CN202748407U - Low-cost single-phase harmonic electric energy meter - Google Patents

Abstract

The utility model discloses a low-cost single-phase harmonic electric energy meter, which comprises a sampling and measuring part, a storage part, a main control unit MCU, a power supply part, a communication part and a display part, and is characterized in that: the front end of the sampling and measuring part samples the current and voltage Signal, one current signal is sent to the metering chip after passing through the low-pass filter, the other current signal directly enters the metering chip, the voltage sampling signal directly enters the metering chip, and the fundamental current signal, the total current signal, and the voltage signal are obtained by metering the metering chip , fundamental electric energy, total electric energy. The utility model has a reasonable structure and solves the problem that the ordinary electric energy meter without a special harmonic measurement chip cannot measure the harmonic.

Description

A low-cost single-phase harmonic energy meter

technical field

The utility model relates to a single-phase harmonic electric energy meter.

Background technique

With the development of science and technology, the improvement of industrial production and people's living standards, a large number of non-linear electrical equipment has been put into operation in the power grid, causing the harmonic components of the power grid to account for an increasing proportion. It not only increases the power supply loss of the power grid, but also interferes with the normal operation of the protection devices and automation devices of the power grid, causing malfunction and refusal of these devices, directly threatening the safe operation of the power grid. The quality of electric energy directly affects the quality of industrial products, so we must control the harmonics generated by non-linear electrical equipment, which requires us to complete the measurement of harmonics first.

At present, the vast majority of electric energy meters on the market do not have the harmonic measurement function. CN101382588A discloses a patent for a harmonic electric energy meter. The harmonic electric energy measurement module of the harmonic electric energy meter includes a voltage and current conversion unit and a DSP calculation module. , the DSP calculation module includes an FFT transformation module and a compensation module for the amplitude and phase of the harmonic parameters. That is to say, the harmonic energy meter needs a dedicated metering unit for measuring harmonics, high-speed sampling and complex digital signal processing to obtain information such as harmonic energy. For the design of harmonic energy meters, the selection of sampling chips is very limited, and the cost is very high, which is not conducive to the promotion and use of harmonic energy meters.

Utility model content

The purpose of the utility model is to provide a low-cost single-phase harmonic energy meter with reasonable structure and the function of accurately measuring harmonics.

The technical solution of the utility model is:

A low-cost single-phase harmonic energy meter, including a sampling and measuring part, a storage part, a main control unit MCU, a power supply part, a communication part, and a display part. After passing through the low-pass filter, it is sent to the metering chip, and the other current signal directly enters the metering chip, and the voltage sampling signal directly enters the metering chip, and the fundamental current signal and total current signal, voltage signal, and fundamental electric energy are obtained through metering chip measurement. total power.

The low-pass filter is a 4th-order filter formed by cascading two two-order elliptic low-pass filters, and each two-order elliptic filter is composed of three single operational amplifiers with a number of resistors and capacitors, two of which are The amplifier cooperates with the corresponding resistors and capacitors to realize the function of two-order elliptic filtering. The voltage gain of the other single operational amplifier is 1, its input resistance tends to infinity, and its output resistance tends to zero. It is used as a voltage follower in the circuit to realize two The first order elliptic filter is isolated from the output.

The first two-order elliptic filter in the two two-order elliptic low-pass filters is composed of operational amplifiers U1, U2, U3, resistors R1, R2, R3, R4, R5, R6, capacitors C1, C2, and the operational amplifier The positive input terminal is grounded, the negative input terminal is connected to the signal, and the signal is input from the R1 terminal. The other end of R1 and C1 are connected in series with U1 to form a first-order low-pass filter, and R2 and C2 are connected in series with U2 to form a first-order filter, where R1 and C1 are respectively It is equal to the value of R2 and C2; the resistor R4 connected to both ends of U2 is a negative feedback resistor, which makes the system work stably; R5, R6 and U3 are used as voltage followers in the circuit to realize the isolation of the second-order elliptic filter and the output. One end of R3 is connected to the output of U3, and the other end is connected to the negative input of U1, which feeds back-end signals to the front input. The second of the two two-order elliptic low-pass filters consists of U4, U5, U6, R7, R8, R9, R10, R11, R12, R13, R14, C3, C4, R7 It is connected in series with C3 and U4 to form a first-order low-pass filter, and R10 and C4 are connected in series with U5 to form a first-order filter. One end of R9 is connected to the negative input end of U5, and the other end is connected to the output end of U3, where R7 and C3 are respectively It is equal to the value of R10 and C4; the resistor R12 connected to both ends of U5 is a negative feedback resistor, and its function is to stabilize the operating point; R13, R14 and U6 are used as voltage followers in the circuit to realize the isolation of the second-order elliptic filter from the output ; One end of R11 is connected to the output of U6, and the other end is connected to the negative input end of U4, and the back-end signal is fed back to the front input end.

The utility model designs a low-cost low-pass filter circuit in the current sampling link, and then uses the common metering chip which also has the characteristics of two current sampling circuits to measure the fundamental wave current and the total current at the same time, so that the fundamental current can be subtracted from the total current. Harmonic current can be obtained from wave current, and data such as active energy and harmonic distortion rate of fundamental wave and harmonic can also be obtained through calculation, which solves the problem that ordinary electric energy meters that do not use special harmonic measurement chips cannot measure harmonics.

The filter circuit of the utility model uses a 4th-order elliptical low-pass active filter to extract the fundamental current from the total current, thereby realizing the measurement of harmonic electric energy and fundamental electric energy, and then realizing the measurement of harmonic electric energy.

The cut-off frequency of the filter designed by the utility model is 60 Hz, the ripple coefficient in the pass band is less than 0.05 dB, and has good filter characteristics. This design has a margin for the cut-off frequency. When the grid current frequency changes slightly, it will not cause negligible attenuation to the fundamental wave signal; the cut-off characteristic of the stop band is good, and it has an attenuation of more than 18dB for 100Hz signals. For practical applications The third harmonic signal (150Hz) with a large medium content has an attenuation of more than 56dB, and it also has an attenuation of about 40dB for other high-frequency signals, which fully meets our needs.

The harmonic current, fundamental active power and total active power can be calculated through the above fundamental current signal, total current signal and voltage signal, and then the harmonic total active power can be obtained by subtracting the two, and can also be calculated Power grid parameters such as current distortion rate.

The low-cost harmonic electric energy meter of the utility model can accurately measure harmonic electric energy, and its filter circuit solves the problem that ordinary electric energy meter metering chips cannot measure harmonic electric energy. Strong performance, the energy meter can accurately measure harmonic energy without using a dedicated metering chip. The utility model has the advantages of low cost and easy maintenance, and can be conveniently put into mass use. The filter circuit in the utility model can be applied to most existing electric energy meters for harmonic measurement.

Description of drawings

Below in conjunction with embodiment the utility model is further described.

Fig. 1 is the structural block diagram of the harmonic electric energy meter of the present utility model;

Fig. 2 is a structural block diagram of the sampling and measuring part of the harmonic electric energy meter of the present utility model;

Figure 3 is a schematic diagram of the low-pass filter circuit.

Detailed ways

A low-cost single-phase harmonic energy meter, including sampling and metering part (metering module), storage part (storage module), main control unit MCU, power supply part (power supply module), communication part (communication module), display part, sampling The front-end sampling of the metering part obtains the current and voltage signals, one current signal passes through the low-pass filter and then is sent to the metering chip, the other current signal directly enters the metering chip, the voltage sampling signal directly enters the metering chip, and the fundamental current signal is obtained by metering the metering chip And total current signal, voltage signal, fundamental wave electric energy, total electric energy.

The low-pass filter is a 4th-order filter formed by cascading two two-order elliptic low-pass filters, and each two-order elliptic filter is composed of three single operational amplifiers with a number of resistors and capacitors, two of which are The amplifier cooperates with the corresponding resistors and capacitors to realize the function of two-order elliptic filtering. The voltage gain of the other single operational amplifier is 1, its input resistance tends to infinity, and its output resistance tends to zero. It is used as a voltage follower in the circuit to realize two The first order elliptic filter is isolated from the output.

The first two-order elliptic filter in the two two-order elliptic low-pass filters is composed of operational amplifiers U1, U2, U3, resistors R1, R2, R3, R4, R5, R6, capacitors C1, C2, and the operational amplifier The positive input terminal is grounded, the negative input terminal is connected to the signal, and the signal is input from the R1 terminal. The other end of R1 and C1 are connected in series with U1 to form a first-order low-pass filter, and R2 and C2 are connected in series with U2 to form a first-order filter, where R1 and C1 are respectively It is equal to the value of R2 and C2; the resistor R4 connected to both ends of U2 is a negative feedback resistor, which makes the system work stably; R5, R6 and U3 are used as voltage followers in the circuit to realize the isolation of the second-order elliptic filter and the output. One end of R3 is connected to the output of U3, and the other end is connected to the negative input of U1, which feeds back-end signals to the front input. The second of the two two-order elliptic low-pass filters consists of U4, U5, U6, R7, R8, R9, R10, R11, R12, R13, R14, C3, C4, R7 It is connected in series with C3 and U4 to form a first-order low-pass filter, and R10 and C4 are connected in series with U5 to form a first-order filter. One end of R9 is connected to the negative input end of U5, and the other end is connected to the output end of U3, where R7 and C3 are respectively It is equal to the value of R10 and C4; the resistor R12 connected to both ends of U5 is a negative feedback resistor, and its function is to stabilize the operating point; R13, R14 and U6 are used as voltage followers in the circuit to realize the isolation of the second-order elliptic filter from the output ; One end of R11 is connected to the output of U6, and the other end is connected to the negative input end of U4, and the back-end signal is fed back to the front input end.

A filter circuit is added to the metering part, combined with an ordinary metering chip, to accurately separate the fundamental current, so as to obtain the total electric energy and the fundamental electric energy, and then subtract the fundamental electric energy from the total electric energy to obtain the harmonic electric energy we need. This makes the ordinary electric energy meter can accurately measure harmonics, and its structural block diagram is shown in Figure 2.

(1) After sampling the current, the total current signal I(t) is obtained;

(2) total current signal obtains fundamental current signal I (t) through _the low-pass filter designed by the utility model, and the attenuation of the designed low-pass filter at signal frequency 50 Hz is very small, and the amplitude-frequency characteristic is comparatively flat. Ripple is less than 0.05dB;

(3) According to the above-mentioned fundamental wave current signal, total current signal and voltage signal, calculate the fundamental wave power of the power grid, the fundamental wave current effective value, the total current effective value, and the total power.

(4) According to the fundamental wave current signal and total current signal, fundamental wave power, total power, fundamental wave electric energy, and total electric energy obtained by the main control MCU from the sampling and metering part, we can get what we need by subtracting the fundamental electric energy from the total electric energy Total harmonic energy; the total current minus the fundamental current signal can get the harmonic current signal, and the harmonic current distortion rate can be obtained by dividing the harmonic current by the fundamental current.

As shown in Figure 2, the input current signal contains fundamental wave and harmonic signal. The utility model sends one total current signal to the metering chip, and the other current signal to a low-pass filter to filter out harmonic components and then sends it to the metering chip. . The purpose of the low-pass filter is to filter out other harmonic signals except the fundamental wave to ensure that there is a small ripple in the passband, especially between 45-55Hz. We use a 4th-order elliptic filter to achieve low-pass filtering , its ripple between 45-55Hz is less than 0.05dB, and its cut-off characteristics are good, it has an attenuation of more than 18dB for 100Hz signals, and has an attenuation of more than 56dB for the main signal (150Hz) that needs to be filtered, and for other high-frequency signals There is also an attenuation of about 40dB, which fully meets our needs.

The 4th-order elliptic active filter not only ensures that the filter has better cut-off characteristics, but also controls the ripple in the passband within a small range, and the attenuation near 50Hz is only 0.01714dB.

The transfer function of the 4th-order elliptic low-pass active filter; when the distance between the pole of the transfer function and the imaginary axis is relatively far, its rise time is relatively short, which means that the system response speed is relatively fast, but the ripple is relatively large, indicating that the system's The response speed is relatively good, but the overall dynamic performance of the system is relatively poor, indicating that its steady-state performance is relatively poor; when the distance between the pole of the transfer function and the imaginary axis is relatively close, its rise time is relatively long, which indicates that the system response speed is relatively slow , but the ripple is small, the overall dynamics of the system is better, and its steady-state performance is better; comprehensively considering the response speed, that is, the cut-off characteristic and the ripple, the 4th-order elliptic low-pass filter designed by the utility model can operate at 45- The ripple between 55Hz is less than 0.05dB, and its cut-off characteristics are good. It has more than 18dB attenuation for 100Hz signal, more than 56dB attenuation for the main signal (150Hz) that needs to be filtered out, and about 40dB attenuation for other high-frequency signals. .

According to the above-mentioned fundamental wave current signal and total current signal, calculate the fundamental wave power of the power grid, the fundamental current effective value, the total current effective value, the total power and the total harmonic power.

Claims (3)

1. A low-cost single-phase harmonic watt-hour meter, comprising a sampling and metering part, a storage part, a main control unit MCU, a power supply part, a communication part, and a display part, is characterized in that: the current and voltage signals obtained by sampling at the front end of the sampling and metering part, One current signal is sent to the metering chip after passing through the low-pass filter, the other current signal directly enters the metering chip, and the voltage sampling signal directly enters the metering chip. 2. A kind of low-cost single-phase harmonic watt-hour meter according to claim 1, characterized in that: said low-pass filter is a 4th-order filter composed of two two-order elliptic low-pass filter cascades, Each two-order elliptic filter is composed of three single operational amplifiers with a number of resistors and capacitors, two of which cooperate with corresponding resistors and capacitors to realize the function of two-order elliptic filtering, and the voltage gain of the other single operational amplifier is 1, and its input The resistance tends to infinity, and the output resistance tends to zero, which is used as a voltage follower in the circuit. 3. a kind of low-cost single-phase harmonic watt-hour meter according to claim 2 is characterized in that: the first two-order elliptic filter in two two-order elliptic low-pass filters is by operational amplifier U1, U2, U3, composed of resistors R1, R2, R3, R4, R5, R6, capacitors C1, C2, the positive input terminal of the operational amplifier is grounded, the negative input terminal is connected to the signal, the signal is input from the R1 terminal, and the other terminal of R1 and C1 are connected in series with U1 Form a first-order low-pass filter, R2 and C2 are connected in series 2, where R1 and C1 are equal to the values of R2 and C2 respectively; the resistor R4 connected to both ends of U2 is a negative feedback resistor; R5, R6 and U3 are used as voltage followers in the circuit One end of R3 is connected to the output of U3, and the other end is connected to the negative input end of U1, and the back-end signal is fed back to the front input end. The second second-order low-pass elliptic filter of the two two-order elliptic low-pass filters consists of U4, U5, U6, R7, R8, R9, R10, R11, R12, R13, R14, C3, C4, R7 It is connected in series with C3 and U4 to form a first-order low-pass filter, and R10 and C4 are connected in series with U5 to form a first-order filter. One end of R9 is connected to the negative input end of U5, and the other end is connected to the output end of U3, where R7 and C3 are respectively It is equal to the value of R10 and C4; the resistor R12 connected to both ends of U5 is a negative feedback resistor; R13, R14 and U6 are used as voltage followers in the circuit; one end of R11 is connected to the output of U6, and the other end is connected to the negative of U4 Input, which feeds the back-end signal to the front input. the

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