Vol 89, No 7 (2018)

It has been demonstrated controlling maximum permissible current overloads and reverse currents of semiconductor power devices using a single device is practically impossible and the actual amplitude–time dependences of permissible current overloads should be determined by a computational analytical method. A new method for generating single and repeating heavy voltage sinusoidal pulses based on application of the principle of discrete superposition of charges in a galvanically isolated control circuit has been presented. A diagram of discrete superposition of charges in a galvanically isolated power circuit has been presented. Distinguishing characteristics of its determination have been shown.

A software method is considered for converting a resistance into binary code that makes it possible to control the current flowing through a transformable resistance. The resolving power of the microcontroller measuring converter (MMC) is set by programmatically in the range from 2 to 16 bits. The resistive sensors with different nominal resistance values not lower than 50 Ω can be used as a transformable resistance. A block diagram of an MMC with an explanation of its operation algorithm, an oscillogram of output signals of a double-channel pulse-width modulator (PWM) built into the microcontroller, and an example of MMC calculation are presented. It is found from the calculated and experimental data that the transforming characteristic of MMC is linear in the range of the most relevant resolution from 8 to 16 bits. The operation of two PWM channels at the same frequency when supplying the measuring and reference circuits with current of the same value makes it possible to exclude the negative influence of external factors: temperature, instability of supply voltage, electromagnetic fields, and changes of parameters of elements as a result of their aging.

The article presents the issues of multicriterial evaluation of a self-contained power supply system as a complex engineering system. The methods of construction of the resulting target quality function in the form of the generalized index are considered. An assessment is given of the advantages and disadvantages of the various approaches in solving such problems. It is proposed to form a generalized quality index in the form of the dependence of the output characteristics inside the considered system and complicated engineering complex including a power supply system. Numerous output characteristics are presented in the form of separate aspects. The problem of assessment is reduced to consideration of two aspects. Methodological tools are given that allow the necessary calculations to be carried out.

A methodological approach for determining the energy intensity of autonomous power supplies in the presence of interruptible power service due to the overrange of supply quality indices has been considered. The modes of operation of the power supply system have been represented in the form of a Markov chain with discrete states and continuous time. The exponential rule of a working time distribution of the power feeds has been adopted. A marked graph of states of the power supply system that consists of the state electric mains, uninterruptible power supply equipment, and a standby diesel power station has been constructed. The matrix of transition probabilities has been created, and the analytical expressions have been obtained to determine ultimate probabilities. Since the ultimate probabilities are the mean relative residence time of the system in the given state, the analytical expression has been deducted to determine operating time of the storage battery used in the equipment of uninterruptible power supply. The operating time of other standby power supplies can be similarly calculated.

The effect of magnetic wedges in a half-closed slot on the magnetic field configuration in the air gap of a brushless dc engine with permanent magnets has been examined. Based on field numerical calculations, it has been established that magnetic wedges recessed into the grooves of slots can almost eliminate the high-frequency magnetic field oscillations caused by stator teeth in the air gap. This effect takes place if the relative magnetic permeability is not lower than 40. In valve engines with magnetic wedges, the eddy currents in conductive array of permanent magnets are suppressed, causing their heating and significantly reducing reactive electromagnetic torques (sticking torques of the rotor). After installing magnetic wedges with protrusions in the slots, the amplitude of the fifth harmonic of the magnetic induction causing the losses in magnets decreases by 13 times. Such an engine has almost no losses in the magnets. The calculations of losses in the magnets indicate that without recommended wedges the eddy currents will occupy the entire volume of magnets. The maximum reactive torque with such wedges reduces by six times. Magnetic wedges with usual location in a semiclosed slot (not recessed into the groove of the slot) have a small effect on the magnetic field configuration in the air gap.