Clawpole in VHDL-AMS with SystemVision^®

A VHDL-AMS model of a clawpole alternator is created using Infolytica's Three-phase Machine Wizard. VHDL-AMS is a portable format which can be read by many circuit and system simulators, including SystemVision from Mentor Graphics. The wizard creates a Response Surface Model (RSM) of the clawpole by driving MagNet to execute a number of static solves at different phase currents and rotor positions. This RSM is embedded in the VHDL-AMS file to create a component which is functionally equivalent to the original MagNet model, but which can be evaluated extremely quickly in a transient circuit simulation.

Results

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The clawpole component is shown here in the SystemVision circuit. In SystemVision it is a simple matter to create this component from the VHDL-AMS file. The pins are automatically labeled from information in the file, and the model parameters, such as the number of turns in the windings, can be modified in a properties dialog. This simple circuit can be modeled in the Educational Version of SystemVision, which is available as a free download.

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This example has already been solved using Infolytica's Transient 3d with Motion solver, and the results of that analysis are shown in Clawpole in motion. The current shown here compare well with that simulation, in particular note that the third harmonic content is clearly evident, showing that the RSM is capturing one of the essential properties of these machines: nonlinearities.

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The diode currents shown here also compare well with the full transient solution. The diode switching behavior can be difficult to simulate, the fact the two simulations give identical results is as much a verification of the transient solution as of the system simulator.

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The phase voltages are shown here. They are much smoother than their counterparts from the MagNet transient simulation, since the circuit simulator can afford to take much smaller time steps. Simulating this transient takes a few seconds in SystemVision, compared to many hours for the MagNet transient simulation.

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One of the benefits of the VHDL-AMS model is the ease with which different operating conditions can be simulated. Shown here is the battery ripple voltage at 1500 rpm and 3000 rpm. In both cases the resistive load has been adjusted such that the battery itself has approximately zero current through it.

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At a lower speed (1500 rpm) the delta-connected diode bridge exhibits the behavior shown here. This result is obtained by simply editing the speed parameter in the clawpole's property dialog. Another version of the clawpole VHDL-AMS model has a separate mechanical terminal which allows an engine to drive the alternator at dynamically changing speeds.