Synthetic loading applied to linear permanent magnet synchronous machines

Abstract

Linear permanent magnet (PM) machines are applicable to a number of prototype renewable energy devices and therefore are candidates for deployment. Synthetic loading for efficiency evaluation of linear PM synchronous machines is described and evaluated. Synthetic loading is a technique that eliminates the need for an external mechanical load to absorb generated shaft power during rated load efficiency tests. As such it is a technique ideally suited to the large linear PM generators proposed for renewable applications. Mathematical expressions for synthetic loading are derived for the linear PM synchronous machine using the dq machine model that includes core loss. Synthetic loading and standard efficiency tests, as methods of efficiency evaluation, are simulated using MATLAB and SIMULINK. Simulation data are verified by experiment for both the synthetic loading test and the standard efficiency test. Simulation and experimental results show that the synthetic loading method is capable of evaluating the efficiency of linear PM synchronous machine under test. The results show good agreement with standard efficiency tests. The key contribution of this work includes the mathematical expressions of synthetic loading applied to linear PM synchronous machines, the hardware and software implementation of the technique and the validation of the synthetic loading as a technique for efficiency evaluation of linear PM synchronous machines

A Novel Synthetic Loading Method for Multiple Three-Phase Winding Electric Machines

“…It shows that the stator flux seen by each of the windings is dependent on the currents in both windings. This means that one can vary the amplitude of the flux seen by winding W1 (governed by the first row in (8)) with the d-axis current of winding W2 through the (3/2)Lmd term (the 4 th element in the 1 st row in (8)). As the flux seen by a winding is responsible for the voltage induced in it (at a fixed speed), the measured voltage seen by the voltage regulator (voltage in W1) can be modified with the d-axis current of W2 so as to increase or decrease the d-axis current commanded by the voltage regulator (reference setting for W1).…”

“…In a nutshell, synthetic loading means that the mechanical load is not required and different operating conditions of the machine under test, including rated current operation and rated temperature rise, are normally achieved by introducing a pulsating torque (by means of current harmonic injection) at a frequency high enough so that the speed of the machine hardly varies due to inertia. The same principle of machine testing has been further used for testing of synchronous machines with field winding [7] and, in more recent times, in relation to permanent magnet synchronous machines of different types [8][9][10].…”