Aleksandrovsky Serhey
@bntu.by
Electricdrive/FITR
RESEARCH, TEACHING, or OTHER INTERESTS
Energy
Scopus Publications
Scopus Publications
B. I. Firago and S. V. Aleksandrovsky
Belarusian National Technical University
Синхронные двигатели с электромагнитным возбуждением и возбуждением от постоянных магнитов используются в различных промышленных установках, включая грузоподъемные машины и механизмы. Однако в большинстве случаев для регулирования скорости двигателей используется зависимое задание частоты питающего двигатель напряжения, т. е. векторное управление. В последнее время появился интерес к использованию частотно-регулируемых синхронных электроприводов с независимым заданием частоты питающего двигатель напряжения (скалярное частотное управление), так как они проще, чем электроприводы с векторным управлением. В то же время по сравнению с частотно-регулируемыми асинхронными электроприводами синхронные имеют меньшие потери мощности, жесткие механические характеристики без обратной связи по скорости, самый простой закон частотного управления – пропорциональный, который, однако, позволяет электродвигателю развивать почти максимальный момент в заданном частотном диапазоне благодаря постоянному магнитному потоку. В статье рассматривается аналитическое исследование переходных процессов электропривода с синхронным двигателем с постоянными магнитами (СДПМ) без демпферной обмотки при линейном изменении частоты питающего двигатель напряжения и линеаризации угловой характеристики. Получены аналитические выражения для угловой скорости и электромагнитного момента СДПМ при пуске, торможении, набросе и сбросе нагрузки. Расчеты угловой скорости и электромагнитного момента СДПМ по этим формулам позволяют оценить качество переходного процесса и определить максимальный электромагнитный момент двигателя, который не должен превышать допустимой величины. Показано, что при постоянном статическом моменте электропривод на основе СДПМ с обычным скалярным частотным управлением имеет незатухающие гармонические колебания скорости, что не позволяет применять его в установках с постоянным статическим моментом. Для устойчивой работы синхронного электропривода в установившемся режиме при постоянном статическом моменте предложен способ скалярного частотного управления электроприводом на основе СДПМ, где применяется отрицательная обратная связь по ускорению ротора. Результаты его расчета сопоставлены с результатами имитационного моделирования с использованием СДПМ фирмы OMRON типа SGMSH-50D мощностью 5 кВт и напряжением 400 В. Сравнение результатов показало эффективность применения предложенного способа управления по демпфированию колебаний СДПМ при постоянном статическом моменте.
B. I. Firago and S. V. Aleksandrovsky
Belarusian National Technical University
In order to improve energy performance and simplify the system of frequency control of the speed of electric drives, the area of application of synchronous frequency-controlled electric drives with both dependent and independent frequency setting of the voltage supplying the engine is being expanded. This is due to the fact that, as compared with asynchronous variable frequency drives, synchronous ones undergo lower power losses and they have rigid mechanical characteristics without speed feedback. Also, the simplest law of frequency control, viz. a proportional one, which, however, provides the maximum electromagnetic torque of the engine unchanged at R1 = 0 at all frequencies due to the constant magnetic flux, is applicable to a synchronous frequency controlled motor. Characteristics and properties of permanent magnet synchronous motors (PMSM) with the dependent frequency setting of supplied voltage (under vector control of PMSM) have been discussed and reviewed in technical literature quite sufficiently. It cannot be said about the PMSM with independent frequency setting reference which work under scalar frequency control. In the present article a comparison of properties and characteristics of vector and scalar frequency controlled PMSM is presented. For a scalar frequency controlled PMSM a function of the relative voltage g on the relative frequency a (g = f(a)) taking into account the PMSM parameters has been defined. The derived function g = f(a) differs from a proportional law of frequency control g = a. It is found that the influence of the parameters on the law of frequency control is small, and it can be applied without adjustment in most cases, in contrast to the frequency control of the asynchronous motor. For scalar frequency control, a method for determining the parameters of synchronous motors has been proposed in accordance with the parameters of synchronous motors with permanent magnets, which are given for operation under vector control. According to the presented methodology the OMRON SGMH-50D engine parameters have been determined for scalar frequency control and the function of g = f(a) have been computed.
B. I. Firago and S. V. Aleksandrovsky
Belarusian National Technical University
The variable speed electrical drives for industrial mechanisms with a constant static torque usually operate in a large range of speeds and loads. Along with this, for any speed of a given range the electrical drive motor is to provide a continuous permissible torque without overheating. Mostly the electrical motors have self-ventilation; the ventilator being located on the motor shaft. In such motors heat dissipation depends on a motor speed. The permissible continuous motor torque is determined out of a heat balance equation where power losses being converted into heat must be transferred in the ambient space and the motor temperature must not be over a permitted level for a given class of winding insulation under the certain ambient temperature. A heat balance equation is usually obtained on a basis of a one-mass motor heat model, i. e. the model that was used in this research. But even the one-mass heat model gives a non-linear heat balance equation. In order to get convenient analytical expressions out of the motor heat balance equation, it is necessary to take some justified assumptions; the latter was also implemented in this research. As a result, formulas have been obtained by which the long-term permissible motor torque can be calculated as a function of the relative speed of the rotor at a given ambient temperature. For the examples presented in the articles we chose (20 and 40 °С as a standard temperature for the thermal calculation of electrical machines). Dependences of a relative permissible continuous motor torque m on a relative frequency value (or relative rotor speed) are presented for three synchronous motors with permanent magnets and rated power of 3; 25 and 250 kW.
B. I. Firago and S. V. Aleksandrovsky
Belarusian National Technical University
As compared to asynchronous frequency-controlled electric drives, synchronous drives are characterized by lower power losses, rigid mechanical characteristics without speed feedback and by the simplest law of frequency control (when the voltage changes proportionally to the frequency). An analytical study of energy factors (power loss, efficiency, power factor) of frequencycontrolled synchronous motor with electromagnetic ignition and with excitation caused by permanent magnets has been fulfilled. The efficiency of the power converter, in this case (i. e. in the case of the frequency converter), depends on the structure of the converter (single-link or two-link), on the power semiconductor devices being used, on additional elements (i. e. chokes, capacitors, transformers, active resistance, etc.). The efficiency of a synchronous electric motor (which is a cofactor of general efficiency of a controlled synchronous electric drive) is of an interest in the scalar frequency control of the mentioned synchronous motor, since there are almost no publications on this subject. Therefore, the energy conversion efficiency of the synchronous motor, which receives energy from the frequency converter at different frequencies and converts to mechanical energy, has been considered. For the convenience of analytical research, we used the widely used concept of relative frequency as the ratio of the current value of the voltage frequency to the nominal one. It is demonstrated that the maximum efficiency is shifted in the direction of a lower load factor with a decrease in the relative frequency of the motor supply voltage. The method of calculating the energy performance of variable frequency synchronous motor that has been developed is illustrated by the graphs of efficiency and cosj for the engine of the SD3 13-34-6 type of the capacity of 500 kW and of a voltage of 6 kV and for a synchronous motor with permanent magnets of the YGT132S4 type of a capacity of 5.5 kW.