the measured power (step S324).

  In this way, in the situation where the error between the A / D conversion value in the normal measurement and the A / D conversion value in the reference measurement is large, the reference measurement is repeated at a cycle shorter than the reference measurement cycle defined in the sampling table. The measured power is updated by the power obtained by the reference measurement and the power obtained by the previous reference measurement. Therefore, power can be measured with high accuracy even in a situation where fluctuation of power supplied through the power line 109 is severe.

  As described above, according to the present embodiment, since the sampling period of A / D conversion is controlled based on the A / D conversion value obtained from the A / D converter 104, the power is supplied via the power line 109. It is possible to measure power with high accuracy even in a situation where fluctuations in power are severe. In the present embodiment, normal measurement for causing the A / D converter 104 to perform A / D conversion at a sampling period depending on the A / D conversion value is performed in synchronization with the measurement period, and an integral multiple of this measurement period. In this cycle, reference measurement was performed to cause the A / D converter 104 to perform A / D conversion with a sufficiently long sampling cycle. In this embodiment, when the A / D conversion value in the normal measurement and the A / D conversion value in the reference measurement are sufficiently approximated, the calculation is performed from the A / D conversion value in the reference measurement. The power was taken as the measured power during normal measurement. Therefore, according to the present embodiment, the calculation amount of the MCU 105 can be reduced and the power consumption of the power measuring apparatus 100 can be reduced while maintaining high power measurement accuracy.

DESCRIPTION OF SYMBOLS 100 ... Electric power measuring device, 101 ... Current transformer, 102 ... Switching element, 103 ... Measuring circuit, 104 ... A / D converter, 105 ... MCU, 106 ... Communication circuit, 107 ... Charging circuit 108 ... secondary battery 109 ... power line.

Claims (5)

In a power measuring device that generates a current according to a current flowing through a power line to be measured and charges the capacitor, and measures the power supplied by the power line using the capacitor as a power source,
An A / D converter for A / D converting a signal indicating a current waveform flowing in the power line in synchronization with a preset sampling period;
Control means for calculating the power supplied by the power line based on the A / D conversion value obtained from the A / D converter,
The power measuring apparatus, wherein the control means controls the sampling period according to the A / D conversion value.   The control means calculates power supplied by the power line based on an A / D conversion value obtained from the A / D converter for each preset measurement cycle. In each measurement cycle, When the reference measurement is performed by performing either the normal measurement in which the A / D conversion is performed at a sampling cycle determined based on the A / D conversion value or the reference measurement in which the A / D conversion is performed at a predetermined sampling cycle. The power is calculated based on the A / D conversion value obtained as a result, and when the normal measurement is performed, the total value of the A / D conversion values obtained by the normal measurement and the normal Compared with the total value of the A / D conversion values obtained by the reference measurement, which is partially thinned in accordance with the measurement, and obtained by the reference measurement when both coincide with each other within a predetermined error range. Power measurement device according to the power calculated from the A / D converted value to claim 1, characterized in that the power at the time of the normal measurements made.   A total value of A / D conversion values obtained by the normal measurement and a total value of A / D conversion values obtained by the reference measurement obtained by thinning a part in accordance with the normal measurement are within a predetermined error range. In the case where they do not coincide with each other, the control means immediately performs reference measurement, and calculates from the power calculated from the A / D conversion value obtained by the reference measurement and the A / D conversion value obtained by the immediately previous reference measurement. The power measurement apparatus according to claim 1, wherein the power supplied from the power line is calculated by averaging power. Comprising a non-volatile memory storing a sampling table for associating a sampling period during normal measurement with an A / D conversion value of the A / D converter;
The control means determines a normal measurement sampling period corresponding to an A / D conversion value of the A / D converter by referring to a sampling table stored in the nonvolatile memory. Item 4. The power measuring device according to Item 2 or 3. A current transformer that outputs a current according to a current flowing through the power line;
A measurement circuit that outputs a voltage according to the output current of the current transformer,
The A / D converter performs A / D conversion of the output voltage of the measurement circuit,
In each measurement cycle, the control means connects the current transformer to the measurement circuit and performs the normal measurement or the reference measurement, and then connects the connection destination of the current transformer from the measurement circuit to the capacitor. The power measuring device according to any one of claims 2 to 4, wherein the capacitor is charged by switching to a charging circuit to be performed.

Images