Control of switched reluctance machines

This thesis is concerned with the control of switched reluctance machines for both motoring and generating applications. There are different control objectives in each case. For motoring operation, there are two possible control objectives. If the SRM is being employed in a servo-type application, the desire is for a constant output torque. However, for low performance applications where some amount of torque ripple is acceptable, the aim is to achieve efficient and accurate speed regulation. When the SRM is employed for generating purposes, the goal is to maintain the dc bus voltage at the required value while achieving maximum efficiency. Preliminary investigative work on switched reluctance machine control in both motoring and generating modes is performed. This includes the implementation and testing through simulation of two control strategies described in the literature. In addition, an experimental system is built for the development and testing of new control strategies. The inherent nonlinearity of the switched reluctance machine results in ripple in the torque profile. This adversely affects motoring performance for servo-type applications. Hence, three neuro-fuzzy control strategies for torque ripple minimisation in switched reluctance motors are developed. For all three control strategies, the training of a neurofuzzy compensator and the incorporation of the trained compensator into the overall switched reluctance drive are described. The performance of the control strategies in reducing the torque ripple is examined with simulations and through experimental testing. While the torque ripple is troublesome for servo-type applications, there are some applications where a certain amount of torque ripple is acceptable. Therefore, four simple motor control strategies for torque ripple-tolerant applications are described and tested experimentally. Three of the control strategies are for low speed motoring operation while the fourth is aimed at high speed motoring operation. Finally, three closed-loop generator control strategies aimed at high speed operation in single pulse mode are developed. The three control strategies are examined by testing on the experimental system. A comparison of the performance of the control strategies in terms of efficiency and peak current produced by each is presented

Design and Control of Power Converters 2019

In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc

Quantization noise analysis of a closed-loop PWM controller that includes Σ-Δ modulation

Σ-Δ modulation is a popular noise shaping technique which is used to move the quantization noise out of the frequency band of interest. Recently, a number of authors have applied this technique to a pulse width modulation (PWM) controller for switching power converters. However, previous analysis has not incorporated the effects of analog-to-digital converter (ADC) resolution or feedback control on the Σ-Δ modulator. In this work, quantization due to ADC resolution and PWM resolution are analyzed, considering the effects of noise-shaping and feedback. A number of simulations have been performed to explore the impact of various design choices on output noise. The study variables included the order of the Σ-Δ modulator, resolution of ADC, resolution of DPWM, the plant and the compensator. The theoretical model developed is used to generate the expected system Power Spectral Density (PSD) curves for each design choice and simulations techniques are used to validate the analysis. Experimental analysis has been performed on a digital voltage-mode control (VMC) synchronous buck converter and the output voltage PSD curves are generated using the welch method and compared with the theoretical and the simulation results. The experimental PSD curves for the 1st-order modulator match the simulation and theoretical PSD curves. This suggests that the theoretical model is a useful approximation and similar methods can be used to analyze the contribution of the quantizers to the output noise of a closed-loop controller system --Abstract, page iii

Five-Level Flying Capacitor Converter used as a Static Compensator for Current Unbalances in Three-Phase Distribution Systems

This thesis presents and evaluates a solution for unbalanced current loading in three-phase distribution systems. The proposed solution uses the flying capacitor multilevel converter as its main topology for an application known as Unbalanced Current Static Compensator. The fundamental theory, controller design and prototype construction will be presented along with the experimental results. The Unbalanced Current Static Compensator main objective is the balancing of the up-stream currents from the installation point to eliminate the negative- and zero-sequence currents originated by unbalanced single-phase loads. Three separate single-phase flying capacitor converters are controlled independently using a d-q rotating reference frame algorithm to allow easier compensation of reactive power. Simulations of the system were developed in MATLAB/SIMULINK™ in order to validate the design parameters; then, testing of the UCSC prototype was performed to confirm the control algorithm functionality. Finally, experimental result are presented and analyzed

POWER QUALITY CONTROL AND COMMON-MODE NOISE MITIGATION FOR INVERTERS IN ELECTRIC VEHICLES

Inverters are widely utilized in electric vehicle (EV) applications as a major voltage/current source for onboard battery chargers (OBC) and motor drive systems. The inverter performance is critical to the efficiency of EV system energy conversion and electronics system electro-magnetic interference (EMI) design. However, for AC systems, the bandwidth requirement is usually low compared with DC systems, and the control impact on the inverter differential-mode (DM) and common-mode (CM) performance are not well investigated. With the wide-band gap (WBG) device era, the switching capability of power electronics devices drastically improved. The DM/CM impact that was brought by the WBG device-based inverter becomes more serious and has not been completely understood. This thesis provides an in-depth analysis of on-board inverter control strategies and the corresponding DM/CM impact on the EV system. The OBC inverter control under vehicle-to-load (V2L) mode will be documented first. A virtual resistance damping method minimizes the nonlinear load harmonics, and a neutral balancing method regulates the unbalanced load impact through the fourth leg. In the motor drive system, a generalized CM voltage analytical model and a current ripple prediction model are built for understanding the system CM and DM stress with respect to different modulation methods, covering both 2-level and 3-level topologies. A novel CM EMI damping modulation scheme is proposed for 6-phase inverter applications. The performance comparison between the proposed methods and the conventional solution is carried out. Each topic is supported by the corresponding hardware platform and experimental validation

Grid-tie Quasi Z-Source Inverter-Based Static Synchronous Compensator

This research work proposes intensive study and mathematical modelling analysis of transformer-less quasi Z-source inverter (qZSI) based static synchronous compensator (STATCOM) system. In this work, a single-phase qZSI is acted as a STATCOM system to compensate the grid reactive power at the point of coupling under different loading conditions. A new controller-based lead compensator is developed to achieve fast DC-link voltage balance across each qZS network. Simulation studies are conducted to evaluate the controller’s performance

High-Efficiency Three-Phase Current Source Rectifier Using SiC Devices and Delta-Type Topology

In this dissertation, the benefits of the three-phase current source rectifier (CSR) in high power rectifier, data center power supply and dc fast charger for electric vehicles (EV) will be evaluated, and new techniques will be proposed to increase the power efficiency of CSRs. A new topology, referred as Delta-type Current Source Rectifier (DCSR), is proposed and implemented to reduce the conduction loss by up to 20%. By connecting the three legs in a delta type on ac input side, the dc-link current in DCSR can be shared by two legs at the same time. To increase the switching speed and power density, all-SiC power modules are built and implemented for CSRs. The switching waveforms in the commutation are measured and studied based on double pulse test. Four different modulation schemes are compared for high efficiency CSR considering the switching characteristics of different device combinations. The most advantageous modulation scheme is then identified for each of the device combinations investigated. A compensation method is proposed to reduce the input current distortion caused by overlap time and slow transition in CSRs. The proposed method first minimizes the overlap time and then compensates the charge gain/loss according to the sampled voltage and current. It is verified that the proposed method can reduce the input current distortion especially when the line-to-line voltage is close to zero. The dc-link current will become discontinuous under light load in CSRs, when the traditional control algorithm may not work consistently well. To operate CSR in discontinuous current mode (DCM), the CSR is modeled in DCM and a new control algorithm with feedforward compensation is proposed and verified through experiments. A protection scheme with fast response time is proposed, analyzed and verified to protect SiC devices from overvoltage caused by current interruption in CSRs. To deal with the harmonics and voltage sag in the input ac voltage, a new control algorithm is proposed. By adding ac current feedback control and proportional-resonant (PR) control, the proposed control algorithm can reduce the input current distortion and dc output voltage ripple under input voltage disturbance

Design and Implementation of Control Techniques of Power Electronic Interfaces for Photovoltaic Power Systems

The aim of this thesis is to scrutinize and develop four state-of-the-art power electronics converter control techniques utilized in various photovoltaic (PV) power conversion schemes accounting for maximum power extraction and efficiency. First, Cascade Proportional and Integral (PI) Controller-Based Robust Model Reference Adaptive Control (MRAC) of a DC-DC boost converter has been designed and investigated. Non-minimum phase behaviour of the boost converter due to right half plane zero constitutes a challenge and its non-linear dynamics complicate the control process while operating in continuous conduction mode (CCM). The proposed control scheme efficiently resolved complications and challenges by using features of cascade PI control loop in combination with properties of MRAC. The accuracy of the proposed control system’s ability to track the desired signals and regulate the plant process variables in the most beneficial and optimised way without delay and overshoot is verified. The experimental results and analysis reveal that the proposed control strategy enhanced the tracking speed two times with considerably improved disturbance rejection. Second, (P)roportional Gain (R)esonant and Gain Scheduled (P)roportional (PR-P) Controller has been designed and investigated. The aim of this controller is to create a variable perturbation size real-time adaptive perturb and observe (P&O) maximum power point tracking (MPPT) algorithm. The proposed control scheme resolved the drawbacks of conventional P&O MPPT method associated with the use of constant perturbation size that leads to a poor transient response and high continuous steady-state oscillations. The prime objective of using the PR-P controller is to utilize inherited properties of the signal produced by the controller’s resonant path and integrate it to update best estimated perturbation that represents the working principle of extremum seeking control (ESC) to use in a P&O algorithm that characterizes the overall system learning-based real time adaptive (RTA). Additionally, utilization of internal dynamics of the PR-P controller overcome the challenges namely, complexity, computational burden, implantation cost and slow tracking performance in association with commonly used soft computing intelligent systems and adaptive control strategies. The experimental results and analysis reveal that the proposed control strategy enhanced the tracking speed five times with reduced steady-state oscillations around maximum power point (MPP) and more than 99% energy extracting efficiency.Third, the interleaved buck converter based photovoltaic (PV) emulator current control has been investigated. A proportional-resonant-proportional (PR-P) controller is designed to resolve the drawbacks of conventional PI controllers in terms of phase management which means balancing currents evenly between active phases to avoid thermally stressing and provide optimal ripple cancellation in the presence of parameter uncertainties. The proposed controller shows superior performance in terms of 10 times faster-converging transient response, zero steady-state error with significant reduction in current ripple. Equal load sharing that constitutes the primary concern in multi-phase converters has been achieved with the proposed controller. Implementing of robust control theory involving comprehensive time and frequency domain analysis reveals 13% improvement in the robust stability margin and 12-degree bigger phase toleration with the PR-P controller. Fourth, a symmetrical pole placement Method-based Unity Proportional Gain Resonant and Gain Scheduled Proportional (PR-P) Controller has been designed and investigated. The proposed PR-P controller resolved the issues associated with the use of the PI controller which are tracking repeating control input signal with zero steady-state and mitigating the 3rd order harmonic component injected into the grid for single-phase PV systems. Additionally, the PR-P controller has overcome the drawbacks of frequency detuning in the grid and increase in the magnitude of odd number harmonics in the system that constitute the common concerns in the implementation of conventional PR controller. Moreover, the unprecedented design process based on changing notch filter dynamics with symmetrical pole placement around resonant frequency overcomes the limitations that are essentially complexity and dependency on the precisely modelled system. The verification and validation process of the proposed control schemes has been conducted using MATLAB/Simulink and implementing MATLAB/Simulink/State flow on dSPACE Real-time-interface (RTI) 1007 processor, DS2004 High-Speed A/D and CP4002 Timing and Digital I/O boards

The Modeling and Advanced Controller Design of Wind, PV and Battery Inverters

Renewable energies such as wind power and solar energy have become alternatives to fossil energy due to the improved energy security and sustainability. This trend leads to the rapid growth of wind and Photovoltaic (PV) farm installations worldwide. Power electronic equipments are commonly employed to interface the renewable energy generation with the grid. The intermittent nature of renewable and the large scale utilization of power electronic devices bring forth numerous challenges to system operation and design. Methods for studying and improving the operation of the interconnection of renewable energy such as wind and PV are proposed in this Ph.D. dissertation.;A multi-objective controller including is proposed for PV inverter to perform voltage flicker suppression, harmonic reduction and unbalance compensation. A novel supervisory control scheme is designed to coordinate PV and battery inverters to provide high quality power to the grid. This proposed control scheme provides a comprehensive solution to both active and reactive power issues caused by the intermittency of PV energy. A novel real-time experimental method for connecting physical PV panel and battery storage is proposed, and the proposed coordinated controller is tested in a Hardware in the Loop (HIL) experimental platform based on Real Time Digital Simulator (RTDS).;This work also explores the operation and controller design of a microgrid consisting of a direct drive wind generator and a battery storage system. A Model Predictive Control (MPC) strategy for the AC-DC-AC converter of wind system is derived and implemented to capture the maximum wind energy as well as provide desired reactive power. The MPC increases the accuracy of maximum wind energy capture as well as minimizes the power oscillations caused by varying wind speed. An advanced supervisory controller is presented and employed to ensure the power balance while regulating the PCC bus voltage within acceptable range in both grid-connected and islanded operation.;The high variability and uncertainty of renewable energies introduces unexpected fast power variation and hence the operation conditions continuously change in distribution networks. A three-layers advanced optimization and intelligent control algorithm for a microgrid with multiple renewable resources is proposed. A Dual Heuristic Programming (DHP) based system control layer is used to ensure the dynamic reliability and voltage stability of the entire microgrid as the system operation condition changes. A local layer maximizes the capability of the Photovoltaic (PV), wind power generators and battery systems, and a Model Predictive Control (MPC) based device layer increases the tracking accuracy of the converter control. The detail design of the proposed SWAPSC scheme are presented and tested on an IEEE 13 node feeder with a PV farm, a wind farm and two battery-based energy storage systems