Bikram Das

Novel reverse regeneration technique of BLDC motor for capacitor charging

This paper illustrates the working of a BLDC motor in the forward motoring and reverse regeneration mode. It proposes a simple method of braking with energy regeneration for a brushless dc motor. This action is accomplished through the inversion of the signals given by the position sensor. During motor operation, the rotor moves clockwise. When the brake signal is applied, the stator field is reversed 180 electric degrees compared with the presented method. The proposed solution simultaneously achieves dual goals - electric brake and the energy regeneration without using additional converter, ultra-capacitor, or complex winding-changeover technique. Since by braking kinetic energy is converted into the electrical energy and then this energy is stored in the battery. Charging of the battery has been understood by looking into the charging current and voltage waveform of the capacitor connected in parallel to the battery. The speed control model of the BLDC motor is built and simulated in this paper. Power electronic components such as inverter, motor have been used and analysis of the different parameters like speed, torque, phase currents, hall sensors output etc. has been discussed during various modes of operation. This model has been built using PSIM (power simulator) software and the Mathworks tool called the Simpower systems. The parts of the Inverter, BLDC motor have been modeled in PSIM whereas controller model has been done using the Simpower systems. The motor model built in PSIM systems is then tied into the MATLAB model with the help of a SIMCOUPLER tool.

Sensorless speed control of DC machine

In this paper a Kalman filter based state feedback controller of a DC machine is designed and implemented in a hardware. A Kalman filter is used to estimate the speed and armature current from noisy measurement of armature current. A state feedback control is designed and simulated in Matlab. The controller designed is implemented in dSPACE. A chopper circuit is designed and fabricated to drive a DC motor. Sensor less speed control is implemented in real time. Experimental results show satisfactory speed and load response.

Solar Photovoltaic array based multilevel inverter for power conditioning in four-wire distribution system

This paper proposes a photovoltaic (PV) array based cascaded H-bridge multilevel inverter (CHBMLI) working active power filter as a shunt for four wire distribution system. This system is used for the power acclimatizing of distribution network as it is composed of linear, nonlinear and unbalanced loads. Solar Photovoltaic formed isolated source for CHBMLI. This active filter minimize line harmonics, minimize neutral wire current about to zero and it also injects real power as per requirement of the system. The grid interface and required reference signal generation is carried out with the help of Instantaneous power theory. The simulation studies are carried out in MATLAB Simulink environment.

SVPWM based decoupled control of active and reactive power for single stage grid connected solar PV system

This paper proposes a control scheme for a 3- level NPC inverter used in a grid connected PV system. The proposed scheme is useful in such way that the active and reactive power can be controlled separately. Such a scheme is applied in the rotating reference frame. The transformation of three-phase quantities (voltage and current) in to rotating reference frame is done by using Clarke and Park transformations. Controllers are designed for both voltage and current. A Space vector modulation scheme is implemented and the DC link capacitor voltages are balanced by appropriate choice of switching sequence by the space vector modulation scheme. The proposed controller is designed with Bode plot and the performance parameters of the overall system have been analyzed. The independent control of active and reactive power for different value of solar insolation is also verified.

Implementation and practical evaluation of an automatic solar tracking system for different weather conditions

This paper mainly focuses on an automatic solar tracking system to maximize the utilization of solar energy and improves the energy conversion efficiency of the photovoltaic (PV) system. It is a closed loop sun positioning mechanism relative to the earth and makes the uniform distribution of solar radiation over an area of the PV panel. The incorporated tracking system is sufficiently devised for two degrees of freedom, being suns Zenith or Elevation and Azimuthal angles, are covering the four principal directions. A photo sensor platform is designed and used for finding the accurate position of the sun and monitoring the weather conditions. It uses two stepper motors for driving the azimuthal and zenith positions of the sun and independently controlled each. The prototype model is designed in such way that it will provide an automatic braking against windstorm or gusts.

Improved single stage grid connected solar PV system using multilevel inverter

A multilevel inverter based single stage grid connected solar PV system is proposed in this paper so as to reduce THD of the inverter voltage and reduce the size of filter circuit. A maximum power point tracking algorithm is implemented to obtain optimal performance of solar cell at different irradiance and temperature. Independent control of active and reactive power flow from inverter to the grid is obtained by implementing the control scheme in synchronously rotating reference frame. For interfacing the PV cell to the grid a 5kVA 3phase 3 level NPC Inverter is designed and fabricated. Space vector modulation scheme is used to generate the switching pulses for the inverter. Redundant switching states of a three level inverter are judiciously chosen to obtain capacitor voltage balancing. One of the most attractive features of a multilevel inverter is that it can generate output voltages with lower value of harmonic distortion and hence filter requirement is less. For hardware implementation the control scheme is implemented with a DSP. Complete scheme is simulated in MATLAB/ Simulink and verified in a 5kVA laboratory prototype.

Different Types of Lithium Coating in Tokamak ADITYA

In fusion devices, conditioning of vacuum vessel wall is important to get better plasma parameters. The impurities affect the plasma parameters such as density, temperature, and confinement time. Lithium coating on plasma-facing components is one of the techniques for wall conditioning to minimize the impurity level and to improve plasma parameters. In the ADITYA tokamak, we have performed a series of experiments with different types of in situ lithium coating. We observed reduction in the impurity level after lithium coating. This paper presents different types of in situ lithium coating in the ADITYA tokamak and the experimental observations.