Research Interest

Power Electronics
Space vector based Advanced PWM Techniques
Renewable Energy Grid Integration
Active Filtering
Power Quality Enhancement

Ph.D. Research Work Overview

Voltage source inverters (VSIs) use pulse width modulation (PWM) techniques to convert DC voltage into AC voltage at high switching frequencies. In PWM, the fundamental space vector is generated using instantaneous volt-second balance, with the error voltage between the fundamental and switching states influencing DC bus current and load current ripple. This study models the DC voltage ripple in the synchronous power factor reference frame by mapping the AC error voltage onto the DC bus. Using this model, a novel PWM switching sequence is proposed to minimize DC bus voltage ripple across various loading conditions.

The proposed method dynamically computes the DC capacitor current polarity to optimize switching states, placing null and active vectors within sampling intervals. Unlike conventional PWM approaches, this method eliminates complex dwell time computations and sector identification, making it simpler and more adaptive to varying loads. Experimental validation on a voltage source inverter setup demonstrates its effectiveness in minimizing DC voltage ripple without affecting AC load current ripple. Additionally, an adaptive PWM selection algorithm is developed for three-phase two-level VSIs, identifying optimal regions for continuous and discontinuous PWMs. This approach ensures minimal DC voltage ripple across all load conditions, improving inverter performance and efficiency. This study is carried out for both the motor drive and grid connected inverter application. The objectives of the Ph.D. research work are as follows:

Minimum DC voltage ripple switching sequence elicitation for dual inverter through AC load error volt-sec computation.
A novel switching vector sequencing method to minimize DC voltage ripple in dual inverter drive without affecting load current ripple.
Minimum DC voltage ripple region investigation for discontinuous and continuous PWM techniques for 3-phase 2-level voltage source inverter.
Enhancing DC Source Ripple Signatures with Discontinuous Reference Wave Transitional Rate Filtering in Grid Interfaced Solar Inverters

Grid connected Inverter Hardware Setup

The overall hardware setup for this research is illustrated in Fig. Objectives 1, 2, and 3 require only inverters and a current sensor. However, Objective 4 necessitates an inverter, a voltage sensor, a current sensor, and a filter inductor. The component-wise hardware setup is detailed as follows:

Voltage Source Inverter

The Voltage Source Inverter (VSI) uses Semikron IGBT switches (SKM100GB12V) for efficient and fast DC-to-AC conversion. These IGBTs are controlled by a Semikron gate driver, which ensures accurate switching and provides essential protection features like overcurrent and overvoltage safeguards. To maintain a stable DC bus voltage, an Alcon DC capacitor is included in the VSI design. The capacitor smooths out voltage fluctuations, ensuring a "stiff" DC bus and minimizing ripple. This setup enhances the reliability and performance of the inverter, improving efficiency and providing a high-quality AC output in power conversion applications.

Three phase AC voltage sensor PCB

The three-phase voltage sensor PCB is designed using LEM LV25P voltage sensors, incorporating an integrated offset circuit to adjust the sensed voltages for communication with the microcontroller. The PCB is rated for a maximum of 746V (Line to Line). Its design, shown in the figure, ensures precise voltage sensing, enabling accurate monitoring and control of power flow. The integrated offset circuit facilitates reliable communication with the microcontroller, supporting efficient and effective power system management.

Hardware implementation of Three phase AC voltage sensor PCB

Figure shows the hardware implementation voltage sensor PCB to measure the three phase AC voltage.

Three phase AC current sensor PCB

The 3D view of the three-phase AC current sensor PCB is shown in Fig.. The PCB is designed using an LEM LA55P current sensor, known for its precision in current measurement. An offset circuit is integrated into the design to adjust the signal, ensuring proper communication with the DSP microcontroller (TMS320F28379D). This setup allows accurate current sensing and reliable signal processing for efficient monitoring and control in power systems. The combination of the current sensor and DSP microcontroller provides a robust solution for high-performance applications.

Hardware Implementation of Three phase AC current sensor PCB

The hardware PCB of the AC current sensor is shown in Fig. The entire PCB is fabricated in the lab using ferric chloride solution for etching, ensuring a custom, cost-effective design. The PCB is specifically designed to handle a maximum phase current rating of 24.59A, making it suitable for precise current measurement in power systems. This design ensures reliable performance, with the sensor accurately monitoring current levels in various applications. The use of lab-based fabrication techniques provides flexibility in the development process, ensuring the PCB meets specific operational requirements.

Level Shifter PCB

The switching pulses from the C2000 microcontroller are in the range of 0-3 volts, but the gate driver circuit requires a voltage input of 0-15 volts. To achieve this, a level shifter circuit is used. This circuit ensures the correct voltage levels are provided, allowing the gate driver to process the signal and generate a 15V signal for turning on the IGBT and a -7V signal for turning it off. The hardware implementation of the level shifter circuit is shown in Fig. 9, ensuring reliable signal conversion for efficient IGBT control.

C2000 TMSF28379D Micro-controller

The control logic and PWMs for the objectives are implemented using the C2000 TMS320F28379D micro -controller. Control circuits developed in MATLAB Simulink are programmed into the micro-controller. Key modules in the F28379D include ePWM, ADC, and DAC modules. The ePWM modules generate switching pulses for the inverter. The ADC modules convert analog signals (voltages and currents) into digital signals for processing by the micro-controller. The DAC modules convert digital signals back into analog form for various stages of the Simulink control model. The C2000 F28379D used in the prototype is shown in Fig.

Power Supply PCB

The 3D view and hardware implementation of the ±15V power supply PCB are shown in Fig.. This supply is crucial for powering several components in the prototype. It is required by LV25P voltage sensors to bias the operational amplifiers inside them and by operational amplifier-based level shifters for level shifting the output from the LV25 sensors.

Power Supply PCB Hardware Implementation

The hardware implementation of the power supply is shown in Fig.. This power supply is essential for providing a ±15V DC voltage required by various components in the prototype, such as the LV25P voltage sensors for biasing operational amplifiers and the operational amplifier-based level shifters for output level shifting. The power supply consists of a diode bridge rectifier, followed by a capacitor to minimize voltage ripple. A voltage regulator (7815 and 7915) is used to stabilize and regulate the output voltage to ±15V for the necessary components.

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