Steven Englebretson

Reliability comparison for 3L-NPC and 3L-ANPC converters for drives application

Compared with NPC converters, Active NPC (ANPC) converters improve the loss distribution among semiconductor devices and thus increase the converter output power rating and switching frequency. However, since more switches with their gate drivers are used in ANPC converters, the impact on the converter reliability is one of the main concerns for drives application. In this paper, the analysis on fault tolerant operation of 3L-ANPC converters under single and multiple device failure conditions is presented. Furthermore, the methodology for reliability function calculation and the reliability comparison of 3L-ANPC and 3L-NPC converters are investigated for drives application. Finally, the results and conclusions are presented.

Analytical model of multiphase permanent magnet synchronous machines for energy and transportation applications

Multiphase (more than three) electric machines and drives were used first to limit current amplitude and later reduce torque ripple with early, six-step converters. More recently, the potential benefits of multiphase drives for electric ship propulsion include improved fault tolerance, improved torque density by harmonic injecting, reduced per-phase power rating, reduced ripple torque, reduced rotor loss, and reduced noise. Since the mid 1990s, R&D effort in the area of multiphase machines and drives has accelerated for new aerospace, electric vehicles, and renewable energy applications, especially off-shore wind because of reliability and size. Among the many multiphase options, N×3-phase systems can be split from existing 3-phase windings and still use conventional 3-phase inverters. This paper provides the analytical synchronous-frame d-q model of the 2×3-phase permanent magnet synchronous machine (PMSM), similar to the conventional three phase d-q model, for the purpose of control development. The developed model is verified with FEA simulation results. This paper also presents how to calculate and scale the parameters of the 2×3-phase PMSM from the baseline 3-phase PMSM. Motor drive engineers seeking the same level of 2×3-phase and 3×3-phase PMSM model as the conventional 3-phase PMSM for control research and development can benefit from this study.

Pole-modulated PM direct-drive generator for wave energy conversion

This paper describes the general design considerations and analysis for a direct-drive generator for wave energy conversion. Direct drive wave energy converters have been proposed in view of the disadvantage of mechanical complexity and low conversion efficiencies in conventional wave energy converters. By directly coupling an electrical generator to an oscillating wave energy device, it is suggested direct-drive power take-off could be a viable alternative to hydraulic based systems. The operation fundamentals, combined with FE (Finite Element) analysis are discussed with the target operation in the low speed high torque requirements. The pole modulated design converts the slow motion to a higher generator output frequency. The generator design principle, comparisons between different topologies, as well as prototype designs at different speeds are analyzed and compared with conventional permanent magnet (PM) type machines.

Current observer based position estimation using the stationary frame equivalent of a synchronous frame PI regulator for PMSM sensorless drives

This paper introduces a new current observer-based position estimation method using the stationary frame equivalent of a synchronous frame PI regulator for a 3-phase PMSM. The introduced method eliminates a positive feedback type of interdependency between the performance of the position estimation and the synchronous reference frame transformation by implementing the position estimation method in the stationary frame. In the proposed method, the major drawbacks of steady-state error caused by regulating ac signals with conventional PI control and high frequency ripple in a state variable caused by sliding mode control of the current observer based estimation approach in the stationary frame, are overcome by using the stationary frame equivalent of a synchronous frame PI regulator. The concept and implementation are simple, straightforward, and intuitive. Simulated and experimental results are provided to confirm the attractive performance characteristics of the resulting position estimation using the proposed method.

Power conversion and control of a magnetic gear integrated permanent magnet generator for wave energy generation

This paper presents results of the control of a magnetic gear integrated permanent magnet synchronous generator (MG-PMSG) using a dedicated power conversion system to deliver power from an oscillating, low speed wave energy converter (WEC). The generator has two rotors and one stator. By magnetic gearing, the low speed of the outer rotor is amplified to the high speed of the inner rotor, which faces the stator winding. The machine is designed with a large number of poles and concentrated winding for simpler and cheaper design. However, concentrated winding can have harmonics in the induced electromotive force (emf), which causes harmonic power flow into the dc link of the power converter. In this work, the control system for power conversion from the MG-PMSG is developed and the harmonic content in the power is analyzed. Since, the generator is driven with oscillating speed to generate oscillating power, an energy storage system is integrated to supply smooth power from the system. All corresponding experimental results are provided.

Core loss estimation in electric machines with flux controlled core loss tester

The complexity of core loss estimation is an essential limitation for electric machine design engineers. It is critical to estimate the core losses and reduce them in the design stage to improve the machine efficiency. Current estimation methods based on the Steinmetz equation and loss separation are not accurate enough even at the rated conditions. This work describes a loss estimation technique combining finite element analysis (FEA) and actual core loss measurements. First, flux waveforms from various parts of the electric machine are determined using finite element analysis (FEA), then identical flux density waveforms are generated in a toroidal wound core made out of the same material as is used in the machine. The loss is measured per unit mass, and then the total motor core loss is calculated by combining the measured W/kg loss values for predefined sections of the motor. Estimation results are provided and compared with the Bertotti iron loss and loss surface methods. The proposed method is shown to improve the accuracy of loss estimation.