Tero Ahonen

Frequency-Converter-Based Hybrid Estimation Method for the Centrifugal Pump Operational State

Research on utilization of a frequency converter and sensorless methods in the drive system diagnostics has been mostly limited to the motor and to the frequency converter itself. However, it has been shown that a frequency converter also allows the sensorless estimation of the operational state of a centrifugal pump providing new opportunities for the diagnostics and control of pumping systems. In this paper, a novel hybrid estimation method for the centrifugal pump operational state is proposed. It is based on the identification of the process by using those flow rate and head estimates produced by QP-curve-based method, which are known to be relatively accurate. After the identification phase, the process model can be used together with the estimates of the frequency converter for the sensorless operational state estimation of the pump. The method is evaluated by laboratory measurements, and its applicability to industrial pumping and fan systems is also discussed.

Design considerations for current transformer based energy harvesting for electronics attached to electric motor

Energy harvesting or scavenging from environment is being researched intensively. The main motivation of the research is to develop a maintenance free energy source for ubiquitous electronics, such as wireless sensors or sensor networks. The on-line condition monitoring of electric motors requires also sensors that are installed at the motor. In this case, the energy required by sensors could be harvested from a magnetic field. In this article, current transformer based energy harvesting is considered. A switch-mode power supply utilizing current transformer is designed. It is tested in laboratory with the mains supply and variable speed drive. According to the tests carried out, the current transformer based power sources are a feasible alternative to supply the electronics attached to an electric motor.

Pump operation monitoring applying frequency converter

Variable speed driven (VSD) pumps are nowadays widely used in industry applications. Variable speed pumping improves operational flexibility of the pump drive compared with throttle control. In many cases this results in energy cost savings. Nowadays, the performance of frequency converters allows their use as an intelligent monitoring device for the pump drive. This provides new possibilities for the maintenance and operation personnel. In this article, some functions provided by the frequency converter for pump condition and operation monitoring are explained. The applicability of a frequency converter for monitoring purposes is also discussed.

Variable speed drive-based pressure optimization of a pumping system comprising individual branch flow control elements

Circulation pumping systems hold energy savings potential, which can be seized with intelligent control. In this paper, a novel variable speed drive based method for minimizing the required pump pressure of a pumping system that has individual branch flow control elements is introduced. The method can be used to save energy for example in central heating circulation applications. Moreover, the presented method is purely software-based and can be implemented using a variable speed drive. The operation of the method was verified with simulations and a laboratory test setup and compared with proportional pressure control.

Estimation accuracy of a vector-controlled frequency converter used in the determination of the pump system operating state

Pump, compressor and fan systems often have a notable energy savings potential, which can be identified by monitoring their operation for instance by a frequency converter and model-based estimation methods. In such cases, sensorless determination of the system operating state relies on the accurate estimation of the motor rotational speed and shaft torque, which is commonly available in vector- and direct-torque-controlled frequency converters. However, frequency converter manufacturers seldom publish the expected estimation accuracies for the rotational speed and shaft torque. In this paper, the accuracy of these motor estimates is studied by laboratory measurements for a vector-controlled frequency converter both in the steady and dynamical states. In addition, the effect of the flux optimization feature on the estimation accuracy is studied. Finally, the impact of erroneous motor estimates on the flow rate estimation is demonstrated in the paper.

Detection of Mass Increase in a Fan Impeller With a Frequency Converter

Fan systems are often responsible for the ventilation of contaminated air, such as exhaust gases. Contaminants can build up on the fan impeller eventually causing a mechanical imbalance, which may lead to the fan breakdown and shutdown of production processes. Usually, the contamination buildup can be detected by visual inspection or from increased vibrations caused by the imbalance on the fan impeller. If the contamination buildup could be detected before the imbalance occurs, the unscheduled maintenance or even the failure of the fan system could be avoided. In this paper, a novel method is presented that can be used to detect the contamination buildup on the fan impeller. The method uses the capability of the frequency converter controlling the fan motor to estimate the rotational speed of the motor and the capability to control the motor torque. The presented method is validated by laboratory measurements.

Optimization strategies of PEM electrolyser as part of solar PV system

Solar and wind power have intermittent nature. In order to guarantee continuous power supply, they need to be accompanied with energy storage systems or bridges between different energy sectors. Hydrogen is a potential candidate for both applications (an energy storage system and bridging technology). Hence, it is interesting to study the practical dynamic properties and limitations of electrolysers in the viewpoint of renewable energy production. This paper studies optimization strategies of a proton exchange membrane (PEM) electrolyser together with a solar photovoltaic (PV) system.

Specific energy consumption of PEM water electrolysers in atmospheric and pressurised conditions

Power electronics enable the interconnection between renewable energy and electrolytic hydrogen production. At ambient conditions, the volumetric energy density of hydrogen is low, and therefore pressurisation is required. This paper studies the effect of the hydrogen outlet pressure from PEM electrolysers on the specific energy consumption of water electrolyser systems.

Soft-Sensor-Based Flow Rate and Specific Energy Estimation of Industrial Variable-Speed-Driven Twin Rotary Screw Compressor

Energy costs are typically the largest cost element in the life-cycle of a compressed-air system (CAS). Real-time usage information as well as historical data can help identify whether the CAS is functioning properly. To this end, modern variable-speed drives are able to provide this information as well as produce soft-sensor estimates of volume flow rate production and specific energy consumption of a CAS. In this paper, an identification (ID) run sequence for a twin rotary screw compressor-operated system is proposed to identify the total system volume, to improve the estimation accuracy of a volume flow rate soft sensor, and to create a specific energy consumption map for the CAS performance monitoring. Laboratory measurements are carried out to evaluate the feasibility of the proposed ID run and related estimations. Moreover, possible usage applications of the proposed methods are discussed.

Comparison of electric motor types for realising an energy efficient pumping system

Energy efficiency in pumping is partially affected by the electric motor efficiency. In addition to low losses, the chosen electric motor type should have feasible reliability and dimensions for pumping systems. This paper studies the applicability of common electric motor types to a future pumping system by comparing motor characteristics with each other; both a qualitative and quantitative evaluation is performed for a 15 kW induction, synchronous reluctance and permanent magnet synchronous motor. Another main object of this paper is to provide basic information for designing a next generation, more energy efficient pumping system.