- April 02, 2020
April 2, 2020 - Ten years of market experience and many years of development work have gone into the devices with the designations PxtFX, PxtEX and PxtRX from Michael Koch GmbH, Ubstadt-Weiher, Germany. They open up possibilities for the active energy management in electric drives. They are characterized by a voltage range, independence from the manufacturer of the drive electronics, and a variety of applications.
The applications are numerous, and they all build on the idea of temporarily storing the excess or necessary electrical energy largely independently of the grid. The choice of the storage media depends also on the application. For example, Koch uses special aluminum electrolytic capacitors for short and very frequent cycles, double-layer capacitor modules for higher energies and less frequent cycles, and batteries for rare cycles. The connecting part between the drive and the electric storage is the active energy management device or system.
Two active devices called PxtFX and PxtRX are complemented by the PxtEX, the modular storage unit with one or more aluminum electrolytic capacitors. The individual applications are manifold, do the devices bring benefits by a single feature or by the combination of two or more features. The first thing that comes to mind is the recuperation of the machine's braking energy. The PxtFX can save up to 1.2 kilowatt hours of energy in its smallest expansion stage in one-second cycles per operating hour. In relation to the application itself, savings of up to 40 percent can be achieved with the active energy management system based on the PxtFX. Often, however, other benefits play a greater role than increasing energy efficiency, such as the compensation of so-called brownouts, safe and defined standstill during blackouts, the possible acceleration of production processes with output increases of up to 50 percent, the reduction of mains load peaks (“peak shaving”) or even the operation of the electric drive independently of the mains supply.
With a current load capability of 20 amps duration and 40 ampere peak for about one minute compared to storage, which may have a maximum voltage of 450 volts DC, the PxtFX can generate up to 18 kilowatts of power. The device can be equipped ex works with a storage volume of two or four kilowatt seconds. Built into the device as standard is the automatic detection of the brake transistor switch-on voltage threshold, which enables the device to work with all commercially available frequency inverters and servo controllers in a plug & play manner. The safety features of the PxtFX protect against reverse polarity of the DC link, against connecting loaded storage devices and overloading the system on both the storage and DC link sides. Koch sees internal fuses as standard. Features of the PxtFX include an SD memory card, an external 24-volt supply, status displays via LEDs, boot loading and reset options and 6 digital I/Os. These are supplemented by output functionalities via a USB module.
If the storage volume of the PxtFX is not sufficient, the device with the designation PxtEX comes into play. A single PxtEX can store two, four or six kilowatt seconds of energy with its aluminum electrolytic capacitors specially developed for the application spectrum of active energy management systems. Connected to the PxtFX via cables with connectors that are protected against reverse polarity, the storage extension directly benefits the system. The individual storage units are internally protected and indicate their charge level visually via a flashing LED. Integrated into the PxtEX as standard is also a safe discharge resistor, which helps to bring the entire system to a voltage level that is safe for humans.