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Open access

K. Kulikowski and A. Sikorski

Efficiency improvement due to direct torque and flux three levels three areas control method applied to small hydroelectric power plant

The paper presents a description of a new DTFC3L3A (direct torque and flux control three levels three areas) control method of induction machine as well as its comparison with the DTC method. The basis for the comparison is the switching frequency of described methods. The proposed method is optimized to reduce number of switchings (which is proportional to switching power losses) in static state, as well as it takes into account the δ angle which makes it possible to obtain a sinusoidal shape of flux within range of low angular frequencies of an asynchronous machine. The paper includes the results of experiments performed on a three level DC/AC inverter for both control methods.

Open access

A. Sikorski, K. Kulikowski and M. Korzeniewski


This paper describes two modern direct torque and flux control methods of an induction machine supplied by a three-level inverter. Additionally, it presents a comparison of the methods both in static and dynamic states. The methods, in a specific way, make use of an increased number of active vectors of the three-level inverter in order to improve control quality and reduce switching frequency. The two methods modify the DTC method by using its advantages and eliminating, at the same time its drawbacks.

In static states the comparison was based on the results of investigations performed for two different load values and three set values of angular speed, whereas in dynamic states the comparison was focused on the behavior of the machine at startup.

The results of the investigations have shown that both methods give very good performance. They are characterized by both sinusoidal shape of flux and low current deformations even at low angular speeds i.e. less than 10% of the nominal value. The presented methods also allow to generate nominal flux for set zero angular speed in order to achieve excitation of the induction machine. The switching frequencies for both methods are very similar in almost the whole range of control but the methods have shown some differences in control quality, particularly for higher torque values.

Open access

P. Falkowski, K. Kulikowski and R. Grodzki


Power electronic three-level AC-DC converters connecting a utility grid with DC supplies are widely used in renewable energy sources. For such distributed systems, the quality of energy is very important. Hence, control algorithms of an AC-DC converter have to provide not only a sinusoidal shape of grid current, but also stable operation during transient states in the grid, e.g. voltage dips or voltage unbalance. This paper deals with the problem of robustness of AC-DC control methods under disturbed grid voltage. Three modern predictive control algorithms are presented and investigated under grid voltage distortions. Experimental results from a laboratory test setup illustrating properties of the described methods are shown.

Open access

M. Korzeniewski, K. Kulikowski, J. Zakis, M. Jasinski and A. Malinowski


Continuous development of intelligent network applications drives the demand for deployment-ready hardware and software solutions. Such solutions are highly valued not only by distributed producers of energy but by energy consumers as well. The use of intelligent network applications enables the development and improvement of the quality of services. It also increases self-sufficiency and efficiency. This paper describes an example of such device that allows for the control of a dual active bridge (DAB) converter and enables its remote control in real time over an IP-based network. The details of both hardware and software components of proposed implementation are provided. The DAB converter gives a possibility to control and manage the energy between two DC power systems with very different voltage levels. Not only information, but also the quality of energy, the direction of power flow, and energy storage systems can be easily controlled through an IP-based network and power electronics converters. Information technology, together with intelligent control of power electronics technology, provides a flexible solution, especially for sustainable smart grids.

Open access

J. Wieczorek, B. Oleksiak, J. Mizera, K. Kulikowski and P. Maj

The paper presents results of a study on the quality of coatings deposited on surfaces of AZ31 magnesium alloy products. In order to obtain protective coatings (corrosion and erosive wear protection), the methods of anodising (specimens A, B and C) and, for comparison, electroless plating (specimen D) were applied. The assessment of coating quality was based on the scratch test results. The results were used for determination of critical loads resulting in coating rupture. The best result was obtained for the specimen B (sulphuric acid anodising in combination with sealing): the critical load was 7.5 N. The smallest value (5.5 N) was observed for the specimen D, i.e. the coating produced using the electroless plating method. Moreover, erosion resistance of the coatings was assessed. In this case, a depth of the wear trace due to an erodent agent (SiC powder) effects was investigated. The results are comparable to those obtained in the scratch test. The poorest erosion resistance is demonstrated by the coating D and the best resistance is observed for the coating B.