Variable speed motor drives are being rapidly deployed for a vast range of applications in order to increase efficiency and to allow for a higher level of control over the system. One of the important areas within the field of variable speed motor drives is the system's operational boundary. Presently, the operational boundaries of variable speed motor drives are set based on the operational boundaries of single speed motors, i.e. by limiting current and power to rated values. This results in under-utilization of the system, and places the motor at risk of excessive power losses. The constant power loss (CPL) concept is introduced in this dissertation as the correct basis for setting and analyzing the operational boundary of variable speed motor drives. The control and dynamics of the permanent magnet synchronous motor (PMSM) drive operating with CPL are proposed and analyzed. An innovative implementation scheme of the proposed method is developed. It is shown that application of the CPL control system to existing systems results in faster dynamics and higher utilization of the system. The performance of a motor drive with different control strategies is analyzed and compared based on the CPL concept. Such knowledge allows for choosing the control strategy that optimizes a motor drive for a particular application. Derivations for maximum speed, maximum current requirements, maximum torque and other performance indices, are presented based on the CPL concept. High performance drives require linearity in torque control for the full range of operating speed. An analysis of concurrent flux weakening and linear torque control for PMSM is presented, and implementation strategies are developed for this purpose. Implementation strategies that compensate for the variation of machine parameters are also introduced. A new normalization technique is introduced that significantly simplifies the analysis and simulation of a PMSM drive's performance. The concepts presented in this dissertation can be applied to all other types of machines used in high performance applications. Experimental work in support of the key claims of this dissertation is provided. / Ph. D.

Artificial Neural Networks (ANNs) have proved to be useful in approximating non- linear systems in many applications including motion control. ANNs advocated in switched reluctance motor (SRM) control typically have a large number of neurons and several layers which impedes their real time implementation in embedded sys- tems. Real time estimation at high speeds using these ANNs is diffcult due to the high number of operations required to process the ANN controller. An insuffcient availability of time between two sampling intervals limits the available computation time for both processing the neural net and the other functions required for the motor drive. One ideal application of ANNs in SRM control is rotor position estimation. Due to reliability issues, elimination of the rotor position sensors is absolutely required for high volume, high speed and low cost applications of SRM's. ANNs provide a means by which drive designers can implement position sensorless drive technology that is both robust and easily implemented. It is demonstrated that a new and novel ANN configuration can be implemented for accurate rotor position estimation in a sensorless SRM drive. Consisting of just 4 neurons, the neural estimator is the smallest of its kind for SRM rotor position estimation. The breakthrough that provided the reduction was the addition of a non- linear input. Typical input spaces for SRM position neural estimators consist of both current,and fux-linkage. The neural network was trained on-line using these inputs and a third, non-linear input provided by a preprocessed product of the two typical inputs. / Master of Science

This thesis proposes control schemes and converter configurations for high power wound field synchronous motor (WFSM) drives. The model for a salient pole WFSM in any general rotating reference frame is developed which can be used to derive models along known rotor (dq) and stator flux (MT) reference frames. Based on these models, the principle of sensor-less stator flux oriented field-oriented control (FOC) for salient pole WFSM is developed. So far in the literature, control of cylindrical rotor machine only has been addressed and the effects of saliency have generally been neglected. The performance of the proposed sensor-less FOC has been demonstrated by experimentally operating a 15.8 HP salient pole WFSM using a three-level IGBT based voltage source inverter (VSI). The principle of FOC has been later extended to the control of current source load commutated inverter (LCI) fed salient pole WFSM drives, where the drawbacks present in conventional self-control method such as rigorous off-line calculation for generation of look up tables, coupling between flux and torque control etc. are eliminated. This thesis also proposes the combination of a VSI with the LCI power circuit to overcome the different disadvantages that are present in the existing LCI topology. Firstly, a novel starting scheme is proposed, where the LCI fed WFSM is started with the aid of a low power auxiliary VSI converter in a smooth manner with sinusoidal motor currents and voltages. This overcomes the difficulties of the present complex dc link current pulsing technique that has drawbacks such as pulsating torque, long starting time etc. In a second mode of operation, it is shown that the VSI can be connected to the existing LCI fed WFSM drive as a harmonic compensator in On-The-Fly mode; this will make the terminal stator current and voltage sinusoidal apart from cancellation of torque pulsations thus improving the drive performance. The above two schemes have potential as retrofit for existing drives. It is possible to combine both the advantages, mentioned above, by permanently connecting the VSI with the LCI power circuit to feed the WFSM. This proposed hybrid LCI/VSI drive can be regarded as a universal solution for high power synchronous motor drives at all power and speed ranges.

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Cascaded H-bridge (CHB) multilevel inverters have significant popularity with motor drives applications due to their modularity, scalability, and reliability. Typical CHB inverters employ diode rectifiers that allow unidirectional power flow from the grid to the load. To capture and utilize the regenerated energy in regenerative applications, regenerative CHB drives were introduced with two-level voltage source converters in the front end to allow bidirectional energy flow. This solution is accompanied by challenges of high number of switches and control circuits, high switching power losses, and massive dimensions. Recently, developing more economic versions of regenerative cascaded H-bridge drives has become one of the hottest topics in power electronics research. In this thesis work, two solutions are proposed for more energy efficient and economic regenerative CHB drives. The first solution is a proposed power cell configuration that reduces the number of switches per cell by two. Additionally, phase alternation connection method and carrier phase-shifting techniques are introduced to address the challenges of the presented configuration. The switch-count reduction reduces the system’s complexity, switches’ cost, and footprint. The second proposed solution is a new controller to operate the front-end converters as fundamental frequency ends (FFEs). The proposed controller is employed in both the conventional regenerative cascaded H-bridge and the proposed reduced switch-count configuration. This solution minimizes the switching power losses, and results in more compact and economic design, with higher DC-link utilization. Theoretical analysis and simulation studies of both proposed solutions show promising performance and capability to be applied as energy-efficient and cost effective regenerative CHB motor drives. Experimental validation of the proposed reduced switch-count configuration is presented for STATCOM operation of a scaled-down 7-Level regenerative CHB drive system. The future work of this thesis includes experimental validation of the proposed FFE controller, and operation of the system with regenerative motor load. / Thesis / Master of Applied Science (MASc)

High power converters are widely used in many industries. At power levels in the range of Mega Watt (MW), power conversion at medium voltage (MV) is preferred due to better efficiency and lower cost. For medium voltages applications, multilevel converters are widely adopted due to the features they offer with respect to two-level converters. Cascaded H-bridge topology is a widely adopted multilevel topology because of its modularity, scalability, and reliability. The conventional cascaded H-bridge topology allows two-quadrant operation. In order to allow fourquadrant operation, an active front end version of the cascaded H-bridge topology has been proposed in literature and recently commercialized. In the field, power converters operates under harsh loading and environmental conditions. The resulting stresses imposed on converter components cause their gradual degradation. In cascaded H-bridge converters, typically power cell components such as power modules, DC-bus capacitors, and control PCBs are v highly stressed. Under these stresses power cell components degrade and require replacement in the field, otherwise unexpected failures may occur. The thesis aim is to address power cell components reliability through proposing novel regenerative cascaded H-bridge converter control schemes to reduce components stresses and failure probability without increasing size, cost, or complexity. First, a novel PWM active front end control scheme has been proposed to reduce the inherent ripple current stresses on the DC-bus capacitors. Second, the thesis proposes a novel grid or near grid switching frequency front end control scheme to reduce stresses on power modules and the power cell cooling requirements. Third, novel cascaded H-bridge front end control schemes are proposed to reduce the sensor count, thereby decreasing failure rate and cutting down cost. The proposed work has been thoroughly validated through detailed 9- cell regenerative cascaded H-bridge system simulation and experimentation. / Thesis / Doctor of Philosophy (PhD)

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