Complete solution provided for medium voltage applications

Last month, automation solutions provider Weg launched the new MVW3000 series of variable-speed drives (VSDs) for voltages from 2.3 kV to 8 kV and power levels from 280 kW to 2 400 kW.

Weg highlights that this series is built using multilevel technology and cascaded H-bridge inverters. The multilevel topology is based on the series connection of three to ten low-voltage (690 V) power modules with insulated-gate bipolar transistor (IGBT) output inverters in H-bridge configuration, depending on the output voltage.

The multilevel topology makes it possible for the VSDs to achieve voltage levels in the medium- voltage range using proven standard low-voltage components (diodes, IGBTs and plastic film capacitors) in a cost-effective manner. As a special feature, the MVW3000 is supplied as a complete system integrated into a switchgear cabinet, including a medium-voltage isolator, fuses, a multilevel feed transformer and a frequency inverter.

“The present voltage and power range is only the first stage in the product evolution. Higher voltages and power levels are already available upon request,” says Weg low-voltage and medium- voltage drive systems product manager Johannes Schwenger.

He adds that the MVW3000 is a high-performance all-in-one solution that eliminates the need for additional medium-voltage switchgear. Schwenger stresses that this VSD system features outstanding input and output parameters, energy efficiency and high availability, along with easy maintenance, modularity and gentle motor handling.

“This makes the VSD system the ideal complement for all commercially available medium- voltage motors and the perfect choice for retrofit projects, owing to its virtually sinusoidal inverter output voltage,” he notes.

Weg highlights that the MVW3000 VSD system provides extremely high drive performance. The mains power factor is above 0.95 kV over the entire motor speed range, without any additional harmonic filter or compensation capacitors.

Further, the integrated device architecture delivers outstanding mains harmonic distortion figures for current and voltage in accordance with IEEE 519, IEC 61800-3 and G5/4-1 certifications. The device complies with the limits stated in these standards even in its basic configuration.

The inverter efficiency, including the transformer, exceeds 95% over the entire motor speed range and is more than 96% with load levels above 40%. The charging circuit for the multilevel power transformer ensures transformer core magnetisation without inrush currents and gentle charging of the direct current link capacitors for the inverter stage.

Weg enthuses that the power transformer enables adaptation of the mains voltage to the motor output voltage and reduction of the common-mode voltage on the motor winding. It also reduces common-mode currents through the motor bearings in order to maximise bearing life.

Moreover, the interfaces between the frequency inverter central process control and the power stage for IGBT control, temperature monitoring, voltage feedback and current feedback are implemented using fibre optics to increase noise immunity and provide effective isolation between the control and power sections. The power stages (H-bridges) are built using plastic film capacitors, semiconductor fuses and an automatic inverter bypass function to provide higher system availability in the event of a fault. The virtually sinusoidal output voltage and current reduce power dissipation, vibrations and torque pulsation in the motor.

In the interests of enhanced reliability and system availability, the MVW3000 is equipped with motor protection devices for protection against overload, overheating and motor rotor blockage. The temperatures of the power stage and transformer are also constantly monitored.

As a package system, the MVW3000 simplifies installation and commissioning. The plug-in power stages facilitate easy maintenance and fast replacement. With dimensions of 3 900 mm × 2 210 mm × 1 100 mm, the VSD system also has a small footprint.

“Further, it can optionally be equipped with all commonly used industrial communication protocols, including modbus, profibus, Devicenet and Ethernet,” concludes Schwenger.