Three-Port Converter System for Street Lighting with Advanced Power Flow Management

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Three-Port Converter System for Street Lighting with Advanced Power Flow Management

Siddhartha Vanjari Electrical Department

Fr. C. Rodrigues Institute of Technology Navi Mumbai, India

[email protected]

Shubham Pawar Electrical Department

[email protected]

Yash Prajapati Electrical Department

[email protected]

Abstract—This paper details the power flow management in a three-port converter (TPC) for a solar lighting system.

Integrating a photovoltaic (PV) source, battery storage, and load, it optimizes energy use and ensures a reliable power supply. The TPC enables efficient power transfer, allowing seamless energy flow from the PV source to the battery for charging and from the battery to the load. The system, derived from traditional DC/DC converters, operates in buck mode for daytime charging and boost mode for nighttime LED power. Controlled by a Pulse Width Modulation (PWM) signal, the bidirectional converter ensures effective power flow. Simulation and experimental results validate the system, with prototype testing demonstrating performance under various conditions.

Index Terms—Three-port converter, Power flow management, Renewable energy integration, Control strategies, Street lighting.

I. INTRODUCTION

Three-port converters (TPCs) are advanced power electronic devices designed to manage the power flow between multiple energy sources and loads. They enable bidirectional power transfer and have gained significant attention due to their ability to integrate renewable energy systems, storage systems, and traditional power grids into a unified power management system. This project focuses on the implementation of power flow management in a TPC for urban street lighting applications.

The need for efficient power management is becoming increasingly critical with the rising adoption of renewable energy sources. Urban street lighting, a significant component of municipal energy consumption, presents a viable application for innovative power management solutions. By integrating solar power, grid electricity, and battery storage, TPCs can optimize energy usage, reduce costs, and enhance sustainability.

II. OBJECTIVES

• Design and develop a three-port converter capable of efficiently integrating renewable energy sources, grid power, and energy storage systems for street lighting applications.

• Optimize the converter topology to ensure seamless power flow among the three ports while maintaining high efficiency and reliability.

• Implement advanced control algorithms to regulate power flow and ensure optimal utilization of energy from different sources.

• Investigate the environmental impact and sustainability benefits of implementing the TPC in street lighting systems.

III. PROJECTOVERVIEW

A. Conventional PV lighting system

Fig. 1 shows a conventional solar LED street lighting system, consisting of a PV panel that charges the batteries via converter 1 during the day. At night, the stored energy powers the LEDs through converter 2. Thus, two converters are necessary in this setup.

Current existing models of street lighting systems using separate converters for PV charging and LED lighting face several limitations:

• Complexity: The use of multiple converters increases system complexity and cost.

• Efficiency: Energy transfer between sources and loads is less efficient due to the separate converter stages.

• Control: Managing power flow between multiple converters requires complex control algorithms.

• Space: Multiple converters occupy more space, making the system less compact.

• Maintenance: More components lead to higher maintenance requirements and potential points of failure.

Fig. 1. Conventional PV lighting system

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B. PV lighting system with a three-port converter

Fig. 2 depicts an alternative public lighting system using a single bidirectional DC-DC converter module to manage power flow based on the time of day. A three-port bidirectional converter from [8] is suitable for solar lighting but not for high-voltage LEDs. A PV driver for standalone lighting in [4]

supports high-voltage LEDs but requires a complex control system due to multiple power switches.

Fig. 2. PV lighting system with a three-port converter

C. Implemented Circuit

Fig. 3. Bidirectional converter of PV lighting system [8]

The converter structure in Fig. 3 operates in two modes.

For battery charging, it functions in buck mode with switches S1 and S3 off and S2 controlled by PWM. During battery discharging, it switches to boost mode with S1 on and S2 off, while S3 is managed by PWM. This ensures efficient operation and seamless transitions between modes, optimizing performance under different battery conditions.

IV. MODES OFOPERATIONS

A. Charging mode

The equivalent circuit for the converter operating in Charg- ing mode (Buck Mode), as described in Fig. 4 and 5. The operating principle in continuous conduction mode (CCM) is detailed as follows:

• Stage 1: [t0-t1]: At t0, switches S1 and S3 are turned off, while switch S2 is turned on. Current flows through inductor L, causing its current to increase linearly. During this stage, capacitor C2 and the battery are charged by the energy from the PV source.

• Stage 2: [t1-t2]: In this stage, all three power switches are turned off, and the body diode of S3 begins to conduct.

The energy stored in inductor L and capacitor C2 is then released to charge the battery.

VBatt

VPV

=DS2 (1)

where DS2 is the duty cycle of switch S2, V_Batt and V_PV are battery voltage and PV supply voltage, respectively.

Fig. 4. Stage 1 [8]

Fig. 5. Stage 2 [8]

B. Discharging Mode

The equivalent circuit of the implemented converter in discharging mode (Boost) is shown in Fig. 6 and 7. The operating principle in continuous conduction mode (CCM) is described as follows:

• Stage 1: [t0-t1]: The power switches S1 and S3 are turned on, and the switch S2 is turned off. The current from the battery flows through inductor L and also charges capacitor C2. The energy stored in the capacitor C1 is discharged to the LED.

• Stage 2: [t1-t2]: At t1, the switch S3 is turned off while the switch S1 is still turned on. The energy stored in the inductor L and the capacitor C2 is released to load LEDs and capacitor C1.

V_LED VBatt

= 1

1−DS3

(2) where DS3 is the duty cycle of switch S3 and VLED is a positive voltage applied across the LEDs.

Fig. 6. Stage 1 [8]

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Fig. 7. Stage 2 [8]

V. DESIGN ANDIMPLEMENTATION

A. Inductors

Given that the converter operates in two modes, each requirement related to the inductor design must be met. When used as a boost converter, the inductor needs to be large enough to load LEDs and small enough to transmit power to the battery in buck mode. In order to support the CCM condition in the buck mode, the minimum inductance value must be met as mentioned in [8] is,

Lmin buck≥ (1−DS2)RB

2f (3)

whereR_B is the equivalent load in the battery, andf is the switching frequency. The minimum inductance value needed to sustain the CCM condition in boost mode as mentioned in [4] is,

L_{min boost} ≥DS3(1−DS3)²RL

2f (4)

whereRL is the resistance of the LED string circuit.

Given that the inductor value for both operating modes needs to be determined, the inductor value is provided by the intersection of equations (3) and (4) in [8] is,

Lmin≥(1−DS2)RBD

2f (5)

whereR_BDis the equivalent load in the low voltage battery.

B. Capacitors

The size of the ripple voltage was taken into account when choosing capacitorsC1in boost mode andC2in buck mode. It is possible to ascertainC1’s minimum capacitance mentioned in [8] as,

C1≥ DS3Vo

RLf^∆V_V^o

o

(6) whereV_o is the output voltage across the LED.

It is possible to ascertain C2’s minimum capacitance mentioned in [8] as,

C2≥ (1−DS2)VOB

8Lf^{2 ∆}_V^V^OB

OB

(7) whereV_OB is the voltage drop across the battery.

C. Battery

The overall energy consumption of the load LEDs dictates the size of the battery. The calculation of battery size takes into account the Watt-hour/day of required energy from the battery as well as the number of days of autonomy. The battery’s Depth of Discharge (DoD) gauges the extent of its discharge.

The capacity that is discharged from a fully charged battery, divided by the battery’s nominal capacity, is known as the DoD. The battery’s Ampere-Hour capacity is determined in [8] using

Ah= E_Total×Days of Autonomy DoD×VBattery

(8) whereV_battery is the nominal voltage of the battery.

D. Solar panels

Different PV panels generate varying amounts of electricity.

To size PV panels, the total peak power (Wp) is calculated based on the energy needed for the solar modules and the panel production factor (4.5 in India). The required energy is found by multiplying the peak energy demand in kWh/day by 1.3 to account for system losses, yielding the total kWh/day the panels must produce.

Wp= Etotal×1.3

4.5 (9)

E. Calculated Values

It is assumed that the light load of a 24W LED bulb is current for 8 hours a day. The main specifications and parameters of the prototype converter are obtained using equations (5), (6),and (7). The parameters are shown in Table I,

TABLE I CALCULATEDVALUES

Parameters Value (Unit)

Inductor L 80µH

Capacitor C1 22µF

Capacitor C2 150µF

Switch S1 TIP31C

Switch S2 and S3 STP105N3LL, 3.5 mΩ

@40A, 10V

Switching Frequency 20 kHz

VI. CONTROLSTRATEGY

The architecture consists of a DC converter function and a controller function for operating the converter. The proposed converter is composed of three switchesS1,S2, and S3. For S2 andS3are paralleled with a freewheeling diode which is to conduct current in the opposite direction to the switch. The controller algorithm is shown in Fig. 9. It starts by reading PV voltage and current. The PV power is obtained by finding the product of current and voltage. If the PV power is lower thanP_minand the electric potential difference of the battery is higher thanV_min, the converter is operating in boost mode. If the PV power is not lower thanP_min and the battery voltage is lower thanV_max, the converter is operating in buck mode.

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Fig. 8. Implemented Three-Port Converter Topology

Fig. 9. Control flow algorithm

VII. SIMULATION ANDVALIDATION

The converter’s performance is evaluated through simulation and experimental validation. Various operating conditions, including changes in load demand and weather conditions, are considered to assess the suitability of the converter for real-world street lighting applications.

A. Buck Mode (Charging of Battery)

Fig. 10. Simulation of Buck Mode in MATLAB Simulink

Based on our requirement, we first performed the simulation in MATLAB Simulink. Fig. 10 shows the Simulink model TPC

converter during buck operation (Charging of battery). In the Simulink model, we obtained the required output voltage to charge the battery. Fig. 11 illustrates the operation of three

Fig. 11. Gate pulse (Buck Mode)

switches (S1, S2, S3) in a buck mode. S1 is mostly ON with a duty cycle of 0.92, while S2 and S3 remain inactive, receiving no pulses. This selective control is essential for effective voltage regulation. Fig. 12 shows the behavior of

Fig. 12. State of charge and voltage of battery (Buck mode)

the State of Charge (SoC) and battery voltage during buck mode. Starting with a 10% SoC and a voltage of 10V, both increase over time, indicating that the buck mode operation progressively raises the battery charge and voltage levels.

B. Boost Mode (Discharging of Battery)

Fig. 13. Simulation of Boost mode in MATLAB Simulink

Based on our requirement, we first performed the simulation in MATLAB Simulink. Fig. 13 shows the Simulink model TPC

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converter during boost operation (disharging of battery). In the Simulink model, we obtained the required output voltage to charge the battery. Fig. 14 shows the operation of three

Fig. 14. Gate pulse (Boost Mode)

switches (S1, S2, S3) in boost mode. S2 operates with a duty cycle of 0.47, while S1 and S3 remain inactive without pulses.

This selective control is crucial for effective voltage regulation.

Fig. 15 shows the State of Charge (SoC) and battery voltage

Fig. 15. State of charge and voltage of battery (Boost mode)

in buck mode. Starting with an SoC of 80% and a voltage of 14V, both values decline over time, reflecting the typical behavior of energy depletion during boost mode operation.

VIII. HARDWAREIMPLEMENTATION

A. Gate driver framework

Gate drivers act as power amplifiers between a controller and IGBT/MOSFET, providing isolation between control and power circuits. The implemented driver circuit for three switches is shown in Fig.16.

B. Buck mode

Fig. 17 shows the output pulses of three gate driver circuits during buck operation, and the pulse duty cycle depends upon the specific input, output voltage, and current. For this nature of signals, the values are:

VPV = 14V VBatt= 11.8V IPV= 1A

Fig. 16. Gate driver circuit using HCPL3120 IC

Fig. 17. Gate driver circuit output (Buck Mode)

C. Boost mode

Fig. 18 shows the output pulses of three gate driver circuits during boost operation, and the pulse duty cycle depends upon the specific input, output voltage, and current. For this nature of signals, the values are:

V_PV= 11V V_Batt= 11.8V I_PV= 0.4A

Fig. 18. Gate driver circuit output (Boost Mode)

D. Three-port converter circuit

Fig. 19 shows the hardware circuit of the three-port converter. It consists of three ports: one for the PV panel (Source), second for the Battery (Storage element), and third for the LED (load).

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Fig. 19. Three-port converter circuit

E. Complete hardware setup

Fig. 20 shows the complete hardware setup of the circuit, consisting of the power circuit, gate driver circuit, three ports (PV, Battery, and Load (LED Bulb)), and microcontroller (Arduino UNO).

Fig. 20. Three-port converter circuit

IX. CONCLUSION

This report examines a Three-Port Converter (TPC) for standalone solar LED lighting systems, adapted from bidirectional DC/DC converters. Operating in buck mode for daytime battery charging and boost mode for nighttime LED power, it uses the MOSFET body diode for simplified power transfer. Simulations and prototype testing confirmed its proper function and algorithm adherence.

The implemented Three-Port Converter (TPC) charges the battery only during daytime. This ensures that variations in solar power do not impact the stability of the street lighting system. The LED streetlights are powered by the charged battery, providing a steady voltage and current, which guaran- tees consistent illumination regardless of fluctuations in solar energy.

High temperatures can increase the resistance in semi- conductor components, leading to higher power losses and reduced efficiency. Low temperatures can decrease the battery’s ability to deliver power effectively, affecting the overall performance of the system. High humidity levels can cause corrosion of metal components and connections, leading to poor electrical connections and potential system failures. Both temperature and humidity can cause fluctuations in the efficiency of power conversion, affecting the overall performance and stability of the TPC system.

The non-isolated TPC advances power electronics by efficiently managing energy among multiple sources and loads, reducing system complexity, cost, and footprint, and enhancing efficiency for applications in renewable energy systems and electric vehicles.

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