Drives and Controls Magazine
Modules cut energy used by any make of drive by up to 40%
Published:  15 April, 2020

A German company, Michael Koch, has developed a series of active energy management devices for VSDs (variable-speed drives) that, it claims, can cut energy use by up to 40% when used with drives of any make. The devices, which are connected to the drive’s DC link, store excess electrical energy, largely independently of the grid.

There is a choice of storage technologies depending on the application. For short, frequent cycles, Koch uses special aluminium electrolytic capacitors. For higher energies and less frequent cycles, it uses double-layer capacitor modules. And for infrequent cycles, it uses batteries.

Koch has been making active energy management systems for drives for about a decade. The new generation of devices, called Pxt, are said to offer “significantly higher functionality”.

There are two active devices (PxtFX and PxtRX) complemented by storage modules (PxtEX) containing one or more capacitors.

One potential application is recovering braking energy from machines to boost their efficiency. In its smallest version, the PxtFX model can save up to 1.2kWh of energy in one-second cycles per operating hour. Energy savings of up to 40% are possible.

The modules can also be used to compensate for brownouts, to achieve safe stops during blackouts, to accelerate production processes by up to 50%, to reduce mains load peaks (peak shaving), or to operate drives independently of the mains supply.

The PxtFX model can produce up to 18kW of power with continuous currents of 20A (40A peak) for about one minute. It is available with storage capacities of 2 or 4 kW-seconds. It can detect brake transistor switch-on voltage thresholds automatically, allowing it to be used in a plug-and-play manner with any frequency inverter or servo controller.

Koch’s PxtFX model can produce up to 18kW of power, with continuous currents of 20A (40A peak), for about one minute

The PxtRX version is designed to deliver continuous currents of 30A (60A peak) for about one minute. Its 800V DC storage voltage allows the device to generate almost 50kW.

If more power is needed for an application, several PxtRX or PxtFX devices can be connected in parallel.

The PxtEX storage modules can store 2, 4 or 6kW-seconds of energy using capacitors specially developed for active energy management applications.

As well as the individual modules, Koch also offers complete ready-to-connect systems in control cabinets. These can operate with cable lengths of up to 20m to a drive’s DC link.