Adjusting engine speed while maintaining power. Speed ​​control of asynchronous motor

A high-quality and reliable rotation speed controller for single-phase commutator electric motors can be made using common parts in literally 1 evening. This circuit has a built-in overload detection module, provides a soft start of the controlled motor and a motor rotation speed stabilizer. This unit operates with voltages of both 220 and 110 volts.

Regulator technical parameters

• Supply voltage: 230 volts AC
• regulation range: 5…99%
• load voltage: 230 V / 12 A (2.5 kW with radiator)
• maximum power without radiator 300 W
• low noise level
• speed stabilization
• soft start
• board dimensions: 50×60 mm

Schematic diagram

The control system module circuit is based on a PWM pulse generator and a motor control triac - a classic circuit design for such devices. Elements D1 and R1 ensure that the supply voltage is limited to a value that is safe for powering the generator microcircuit. Capacitor C1 is responsible for filtering the supply voltage. Elements R3, R5 and P1 are a voltage divider with the ability to regulate it, which is used to set the amount of power supplied to the load. Thanks to the use of resistor R2, which is directly included in the input circuit to the m/s phase, the internal units are synchronized with the VT139 triac.

The following figure shows the arrangement of elements on a printed circuit board. During installation and startup, attention should be paid to ensuring safe operating conditions - the regulator is powered by a 220V network and its elements are directly connected to the phase.

Increasing regulator power

In the test version, a BT138/800 triac with a maximum current of 12 A was used, which makes it possible to control a load of more than 2 kW. If you need to control even larger load currents, we recommend installing the thyristor outside the board on a large heatsink. You should also remember to select the correct FUSE fuse depending on the load.

In addition to controlling the speed of electric motors, you can use the circuit to adjust the brightness of lamps without any modifications.

Commutator motors can often be found in household electrical appliances and power tools: washing machine, grinder, drill, vacuum cleaner, etc. Which is not at all surprising, because commutator motors allow you to obtain high speeds and high torque (including high starting torque ) - which is what you need for most power tools.

In this case, commutator motors can be powered by both direct current (in particular, rectified current) and alternating current from a household network. To control the rotor speed of a commutator motor, speed controllers are used, which will be discussed in this article.

First, let's remember the design and principle of operation of a commutator motor. The commutator motor necessarily includes the following parts: rotor, stator and brush-collector switching unit. When power is applied to the stator and rotor, their magnetic fields begin to interact and the rotor eventually begins to rotate.

Power is supplied to the rotor through graphite brushes that fit tightly to the commutator (to the commutator lamellas). To change the direction of rotation of the rotor, it is necessary to change the phasing of the voltage on the stator or on the rotor.

The rotor and stator windings can be powered from different sources or can be connected in parallel or in series with each other. This is how commutator motors of parallel and series excitation differ. It is the series-excited commutator motors that can be found in most household electrical appliances, since such inclusion makes it possible to obtain a motor that is resistant to overloads.

Speaking about speed controllers, first of all we will focus on the simplest thyristor (triac) circuit (see below). This solution is used in vacuum cleaners, washing machines, grinders, and shows high reliability when operating in alternating current circuits (especially from a household network).

This circuit works quite simply: at each period of the mains voltage, it is charged through a resistor to the unlocking voltage of the dinistor connected to the control electrode of the main switch (triac), after which it opens and passes current to the load (to the commutator motor).

By adjusting the charging time of the capacitor in the triac opening control circuit, the average power supplied to the engine is regulated, and the speed is adjusted accordingly. This is the simplest regulator without current feedback.

The triac circuit is similar to a regular one; there is no feedback in it. To provide current feedback, for example to maintain acceptable power and avoid overloads, additional electronics are required. But if we consider the options from simple and straightforward circuits, then the triac circuit is followed by a rheostatic circuit.

The rheostat circuit allows you to effectively regulate speed, but leads to the dissipation of a large amount of heat. This requires a radiator and effective heat removal, which means energy loss and low efficiency as a result.

Regulator circuits based on special thyristor control circuits or at least on an integrated timer are more effective. Switching of the load (commutator motor) on alternating current is carried out by a power transistor (or thyristor), which opens and closes one or more times during each period of the network sinusoid. This regulates the average power supplied to the engine.

The control circuit is powered by 12 volts DC from its own source or from a 220 volt network through a quenching circuit. Such circuits are suitable for controlling powerful motors.

The principle of regulation with DC microcircuits is of course. A transistor, for example, opens with a strictly specified frequency of several kilohertz, but the duration of the open state is regulated. So, by rotating the handle of the variable resistor, the rotation speed of the rotor of the commutator motor is set. This method is convenient for maintaining low speeds of a commutator motor under load.

Better control is direct current regulation. When PWM operates at a frequency of about 15 kHz, adjusting the pulse width controls the voltage at approximately the same current. Let's say, by adjusting the constant voltage in the range from 10 to 30 volts, they get different speeds at a current of about 80 amperes, achieving the required average power.

If you want to make a simple regulator for a commutator motor with your own hands without any special requests for feedback, then you can choose a thyristor circuit. All you need is a soldering iron, a capacitor, a dinistor, a thyristor, a pair of resistors and wires.

If you need a higher-quality regulator with the ability to maintain stable speeds under dynamic loads, take a closer look at regulators on microcircuits with feedback that can process the signal from the tachogenerator (speed sensor) of a commutator motor, as is implemented, for example, in washing machines.

Andrey Povny

24.02.2016

Allows you to control engines without losing power. A prerequisite for this is the presence of a tachometer (tachogenerator) on the electric motor, which allows you to provide feedback from the motor to the control board, namely the microcircuit. To put it in simpler terms, so that everyone can understand, something like this happens. The motor rotates at a certain number of revolutions, and a tachometer installed on the electric motor shaft records these readings. If you start to load the engine, the shaft speed will naturally begin to drop, which will also be recorded by the tachometer. Now let's look further. The signal from this tachometer goes to the microcircuit, it sees this and gives a command to the power elements to add voltage to the electric motor. Thus, when you pressed the shaft (apply a load), the board automatically added voltage and the power on this shaft increased. And vice versa, let go of the motor shaft (the load was removed from it), she saw this and reduced the voltage. Thus, the speed does not remain low, but the moment of force (torque) remains constant. And most importantly, you can adjust the rotor speed over a wide range, which is very convenient in the use and design of various devices. Therefore, this product is called “Board for adjusting the speed of commutator motors without loss of power.”

But we saw one feature: this board is only applicable for commutator motors (with electric brushes). Of course, such motors are much less common in everyday life than asynchronous ones. But they have found wide application in automatic washing machines. This is exactly why this circuit was made. Especially for the electric motor from an automatic washing machine. Their power is quite decent, from 200 to 800 watts. This allows them to be widely used in everyday life.

This product has already found wide application in people's households and has widely covered people engaged in various hobbies and professional activities.

Answering the question - Where can I use the motor from a washing machine? A list has been compiled. Homemade wood lathe; Grinder; Electric drive for concrete mixer; Sharpener; Electric drive for honey extractor; Straw cutter; Homemade pottery wheel; Electric lawn mower; Wood splitter and much more where mechanical rotation of any mechanisms or objects is necessary. And in all these cases, this board “Adjusting the speed of electric motors with maintaining power on the TDA1085” helps us.

Crash test of speed control board

Allows you to control engines without losing power. A prerequisite for this is the presence of a tachometer (tachogenerator) on the electric motor, which allows you to provide feedback from the motor to the control board, namely the microcircuit. To put it in simpler terms, so that everyone can understand, something like this happens. The motor rotates at a certain number of revolutions, and a tachometer installed on the electric motor shaft records these readings. If you start to load the engine, the shaft speed will naturally begin to drop, which will also be recorded by the tachometer. Now let's look further. The signal from this tachometer goes to the microcircuit, it sees this and gives a command to the power elements to add voltage to the electric motor. Thus, when you pressed the shaft (apply a load), the board automatically added voltage and the power on this shaft increased. And vice versa, let go of the motor shaft (the load was removed from it), she saw this and reduced the voltage. Thus, the speed does not remain low, but the moment of force (torque) remains constant. And most importantly, you can adjust the rotor speed over a wide range, which is very convenient in the use and design of various devices. Therefore, this product is called “Board for adjusting the speed of commutator motors without loss of power.”

But we saw one feature: this board is only applicable for commutator motors (with electric brushes). Of course, such motors are much less common in everyday life than asynchronous ones. But they have found wide application in automatic washing machines. This is exactly why this circuit was made. Especially for the electric motor from an automatic washing machine. Their power is quite decent, from 200 to 800 watts. This allows them to be widely used in everyday life.

This product has already found wide application in people's households and has widely covered people engaged in various hobbies and professional activities.

Answering the question - Where can I use the motor from a washing machine? A list has been compiled. Homemade wood lathe; Grinder; Electric drive for concrete mixer; Sharpener; Electric drive for honey extractor; Straw cutter; Homemade pottery wheel; Electric lawn mower; Wood splitter and much more where mechanical rotation of any mechanisms or objects is necessary. And in all these cases, this board “Adjusting the speed of electric motors with maintaining power on the TDA1085” helps us.

Crash test of speed control board

Induction motors are used in machine tools and other equipment as electric drives to drive moving parts. Their widespread use is due to their simple design and relatively low cost. In these conditions, adjusting the speed of an asynchronous motor is important, allowing it to work in a wide variety of conditions. Standard designs involve mechanical transmission systems, which are not very convenient under certain circumstances. Electric control offers a number of advantages, despite all the difficulties associated with the connection.

Adjustment methods

Electrical speed control allows you to accurately and smoothly adjust the required operating modes. This operation can be performed in several ways at once, related to changes in engine parameters and electric current.

First of all, the voltage supplied to the stator, as well as the auxiliary resistance of the rotor circuit, can change. In addition, the rotation speed is related to the change in the number of pole pairs and the frequency of the current.

With the last two methods, the rotation speed changes without a significant reduction in power and loss of efficiency. They all have their advantages and disadvantages, but, in general, they are successfully used for adjustment. These methods are considered most suitable for asynchronous motors with a squirrel-cage rotor design. These motors are most often used in the manufacturing sector.

Features of frequency regulation

Frequency regulation is most often used, which is done using semiconductor converters. Their action is based on the features of asynchronous motors. Here the magnetic field rotates with a frequency related to the frequency of the electrical network voltage.

In order for the engine to operate efficiently, the voltage must also be changed simultaneously with the frequency. The change in voltage value is closely related to the load torque. Under constant load, the voltage will change in proportion to the frequency.

With the help of modern devices, the speed of an asynchronous motor can be adjusted over a wide range. If necessary, acceleration or deceleration of units can be applied, depending on certain technological operations. To set the required parameters, special control modules are used. Power switches are special high-power transistors. At high switching frequencies, current distortion is minimal.

How to determine the speed of an electric motor by winding

To perform many types of work on wood, metal or other types of materials, it is not high speeds that are required, but good traction. It would be more correct to say - the moment. It is thanks to him that the planned work can be completed efficiently and with minimal power losses. For this purpose, DC (or commutator) motors are used as a drive device, in which the supply voltage is rectified by the unit itself. Then, to achieve the required performance characteristics, it is necessary to adjust the speed of the commutator motor without loss of power.

Features of speed control

It is important to know, what each engine consumes when rotating not only active, but also reactive power. In this case, the level of reactive power will be higher, which is due to the nature of the load. In this case, the task of designing devices for regulating the rotation speed of commutator motors is to reduce the difference between active and reactive powers. Therefore, such converters will be quite complex, and it is not easy to make them yourself.

You can construct only some semblance of a regulator with your own hands, but there is no point in talking about saving power. What is power? In electrical terms, it is the current drawn multiplied by the voltage. The result will give a certain value that includes active and reactive components. To isolate only the active one, that is, to reduce losses to zero, it is necessary to change the nature of the load to active. Only semiconductor resistors have these characteristics.

Hence, it is necessary to replace the inductance with a resistor, but this is impossible, because the engine will turn into something else and obviously will not set anything in motion. The goal of lossless regulation is to maintain torque, not power: it will still change. Only a converter can cope with such a task, which will control the speed by changing the duration of the opening pulse of thyristors or power transistors.

Generalized controller circuit

An example of a controller that implements the principle of controlling a motor without power loss is a thyristor converter. These are feedback proportional integrated circuits that provide strict regulation characteristics, ranging from acceleration and braking to reverse. The most effective is pulse-phase control: the repetition rate of the unlocking pulses is synchronized with the network frequency. This allows you to maintain torque without increasing losses in the reactive component. The generalized diagram can be represented in several blocks:

• power controlled rectifier;
• rectifier control unit or pulse-phase control circuit;
• tachogenerator feedback;
• current control unit in the motor windings.

Before delving into a more precise device and principle of regulation, it is necessary to decide on the type of commutator motor. The control scheme for its performance characteristics will depend on this.

Types of commutator motors

At least two types of commutator motors are known. The first includes devices with an armature and an excitation winding on the stator. The second includes devices with an armature and permanent magnets. It is also necessary to decide, for what purpose is it necessary to design a regulator:

Motor design

Structurally, the engine from the Indesit washing machine is simple, but when designing a controller to control its speed, it is necessary to take into account the parameters. Motors may have different characteristics, which is why the control will also change. The operating mode is also taken into account, which will determine the design of the converter. Structurally, the commutator motor consists from the following components:

• An armature, it has a winding laid in the grooves of the core.
• Collector, a mechanical rectifier of alternating mains voltage, through which it is transmitted to the winding.
• Stator with field winding. It is necessary to create a constant magnetic field in which the armature will rotate.

When the current in the motor circuit, connected according to the standard circuit, increases, the field winding is connected in series with the armature. With this inclusion, we also increase the magnetic field acting on the armature, which allows us to achieve linearity of characteristics. If the field remains unchanged, then it will be more difficult to obtain good dynamics, not to mention large power losses. It is better to use such motors at low speeds, since they are more convenient to control at small discrete movements.

By organizing separate control of the excitation and armature, it is possible to achieve high positioning accuracy of the motor shaft, but the control circuit will then become significantly more complicated. Therefore, we will take a closer look at the controller, which allows you to change the rotation speed from 0 to the maximum value, but without positioning. This might come in handy, if a full-fledged drilling machine with the ability to cut threads will be made from a washing machine engine.

Scheme selection

Having found out all the conditions under which the motor will be used, you can begin to manufacture a speed controller for the commutator motor. You should start by choosing a suitable scheme that will provide you with all the necessary characteristics and capabilities. You should remember them:

• Speed ​​regulation from 0 to maximum.
• Providing good torque at low speeds.
• Smooth speed control.

Looking at many schemes on the Internet, we can conclude that few people are creating such “units”. This is due to the complexity of the control principle, since it is necessary to organize the regulation of many parameters. Thyristor opening angle, control pulse duration, acceleration-deceleration time, torque rise rate. These functions are handled by a circuit on the controller that performs complex integral calculations and transformations. Let's consider one of the schemes, which is popular among self-taught craftsmen or those who simply want to put to good use an old motor from a washing machine.

All our criteria are met by a circuit for controlling the rotation speed of a brushed motor, assembled on a specialized TDA 1085 microcircuit. This is a completely ready-made driver for controlling motors that allow you to adjust the speed from 0 to the maximum value, ensuring torque maintenance through the use of a tachogenerator.

Design Features

The microcircuit is equipped with everything necessary for high-quality engine control in various speed modes, from braking to acceleration and rotation at maximum speed. Therefore, its use greatly simplifies the design, while simultaneously doing all universal drive, since you can choose any speed with a constant torque on the shaft and use it not only as a drive for a conveyor belt or drilling machine, but also for moving the table.

The characteristics of the microcircuit can be found on the official website. We will indicate the main features that will be required to construct the converter. These include: an integrated frequency-to-voltage conversion circuit, an acceleration generator, a soft starter, a Tacho signal processing unit, a current limiting module, etc. As you can see, the circuit is equipped with a number of protections that will ensure stable operation of the regulator in different modes.

The figure below shows a typical circuit diagram for connecting a microcircuit.

The scheme is simple, so it can be completely reproducible with your own hands. There are some features that include limit values ​​and speed control method:

If you need to organize a motor reverse, then for this you will have to supplement the circuit with a starter that will switch the direction of the excitation winding. You will also need a zero speed control circuit to give permission for reverse. Not shown in the picture.

Control principle

When the rotation speed of the motor shaft is set by a resistor in output circuit 5, a sequence of pulses is formed at the output to unlock the triac by a certain angle. The speed of rotation is monitored by a tachogenerator, which occurs in digital format. The driver converts the received pulses into an analog voltage, which is why the shaft speed is stabilized at a single value, regardless of the load. If the voltage from the tachogenerator changes, the internal regulator will increase the level of the output control signal of the triac, which will lead to an increase in speed.

The microcircuit can control two linear accelerations, allowing you to achieve the dynamics required from the engine. One of them is installed on the Ramp 6 pin of the circuit. This regulator is used by washing machine manufacturers themselves, so it has all the advantages to be used for domestic purposes. This is ensured by the presence of the following blocks:

Usage similar scheme provides full control of the commutator motor in any mode. Thanks to forced acceleration control, it is possible to achieve the required acceleration speed to a given rotation speed. Such a regulator can be used for all modern washing machine motors used for other purposes.