Design of solar metal halide lamp controller based on C8051F920

In today's world where energy shortage and environmental pollution are becoming increasingly serious, how to effectively utilize clean solar energy is becoming an energy strategy for sustainable development in various countries. At present, most lighting equipment still uses traditional energy for lighting, so making full use of solar energy as the energy supply for lighting equipment is of great significance in terms of energy conservation and environmental protection.
To this end, a metal halide lamp controller with solar power supply function is designed. The controller has both the function of metal halide lamp electronic ballast and solar charger. As an electronic ballast, the controller has the advantages of high power factor, stable operation and small size compared with traditional ballasts. As a controller with solar power supply function, according to the setting, the controller controls the solar charging system to charge the 12 V/100 Ah battery during the day and makes the metal halide lamp work at night. Since solar photovoltaic panels are easily damaged by lightning in the natural environment, the controller also takes into account the protection function of lightning strike when designing.

1 Overall structure of the controller
The controller uses a micro-packaged C8051F920 single-chip IC as the CPU. As a highly integrated (SoC) and high-speed (100 MIPS) IC, the C8051F920 has the following features:
(1) High-performance integrated analog peripherals. When collecting data, external analog components and system calibration and multi-channel high-speed sampling can generally be eliminated, which is conducive to power-saving design. At the same time, external clock devices can also be eliminated. The analog signal wiring has been completed on the chip, so the PCB design can be simplified and the noise performance of the system can be improved. It has a 10-bit resolution ADC and a high-precision internal oscillator (1.5%).
(2) External communication interface. UART, SM-Bus/12c, SPI can be selected as a serial communication interface through software, and it has special serial interfaces USB 2.0, CAN 2.0B, 16-bit and 8-bit multiplexed and non-multiplexed parallel data buses.
(3) High-performance digital I/O. It has a counter/timer PCA module, and the I/O can be dynamically configured in real time.
The hardware structure block diagram of the controller is shown in Figure 1.

The solar photovoltaic panel is connected to the photovoltaic signal processing circuit, and the photovoltaic voltage is sent to the 12 V battery through the PWM charging control circuit. During normal operation, the output voltage of the 12 V battery is boosted and rectified by the secondary induction of the high-frequency planar transformer to the full-bridge circuit. At the same time, the 12 V output voltage is connected to the voltage conversion circuit to supply power to other circuits of the controller.
The full-bridge drive circuit is connected to the ignition circuit and the metal halide lamp. The full-bridge drive circuit uses the UBA2032 chip. When the metal halide lamp is short-circuited, the full-bridge drive short circuit can shut down the full bridge. The keyboard and display human-machine interface can set the ignition time, mode, charging overvoltage protection range, etc. The boost rectifier circuit is connected to the switch control circuit to boost the input 12 V to 60-120 V for the metal halide lamp to work.
The MCU monitoring circuit is connected to the PWM charging circuit, the voltage conversion circuit, the full-bridge drive circuit, the keyboard and display human-machine interface to control the charging and discharging of the 12 V battery, the ignition coil, the start-up and stable operation of the metal halide lamp and the circuit protection. The ignition circuit rectifies the boosted negative voltage and forms a 10-20 kV lighting voltage together with the lighting coil. The signal detection and conversion circuit has the function of detecting the current voltage and current of the 12 V battery, the battery charging current, and the voltage of the photovoltaic signal processing circuit. [page]

The photovoltaic signal processing circuit includes a signal reverse connection protection circuit, a photovoltaic voltage sampling circuit and a lightning protection circuit. Among them, the signal reverse connection protection circuit can prevent the photovoltaic signal reverse connection input from damaging the controller circuit. The voltage sampling circuit provides the sampled photovoltaic voltage signal to C8051F920. The lightning protection circuit can prevent lightning and lightning in the sky from being introduced into the controller and causing damage. The PWM charging control circuit will charge the battery, and the PWM signal output by the MCU is used to drive the high-power MOS tube to control the size of the charging voltage to avoid damage to the battery.
2.2 Electronic ballast circuit design
The boost rectifier circuit includes a flyback boost high-frequency planar transformer, a fast recovery rectifier diode and a protection circuit. The primary of the high-frequency planar transformer is connected to the input end of the power supply and the power MOS tube, and the secondary is connected to the rectifier diode and the protection circuit. When the metal halide lamp is started, the secondary provides a DC voltage of about 400 V, which is converted into a DC voltage of 1,200 V by the triple voltage rectifier circuit. During normal operation, the secondary of the transformer provides a DC voltage of 60 to 120 V. The boosted voltage signal is transmitted to C8051F920 through LM2902 to realize voltage sampling detection.
The full-bridge drive circuit adopts the UBA2032 high-voltage single-chip IC launched by Philips. The UBA2032 chip integrates voltage regulators, oscillators, input signal delay and bridge prohibition circuits, control logic, high/low voltage level shifters, high-end left/right drivers and low-end left/right drivers and other unit circuits. When the metal halide lamp is short-circuited, the full-bridge driver short circuit can turn off the full bridge to protect the metal halide lamp.
The keyboard display circuit is connected to the SPI interface of C8051F920, which can realize the setting of lighting time, mode, charging overvoltage protection range, etc. ZLG7290 is a new keyboard and display interface chip with I2C bus. The keyboard and display circuit designed with this chip can be unplugged after setting the parameters, which simplifies the controller hardware and software design. The signal detection and conversion circuit converts the charging current and the lighting current into corresponding voltages on the sampling resistor, and amplifies them to a suitable range to the A/D input of the MCU; on the other hand, the lighting voltage signal of the lighting current signal is connected to the switch control circuit through the amplification and comparison circuit to directly control the open circuit and short circuit protection of the lamp.
2.3 Design of the ignition circuit
The operation of the metal halide lamp can be divided into three stages: the electrode releases free electrons, and the electrons are accelerated in the external electric field; the kinetic energy of the free electrons is converted into the excitation energy of the gas atoms; and the excitation energy is converted into light energy.
Figure 3 is the volt-ampere characteristic curve of the metal halide lamp.

Since the metal halide lamp is filled with inert gas, its breakdown voltage is very high, usually required to reach about 20 kV, so the ignition circuit is required to provide a sufficiently high voltage. Based on this, by connecting the secondary of the transformer to the triple voltage ignition circuit shown in Figure 4, a voltage of 1200 V can be obtained. After connecting the lighting coil to the metal halide lamp, a lighting voltage of about 20 kV can be obtained at the two poles of the metal halide lamp. [page]

3 Charging system software design
The software adopts modular design, and its workflow is shown in Figure 5. The voltage of the solar photovoltaic panel and the battery is detected in real time through the program. When charging the battery during the day, the PWM charging voltage is controlled to avoid damaging the battery due to excessive charging voltage; at night, the charging circuit is turned off, and the battery voltage and lighting mark are detected. The lighting program is started only when the set lighting requirements are met.

4 Conclusion This paper
introduces the design of a metal halide lamp controller with solar power supply function. The dual functions of electronic ballast and solar charging are realized by using C8051F920 single chip microcomputer. After fully understanding the working characteristics of metal halide lamps, the sub-circuits of the controller are designed. After test measurement, the working current of the whole machine is less than 20 mA, which greatly reduces the power consumption of the controller itself. After real-time detection of the battery power, the controller controls the working state of the solar charging system and the various working states of the lamp, which can make the metal halide lamp run reliably and stably, meeting the design requirements.