<span lang="EN-US">Square root calculation is a widely used task in real-time control systems especially in those, which control power electronics: motors drives, power converters, power factor correctors, etc. At the same time calculation of square roots is a bottle-neck in the optimization of code execution time. Taking into account that for many applications approximate calculation of a square root is enough, calculation time can be decreased with the price of precision of calculation. This paper analyses existing methods for fast square root calculation, which can be implemented for fixed point microcontrollers. It discusses algorithms’ pros and cons, analyses calculation errors and gives some recommendations on their use. The paper also proposes an original method for fast square root calculation, which does not use hardware acceleration and therefore, is suitable for implementation at a variety of modern Digital Signal Processors, which have high-speed hardware multipliers, but do not have effective dividers. The maximum relative error of the proposed method is 3.36% for calculation without division, and can be decreased to 0.055% using one division operation. Finally, the most promising methods are compared and results of their performance comparisons are depicted in tables. </span>

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This paper describes high-performance novel Interior Permanent Magnet Synchronous Motor (IPMSM) drive for compact washing machine. The motor has been designed to decrease size of the existing drives and create more compact washing machine. It utilizes inner rotor motor scheme in contrast to the conventional drives, which use outer rotor motor scheme. The control system of the developed drive implements all necessary features for such drives. It includes Maximum Torque Per Ampere (MTPA) control for full utilizing of the motor capabilities and sixth harmonic suppression algorithm for eliminating of the six order harmonic (in dq reference frame) of the current, which increases power loss and produces acoustic noises. Control system also implements field-weakening algorithm, which rotates motor at 300% of rated speed, and is used for spin-dry modes.

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Interior permanent magnet synchronous motor (IPMSM) efficiency can be improved by using maximum torque per ampere control (MTPA). MTPA control utilizes both alignment and reluctance torques and usually requires information about the magnetization map of the electrical machine. This paper proposes an adaptive MTPA algorithm for sensorless control systems of IPMSM drives, which is applicable in industrial and commercial drives. This algorithm enhances conventional control schemes, where the output of the speed controller is the commanded stator current and the direct current is calculated using an MTPA equation; therefore, it can be easily implemented in the previously developed drives. The proposed algorithm does not use any motor parameters for the calculation of the MTPA trajectory, which is important for systems operating in changing environmental conditions, because motor inductances and flux linkage strongly depend on the stator current and the rotor temperature, respectively. The proposed algorithm continuously varies the current phase and in such a way it tries to minimize the magnitude of the stator current at the applied load torque. The main contribution of this paper is the development of a technique to overcome the main disadvantage of seeking algorithms–the necessity of a precision information about the rotor position. The proposed method was verified experimentally.

This paper discusses open phase faults, which can happen in a system grid-converter-motor drive, and measures to properly handle this type of fault. The authors of this paper provide classification of algorithms used for the detection of the loss of phase and explain the distinctive features of each group of methods. They review existing algorithms, which are based on the analysis of the current signals, discuss their pros and cons and suggest possible areas of usage for each group of methods. The authors also propose one novel method for detection of open phase, which was developed for low-cost systems with low resolution analog-to digital converters (ADC). This paper mainly considers methods for three-phase motors as the most popular machines, however some algorithms can be used in multiphase drives. The authors of the paper also share their more than 20 years' experience combined, in this area, which was obtained by developing industrial and commercial drives, and focus on the requirements of the IEC/UL 60730 safety standard, where the phase-loss detection algorithm is one of the essential parts of control system.