The devices in the Pxt family are used for energy management to store and provide energy from and in DC circuits of drive applications. The energy from a DC circuit with a high voltage level is converted into energy with a lower voltage level and stored using a DC/DC converter. Capacitive or chemical storage devices such as capacitors are used as storage devices. If required, the stored energy is then converted back to a higher DC voltage level and is available for the application.

The possible uses of the devices as a central control unit for the energy balance range from the recuperation of braking energy to UPS applications and supporting the DC link voltage in cyclical applications, through to a combination of such applications. Peak load reduction can also be managed by the devices, either automatically or controlled externally by a PLC. Automatic load peak reduction requires the installation of an optional measuring point device; external communication is not required.

Communicate when required

Communication with the higher-level PLC is required for controlled peak load reduction. Peak loads are detected by the PLC and suitable countermeasures are transmitted to the Pxt devices by PLC command. Although these have built-in communication interfaces, these are reserved for communication with the devices connected to the system-internal K-bus. The PxtMX module meets the requirements in terms of connection to a planned or existing fieldbus system and for optimum use of the Pxt devices.

The PxtMX is a modular, expandable adapter board that is housed in its own casing and can be simply plugged onto a Pxt device casing. In addition to its hardware-related basic functions, for example digital I/O interface, the module has a higher-level function whose aim and purpose is to connect the devices of the modular active energy management system that work together as a group, simplify communication and adapt it to the application requirements in a targeted manner. The PxtMX therefore creates a system image and then automatically takes over the handling and pre-control of the individual connected Pxt devices. This makes it very easy to address the devices in the network, as it is not necessary to contact each PxtFX or PxtRX device individually. The PxtMX acts as a gateway for the system and connects a PLC to the Pxt system's internal K-bus via fieldbus.

Ethercat at the start

Koch is entering the race with Ethercat, a fieldbus that is particularly widespread in electrical drive technology and is internationally standardized in several IEC standards (IEC 61158, IEC 61784, IEC 61800), part of ISO 15745 and also a SEMI standard (E54.20). The communication or data transmission itself is divided into SDO and PDO. The process data objects (PDO), which are retrieved very quickly and cyclically, are exciting for the performance of the machine or system. The central information here is the system performance currently available. This is not a static value, but is calculated using all relevant parameters - including the limit load integral I²t and the heat sink temperature. Other examples of PDOs are power specifications and the voltages or voltage curves in the DC link and memory. Service data objects (SDO), on the other hand, are only communicated on request, i.e. acyclically. Examples include device statuses such as Error (all devices disabled), Warnings (information during operation) or the heat sink temperature. This provides the user - even in a remote control room - with all relevant information and active intervention options in order to make optimum use of the entire system.

Further tasks of the PxtMX are the retrieval and visualization of application-related system-internal data and information as well as data exchange with a higher-level control system. The module can use the Pxt system to influence the storage of energy and ensure that sufficient energy is available in the event of faults and loads. It enables these control options to be integrated into manual or automated processes. Further processing and evaluation via standardized protocols are also part of its range of tasks. By evaluating the load requirements on the network side, the PxtMX can detect power peaks and take targeted countermeasures to protect and relieve the infrastructure.

Retrieve and analyze performance parameters

The author: Michael Koch is the managing partner of Michael Koch GmbH in Ubstadt-Weiher.

© Michael Koch

Active energy management gains in importance with the fieldbus option thanks to the extended adaptability to the customer application via the PxtMX, as the relevant information can be accessed directly via the fieldbus system. Application-specific data, such as the maximum storage voltage and the isolation voltage between storage and feedback to the drive system, can be queried, as can the dynamic data, i.e. currents and voltages of the active energy management system over time. This allows evaluations and comparisons to be made, from which various conclusions can be drawn that are not limited to the energy balance of the drive system. Cross-location analyses and comparisons of drive systems are also possible, which can then be used as a further source of information or basis for decision-making. On the way to greater energy efficiency and greenhouse gas reduction, the PxtMX helps to communicate crucial data in real time.