Application of CSE7759 in smart socket and embedded power metering module

With the improvement of living standards, the concept of green environmental protection is becoming more and more popular. People need to know the power consumption and operation status of each electrical appliance in the home in real time, and find out the links of energy waste in the home in time to contribute to the green earth. Therefore, smart sockets or home appliances with built-in metering modules are entering people's lives with the popularization of the Internet of Things.

1. System Design

The principle block diagram of this system is shown in Figure 1.

Figure 1: Block diagram

The metering chip used in this system is CSE7759 produced by Shenzhen Xinhai Technology Co., Ltd. This chip can provide active power, active energy, current effective value, and voltage effective value in the form of pulses.

1. Measurement design

(1) Current signal sampling

The equivalent circuit of current sampling is shown in Figure 2. When current flows through the manganese copper shunt, a voltage drop will be generated on the current sampling channel of the metering chip. Different current signals form different voltage drops on the shunt. The metering chip collects the voltage signal formed on the shunt to realize the collection of the current signal. The resistance of the shunt should not be too large. When a large current flows through, if the resistance of the shunt is too large, it is easy to cause the shunt to heat up, thereby affecting the size of the shunt resistance.

(2) Voltage signal sampling

Voltage sampling usually collects the signal on the neutral line. Since the voltage signal is large, the voltage signal is sampled directly by reducing the voltage through a resistor network. In principle, the voltage sampling signal should not exceed half of the maximum allowable input value of the channel. The maximum allowable input signal of the CSE7759 voltage channel is 470mv, so the maximum sampling signal of the voltage channel should be set to about 230mv during design.

(3) Power calibration

Load a standard load (the power value is known as P0) and measure the output period T0 of the pulse output terminal CF of the metering chip 7759. Since the output period of CF is 0 when there is no load, and since the power value is linear, we have:

Power calibration coefficient KP=(T0-0)/(P0-0) i.e. KP=T0/P0

When an unknown load is loaded, the pulse period T1 is measured by the MCU. If T0/P0=T1/P1, then P1=T1/KP

(4) Voltage and current calibration

The calculation method of voltage and current is the same as the calculation method of power

2. Communication Design

The communication module uses a small wireless module with an operating frequency of 433MHz, and the module uses the SPI bus to communicate with the MCU. Through this wireless module, the power, voltage, and current can be calibrated, and the power consumption data of each load can be read.

2. Conclusion

CSE7759 has the characteristics of small size (SOP8 package), built-in oscillator, simple peripheral circuit, high precision, etc., which can make the entire PCB very small, meeting the needs of miniaturization of smart socket-level home appliance metering modules. At the same time, it also has rich functions (can provide voltage RMS, current RMS and instantaneous power) and high precision, and is the best choice for energy metering chips in smart sockets and home appliance metering modules.

The smart socket and home appliance metering module designed based on CSE7759 has been tested and can accurately measure the power consumption of electrical appliances.