Частотный Преобразователь Схема Электрическая Принципиальная

Циркуляркой уже полным ходом пилили на конденсаторах, когда появился необходимый вариант прошивки. Модули содержат шесть силовых ключей и схему управления.

Рядом с микропроцессором показан SWD -разъем P2 интерфейса прошивки микропроцессора и отладки кода с последовательным доступом. Убеждаемся, что привод функционирует.

Они задействованы для измерений напряжений шины постоянного тока, аналогового входа, фазных противо-ЭДС. И с одной парой полюсов и с мя.
Cтруктура и схема преобразователя частоты. Часть 1.

Долгий является также автором цикла статей о микроконтроллерах и многих других конструкций. Три диода и десяток резисторов, подключенных к процессору — хоть и не лучше схемотехническое решение, но решать задачу подхвата ротора или промышленной сети .

Следует отметить, что по современной терминологии подобные генераторы-формирователи называются контроллерами. Первый метод основан на назначении определенной зависимости чередования последовательностей широтно-импульсной модуляции ШИМ инвертора для заранее подготовленных алгоритмов.

Каков принцип частотных методов регулирования?

Также происходит насыщение магнитопровода статора. Конечно можно было бы взять в магазине фирменный частотник, но все-таки вариант самостоятельного изготовления оказался для меня наиболее приемлемым.

Выходное напряжение изменяется с помощью отношения между длительностью открытого и закрытого состояния, причем для получения требуемого напряжения это отношение можно менять. Следует отметить, что по современной терминологии подобные генераторы-формирователи называются контроллерами.

Подключение электродвигателя через частотный преобразователь. Плюсы и минусы

Функциональная схема подключения частотного преобразователя

При ее использовании получается произвести достаточно хорошую синусоидальную ШИМ с возможностью изменять напряжение. Крутим мотор-колесо коляски рукой, нажимаем кнопку «Пуск». Можно делать копии содержимого данной папки в родительской, переименовывать её и одноименные файлы с расширениями ewp, ewd, dep.

Обычный инвертор тока промежуточной цепи изменяющегося напряжения.

Способ ограничения зависит от вида модуляции. А так же функцию обработки прерывания таймера.

А так же функцию обработки прерывания таймера.

Они обеспечивают широкий диапазон регулировки частот, обладают высоким КПД и другими отличными техническими характеристиками. Справа от моста изображены операционные усилители нормирующие сигналы датчиков тока.

Преимуществом управляемых выпрямителей является их способность возвращать энергию в питающую сеть. Имеются три основных варианта задания режимов коммутации в инверторе с управлением посредством широтно-импульсной модуляции.

При этом амплитуда и частота напряжения на выходе преобразователя регулируются по скольжению и нагрузочному току, но без использования обратных связей по скорости вращения ротора.
ПОДКЛЮЧЕНИЕ ЧАСТОТНИКА к однофазному асинхронному двигателю.

Преобразователь частоты

Ответ на главный вопрос жизни, вселенной и бездатчикового электропривода — Чтобы избежать этих негативных последствий, при уменьшении частоты приходится снижать и эффективное значение напряжения на обмотках двигателя.

Функционирование без датчика положения. Таким образом, амплитуда отрицательных и положительных импульсов напряжения всегда соответствует половине напряжения промежуточной цепи. Способ векторов точнее и эффективнее.

Выходные сигналы с элементов DD3. Данные документируются протоколом обмена и используются пользователями, создающими программы управления для электронной техники и контроллеров.

Использование в работе частотника дает возможность работать двигателю без перерыва, экономично. Большая часть экономической эффективности заключается в возможности регулирования при помощи частотного преобразователя технологических характеристик процессов, температуры, давления, скорости движения, скорости подачи главного движения.

Данные параметры также регулируются широтно-импульсной модуляцией, а сама ширина импульсов модулируется по синусоидальному закону. Промежуточная цепь одного из трех типов: a преобразующая напряжение выпрямителя в постоянный ток. Примечание: для большинства приложений использование только пропорциональной и интегральной составляющей без использования дифференциальной составляющей даёт хорошие результаты. Такой вид управления инвертором называется амплитудно-импульсной модуляцией АИМ.

Такие преобразователи используются в мегаваттном диапазоне мощности для формирования низкочастотного питающего напряжения непосредственно из сети частотой 50 Гц, при этом их максимальная выходная частота составляет около 30 Гц. Все это управляется при помощи двух кнопок и одного переключателя, который изменяет направление вращения вала. Резисторы, соединил параллельно по кОм с помощью затворных проходных конденсаторов, позади платы их напаял. А удерживание инициирует дальнейший разгон до 50 Гц в течении приблизительно 2 секунд. SFAVM SFAVM — пространственно-векторный способ модуляции, который позволяет случайным образом, но скачкообразно изменять напряжение, амплитуду и угол инвертора в течение времени коммутации.

В описываемой схеме вполне возможно применить драйверы IR или IR В каждом из проектов имеются 7 файлов: mckits.

Механические устройства не могут выполнить такие функции. Также происходит насыщение магнитопровода статора. Моторы переделывают электроэнергию в механическое движение. Катушка индуктивности преобразует изменяющееся напряжение выпрямителя в изменяющийся постоянный ток.
Самодельный частотный преобразователь 220-380V собственной сборки

Схема прямого матричного преобразователя Непрямой матричный преобразователь indirect matrix converter состоит из двунаправленного трехфазного выпрямителя, виртуального звена постоянного тока и трехфазного инвертора.

Диоды позволяют току протекать только в одном направлении: от анода А к катоду К. И они творят революцию — успешно перевели на веб-платформу комплекс программных средств для разработки электрических принципиальных схем и печатных плат.

Состоит из выпрямителя и фильтрационных устройств.

Эти значения времени коммутации должны устанавливаться таким образом, чтобы допускать только минимум высших гармоник. Печатная плата комплекта разработчика устройств управления электродвигателями Есть особенность, которую должен учитывать разработчик устройств управления электродвигателями. В наше время существует несколько компоновок инверторов с управляемыми ключами: запираемые GTO тиристоры; биполярные IGBT-транзисторные ключи с затвором.

Выходное напряжение является результатом комбинации сегментов входного напряжения в котором основная гармоника следует за опорным сигналом. Транзистор-прерыватель управляет напряжением промежуточной цепи Фильтр промежуточной цепи сглаживает прямоугольное напряжение после прерывателя. Три проекта написаны так, чтобы в режиме сравнения файлов по содержимому однозначно идентифицировалось все, что с ней связано параметры, межблочные связи, расчетный код.

В состав преобразователей частоты входят четыре основных элемента: Рис. Нажимаем кнопку Event в окне программы. Аварийные ситуации при этом сводятся на нет.

Электрическая принципиальная схема частотного преобразователя

Частота задается конденсатором C1, регулировка частоты осуществляется переменным резистором R2. Проекты пошаговой разработки программного кода цифровой системы управления В дополнение к аппаратной части, инженеру предоставлен комплект проектов для пошаговой разработки программного кода векторной системы управления.

Задача перевода объекта из одного состояния в другое решается «программной машиной состояний». Расчёт производится по значению ошибки управления — расхождению между заданным значением и значением сигнала обратной связи обычно показания датчика какого-либо технологического параметра. Электрическая принципиальная схема комплекта разработчика устройств управления электродвигателями В нижней части схемы изображены импульсный преобразователь напряжения и линейные стабилизаторы, питающие фрагменты схемы. Основным различием способов являются критерии, которые используются при вычислении значений активного тока, тока намагничивания магнитного потока и крутящего момента.
Частотник для регулирования оборотов трёхфазного двигателя

90000 Understanding Scalar (V / f) Control for Induction Motors 90001 90002 In this article we will try to understand how scalar control algorithm is implemented for controlling induction motor speed with relatively straightforward calculations, and yet achieve a reasonably good linearly variable speed control of the motor. 90003 90002 Reports from many top market analysis reveal that induction motors are the most popular when it comes to handling heavy industrial motor related applications and jobs.The main reasons behind the popularity of induction motors are basically due to its high degree of robustness, greater reliability in terms of wear and tear issues, and comparatively high functional efficiency. 90003 90002 That said, induction motors have one typical downside, as these are not easy to control with ordinary conventional methods. Controlling induction motors is relatively demanding owing to its rather complex mathematical configuration, which primarily includes: 90003 90008 90009 Non-linear response at core saturation 90010 90009 Instability in the form oscillations due to varying temperature of the winding.90010 90013 90002 Due to these critical aspects implementing induction motor control optimally demands a thoroughly calculated algorithm with high reliability, for example using a «vector control» method, and additionally using a microcontroller based processing system. 90003 90016 Understanding Scalar Control Implementation 90017 90002 However there exists another method that can be applied for implementing induction motor control using a much easier configuration, it is the scalar control incorporating non-vector drive techniques.90003 90002 It is actually possible to enable an AC induction motor into a steady state by operating it with a straightforward voltage feedback and current controlled systems. 90003 90002 In this scalar method, the scalar variable may be tweaked once its right value is achieved either by experimenting practically or through suitable formulas and calculations. 90003 90002 Next, this measurement can be used for implementing motor control via an open loop circuit or through a closed feedback loop topology.90003 90002 Even though the scalar method of control promises a reasonably good steady-state results on the motor, its transient response may not be up to the mark. 90003 90016 How Induction Motors Work 90017 90002 The word «induction» in induction motors refers to the unique way of its operation in which magnetizing the rotor by the stator winding becomes a crucial aspect of the operation. 90003 90002 When AC is applied across the stator winding, the oscillating magnetic field from the stator winding interacts with the rotor armature creating a new magnetic field on the rotor, which in turn reacts with the stator magnetic field inducing a high amount of rotational torque on the rotor.This rotational torque renders the required effective mechanical output to the machine. 90003 90034 What is 3-Phase Squirrel Cage Induction Motor 90035 90002 It is the most popular variant of induction motors and is extensively used in industrial applications. In a squirrel cage induction motor, the rotor carries a series of bar like conductors surrounding the axis of the rotor presenting a unique cage like structure and hence the name «squirrel cage». 90003 90002 These bars which are skewed in shape and running all around rotor axis are attached with thick and sturdy metal rings at the ends of the bars.These metal rings not only help to secure the bars strongly in place but also enforce an essential electrical short circuiting across the bars. 90003 90002 When the stator winding is applied with a sequencing 3-phase sinusoidal alternating current, the resulting magnetic field also begins moving with the same speed as the 3 phase stator sine frequency (ωs). 90003 90002 Since the squirrel cage rotor assembly is held within the stator winding, the above alternating 3 phase magnetic field from the stator winding reacts with the rotor assembly inducing an equivalent magnetic field on the bar conductors of the cage assembly.90003 90002 This forces a secondary magnetic field to build up around the rotor bars, and consequently this new magnetic field is forced to interact with the stator field, enforcing a rotational torque on the rotor which tries to follow the direction of the stator magnetic field. 90003 90002 In the process the rotor speed tries to attain the stator’s frequency speed, and as it approaches the stator synchronous magnetic field speed, the relative speed difference e between the stator frequency speed and the rotor rotational speed begins decreasing, which causes a decrease in the magnetic interaction of the rotor’s magnetic field over the stator’s magnetic field, eventually decreasing the torque on the rotor, and the equivalent power output of the rotor.90003 90002 This leads to a minimum power on the rotor and at this speed the rotor is said to have acquired a steady-state, where the load on the rotor is equivalent and matching the torque on the rotor. 90003 90002 The working of an induction motor in response to a load may be summarized as explained below: 90003 90002 Since it becomes mandatory to maintain a fine difference between the rotor (shaft) speed and the inner stator frequency speed, the rotor speed which actually handles the load, rotates at a slightly reduced speed than the stator frequency speed.Conversely, if we suppose the stator is applied with 50Hz 3 phase supply, then the angular speed of the this 50Hz frequency across the stator winding will be always slightly higher than the response in the rotor’s rotational speed, this is inherently maintained to ensure an optimal power on the rotor. 90003 90034 What is Slip in Induction Motor 90035 90002 The relative difference between the stator’s angular speed of frequency and the rotor’s responsive rotational speed is termed as the «slip».The slip needs to be present even in situations where the motor is operated with a field-oriented strategy. 90003 90002 Since the rotor shaft in induction motors does not depend on any external excitation for its rotation, it can work without conventional slip rings or brushes ensuring virtually zero wear and tear, high efficiency and yet inexpensive with its maintenance. 90003 90002 The torque factor in these motors is determined by the angle established between the magnetic fluxes of stator and the rotor.90003 90002 Looking at the diagram below, we can see that the speed of rotor is assigned as Ω, and the frequencies across stator and the rotor are determined by the parameter «s» or the slip, presented with the formula: 90003 90002 90065 s = (90066 ω 90067 90066 s 90067 90066 — 90067 90066 ω 90067 90066 r 90067) / 90066 ω 90067 90066 s 90067 90080 90003 90002 In the above expression, s is the «slip» which exhibits the difference between the stator’s synchronous frequency speed and the actual motor speed developed on the rotor shaft.90003 90034 Understanding the Scalar Speed ​​Control Theory 90035 90002 In induction motor control concepts where V / Hz technique is employed, the speed control is implemented by adjusting the stator voltage with respect to frequency such that the air gap flux is never able to deviate beyond the expected range of the steady-state, in other words it is maintained within this estimated steady-state value, and hence it is also called the 90065 scalar control 90080 method since the technique heavily depends on the steady-state dynamics for controlling the motor speed .90003 90002 We can understand the working of this concept by referring to the following figure, which shows the simplified scheme of a scalar control technique. In the set up it is assumed that stator resistance (Rs) is zero, while the stator leakage Inductance (LIs) impressed upon the rotor leakage and magnetizing inductance (LIr). The (LIr) which actually depicts the magnitude of the air gap flux can be seen to have been pushed prior to the total leakage inductance (Ll = Lls + Llr). 90003 90002 Due to this, the air gap flux created by the magnetizing current gets an approximate value close to the stator’s frequency ratio.Thus the phasor expression for a steady-state assessment can be written as follows: 90003 90002 For Induction motors which may be running at their linear magnetic regions, the Lm will not change and remain constant, in such cases the above equation may be expressed as : 90003 90002 Where V and Λ are the stator voltage values ​​and stator flux respectively, whereas Ṽ represents the phasor parameter in the design. 90003 90002 The last expression above clearly explains that as long as the V / f ratio is held constant regardless of any change in the input frequency (f), then the flux also remains constant, which enables the toque to operate without depending on the supply voltage frequency.That implies if ΛM is maintained at a constant level, the Vs / ƒ ratio would also be rendered at a constant relevant speed. Therefore whenever the speed of the motor is increased, the voltage across the stator winding will also need to be proportionately increased, so that a constant Vs / f could be maintained. 90003 90002 However here the slip being the function of the load attached to the motor, the synchronous frequency speed does not depict the real speed of the motor. 90003 90002 In an absence of a load torque on the rotor, the resultant slip may be negligibly small, allowing the motor to attain close to synchronous speeds.90003 90002 That is why a basic Vs / f or a V / Hz configuration usually may not have the capability of implementing accurate speed control of an induction motor when the motor is attached with a load torque. However a slip compensation may be quite easily be introduced in the system along with speed measurement. 90003.90000 Single Phase Variable Frequency Drive VFD Circuit 90001 90002 The post discusses a single phase variable frequency drive circuit or a VFD circuit for controlling AC motor sped without affecting their operational specifications. 90003 90004 What is a VFD 90005 90002 Motors and other similar inductive loads specifically do not «like» operating with frequencies that might be not within their manufacturing specs, and tend to become a lot inefficient if forced to under such abnormal conditions.90003 90002 For example a motor specified for operating with 60Hz may not be recommended to work with frequencies of 50 Hz or other ranges. 90003 90002 Doing so can produce undesirable results such as heating up of the motor, lower or higher than the required speeds and abnormally high consumption making things very inefficient and lower life degradation of the connected device. 90003 90002 However operating motors under different input frequency conditions often becomes a compulsion and under such situations a VFD or a variable frequency Drive circuit can become very handy.90003 90002 A VFD is a device which allows the user to control the speed of an AC motor by adjusting the frequency and voltage of the input supply as per the motor specifications. 90003 90002 This also means that a VFD allows us to operate any AC motor through any available grid AC supply regardless of its voltage and frequency specs, by suitably customizing the VFD frequency and voltage as per the motor specifications. 90003 90002 This is normally done using the given control in the form of a variable knob scaled with different frequency calibration.90003 90002 Making a VFD at home may sound to be a difficult proposition, however a look at the design suggested below shows that after all it’s not so difficult to build this very useful device (designed by me). 90003 90022 90023 Circuit Operation 90024 90025 90002 The circuit can be fundamentally divided into two stages: The half brige driver stage and the PWM logic generator stage. 90003 90002 The half bridge driver stage uses the half bridge driver IC IR2110 which single handedly takes care of the high voltage motor drive stage incorporating two high side and low side mosfets respectively.90003 90002 The driver IC thus forms the heart of the circuit yet require just a few components for implementing this crucial function. 90003 90002 The above IC however would need a high logic and a low logic in frequencies for driving the connected load at the desired specific frequency. 90003 90002 These hi and lo input logic signals become the operating data for the driver IC and must include signals for determine the specified frequency as well as PWMs in phase with the mains AC. 90003 90002 The above info are created by another stage comprising a couple of 555 ICs and a decade counter.IC 4017. 90003 90002 The two 555 ICs are responsible for generating the modified sine wave PWMs corresponding to the full wave AC sample derived from a stepped down bridge rectifier output. 90003 90002 The IC4017 functions as a totem pole output logic generator whose alternating frequency rate becomes the MAIN frequency determine parameter of the circuit. 90003 90002 This determining frequency is plucked from pin # 3 of IC1which also feeds the IC2 triggering pin out and for creating the modified PWMs at pin # 3 of IC2.90003 90002 The modified sine wave PWMs are scanned at the outputs of the 4017 IC before feeding the IR2110 in order to superimpose exact «print» of the modified PWMs at the output of the half bridge driver and ultimately for the motor which is being operated. 90003 90002 Cx and the 180k pot values ​​should be appropriately selected or adjusted in order to provide the correct specified frequency for the motor. 90003 90002 The high voltage at the drain of the high side mosfet must also be calculated appropriately and derived by rectifying the available mains voltage AC after suitably stepping it up or stepping it down as per the motor specs.90003 90002 The above settings will determine the correct volts per Hertz (V / Hz) for the particular motor. 90003 90002 The supply voltage for both the stages can be made into a common line, same for the ground connection. 90003 90002 TR1 is a stepped down 0-12V / 100mA transformer which provides the circuits with the required operating supply voltages. 90003 90022 The PWM Controller Circuit 90025 90002 You will have to integrate the outputs from the IC 4017 from the above diagram to the HIN and LIN inputs of the following diagram, appropriately.Also, connect the indicated 1N4148 diodes in the above diagram with the low side MOSFET gates as shown in the below diagram. 90003 90022 The Full Bridge Motor Driver 90025 90002 90063 Update: 90064 90003 90002 The above discussed simple single VFD design can be further simplified and improved by using a self oscillatory full bridge IC IRS2453, as shown below: 90003 90002 Here the IC 4017 is completely eliminated since the ful bridge driver is equipped with its own oscillator stage, and therefore no external triggering is required for this IC.90003 90002 Being a full bridge design the output control to the motor has a full range of zero to maximum speed adjustment. 90003 90002 The pot at pin # 5 of IC 2 can be used for controlling the speed and the torque of the motor through PWM method. 90003 90002 For V / Hz speed control the Rt / Ct associated with the IRS2453 and R1 associated with IC1 can be respectively tweaked (manually) for getting appropriate results. 90003 90022 Simplifying Even More 90025 90002 If you find the full bridge section overwhelming, you can replace it with a P, N-MOSFET based full bridge circuit as shown below.This variable frequency driver uses the same concept except the full-bridge driver section which employs P-channel MOSFETs at the high side and N-channel MOSFETS on the low side. 90003 90002 Although the configuration may look inefficient due to the involvement of P-channel MOSFETs (due to their high RDSon rating), the use of many parallel P-MOSFETs might look like an effective approach for solving the low RDSon issue. 90003 90002 Here 3 MOSFETs are used in parallel for the P-channel devices to ensure minimized heating of the devices, on par with the N-channel counterparts.90003 90084 About Swagatam 90085 90002 I am an electronic engineer (dipIETE), hobbyist, inventor, schematic / PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. 90087 If you have any circuit related query, you may interact through comments, I’ll be most happy to help! 90003.90000 Introduction to Variable Frequency Drive Controller for Induction Motor 90001 90002 Introduction 90003 90004 Single-phase induction motors are extensively used in appliances and industrial controls. The Permanent Split Capacitor (PSC) single-phase induction motor is the simplest and most widely used motor of this type. 90005 90004 By design, PSC motors are unidirectional, which means they are designed to rotate in one direction. By adding either extra windings, and external relays and switches, or by using gear mechanisms, the direction of rotation can be changed.In this idea, we will discuss in detail, how to control the speed of a PSC motor in both directions using a PIC16F72 microcontroller and power electronics. 90005 90004 The PIC16F72 microcontroller was chosen because it is one of the simplest and low-cost general-purpose microcontrollers Microchip has in its portfolio. Even though it does not have the PWMs in hardware to drive complementary PWM outputs with dead-band inserted, all PWMs are generated in firmware using timers and output to general-purpose output pins.90005 90002 What is Variable Frequency Drive? 90003 90004 Variable Frequency Drive or VFD is the way that enables controlling of the speed of induction motor by applying varying frequency of AC supply voltage. By controlling the output AC frequency, it is possible to drive the motor at different speeds based on the requirements. These are adjustable speed drive largely used in industrial applications such as pumps, ventilation systems, elevators, machine tool drives, etc It is essentially an energy-saving system.Therefore the first requirement is to generate a sine wave with different frequencies for VFD. 90005 90002 What is the technology adopted in VFD? 90003 90004 It is the system that gives AC output with varying frequency to control the speed of the motor according to the needs. Single Phase Variable Frequency Inverters are more common since most devices are working in Single-phase AC supply. It consists of a full-wave bridge rectifier to convert 230/110 Volt AC to approximately 300/150 volt DC.The output DC from the bridge rectifier is smoothed by a high-value smoothing capacitor to remove the ripples of AC. This fixed voltage DC is then fed to the frequency generating circuit formed of MOSFET (Metal oxide field effect transistor) / IGBT (Isolated Gate Bipolar Transistor) transistors. This MOSFET / IGBT circuit receives the DC and converts it into AC with variable frequency to control the speed of the device. 90005 90004 The frequency change can be achieved using electronic circuits or Microcontroller.This circuit varies the frequency of voltage (PWM) applied to the gate drive of the MOSFET / IGBT circuit. Thus AC voltage of varying frequency appears at the output. The Microcontroller can be programmed to change the frequency of the output according to the needs. 90005 90020 90020 90022 90002 The VFD System: 90003 90004 The Variable Frequency Device has three parts like an AC motor, a Controller, and an Operating interface. 90005 90004 The AC motor used in VFD is generally a three-phase induction motor even though the single-phase motor is used in some systems.Motors that are designed for fixed-speed operation is generally used, but some motor designs offer better performance in VFD than the standard design. 90005 90004 The Controller part is the solid electronic power converter circuit to convert AC to DC and then to quasi sine wave AC. The first part is the AC to DC converter section having a full-wave rectifier bridge usually a three phases / single phase full wave bridge. This DC intermediate is then converted into quasi sine wave AC using the inverter switching circuit.Here MOSFET / IGBT transistors are used for inverting DC to AC. 90005 90004 The inverter section converts DC to three channels of AC to drive the three-phase motor. The Controller section can also be designed to give improved power factor, less harmonic distortion and low sensitivity to input AC transients. 90005 90002 Volts / Hz controlling: 90003 90004 The controller circuit regulates the frequency of the supplied AC to the motor through the volts per hertz control method. AC motor requires variable applied voltage when the frequency changes to give the specified torque.For example, if the motor is designed to work in 440 volts at 50Hz, then the AC applied to the motor must be reduced to half (220 volts) when the frequency changes to half (25Hz). This regulation is based on the Volts / Hz. In the above case, the ratio is 440/50 = 8.8 V / Hz. 90005 90002 90038 90038 Other voltage controlling methods: 90003 90004 Besides Volts / Hz controlling, more advanced methods like Direct Torque Control or DTC, Space Vector Pulse Width Modulation (SVPWM), etc are also used to control the speed of the motor.By controlling the voltage in the motor, the magnetic flux and torque can be controlled precisely. In the PWM method, the inverter switches produce a quasi sine wave through a series of narrow pulses with Pseudo sinusoidal varying pulse durations. 90005 90002 Operating Interface: 90003 90004 This section allows the user to start / stop the motor and to adjust the speed. Other facilities include motor reversing, switching between manual and automatic speed control, etc. The operating interface consists of a panel with display or indicators and meters for showing the speed of the motor, applied voltage, etc.A set of keypad switches are generally provided for controlling the system. 90005 90002 Inbuilt -Soft Start: 90003 90004 In an ordinary induction motor, switched on using an AC switch, the current drawn is much higher than the rated value and can increase with the increased acceleration of the load to attain the full speed of the motor . 90005 90004 On the other hand in a VFD controlled motor, initially low voltage at low frequency is applied. This frequency and voltage increase at a controlled rate to accelerate the load.This develops almost more torque than the rated value of the motor. 90005 90002 VFD Motor Commutation 90054: 90055 90003 90004 The frequency and applied voltage are first reduced to a controlled level and then kept on decreasing until it becomes zero and the motor shuts down. 90005 90059 Application Circuit to control the speed of Single Phase Induction Motor 90060 90004 The approach is relatively easy as far as the power circuit and control circuit are concerned. On the input side, voltage doublers are used and on the output side an H-bridge, or 2-phase inverter, is used as shown in Figure 2.One end of the main and start windings are connected to each half-bridge and the other ends are connected to the neutral point of the AC power supply. 90005 90004 The control circuit requires four PWMs with two complementary pairs with a sufficient dead band between the complementary outputs. The PWM dead bands are PWM0-PWM1 and PWM2-PWM3. The PIC16F72 does not have PWMs designed in the hardware to output the way we need. Concerning VF, the dc bus is synthesized by varying the frequency and amplitude.This will give two sine voltages out of phase. 90005 90004 If the voltage applied to the main winding lags the start winding by 90 degrees, the motor runs in one (i.e., forward) direction. If we want to change the direction of the rotation then the voltage applied to the main winding is to conduct the start winding. 90005 90004 I hope you have got an idea about the variable frequency drive for the induction motor from the above article. so if you have any queries on this concept or the electrical and electronic project please leave the comments section below.90005 90004 90070 90070 90005.90000 Changing an Induction Motor’s Power Supply Frequency Between 50 and 60Hz> ENGINEERING.com 90001 90002 Induction motors, both single and polyphase, are designed for use with a particular frequency of AC power. Occasionally we’re confronted with a ‘wrong’ frequency motor. In this article I’ll help you understand the ramifications. 90003 90002 There are a large number of interacting relationships in a motor’s design. There are first order, second order and probably even third order aspects that are all balanced to produce a dependable motor with the desired characteristics.90003 90002 I’ll be discussing only the First Order aspects. 90003 90002 1) 90009 Rotational speed is a direct function of the power frequency. 90010 Very simply, if you 90011 90009 drop the frequency, the motor will slow down 90010 90014. Conversely, if you 90009 90011 raise the frequency, the motor will speed up. 90014 90010 The speed change that results will be proportional to the frequency change. 90003 90002 2) 90009 Cooling is a direct function of rotational speed.90010 The motor’s fan is attached to the motor’s spinning rotor so it will experience the same speed-up or slow down the motor does. If the motor slows down, its cooling will drop (and at a faster rate than the slow down). If the motor speeds up its cooling will increase rapidly. 90003 90002 3) 90009 The magnetic capacity of the motor’s magnetic (iron) circuit is designed to the relationship: voltage / frequency (V / f). 90010 If the frequency drops the V / Hz goes up. This means that the motor needs a larger magnetic circuit.Without it, the magnetic circuit can be overloaded. This is called saturation and it leads to a rapid increase in current draw and a corresponding large increase in temperature, a motor’s chief enemy. 90003 90002 If the frequency increases, the V / Hz drops with no issues since the magnetic circuit will remain plenty large enough. [Sneaking in a second order consideration here, the motor may have a worse power factor.] 90003 90002 With the above aspects in mind let’s explore what it all means when applied to that unfortunate motor you have in your machine.90003 90002 90003 90002 90009 If the motor is a 50Hz unit and you’re going to be using it in 60Hz-land it will spin 20% faster. 90010 90037 Horsepower (hp) is proportional to Torque times RPM. Since the motor’s torque is not going to change appreciably with an increase in frequency it will now provide 20% more hp. Your 8hp motor just got promoted to being a 10hp motor. Something for almost nothing! 90003 90002 But wait! Spinning a load 20% faster is very likely going to increase its power demand by at least 20%! If the load cyclically accelerates or decelerates in operation it will be subject to greater mechanical forces.Too much? If the motor is driving centrifugal loads their demand may even go up by the square of the speed increase. Centrifugal pumps would be an example of this. Fans, depending on their style, can also experience a squared increase in demand. 90003 90002 A bright spot in this is that the motor’s cooling fan is a centrifugal fan that will move much more air. 90003 90002 The motor’s V / Hz goes down when up-frequencying a motor, informing us that the magnetic circuit will have no trouble carrying the increased load.We’re good there. 90003 90002 90003 90002 90009 If the motor is a 60Hz unit and you’re going to be using it in 50Hz-land it will spin 20% s-l — o — w —- e —— r. 90037 90010 This also translates to 20% less horsepower. On the bright side, turning the load slower usually means it will be demanding less power. That’s good, because the motor was just demoted 20% of its hp too. All that and the cooling fan is providing less too. But the 800 pound gorilla here is the V / Hz ratio.It just went up 20%! Not good. This means that during parts of every power line cycle the magnetic structure of the motor will probably be overloaded. 90003 90002 When this happens the motor’s ability to limit current via reactance is lost. This will cause excessive current to flow heating the motor via I squared R losses. The only recourse here is to correct the V / Hz with the variable that is reasonably easy to adjust — V the voltage. Lower the voltage with a transformer to correct the V / Hz ratio.I’ll discuss that in moment. 90003 90002 Back to the load. Will it still do the job at the lower speed? A pump may no longer have the head needed to accomplish its task. A machine’s throughput will likely drop 20%. Will you still process enough product in a given time? 90003 90002 90003 90002 90009 Example — You have 60Hz power for a 50Hz machine. 90010 90037 Let’s say you just got a great deal on a machine. As it’s being wired up you realized that it has 50Hz on its nameplate and you have 60Hz power.STOP. 90003 90002 The machine will be running 20% ​​faster! Is this going to be a problem? If it is, can the speed be returned to design speed by changing a pulley size to drop the speed 20% back to where it was? 90003 90002 Once this assessment has been done and sheaves are changed or other modifications are done to help mitigate the speed / power issues, move on to the next step. Read the nameplate to get the Full Load Amperage commonly known as the FLA rating for the motor at the voltage you’ll be running it with.90003 90002 Using a clamp-on ammeter, run the machine and check to see the amperage is below the FLA. If it is you can proceed with running the machine as desired. Do check to see that it’s still under FLA when fully loaded. 90009 If it’s over FLA you must do some sort of load mitigation. 90010 90003 90002 90003 90002 90009 Example — You have 50Hz power for a 60Hz machine. 90010 90037 You receive a machine and since you are in 50Hz land, the 60Hz label is bothering you.As well it should! 90003 90002 Again, realizing the machine will run 20% slower, will it get the job done? In this case you can not change pulley sizes to correct the speed because the motor just lost 20% of its horsepower nameplate rating. If you change pulleys it will likely be overloaded — seriously. 90003 90002 If the machine can run 20% slower there may still be hope. Even though it is going to lose cooling with its internal fan running more slowly, running the load slower and with a 20% less powerful motor will likely even out.The V / Hz increase may still get you. 90003 90002 At this point if your assessment shows you will probably be alright with the slower speed, again check the nameplate for the FLA. Run the machine and 90009 90011 quickly 90014 check the running current with an ammeter 90010. If it’s below FLA proceed to load the machine while closely monitoring things. If you stay below FLA it will probably be OK. 90003 90002 But! Running at FLA now that the cooling fan has reduced ability is still possibly going to be a problem.You should monitor the motor’s temperature and assure yourself that after extended running time, under load, it remains below the nameplate temperature rise. 90003 90002 If even unloaded you’re seeing FLA or more you will need to reduce the voltage because the motor is probably saturating. Before going to the bother of adding buck transformers, seriously consider changing out the motor for the correct 50Hz version. Remember you may need to up the rated horsepower if you’re going to change gear ratios to return the machine back to its original speed.90003 90002 90003 90002 90009 But wait! What about single phase motors? 90010 90037 A last issue that must be faced is single phase motors. Everything described above applies to them but there’s a couple of added flies-in-the-ointment. Single phase motors have a start winding. Since single phase power has no inherent rotational component, as three phase does, a start winding provides the needed large torque to get the motor spinning. The start winding is a very large load and as such can usually only operate for a few seconds.More than a few seconds and smoke will start issuing forth. 90003 90002 A centrifugal switch is usually included on the rotor to control the power to the start winding. It remains closed so when power is applied to the motor, both windings, the run and the start, are both energized. As the motor quickly reaches speed, the centrifugal aspect of the switch opens the start winding, disconnecting it from further operation. 90003 90002 When a 50Hz single phase motor is brought to 60Hz the start function can be upset because the motor reaches the centrifugal switch speed 20% earlier than normal.When it does, the starting torque of the motor is suddenly reduced. It could fail to speed up further and never reach normal running speed. If that happens, smoke is on the way! 90003 90002 Conversely when a 60Hz single phase motor is brought down frequency the switch could well not ever reach opening speed. Given that the switch opening speed setpoint is usually set at around 80% of running speed, you can see the potential for a problem. Remember the motor is going to turn 20% slower.If it does not reach switch speed, smoke is definitely on the way! You’ll be seeing it momentarily. 90003 90002 Single phase motors can often have two kinds of capacitors associated with them. The first is a run capacitor. The run capacitor increases the motor’s regular running torque. The second, is a starting capacitor used to increase the starting torque. When the supply frequency is raised these capacitors increase their effects resulting in more torque. Usually this is not a problem.But if you’re lowering the frequency, they lose their effects and starting and / or running torques are reduced. That can be a problem. However, if the load is being spun more slowly it may balance out. 90003 90002 Since single phase motors are usually smaller it’s often more effective to just replace them. 90003 90002 So. Now you know why you got such a ‘great deal’ on your machine buy. 90003 90002 90003 90002 90009 About the Author 90010 90037 Keith Cress is a ‘broad spectrum’ consultant that finds himself involved in everything from embedded controller designs to passenger rail car power systems.Keith can be reached at 90009 [email protected] 90010 90003 90002 Keith is a member of the Engineering Writers Guild at 90009 www.eng-tips.com 90010. He is also an MVP. Follow Keith (itsmoked) at 90009 http://www.eng-tips.com/userinfo.cfm?member=itsmoked 90010 90003 .

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