Ranjan K. Behera

Common-Mode Voltage and Vibration Mitigation of a Five-Phase Three-Level NPC Inverter-Fed Induction Motor Drive System

Common-mode (CM) voltage is one of the main reasons for the flow of bearing currents in induction motors (IM) that ultimately leads to the bearing failure and causes severe vibrations. For three-phase IM drives, many works have been reported either on the reduction or on the elimination of CM voltages that are generated due to pulse width modulation (PWM) action of the feeding power converters. However, for five-phase IM drives, very few studies are available with the perspective of the CM voltage elimination. Also, the effect of CM voltage on the mechanical vibrations of a five-phase IM has not been reported in the literature. Hence, in this paper, firstly, the modeling of CM current generated in the five-phase IM is done and its expression based on admittance transfer function is derived. Then the CM voltage is eliminated from a five-phase three-level neutral point clamped (NPC) voltage source inverter. The space vector pulse width modulation (SVPWM) technique is developed for the elimination of CM voltages. Only those switching states are selected which give zero CM voltage. The same selected switching states also give the balanced dc link capacitor voltages. Its effect is observed on the mechanical vibration of the motor and it is correlated with the CM current. The mechanical vibration is observed for both, with and without CM voltage elimination. Both the simulation and experimental results are given to validate the concept proposed.

A Novel Controller Design for Grid-side Converter of Doubly Fed Induction Generator for Wind Power Interface: An Experimental Investigation

Abstract This article presents a novel controller design for the grid-side converter of a doubly fed induction generator for wind power interface. The dynamics of the DC-link voltage and phase currents are modeled systematically in a synchronously rotating reference frame. In this controller structure, sensor and signal transportation delay in the feedback path is considered. It is noted that the presence of any pole in the feedback loop appears as zero in the closed-loop transfer function. In order to cancel out its effect, the reference to the current controller is modified to cancel the zero. The current and voltage controllers are designed separately. The grid-side converter has been simulated for forward and reverse power flow conditions. The input power factor can be nearly unity, leading, or lagging, according to the doubly fed induction generator requirement. The simulation and experimental results show that employment of the proposed control algorithm leads to improved dynamic response.

Analysis of Experimental Investigation of Various Carrier-based Modulation Schemes for Three Level Neutral Point Clamped Inverter-fed Induction Motor Drive

The harmonic analysis of the stepped waveform of the three-level inverter, based on number of triangular carriers and a sinusoidal modulating signal has been described. Analytical solutions of different multilevel pulse width modulation (PWM) strategies for three-level neutral point clamped (NPC) has been presented. Analysis of the total harmonic distortion (THD) of voltage and stator current has been carried out by simulation study. These solutions show that in-phase sinusoidal pulse width modulation (IPSPWM) strategy shows better spectral performance compared to the phase opposite sinusoidal pulse width modulation (POSPWM) and dipolar modulation techniques. This is because of the fact that it places significant harmonic energy in to main carrier component and relies on the cancellation of this component between phase legs when the line-to-line voltages are formed. All these techniques are applied to an induction motor drive for comparison. Torque ripple is also estimated for different techniques. A laboratory model is developed to verify validity of different modulation schemes.

Analysis and experimental investigation for grid-connected 10 kW solar PV system in distribution networks

In this paper, the dynamic performance of a grid connected photovoltaic (PV) power system of a distribution networks is studied and experimental results are presented. Due to oscillating nature of the PV power plant, the grid integration requires stable and steady power injection with good power quality (PQ). Hence, the PQ analysis has been carried out under different climate conditions at 10 kW Solar Power Plant (SPP). This SPP can operate in grid connected or in isolated mode. The proposed PV power plant system is modelled and its performance is studied. This integrating model is composed of boost converter, maximum power point tracking (MPPT) control, inverter and filter design. It also explains the behaviour of system response whether it is stable and unstable condition. It is analyzed that the presence of high penetrated grid connected solar PV system will exhibit low PQ issues like voltage variations and harmonics. To study this effect a 10 kW SPP is developed for verifying the performance of the system.

A Utility Friendly High Power Induction Motor Drive with Direct Torque and Flux Control

In this paper, a three-level neutral point clamped (NPC) front-end ac-dc converter supplying a three-level inverter fed induction motor drive operating under direct torque and flux control (DTFC) is presented. The three-level ac-dc converter draws sinusoidal ac current from the supply and keeps the dc-link voltage constant. Hysteresis current controller is used for current control of the front-end converter because of its simplicity, easy implementation and good performance. A diode clamped multilevel inverter is used for driving induction motor operating under DTFC scheme. A new technique that ensures constant flux control for forward motoring and reverse motoring is proposed. This technique enables soft starting of the drive. In the proposed drive system, the DTFC principle can be applied in the entire speed range. Simulation results of three-level converter-inverter system demonstrate the validity of the proposed hysteresis current control method. The converter is found to be stable for a large range of hysteresis band. DC link voltage across each capacitor is maintained constant and balanced. The simulation results of the complete drive system are presented here for both forward and reverse motoring operations with regeneration.

High performance induction motor drive: A dither injection technique

In this paper, a three-level inverter fed induction motor drive operating under Direct Torque Control (DTC) is presented. DTC do not show good performance in low speed region due to stator flux demagnetization that relates to variation in stator resistance. Here, a sinusoidal wave is used as dither signal of minute amplitude (for torque hysteresis band and flux hysteresis band respectively) in the error block. Hence, this method is used to take care of the demagnetizing effect of flux vector near sector boundary. In this paper, sinusoidal dithering technique is applied to study the effect of settling time, flux demagnetizing effect, dc drift and initial value problem, flux and current ripple reduction. A laboratory prototype of the drive system has been developed and the simulation and experimental results are reported.

Simulation study of permanent magnet synchronous machine direct drive wind power generator using three level NPC converter system

In this paper, two three-phase three-level Neutral Point Clamped (NPC) converters connected back-to-back are used for a direct drive wind power generator. A permanent magnet synchronous generator (PMSG) is used as the generator, which is driven by the wind turbine. Main problem of voltage unbalance in each electrolyte capacitor is controlled by using a simple chopper control circuit. A simple hardware method for balancing the Neutral Point (NP) voltage is proposed, which allows enhanced ride-through performance. This method can effectively balance the NP voltage without the limitations of modulation methods and load conditions. It also provides increased ride-through capabilities for the inverter during input voltage sags. Because of the NP balancing, the necessary size of the dc-bus capacitors is reduced. Here, MATLAB/SIMULINK simulation results are presented for the validity of proposed scheme.

Performance improvement of a wind power distribution station using a dynamic voltage restorer

This paper discusses the dynamic voltage restorer (DVR) supported wind power generator connected to the grid to improve the low voltage ride through (LVRT) capability of the grid. The wind power generators are connected to the grid through a feeder to the distribution system and the DVR is connected to the point of common coupling (PCC), where loads are connected. The main aim of the DVR is to regulate the voltage at the load terminal irrespective of sag/swell, distortion, or unbalance in the grid voltage. The proposed DVR structure is operated in such a fashion that it does not supply or absorb any active power during the steady-state operation. Dead beat control algorithm is used for the control of DVR. The DVR supported wind power system operation is verified through extensive simulation study and a prototype experimental setup is built for experimental verification.

Describing Function Analysis and Experimental Investigation of a High Power Utility Friendly AC-DC Converter System

In this paper, a utility friendly synchronous link three level diode clamped AC-DC converter having rectification and regeneration capability is presented. The three-level AC-DC converter draws sinusoidal AC current with low harmonics from the supply and keeps the DC-link voltage constant. Hysteresis current controller is used for current control because of its simplicity, easy implementation and good performance. The paper presents an analysis for limit cycle control of switching logic for the three-level synchronous link converter. The ideal hysteresis current control method leads to infinite frequency and that results in chattering phenomenon. In medium and high voltage converter applications, the switching elements, such as IGBT and GTO, have finite switching frequency. To bring the switching frequency into the limit of practical devices, hysteresis logic with a suitable band width (h) is required. The hysteresis logic being non-linear, describing function (DF) analysis is applied with non-linearity replaced by its DF. Thus, by using DF analysis, the maximum possible switching frequency for a given hysteresis band can be predicted. The closed-loop control scheme with hysteresis current control is implemented for the three-phase three-level synchronous link converter (SLC). Simulation and laboratory prototype test results demonstrate the validity of the proposed hysteresis current control method. The converter is found to be stable for a large range of hysteresis band

An Improved DTC Technique for Low-Speed Operation of a Five-Phase Induction Motor

In this paper, an improved direct torque control (DTC) technique of a two-level inverter-fed five-phase induction motor (FPIM) drive for low-speed operation is presented. The operation of the FPIM with distributed winding requires the elimination of third-harmonic voltage, which, if not taken care of, would generate distorted stator current. For this, the concept of virtual vectors (VVs) is utilized. Before selecting the VVs for the DTC operation, a theoretical analysis is carried out to find the effects of these VVs on the torque and flux response of the FPIM under different speed and loading conditions. It is found that the rotor speed plays a crucial role in the selection of VVs. A particular VV has different effects on the torque change as speed varies. This analysis helps in the selection of VVs, hysteresis torque bandwidth, flux bandwidth, and efficient formation of sectors. Furthermore, in this paper, the performance of the FPIM during low-speed operation is improved by avoiding the demagnetization of the stator flux. To achieve this, a new modified lookup table is proposed. Superiority of the proposed method over the reported approaches is illustrated by experimental results.