The following diagram shows the electrical model of a Y-wired BLAC motor:
The power in any motor can be calculated as the sum of each phase power (product of RMS current and RMS voltage). In the case of a phase-balanced motor:
In a Y-connected motor,
- The phase current () is the current in RMS seen at the Servo Drive output terminals.
The phase voltage () is defined as:
where is the RMS voltage difference between two output terminals of the Servo Drive. The use of the Space Vector Modulation (SVM) allows the use of all the DC-bus voltage as line voltage amplitude.
where is the modulation index (percentage of output voltage respect DC-bus voltage). The maximum modulation index provide by an Ingenia Servo Drive is defined as "Bus Voltage utilization" on the product manuals.
Therefore, the power delivered to the motor power can be defined as:
Power in a Δ-wired motor
From the point of viwe of a Servo Drive, the power provided to a Δ-wired motor is exactly the same. However, the voltage and current values are shared different within the phases:
In a Δ-wired motor:
- The phase current () is not the current seen at the Servo Drive. On the contrary, it is defined as:
where is the current in RMS seen at the Servo Drive output terminals.
The phase voltage () is the RMS voltage between is the voltage difference between two output terminals of the Servo Drive, defined in (3).
Therefore, the total power in a Δ-wired motor results as:
Which, from the point of view of a servo drive, is equivalent to (4)