1 Introduction
The current electric energy measurement chip has the function of electric energy measurement, that is, it can measure the voltage, current, and electric energy consumed by the electric equipment, based on such functions are very complete. In the actual electricity use process, there is always a certain percentage of electrical leakage. In response to this phenomenon, there are many leakage detection and leakage protection devices on the market, but they are all used as another external device to be installed outside the meter [1]. Even so, such leakage detection equipment still has such problems:
(1) Classification of leakage detection specifications: Generally, the general leakage levels are divided into specifications such as 6 mA, 10 mA, 30 mA or more than 100 mA, and often a leakage detection device can only detect or protect against one specification. This results in that leakage detection equipment of different specifications can only be selected for different electrical appliances, and leakage detection equipment of different specifications cannot be mixed, otherwise it will cause false detection or false alarms [2].
(2) Leakage detection often can only distinguish the leakage current, but cannot analyze what kind of equipment is leaking. Because the current leakage detection method is simply to detect the leakage current, it does not analyze the other electric energy characteristics of the equipment, so it cannot determine what kind of equipment leakage is, so it is impossible to carry out targeted alarms or processing [3, 4].
2 Scheme design
Figure 1 shows the schematic diagram of the circuit connection of this design. It includes the electric energy metering chip IC1, which can make the BL6523 series or BL093X series metering chips produced by Shanghai Belling, the residual current transformer CT1, the metering current transformer CT2, the metering voltage transformer PT, MCU and Relay drive. Figure 2 shows a schematic diagram of the internal structure of the energy measurement chip IC1.
It can be seen in Figure 2 that the energy measurement chip IC1 has the following pins: IAN pin and IAP pin, IBN pin and IBP pin, VP pin and VN pin, VREF pin, and two GND pins , VDD pin, /RST pin, CF pin, CF1 pin and CF2 pin, RX pin and TX pin.
Among them, the IAN pin and the IAP pin form the first current sampling channel, the IBN pin and the IBP pin form the second current sampling channel, and the VP pin and the VN pin form the voltage sampling channel. The VREF pin provides the reference voltage for the energy measurement chip IC1, the VDD pin provides the reference voltage source for the energy measurement chip IC1, the GND pin is grounded, the /RST pin is used for reset, and the CF pin, CF1 pin and CF2 pin are Three output pins, RX pin and TX pin are serial ports, RX pin is used for signal input, TX pin is used for signal output.
The energy measurement chip IC1 also includes a signal processing module and UART (Universal Asynchronous Receiver Transmitter). The signal processing module is respectively connected with the first current sampling channel, the second current sampling channel and the voltage sampling channel. The signal processing module is also connected to the UART, which provides a serial port.
The first current sampling channel is used to sample the leakage current of the electrical circuit and transmit the leakage current to the signal processing module. The signal processing module uses the comparison relationship between the leakage current and a preset threshold to perform leakage detection. The second current sampling channel is used to sample the electric current of the electric circuit and transmit the electric current to the signal processing module. The voltage sampling channel is used to sample the electric voltage of the electric circuit and transmit the electric voltage to the signal processing module. The signal processing module uses electric current and electric voltage to measure electric energy.
In order to sample the leakage current of the electric circuit, the connection mode of the first current sampling channel is as follows. The first current sampling channel (ie IAN pin and IAP pin) is connected to the secondary of the residual current transformer CT1, and the primary of the residual current transformer CT1 is connected in series between the live line L and the neutral line N of the power circuit.
When there is no leakage in the electric circuit, the incoming line current between the live line L and the neutral line N is equal to the present current, and the residual current transformer CT1 will not generate a magnetic flux signal. When there is a leakage current in the electrical circuit, a current difference occurs between the live line L and the neutral line N. According to Kirchhoff’s law, an induced voltage is generated in the coil of the residual current transformer CT1, and the secondary of the residual current transformer CT1 generates induction Signal, the first current sampling channel samples the sensing signal and transmits the sensing signal to the signal processing module. The signal processing module performs analog-to-digital conversion on the induction signal to obtain the leakage current waveform, and obtains the amplitude of the leakage current by digital signal processing on the leakage current waveform, and sends an alarm when the amplitude exceeds a preset threshold.
3 Setting of leakage preset threshold
Connect the serial port to the MCU, the MCU inputs an instruction to set the preset threshold, the serial port transmits the instruction input by the MCU to the signal processing module, and the signal processing module sets the preset threshold according to the instruction. In order to be suitable for different use environments and meet the requirements of different leakage detection levels, different preset thresholds can be set. Specifically, the signal processing module includes a number of alarm registers. The serial port is connected to the alarm register. The serial port sets at least one register value of the alarm register according to the instruction input by the MCU, and each register value corresponds to a preset threshold. As shown in Table 1.
Take the need to meet the leakage level detection of 6 mA as an example. The MCU input command is transmitted to the alarm register through the serial port. The alarm register sets the register value to 000. The preset threshold at this time is 8 mV. If the amplitude of the leakage current exceeds 8 mV, an alarm is issued.
This program provides two alarm methods.
(1) The CF1 pin and CF2 pin are used as the drive output pins for connecting the relay drive, and the drive output pin sends out an alarm by outputting the drive signal used to drive the relay drive action.
(2) The CF pin is used as a pulse output pin for outputting alarm pulses, and the pulse output pin generates an alarm by outputting alarm pulses. The CF pin can also have the function of measuring pulse output, and the alarm pulse can be a fast pulse different from the normal measuring pulse.
In order to realize electric energy measurement, the connection of the second sampling channel is as follows: the second sampling channel (ie IBN pin and IBP pin) is connected to the secondary of the metering current transformer CT2, and the primary of the metering current transformer CT2 is connected in series with On the live wire L of the electrical circuit; the connection of the voltage sampling channel is: the voltage sampling channel (ie VP pin and VN pin) is connected to the secondary of the measuring voltage transformer PT, and the primary of the measuring voltage transformer PT is connected in parallel Between the live wire L and the neutral wire N of the electric circuit,
The second current sampling channel samples the secondary current signal of the metering current transformer CT2 and transmits the current signal to the signal processing module. The voltage sampling channel samples the voltage signal between the live wire L and the neutral wire N and transmits the voltage signal to the signal Processing module.
The signal processing module performs analog-to-digital conversion on the current signal to obtain the current electric waveform (current electric waveform includes the live wire electric waveform and the neutral electric waveform), and performs the analog-digital conversion on the voltage signal to obtain the voltage electric waveform. Digital signal processing is performed on the electric current waveform and the electric voltage waveform to obtain several parameters for electric energy measurement, such as current and voltage effective value, power factor, active/apparent power value, active/apparent energy value, etc. The serial port can output the above parameters to the connected MCU, and the serial port can also output the current and voltage waveforms to the connected MCU.
4 Judgment of leakage equipment
The electric energy metering device of this scheme can also realize the judgment of what kind of equipment the electric equipment is, especially for the electric equipment with leakage under the cooperation of the electric energy metering chip IC1 and the MCU.
Specifically, the MCU prestores at least one characteristic waveform of a known electrical device. The characteristic waveform includes the live wire current waveform, the neutral wire current waveform, and the voltage waveform of the known electrical device at certain specific times during use. Known electrical equipment can be freely selected, such as commonly used electrical equipment in households, washing machines, air conditioners, refrigerators, etc. The characteristic waveforms of different electrical equipment are not completely the same, and the characteristic waveform of each known electrical equipment is made Become a library, stored in MCU registers.
As shown in Figure 3, the UART of the energy measurement chip IC1 outputs the electricity consumption waveforms (including the live wire electricity waveform, the neutral wire electricity waveform and the voltage electricity waveform) of the unknown electric equipment to the MCU through the serial port, and the MCU compares the electricity consumption Waveform and the characteristic waveform prestored in the register, find out the characteristic waveform in line with the electric waveform, and output the judgment result of the unknown electric equipment. The unknown electric equipment is the known electric equipment corresponding to the found characteristic waveform. For example, after comparison, the electric waveform of the unknown electric device is the same as the characteristic waveform of the refrigerator, and then it can be determined that the unknown electric device is the refrigerator.
5 Conclusion
Through experimental demonstration, the energy metering chip and the improved metering circuit of this design scheme can achieve traditional energy metering and complete the measurement of voltage, current, and electrical energy by the energy metering chip. It can also be based on the preset threshold value. Different, carry out leakage detection of different specifications, and carry out different alarm output. According to the pre-written voltage and current power waveforms of the known electrical equipment, the actual leakage electrical equipment is analyzed to determine what kind of equipment the leakage electrical equipment is, which has a good application prospect.
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