Energy recovery systems – using high speed generators to capture energy

Energy Recovery Systems from KEB combine lots of the company’s unique leading-edge technology. These systems also highlight the breadth of KEB products and its ability to integrate these together to provide a comprehensive turnkey solution, says Jonathan Bullick of KEB Automation (USA).

An Energy Recovery System (ERS) or Energy Conversion System (ECS) is an electronic system that controls turbomachinery and converts energy from some sort of process. The process involves converting high-frequency electrical power to something usable on the mains or building power (e.g. 50 or 60Hz). Typical processes could be geothermal, air separation, or waste heat recovery.

Application overview

In a KEB Energy Recovery System, a KEB load drive controls the speed of the generator. The set speed is controlled via a master control system. When the process gas is introduced, the load drive regulates the generator speed. As energy is returned to the electrical system, the Active Front End (AFE) is able to return energy to the building power or utility.

High-speed turbomachinery

High-speed motor/generator applications are demanding. Control instabilities and imperfections that are masked at low speeds can become critical at high speeds. KEB has much experience of running high speed asynchronous and synchronous generators.

The turbomachinery used in energy recovery processes typically use special purpose high-speed generators. The generators are normally equipped with special magnetic bearings or airfoil bearings and can spin in excess of 100,000 rpm. The advantage of using high-speed generators is that they’re extremely compact, efficient, and have a high power density.

KEB drives are capable of outputting frequencies up to 1,600Hz which is required to run these generators/motors. However, it is not only the listed output frequency and hardware that separates KEB from other drive suppliers.KEB’s SCL algorithm provides better speed and torque regulation than commonly used V/Hz control. Another advantage is that SCL does not require encoder feedback – this is difficult to achieve at high speeds.

SCL-optimised generator control creates less rotor heating and increased energy output, which benefits the motor manufacturer and the end user. SCL also offers plenty of flexibility with parameter adjustments, which allows the KEB system to work with a variety of different generator types and designs characteristics.

Another reason KEB is well suited for high-speed drive applications is the company’s experience in designing and supplying sinewave filters. A sinewave filter cleans up the drives PWM output and provides a sinusoidal waveform to the motor winding. This also helps reduce motor heating, which is critical to a high-performance system.

Air-cooled or water-cooled

KEB offers both air- and water-cooled drives. Often, there will be liquid cooling in the system already. Liquid-cooled drives offer a number of advantages, particularly if the systems are to be installed at high altitudes or in high ambient temperatures. Air-cooled versions are often preferred for their simplicity. KEB can provide both solutions, depending on the application requirements.

High power – with scalable offerings

The purpose of installing an Energy Recovery System is to reduce overall energy usage and save the facility money. This means that smaller systems are not likely to provide sufficient ROI and warrant the investment. Also, at some power threshold, the systems become economically feasible.

KEB’s energy recovery concept can be easily scaled across different power ranges. With optimisation, it becomes easier to make a business case for investing in an energy conversion system. KEB offers Active Front End (AFE) technology with low harmonic distortion (THiD). AFE is of interest to those looking to generate power back to the mains. The clean generated power will not create issues for other electrical loads and the power factor can even be compensated for as required.

Full Panelised system

KEB offers a standalone drive panel that includes all the drive, filter, and control necessary to control the motor-generator. A C6 HMI LC provides drive diagnostics and the ability to make parameter adjustments. The HMIs are delivered with a CONNECT runtime, which means the systems can provide remote access. This gives the option to provide remote maintenance and future PLC upgrades.

The HMI LC can also act as a network gateway. The KEB panel can tie in with the processes’ master control via another network protocol such as Modbus, EtherNet/IP, or Profinet.

Turnkey solution

KEB can provide individual components or a complete turnkey solution.

The KEB conversion system includes a grid protection relay and an EMI filter to mitigate high-frequency noise. There is also provision to detect an emergency situation and then safely disconnect the system. These are features that would need to be considered and implemented anyway. In this case, they are already engineered by KEB into a system that can be easily integrated into the process and quickly implemented into a customer system.