Smart solar hybrid streetlight system developed

STMicroelectronics has devised a smart solar hybrid light-emitting diode (LED) streetlight system, developed as a pilot project and implemented in the car park at one of its campuses.

The standalone solar system features an AC-DC LED driver as a backup power supply in case of unavailability of the battery. If the battery is absent or on low charge, the system automatically switches to the constant current AC-DC LED driver.

The AC-DC LED driver works on quasi-resonant mode (QR) based power factor correction (PFC) using a single-stage single switch with primary sensing control. The commercial LED driver HVLED001A is used for driving the LED.

The battery energy storage element is used as a main power supply input for the LED driver. The battery is charged using a maximum power point tracking (MPPT) scheme during daytime — an efficient scheme for charging the battery using solar radiation. The measured efficiency of the MPPT stage power converter is more than 97%.

The proposed DC LED driver is a two-phase boost DC-DC converter. The DC-DC converter helps to reduce the size of the DC bulk capacitor, which is recommended at the load side for filtering purposes. It also enhances the life of the LED driver system.

The efficiency of the DC-DC LED driver stage is more than 95%. This high-efficiency power conversion is made possible through the use of efficient MOSFETs and gate driver ICs. The LED driver produces a constant current, which further enhances the life of the LED.

Onboard measurement and decision-making are performed by a highly efficient digital power conversion microcontroller (STM32F3). The streetlights are connected to each other by a 6LoWPAN mesh network implemented using a commercially available sub-GHz device called SPIRIT1. Streetlight nodes talk to each other over 6LoWPAN mesh technology using the free industrial, scientific and medical (ISM) radio band (868 MHz).

The lights nodes with solar panels talk to the data concentrator unit (DCU) using 6LoWPAN mesh technology. The light conditioning unit (LCU) is powered both by mains and solar panels. There is a provision for auto on/off/dimming of the lights by sensing the ambient light and movement. The system comes with a rudimentary command and control centre that allows the end user to control the individual light nodes or a group of light nodes from any place.

Figure 1: Smart solar street hybrid lighting management system.

Figure 1 (above) shows the smart solar hybrid light management system. Figure 2 shows the installed light at the car park with the STMicroelectronics-developed electronic board. The data concentrator unit (DCU) comes with an onboard GSM module to communicate with cloud applications using GPRS/3G/4G mobile network technology.

Figure 2a: The installed LED streetlight.

Figure 2b: The electronic board (LCU).

Figure 3 shows the DCU with inter-LCU distance. Users can control individual light nodes or can broadcast commands to all the light nodes. There is a provision for scheduling on/off/dimming of light nodes based on an astronomical clock.

Figure 3a: Inter-DCU distance. For a larger image, click here.

Figure 3b: The DCU board.

The cloud platform is tested on the Microsoft Azure and data analytics are performed on the data received by the DCU using the tools provided by Microsoft Azure. Figure 4 shows the cloud web application.

Figure 4: The cloud web application. For a larger image, click here.

The prototype of the LED driver has been experimentally verified, manufactured and deployed at the STMicroelectronics campus using 30 existing poles in an area measuring 100 x 150 m². The conversion efficiency of each stage is more than 90%, with good power quality and continuous operation.