Intelligent solar hybrid LED street light system

March 21, 2022

This system solution provides a smart solar hybrid light-emitting diode (LED) street light system. This system is an experimental project targeting LED street lights in the STMicroelectronics Park parking lot. It is an independent solar system with an AC-DC LED driver as a backup power source to prevent battery shortage. It automatically switches to a constant current AC/DC LED driver without a battery or low battery. This AC/DC LED driver uses the Quasi-Resonant (QR) mode Power Factor Correction (PFC), which uses single-stage single-switching and primary-level sensing-specific control. Used to drive the LED is HVLED001A, which is already commercialized LED driver.

The main power supply for LED drivers is from energy storage components such as batteries. The battery is charged by means of Maximum Power Point Tracking (MPPT). According to the available literature, MPPT is quite efficient when using solar radiation to charge a battery. The efficiency measured by the MPPT stage power converter is over 97%. A 2-phase boost direct current (DC-DC) converter is recommended as the DC LED driver. The 2-phase AC-DC converter helps to reduce the size of DC large-capacity capacitors and is recommended to be placed on the load side for filtering purposes.

According to the literature data, failure of the power converter due to aging will become a weakness. Finally it will enhance the life of the LED drive system. The efficiency of the direct DC LED driver stage is also higher than 95%. The power conversion efficiency is improved because of the use of high efficiency metal oxide semiconductor field effect transistors (MOSFETs) and gate drive ICs. The LED driver operates at a constant current and is another parameter that enhances the life of the LED. High-efficiency digital power conversion microcontrollers (STM32F3) have been used to successfully perform measurement and decision-making operations on the board.

All street lights are linked to each other via a 6LoWPAN mesh network, which is built using a commercial Sub-GHz component called SPIRIT1. The streetlight nodes communicate with each other via the 6LoWPAN grid technology using the free ISM (Industrial, Scientific and Medical) radio channel (868 MHz). A streetlight node with a solar panel is a lighting node that can talk to the data concentrator unit on the 6LoWPAN technology (grid).

The Light Conditioning Unit (LCU) is powered by the power grid and solar panels. As long as the ambient light and the environment are sensed, the light automatic on/off/adjustment function can be provided. The system also comes with an instruction and control center that has not yet fully developed, allowing end users to control single or group of lighting nodes from any location.

Figure 1 shows a smart solar hybrid lighting management system. Figure 2 shows the lighting equipment installed in the parking lot, which contains the circuit board developed by STMicroelectronics. The Data Concentrator Unit (DCU) comes with an on-board pan-European Digital Mobile Telecommunications System (GSM) module that can be used with the General Packet Radio Service/Third Generation/Fourth Generation (GPRS/3G/4G) Network technology cloud applications communicate. Figure 3 shows the lighting control unit in the data center unit. The user can control a single lighting node or propagate instructions to all lighting nodes. The time course of the lighting node on/off/adjustment can be arranged according to the astronomical clock. The cloud platform is tested on Microsoft's Azure and uses the tools provided by Microsoft Azure to perform data analysis on the data received by the data central unit. Figure 4 shows the cloud network application. The prototype of this LED driver has been experimentally validated and produced in the STMicroelectronics Park and deployed on 30 existing poles in the 100x150 square meter area. The conversion efficiency of each stage is over 90%, and the power quality and operational reliability are also excellent.