The DC-INDUSTRIE project, by means of direct current networks, aims to support both the energy transition and energy efficiency, as well as Industry 4.0, says Philip Crowe.
The continued focus on improving energy efficiency and sustainability remains a major driving force for innovation in mechanical and electrical engineering arenas. Improved speed control using variable speed drives (VSDs) has produced a significant energy saving, but the next step needs to be much bolder – the implementation of a direct current (DC) grid within industrial premises has the potential to reduce operating costs and take advantage of renewable energy sources.
The German Electrical and Electronic Manufacturer's Association (Zentralverband Elektrotechnik und Electronikindustie or ZVEI) initiated the DC-INDUSTRIE research project along with 21 industrial companies and four research institutes. Together they are jointly working on the project to implement the energy transition in industrial production and, therefore, bring more energy efficiency and energy flexibility into industrial production.
Among those involved is Bauer Gear Motor, which is part of the Altra Industrial Motion Corporation, and Karl-Peter Simon, Bauer’s Managing Director, who is taking a leading role in the research.
Karl-Peter Simon says, “This research project has the potential to benefit a large number of manufacturing industries, with one large automotive company already planning to implement some of the recommendations in a new test facility. Bauer is keen to use its expertise to help deliver this innovative vision and make a significant contribution to improving energy efficiency.”
In the industrial sector, electric motors account for about 70 per cent of electricity consumption and are thus the most significant load of electrical energy. Reducing the energy requirements of these drive systems by increasing their efficiency contributes to an equivalent reduction in CO2 emissions.
Since January 1, 2017, all new 3-phase motors sold in Europe with rated power from 0.75 to 375 kW must conform to energy efficiency class IE3, or alternatively IE2 for use in frequency inverter operation. These efficiency classes are specified for three-phase asynchronous motors operating at nominal speed and nominal torque. However, experience has shown that an energy efficiency regulation of a component can only sustainably reduce energy in certain operating modes.
With this in mind, the DC-INDUSTRIE project, by means of direct current networks, aims to support both the energy transition and energy efficiency, as well as Industry 4.0. The project is sponsored by the Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie or BMWi) and has a term of three years.
However, if the three-phase motor is operating in the braking mode, e.g. in a crane that is in lowering mode, the energy flow changes. But, this energy cannot be fed back into the grid by the frequency inverter because the input rectifier only allows the energy to flow in one direction. Therefore, the energy that is fed back must be dissipated via the direct current voltage circuit of the frequency inverter.
For this purpose, a brake chopper is connected to the intermediate circuit. This monitors the intermediate circuit voltage with regard to the voltage level. If the intermediate circuit voltage exceeds a set threshold value, the brake chopper switches the braking resistor between the positive and the negative pole of the intermediate circuit. This is usually an additional external braking resistor that converts the braking energy into heat energy.
In order to achieve significant progress in energy efficiency and system cost optimisation, new approaches are needed. To enable energy efficiency, energy transition and Industry 4.0, new grid structures are required.
Through the direct supply of all electric motors via a frequency inverter with direct current power supply, all installed motors are connected via a common direct current voltage grid. Furthermore, a direct current voltage network essentially only causes ohmic transmission losses. Compared to an alternating voltage network, the capacitive and inductive line losses are eliminated.
In addition, the central direct current voltage network offers the possibility of integrating photovoltaics directly at the direct current voltage level. In this case also, conversion from DC to AC is not required to be done by an inverter. This grid infrastructure offers the possibility of optimizing the purchase of energy and to stabilise the grid.
Through the elimination of the input rectifier and the grid filter with frequency inverters, these can be designed more cost-effectively and more compactly. This simplifies integration into the motor, which can significantly increase the degree of acceptance. Variable speed motors allow for a reduction in variants and energy savings. They provide status signals from all DC-fed drivers, which are of great importance for flexible and safe production control.
Grid management makes it possible to optimize operational management in terms of energy costs. The accessible information enables preventive production control measures to significantly increase the availability of production. This is a prerequisite for the successful implementation of Industry 4.0.
This research project has the potential to benefit a large number of manufacturing industries, with one large automotive company already planning to implement some of the recommendations in a new test facility.
Karl-Peter Simon, Managing Director, Bauer Gear Motor