The goal of this paper is to present the topology, the control design and the experimental results of the 37 kW high performance quasi direct ac-ac converter prototype. The control algorithms and the strategy adopted in this paper are well suited for the ac drives application area. The complete ac-ac system is presented, but the main research interest was focused on the input conversion stage with the scope of meeting the following specifications: unity power factor operation; low input current harmonics; regeneration capability; reduced size of reactive components; full exploitation of the supply voltage. Although the output power inverter determines the overall drive performance, it has been treated only marginally since the conventional field oriented control was used. The overall system control has been designed to tightly balance the power flow in the system. Therefore, a small plastic film capacitor was used instead of the big electrolytic one, as with indirect ac-ac converters. The feed-forward load component has been added to the current reference of the source converter and thus, improving performances were obtained during the transients because of the fast control response to load changes (the feed-forward component was introduced in the inner control loop of the system). The stationary and transitory performances of the ac-ac converter system are shown through the experimental results, and so are the motor and regenerative operations.
