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A switching state selection scheme for a five level stacked multilevel inverter for open end winding motor drive is presented in this work. Using the proposed scheme, converter can be operated with a single DC supply and with zero common mode voltage. In addition, the switching transition of high voltage switches occurs at zero voltage conditions. The degree of freedom provided by the redundant switching states and voltage vectors of the inverter topology is utilised to design the modulation scheme. The proposed switching state selection leads to inherent capacitor balancing without using any extra sensors and fundamental frequency switching of the high voltage switches of the topology. The modulation scheme uses triangular carrier comparison and hence avoids the complexity of sub-sector identification and dwell time calculation. Half wave symmetry in output waveforms is ensured by maintaining synchronous sampling with constant samples per fundamental cycle. The inverter topology and the effectiveness of state selection scheme is experimentally validated on an open end winding induction motor drive and experimental results showing steady state and dynamic operation are presented.

Conventional pulse width modulation (PWM) schemes for dual inverter fed drive synthesise the reference voltage as a switched average of minimum three voltage vectors from individual inverters. As a result, the number of transitions in the inverter increases. This paper introduces a family of PWM methods, where the reference voltage is synthesised as a switched average of only two voltage vectors from individual inverter. This leads to simultaneous clamping of two phases, thus reducing the number of switching transitions in the inverter. The concept and realisation of the proposed PWM are discussed and compared with conventional bus clamping PWM methods on the basis of inverter power loss and common mode voltage generation. The proposed PWM is experimentally validated on an open end winding induction motor drive operating with open loop control. Synchronised carrier modulation is considered for PWM generation.

A five level inverter topology with single DC supply is analysed for an open end winding induction motor (OEWIM) drive. A carrier based modulation scheme is proposed to eliminate the common mode (CMV) and differential mode voltages (DMV). The modulation scheme utilises the voltage vector and switching state redundancy of the inverter topology. The voltage vector redundancy is used to eliminate the DMV and switching state redundancy is used to eliminate the CMV. Compared to the conventional level shifted PWM method, the proposed modulation scheme offers improved harmonic performance and also ensures self-balancing of capacitor voltages. The simulation studies are carried out in MATLAB for an OEWIM drive operating with open-loop constant Volts-per-Hertz control. The modulation scheme is implemented using TMS320F28379D controller board and an FPGA module.

Conventional predictive controller selects the optimal switching state out of the available switching states by appropriate cost function optimisation. The direct application of the optimal switching state without a modulator restricts the use of carrier interleaving techniques with predictive control of parallel converters. The paper proposes a constant switching frequency predictive controller for parallel AC/DC converters with an intermediate modulation stage. The paper combines the generalised discontinuous pulse width modulation (GDPWM) technique with carrier interleaving for reducing both the switching losses of the converter and the harmonic distortion of grid currents. The parallel converter operate with separate DC loads for mitigating the flow of circulating currents. The controller guarantees good and quick dynamic response. The performance of the proposed controller-modulation is evaluated using MATLAB/SIMULINK. The paper analyses the performance of the parallel rectifier with individual converters operating at different DC load voltages and different power factor angles.

A carrier based hybrid pulse width modulation (PWM) strategy for dual inverter with reduced switching loss is proposed in this paper. The proposed hybrid modulation scheme clamps each phase 60° continuously to the DC bus mid-point at all load power factors and results in reduced switching loss for lower modulation range. The hybrid scheme is obtained after comparing different combinations of level shifted and decoupled PWM methods based on average switching energy loss, current harmonic distortion, common mode and differential mode voltage switchings. All PWM methods are analysed on a dual inverter fed induction motor (IM) drive operated with open loop v/f control. From the analysis, it is observed that the proposed carrier based hybrid PWM scheme results in upto 20% reduction in switching loss as compared to the conventional bus clamping PWM methods for low speed operations. The hybrid PWM also has improved performance in terms of common mode and differential mode voltage switchings. The performance of PWM methods are experimentally validated on an open end winding IM drive. The PWM methods are generated using triangle carrier comparison with synchronous sampling.

In this paper, a constant switching frequency predictive control method for a three-level flying capacitor active front end converter is presented for the first time. This predictive control scheme results in reduced switching frequency operation of the converter with reduced computation burden compared to conventional predictive control methods. For the predictive controller, the cost function is defined in terms of grid current error vector in synchronously rotating $d-q$ frame and the condition for optimal converter voltage vector is derived. The optimal converter voltage vector is then synthesized using level shifted carrier based space vector modulation. Thus the proposed method overcomes the disadvantage of variable switching frequency in predictive based control methods. The controller ensures very low harmonic distortion of line currents with minimum computational requirement of the predictive controller. The performance of the proposed predictive controller is analysed using MATLAB/SIMULINK and the results are compared with that of a conventional PI based control. It can be observed that the proposed controller results in similar performance in terms of harmonic spectrum, better performance in response time and decoupled control compared to a classical PI based controller and can be readily used for grid connected power conversion applications and distributed generation systems.

In dual inverter fed open end winding induction motor drives (OEWIM), the reference voltage can be synthesized either by level shifted carrier based space vector modulation (SVM) techniques or by using decoupled SVM methods. In level shifted SVM, each phase leg is switched for half the fundamental cycle and therefore has lower switching loss compared to decoupled methods. Bus clamping sequence (CS) pulse width modulation (PWM) technique also results in reduced switching loss. In this paper, decoupled and level shifted SVM methods are compared in terms of switching loss, common mode voltage (CMV) switching and stator current ripple. From the analysis, it is observed that level shifted clamping sequence SVM for a dual inverter fed OEWIM results in reduced switching loss and reduced number of CMV switching at the cost of increased stator current ripple. Compared to decoupled clamping sequence, level shifted clamping sequence has nearly 50% reduction in switching loss and CMV. Also, clamping sequence applied to decoupled method results in improved harmonic performance but has moderately increased switching loss. Various SVM methods are simulated in MATLAB Simulink for an open-loop volts per hertz (V/f) controlled induction motor drive with fixed number of samples per sector.

In this paper, a hybrid space vector modulation (SVM) scheme with reduced harmonic ripple for a dual inverter fed open end winding induction motor (OEWIM) for various fundamental frequencies and operating power factors is presented. Various SVM methods are compared based on the harmonic distortion to identify the zones of superior performance and to propose a hybrid SVM for the entire operating range. In dual inverter fed OEWIM drives, the reference voltage can be synthesized by level shifted carrier based SVM method or by using decoupled SVM method. In the decoupled SVM method, each inverter can be switched independently of each other, thus different SVM techniques can be applied in the individual inverter. This paper exploits the above possibility and analyses combinations of conventional SVM and bus clamping SVM applied to the individual inverters in terms of their harmonic performance. Harmonic performance of various SVM techniques are compared using the concept of stator current ripple and is analysed for various fundamental frequencies and operating power factors to find an optimum method over the entire modulation range. The SVM methods are analysed using MATLAB Simulink by operating an induction motor drive under open-loop volts per hertz control scheme with fixed number of samples per fundamental frequency.

Vector control of induction motor is preferred as it gives independent control of flux and torque. For vector control knowledge of flux and speed is required. To eliminate the sensors, observers are used to estimate the flux and speed rather than measuring it. Sliding mode approach is popular due to its robust nature and very suitable for nonlinear system. This paper designs a sliding mode observers for speed control of induction motor. The sliding mode observer is verified experimentally. The experiment is carried out on a closed loop system consisting of induction motor, PI controller and the proposed estimator.