BIDIRECTIONAL AC-DC CONVERTERS USING ONE CYCLE CONTROL (OCC) FOR ELECTRIC VEHICLES

The electric vehicle (EV) market has seen a rapid growth in the recent past. With an increase in the number of electric vehicles on road, there is an increase in the number of high capacity battery banks interfacing the grid. The battery bank of an EV, besides being the fuel tank, is also a huge energy storage unit. Presently, it is used only when the vehicle is being driven and remains idle for rest of the time, rendering it underutilized. Whereas on the other hand, there is a need of large energy storage units in the grid to filter out the fluctuations of supply and demand during a day. EVs can help bridge this gap. The EV battery bank can be used to store the excess energy from the grid to vehicle (G2V) or supply stored energy from the vehicle to grid (V2G ), when required. To let power flow happen, in both directions, a bidirectional AC-DC converter is required. This thesis concentrates on the bidirectional AC-DC converters which have a control on power flow in all four quadrants for the application of EV battery interfacing with the grid. This thesis presents a bidirectional interleaved full bridge converter topology. This helps in increasing the power processing and current handling capability of the converter which makes it suitable for the purpose of EVs. Further, the benefit of using the interleaved topology is that it increases the power density of the converter. This ensures optimization of space usage with the same power handling capacity. The proposed interleaved converter consists of two full bridges. The corresponding gate pulses of each switch, in one cell, are phase shifted by 180 degrees from those of the other cell. The proposed converter control is based on the one-cycle controller. To meet the challenge of new requirements of reactive power handling capabilities for grid connected converters, posed by the utilities, the controller is modified to make it suitable to process the reactive power. A fictitious current derived from the grid voltage is introduced in the controller, which controls the converter performance. The current references are generated using the second order generalized integrators (SOGI) and phase locked loop (PLL). A digital implementation of the proposed control ii scheme is developed and implemented using DSP hardware. The simulated and experimental results, based on the converter topology and control technique discussed here, are presented to show the performance of the proposed theory.

Digital geometric-sequence control technique for bidirectional dual active bridge DC-DC converters used in future electric vehicles

Bidirectional DC-DC converters are widely used in different applications such as energy storage systems, Electric Vehicles (EVs), UPS, etc. In particular, future EVs require bidirectional power flow in order to integrate energy storage units into smart grids. These bidirectional power converters provide Grid to Vehicle (V2G)/ Vehicle to Grid (G2V) power flow capability for future EVs. Generally, there are two control loops used for bidirectional DC-DC converters: The inner current loop and The outer loop. The control of DAB converters used in EVs are proved to be challenging due to the wide range of operating conditions and non-linear behavior of the converter. In this thesis, the precise mathematical model of the converter is derived and non-linear control schemes are proposed for the control system of bidirectional DC-DC converters based on the derived model. The proposed inner current control technique is developed based on a novel Geometric-Sequence Control (GSC) approach. The proposed control technique offers significantly improved performance as compared to one for conventional control approaches. The proposed technique utilizes a simple control algorithm which saves on the computational resources. Therefore, it has higher reliability, which is essential in this application. Although, the proposed control technique is based on the mathematical model of the converter, its robustness against parameter uncertainties is proven. Three different control modes for charging the traction batteries in EVs are investigated in this thesis: the voltage mode control, the current mode control, and the power mode control. The outer loop control is determined by each of the three control modes. The structure of the outer control loop provides the current reference for the inner current loop. Comprehensive computer simulations have been conducted in order to evaluate the performance of the proposed control methods. In addition, the proposed control have been verified on a 3.3 kW experimental prototype. Simulation and experimental results show the superior performance of the proposed control techniques over the conventional ones.

The Impact of Geographic Mobility on Canadian Military families and their Children’s Access Special Education Services

To achieve academic success, children with learning-related disabilities often receive special education supports at school. Currently, Canada does not have a federal department or integrated national system of education. Instead, each province and territory has a separate department or ministry that is responsible for the organization and delivery of education, including special education, at the elementary level. At the macro (national) level, inclusive education is the policy across Canada. However, each province and territory has its own legislation, definitions, and policies mandating special education services. These variations result in little consistency at the micro (individual school) level. Differences between eligibility requirements, supports offered, and delivery methods may present challenges for highly mobile families who must navigate new special education systems on behalf of their children with medical or learning challenges. One of the defining features of the Canadian military lifestyle is geographic mobility. As a result, many families are tasked with navigating new school systems for their children, a task that may be more difficult when children require special education services. The purpose of this study is to explore the impact of geographic mobility on Canadian military families and their children’s access to special education services. The secondary objective was to gain insight into supports that helped facilitate access to services, as well as supports that participants believe would have helped facilitate access. A qualitative approach, interpretive phenomenological analysis (IPA), was employed due to of its focus on individuals’ experiences and their understandings of a particular phenomenon. IPA allowed participants to reflect on the significance of their experiences, while the researcher engaged with these reflections to make sense of the meanings associated with their experiences. Nine semi-structured interviews were conducted with civilian caregivers who have a child with special education needs. An interview guide and probes were used to elicit rich, detailed, first-person accounts of their experiences navigating new special education systems. The main themes that emerged from the participants’ combined experiences addressed the emotional components of experiencing a transition, factors that may facilitate access to special education services, and career implications associated with accessing and maintaining special education services. Findings from the study illustrate that Canadian families experience many, and often times severe, barriers to accessing special education services after a posting. Furthermore, the impacts reported throughout the study echo the existing American literature on geographic mobility and access to special education services. Building on the literature, this study also highlights the need for further research exploring factors that create unique barriers to access in a Canadian context, resulting from the current special education climate, military policies, and military family support services.