Faculty Publications

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Author: search.filters.author.Karthikeyan, A.

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    Sensor-less estimation of rotor position in a doubly fed induction machine
    (Springer International Publishing, 2017) Saravana Ilango, G.S.; Nagamani, C.; Asha Rani, M.A.A.; Jaya Bharata Reddy, M.J.; Karthikeyan, A.
    For a precise power or speed control of a Doubly Fed Induction Machine (DFIM), with a good dynamic and steady state response, accurate information of rotor position and speed is essential. Thus, the signal processing stage should be provided with accurate speed/position information either through use of physically mounted shaft encoder or through robust sensor-less estimation. Usually, there is a large separation between the signal processor and the turbine shaft, such as in wind power generation. Hardwired shaft-mounted sensors involve ungainly cabling and require perfect mounting, periodic maintenance, and added cost. Sensor-less schemes involve estimation of speed and/or rotor position by means of a digital signal processor and a set of voltage and current sensors that are already part of the speed or power control system. Various studies are reported on sensor-less estimation of rotor position or speed. Typically, there are two broad categories: closed loop and open loop schemes. The open loop techniques usually involve computations based on the machine model while utilizing the measured voltage and current signals. The closed loop schemes are based on Model Reference Adaptive System (MRAS) techniques or observer-based techniques. In this chapter, an introduction to the operation of a DFIM, significance of rotor position, and an overview of the sensor-less rotor speed/position computation techniques for a DFIM are presented. Further, two typical schemes for a grid-connected DFIM are described in detail, out of which, one is an open loop scheme while the other is a closed loop scheme. The efficacy of the schemes is demonstrated through simulations and experimental results. In this chapter, a brief introduction about the grid-connected doubly fed induction machine is given in Sect. 5.1. The mathematical model of a DFIM and the basics of decoupled control of DFIM in generating mode along with the control aspects of the back-to-back converters (RSC and FEC) are presented in Sect. 5.2. The significance of rotor position and speed and a brief review of the sensor-less estimation techniques for the control of DFIM are discussed in Sect. 5.4. Section 5.5 presents the underlying theory and the mathematical formulation of the techniques for sensor-less estimation of rotor position. Further, one of the recently reported techniques under each category is considered for illustration in Sects. 5.5.1 and 5.5.2. Details of control implementation, test results, and comparison with other schemes are presented in Sect. 5.5.3. Section 5.6 presents the overall conclusions. © Springer International Publishing AG 2017.
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    Speed loop pseudo derivative feedback controller based direct torque controlled permanent magnet synchronous motor drive
    (Institute of Electrical and Electronics Engineers Inc., 2017) Koothu Kesavan, K.K.; Venkatesa Perumal, B.V.; Karthikeyan, A.; Nagamani, C.
    This paper presents a comprehensive evaluation of PI controller and proposed pseudo derivative feedback (PDF) controller based direct torque controlled (DTC) permanent magnet synchronous motor (PMSM) drive. The proposed controller eliminates oscillation and overshoot in the actual rotor speed and significantly reduces the flux, torque and stator current ripples. The performance of the proposed controller is tested for different cases viz., no load starting response, load variations at rated speed, wide speed reversal and low speed regions including standstill condition at rated torque. The simulations are carried out through MATLAB/Simulink environment for 1.2hp PMSM drive and results demonstrates the efficacy of the proposed controller. © 2016 IEEE.
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    Pseudo derivative feedback current controlled sensorless PMSM drive with flux-Torque based MRAS estimator for low speed operationestimator for low speed operation
    (Institute of Electrical and Electronics Engineers Inc., 2017) Karthikeyan, A.; Koothu Kesavan, K.K.; Venkatesa, P.B.; Nagamani, C.
    In this paper, a simple and robust speed estimator and Pseudo Derivative Feedback (PDF-PDF) controller are proposed for sensorless PMSM drive to improve its performance at standstill and low speed regions. The speed estimator is formed using stator flux and electromagnetic torque based model reference adaptive system, which performs better during transient conditions and reduces steady state error for wide rotor speed variations which includes low speed regions. The proposed PDF-PDF controller reduces the overshoot and improves settling time of the system. The stability of the proposed estimator is verified through small signal model and the machine parameter sensitivity is also analyzed. The performance of the proposed estimator and controller is validated by considering variation in the low speed regions which includes standstill condition. The simulations are carried out through MATLAB/Simulink and it is also experimentally verified through FPGA controller based 1.2hp laboratory prototype PMSM drive. It is found that the maximum estimated rotor speed and position error are ±2 rad/s and ±1° respectively during low speed operation at transient and steady state conditions. ©2017 IEEE.
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    DSC filter based unit vector estimator for reference generation and control of dynamic voltage restorer
    (Institute of Electrical and Electronics Engineers Inc., 2017) Kasyap, M.S.; Karthikeyan, A.; Venkatesa Perumal, B.V.; Nagamani, C.
    DVR control requires a robust algorithm for computing grid voltage magnitude and phase angle. Conventional SRF-PLL performs poorly as it cannot filter out negative sequence voltages and harmonics that could occur in the grid voltage. In this paper a Positive and Negative Sequence Extractor (PNSE) is formed by a Delayed Signal Cancellation (DSC) filter, which filters harmonics and extracts Instantaneous Symmetrical Components (ISC) of the source voltage in stationary reference frame. The phase angle information of the grid voltage is derived by computing the unit vectors of the ISC in stationary frame. This eliminates the need for a conventional PLL and thus simplifies the reference generation algorithm. A PI controller tracks the capacitor reference voltage in synchronous reference frame to restore the fundamental load voltage while resonant controllers are tuned to mitigate the lower order odd harmonics in the load voltage. Simulation studies carried out in PSCAD/EMTDC for a Medium Voltage DVR model shows that the presented control works effectively for all the test cases considered such as voltage sags and harmonics. © 2016 IEEE.
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    Four quardrant operation of direct torque controlled PMSM drive using speed loop PDFF controller
    (Institute of Electrical and Electronics Engineers Inc., 2018) Karthikeyan, A.; Koothu Kesavan, K.K.; Nagamani, C.
    This paper presents a comprehensive evaluation of proposed speed loop pseudo derivative feedforward (PDFF) controller based DTC, speed loop PI based direct torque controller (DTC) and speed loop PI based hysteresis current controller (HCC) for permanent magnet synchronous motor (PMSM) drive. The proposed controller reduces the torque and stator current ripples and significantly reduces overshoot and oscillation in the actual rotor speed. The proposed controller is verified for different cases viz., forward and reverse motoring, forward and reverse braking operation. The simulations are carried out through MATLAB/Simulink for 1.2 hp PMSM drive and results demonstrates the efficacy of the proposed controller. © 2018 IEEE.
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    Standalone single stage PV fed reduced switch inverter based independent control of two PMSM drive
    (Institute of Electrical and Electronics Engineers Inc., 2018) Karthikeyan, A.; Koothu Kesavan, K.K.; Abhilash Krishna, D.G.; Nagamani, C.
    This paper proposes a standalone singe stage PV fed air cooler which consists of two motors (fan blower and water pump). The proposed system comprises of PV source, reduced switch inverter and two PMSM drive. The proposed system aims at reducing the switching losses and overall cost by using reduced switch inverter. The reduced switch inverter uses only eight switches whereas the conventional VSI utilizes twelve switches. In the proposed scheme, blower and pump are independently controlled using field oriented control scheme where speed reference is obtained using Perturb and Observe (PO) technique. Simulation studies for the proposed PV fed two 400 W PMSM driven blower and pump is performed using MATLAB platform and respective results are presented to show the efficacy of the system. © 2018 IEEE.
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    Uncertainity and disturbance estimator based control of transformerless DVR
    (Institute of Electrical and Electronics Engineers Inc., 2018) Karthikeyan, A.; Abhilash Krishna, D.G.; Kurra, S.; Koothu Kesavan, K.K.
    This paper presents Uncertainty and Disturbance Estimator (UDE) based control for Transformerless Dynamic Voltage Restorer (TDVR). The proposed UDE based control algorithm for TDVR mitigate the voltage disturbances and maintain robustness during parameter (filter) variations. The control equation of UDE is derived based on the dynamic model of a voltage source inverter along with the LC filter. The proposed UDE control estimates the uncertainties and disturbances by an appropriate filter (loop filter involved in the derived UDE control law) and used for further synthesis, thus accounts for robustness. The simulation studies are performed for 230 V low voltage (LV) system in MATLAB to verify the efficacy of UDE control for symmetric and asymmetric voltage sags along with the parameter mismatch (inverter filter) conditions. © 2018 IEEE.
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    Virtual Impedance based DFCL for DVR during Downstream Faults
    (Institute of Electrical and Electronics Engineers Inc., 2018) Karthikeyan, A.; Abhilash Krishna, D.G.; Nagamani, C.
    This paper proposes a Downstream Fault Current Limiter (DFCL) for DVR during downstream faults. It Is based on the concept of Virtual Impedance (VI) which introduces the impedance in series to the system to suppress the large fault currents in the line. In the present work no additional equipment is involved for limiting the fault current and DVR itself is controlled such that FCL operation is ensured. The proposed VI based FCL features flexible implementation and can effectively suppress the fault current during the downstream faults and thereby the DVR is protected along with restoration of PCC voltages. Simulation studies are performed for 10 kV system using PSCAD/EMTDC platform and respective results are presented which proves the feasibility and efficacy of the proposed FCL. © 2018 IEEE.
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    Single stage PV fed reduced inverter based PMSM for standalone water pumping application
    (Institute of Electrical and Electronics Engineers Inc., 2018) Karthikeyan, A.; Koothu Kesavan, K.K.; Varsha, S.; Venkatesa Perumal, B.; Mishra, S.
    This paper proposes a standalone PV fed PMSM drive for water pumping. The proposed system aims at reducing the switching losses and overall cost by using reduced switch inverter. The proposed system comprises of a PMSM drive, fed by PV source through an inverter employing reduced number of switches. The inverter uses only four switches whereas the conventional VSI utilizes six switches. Field oriented control scheme is employed to control the PMSM drive. Perturb and Observe (PO) MPPT technique is used to generate a speed reference to PMSM drive. Simulation studies for the proposed PV fed 400 W PMSM driven water pumping system are performed using MATLAB platform and respective results are presented to show the efficacy of the system. © 2018 IEEE.
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    Stator flux based MRAS speed and stator resistance estimator for sensorless PMSM drive
    (Institute of Electrical and Electronics Engineers Inc., 2018) Karthikeyan, A.; Koothu Kesavan, K.K.; Nagamani, C.
    In this paper, a simple and robust speed and stator resistance estimator is proposed for sensorless permanent magnet synchronous motor drive to improve its performance at standstill and low speed regions. The speed and stator resistance estimator is formed using stator flux based model reference adaptive system, which yields fast transient response, reduces steady state error for low rotor speed variation and load disturbances. The proposed method improves the performance of the drive at low speed regions. The simulations are carried out through MATLAB/Simulink environment and results show the effectiveness of the sensorless PMSM drive. The maximum estimated rotor speed and position error are found to be are ±3 rad/s, ±1 °respectively, during low speed operation at transient and steady state conditions. © 2017 IEEE.