THE CASCADED HARMONIC SYNCHRONOUS MACHINE

Riad  B. CHEDID

This thesis presents a theoretical and practical study of a low speed electrical machine christened "Cascaded harmonic synchronous machine" (CHSM). Applications may be found in the fields of hydro‑power, wind energy and low speed drives.

The main distinguishing features of the CHSM are:

     - Generation of mains power from low‑shaft speeds through the use of a special filter connected to the stator winding rather than through a large number of poles.

      -  Realization of the machine in both single‑phase and three‑phase form.

Other features such as the absence of brushes, the possibility of using a cage type rotor and permanent magnet excitation could be profitably incorporated.

In this project, analytical models for both the single‑phase and three‑phase CHSM have been developed and studied. As a result, a generalized equivalent circuit was developed and used to predict the machine's performance, as well as to provide criteria for an optimized practical design. Two‑port network theory was successfully applied to the above-mentioned circuit for both generating and motoring modes of operation. The magnetic field of the proposed machine was modeled by a combination of classical finite element and harmonic balance methods. Flux plots for the d.c. Flux and fluxes associated with various harmonics were obtained, and open‑circuit and short‑circuit tests were simulated for several shaft speed step‑down levels. Results obtained from the studies of the magnetic finite element analysis compare well with those derived from tests.

From the above studies, a systematic approach for optimal machine design was developed. This covers problems of excitation, types of windings, form of rotor core, types of filters and other related topics.

In parallel with the theoretical work, several prototypes were built and a comparison between predicted and experimental results showed good agreement. It was found that the four‑pole CHSM is efficient at half-synchronous speed but at lower speeds the available power decreases substantially, therefore further research is required if lower gearings are to be made viable.