Application design of intelligent energy-saving socket

1. Introduction to the main chip HLW8012 of the smart socket solution

HLW8012 provides a highly accurate and low-cost energy measurement solution for socket manufacturers and smart home manufacturers. This integrated chip is designed for residential single-phase energy meters or smart sockets, and can accurately measure the effective value of current IRMS and voltage VRMS, active power and electricity.

Internal structure of HLW8012

The internal structure of HLW8012 is shown in Figure 1. It consists of two programmable gain amplifiers, two Δ-Σ modulators, matching high-speed filters, power calculation, power monitoring, serial interface and corresponding function registers. The two programmable amplifiers collect voltage and current data, the Δ-Σ modulator samples and processes the analog quantity, filters the available voltage and current digital signals, and outputs the calculated power value, voltage effective value and current effective value through pulse indication.

2. Working Principle of Chip HLW8012

The V1P and V1N pins of HLW8012 input current signal waves. The current channel integrates a fixed gain amplifier, and the maximum differential input signal allowed is ±43.75mV; the maximum input signal allowed by the voltage channel is ±700mV. HLW8012 can use low-cost manganese copper sampling resistors or current transformers to measure current, and use voltage divider resistors or voltage transformers to measure voltage. The pulse output frequency of the chip is proportional to the active energy.

3. Main features of HLW8012

High frequency pulse CF, indicating active power, meets the accuracy requirements of 50/60Hz IEC 687/1036 standards and achieves ±0.2% accuracy within a 1000:1 range.

High frequency pulse CF1, can be configured to output current RMS or voltage RMS, with an accuracy of ±0.5% within a 500:1 range.

Built-in power supply monitoring circuit, when the power supply voltage drops to 4V, the chip enters reset state.

· Built-in 2.43V voltage reference source.

5V single power supply, working current is less than 3mA.

SOP8 package

Figure 2 is the functional block diagram of the intelligent energy-saving socket, which consists of a power module, a main controller module, an electric energy signal acquisition circuit, and a wireless communication module. The figure shows the functional block diagram of the intelligent energy-saving socket, which consists of a power module, a main controller module, an electric energy signal acquisition circuit, and a wireless communication module. The main controller is NEC's 9234. To eliminate the serial communication baud rate error, the crystal oscillator is set to 11.0592M. The power supply part uses an AC-DC circuit, which converts 220V to 12V, and then converts it to 5V through a voltage regulator chip to provide power to the main control MCU NEC9234, the electric energy metering IC HLW8012 and the relay. Since most of the current wireless modules use a 3.3V working power supply, the 5V power supply needs to be stepped down to 3.3V by DC-DC before being provided to the WIFI wireless module, such as a timer switch, overload alarm, etc.

Functional block diagram of smart energy-saving socket

1 Power circuit

Smart socket power circuit

There are two power supply circuits. One is to convert AC 220V into 12V power through AC-DC. The SY50103 chip is used to provide 1A current, and the ripple is controlled within 100mV. The advantages of the switching power supply are low power, high conversion efficiency, and small size, which is suitable for placing in a smaller socket. The switching power supply circuit diagram is shown in the figure below: The relay uses a 12V 10A relay. The cost of a 12V relay is lower than that of a 5V relay. Since the main controller and the energy metering IC need to provide a 5V power supply, and the wireless WIFI module is powered by a 3.3V power supply, the 12V power supply is divided into two paths after it comes out. One path uses the voltage regulator chip 78L05 to reduce the power supply to 5V to provide power to the MCU and HLW8012; the other path uses a DC-DC chip to convert 12V to 3.3V to provide power to the wireless module.

2 Metering function circuit

The sampling circuit includes two parts: current signal sampling and voltage signal sampling.

The voltage sampling collects the voltage on the neutral line signal. Since the voltage signal is large and the effective value is 220V, sampling is achieved by reducing the voltage through a resistor network. The voltage is divided by connecting 6 470K resistors and 1 1K resistor in series, and then connected to the voltage input sampling terminal V2P pin of the metering chip HLW8012.

The V1P and V1N pins of HLW8012 are current sampling channels, which collect the voltage drop across the manganese copper resistor. When the current flows through the manganese copper resistor, a voltage drop will be generated. The voltage drop of manganese copper resistors with different resistance values ​​is different. The resistance value of manganese copper resistor is generally 2 milliohms or 5 milliohms. The resistance value should not be too large. When a large current passes through, the resistance value of the sampling resistor is too large and it is easy to cause heat, which will affect the resistance value of the sampling resistor and make the measurement result inaccurate.

The internal DSP of HLW8012 has a certain gain. After the frequency conversion module, the active power and current effective value

The output frequency of the voltage RMS can be calculated by the following formula:

(1) Active power calculation formula:

(2) Current effective value calculation formula:

(3) Voltage effective value calculation formula:

V1: Voltage signal on the current channel pin

V2: Voltage signal on the voltage channel pin

Fosc: Built-in crystal oscillator, typical frequency is about 3.579MHz

Vref: built-in reference source, typical voltage is 2.43V

The main controller is a single-chip microcomputer NEC 9234, which is the core controller of the entire circuit. It reads the load current effective value, voltage effective value and load power. And it can turn the load power on or off through the relay. The controller can transmit the relay's switch status, working time, power consumption, voltage effective value and current effective value data to the server through the wireless WIFI module. The server stores and analyzes the data to achieve a more intelligent control purpose.

Four intelligent socket software design

Main program flow chart:

Conclusion

The smart socket solution using HLW8012 can accurately measure the power consumption of electrical appliances; this solution reduces the number of peripheral components, improves the measurement accuracy of the system, and has the advantages of high reliability, high accuracy and low cost.