STUDY OF PHYSICAL PROCESSES IN THE DIRECT CURRENT LINK OF THE LOADING-BACK SCHEME OF ASYNCHRONOUS MACHINES

The article notes the tendency of introducing asynchronous engines, entailing the necessity to introduce the equipment which is intended to carry out maintenance, repair and acceptance check-outs. The general part of test circuits for asynchronous motors by the loading-back method with two controlled inverters is emphasized. The mathematical model of similar schemes’ functioning is shown. The article gives the results obtained by mathematic simulation of physical processes in the direct current link in the loading-back scheme for asynchronous machines Significant ripple voltage of constant voltage and DC in these circuits is noted. The issue of measuring power in the DC link passing through one inverter to the test engine and through another inverter from the load generator is considered. The authors carried out calculation of the capacities mentioned in the steady state modes for asynchronous machines with nominal power of 0.37 kW, 5.5 kW and 250 kW at different values of capacitor capacitance included in the DC link. Basing on the results of calculations, the authors found the dependence between the relative value of the procedural error in determining power in the DC link by the product of the current values of pulsed voltages and current. The current value from the product of instantaneous values of voltage and current at some time interval was taken as the true value of power. It is shown that at the capacitor capacity above some critical value this procedural error does not exceed 0.9% at the nominal power of the test engines 0.37 kW; 0.3% – at the power of 5.5 kW; 0.2% – at the power of 250 kW. This error increases dramatically when capacitor capacitance decreases. It is shown that the value of the capacitance corresponding to the inflection of the considered dependence approximately corresponds to the value necessary for limiting ripple voltage in the DC link of up to 600 V.

An Analytical Approach for Design of a Cross-Connected Fibonacci Switched Capacitor Converter

Switched capacitor converters (SCCs) are used for low-power applications because they are designed without magnetic components. Among various types of SCCs, the Fibonacci SCC (FSCC) features a small size and high voltage gain. However, the FSCC performance can be more improved, which leads to suggest a cross-connected FSCC (CCFSCC). However, in the considered four-terminal equivalent circuit model for analyzing the CCFSCC, some circuit parameters, such as the operation frequency and capacitor capacitance of the SCC are neglected. In this paper, we propose an analytical approach to optimize the CCFSCC circuit parameters by deriving its voltage gain function. The validity of the addressed methodology is confirmed by comparing the outcomes with the results of simulations and experiments. It is shown that the average errors between the calculated and experimental voltage gains are 9%, and the average absolute errors between the calculated and simulated ones are under 0.1.

Nominal and Actual Values of Inductor and Capacitor Parameters at High Frequencies

Coil inductance and capacitor capacitance depend on overall dimensions, structure, and ambient factors. They do not vary with frequency. Reactive component impedance is determined by inductance or capacitance respectively, if active resistance is not considered. This is true for the frequencies which are significantly lower than the self-resonant frequency of the component. Parasitic parameters contribution increases on approaching the self-resonant frequency. Therefore, the componentʼs actual inductance and actual capacitance on operating frequency are defined. They are provided by manufacturers and differ from the nominal values. The actual values provide more accurate impedance of components near the considered frequency. Significant deviation from the considered frequency can cause impedance mismatch even more than the nominal values can provide. Frequency response of the high-frequency circuits such as analog filters and impedance match networks are determined by components impedance, not the nominal values. Thus, calculated values must be close to the actual values. The purpose of this article is to justify actual values application instead of nominal values.

Optimization of a single-phase capacitor induction motor by applying a surrogate field-circuit model

Purpose – The purpose of this paper is to present optimization of a single-phase capacitor induction motor with respect to efficiency and starting torque by using surrogate field-circuit model for steady-state. As variables, dimensions of the rotor slots and capacitor capacitance were assumed, whereas outputs were the motor performance characteristics. Searching for a motor design of maximum starting torque or maximum efficiency were objectives of the optimization. To verify design solutions, rated load and locked rotor tests of the optimized motors were performed by computer simulation which confirmed better performance parameters of the optimized motors. Design/methodology/approach – The paper presents optimization procedure of a single-phase capacitor induction motor by applying response surface methodology for surrogate 2D field-circuit model of the motor. For solving the problem a single-objective and bi-objective approach were applied. Findings – The carried out calculations showed that obtained new structures of the capacitor induction motor have better starting properties – the higher ratio of starting to rated torque. It was also obtained the motor construction with higher efficiency and lower stator current at the same time. Originality/value – The main advantage of the formulated optimization procedure was application of the SSO (sequential surrogate optimization) algorithm which exploits a polynomial surrogate model and genetic algorithm to find minimum of the objective functions and also to speed up computations.

Analysis of a single-phase capacitor induction motor operating at two power line frequencies

Analysis of a single-phase capacitor induction motor operating at two power line frequenciesThe paper presents a modelling mathematical tool for prediction of dynamic and steady-states operation of the single-phase capacitor induction motor for different values of the capacitor capacitance and different frequency of voltage supply at no-load and rated load conditions. Developed mathematical model of the capacitor induction motor was implemented for calculation using Matlab/Simulink software. Presented simulation results may be utilized to achieve better starting quality of single-phase capacitor induction motors.