Smooth start of 24V DC motor. Application of the KR1182PM1 microcircuit. Smooth start of the electric motor. Starting an electric motor by switching windings

Smooth start of the electric motor in Lately is being used more and more often. Its areas of application are varied and numerous. These are industry, electric transport, utilities and Agriculture. The use of such devices can significantly reduce starting loads on the electric motor and actuators, thereby extending their service life.

Starting currents

Starting currents reach values 7...10 times higher than in operating mode. This leads to a “sag” of voltage in the supply network, which negatively affects not only the operation of other consumers, but also the engine itself. The start-up time is delayed, which can lead to overheating of the windings and gradual destruction of their insulation. This contributes to premature failure of the electric motor.

Soft start devices can significantly reduce the starting load on the electric motor and the electrical network, which is especially important in rural areas or when the engine is powered from an autonomous power plant.

Overload of actuators

When the engine starts, the torque on its shaft is very unstable and exceeds the rated value by more than five times. Therefore, the starting loads of the actuators are also increased compared to operation in steady state and can reach up to 500 percent. Instability of the starting torque leads to shock loads on the gear teeth, shearing of keys and sometimes even twisting of the shafts.

Electric motor soft start devices significantly reduce starting loads on the mechanism: the gaps between the gear teeth are smoothly selected, which prevents their breakage. Belt drives also smoothly tension the drive belts, which reduces wear on the mechanisms.

In addition to a smooth start, the smooth braking mode has a beneficial effect on the operation of mechanisms. If the engine drives the pump, then smooth braking avoids water hammer when the unit is turned off.

Industrial soft starters

Currently produced by many companies, for example Siemens, Danfoss, Schneider Electric. Such devices have many functions that are user programmable. These are acceleration time, deceleration time, overload protection and many other additional functions.

With all the advantages, branded devices have one drawback - a fairly high price. However, you can create such a device yourself. At the same time, its cost will be small.

Soft start device based on KR1182PM1 microcircuit

The story was about specialized chip KR1182PM1, representing the phase power regulator. Were considered standard schemes its inclusion, devices for soft starting of incandescent lamps and simply power regulators in the load. Based on this microcircuit, it is possible to create a fairly simple soft-start device for a three-phase electric motor. The device diagram is shown in Figure 1.

Figure 1. Scheme of the motor soft start device.

A soft start is carried out by gradually increasing the voltage on the motor windings from zero to the nominal value. This is achieved by increasing the opening angle of the thyristor switches over a time called the startup time.

Description of the circuit

The design uses three phase electric motor 50 Hz, 380 V. The star-connected motor windings are connected to the output circuits indicated in the diagram as L1, L2, L3. The center point of the star is connected to the network neutral (N).

The output switches are made on thyristors connected back-to-back - in parallel. The design uses imported 40TPS12 type thyristors. At a low cost, they have a fairly large current - up to 35 A, and their reverse voltage 1200 V. In addition to them, the keys contain several more elements. Their purpose is as follows: damping RC circuits connected in parallel with the thyristors prevent false switching on of the latter (in the diagram these are R8C11, R9C12, R10C13), and with the help of varistors RU1...RU3 switching noise is absorbed, the amplitude of which exceeds 500 V.

DA1...DA3 microcircuits of type KR1182PM1 are used as control nodes for output switches. These microcircuits were discussed in some detail in. Capacitors C5...C10 inside the microcircuit form a sawtooth voltage, which is synchronized with the network voltage. The thyristor control signals in the microcircuit are generated by comparing the sawtooth voltage with the voltage between microcircuit pins 3 and 6.

To power relays K1…K3, the device has a power supply, which consists of only a few elements. This is transformer T1, rectifier bridge VD1, smoothing capacitor C4. At the output of the rectifier is installed integral stabilizer DA4 type 7812 provides 12 V output voltage, and protection against short circuits and output overloads.

Description of the operation of the soft starter for electric motors

Mains voltage is supplied to the circuit when power switch Q1 is closed. However, the engine does not start yet. This happens because the windings of relay K1...K3 are still de-energized, and their normally closed contacts bypass pins 3 and 6 of microcircuits DA1...DA3 through resistors R1...R3. This circumstance prevents capacitors C1...C3 from charging, so the microcircuit does not generate control pulses.

Putting the device into operation

When the toggle switch SA1 is closed, the 12 V voltage turns on relay K1…K3. Their normally closed contacts open, which makes it possible to charge capacitors C1...C3 from internal current generators. Along with the increase in voltage on these capacitors, the opening angle of the thyristors also increases. This achieves a smooth increase in voltage on the motor windings. When the capacitors are fully charged, the switching angle of the thyristors will reach its maximum value, and the rotation speed of the electric motor will reach the rated speed.

Engine shutdown, smooth braking

To turn off the engine, open switch SA1. This will turn off relay K1...K3. They are normal - the closed contacts will close, which will lead to the discharge of capacitors C1...C3 through resistors R1...R3. The discharge of the capacitors will last for several seconds, during which time the engine will stop.

When starting the engine, significant currents can flow in the neutral wire. This happens because during smooth acceleration the currents in the motor windings are non-sinusoidal, but there is no need to be particularly afraid of this: the starting process is quite short-lived. In steady-state mode, this current will be much less (no more than ten percent of the phase current in the nominal mode), which is due only to the technological dispersion of the winding parameters and the “misalignment” of the phases. It is no longer possible to get rid of these phenomena.

Details and design

To assemble the device, the following parts are required:

Transformer with a power of no more than 15 W, with an output winding voltage of 15...17 V.

Relays K1...K3 are suitable for any coil voltage of 12 V, having a normally closed or switching contact, for example TRU-12VDC-SB-SL.

Capacitors C11…C13 type K73-17 for an operating voltage of at least 600 V.

The device is made on a printed circuit board. The assembled device should be placed in a plastic case of suitable dimensions, on the front panel of which switch SA1 and LEDs HL1 and HL2 should be placed.

Motor connection

The connection between switch Q1 and the motor is made with wires whose cross-section corresponds to the power of the latter. The neutral wire is made of the same wire as the phase wires. With the component ratings indicated in the diagram, it is possible to connect motors with a power of up to four kilowatts.

If you plan to use a motor with a power of no more than one and a half kilowatts, and the start-up frequency will not exceed 10...15 per hour, then the power dissipated by the thyristor switches is insignificant, so radiators can not be installed.

If you plan to use a more powerful engine or the starts will be more frequent, you will need to install thyristors on radiators made of aluminum strip. If the radiator is supposed to be used as a common one, then the thyristors should be isolated from it using mica spacers. To improve cooling conditions, you can use heat-conducting paste KPT-8.

Checking and setting up the device

Before switching on, first of all, you should check the installation for compliance with the circuit diagram. This is the basic rule, and you cannot deviate from it. After all, neglecting this check can lead to a bunch of charred parts, and for a long time discourage you from doing “experiments with electricity.” The errors found should be eliminated, because after all, this circuit is powered from the network, and it is not to be trifled with. And even after this check, it is still too early to connect the engine.

First, instead of the engine, you should connect three identical incandescent lamps with a power of 60...100 W. During testing, it is necessary to ensure that the lamps “ignite” evenly.

The uneven turn-on time is due to the scatter in the capacitances of capacitors C1...C3, which have a significant tolerance on capacitance. Therefore, it is better to immediately select them using the device before installation, at least with an accuracy of up to ten percent.

The shutdown time is also determined by the resistance of resistors R1…R3. With their help you can adjust the shutdown time. These settings should be made if the spread in the on-off time in different phases exceeds 30 percent.

The engine can be connected only after the above checks have passed normally, not to say even perfectly.

What else can be added to the design?

It has already been said above that such devices are currently produced by different companies. Of course, it’s impossible to replicate all the functions of branded devices in such a homemade device, but you can still probably copy one.

We are talking about the so-called. Its purpose is as follows: after the engine has reached its rated speed, the contactor simply bridges the thyristor switches with its contacts. The current flows through them, bypassing the thyristors. This design is often called a bypass (from the English bypass - bypass). For such an improvement, additional elements will have to be introduced into the control unit.

Boris Aladyshkin

Smooth start asynchronous motor- it's always difficult task, because running an induction motor requires large current and torque, which may burn out the motor winding. Engineers are constantly proposing and implementing interesting technical solutions to overcome this problem, for example, using a switching circuit, autotransformer, etc.

Currently, similar methods are used in various industrial installations for the uninterrupted operation of electric motors.

The principle of operation of an induction electric motor is known from physics, the whole essence of which is to use the difference between the rotation frequencies of the magnetic fields of the stator and rotor. The magnetic field of the rotor, trying to catch up with the magnetic field of the stator, contributes to the excitation of a large starting current. The motor runs at full speed, and the torque value also increases along with the current. As a result, the winding of the unit may be damaged due to overheating.

Thus, it becomes necessary to install a soft starter. Soft starters for three-phase asynchronous motors allow you to protect units from the initial high current and torque that arise due to the sliding effect when operating an induction motor.

Advantages of using a circuit with a soft starter (SPD):

reduction of starting current;
reduction in energy costs;
increasing efficiency;
relatively low cost;
achieving maximum speed without damaging the unit.

How to start the engine smoothly?

There are five main soft starting methods.

High torque can be created by adding an external resistance to the rotor circuit as shown in the figure.

By including an automatic transformer in the circuit, the starting current and torque can be maintained by reducing the initial voltage. See the picture below.

Direct launch is the simplest and most cheap way, because the induction motor is connected directly to the power source.
Connections using a special winding configuration - the method is applicable for motors intended for operation under normal conditions.

Using SCP is the most advanced method of all the methods listed. Here, semiconductor devices such as thyristors or SCRs, which control the speed of an induction motor, successfully replace mechanical components.

Commutator motor speed controller

Most circuits for household appliances and electrical tools are based on a 220 V commutator motor. This demand is explained by its versatility. The units can be powered from direct or alternating voltage. The advantage of the circuit is due to the provision of effective starting torque.

To achieve a smoother start and have the ability to adjust the rotation speed, speed controllers are used.

You can start an electric motor with your own hands, for example, in this way.

Characteristic of any electric motor during the startup process is a multiple excess of current and mechanical load on the driven equipment. At the same time, overloads of the supply network also occur, creating a voltage drop and deteriorating the quality of electricity. In many cases, a soft starter (soft starter) is required.

The need for smooth starting of electric motors

The stator winding is an inductance coil consisting of active resistance and reactive. The value of the latter depends on the frequency of the supplied voltage. When the engine starts, the reactance changes from zero, and the starting current has a large value, many times greater than the rated one. The rotation torque is also high and can destroy the driven equipment. During braking mode, current surges also appear, leading to an increase in the temperature of the stator windings. In the event of an emergency caused by motor overheating, repairs are possible, but the parameters of the transformer steel change and the rated power is reduced by 30%. Therefore, a soft start is necessary.

Starting an electric motor by switching windings

The stator windings can be connected in star and delta. When all ends of the motor windings are brought out, you can switch the star and delta circuits from the outside.

The soft start device for an electric motor is assembled from 3 contactors, a load relay and a time relay.

The electric motor starts in a star configuration when contacts K1 and K3 are closed. After an interval specified by the time relay, K3 is turned off and the delta circuit is connected by contactor K2. At the same time, the engine reaches full speed. When it accelerates to rated speed, the starting currents are not so large.

The disadvantage of the circuit is that a short circuit occurs when two circuit breakers are turned on simultaneously. This can be avoided by using a switch instead. To organize reverse, another control unit is needed. In addition, according to the "triangle" circuit, the electric motor heats up more and works harder.

Frequency control of rotation speed

The motor shaft rotates magnetic field stator. The speed depends on the frequency of the supply voltage. The electric drive will work more efficiently if the voltage is additionally changed.

The soft start device for asynchronous motors may include a frequency converter.

The first stage of the device is a rectifier, which is supplied with three-phase or single-phase network. It is assembled on diodes or thyristors and is designed to generate a pulsating DC voltage.

In the intermediate circuit, the ripples are smoothed out.

In the inverter, the output signal is converted into a variable signal of a given frequency and amplitude. It works on the principle of changing the amplitude or width of the pulses.

All three elements receive signals from the electronic control circuit.

Operating principle of the soft starter

An increase in starting current by 6-8 times and torque requires the use of a soft starter to perform the following actions when starting or braking the engine:

gradual increase in load;
reduction of voltage drop;
control of starting and braking at certain times;
reduction of interference;
protection against voltage surges, phase loss, etc.;
increasing the reliability of the electric drive.

The motor soft starter limits the amount of voltage supplied at the moment of starting. It is adjusted by changing the opening angle of the triacs connected to the windings.

Starting currents must be reduced to a value no more than 2-4 times higher than the nominal value. The presence of a bypass contactor prevents the triacs from overheating after it is connected after the motor has spun up. Switching options are single-, two- and three-phase. Each circuit is functionally different and has a different cost. The most advanced is three-phase regulation. It is the most functional.

Disadvantages of soft starters based on triacs:

simple circuits are used only with light loads or at idle start;
prolonged startup leads to overheating of windings and semiconductor elements;
The shaft rotation torque is reduced and the engine may not start.

Types of AMR

The most common regulators are open-loop regulators on two or three phases. To do this, the voltage and start time are preset. The disadvantage is the lack of torque control based on the engine load. This problem is solved by a device with feedback along with performing additional functions of reducing the starting current, creating protection against phase imbalance, overload, etc.

The most modern soft starters have continuous load monitoring circuits. They are suitable for heavily loaded drives.

Selection of soft starter

Most soft starters are voltage regulators based on triacs, differing in functions, control circuits and voltage change algorithms. IN modern models softstarters are used phase methods regulation of electric drives with any starting modes. Electrical circuits can have thyristor modules for different numbers of phases.

One of the simplest is a soft start device with single-phase regulation through one triac, which only allows softening the mechanical shock loads of motors with a power of up to 11 kW.

Two-phase regulation also softens mechanical shocks, but does not limit current loads. The permissible engine power is 250 kW. Both methods are used based on reasonable prices and the characteristics of specific mechanisms.

The multifunctional three-phase soft starter has the best specifications. Here the possibility of dynamic braking and optimization of its operation is provided. The only disadvantages that can be noted are the high prices and dimensions.

Take the Altistart soft starter as an example. You can select models for starting asynchronous motors whose power reaches 400 kW.

The device is selected according to its rated power and operating mode (normal or heavy).

Selection of soft starter

The main parameters by which soft starters are selected are:

the maximum current strength of the soft starter and the motor must be correctly selected and match each other;
the parameter for the number of starts per hour is set as a characteristic of the soft starter and should not be exceeded when operating the engine;
the specified device voltage should not be less than the mains voltage.

Soft starter for pumps

The soft start device for the pump is designed primarily to reduce hydraulic shocks in pipelines. Advanced Control soft starters are suitable for working with pump drives. The devices almost completely eliminate water hammer when pipelines are full, allowing you to increase the service life of the equipment.

Smooth starting of power tools

Power tools are characterized by high dynamic loads and high speeds. Its obvious representative is the angular Sander(angle grinder). Significant inertial forces act on the working disk at the beginning of rotation of the gearbox. Large current overloads occur not only during startup, but also every time the tool is fed.

The soft start device for power tools is used only for expensive models. An economical solution is to install it yourself. This can be a ready-made block that fits inside the tool body. But many users assemble a simple circuit themselves and connect it to the power cable.

When the motor circuit is closed, voltage is applied to the phase regulator KR1182PM1 and capacitor C2 begins to charge. Due to this, triac VS1 is turned on with a delay that gradually decreases. The motor current gradually increases and the speed increases gradually. The engine accelerates in approximately 2 seconds. The power supplied to the load reaches 2.2 kW.

The device can be used for any power tool.

Conclusion

When choosing a soft starter, it is necessary to analyze the requirements for the mechanism and characteristics of the electric motor. Manufacturer's specifications can be found in the documentation supplied with the equipment. There should be no mistakes when choosing, since the functioning of the device will be disrupted. It is important to consider the speed range to select the best drive/motor combination.

Smooth start

brushed DC motor

(DPT)

There may be a need to smoothly turn on a commutator motor, for example, to prevent current surges in power circuits. Or preventing sharp impacts on the drive transmission. It’s a good idea to set the headlights to turn on to increase the life of the lamps.

In my case, it was necessary to supply maximum power to the running electric motor of an electric vehicle with the electronic control key removed from the PWM control mode to prevent it from overheating at maximum load.

In Fig. 1 and fig. 2 shows two implementation diagrams of such devices.

Design 1:

A simple circuit of a soft start circuit using an integrated timer KR1006VI1 (or imported 555 series)

Fig.1. Design 1

When a voltage of 12V is applied, the timer with trim elements (PWM) starts and begins to generate pulses at the output of IC 3 with a constant frequency and a pulse width that varies over time. The time is set by the capacitance of capacitor C1. Next, these pulses are fed to the gate of a powerful field effect transistor which controls the load at the output of the device. R3 is strictly 2Mohm. The operating voltage of electrolytic capacitors is 25 volts.
Note: This device is located as close to the fan as possible otherwise, interference may arise that will interfere with the normal operation of the car (of course, the Zhiguli is not an obstacle).

Design 2:

No less simple circuit on the same integral timer.

Fig.2 Design 2

Design 3:

Circuit applied to an electric car. The device is started using the "Start" button.

Fig.2 Design 3

The value of resistor R2 must be at least 2.2 mOhm, otherwise there will be no full (100%) opening of the transistors.
The power supply of the circuit is limited at 7.5V using a KS175Zh zener diode in order to limit the control voltage supplied to the gate of the transistors. Otherwise, the transistor bases go into saturation.
The device is turned on using the "On" button by applying power, while simultaneously unlocking the power transistors. When the device is turned off, linear mode is prevented when the power supply to the control circuits is reduced; the transistors close instantly.

MINISTRY OF EDUCATION AND SCIENCE OF UKRAINE

DEPARTMENT OF AUTOMATIC CONTROL SYSTEMS I

ELECTRIC DRIVE

COURSE PROJECT

DISCIPLINE: “ELECTRIC DRIVE THEORY”

ON THE TOPIC: “SOFT START OF A CONTINUOUS STREAM ENGINE

BY SYSTEM “PULSE WIDTH CONVERTER – MOTOR”

POSITIONAL STRUM“

Rozrobiv:

Kerivnyk:

CALENDAR PLAN

№	Names of stages course project	Lines of project stages
1	Analysis of technical specifications and selection of pulse width converter	15 June 2002
2	Analysis of functional diagrams and development of technical documentation	30 June 2002
3	Development of the transistor control system and preparation of the printed circuit board	November 20, 2002
4	Design of equivalent circuits	30 leaf fall 2002
5	Pobudova static, mechanical and dynamic characteristics	5th birthday 2002
6	Selecting power elements and setting up circuit parameters	10 breast 2002
7	Rozrahunok energy characteristics	25 Breast 2002
8	Mathematical modeling	10 June 2003
9	Project design	27 June 2003

Student _____________

Kerivnyk _____________

“_______”______________________200 RUR

PERELIK SMALL POZNACEN

SHIP - pulse width converter

DPT - stationary engine

AD - asynchronous motor

IP - impulse converter

EOM – electronic computing machine

IDK - vimi-diagnostic complex

SD - stepper motor

VFD - variable frequency drive

Efficiency - coefficient of corysmic action

GPI - sawtooth generator

ZAVDANNYA

for a student's course project

____________________________________

1. Topic of work: Soft start of a stationary jet motor using the system “Pulse width reversal – stationary jet motor.” The main part is the design of a soft start system for a stationary jet engine based on a PIC 16F 877 microcontroller

2. Line of the student’s completed work 01/28/03

3. Output data before operation, technical characteristics of the engine, technical characteristics of other systems of pulse width modulators

4. Substitution of an explanatory note, analysis of the main pulse converters and selection of the most optimal one, development of technical documentation for the stand, development of the principle and functional circuits, selection of power elements iv.

5. Date of publication 200 RUR

CALENDAR PLAN.. 2

THE OVERLINK OF THE MENTAL POSITIONS. 3

ZAVDANNYA.. 4

Introduction. 6

1. Advantages and disadvantages of the SHIP - DPT system. 8

1.1 Pulse converters DC voltage (general information) 8

1.2 Analysis of existing pulse converters. 8

2. Functional diagram of the laboratory stand. eleven

3. Development of technical documentation for the laboratory bench of the SHIP - DPT system. 13

3.1 General form laboratory stand. 13

3.2 Schematic diagram stand after modification. 15

3.3 List of functional capabilities of the laboratory stand. 16

3.4 Control system based on microcontroller PIC 16F 877. 17

4. Calculation of equivalent circuit. 24

5. Static characteristics of the SHIP - DPT system. 26

6. Selection of power elements. 31

6.1 Selecting a power transformer. 31

6.2 Selecting a power transistor. 32

6.3 Selecting a reverse diode. 33

7. Calculation of the converter. 35

8. Calculation of energy characteristics. 42

9. Mathematical model of the SHIP – DPT system. 45

Introduction

Electrical energy storage is becoming an important part of the overall protection trend. environment. Electric motors that drive systems in everyday life and in industry consume a significant portion of the energy produced. Most of these motors operate in unregulated mode and therefore with low efficiency. Recent advances in the semiconductor industry, especially in power electronics and microcontrollers, have made variable speed drives more practical and significantly less expensive. Today, variable speed drives are required not only in highly professional and heavy-duty industrial applications such as processing machines or cranes, but increasingly in household appliances, e.g. washing machines, compressors, small pumps, air conditioners, etc. These drives, controlled by advanced algorithms using microcontrollers, have a number of advantages:

increasing the energy efficiency of the system (speed regulation reduces power losses in engines)

improved performance (digital control can add features such as intelligent closed loops, changing frequency properties, controllable fault range, and the ability to interface with other systems)

simplification of electromechanical energy conversion (variable drives eliminate the need for transmissions, gearboxes, gearboxes) ease of updating software Microcontroller-based systems with flash memory can quickly change as needs increase. The main condition for their use is to maintain the total cost of the system within reasonable limits. For a number of systems, especially in the home, the total cost should be equivalent to the cost of the unregulated option.

1. Advantages and disadvantages of the SHIP - DPT system

1.1 Switching DC-DC converters (general information)

Changing the consumer voltage value using pulse converters (IP) is called pulse regulation.

Using a pulse converter, the voltage source is periodically connected to the load. As a result, voltage pulses are formed at the output of the converter. Load voltage regulation can be done in three ways:

changing the conductivity interval of the switch at a constant switching frequency (pulse width)

changing the switching frequency at a constant interval of switch conductivity (frequency-pulse)

changing the switching frequency and the conduction interval of the switch (time-pulse)

In this case, the relative conduction time of the switch is regulated, which leads to a smooth change in the average voltage value at the load (in our case, at the DPT armature)

1.2 Analysis of existing pulse converters

The PWB circuit with parallel capacitive switching is shown in Figure 1.1.

Figure 1.1. PWB with parallel capacitive switching

The disadvantage of PSG with parallel capacitive switching is that during the switching process, the voltage at the load reaches double the supply voltage. Another disadvantage is the difficulty of setting up a resonant circuit with capacitor ‘C’ and inductor ‘Dr’.

Figure 1.2 shows a PWB circuit with an additional switching thyristor and a linear choke in the switching unit.

The disadvantage of the circuit is the connection of the switching circuit with the load circuit. This feature complicates switching in light load modes and makes it impossible for the device to operate at idle.

Figure 1.3 shows a diagram of a non-reversible power supply with a sequential key element.

Figure 1.3. Irreversible SPIKE

This circuit is the most suitable for our purpose, since it is characterized by a small number of elements, simplicity of design, fairly high speed and reliability.

Operating principle:

When the VT transistor is turned off from the power supply, energy is consumed. When the transistor VT is turned off, the load current due to E.M.F. self-induction retains its previous direction, closing through the reverse diode VD. Due to the fact that the power source, as a rule, has an inductance, to protect the transistor from overvoltages that occur when the power supply circuit is interrupted, a low-pass filter is installed at the input of the power supply, the output link of which is the capacitor Swx.

2. Functional diagram of the laboratory stand

The functional diagram of an existing laboratory stand is shown in Figure 2.1

Figure 2.1 Functional diagram of the stand

The functional diagram shows the main elements of the stand and the functional interactions between them.

The main element of the stand is the ACS 300 frequency converter. Through it, power is supplied to the asynchronous motor with a squirrel-cage rotor M1 - AOL2-21-4. The stand provides the ability to operate asynchronous dynamic braking mode. It is also possible to control the speed of an asynchronous motor, currents and voltages of both IM and DPT.

In the power circuit of the IM there are a three-phase current sensor and a three-phase voltage sensor, the data from which is supplied through the communication unit to the EOM. The communication unit and the EOM form a measuring and diagnostic complex (IDC). The IDK also receives signals from other sensors and control elements