Efficiency Testing of Electrical Machines and Electrical Inverters – Described from a User Perspective

When designing an electric motor drive system, no matter what the application is, there are three elements:

  • power source
  • power converter
  • motor

Often, these elements come in the form of a battery acting as a DC Bus – an inverter which changes the DC power to AC power – and a motor which uses the AC power to convert electrical energy into mechanical power. This is sometimes referred to as electro-mechanical power conversion.

What are the engineers trying to achieve?

When designing these systems, engineers are typically trying to maximize efficiency across a drive cycle. They do this by maximizing the torque per amp for as many points as possible. This is sometimes done with clever machine design, and at other times with implementing the appropriate control technique. The inverter, control, and motor – all need to play nicely together to maximize this goal, but often these things are developed separately. This leads to issues like a very efficient motor but poor efficiency in the inverter. This has led to system level workers and engineers trying to maximize the Power Factor across the system. A slightly less efficient motor can be worthwhile, if it increases the efficiency of the Motor Drive.