Synthetic Loading Technique Research Articles

The Synthetic Loading Technique Applied to the PM Synchronous Machine

The application of the synthetic loading technique to permanent magnet (PM) synchronous machines is investigated. Mathematical equations for synthetic loading are developed. From the equations, a quadrature-axis current algorithm is proposed from which rotor speed and the stator direct- and quadrature-axis voltage and current equations are derived. The impact that synthetic loading frequency has on the dc-link voltage and the inverter phase-leg volt-ampere rating are analyzed. This shows that the synthetic loading technique requires an increased dc-link voltage and inverter volt-ampere rating compared to the standard efficiency test method. Synthetic loading is verified experimentally using a surface-mount PM synchronous machine. Simulation and experimental results are compared with the standard efficiency test. The simulation and the experimental results show that the synthetic loading technique is capable of evaluating the losses in the PM synchronous machine.

The Effect of Direct Axis Current on the Performance of the Synthetic Loading Technique

Synthetic loading is a technique that forces the machine under test to operate at rated speed, torque, and flux without the need for the test machine to be connected to an external load. The technique has been successfully applied to permanent magnet machines but it requires an inverter voltampere (VA) rating that is 1.51 pu of the rated value due to the need for instantaneous phase currents and voltages that are higher than the rated value. In order to reduce the VA rating, it is possible to inject direct axis current. This has important consequences. It reduces the ac perturbation current thereby reducing the peak instantaneous phase current. Also, by reducing the ac perturbation current, the rotor speed variation is reduced, thereby reducing the instantaneous phase voltage requirement. Both these effects reduce the VA rating of the inverter. However, this paper demonstrates through simulation and experiment that such a scheme increases the iron losses in the machine. This is important as it alters the distribution of losses which is not a desired consequence. The effect of direct axis current on the iron loss and the machine efficiency during synthetic loading is assessed and evaluated as is the effect on the minimum dc link voltage and the inverter VA requirements used to conduct the synthetic loading technique. Simulation and experimental results are used to demonstrate the effects and validate the conclusions that while direct axis current injection reduces the inverter VA rating, it reduces the accuracy of the synthetic loading technique.

A novel method for rapid efficiency measurement of three phase induction motors

This paper describes a novel method for rapid full load efficiency evaluation of three phase induction motors using the synthetic loading technique, without the need to connect a load to the machine's drive shaft. The new method uses a digital signal processor (DSP) controlled high switching frequency power electronic inverter to synthetically load the induction machine, while using a new real time data acquisition system to accurately determine and record the machine's performance. The method proposed considerably reduces the testing time compared with conventional methods of efficiency measurement and the accuracy of the result is maintained. Moreover the use of the power electronic inverter allows a comprehensive control over all the quantities which determine the rate at which the power is dissipated inside the induction machine. This method can also directly quantify rotational losses of the induction motor under test.

Impedance Measurement in Frequency-Halving Networks Using a Two-Frequency Synthetic Loading Technique

A technique is described which removes a major difficulty in the design of wide-band frequency-halving networks: the accurate characterization of the "pumped" input output impedances at the plane of the varactors. The procedure permits the use of realistic input, output power levels with the input at twice the output frequency.