Voltage source VFDs using PWM technology have been around for a long time and is mature technology. Almost all low voltage VFDs these days are voltage source PWM drives. A simple diagram of a voltage source PWM drive is shown on the left.
Robicon Siemens Perfect Harmony MV VFDs are based on this low voltage PWM technology. The VFDs use what is known as cascaded H bridge topology. In essence, there are a number of low voltage three phase inputs to the cell that gets rectified and produces a single phase low voltage output on each power cell.
The cells are then connected in a cascaded form to generate the medium voltage. Depending on the output voltage of the MV VFD and whether the MV VFD has redundant power cell bypass capability, there can be anywhere from nine to eighteen power cells in a redundant cell bypass Siemens Robicon MV VFD. See this blog which discusses redundant power cells in this unit.
The older series Robicon Perfect Harmony MV VFDs have at least 4 cells per phase while most of the newer series Robicon Perfect Harmony VFDs have 3 cells per phase for 4160V medium voltage VFDs.
The number of power cells in each phase depends on the low voltage on the secondary side of the phase shifting transformer that feeds the individual cells and also the cell design. The secondary side of the phase shifting transformer can be rated for 480V on some VFDs and there are 690V on secondary side of the phase shifting transformers on the newer drives (Gen III and Gen IV). The three separate phases of the cascaded cells are then connected in Y configuration.
Over the years EMA has been repairing the Siemens Robicon Perfect Harmoney power cells both at our shop and in the field.
Until now we have repaired the cells here at our shop and tested them without a VFD; we have been successful at these repairs. However, to better serve our customers we have recently purchased a Siemens Robicon Perfect Harmony VFD that we are able to run the following Power cells on:
- The Harmony Drive,
- Gen II,
- Gen III,
- Gen IV.
We have successfully repaired and tested all these power cells on our test stand.
This is a significant expense for EMA, but we feel our customers deserve no less. Give us an opportunity to help with your Siemens Robicon Perfect Harmony Medium Voltage VFD repairs. You will find us competitive and timely in delivering results on the Siemens Robicon Perfect Harmony MV VFDs.
You can contact us at 770-448-4644770-448-4644 OR by any of the contact methods on the right of this page. We also haveRobicon Siemens Perfect Harmony Powercells for exchange and sale, as well as complete drives.
No One, Anywhere is Better at Drives than we are.