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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.