M. S. Jamil Asghar

Development of microcontroller-based maximum power point tracker for a photovoltaic panel

Maximum power point trackers (MPPT) are used to operate a solar photovoltaic (PV) panel at its maximum power point (MPP). In this paper a microcontroller based MPPT is realized. Two tracking algorithms, namely, perturb and observation (PAO) algorithm and maximum power point voltage (MPPV) algorithm have been implemented. The MPPT is tested under varying insolation and load conditions. It has been shown that with PAO algorithm, the controller takes significant time to track the MPP. Moreover, the operating point oscillates around the MPP. The large tracking time and oscillations around the MPP result in significant energy loss during the tracking process. The wastage of power is more significant in rapidly changing atmospheric condition, as the controller has to search for new operating point more frequently. On the other hand, with the MPPV algorithm, the MPP is tracked very quickly with no oscillations around the MPP

Multilevel converter topology for solar PV based grid-tie inverters

A solar PV based grid tie inverters are used for dc-ac conversion. The conventional line commutated ac-to-dc inverters have square-shaped line current which contains higher-order harmonics. The line current with the high harmonic contents generates EMI and moreover it causes more heating of the core of distribution/ power transformers. Alternatively, PWM based inverters using MOSFET/IGBT switches are also used for the same purpose. However, apart from higher switching losses, the power handling capability and reliability of these devices are quite low in comparison to thyristors/ SCR. Nevertheless, the conventional thyristor based forced commutated inverters are not suitable for PWM applications due to the problems of commutation circuits. A pure sinusoidal line current or waveform with low harmonic contents is the most desirable for grid tie inverters. In the present work, various multilevel line commutated inverter topologies has been proposed and analyzed which improves the wave shape and hence reduces the total harmonic distortion (THD) of the line current in a grid tie line commutated inverter. The scheme has successfully been implemented and tested. Moreover, the performance of the proposed topology is far better than the conventional line-commutated inverter. It reduces THD, losses, switching stress and EMI.

Speed control of wound rotor induction motors by AC regulator based optimum voltage control

Wound-rotor induction motors are generally used for high torque and adjustable speed conditions. At lower speeds, either power is wasted in rotor resistances or power is pumped back from the rotor circuit to grid using different standard energy recovery methods. At low torque and low speed conditions, the power wastage in the rotor circuit becomes enormously high. Furthermore, if stator voltage control method is used it is effective for fan type loads only. For constant torque loads, the speed control range thus achieved is very limited. An efficient, low cost, simple speed control scheme is presented for wound rotor induction motors. Both stator voltage control and rotor resistance control methods are combined together and an optimum condition is found for voltage control. A thyristor based AC regulator used for stator voltage control, works efficiently at this condition. Then the rotor resistance is controlled for the adjustable speed requirements. A full speed control range has achieved, i.e. about zero to the rated speed. The motor operates satisfactorily even at very low torque and low speed conditions.

Modeling and simulation of variable frequency transformer for power transfer in-between power system networks

Recently a variable frequency transformer (VFT) has been used as a flexible ac link between two power systems. It avoids both HVDC link and FACTS based power transmission control system. Basically, it is a rotating transformer whose torque and speed are adjusted to control the power transmission. In this paper, a simulated model of VFT is used as a controllable bidirectional power transmission device that can transfer power in-between power system networks. A digital simulation model of VFT and its control system models are developed with MATLAB and a series of studies on power transmission between power system networks are carried out with this model. The response characteristics of power transfer under various torque conditions are discussed. The voltage, current, torque and speed plots are also obtained. Thus, the VFT concept and its advantages are verified by simulation results. It has distinct advantages in terms of controllability over conventional phase angle regulating transformers and does not inherently produce harmonics in case of many HVDC and FACTS technologies.

A Personal-Computer based Controller for Performance Improvement of Grid-Connected Wound-Rotor Induction Generators

To optimize the operation of wind energy conversion systems (WECS), various types of power electronic converters had been employed between the generator and the grid. Stator voltage control has been used for improvement of power factor in grid-connected induction generators. However, this method reduces the efficiency drastically. Also the control range is limited. Two schemes are presented to improve the performance of grid connected wound rotor induction generators. Scheme-I is used for maximizing efficiency and scheme-II is used for maximizing power factor. Voltage control together with slip control is applied for this purpose. The power-factor, hence the reactive power demand remains nearly constant throughout the range of operation using scheme-II. These schemes are very useful for wind power based generation where wind speed varies over wide range as well as abruptly. A very fast personal-computer based power electronic controller has been developed and tested using very commonly used IC chips at a very low cost. It consists of eight digital and one analog output lines, and four (expandable to eight) digital and eight analog input lines, all controllable and connected to the CPU. A complete control strategy is also presented to implement the control schemes.

Performance improvement of grid-connected wound rotor induction generators

Input voltage control has been used for improvement of power factor in grid-connected induction generators. However, this method reduces the efficiency drastically due to high output current and control range is also limited. In the proposed scheme both the voltage control and slip control are employed. Two schemes are presented. Scheme-I is used for maximizing efficiency. An optimum voltage and slip control by rotor resistance is applied such that the efficiency is maximized at every operating point. The scheme-II is used for maximizing power factor. A reduced and constant optimum voltage is applied throughout the range of control. The rotor resistance is varied to operate it at desired slip for optimum power-factor. Here power-factor hence the reactive power demand remains nearly constant throughout the range of operation. These schemes are very useful for wind power based generation where wind speed varies over wide range as well as abruptly

Rotating magnetic field based instantaneous angular speed measurement of low speed rotating machines

For early fault detection and health monitoring of low speed machines the instantaneous angular speed (IAS) measurement with high resolution and accuracy is required. The results show that IAS measurement is much more superior to the conventional methods i.e. analyzing acoustic waveforms, temperature variations, and vibrations etc. However accurate IAS measurement becomes very difficult due to slow and noisy response of the rotary transducers for low speed rotating machines. In the proposed technique, a fast rotating magnetic field (RMF) is used to measure the IAS for low-speed machines. An independent ac source is used to generate a balanced three-phase ac voltage, which is applied to the stator windings of a synchro whose rotor is coupled with the rotating member or rotor of a motor. The RMF in the air gap generates emf in the rotor of synchro whose frequency depends upon the slip speed. Since the RMF revolves at a speed, several times the speed of the rotating member or the rotor of motor, hence the IAS measurement becomes very fast and accurate. The proposed scheme is tested successfully for instantaneous change of speed within a range of 0 to 2 rpm.

Very Fast Measurement of Speed by Rotating Magnetic Field

For very low speed measurement, the output voltage of a tachometer type transducer and the voltage/noise ratio become very low. Moreover, it becomes stable only after several revolutions and it causes a delay of the order of several tens of second. In this work, a synchro based fast speed measurement technique is proposed. A balanced three-phase voltage is applied to the stator windings of synchro. It produces rotating magnetic field (RMF) which rotates at synchronous speed in the air gap. The induced emf generated in rotor of synchro and its frequency depend upon slip. The fast revolving RMF is used to measure the speed at very fast rate. A frequency meter connected at the output of rotor measures the frequency and hence speed. When RMF revolves at a speed, several times the speed of the rotor (which is physically coupled to the rotating member), the measurement becomes very fast. For very low speed of the rotor, the RMF rotates several times even before completion of one revolution of the rotor. Thus the output of synchro varies immediately and several times faster than the rotor itself. For lower speed and higher slip, the magnitude of the output voltage is unaffected, even at zero rpm. The scheme is very attractive for very low or super low speed for fast tracking and generation of feedback control signals.

Fuzzy Control Assisted Vehicle-to-Home (V2H) Energy Management System

Abstract In developing and underdeveloped countries, the electric power generation doesn’t suffice the electrical energy demand. With no or incorrect peak load controlling schemes, load shedding is very common. Regular unscheduled power outage for hours creates the demand for residential microgrid and the need of home-based standby power supply. Normally, a low-capacity stand-by inverter power supply is used for essential/emergency loads. Electric vehicle batteries have massive energy storage capacity and can be potentially utilized as backup power supply for most of the home loads during load shedding or blackout. Moreover, solar energy can also be utilized to charge plug-in electric vehicles (PEVs) to further enhance the backup power for home loads and to make it a residential microgrid. In this work, a fuzzy logic inference system is utilized for efficient power management and utilization of V2H. It imitates the decision-making process of charging/discharging of the PEV battery through priority decision-making of power management and emergency backup power supply of a typical home in developing countries like India.

Load shedding mitigation through plug-in electric Vehicle-to-Home (V2H) system

Electric vehicle batteries have massive energy storage capacity and can potentially utilize also as backup power supply for home loads during load shedding or blackout. Additionally, solar energy can be utilized to charge plug-in electric vehicles (PEVs) to further enhance the backup power for home loads. In this work, a fuzzy logic inference system is utilized for efficient power management and utilization of V2H. It imitates the decision-making process of charging/discharging of the PEV battery through priority decision making of power management and emergency backup power supply of a typical home in developing countries like India.