Toshiba Mitsubishi-Electric Industrial Systems Corp. (TMEIC) announced its new medium voltage drive, the TMdrive-MVe2. The drive’s unique design supports higher voltage motors without the need for an output transformer, and avoids many problems associated with older variable frequency drive designs, such as low efficiency, low input power factor, and output harmonics.
TMdrive-MVe2 family of drives gives the user a choice of voltage output and power level. The different drives available range from 3 kV to 11 kV at power levels up to 3,860 kW. The drive uses Pulse Width Modulation (PWM) to create a voltage sine wave output by means of several inverter power modules.
To create the required Medium Voltage output to the motor, the inverter modules are connected in a series so the output is the sum of the module outputs. Only two modules in series per phase are required for the 3 kV output, only three for the 6 kV output, and only 5 for the 11 kV output.
Compared to earlier MV drive designs and other multi-level drives on the market, the unique MVe2 design reduces the module count providing a cost reduction and significant improvement in reliability.
TMdrive-MVe2 benefits include:
- Energy Savings. Regenerative braking puts energy back into the supply when the load is slowing down.
- High Efficiency and Power Factor. High electrical conversion efficiency of 97 percent results from the low switching losses of the main circuit elements and the low input side harmonic currents, which also eliminate the need for harmonic filters or power factor improving capacitors.
- No Speed Sensor Required. Stable speed control is achieved without requiring a motor speed sensor since the drive accurately calculates motor speed from the motor current and voltage.
- Compact Size. The TMdrive-MVe2 is one of the world’s smallest size 6 kV class drives, allowing transportation in general-purpose containers, simplifying shipping and lowering costs. No rear access is required so the required plant installation space is also minimized.
- High Reliability. The TMdrive-MV family of drives has a proven history of fleet reliability with 12-year MTBF.
- Simplified Maintenance. Using identical rack mounted cell inverters, which are easily withdrawn and inserted, allows the repair time (MTTR) to be as short as 30 minutes.
- Smooth Output to Motor. The multilevel pulse width modulated control produces an output waveform close to a sign wave, so an output filter is not required, and motors do not require surge protection.
- Convenient Motor Starting. Using the drive to soft start the motor controls the starting current and reduces the inrush current.