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Purpose -To develop general forms of multiscalar models of the induction motor and to present properties of the sensorless control systems based on such models. Design/methodology/approach -Previously presented multiscalar model of the induction motor based on a stator current and rotor flux vector is generalized as a model of type 1. New model of type 2 is defined for stator current and the vector which is directly controlled by a voltage vector. The above models are applied in a sensorless control system with speed observer. Dynamical properties of the sensorless control systems are investigated by simulations and experiments. Findings -Application of the multiscalar model of type 2 results in higher exactness of sensorless control system than application of the multiscalar model of type 1. Controlled variables are more smooth in transients.Research limitations/implications -This is not an analytical proof of stability of the control systems. Practical implications -Provides very useful information for development of sensorless control systems for the induction motor. Originality/value -This paper extends the known method of nonlinear control of the induction motor to the general form. It is possible to choose the sensorless control system of better properties than those used so far.

Abstract:This article presents measurements of electric power absorbed by a newly built facility for office and scientific research activities. These measurements highlighted the need for compensation of capacitive reactive power-not predicted by the designer-due to the vast use of LED lighting in the facility. The article also describes a reactive power compensation system, designed on the basis of the above-mentioned measurements, and the introduced control and measurement system that enables on-site monitoring and online analysis of consumed energy and power. The research was carried out using popular LED lighting sources available on the local market (Poland). Basic electrical parameters of the locally available LEDs were measured as a function of the changes in harmonic levels occurring in the supply voltage. The test illustrated that samples were characterized by a very low power factor, which decreased as the level of harmonic disturbances increased. On the basis of the measurements, the authors suggest that obligatory requirements should be introduced in regard to the minimum power factor at the level of 0.9 for popular LED lighting sources (below 25 W).

This paper presents the analysis of an energy management system (EMS) implemented to fulfill the requirements of a microgrid (MG) power supply owned by a small industrial company and connected to the rural power system. The main goal of this system is to ensure connection with the existing rural power system in terms of energy exchange, as well as to perform islanding mode operation of the microgrid based on the energy demand of the company. Power generated in the implemented microgrid is based on a hybrid system supported by renewable energy sources and an energy storage system. The aim of the developed energy management system implemented in this MG power system is to enable the microgrid to operate according to scheduled diagrams related to different load events. The presented investigation, analysis, and assessment of the implemented energy management system are based on the on-site measurements and observations of the long-term operation of the microgrid concerning the hybrid renewable energy-based generation system and the company energy demand, which is useful from perspective of the predicted deficiency of electrical energy in Poland, both for customers and transmission system operators. Furthermore, the observed drawbacks and failures of the implemented EMS and the MG are pointed out and discussed to overcome and minimize these disadvantages, and to improve the operational reliability of the whole system.