Stability Analysis and Control Design for Hybrid AC-DC More-Electric Aircraft Power Systems

This thesis studies the stability of a more-electric aircraft (MEA) power system with hybrid converters and loads, and proposes a control design method using state feedback. The MEA is aimed to replace the conventional nonelectric power in aircraft with electric power in order to reduce the size and weight of the aircraft power system. This thesis considers a model of the MEA power system consisting of the following components: converters with uncontrolled diodes and controlled rectifiers, ideal constant power loads (CPL), and non-ideal CPL driven by electromechanical actuators. The system has narrow stability range under the conventional two-loop PI control. To improve control performance, a full-state feedback control method is developed that can significantly increase the stability margin of the MEA power system

An Integral Battery Charger with Power Factor Correction for Electric Scooter

This paper presents an integral battery charger for an electric scooter with high voltage batteries and interior-permanent-magnet motor traction drive. The battery charger is derived from the power hardware of the scooter, with the ac motor drive that operates as three-phase boost rectifier with power factor correction capability. The control of the charger is also integrated into the scooter control firmware that is implemented on a fixed-point DSP controller. Current-controlled or voltage-controlled charge modes are actuated according to the requirements of the battery management system, that is embedded into the battery pack. With respect to previous integrated chargers, the ac current is absorbed at unitary power factor with no harmonic distortion. Moreover, no additional filtering is needed since the pulsewidth modulation ripple is minimized by means of phase interleaving. The feasibility of the integral charger with different ac motors (induction motor, surface-mounted phase modulation motor) is also discussed, by means of a general model purposely developed for three-phase ac machines. The effectiveness of the proposed battery charger is experimentally demonstrated on a prototype electric scooter, equipped with two Li-ion battery packs rated 260 V, 20 A

Design and Control of Electrically Excited Synchronous Machines for Vehicle Applications

Electrically excited synchronous machines (EESMs) are becoming an alternative to permanent magnet synchronous machines (PMSMs) in electric vehicles (EVs). This mainly attributes to the zero usage of rare-earth materials, as well as the ability to achieve high starting torque, the effectiveness to do field weakening and the flexibility to adjust power factor provided by EESMs. Furthermore, in case of converter failure at high speed, safety can be improved by shutting down the field current in EESMs. The purpose of this study is to investigate the potential application of EESMs in EVs. To achieve this aim, several topics are covered in this study. These topics are studied to confront the challenges before EESMs could become prevalent and to maximumly use the advantages of EESMs for EV applications. In control strategies, the challenge is to properly adjust the combination of stator and field currents so that high power factor and minimum copper losses can be achieved. To tackle this, control strategies are proposed so that reactive power consumption and total copper losses are minimized. With the proposed strategies, the output power is maximized along the torque-speed envelope and high efficiency in field-weakening is achieved. In dynamic current control, due to the magnetic couplings between field winding and stator winding, a current rise in one winding would induce an electromagnetic force (EMF) in the other. This introduces disturbances in dynamic current control. In this study, a current control algorithm is proposed to cancel the induced EMF and the disturbances are mitigated. In machine design, high starting torque and effective field weakening are expected to be achieved in the same EESM design. To realize this, some criteria need to be satisfied. These criteria are derived and integrated into the design procedure including multi-objective optimizations. A 48\ua0V EESM is prototyped during the study. In experimental verification, a torque density of 10 N\ub7m/L is achieved including cooling jacket. In field excitation, a contactless excitation technology is adopted, which leads to inaccessibility of the field winding. To realize precise control of field current in a closed loop, an estimation method of field current is proposed. Based on the estimation, closed-loop field current control is established. The field current reference is tracked within an error of 2% in experimental verifications. The cost of an EESM drive increases because of the additional converter used for field excitation. A technique is proposed in which the switching harmonics are extracted for field excitation. With this technique, both stator and field windings can be powered using only one inverter. From all the challenges tackled in this study, it can be concluded that the application of EESMs in EVs is feasible

Modeling and Analysis of Active Front-End Induction Motor Drive for Reactive Power Compensation

In this thesis, an active front end induction motor drive for reactive power compensation is analyzed. The classical vector control approach for high performance control of an induction motor drive is a well established industry standard today. The same idea of decoupled control is extended to the line-side PWM converter for achieving better dynamic performance. The system model is obtained using d-q rotating frame theory. The iqe component of line currents is used to control the reactive power. The idecomponent is used to control the dc-link voltage and also to supply active power required by the motor. A high gain feedback controller with input-output linearization is presented to remove coupling between iqe and ide currents. A load power feed-forward loop is added to the dc-link voltage controller for fast dynamic response. The drive performance is analyzed to define system specifications. The motor acceleration, deceleration, and variable power factor operation (reactive power compensation) of the active drive system are demonstrated. The motor load is varied from no load to full load in steps of 10% each. For each step the device currents, switching power loss, line harmonics, and dc-link ripples are plotted. This data is used to derive conclusions that define system specifications and also state operating limits. The control of the drive system is implemented in MATLAB-SIMULINK. The complete system hardware is implemented in commercially available simulation tool, PSIM. The two software packages are interlinked using an interface module

Modeling and Control of a Doubly-Fed Induction Generator for Wind Turbine-Generator Systems

Wind energy plays an increasingly important role in the world because it is friendly to the environment. During the last decades, the concept of a variable-speed wind turbine (WT) has been receiving increasing attention due to the fact that it is more controllable and efficient, and has good power quality. As the demand of controllability of variable speed WTs increases, it is therefore important and necessary to investigate the modeling for wind turbine-generator systems (WTGS) that are capable of accurately simulating the behavior of each component in the WTGS. Therefore, this thesis will provide detailed models of a grid-connected wind turbine system equipped with a doubly-fed induction generator (DFIG), which includes the aerodynamic models of the wind turbine, the models of the mechanical transmission system, the DFIG models and the three-phase two-level PWM voltage source converter models. In order to obtain satisfying output power from the WTGS, control strategies are also necessary to be developed based on the previously obtained WTGS models. These control schemes include the grid-side converter control, the generator-side converter control, the maximum power point tracking control and the pitch angle control. The grid-side converter controller is used to keep the DC-link voltage constant and yield a unity power factor looking into the WTGS from the grid-side. The generator-side converter controller has the ability of regulating the torque, active power and reactive power. The maximum power point tracking control is used to provide the reference values for the active power at the stator terminals. The pitch angle control scheme is used to regulate the pitch angle and thus keep the output power at rated value even when the wind speed experiences gusts. Various studies in the literature have reported that two-level converters have several disadvantages compared with three-level converters. Among the disadvantages are high switching losses, high dv/dt, and high total harmonic distortion (THD). Hence, the models and field oriented control schemes for three-level neutral-point-clamped (NPC) converters are also investigated and applied to a WTGS. Besides, an advanced modulation technology, namely, space vector PWM (SVPWM), is also investigated and compared to traditional sinusoidal PWM in a WTGS