Jiangbiao He

Calculation of Magnet Losses in Concentrated-Winding Permanent-Magnet Synchronous Machines Using a Computationally Efficient Finite-Element Method

The proposed hybrid method combines computationally efficient finite-element analysis (CE-FEA) with a new analytical formulation for eddy-current losses in the permanent magnets (PMs) of sine-wave current-regulated brushless synchronous motors. The CE-FEA only employs a reduced set of magnetostatic solutions yielding substantial reductions in the computational time, as compared with the conventional FEA. The 3-D end effects and the effect of pulsewidth-modulation switching harmonics are incorporated in the analytical calculations. The algorithms are applied to two fractional-slot concentrated-winding interior PM motors with different circumferential and axial PM block segmentation arrangements. The method is validated against 2-D and 3-D time-stepping FEA.

Application of wide bandgap devices in renewable energy systems — Benefits and challenges

The rapid development of renewable energy systems (RES), especially photovoltaic (PV) energy and wind energy, poses increasing requirements for highpower, low-loss, fast-switching, and reliable semiconductor devices to improve system power capacity, efficiency, power density and reliability. The recent commercialization of wide bandgap (WBG) devices, specifically Silicon Carbide (SiC) and Gallium Nitride (GaN) devices, provides very promising opportunities for meeting such requirements with their attractive features of high voltage blocking capability, ultra-low switching losses, fast switching speed, and high allowable operating temperatures. This paper analyzed the performance benefits and application challenges of using SiC or GaN devices in both PV and wind energy conversion systems. Solutions to these challenges of using WBG devices in various RES were reviewed and proposed, and the benefits of using such emerging devices were confirmed in simulation based on a 250 kW commercial-scale PV inverter and a 250 kW doubly fed induction generator wind turbine system.

A review of mitigation methods for overvoltage in long-cable-fed PWM AC drives

The phenomenon of overvoltage at motor terminals in long-cable-fed PWM AC drives poses a severe stress on motor insulation systems. The overvoltage is typically caused by the high change rate of the inverter output voltage (dv/dt) and the surge impedance mismatch between the inverter, connecting power cable and the motor. This paper presents a comparative survey of the existing methods of overvoltage suppression, which includes passive filters at both motor terminals and inverter terminals. The design methodologies, effectiveness, and practical applicability of these passive filters are discussed through computer simulations based on Ansys/Simplorer 9.0, and the promising approaches are recommended for researchers and industrial users.

Diagnosis of open-circuit switch faults in multilevel active-NPC (ANPC) inverters

Multilevel converters have been widely used in traction drive systems due to their attractive output performance. However, one major disadvantage of multilevel converters is the large number of switching devices employed, which could increase the failure probability of drive systems. Thus, an effective diagnosis method for switch faults in multilevel converters is of high importance for the fault-tolerant operation of such drive systems. This paper introduces an on-line diagnosis method for open-circuit switch faults that could happen in one of the most promising multilevel converters: Active Neutral-Point-Clamped (ANPC) converter. This diagnostic method is implemented based on the comprehensive information of pole voltages, phase currents, and switching states of ANPC inverters. Compared with the existing diagnostic methods in the literature, the presented method in this paper has lower cost and shorter detection time (less than one fundamental cycle). Simulation results verified the effectiveness and robustness of the introduced fault diagnosis method.

Calculation of magnet losses in concentrated-winding permanent magnet synchronous machines using a Computationally Efficient - Finite Element method

The proposed hybrid method combines Computationally Efficient-Finite Element Analysis (CE-FEA) with a new analytical formulation for eddy-current losses in the permanent magnets (PMs) of sine-wave current regulated brushless synchronous motors. The CE-FEA only employs a reduced set of magnetostatic solutions yielding substantial reductions in the computational time as compared with conventional FEA. The 3D end effects and the effect of PWM switching harmonics are incorporated in the analytical calculations. The algorithms are applied to two fractional-slot concentrated-winding interior permanent magnet motors with different circumferential and axial PM block segmentation arrangements. The method is validated against 2D and 3D Time Stepping (TS) FEA.

Sliding mode observer based position self-sensing control of a direct-drive PMSG wind turbine system fed by NPC converters

Information of rotor position and speed plays an crucial role in variable-speed wind energy conversion systems. Traditional sensors based position detection methods not only increase hardware complexity and system cost, but also face severe challenges on reliability caused by the disturbances from the varying weather and harsh operating conditions in wind energy generation sites. Thus, with the aim of eliminating position sensors and developing a reliable position self-sensing technique, this paper proposes a position self-sensing control method based on sliding mode observer for a 2 MW permanent magnet synchronous generator (PMSG) wind turbine system. In addition, a three-level neutral-point-clamped (NPC) back-to-back converter with space vector pulse width modulation (SVPWM) is developed for the full-scale power conversion, which has lower voltage stress on the switching devices and less harmonic distortion in the output voltage compared with those in traditional two-level power converters. Simulation analysis is carried out to verify the effectiveness of the proposed self-sensing method and the three-level SVPWM based back-to-back NPC converter. The simulation results soundly justified the feasibility of the proposed control scheme and power conversion strategy.

Application and losses analysis of ANPC converters in doubly-fed induction generator wind energy conversion system

This paper presents the application and losses analysis of three-level active neutral-point-clamped (ANPC) back-to-back converters in a doubly-fed induction generator (DFIG) wind energy conversion system (WECS). A phase-shifted sinusoidal PWM strategy with the advantages of doubling the apparent switching frequency and better balancing loss distribution among switches is employed for the ANPC back-to-back converters. Comparative losses analysis between three-level ANPC and traditional NPC converters is conducted based on the applications in a 1.5 MW DFIG WECS. Moreover, dynamic modeling and control strategies for the DFIG WECS are introduced. Finally, simulation analysis of the three-level ANPC converters excited 1.5 MW DFIG WECS is carried out. The simulation results verified the advantages of ANPC converters and the corresponding modulation strategy on improving loss distribution and doubling apparent switching frequency in this WECS application.

Power cycling lifetime improvement of three-level NPC inverters with an improved DPWM method

This paper investigates the power cycling lifetime of a three-phase three-level neutral-point-clamped (NPC) inverter used in a 50-kVA adjustable speed drive (ASD). Considering the short lifetime of NPC inverters under low output frequency conditions, an improved discontinuous pulse width modulation (DPWM) method is introduced to extend the inverter lifetime. This improved DPWM method is achieved by injecting a zero-sequence signal with relative high frequency into the voltage reference signals, which is in order to obtain lower swing value of the junction temperatures in the Insulated Gate Bipolar Transistors (IGBTs). Both simulation and experimental results are presented to verify the effectiveness of this solution.

A fault-tolerant topology of T-Type NPC inverter with increased thermal overload capability

Reliability of multilevel power converters has received increased attention over the past few years, due to the relatively high component failure probability caused by the large number of switching devices utilized in the converter topologies. Thus, the fault-tolerant operation of multilevel converters plays an essential role in safety-critical industrial applications. This paper introduces an improved fault-tolerant inverter topology based on the conventional three-level T-Type neutral-point-clamped (NPC) inverter. Unlike other existing three-phase four-leg fault-tolerant inverter topologies, the fault-tolerant T-Type inverter topology proposed here can significantly enhance the overall thermal overload capability of the inverter, in addition to providing desired fault-tolerant capability. The operating principle of this proposed fault-tolerant T-Type inverter is detailed in this paper, and simulation results are presented to verify the advantages of this improved inverter topology.

A flux-weakening control approach for interior permanent magnet synchronous motors based on Z-source inverters

This paper presents a flux-weakening solution by employing the voltage boost capability of Z-source inverters to overcome the voltage limitation in conventional drives for high-speed applications, e.g. hybrid/electric vehicles. In this control strategy, a flux-weakening algorithm has been developed to achieve constant output power of an interior permanent magnet synchronous motor (IPMSM). Correspondingly, a flux-weakening control strategy including a closed-loop speed control is presented. Compared to existing flux-weakening methods, this attractive control strategy allows an IPMSM to largely extend its constant power speed range and operate at higher speed with larger torque. Theoretical analysis is given in detail, and corresponding simulation results are presented to verify the presented control technique.