Hongrae Kim

Discrete-Time Current Regulator Design for AC Machine Drives

This paper analyzes the behavior of discrete-time current regulators for ac machines operating at high ratios of fundamental-to-sampling frequencies, a situation common for high-speed automotive drives and large-traction drives. At high ratios of fundamental-to-sampling frequencies, highly oscillatory, or unstable, response can occur if the current regulator design does not properly incorporate the effects of the discrete nature of the controller, including delays between the sampling of signals and the application of the voltage commands through pulse-width modulation (PWM). This paper investigates these issues for different design methods and current regulator topologies. As part of this investigation, a simple discrete-time domain ac machine model is developed that includes the delays associated with PWM. This model is then used to design a discrete-time domain version of the complex vector PI current regulator that demonstrates improved response compared with the other regulators studied. Simulation and experimental results are provided to compare the performance, stability, and robustness of the current regulators analyzed.

Discrete-time current regulator design for AC machine drives

This paper analyzes the behavior of discrete-time current regulators for AC machines operating at high ratios of fundamental-to-sampling frequencies, a situation common for high speed automotive drives and large traction drives. At high ratios of fundamental-to-sampling frequencies, highly oscillatory, or unstable, response can occur if the current regulator design does not properly incorporate the effects of the discrete nature of the controller, including delays between the sampling of signals and the application of the voltage commands through pulse-width modulation (PWM). This paper investigates these issues for different design methods and current regulator topologies. As part of this investigation a simple discrete-time domain AC machine model is developed that includes the delays associated with PWM. This model is then used to design a discrete-time domain version of the complex vector PI current regulator that demonstrates improved response compared with the other regulators studied. Simulation and experimental results are provided to compare the performance, stability, and robustness of the current regulators analyzed.

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.

Instability detection and protection scheme for efficiency optimized v/f driven synchronous reluctance motors (SynRM)

This paper introduces a new method to stabilize synchronous reluctance motors (SynRMs) driven by efficiency optimized V/f control utilizing optimized flux. Efficiency optimized V/f driven SynRMs are prone to instabilities. Specifically, it becomes unstable for either fast ramp acceleration or large load disturbances. For example, in an efficiency optimized V/f control scheme, flux is reduced under low load to improve efficiency. However, a large load increase would lead to loss of synchronisation under this condition. In this paper, a stability analysis of efficiency optimized V/f driven SynRM is performed. Instability threshold indicators using power factor and stator current angle are proposed. A novel instability protection scheme is introduced and verified in experiment.

Stability Study of Electric Vehicle Power Electronics Based Power System

The main objective of the paper is to do stability assessment of power electronics based electrical power system of TOSA electric bus. This paper mainly focuses on the stability of the common dc bus that multiple power converters are connected to. The TOSA bus electrical power system is modeled with Matlab/Simulink. The common dc bus stability is investigated under different operating conditions.

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.

Modeling, simulation and performance evaluation of cage rotor permanent magnet motor fed by variable speed drive

With increasing demand for higher efficiency, engineers are looking for an alternative solution to replace induction motors (IMs) in many applications. One of the very promising topologies is the permanent magnet (PM) motor with a squirrel cage on the rotor, which is referred to as the cage rotor PM motor in this paper. Based on the literature survey, the cage rotor PM motors have been studied and compared to IMs for direct on-line applications. Some studies also investigated the performance of line start PM motors (LSPMs) using a conventional VSD by comparing it to an IM using the same VSD. The comparative evaluation shows that, in most operating conditions, the LSPM drive provides better performance (usually higher efficiency) than the IM drive. In this paper, a d-q dynamic analytical model of the cage rotor PM motor is derived. The model is intended to be used in place of finite element analysis (FEA) and for purposes of control development. The model is implemented in Matlab/Simulink and used to study the behavior of different types of the cage rotor PM motor; line-start PM and light cage PM motors, when fed by a standard, scalar controlled drive. The analytical results are verified against the FEA, which shows excellent agreement.

Active compensator augmented diode bridge rectifier wind system

This paper introduces the new concept of an active compensator augmented diode bridge rectifier wind system. The active compensator is used to inject reactive power to optimize the generator operation by adjusting the q- and d-axis currents to the optimal operating points. The size of the active compensator is a fraction of the full rating of the system. Therefore, the proposed idea is able to offer a cost-effective and optimal wind generator-power electronics solution. In this paper, the control method of the proposed system is also discussed. The introduced concept is verified with simulation results.