Jussi Tamminen

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.

Influence of motor operating parameters on discharge bearing current activity

While the cause-and-effect chains of inverter-induced bearing currents have been well understood today, not much is known about the damage mechanism inside the bearings. Research has suggested that the bearing degradation is approximately proportional to the frequency of occurrence of the bearing currents. For bearing currents that occur statistically distributed-such as discharge bearing currents-this parameter has not been thoroughly researched yet. In this paper, we present an analysis of the influence of different motor operating parameters on the frequency of occurrence (“discharge activity”) of discharge bearing currents, using a non-intrusive detection method. When analyzed individually, the motor speed, motor shaft temperature, inverter switching frequency, and inverter dc-link voltage influence the discharge activity. However, the overall running time of the motor, the state-steady-state versus instantaneous-and the “operating history” on the time-scale of several days have the strongest effect on the frequency of the discharge bearing current occurrence.

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.

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.

Component selection tool to maximize overall energy conversion efficiency in a pumping system

Often, the components of a pumping system are not selected from the perspective of the total system, as the individual components are selected using different programs. In this paper, a selection tool that optimizes the energy conversion efficiency of a pumping system according to actual process requirements is introduced. The tool requires only the catalog data of the components. Its application to an industrial pump system sizing, and thereby, to a component selection problem is demonstrated.

Detecting the correct rotational direction of a centrifugal device with a variable speed drive

A wrong rotational direction of a centrifugal device is detrimental for the service life and energy efficiency of the device. However, in some cases, visual inspection of the correct rotational direction is difficult or even impossible. This paper presents a sensorless method that can detect the correct rotational direction of a centrifugal device. The method is verified by laboratory tests for a pump and blower system.

Variable speed drive-based fan impeller contamination build-up detection: Industrial case study

Contamination build-up can be considered as a root cause for the imbalance of the fan impeller. This contamination build-up can be detected without sensors by using a variable speed drive. In this paper, the use of the contamination detection method in the case of a rotational speed controlled industrial fan is examined.