KR20130028460A - An electric meter for sensing current of three phase system utilizing shunt resistors - Google Patents

Abstract

PURPOSE: A watt-hour meter of a three-phase power system using shunt resistors is provided to measure power without distortion even when a current contains a lot of direct current components. CONSTITUTION: A watt-hour meter includes a shunt resistor part(310), an independent power supply part(330), and a measuring unit(300). The shunt resistor part is serially connected to one of the three-phase currents and measures the current. A control part calculates power consumption by using the measured current value from the shunt resistor part. The independent power supply part supplies power independent of three-phase power to the measuring unit. [Reference numerals] (310) Shunt resistor part; (320) Control part; (330) Power supply part; (340) Communication part

Description

Power meter for three-phase power system using shunt resistor {AN ELECTRIC METER FOR SENSING CURRENT OF THREE PHASE SYSTEM UTILIZING SHUNT RESISTORS}

The present invention relates to an apparatus for measuring the amount of power of a three-phase power system, and more particularly to an electronic wattmeter for measuring the amount of power by performing a current detection using a shunt resistor.

1 illustrates a method of sensing voltage and current in an electronic wattmeter of a three phase power system. Since power P = voltage V x current I, it is necessary to measure the phase voltage 7 and the load current 6 in order to measure the load power consumed. Measuring voltages and currents on digital boards requires converting voltages and currents ranging from hundreds of volts to tens of amps to signals of tens to hundreds of milli-volts.

In electronic watt-hour meters, phase voltages (7), usually hundreds of volts, are converted to values of several millivolts, much smaller than phase voltages, using resistor voltage dividers (1, 2), and phase currents (load currents) of tens of amperes (6). ) Is made small by a few milli-amps through a current transformer and then flowed into a resistor (4) to convert it into a voltage of tens to hundreds of milli-volts. The converted analog signal is converted into a digital signal by an analog-to-digital converter (ADC) in the controller 5 (Micro Control Unit (MCU)), and the MCU 5 processes the signal to measure voltage, current, and power. The cumulative amount of power can be calculated over time.

Current transformer, CT (Current Transformer) used to measure the phase current, uses the principle of converting the induced magnetic force generated when the load flows between the conductors into a small current using the core and the secondary winding. There are some problems with this structure. 1) CT is an expensive part due to the structure of the core core and the secondary winding (1000 to 2500 turns). In addition, 2) the core core is responsible for transmitting the induced magnetic force. If the ferromagnetic material, such as an external magnet, is in close proximity, it is likely to cause distortion of the signal or to lose the CT's own function.

3) Current components cause distortion of signal transmission, and continuous direct current can cause saturation of the core core, resulting in loss of function. In addition, 4) signal deformation (size deformation, phase deformation) may occur while the signal is generated by the core core and the secondary winding.

Disadvantages of 2) in metering power meter can be the loss of metering ability by using strong magnet, and the disadvantage of 3) is to prevent current from increasing current through half wave rectifier and using it to measure current. This can lead to loss of weighing capacity. The disadvantage of 4) increases the complexity of the software because the signal distortion must be compensated or compensated through the controller.

Therefore, in the case of the meter of the single-phase power supply, the trend of abandoning the conventional method using CT and directly measuring current using a shunt resistor and measuring the amount of power is increasing.

However, in the three-phase power system meter, each phase current can be converted into a small value voltage signal by a shunt resistor, but each of these converted signals has a potential difference (voltage difference) as much as the line voltage. There was still a technical problem that could not be combined within the digital board of the company, which forced CT to still be used.

The electricity meter according to an embodiment of the present invention can solve the above-mentioned problems and provide a simple configuration.

Disclosed is a power meter of a three-phase power supply using a shunt resistor according to an embodiment of the present invention. The wattmeter includes: a shunt resistor unit connected to one of three-phase currents to measure current; And a control unit that calculates an amount of power consumed by using the current value measured by the shunt resistor unit.

The electricity meter may further include an independent power supply unit supplying power independent of the three-phase power supply to the measurement unit.

In addition, the measurement unit may exist one for each phase power source for measuring the amount of power of each of the three-phase power source. Each measuring unit includes an insulated communication unit, and calculates the total power of the three-phase power source by transmitting or receiving the amount of power measured in each phase through the communication unit.

In addition, the measurement unit may further include a voltage divider for measuring the voltage of the three-phase power source. The controller calculates the amount of power consumed in each phase by using the measured current value and the measured voltage value, and calculates the total power consumption by integrating the amount of power consumed in each phase.

In addition, the shunt resistor unit may measure a voltage drop across its own end to measure a current using its resistance value.

The electricity meter according to one embodiment of the present invention can perform current measurement without distortion under any strong magnet influence, and can measure without distortion even if a large amount of DC component is included in the current. In addition, since the linear element shunt resistor is used, the measurement linearity is excellent, and the sensor itself can be implemented in a very simple configuration.

1 shows a wattmeter of a three phase power system according to the invention.
Figure 2 shows a wattmeter of a three-phase power system using a shunt resistor according to the present invention.
3 shows a block diagram of a wattmeter of a three phase power system according to the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and should be construed in a sense and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention, and not all of the technical ideas of the present invention are included. Therefore, It is to be understood that equivalents and modifications are possible.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 shows a power meter according to an embodiment of the present invention. 2 shows a three phase power system (R phase, S phase and T phase). The voltage divider resistors 1 and 2 for phase voltage measurement are connected in parallel to the three-phase power line. Specifically, all phases are connected. In addition, for the phase current measurement, the shunt resistors 4r, 4s, and 4t are connected in series to a power line through which one of the three phase currents flows.

Measurement units 15, 16 and 17 are shown for phase voltage and phase current measurements. Each measurement unit may be supplied with power 9, 10 and 11 in an isolated state using a switching scheme such as Switching Modulation Power Supply (SMPS) from the voltage supply module 8. The controllers 12r, 12s, and 12t may receive phase current and phase voltage values measured through the shunt resistors 4r, 4s, and 4t and the voltage divider resistors 1 and 2 to calculate power values of the corresponding phases. In addition, each of the control units 12r, 12s, and 12t may communicate with each other to integrate the total power value consumed in the three-phase power system.

To this end, each of the control units 12r, 12s, and 12t may include communication units 13 and 14 in a separated or insulated state. In FIG. 2, two communication units between the control units 12r and 12s and two between the control units 12r and 12t are illustrated, but each control unit may have a separate communication unit.

In addition, the measuring units 15, 16 and 17 for measuring the phase voltage and the phase current may be provided with the power supplies 9, 10 and 11 independent of the other phases, and the ground may likewise be individually provided.

The amount of power can be obtained by multiplying the voltage waveform and the current waveform to accumulate over time. The electricity meter according to an embodiment of the present invention may calculate the total amount of power by calculating the power of the R phase, the S phase, and the T phase based on a single phase, and then integrating the values of the three phases.

In addition, the wattmeter according to an embodiment of the present invention may be configured to include the measuring unit (15, 16 and 17) for each phase in order to measure the phase current using the shunt resistor. Inputting the voltage across the shunt resistor installed in each phase to a single ADC or MCU for phase current measurement will cause the ADC or MCU to break because the difference in line voltage between each phase, i.e. the potential difference, is applied to the ADC or MCU as it is. . Therefore, in order to integrate power calculation in one controller (or MCU), power and ground and digital signals must be separated according to each phase to achieve stable implementation.

In FIG. 2, the phase voltage of the R phase is converted into several milli-volts through the voltage divider 1a and 2a for the R phase, and the control unit 12r, the ADC, or the MCU may convert the digital signal. The current of the R phase may be converted into a digital signal by detecting the voltage drop generated when the current flows through the shunt resistor 4r of the R phase. The controller 12r may obtain power by multiplying a voltage and current value converted into a digital signal and accumulate with time to obtain power or amount of R phase.

The phase voltage of the S phase is converted into several milli-volts through the voltage divider 1b and 2b for the S phase, and the control unit 12s may convert it into a digital signal. The current of the S phase may be converted into a digital signal by detecting the voltage drop generated when the current flows through the shunt resistor 4s of the R phase. The controller 12s may obtain power by multiplying a voltage and current value converted into a digital signal, and accumulate with time to obtain power or amount of S phase.

The power or amount of power of the T phase is also processed in the same manner as the S phase and the R phase by using the divided resistors 1c and 2c and the shunt resistor 4t of each phase in the same manner as the above-described S and R phases. The processed sample value or power (or power amount) values for the S phase and the T phase can be transferred to the control unit 12t through the insulated communication units 13 and 14 and integrated with the values for the R phase. In addition, although two communication sections 13 and 14 are shown in FIG. 2 as mentioned above, each measuring unit 15, 16 and 17 may comprise a separate communication section. In addition, although the control unit 12r has been described as receiving power amount values for the phase from the other control units 12s and 12t, a separate component that receives and integrates the power amount values of the respective control units 12r, 12s and 12t. (Not shown) may exist.

Since the wattmeter according to an embodiment of the present invention uses a shunt resistor without using a CT, it is possible to perform stable current measurement under the influence of any strong magnet. In addition, since the CT cannot convert the DC component, there is a case in which only a unidirectional current signal is used by using a diode or the like in order to exploit and conduct it, and this can be prevented by measuring a phase current using a shunt resistor. In addition, since the shunt resistor is a linear passive element, the linearity of the measured value can be guaranteed, and since the wattmeter according to the embodiment of the present invention is a structure using a resistor, the shunt resistor can be simply configured as compared to the wattmeter using the CT.

3 shows a wattmeter in accordance with one embodiment of the present invention. The wattmeter is a wattmeter of a three-phase power supply using a shunt resistor, and includes a shunt resistor unit 310 connected to one of three-phase currents to measure an amount of current; Independent power supply unit 330 for supplying power independent of the three-phase power; And a control unit 300 that calculates the amount of power consumed using the amount of current measured by the shunt resistor.

The shunt resistor unit 310 may be a resistor connected in series to the current flow of the three-phase power source. The shunt resistor 310 should be a small value because the voltage drop should be minimized. For example, the resistance value may be about 100 μΩ to 120 μΩ, but is not limited thereto. The shunt resistor unit 310 may measure the amount of current using its resistance value by measuring the voltage drop across both ends thereof.

The independent power supply unit 330 may provide a power independent of the three phase power. Being independent of the three-phase power supply means that it must be isolated or separated so as not to be affected by the three-phase power supply. In order to configure each phase current or phase voltage similar to measuring the current or voltage for a single phase, it is required to eliminate the line voltage difference between each phase. If, without such an independent power supply unit 330, the voltage drop value through the three shunt resistor unit 310 is detected and input to each of the control unit 320, these values eventually result in a voltage difference of about 380 volts, the control unit 320 will be damaged. Accordingly, each measuring unit 300 preferably includes independent power supplies 330 independent of the power of each measuring unit.

The controller 320 may be a general microprocessor, a microcontroller, a controller, or the like. The controller 320 may calculate a power value using the measured voltage value and the measured current value, and accumulate the power value over time to calculate the total amount of power consumed.

The measurement unit 300 may further include a voltage divider (1a to 1c and 2a to 2c of FIG. 2) for measuring the voltage of the three-phase power source. In addition, the controller 320 may calculate the amount of power consumed in the phase using the measured current amount and the measured voltage, and calculate the total power consumption by integrating the amount of power consumed in each phase.

One measurement unit 300 may exist for each phase power source to measure the amount of power of each of the three phase power sources, and each measurement unit includes an insulated communication unit 340, and the amount of power measured in each phase through the communication unit. The total amount of power can be calculated by sending or receiving. Meanwhile, although the controller 320 is illustrated as being present in all the measurement units 300, the controller 320 may be provided only in any one of the measurement units 300 corresponding to each phase. In addition, even if the control unit 320 is included in each measurement unit 300, there is a separate control unit (not shown), so that the control unit receives the amount of power from the control unit 320 of each measurement unit 300 Receive and calculate the total amount of power.

Having described the embodiments of the present invention above, those of ordinary skill in the art will recognize that these embodiments are illustrative rather than limiting, and that various changes and modifications may be made without departing from the scope or spirit of the invention Variations, and modifications may be made without departing from the scope of the present invention.

Claims (7)

As a power meter of a three-phase power supply using a shunt resistor,
A shunt resistor unit connected to one of three-phase currents to measure current; And
And a control unit that calculates the amount of power consumed by using the current value measured by the shunt resistor unit.
The method of claim 1,
A power meter further comprising an independent power supply for supplying power independent of the three-phase power to the measurement unit.
The power meter of claim 1, wherein the measuring unit is present for each phase power source to measure the amount of power of each of the three phase power sources.
The electricity meter of claim 1, wherein each measurement unit includes an insulated communication unit, and calculates the total amount of power of the three-phase power source by transmitting or receiving an amount of power measured in each phase through the communication unit.
The method of claim 1, wherein the measuring unit,
A power meter further comprising a voltage divider for measuring the voltage of the three-phase power source.
6. The apparatus of claim 5,
A power meter that calculates the amount of power consumed in each phase using the measured current value and the measured voltage value, and calculates the total power consumption by integrating the amount of power consumed in each phase.
The wattmeter of claim 1, wherein the shunt resistor unit measures a voltage drop across both ends of the shunt resistor to measure a current using its resistance value.

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