Ian Wallace

A current source PWM inverter with actively commutated SCRs

Conventional SCR based current source inverters suffer from poor waveform quality due to six step switching. Pulse width modulated current source inverters typically require gate turn off devices with reverse voltage blocking capability which have limited their application. In this paper, a new pulse width modulated current source inverter topology using one gate turn off switch and six SCRs is presented. The converter uses active commutation to realize pulse width modulation in a conventional SCR based current source inverter. Modulation techniques for the proposed inverter, simulation and experimental results are described in the paper. This topology is suitable for high performance, high power applications.

Increasing the dynamic torque per ampere capability of induction machines

A method for increasing the dynamic torque per ampere capability of induction machines is presented. The method developed is based on use of an indirect field-oriented controller (IFOC) for the induction machine. A dynamic method which achieves transient torques over 35% greater than the prior methods is identified. The limitations of the method and its sensitivity to detuning are examined.<<ETX>>

Verification of enhanced dynamic torque per ampere capability in saturated induction machines

An easily implemented technique for dynamic torque per ampere enhancement under high levels of motor saturation is described and validated via substantial experimental results. A saturation model assuming only d-axis saturation is utilized in field-oriented control of the experimental system, and the results are compared to theoretical predictions based on the same saturation model. In order to help users to optimize this technique, the authors discuss motor selection issues for the production of this dynamic torque enhancement. An experimental illustration of the use of the torque enhancement principle to break away a load with high static friction is presented to demonstrate the practical application of the concept. Measurement methods used to evaluate the dynamic properties of the electromagnetic torque are presented in sufficient detail so that users have appropriate tools for performing such work.<<ETX>>

New developments in resonant DC link inverters

Soft switching inverters differ significantly from hard switching PWM inverters in the areas of device behavior, modulation methods, design trade-offs, output spectra, and load performance. This paper outlines and discusses the foundations of these differences as well as presenting substantial new data to show the current status of resonant DC link inverters. This data covers performance issues such as efficiency, conducted EMI, output THD, suitability for operation with long motor cables, as well as device utilization and rating.

Inductor design for high power applications with broad spectrum excitation

The design of high-power inductors for applications with broad current spectrum excitation is a challenging task. The resonant inductor of a resonant DC-link inverter (RDCLI) is one such example. The inductor current consists of a resonant current component, a DC component, which supplies the active power to the load and a modulation component, which depends on the modulation strategy. In addition, the frequency and amplitude of the dominant current components change with operating point. Conventional inductor designs for single-frequency excitation do not perform well in broad-spectrum applications. In order to improve these designs, the impact of broad current spectrums on winding design, core selection, power density, and thermal-handling capability must be investigated. In this paper, alternate inductor topologies, which better address the above issues, are proposed and investigated.

Feedback linearization of current regulated induction motors

This paper proposes two nonlinear feedback control approaches leading to decoupling schemes for torque and flux control of current regulated induction motors. These results are applications of the theory of input-output linearization of nonlinear systems via dynamic state-feedback control. Simulation and experimental results for a 275 kW four-quadrant wind generation application employing a DSP controlled resonant DC link inverter are presented.

Design considerations for a soft-switched modular 2.4-MVA medium-voltage drive

A new six-phase, 2.4 MVA, soft-switched, medium voltage drive system utilizing series stacked modules with low voltage devices has been developed. The drive system combines a new soft-switched DC-DC converter with resonant DC link inverter technology to deliver extremely low THD sinusoidal output, high power density and high efficiency. The series stacked configuration with the associated single-phase loading lead to unique power and control design challenges. Device selection, control of parasitic elements, sensing methods for converter control, custom magnetic component design and clamping techniques have lead to a substantial improvement in device voltage utilization. The DC-DC converter controls must regulate the intermediate DC bus voltage under single phase loading while balancing transformer excitation and maintaining zero voltage switching, among other tasks. Proper control of the RDCL inverter requires the selection and tuning of the appropriate modulator and understanding its affect on the power circuit ratings.

Evaluation of actively clamped resonant link inverter for low output harmonic distortion, high power density power converters

The suitability of a soft-switched actively clamped resonant DC link (ACRDCL) inverter for low output harmonic distortion/high power density power conversion is evaluated. Modulation and control techniques for achieving low harmonic distortion are described. Performance and power density of the ACRDCL inverter are maximized through the optimal design of the clamp circuit, resonant components, and output filter components. For the same output kVA, efficiency and harmonic performance as the ACRDCL inverter, hard-switched designs are compared. The ACRDCL inverter simulation and design are validated experimentally.