combining reactor

[greenurth]

In an 850HP AC dynamometer application I'm seeing a single 3-phase combining reactor connected to the output of (2) inverters. For each phase... reactor line connection X1 is to one inverter and X2 to the remaining inverter. Reactor load connection is from X3 (center tap) to the AC motor.

Inductance specifics: X1 to X2 = 30 mmH
X1, X2 input = 486 AMPs
X3 output = 972 AMPs

I'm unfamiliar with combining reactors and having trouble understanding how (or why) the drives benefit from being output paralleled? Also, what effect does this arrangement have on interconnecting cable between drive/reactor and reactor/motor? Any forum help or insight is appreciated. 3/8

 

[electricuwe]

The reactor (or interphase transformer) is necessary to parallel the two inverters. Basicly two modes of operation are possible:

- Inverters are operated with the same PWM pattern:
The reactor allows the Inverter outputs to be at different voltages for a certain, small amount of time (some µs) due to propagation delay and switching time differences in the drivers and power semiconductors (quite small reactor). Without reactor, current imbalance would result.

-Inveters are operated with interleaved PWM patterns:
Reactor creates a multistep output waveform, enabling paralleling an reduced current ripple in the motor at the same time (quie large reactor)