Design and Implementation of a Photovoltaic High-Intensity-Discharge Street Lighting System

This paper presents a photovoltaic (PV) high-intensity-discharge (HID) street lighting system. A single-ended primary inductance converter (SEPIC) is studied for maximum power point tracking (MPPT) and battery charging. High conversion efficiency and high MPPT accuracy can be achieved under different atmospheric conditions. A pulse-current-charging scheme with an adaptive rest-period is also applied to avoid battery overcharging. An electronic ballast circuit is also designed to release the solar energy stored in battery for powering HID lamps. The studied PV HID street lighting system is connected to the ac-line utility with a SEPIC power factor correction converter. High input power factor can be achieved when energy is drawn from the ac-line utility to drive the HID lamp and to prevent the battery from over-discharging. The proposed PV HID street lighting system has the advantages of high power density, simple circuit, and long lifetime. The operating principle and design considerations were analyzed and discussed in detail. A laboratory prototype was implemented and tested. The experimental results were shown to verify the feasibility of the proposed scheme.

I. Introduction

The photovoltaic (PV) street lighting systems shown in Fig. 1 have been used in many developing countries. They are highly economical when used in newly built urban road sections and remote rural areas without an electricity network. During daytime, the battery is charged by a PV panel. At night, the solar energy stored in the battery is released to power the streetlights. High-intensity-discharge (HID) lamps are commonly used as streetlight sources because of their high luminous efficacy, good color rendition, and long lifetime [1]–[3]. The HID lamp needs an auxiliary circuit called a “ballast” to ensure stable lamp operation because of its negative impedance characteristics [4]. Fig. 2(a) shows the conventional PV HID street lighting system with a PV inverter that releases the solar energy in the battery to the ac-line utility. The boost maximum power point tracking (MPPT) PV charger is applied to extract maximum power from the PV panel under all solar irradiation conditions [5]–[10]. A boost power factor correction (PFC) circuit is series connected with the electronic ballast to achieve high power factor input and drive the HID lamp. This PV HID street lighting system has the drawbacks of high circuit complexity and low system efficiency due to a four-stage power conversion from the PV panel to the HID lamp. Fig. 2(b) shows another PV HID street lighting system with a high-voltage dc bus (e.g., 400 V) design. High conversion efficiency can be achieved due to only two-stage power conversion. However, the use of a high-voltage battery bank causes maintenance and safety issues. The voltage imbalance among series-connected battery stacks during charging and discharging process damages the batteries. Fig. 2(c) shows a PV HID street lighting system with a low-voltage dc bus (e.g., 24 V or 48 V) design. The use of a high-voltage battery bank can be avoided. However, the conversion efficiency at PFC mode is reduced due to the addition of a voltage-step-down battery charger behind the boost PFC stage. Fig. 3 shows the proposed PV HID street lighting system. With a single-ended primary inductance converter (SEPIC) PFC converter, the proposed PV HID street lighting system is connected to the ac-line utility. As such, the HID street lighting system will not be extinguished even if the battery is fully discharged. High efficiency performance can be achieved due to only two-stage power conversion both at PV mode and PFC mode. A SEPIC is also used for MPPT and battery charging under a wide range of PV panel voltage variations. A pulse-current battery-charging scheme with an adaptive rest period is proposed to avoid battery overcharging. The state of charge (SOC) is estimated to prolong battery lifetime. The solar energy stored in the battery can be released to power the HID lamp at night using the studied electronic ballast circuit. In the following sections, the system configuration and characteristic analysis will be addressed in detail. Fig. 1.

PV street lighting systems during (a) daytime and (b) night operations.

Fig. 2.

Conventional PV HID street lighting systems with (a) PV inverter, (b) high-voltage dc bus, and (c) low-voltage dc bus.

Fig. 3.

Proposed PV HID street lighting system.