Behzad Vafakhah

A New Space-Vector PWM With Optimal Switching Selection for Multilevel Coupled Inductor Inverters

Multilevel space vector pulsewidth modulation (SVPWM) control is shown to be a very useful tool for coupled inductor inverters as six independent pulsewidth modulation (PWM) signals are required, and there is additional complexity of meeting the performance requirements for the coupled inductor while balancing the winding common-mode dc current and generating high-quality multilevel PWM output voltages. A new multilevel SVPWM technique with a five-segment switching sequence is described, where half-wave symmetrical PWM voltage waveforms are used to balance the inductor common-mode dc voltages and also to avoid all possible switching states with a high winding current ripple. The proposed SVPWM is shown to have better inverter performance, compared with traditional carrier-based and the original multilevel SVPWM schemes at low modulation depths. Inverter operation with the proposed SVPWM is validated through simulation and experimental results.

Multicarrier Interleaved PWM Strategies for a Five-Level NPC Inverter Using a Three-Phase Coupled Inductor

Multicarrier interleaved pulsewidth modulation (PWM) techniques are presented for a five-level neutral point clamped inverter using a three-phase coupled inductor. The inverter operation is demonstrated using a simple multicarrier interleaved PWM algorithm. Since both the inverter and inductor power losses are closely linked to the magnitude of the inductor current ripple, improved multilevel interleaved PWM techniques are presented based upon the concept of interchangeability of switching states in each phase. The proposed PWM techniques, which are easier to implement when compared to multilevel space-vector PWM techniques, also exploit the use of switching states with a high-effective winding inductance to minimize the inductor current ripple. Simulation results are presented to illustrate the improvements obtained in the inverter waveforms and their harmonic spectrum. Experimental results demonstrate how the inductor current ripple and the related power losses are significantly reduced using the proposed PWM scheme.

Interleaved Discontinuous Space-Vector PWM for a multi-level PWM VSI using a 3-phase split-wound coupled inductor

A multi-level interleaved Discontinuous Space Vector PWM (DSVPWM) method is presented for a 3-level 3-phase PWM VSI using a 3-phase split-wound coupled inductor. The selection of a suitable pwm switching scheme for this topology is based on the dual requirements for a high quality multi-level pwm output voltage together with the need to minimize high frequency currents and losses in the coupled inductor and the inverter switches. Suitable switching states are described for the DVSPWM over the entire range of amplitude modulation depth. This pwm scheme minimizes the coupled inductor high frequency winding current ripple and also produces 3-level pwm output voltage waveforms at twice the inverter switching frequency. The inverter operation is examined using simulation tests. Extensive experimental test results are used to obtain the inverter performance as a variable frequency drive when operated in steady-state and during transient conditions.

A five/nine-level twelve-switch neutral point clamped inverter for high speed electric drives

A twelve-switch, three phase, five/nine level inverter is presented for applications using a high speed electric machine with a relatively low per-unit leakage reactance. By reducing the voltage blocking requirement of the semiconductors, the neutral point clamped variant of the coupled inductor inverter topology (NPC-CI) is more suited to high DC bus voltages, and features a significant reduction in magnetic material required over six-switch coupled inductor inverters. This paper describes the operational and design techniques for the NPC-CI inverter. A simple continuous PWM technique for operation with a three-limb core is presented and the specific design challenges involved in the NPC-CI inverter are highlighted: designing the three-limb coupled inductor, the natural balancing action of the split-dc link, semiconductor stresses, inverter construction and practical considerations for inverter operation of the drive. Machine performance is then illustrated on an unloaded 18,000 rpm 15HP induction machine to emphasize the harmonic quality improvement, and on a loaded 2HP utility speed induction machine to demonstrate transient performance.

Space-vector PWM for inverters with split-wound coupled inductors

This paper proposes a space-vector pulse width modulation (SVPWM) technique suitable for inverters with a coupled inductor output. The proposed approach is based on multi-level SVPWM and can offer superior performance when compared to other modulation techniques suitable for coupled inductor topologies. In particular the approach addresses issues related to common mode dc current balance in a three-limb inductor core and coupling between limbs in a three-limb core. The proposed approach provides a multi-level output voltage waveform while the total winding current distortion is significantly improved. This is achieved by appropriate choice of switching states such that effective low inductance modes are eliminated while generating half-wave symmetrical switching frequency voltage waveforms. The method presented is computationally simple and does not additional feedback signals when compared to conventional three-level SVPWM algorithms. The operation of the proposed drive structure is investigated by means of simulation results and verified by experimental results.

Multi-carrier interleaved PWM strategies for a new five-level NPC inverter using a 3-phase coupled inductor

Multi-carrier interleaved PWM techniques are presented for a new five-level Neutral Point Clamped (NPC) inverter using a 3-phase coupled inductor. The operation of the proposed topology relies on the dual requirements of balancing the DC bus capacitor voltages and the inductor common mode currents together. The inverter performance is dependent on the PWM strategies minimizing the inductor current ripple and associated inductor losses. The inverter operation is verified by a simple multi-carrier interleaved PWM algorithm. An improved multilevel interleaved PWM technique is developed based on interchangeable switching states in each phase. The proposed method exploits the use of switching states with a high-effective inductance to minimize the inductor current ripple. The new approach is easier to implement compared to multi-level space vector PWM techniques. The drive operation with the proposed PWM schemes is demonstrated using simulation and experimental results. The inverter performance has been significantly improved by lowering the inductor losses.

Performances of PI and Fuzzy-Logic Speed Control of Field-Oriented Induction Machine Drives

A proportional-integral and fuzzy-logic speed controllers operating in indirect field-orientation are designed and compared experimentally in this paper, using a 2-HP 3-phase induction machine drive. The speed tracking capability of the two controllers are compared under no-load and various load conditions with different reference speeds. The performances of the drive are also evaluated under sudden electric and mechanical disturbances. Simulation and DSP experimental results on a 2HP 230 V/5.8 A Delta-connected 3-phase induction machine show that the performance of the fuzzy-logic controller is more satisfactory than that of the proportional-integral controller in a number of cases and, hence, can be a suitable candidate for high-performance industrial applications.

Emulation of flywheel energy storage systems with a PMDC machine

This paper presents a control strategy to emulate a flywheel energy storage system (FESS) with a permanent magnet DC machine (PMDC). The PMDC machine is coupled to a vector-controlled surface-mount permanent magnet synchronous machine (PMSM), allowing the investigation of PMSM control strategies. Simulation and experimental results using a TMS320F2812 DSP module confirm bidirectional constant power transfer during acceleration and deceleration modes. In both cases, the proposed scheme shows excellent potential and allows the demonstration of possible applications of PMSM control schemes for various flywheel applications.

Reducing losses in multilevel coupled inductor inverters using interleaved discontinuous SVPWM

This paper presents generalized interleaved Discontinuous Space Vector PWM (DSVPWM) schemes for 3-level 3-phase 6-switch split-wound Coupled Inductor Inverters (CII). A simplified approach is applied to the generation of interleaved DSVPWM schemes with the need to minimize high frequency current ripple and associated losses in the coupled inductor and the inverter. The performance of the CII is investigated and compared for DSVPWM schemes. The current ripple is analyzed based on the position of the discontinuous period for several DSVPWM schemes with different loads and power factors. Regardless of the loads, 60º discontinuous SVPWM around the positive and negative peaks of the fundamental reference voltage, DSVPWM1, lowers losses in the coupled inductor. The simulation and experimental results validate the drive performance.

A compact variable speed drive for mobile flywheel energy storage systems

This paper presents the development and testing of a compact drive system for a mobile flywheel energy storage system. The drive is required to be capable of 120kW output power at frequencies up to 933Hz, with minimal harmonic content. Development of the drive topology, design methodology, test facility and experimental results are presented.