In this paper, a six-step 120-degree induction motor drive with long cables connected to the induction motor at medium voltage level is analysed for predicting resonance frequency. These systems can be preferred to PWM-based drives in facilities such as geothermal power plants, mine plant and submarine oil wells, since the dead-time control is not issue in the inverter operation. The motor drive in the system contains semiconductor switching elements which generate the current and voltage harmonics in a wide range of frequency spectrum. The voltage and current harmonics at the inverter output lead to the resonance problems, torque and rotor speed fluctuations due to the capacitive effect of the long cables and the inductive effects of the cables, motors and transformers. The resonance in the network creates the overvoltage and overcurrent which can cause damage to the electrical components within the system. In this paper, analysis of resonance frequency at six-step 120-degree induction motor drive with long cable connection in a geothermal plant is performed first time in an analytical approach and C-type filter is suggested to suppress the resonance.
This paper presents a model of a multi-machine system and examines the efficacy of power system stabilisers and static VAR compensator in transient stability enhancement. The main contribution of this work is a compact, user-friendly and comprehensive model to analyse and reinforce the system stability through a coordinated focus on damping of electromechanical oscillations and suppression of voltage deviations. The model is developed by integration of various mathematical equations pertaining to synchronous machines and some network equations. To test the effectiveness of the proposed model, MATLAB-based simulations are carried out by subjecting the system to challenging transients. The performance evaluation of the model incorporating both power system stabilisers and static VAR compensator is tested against the individual performance of each. It is found that the model is effective in maintaining transient stability as well as improving transient stability limits.
This paper presents the design and simulation of multilevel inverter topologies configuring nested arrangement. It has the remarkable feature of reduced number of diodes and concomitantly higher efficiency compared to the neutral-point clamped (NPC) inverter topology. The simulation of nested multilevel topology is fulfilled for four, five, six, seven, eight and nine output voltage levels having connected with a three phase star connected RL load. The performance comparison for different output voltage levels is accomplished in terms of total harmonic distortion (THD). The carrier-based sinusoidal PWM techniques, namely, phase disposition (PD), phase opposition disposition (POD) and alternative phase opposition disposition (APOD) are adopted here in order to reduce harmonic distortion in the output voltage as well as load current. The harmonic analysis is carried out through FFT analysis. The simulation is performed using MATLAB/Simulink software version R2012b.
This paper investigates the performance of transformer-less distribution static compensator (DSTATCOM) integrated at the side of the utility distribution system for four different control strategies, viz., unit template (UT) theory, synchronous reference frame (SRF) theory, instantaneous reactive power theory (IRPT) and power balance theory (PBT). The simulation models for the three-phase three-wire power system have been designed to achieve unity power factor with different loading conditions (balanced and unbalanced linear and nonlinear loads). The DC-link is self-supported, i.e., no energy storage element is used but a DC-link capacitor is used only. DSTATCOM fulfils almost all the objectives related to the current related power quality problems created by different types of load. Here, it eliminates the harmonics, compensates reactive power which reduces the burden on the grid, makes the grid power factor unity and eliminates the load unbalances. Here, steady-state and dynamic state analysis has been discussed and comparative results have been presented.
In remote locations with rich solar insolation, simple and effective nano-gird schemes for day-hours feeding of the important pumping loads and auxiliary ac loads are highly desired. In this paper, a pump drive based on a PV doubly-fed induction motor is introduced. The desired operational features of such nano-grid such as unity power factor of the pump drive, stable supply of auxiliary ac load, and flexible distribution of power between pumping and ac auxiliary load as well as maximum power point tracking could be all realised using a partially rated rotor side PWM inverter along with an off-the-shelf full-rating standard inverter. The paper explains the design of the different necessary control loops such as the MPPT loop, the dc-link loops and the rotor current loops. The dynamic performance of the system is tested under varying insolation and auxiliary ac load conditions.
In order to overcome the intermittence of renewable energy sources, such sources are connected in parallel forming hybrid systems. One of these hybrid systems is presented in this paper aiming to investigate and improve its dynamic performance. The hybrid energy system is composed of photovoltaic (PV) arrays and wind turbine (WT) that drives a doubly-fed induction generator (DFIG). Both the PV and WT are linked together through a DC-capacitor link. In order to improve the dynamic performance, a Particle-Swarm Optimization algorithm is implemented to tune the gains of the applied controllers. The obtained optimum gains are then implemented in a simulation model using the simulink program (MATLAB). Results in the case of optimized gains are compared with initial-design results in the relevant literature. Results show that the dynamic performance of the hybrid energy system with PSO is improved in terms of speed and steady-state error.
Typically, the photovoltaic (PV)-fed houses are based on AC networks. However, a transition to DC networks is currently running due to the proliferation of DC microgrids and the merits of DC systems. This paper considers three distinct designs: AC-based, DC-based and hybrid (AC and DC)-networks. A comparison between three configurations is done based on essential aspects such as the efficiency and the cost. Basic design features such as circuit breakers and cross section area of cables are included. Although the DC-based network has more merits compared to the AC-based network, problems such the DC circuit breakers and the availability of DC-based appliances still present some challenges. Thus, the study found that a proper combination of AC- and DC-based appliances is currently the best choice for PV-based houses.
In the modern times, the pertinence of a single power electronics conversion system used in DC microgrids for facilitating energy transfer between energy generating systems and storage elements with inherent bidirectional capability has increased significantly. A dual active bridge (DAB) converter having two DC-AC converters connected back to back through a high frequency transformer is used as a power electronics conversion system for obtaining highly efficient bidirectional power conversion. In this paper, performance of DAB converter with single phase shift (SPS) is evaluated with solar photovoltaic cell on high voltage DC-bus and battery on the low voltage DC-bus. Linear load is connected in this system at the high voltage DC-bus. A step variation in load is applied and at this instant the power flows from the batteries to supply the increased load demand. Optimal operating range of converter along-with efficiency is obtained.
In this paper, the optimisation of the PID controller employing the PSO algorithm for the interleaved buck-boost power converter is outlined. Currently, buck-boost power converters are broadly used in several application areas like the photovoltaic system, uninterruptable power supplies, and electric vehicle. The buck-boost power converter can be connected in parallel with one or more other buck-boost converters (multi phasing) or the interleaved configuration so less filtering requirement to suppress the ripple is needed and the effective resultant frequency is increased and thus high reliability and efficiency for the power converter is achieved. The switching pulses for these converters are sequenced or interleaved in time to give the required phase shift between the interleaved buck-boost converters. The control circuit for this interleaved buck-boost converter is tuned by the PSO algorithm. The system is tested firstly by changing the input voltage and secondly by changing the output load resistance. The Simulations and the operational dynamical performance of the interleaved buck-boost converter with PID controller employing PSO algorithm results are executed using MATLAB software.
This paper presents a new sensorless speed and secondary winding resistance estimation technique for brushless doubly fed reluctance generator (BDFRG) using least mean square (LMS) algorithm. Detailed mathematical derivation of the algorithm is explained and simulation results in MATLAB Simulink are shown for sensorless direct torque control (DTC) of BDFRG using LMS algorithm. A comparison to traditional speed estimation technique for BDFRG using primary winding flux linkage formula in stationary frame is then held to show the advantages of this proposed technique over the traditional method of speed estimation. Power electronics of the drive system is also simulated to consider effect of harmonics injected by electronic switches on both algorithms.
In recent years, multilevel inverters have become popular and widely accepted for high-power and high-voltage applications. Their performance is much superior to conventional two-level inverter as the level of the inverter increases. They produce superior quality output with less harmonic distortion. In this paper, simulation analysis of seven-level diode clamped inverter fed to interior permanent magnet synchronous motor (IPMSM) drive has been done for higher power applications. Two modulation techniques such as sinusoidal pulse width modulation (SPWM) and unified space vector pulse width modulation (USVPWM) are used. The carrier space vector pulse width modulation gives the same output reference wave as space vector pulse width modulation (SVPWM) without the actual calculation of the angle and sector location of space vector as in case of space vector modulation. The inverter output is fed to interior PMSM drive and the closed loop operation has been done using field oriented control (FOC). Speed-torque characteristics for various load conditions are studied. The output voltage and current harmonics are analysed for seven-level diode clamped inverter using SPWM and USVPWM techniques in MATLAB Simulink software.
Direct torque control (DTC) is known to produce the fastest torque response in AC drives. In this paper, a wind turbine emulation (WTE) system using a squirrel cage induction motor (SCIM) working in a DTC mode is designed, implemented, and tested experimentally using Hardware-in-loop (HIL). The flux estimation is based on the current model where two stator currents and the rotor speed are measured. The DTC is realised using a space vector modulator to avoid variable switching frequency associated with the DTC switching tables. dSPACE MicroLabBox is used to handle the real-time control programmed in SIMULINK. Typhoon HIL402 is used to emulate the inverter, the machine, the connected mechanical load, and the feedback sensors of the current dc link voltage and speed. Thanks to the great flexibility offered by the HIL technique, a variety of tests has been conducted to validate the overall system performance. The tests include step change of load, step change of wind speed, operation under stochastic wind spe...
In this article, hybrid wind-diesel system is powered with a genetically tuned fuzzy controlled flywheel for improving its frequency control. Flywheel is interfaced with the system through an electrical machine (generator/motor) and an electronic converter for synchronization. Fuzzy logic controller for the flywheel is designed in such a way that it continuously controls the system frequency and simultaneously satisfies the operational constraints of flywheel. Fuzzy logic controller is optimized by genetically tuning its membership functions. Regulated variable based on frequency deviation of system and speed characteristics of flywheel is introduced to reach out to the optimized membership functions. Necessary modeling has been done and effectiveness of the assembly has been confirmed by the simulation results.
STATCOM is taking challenges skilfully in the field of power system to maintain the AC bus voltage constant and to compensate for reactive power. When the STATCOM is integrated with energy storage device through DC/DC buck-boost converter, it compensates the active power also. In this paper, the regulation of DC link voltage to its rated value has been done to compensate simultaneous active and reactive power demanded by the load. The circuit model, mathematical expressions and MATLAB/Simulation model based on the mathematical model has been analysed. The hysteresis current control (HCC) strategy is used to generate the pulses for the 6-pulse 2-level voltage source converter (VSC). The conventional PI controller is used to generate the reference current direct and quadrature axis components. The PI controller is also used to generate the modes, whether it works in buck mode or boost mode. These modes decide the charging and discharging of supercapacitor. Here total reactive power is taken by STATCOM and the grid reactive power is near to zero and hence the burden on the grid is drastically reduced.
A robust sensorless control of doubly-fed induction motor (DFIM) is proposed in this paper. The stator of the DFIM is connected to the grid and the rotor is fed via controlled voltage source. Since the speed or flux measurement is not used, the sensorless control is achieved by using multirate output feedback (MROF)-based output feedback technique. The robustness towards parametric variations and matched disturbances is achieved by using MROF-based sliding mode control (SMC). The linear equations of doubly-fed induction motor are utilised for application of MROF and the state reference commands are computed from torque and speed reference commands separately. The proposed MROF-SMC controller is shown to be tracking given torque and speed commands.
This paper describes the design, development and analysis of an adaptive predictive wide-area damping controller (WADC) which is employed to enhance transient stability of a two-area power system. Based on system identification and adaptive generalised predictive control, the proposed controller is used in such a way that its output signal is added to the excitation system of the already chosen generator. A state-variable-based adaptive generalised predictive control formulation has been employed in this work. In order to increase the effectiveness of the proposed controller, a modified-regulated variable has been used which utilises the outputs at the previous instants to generate the input of predictive controller. For identifying the system model, a recursive least-squares algorithm (RLSA) has been used. The results obtained from the simulation studies clearly show the effective damping of inter-area oscillations as well as the reduction in effect of time-delay in remote signals by the proposed controller.
This paper deals with the automatic generation control (AGC) problem of a wind embedded two-area power system. Two areas are interconnected through parallel AC/DC transmission system with wind generation embedded in one of the control areas. The introduction of wind energy makes the control problem more challenging and therefore an energy storage emulating the dynamic effects of inertia is used to improve the dynamic performance of the system. The phase locked loop (PLL) dynamics are also considered by introducing a second-order function. Various modelling and control design aspects relevant to the problem are covered. Simulation studies are carried out in MATLAB/Simulink environment and the various controller parameters involved are tuned using genetic algorithm (GA) toolbox in MATLAB.
A battery energy storage system (BESS) can help improve distribution networks in two ways. First, on the technical side, it can support grid operations by providing voltage or frequency regulation, and help in a black start following a major fault. Second, on the economic aspect, BESS can be employed to help create profits through energy arbitrage (EA) and a reduction in various utility charges. In this paper, a planning study is proposed for determining the size and scheduling of the BESS in order to generate profit from EA. The study considers three different data sets as well as rules and regulations from three different jurisdictions throughout the world, namely, Ontario, Canada, Queensland, Australia, and New York West, USA, to investigate the potential of EA and to optimise the size and operation profile of the BESS. The results demonstrate the economic feasibility of employing the BESS for EA in each jurisdiction and show the optimal sizing and scheduling of the BESS in each case.
In this paper, an extensive study on the operation, control and performance of a hybrid photovoltaic and wind turbine system is presented. The study includes the operation of the hybrid system under different weather conditions which are reflected as a change in the wind speed and irradiance. Various loading conditions are investigated such as a change in active and reactive power demands for static and dynamic loads. The performance of the hybrid system is examined via MATLAB/SIMULINK simulations.
