R&D Activities
R&D Activities
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- Investigations into the Load Sharing and Voltage Regulation Issues with Low-Voltage DC-Microgrid Systems
In a dc microgrid (DCM), good load sharing and voltage regulation are desirable for the system's economic operation and better reliability. But load sharing and voltage regulation are affected by practical factors like sensor calibration errors and cable resistances. To tackle these issues, various decentralized, centralized and distributed droop control methods are proposed in the literature. Among these, the centralized droop control method is not utilized due to high cost and poor reliability. From a detailed literature survey, it is observed and noted that there is scope for improving the performance of the existing decentralized and distributed control schemes. Hence, in this work, two types of droop control methods are proposed to overcome the drawbacks of the various existing droop control methods.
In the first type, three novel decentralized, non-linear, non-communication based droop control algorithms are proposed, which address the limitations shown by the conventional and other improved droop control methods. Here, the effect of cable resistance and sensor gain errors associated with the voltage sensors are considered. In all proposed schemes, the droop gains are adaptively changed based on a few simple algorithms. These proposed methods enhance the performance in terms of load sharing accuracy and voltage regulation compared to other existing non-communication based droop control techniques.
In the second type, a low bandwidth communication (LBC) based average voltage regulation (CAVR) scheme for a droop controlled DC microgrid is proposed. Here, the LBC is utilized only to exchange the output voltage information, while all other calculations and control are realized locally, ensuring distributed nature to the control scheme. In this method, the traffic in the communication line is low as only one piece of information is passed over the communication channel. Hence, the proposed method can be realized with relatively low communication speeds. Accurate load sharing is achieved by selecting a high value of droop constants for the individual converter. As a high value of droop constants are chosen, the load sharing with the proposed method is nearly independent of the cable resistance.
Fig. DC Microgrid Architecture Considered in this Study
Fig. Control structure of the proposed CAVR method
- Novel Multi-port DC-DC Converter Topologies
DC-DC converters with multi-input and/or multi-output terminals are called multiport converters. These converters are divided into – (i) multi-input single-output, (ii) single-input multi-output, and (iii) multi-input and multi-output converter. Unlike a conventional two-port DC-DC converter, a multiple port converter can harvest power from numerous sources and deliver it to single or multiple loads. Also, with a multiport converter, power from a single source can be delivered to more than one load using a single power converter topology. Hence, multiport converters are compact, economical and improve the system performance. These converters are extensively used in renewable energy sources (RESs) and microgrid systems.
From our research work, we have proposed two novel non-isolated multiport DC-DC converters for RESs and storage units to efficiently interface to a bipolar dc microgrid (BDCMG).
The first converter is a new four-port, dual-input-dual-output (DIDO) DC-DC converter that is proposed to interface photovoltaic (PV) and fuel-cell (FC) sources to a low-voltage BDCMG. This proposed topology is unidirectional, efficient, and compact. It has fewer circuit elements with only one inductor as compared to the conventional non-isolated DC-DC converters. The proposed converter regulates one of the DC bus's pole voltages and ensures MPPT of the PV source. Further, the converter can be operated as a single-input-dual-output (SIDO) converter. The control complexity of the proposed converter is low as it can be operated in various modes with only one set of controllers. Further, the proposed converter's loss modelling and efficiency analysis are also carried out, and its efficacy and performance are validated by detailed simulation and experimental results under various operating conditions.
The second converter is a novel non-isolated boost-SEPIC type interleaved (BSTI) DC-DC converter. This converter enables power from a single source to be fed into two poles of the BDCMG, thereby enhancing the efficiency and reliability of the BDCMG system. The proposed converter can support bidirectional operation with synchronous rectification. Further, in this converter, the input current ripple is low due to interleaved operation. The operating modes, steady-state operation, dynamic characteristics, controller design and experimental validation are carried out as part of this research work.
Fig. Proposed multiport dc-dc converters (a) PV-FC converter and (b) BSTI converter
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- A Novel PR Controller for Single-Phase UPS Inverter
Modern uninterrupted power supplies (UPS) are gaining popularity as they can deliver clean and high-quality power under extreme load condition for sensitive devices (like medical, military and communication equipment). Traditional proportional-integral (PI) based control for the UPS system provides high-quality output but suffers from the poor dynamic response. In one of our research papers, a novel proportional resonant (PR) controller is proposed to control a single-phase inverter's output voltage. The proposed controller provides a fast-dynamic response, low or zero steady-state error, and reduced total harmonic distortion (THD). A detailed step by step procedure to design the novel controller is presented based on the specific criteria (like steady-state error, overshoot, etc.). Due to the fast response, the proposed PR controller is also suitable for EV charging applications (specifically to the vehicle to load charging). Simulation and experimental results are presented to validate the feasibility and efficacy of the proposed controller.
Fig. Control block diagram of the UPS inverter system with the propose NPR controller
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- Power Electronics Application to Electric Vehicles (EVs)
Imminent exhaustion of fossil fuels, their rising cost, and concerns about climate change have led to extensive exploration of high efficiency and less polluting systems. In this regard, electric vehicles (EVs) are gaining popularity as they have superior well-to-wheel efficiency and have far fewer moving parts compared to conventional internal combustion engine (ICE) powered vehicles.
However, despite its numerous benefits, there are issues and challenges pertaining to EV, including high cost, dependence on charging stations, etc. In a country like India, where the per-capita income is relatively low, high EV penetrations would be a challenge due to the high price of EVs, mainly due to importing most of the EV components. Furthermore, there is limited charging infrastructure in India, and the available charging stations are mostly confined to tire-1 and tire-2 cities. There is also little research work on EV chargers for two and three-wheeler applications (which is more Indian centric), as most of the reported/manufactured onboard chargers (OBCs) work only in grid-to-vehicle (G2V) mode and lack smart and advanced features. Furthermore, it is also observed that compared to G2V mode, OBCs encounters interfacing and power quality issues when operating at autonomous mode (i.e. in vehicle-to-home or vehicle-to-load (V2L) mode). It is also seen that with the existing control scheme for OBCs in V2L mode, the system has a relatively poor dynamic response and are computationally intensive.
Our research team is currently working towards a low cost and high-performance EV-OBC (specifically for two and three-wheeler application) to overcome the issues listed above. As part of this research, we are developing a novel single-stage power converter topology capable of operating with unity power factor, high-power quality and superior dynamic response. The proposed OBC shall be designed to work in autonomous mode by supporting home loads during power outages or charging another EV during an emergency condition. To overcome the interfacing issue of the OBC in autonomous mode, a smart connector box shall be designed and developed. To achieve fast dynamic response, low or zero steady-state error, and reduced total harmonic distortion (THD), a novel proportional resonant (PR) controller shall be employed to control the proposed OBC. Theoretical analysis, detailed simulations, and experimental results (with a scaled-down laboratory prototype) shall be presented to demonstrate the efficacy of the proposed OBC with the advanced control algorithm.
As part of our research in power electronics applications to electric vehicles, we are also working on the following aspects:
· Novel power converter topologies for EVs.
· High performance and sensorless control of EV motor drive.
· Advanced and compact battery management system (BMS).
Fig. (a) Block diagram of the proposed single-stage EV-OBC; (b) BMS Architecture; (c) Block diagram of sensorless BLDC motor drive for EV; (d) Cell balancing architecture for EV batteries.
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- High Voltage Gain Power Converters
DC-DC converters with high step-up and step-down voltage rations are used in numerous modern power electronic-based systems like electric vehicles (EVs), microgrids, uninterrupted power supplies, grid-tied/islanded renewable energy systems, etc. In these applications, a high-gain dc-dc converter forms a critical link between two DC buses (as shown in Fig. 1).
High-gain dc-to-dc power conversion can be achieved through high-frequency transformer isolation. But, isolated dc-dc converters suffer from voltage spike issues due to leakage inductance, resulting in high voltage stress across the switches. Multiple non-isolated bidirectional dc-dc converters have recently been published in the literature. Most of these dc-dc converters have low voltage stress across the switches and are apt for applications that demand very high voltage gain (either in boost or buck mode). However, most existing high-gain dc-dc converter utilizes many passive and active components to achieve high gain. Furthermore, from an exhaustive literature study, it is noticed that there some of the state-of-the-art high gain converters lack bidirectional capability and demand complex control schemes, etc. Also, few existing converters have high voltage and current stress across switches/diodes/capacitors, lack common ground, exhibit poor efficiency, etc.
Our research team is working towards low-cost, high-gain dc-dc power converters with the following features: low component count, non-isolated power converter, low voltage stress across switches/diodes/capacitors, capability to operate the converter in voltage and current control mode, simple control scheme, bidirectional capability, wide duty ration operation, high efficiency, high power density, etc.
Fig. 1. Block diagram of the high-gain dc-dc converter, Fig. 2. Proposed high-gain dc-dc converter, and Figs. 3 and 4. 3D layout and protoype of an interleaved boost dc-dc converter.
For more details, click the below links:
- Universal & Integrated Onboard EV Charger
Our research team has developed an innovative Universal Onboard EV Charger, a game-changing solution as we transition towards an electric vehicle-dominated future. This innovative charger addresses the challenges of varied input sources, paving the way for faster and more efficient EV charging experiences while simplifying charging infrastructure.
The Universal Onboard EV Charger boasts unparalleled flexibility by seamlessly adapting to various input sources, including AC single-phase supply, AC three-phase supply, and DC grid. Its ingenious design, utilizing relays and reconfiguration, efficiently interfaces with different source types, making it a versatile and adaptive charging solution.
At the core of this proposed universal charger lies a sophisticated configuration featuring a three-phase VSC type converter for three-phase grids, a single-phase totem-pole converter with two-phase interleaving for single-phase grids, and a DC-DC converter with three-phase interleaving for DC inputs. Astonishingly, the charger achieves its impressive functionality with just six power electronics switches, enabling a full power rating for three-phase and DC sources, as well as a two-third power rating for AC single-phase sources. Furthermore, the charger is bidirectional, supporting vehicle-to-grid (V2G), vehicle-to-vehicle (V2V), and vehicle-to-load/home (V2L) functionalities.
To ensure smooth operation and precise control of the input side inductor currents, the charger is equipped with a meticulously designed type-2 lead compensator. Additionally, the development of three-phase PLL and single-phase SOGI PLL ensures perfect synchronization with AC three-phase and AC single-phase grid sources, guaranteeing optimal charging performance, efficiency, and reliability.
Extensive simulations conducted using MATLAB Simulink demonstrated the charger's capabilities, showcasing a remarkable 6.6KW power rating, a phase voltage of 230 Vrms for AC grid sources, a 230V DC grid input, and an 800V DC output. A scaled-down prototype further validated the charger's practical functionality with a power capacity of 500W, 100V AC/DC input, and 200-250V DC output, reaffirming its real-world applicability.
The Universal Onboard EV Charger represents a significant step forward in the world of EV charging, providing a versatile and efficient solution that adapts to the diverse charging infrastructure. With its ability to cater to various power grids and sources, it empowers EV owners with a seamless charging experience and contributes to the widespread adoption of sustainable transportation. As we continue to push the boundaries of electric vehicle technology, the Universal Onboard EV Charger holds great promise in shaping a greener and cleaner future for generations to come.
Fig. Photograph of the developed 500 W universal charger (courtesy: Mr. Praveen Raj, Ms. Aditi Nalkande, and Mr. Sourav Prasad)
For more details, click the below links:
- Digital Control Development for Four-Phase SRM Drive
In the realm of medium-power, high-volume applications, Switched Reluctance Motor (SRM) drives offer significant advantages over other motor types. To capitalize on these benefits, it is essential to optimize SRM drives to reduce costs without compromising performance. Our research focuses on the design and development of a novel SRM drive with enhanced performance, encompassing comprehensive control development procedures, dynamic simulation, analysis, and experimental validation.
The characterization of the SRM is conducted using finite element analysis (FEA), which is utilized in the development of the MATLAB Simulink simulation model. This model facilitates parametric simulation studies. A linear SRM model for control design is developed through small signal analysis. Speed and current controllers are then designed using the K-factor method. The proposed drive's effectiveness is rigorously evaluated across various operating modes.
Moreover, our research delves into the design of a digital control algorithm for the SRM motor drive, implemented on the DSP microcontroller TMS320F28379D. This implementation, based on the designed controllers, is used to further assess the drive's performance.
Photograph of the SRM drive experimental setup developed in the lab (courtesy: Mr. Faheem Ali)
For more details, click the below links:
- Design and Development of Low Power Wind Turbine System
Our research team has designed and developed a 500–1000 W BLDC-based wind turbine system, primarily targeting telecom tower applications. This work emphasises achieving maximum power point tracking (MPPT) under fast-changing wind conditions. A novel MPPT algorithm has been proposed and implemented, enabling significantly quicker MPPT convergence compared to traditional methods. Additionally, the system supports seamless switching between various operating modes such as voltage control and speed control, ensuring minimal disruption and maximising wind power utilisation tailored for telecom towers. The developed prototype has been rigorously tested in laboratory settings, including both simulated environments and wind tunnel setups. Field testing, research publications, and patent filings are currently in progress.
Project funded by MoveAir GmbH, Berlin, Germany.
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