Performance benefits of resolving current in open-loop AC drives

The authors describe the use of the simple mathematical techniques of high bandwidth resolving of the three phase output currents of an AC drive into active and reactive components. The system feedbacks that may be derived from this, and the performance improvements (compared with traditional current feedback techniques) that may be achieved by this method are also described. These include: fast current limit; ability to handle shock loads; high starting torque with low ripple (achieved by accurate dead-time compensation), stabilisation of unstable motors; handling of overhauling loads; and fast synchronisation to a rotating motor. Practical measurements of the improvements are presented. The methods and features are implemented in volume manufactured drives