Tapas Kumar Saha

Design Optimization and Dynamic Performance Analysis of a Stand-Alone Hybrid Wind–Diesel Electrical Power Generation System

An algorithm for optimal sizing of all the components of a stand-alone hybrid wind-diesel electrical power generation system, in the sense of minimum energy cost is reported in this paper. The total system reactive power balance condition, which is not often considered for designing stand-alone systems, is included with others in the nonlinear constrained optimization technique employed to maximize the wind turbine output. The dynamic performance of the hybrid system during different load and wind speed transients under optimal load sharing condition (as predicted by the aforementioned algorithm) between the two generators is verified in real time on a laboratory prototype of the hybrid system. These experimental results are also presented.

Sliding-Mode Control of PWM Dual Inverter-Based Grid-Connected PV System: Modeling and Performance Analysis

This paper proposes a novel robust and adaptive sliding-mode (SM) control for a cascaded two-level inverter (CTLI)-based grid-connected photovoltaic (PV) system. The modeling and design of the control scheme for the CTLI-based grid-connected PV system is developed to supply active power and reactive power with variable solar irradiance. A vector controller is developed, keeping the maximum power delivery of the PV in consideration. Two different switching schemes have been considered to design SM controllers and studied under similar operating situations. Instead of the referred space vector pulsewidth modulation (PWM) technique, a simple PWM modulation technique is used for the operation of the proposed SM controller. The performance of the SM controller is improved by using an adaptive hysteresis band calculation. The controller performance is found to be satisfactory for both the schemes at considered load and solar irradiance level variations in simulation environment. The laboratory prototype, operated with the proposed controller, is found to be capable of implementing the control algorithm successfully in the considered situation.

Robust voltage regulation of DC-DC PWM based buck-boost converter

This paper investigates the performance of DC-DC PWM based buck-boost converter with two degree-of-freedom (2 DOF) control to meet the loop robustness goals as well as to shape the output voltage response according to requirement. The design technique of this controller is simpler than that of the robust control techniques, such as H∞, control, μ-synthesis, applied in literature for converters. Moreover, 2 DOF control is already established in literature to provide robust compensation to boost converter. The performance of the buck boost converter is examined in the presence of (i) 60% perturbation in load current, (ii) 25% perturbation in input voltage and (iii) high frequency measurement noise. The 2 DOF control scheme has been shown to achieve the output regulation and obtain fast recovery in output voltage response, through simulation.

Cascaded two level inverter based grid connected photovoltaic system: Modelling and control

In this paper, isolated source cascaded two level inverter (CTLI) has been proposed for grid connected photovoltaic system. The system is operated to supply active power with available solar irradiance and to supply reactive power in absence of it. The conventional CTLI is controlled through vector control topology to provide controlled active and reactive power in the said conditions. The photovoltaic system is modelled and tested with the controlled grid connected CTLI, for solar irradiance variation, and reference reactive power variation in simulation environment. The control scheme has been introduced for dc link voltage of the dual level inverter. The dc link voltage is found to be maintained at required level for both type of power supply.

Design and performance analysis of two degree-of-freedom (2 DOF) control of DC-DC boost converter

The application of the two degree-of-freedom (2 DOF) theory to control non-minimum phase DC-DC switching converters is investigated in this paper. The robust control techniques mostly used to attain a regulated output voltage, even under perturbed condition, for DC-DC boost converter are, H∞ (both linear and nonlinear), μ-synthesis, genetic algorithm, linear quadratic regulator (LQR) control. All of these control techniques are one degree-of-freedom (1 DOF) i.e. conventional error-driven in nature. The 1 DOF control technique suffers from the limitation that there exists a compromise between response and loop goal performances. To overcome this, in the present work, a 2 DOF linear time-invariant (LTI) controller has been designed to achieve the performance goals of DC-DC PWM based boost converter. A 2 DOF controller provides additional degree-of-freedom so as to meet the loop robustness goals as well as to shape the output response according to requirement. The design technique of this controller is simpler than that of the robust control techniques mentioned above. The 2 DOF control scheme has been shown to achieve the output regulation even in the presence of 60% perturbation in load current and obtain fast recovery in output voltage response, through simulation. The veracity of the simulation results has been established through a real-time experimental setup of the boost converter.

Performance Analysis of Optimally Operated DOIG Based Stand-Alone Wind Power Generation System at Different Sites

An algorithm is developed for optimal sizing of wind driven stand-alone double output induction generator (DOIG). Nonlinear constrained optimization technique is used to trace the maximum power generated by the system for a given machine and converter rating. Both inequality and equality nonlinear constraints are considered. Among them the most significant one is the reactive power balance constraints, which is not often considered for stand alone systems. The problem is solved in MATLAB environment. The same algorithm is then used to accommodate different ratings of machines and converters to find the maximum powers as function of wind velocity, load power factor and components size. Weibull distribution is considered for modeling the wind velocity probability density function of seven Indian sites. The probability density of load power factor is considered to be distributed following Normal distribution. The joint probability of a particular velocity and a particular load power factor is calculated and used to measure the energy, captured by the system at a given site for different machine-converter combinations. The installation and O&M costs are considered to follow the present day trends. The proposed method finally finds the optimum combination of machine and converters (stator and rotor sides) to get minimum cost of energy. It is shown that the proposed wind energy conversion systems (WECS) can produce energy at a competitive low rate for moderately windy sites.

Performance analysis of a digitally controlled wind turbine emulator

This paper presents a digital control scheme for wind turbine emulator. The wind turbine is emulated with a separately excited dc motor. The controller is considered to be in the proportional-integral (PI) form, and is designed in digital time domain. These digital PI controllers are employed here for both speed and current controls. The performance of the digital control scheme proposed is simulated in MATLAB-SIMULINK environment considering the dc motor to be a continuous-time plant. The digital controllers are shown to exhibit successful tracking of the speed reference command. The veracity of the simulation results are established through real-time implementation of the digital control scheme for the dc motor under consideration. The digital control is implemented here with a digital signal processor (DSP) control board dSPACE1104. The experimental results are found out to be in good agreement with that obtained in simulation.

Adaptive fuzzy parameter scheduling scheme for GSA based optimal Proportional Integral Derivative and lag-lead control of a DC Attraction type Levitation System

Magnetic levitation system is inherently unstable and strongly nonlinear in nature. Fixed optimal gain controllers designed at some nominal operating conditions fail to provide the best control performance over a wide range of off-nominal operating conditions. In this paper, an adaptive fuzzy parameter scheduling scheme for Gravitational Search Algorithm (GSA) based optimal Proportional Integral Derivative (PID) and Lag-Lead controllers has been proposed to control a single actuator based DC Attraction type Levitation System (DCALS). A Takagi-Sugeno (T-S) fuzzy inference system is used in the proposed controllers. The inference system is extremely well suited to the task of smoothly interpolating linear gains across the input space when a strongly non-linear DCALS moves around in its operating space. Simulation results show that both proposed adaptive fuzzy PID and Lag-Lead controllers offer better performance than fixed gain controllers at different operating conditions.

Effect of wind speed and load power factor variation on optimal sizing of the machine and converters for double output induction generator based stand-alone wind energy conversion systems

In this paper, an algorithm for finding out the optimal ratings of the machine and power electronic converters of a wind turbine driven stand-alone double output induction generator based variable speed constant frequency generation system is reported, which seeks to minimize the cost of energy generation. The nonlinear constrained optimization technique employed includes, among others, the reactive power balance constraints, which are not often considered for stand-alone systems. For this purpose, the load power factor is modeled as a random variable with known probability density function. The total energy captured is calculated for a given wind velocity density function and load power factor density function. The proposed method finally finds the optimum combination of machine and converter ratings, which results in minimum cost of energy. The effects of changes in load power factor and wind velocity distribution are also discussed in detail.

Modeling and performance analysis of digital control drive of induction machine in synchronous reference frame

This paper presents the modelling and development of a digital lag-lead compensator for speed control of induction machine. The compensator is implemented using indirect field oriented vector control strategy along with space vector pulse width modulation (SVPWM) switching technique. The speed is control is achieved using speed feedback signal from the machine. The sensorless model reference adaptive system (MRAS) technique is also used to estimate the speed and the estimated signal is used as feedback to the controller. This development in digital domain has been implemented in simulation environment and the performance is found to be satisfactory for both step changes in load and speed command.