Shantha Gamini Jayasinghe

Flying Supercapacitors as Power Smoothing Elements in Wind Generation

This paper presents a capacitor-clamped three-level inverter-based supercapacitor direct integration scheme for wind energy conversion systems. The idea is to increase the capacitance of clamping capacitors with the use of supercapacitors and allow their voltage to vary within a defined range. Even though this unique approach eliminates the need of interfacing dc-dc converters for supercapacitors, the variable voltage operation brings about several challenges. The uneven distribution of space vectors is the major modulation challenge. A space vector modulation method is proposed in this paper to address this issue and to generate undistorted currents even in the presence of dynamic changes in supercapacitor voltages. A supercapacitor voltage equalization algorithm is also presented. Moreover, control strategies of the proposed system are discussed in detail. Simulation and experimental results are presented to verify the efficacy of the proposed system in suppressing short-term wind power fluctuations.

A Dual Inverter-Based Supercapacitor Direct Integration Scheme for Wind Energy Conversion Systems

This paper presents a new direct integration scheme for supercapacitors that are used to mitigate short term power fluctuations in wind power systems. The proposed scheme uses the popular dual inverter topology for grid connection as well as interfacing a supercapacitor bank. The dual inverter system is formed by cascading two 2-level inverters named as the “main inverter” and the “auxiliary inverter”. The main inverter is powered by the rectified output of a wind turbine coupled permanent magnet synchronous generator. The auxiliary inverter is directly connected to a super capacitor bank. This approach eliminates the need for an interfacing dc-dc converter for the supercapacitor bank and thus improves the overall efficiency. A detailed analysis on the effects of non-integer dynamically changing voltage ratio is presented. The concept of integrated boost rectifier is used to carry out the Maximum Power Point Tracking (MPPT) of the wind turbine generator. Another novel feature of this paper is the power reference adjuster which effectively manages capacitor charging and discharging at extreme conditions. Simulation results are presented to verify the efficacy of the proposed system in suppressing short term wind power fluctuations.

A dual inverter based supercapacitor direct integration scheme for wind energy conversion systems

Interfacing converters used in connecting energy storage systems like supercapacitors and battery banks to wind power systems introduce additional cost and power losses. This paper therefore presents a direct integration scheme for supercapacitors used in mitigating short-term power fluctuations in wind power systems. This scheme uses a dual inverter topology for both grid connection and interfacing a supercapacitor bank. The main inverter of the dual inverter system is powered by the rectified output of a wind turbine-coupled permanent-magnet synchronous generator. The auxiliary inverter is directly connected to the supercapacitor bank. With this approach, an interfacing converter is not required, and there are no associated costs and power losses incurred. The operation of the proposed system is discussed in detail. Simulation and experimental results are presented to verify the efficacy of the proposed system in suppressing short-term wind power fluctuations.

Sizing and modeling of a standalone hybrid renewable energy system

This paper presents optimal sizing, modeling and performance analysis of a standalone PV/Wind/Battery Hybrid Energy System (PWB-HES) for an off-grid residential application in Ansons Bay, Tasmania, Australia. The aim of the study is to find the optimal size of the photovoltaic (PV) panel, wind generation system (WGS) and battery storage (BS) that can satisfy the varying load demand throughout the year. In the proposed PWB-HES sources and the battery are connected to a common DC bus. A voltage source inverter is used to connect the dc bus to the ac side. The optimal combination of sources and energy storage was obtained based on solar irradiance, wind speed and typical residential demand of the selected site. The optimal sizing algorithm was implemented using the HOMER software. The optimal system is then modeled and simulated with SIMULINK software in order to examine the complementary characteristics of the solar and the wind power system to satisfy the load demand. Simulation results showed that the PWB-HES with optimal size obtained through HOMER is able to meet the load demand amidst the changes in solar irradiance and wind speed.

Marine propulsion PM motor control under inverter partial fault

Fault tolerance is an essential feature in marine and naval electric propulsion drives. Therefore, there is a growing research interest in developing fault tolerant technologies for marine applications. This paper investigates the control and operation of an inverter fed PM propulsion motor under a specific power electronic failure case. Compared to the technologies reported in literature, this paper formulates a special control strategy for the motor operation during the situation where only one high side switch and one low side switch in two different phases are operational in a standard three-phase six-switch inverter. The proposed control strategy assumes that the remaining switches are failed in open circuit while the corresponding anti-parallel diodes are functional. The mathematical background of the two quadrant control strategy is formulated. The operation is analyzed in the context of marine propulsion power/speed requirements. Simulations for a 50 kW three-phase fault tolerant motor is presented for the operation with the proposed dual switch control strategy. Controllability of motor torque for speeds up to 45% rated speed corresponding to approximately 9% rated propulsion power output is achieved without overrating the device current ratings.

Predictor-based model reference adaptive control of an unmanned underwater vehicle

Unmanned Underwater Vehicles (UUVs) are being deployed in advanced applications that require precise manoeuvring close to complex underwater structures such as oilrigs and subsea installations or moving objects such as ships and submarines. The effect of vehicles hydrodynamic parameter variations is significant in such scenarios and in extreme conditions the UUV may experience loss of control. In addition, external disturbances and actuator failures degrade the performance of the UUV. Adaptive control has been identified as a promising solution that can improve the performance in such situations. However, adaptive control is not widely used in UUVs mainly due to the trade-off between fast learning and smooth control signals. The latter can be guaranteed at low learning rates but require additional input to improve learning. The Predictor Model Reference Adaptive Control (PMRAC) is one such method that uses a prediction error to improve learning. In this paper, the performance of PMRAC in UUV applications is investigated and compared to standard Model Reference Adaptive Control (MRAC) at low learning rates under normal operational conditions, partial actuator failure, and under the influence of external disturbances. Simulation results show that PMRAC significantly reduces the tracking error compared to MRAC. In addition, PMRAC is less affected and recovers quickly from actuator failure and external disturbances, while generating smooth control signals with less oscillation compared to MRAC.

Hybrid cascaded multilevel inverter with supercapacitor energy storage for grid integration of renewable energy systems

Short-term power exchange using supercapacitors is actively pursued in the renewable energy sector. The most common approach taken in integrating supercapacitors into the power conversion system is the connection to the dc-link of the grid connecting inverter through an interfacing dc-dc converter which introduces additional power losses. Therefore, this paper proposes to use the grid-side inverter itself as the interface for supercapacitors and thereby eliminate the need of an additional converter. The inverter used in this study is the well-known hybrid cascaded multilevel inverter which consists of a two-level inverter and three series-connected H-bridge modules. In the proposed system three supercapacitor banks are directly connected to dc-links of H-bridge modules. The supercapacitor charging/discharging method used in the proposed system, corresponding control strategies and the supercapacitor sizing method used to estimate the required capacity are presented in this paper. Simulation results and a power loss analysis are also presented to show the efficacy of the proposed system.

Fuel Cell Power Management Using Genetic Expression Programming in All-Electric Ships

All-electric ships (AES) are considered as an effective solution for reducing greenhouse gas emissions as they provide a better platform to use alternative clean energy sources such as fuel cells (FC) in place of fossil fuel. Even though FCs are promising alternative, their response is not fast enough to meet load transients that can occur in ships at sea. Therefore, high-density rechargeable battery storage systems are required to achieve stable operation under such transients. Generally, in such hybrid systems, dc/dc converters are used to interface the FC and battery into the dc link. This paper presents an intelligent FC power management strategy to improve FC performance at various operating points without employing dc/dc interfacing converters. A hybrid AES driveline model using genetic programming is utilized using Simulink and GeneXProTools4 to formulate operating FC voltage based on the load current, FC air, and fuel flow rates. Genetic algorithm is used to adjust air and fuel flow rates to keep the FC within the safe operating range at different power demands. The proposed method maintains FC performance as well as reduces fuel consumption, and, thereby, ensures the optimal power sharing between the FC and the lithium-ion battery in AES application.

Dual inverter system with integrated energy storage for grid connected photovoltaic systems

Smooth and fluctuation free power dispatch is strongly encouraged by grid operators and therefore energy storage is becoming an indispensable part in modern large scale grid connected photovoltaic (PV) systems. As a result, associated power converter topologies and energy storage interfacing technologies are currently receiving unprecedented attention. The most common energy storage interfacing technique used in grid connected PV systems is the use of an additional power electronic converter between the energy storage system and the grid connecting inverter. Taking the disadvantages of this implementation into account this paper proposes a dual inverter based battery direct integration scheme for grid connected PV systems. In this approach, the generation of proper multilevel voltage waveforms is a complicated process, particularly when the battery is charging. A modified space vector modulation method and switching strategy are proposed in this paper to address this issue. Simulation results are presented to prove the efficacy of the proposed topology and the modulation technique.

Command governor adaptive control for an unmanned underwater vehicle

This paper presents the design and simulation of a command governor based adaptive controller (CGAC) for a remotely operated underwater vehicle. The command governor modification is applied for the first time to an underwater vehicle simulation of the actual vehicle for improved transient performance and disturbance rejection. The vehicle dynamics are assumed to be decoupled thus allowing for the design of separate heading and depth controllers. The results show that in contrast to standard adaptive controllers, command governor based adaptive controllers are able to produce better transient performance as well as improve the overall response even at low learning rates. Furthermore, simulation results verify the disturbance rejection capability of the command governor based adaptive controller, which is necessary to effectively and safely operate an unmanned underwater vehicle in real environments.