Emulating large, time varying rotary power loads at low cost

A high performance, high power dynamometer system is proposed. By using a field controlled DC generator (rather than a DC motor) 10-200 HP high-bandwidth loads can be accurately emulated. The implementation is both economical to build and to operate. Because power loads are sometimes needed (for instance, they are required when testing motor efficiency), the approach emulates power loads, rather than the commonly emulated torque loads. By emphasizing only the pertinent dynamics, a simplified model appropriate for control is found, but the model is still nonlinear and parameter dependent. A linearizing control which also measures parameter changes without the need for specialized instruments is proposed. The control applies to machines which maintain nearly a constant velocity over large loads, so it is appropriate for induction motors, synchronous motors, etc. Experimental tests using both standardized motor efficiency trajectories and power measurements from an oilfield pumpjack confirm the system's ability to respond as quickly and as accurately as the best methods previously proposed, but at a fraction of the implementation and operational costs.