JPH04240574A - Method for measuring fundamental wave power and higher harmonic power of strain wave power supply - Google Patents

Abstract

PURPOSE:To measure fundamental wave power and higher harmonic power by measuring the effective values of voltage and a current by an effective value indication type meter and storing the waveforms of both of them in a waveform memory apparatus and measuring average power by a voltmeter. CONSTITUTION:The effective values of voltage and a current are measured and the waveforms of both are simultaneously stored and average power is measured by a voltmeter. Next, the stored waveforms are subjected to FFT analysis to respectively determine the ratios of respective higher harmonics to a fundamental wave. By taking the sum of the values obtained by squaring the respective ratios from the order corresponding to the fundamental wave to the order of higher harmonics to be considered, the ratio of the effective value of a strain wave to the effective value of the fundamental wave is calculated and the fundamental wave effective values of line voltage and a phase current are determined. From the stored waveforms, the phase difference of the voltage and current of the fundamental wave is calculated. The phase difference of the fundamental waves of phase voltage and line voltage is 30 (150) deg. because both of a power supply and load are in an equilibrium state. By correcting this phase difference, fundamental wave power is calculated. Next, higher harmonic power is calculated by subtracting the calculated fundamental wave power from the average power of a wattmeter.

Description

[Detailed description of the invention]

001

[Industrial Application Field] In the case of equipment having a distorted wave power source, it is necessary to accurately evaluate the performance of the equipment by measuring the fundamental wave voltage, fundamental wave current, fundamental wave power, or harmonic power.

002

2. Description of the Related Art Up to now, even in the case of a distorted wave power source, average power has been measured to evaluate performance such as efficiency. However, the average power is the sum of the fundamental wave power and the harmonic power.

003

[Problems to be Solved by the Invention] When energy conversion is performed, the fundamental wave component is often the main component of the conversion. In this case, the ratio of fundamental wave power to harmonic power is a major criterion for evaluating performance. This creates the problem of measuring fundamental wave power and harmonic power in addition to the conventional average power. Furthermore, since the fundamental wave power and harmonic power are measured, there arises the problem of measuring the fundamental wave voltage and fundamental wave current. It is an object of the present invention to provide a method for measuring fundamental voltage and current, as well as fundamental power and harmonic power.

004]

[Means for Solving the Problems] In order to solve the above object, the measuring method of the present invention implements the following means. Measure the effective voltage value and effective current value using a voltmeter that indicates an effective value and an ammeter that indicates an effective value. A voltage waveform and a current waveform are simultaneously stored in a waveform storage device. Measure the average power with a power meter. After implementing the above measures, the fundamental wave effective values of voltage and current can be determined as follows. The following explanation is the same for both voltage and current. The stored waveform is harmonically analyzed to determine the ratio of each harmonic to the fundamental wave. By summing the squares of these ratios from the order corresponding to the fundamental wave to the harmonic order corresponding to the high cutoff frequency of the frequency characteristic of the effective value indicating instrument, the effective value of the distorted wave relative to the effective value of the fundamental wave can be calculated. The ratio of can be found. In this way, the effective value of the fundamental wave of voltage and current is determined from the effective value of the distorted wave and the ratio of the effective value of the distorted wave to the effective value of the fundamental wave determined from each harmonic. Fundamental power and harmonic power can be determined as follows. Find the phase difference between the voltage and current of the fundamental wave from the memorized waveform. Since the phase difference between the voltage and current of the fundamental wave changes depending on various wiring methods and the position of waveform measurement, the phase angle is calculated depending on the measurement circuit. The fundamental wave power is determined from the fundamental wave effective value of the voltage, the fundamental wave effective value of the current, and the phase angle determined by the measurement method according to claim 1 of the present invention. Next, the harmonic power is obtained by subtracting the fundamental wave power from the average power of the wattmeter. The accuracy of harmonic power depends on the power accuracy and frequency characteristics.

005]

[Operation] The fundamental wave power and harmonic power measurement of the present invention can be applied not only to a single phase but also to a three phase case. The waveform measurement position is a voltage and current measurement position when performing conventional power measurement. Voltage and current waveform measurements vary depending on the various wiring methods. When measuring single-phase power, a pair of waveform measurements are performed. If the load is balanced in three-phase four-wire measurement, the voltage and current waveforms will be measured as a pair, but if the load is unbalanced, it is necessary to measure the waveforms for all phases. In the case of a three-phase, three-wire system, if the load is balanced, there will be only one pair of voltage and current waveforms.

006

[Embodiment] Here, we will discuss the case of a three-phase, three-wire system in which both the power supply and the load are balanced. In this case, the voltage and current waveforms will be measured as a pair. The voltage waveform measures the line voltage waveform between any two lines. The current waveform of one of the two wires used to measure the voltage waveform is measured using a non-inductive standard resistor or the like. These waveforms are simultaneously stored in the waveform storage device. A device for storing waveforms must have frequency characteristics, sampling time, and number of storage elements to record the measured waveform with sufficient accuracy. Although effective value indicating type voltmeters and ammeters do not necessarily need to have frequency characteristics over a wide range, they are required to have frequency characteristics over a wide range in order to make accurate measurements. When measuring harmonic power, a power meter needs to have frequency characteristics over a wide range. The following measurements are performed using the above measuring device. Measure the effective voltage value and effective current value using a voltmeter that indicates an effective value and an ammeter that indicates an effective value. A voltage waveform and a current waveform are simultaneously stored in a waveform storage device. Measure the average power with a power meter. After carrying out the above means, the fundamental wave effective values of line voltage and phase (line) current can be determined as follows. The stored waveform is subjected to FFT analysis to determine the ratio of each harmonic to the fundamental wave. The harmonic orders considered when determining the fundamental wave effective value are up to the harmonic order corresponding to the high cutoff frequency of the frequency characteristic of the effective value indicating voltmeter or ammeter. The ratio of the effective value of the distorted wave to the effective value of the fundamental wave is obtained by summing the square of the ratio of each harmonic to the fundamental wave from the order corresponding to the fundamental wave to the order of the harmonic to be considered. Determine the fundamental wave effective values of the phase voltage and phase current. Find the phase difference between the voltage and current of the fundamental wave from the memorized waveform. Since the phase difference between the fundamental wave of the line voltage and the fundamental wave of the phase current has been found, the phase difference between the fundamental wave of the phase voltage and the line voltage is balanced for both the power supply and the load, so
There is a difference of 30 (150) degrees. Correct this and find the fundamental wave power. Next, subtract the found fundamental wave power from the average power of the wattmeter to find the harmonic power.

007]

[Effect of the invention] Currently, with the development of digital technology, digital power meters with good frequency characteristics have appeared, but their power measurement is the average of instantaneous power, which is the product of instantaneous voltage and instantaneous current, over time. Measured in power. By adding a waveform storage device to these digital power meters and adding a program according to the method provided by the present invention,
Fundamental power and harmonic power can be easily measured. Furthermore, it is also possible to simultaneously measure the fundamental wave effective values of voltage and current. In the case of a PWM power supply, which is one type of distorted wave power supply, the fundamental wave voltage can be measured with a rectifying voltmeter that indicates an average value and converts to an effective value. However, in the case of other distorted wave power supplies, the fundamental wave voltage Voltage cannot be measured with a rectifying voltmeter that indicates an average value and converts to an effective value. The method of the present invention makes it possible in principle to measure any strain voltage within the measurement range of the effective value indicating instrument.

Claims (2)

[Claims] Claim 1: Measure the effective values of voltage and current with an effective value indicator type instrument, memorize the voltage and current waveforms, and obtain the fundamental wave effective values of strain voltage and current by harmonic analysis of the waveforms. Measurement method [Claim 2] Distorted waves obtained by measuring the effective values of voltage and current with an effective value indicating meter, measuring the average power with a wattmeter, memorizing the voltage and current waveforms, and performing harmonic analysis of the waveforms. Measuring method of fundamental wave power and harmonic power input to equipment connected to power supply