Asynchronous AC motors are the most used electric motors in absolutely all economic areas. Their advantages include structural simplicity and low price. In this case, regulation of the speed of an asynchronous motor is of no small importance. Existing methods are shown below.
According to the block diagram, the speed of the electric motor can be controlled in two directions, that is, by changing the quantities:
- speed of the stator electromagnetic field;
- engine slip.
The first correction option, used for models with a squirrel-cage rotor, is carried out by changing:
- frequencies,
- number of pole pairs,
- voltage.
The second option, used for modification with a wound rotor, is based on:
- change in supply voltage;
- connecting a resistance element to the rotor circuit;
- use of a valve cascade;
- use of dual power supply.
Due to the development of power conversion technology, all kinds of frequency drives are currently being manufactured on a large scale, which has determined the active use of variable frequency drives. Let's look at the most common methods.
Just ten years ago, there were a small number of ED speed controllers in the retail chain. The reason for this was that cheap high-voltage power transistors and modules had not yet been produced.
Today, frequency conversion is the most common method of regulating the speed of motors. Three-phase frequency converters are created to control 3-phase electric motors.
Single-phase motors are controlled:
- special single-phase frequency converters;
- 3-phase frequency converters with capacitor elimination.
Schemes of speed controllers for asynchronous motors
For engines used for everyday use, you can easily perform the necessary calculations and assemble the device on a semiconductor chip with your own hands. An example of a motor controller circuit is shown below. This scheme makes it possible to control the parameters of the drive system, maintain maintenance costs, and reduce electricity consumption by half.
The schematic diagram of the EM rotation speed controller for everyday needs is greatly simplified if a so-called triac is used.
The rotation speed of the motor is regulated using a potentiometer that determines the phase of the input pulse signal that opens the triac. The image shows that two thyristors connected in back-to-back parallel are used as switches. The 220 V thyristor speed controller ED is often used to regulate loads such as dimmers, fans and heating equipment. The technical indicators and operating efficiency of the propulsion equipment depend on the rotation speed of the asynchronous motor.
I present to your attention a three-phase power regulator on a microcontroller.
The device regulates the power in an active load connected by a delta or star, without using a neutral conductor. Designed for use with resistance furnaces, hot water boilers, three-phase heating elements and even incandescent lamps, subject to the condition of symmetrical load in the phases. Two modes of operation - regulation using the Bresenham algorithm, and phase regulation method. The device was intended to be as simple as possible and easy to replicate. Control by buttons or potentiometer, LED indicator of operating modes (optional), LED indicating the status of the device.
Attention! Life-threatening voltage present! For experienced users!
For convenience, the device diagram is divided into functional blocks. This makes it possible to make further changes and improvements to the design, without radically reworking the entire circuit. Each block will be described separately below.
Power circuit
The author's version was built on powerful optothyristor modules MTOTO 80 - 12. Each module contains two back-to-back eighty-amp optothyristor modules. Three modules are used, one for each phase. Control pulses arrive simultaneously at both power switches, but only the one to which voltage is applied in direct polarity will open. The modules are replaceable with thyristor or triac assemblies, or individual thyristors and triacs. Modular assemblies are more convenient to install, have an insulated substrate, and simplify the galvanic isolation of the control circuit. When using separate thyristors or triacs, you will need to install additional pulse transformers or optocouplers. You will also need to select current-limiting resistors of optocouplers (R32 – R34) for the copies you have. The microcontroller generates control pulses, which are amplified by composite transistors T7-T9. The pulses are modulated at high frequency to reduce the current through optocouplers; this also makes it possible to use small-sized pulse transformers (hereinafter referred to as TI). The optocouplers or TI are powered by an unstabilized voltage of 15V.
It is mandatory to install RC circuits in parallel with the thyristors. In my version, these are resistors PEV-10 39 Ohm and capacitors MBM 0.1 µF 600V. The modules are installed on a radiator and heat up during operation. Load three-phase nichrome heater, maximum current 60A. There were no failures during two years of operation.
The diagram does not show, but must be installed, a circuit breaker for the calculated load; it is also advisable to install a separate circuit breaker for the phases of the synchronization unit. The device is connected to a 3x380 volt network in compliance with the phase rotation A-B-C; if the rotation is incorrect, the device will not work. The neutral wire is needed to connect the power supply transformer if its primary winding is 220 volts. When using a 380 volt transformer, a neutral conductor is not needed.
Protective grounding of the device body is mandatory!
No explanation is needed, two voltages are used - unstabilized 15 volts and stabilized 5 volts, consumption in the author’s version was up to 300 mA, largely dependent on the LED indicator and the power elements used. You can use any available parts, there are no special requirements.
Contains three identical channels. Each channel is connected between two phases, i.e. channels are included in a triangle. At the moment of equality of the phase voltages (the point of intersection of the sinusoids), a pulse is generated that is used for synchronization in the MC. The details are not critical, but you need to adhere to the values for more accurate synchronization. If you have a two-beam oscilloscope, it is advisable to select resistors R33, R40, R47 to adjust the moment of pulse formation to the point of intersection of the sinusoids. But this is not a prerequisite. The AOT 101 optocouplers used can be replaced with any similar and available ones, the only requirement for them is a high breakdown voltage, since it is the optocouplers that galvanically isolate the control unit from the network. You can find a simpler zero detector circuit and assemble it, but taking into account the connection to phase-to-phase 380 V. It is very advisable to use fuses, as shown in the diagram, it is also advisable to use a separate circuit breaker for this unit.
Control and display unit
This is the main block. The ATmega8 microcontroller issues control pulses to the thyristors and provides an indication of operating modes. Powered by an internal oscillator, clock 8 MHz. The fuses are shown in the picture below. Seven-segment LED indicator with a common anode, three characters. Controlled through three anode switches T1-T3, segments are switched by a shift register. You don't have to install the indicator, register, and related elements if you don't need to customize your work. You can install any available type of indicator, but you will need to select current-limiting resistors in the segment circuit. The HL1 LED shows the main status of the device.
Start and stop is carried out by switch SB1. Closed state - Start, open state - Stop. Power adjustment is either from the Up, Down buttons, or from the R6 controller, the choice is made through the menu. Any small-sized inductor L is needed for better filtering of the reference voltage of the microcontroller ADC. Capacitors C5, C6 need to be installed as close as possible to the power pins of the MK and the register; in my version they were soldered onto the legs on top of the microcircuits. In conditions of high currents and strong interference, they are necessary for reliable operation of the device.
Power regulator operation
Depending on the selected firmware, regulation will be carried out either by the phase-pulse method or by the method of skipping periods, the so-called Bresenham algorithm.
With phase-pulse control, the voltage at the load smoothly changes from almost zero to maximum by changing the opening angle of the thyristors. The pulse is issued twice per period, simultaneously to both thyristors, but only the one to which voltage is applied in direct polarity will be open.
At low voltages (large opening angle), overshoot is possible due to the inaccuracy of the synchronization pulse at the moment of intersection of the sinusoids. To eliminate this effect, by default the lower limit is set to 10. Through the menu, if necessary, you can change it in the range from 0 to 99. In practice, this has never been required, but it all depends on the specific task. This method is suitable for adjusting the luminous flux of incandescent lamps, provided they have the same power in each phase.
It is also important that the phase rotation of the network is correct A-B-C. To check, you can test for correct phase rotation when turning on the device. To do this, when turning on the device, when the symbols - 0 - are displayed on the indicator, keep the button pressed menu, if the phasing is correct, the indicator will display the symbols AbC, if there is no ACb, and you need to swap any two phases.
If you release the button menu the device will switch to main operating mode.
When using regulation by skipping periods, phasing is not required and the test is not included in the firmware. In this case, the thyristors open simultaneously; you can imagine them as a simple starter that switches all three phases at once. The more power is needed at the load, the more times per unit time the thyristors will be in a conducting state. This method is not suitable for incandescent lamps.
The device does not require configuration.
When turned on, the settings are read from the non-volatile memory of the MK; if there are no values in the memory or they are incorrect, the default values are set. Next, the MK checks for the presence of synchronization pulses and the state of switch SB1. If SB1 in the open state does not issue control pulses, a message is displayed on the indicator OFF, LED HL1 flashes at high frequency. If you close SB1, the current power setting will be displayed on the indicator, control pulses will be generated, and the HL1 LED will light constantly. If at startup or during operation control pulses disappear for more than 10 seconds, the indicator will display numbers 380 , the LED will blink at a low frequency, the thyristor control pulses will be removed. When synchronization pulses appear, the device will return to operation. This was done due to a poor network at the location where the device was used, frequent interruptions and phase imbalances.
The menu contains four submenus, switchable by button menu, if the button is not pressed for a while, the currently set power level is displayed conditionally from 0 to 100. Power level can be changed using buttons Up or Down, or, if enabled (by default), by a potentiometer.
Long press button menu switches submenu.
Submenu 1 the indicator shows Grˉ this is the upper limit of power regulation when pressing the buttons Up or Down, the current value will be shown, it can be changed up or down, within the limits. The default value is 99.
Submenu 2 on the indicator Gr_ This is the lower limit of power regulation, everything is the same, the default value is 10.
Submenu 3 shows whether the reference from the potentiometer is used 1 - yes 0 - no. On the indicator 3-1 or 3-0 , selection by pressing buttons Up or Down. Default – used(1).
Submenu 4 on the indicator ZAP, when you press any of the buttons Up or Down, The current values will be written to the non-volatile memory of the MK. When recording, the inscription will flash once ZAP. The control limits will be recorded, whether the potentiometer is enabled and the current power value if it is set using the buttons and the potentiometer is not used.
Next press menu, will switch to the main menu, the power value will be displayed. Also, not pressing the buttons for a long time will switch the menu to the main one.
You don't have to use the seven-segment LED indicator if you don't need to change anything, in which case everything will work, adjustable from 10 to 99 using a potentiometer. The device status will be shown by LED HL1. The indicator itself was needed at the debugging stage and for subsequent modernization. There are plans to build a regulator for an inductive load on this base, and to make a soft start device for an asynchronous motor.
The printed circuit board was developed for the synchronization unit and for the control unit, but in the end, due to rework, the control unit was made in a hinged way, on a breadboard. The printed circuit board is "as is" in the archive, the seven-segment indicator layout is made to match the indicator I have, if necessary, you can programmatically change the corresponding output segments. Some parts (RC circuits, resistors and diodes of the power circuit, power supply elements, buttons, potentiometer and LEDs) were also mounted using a hinged method.
The archive contains the board of the control unit and synchronization unit, in sprint layout format, and diagrams in Splan 7 format, there are also two firmware options for phase-pulse control and period skip control. The MK was sewn with a “five wires” programmer running the Uniprof program, you can download it on the author’s website http://avr.nikolaew.org/
fuses are presented below.
Fuses are given for installation in this program, when using another - Remember that enabled FUSE is FUSE without a checkmark!
Printed circuit boards are not optimal, and most likely, when repeated, they will have to be modified to fit the available parts, and the specific configuration and arrangement of elements (buttons, potentiometer, indicator, diodes and optocouplers). Also pay attention to the contact pads; if drilling holes with a diameter of 0.5-0.7 mm is difficult, then before printing you need to increase the size of the contact pads. The main requirement for a synchronization unit is to keep in mind that the voltage is high and there can be a breakdown on the surface of the PCB and on the surface of the parts, so it is advisable to use lead parts with a large distance between the leads. For the same reason, the bridges are made up of separate diodes. No need to save space and textolite! the voltage at individual points on the synchronization board can reach 600 volts! After manufacturing, the board must be coated with electrical insulating varnish, preferably in two or three layers, to prevent breakdown due to dust.
The video is presented when operating in phase-pulse control mode, on an oscilloscope the signal from current transformers connected in two phases, the load is three incandescent lamps of 1 kW each. The video shows a device layout used for debugging.
Literature
- V.M. Yarov. "Power sources for electric resistance furnaces" textbook, 1982.
- A.V. Evstifeev "AVR microcontrollers of the Mega family, user manual" 2007.
List of radioelements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad | |
|---|---|---|---|---|---|---|---|
| Power circuit. | |||||||
| T1-T6 | Optocoupler | FOD8012 | 6 | To notepad | |||
| T7-T9 | Bipolar transistor | KT972A | 3 | To notepad | |||
| C4-C6 | Capacitor | 0.1 µF 600 V | 3 | Paper | To notepad | ||
| R29-R31 | Resistor | 39 Ohm | 3 | To notepad | |||
| R32-R34 | Resistor | 18 ohm | 3 | To notepad | |||
| R36-R38 | Resistor | 1 kOhm | 3 | To notepad | |||
| Rn | 3-phase current consumer | 1 | To notepad | ||||
| A, B, C | Terminal clamp | 3 | To notepad | ||||
| VR2 | Linear regulator | LM7805 | 1 | To notepad | |||
| VD2 | Diode | 1 | To notepad | ||||
| VDS5 | Diode bridge | 1 | To notepad | ||||
| HL2 | Light-emitting diode | 1 | To notepad | ||||
| C9 | 470 µF | 1 | To notepad | ||||
| C10, C13 | Capacitor | 0.1 µF | 2 | To notepad | |||
| C11 | Electrolytic capacitor | 10 µF | 1 | To notepad | |||
| C12 | Electrolytic capacitor | 100 µF | 1 | To notepad | |||
| R36 | Resistor | 910 Ohm | 1 | To notepad | |||
| FU1 | Fuse | 1 | To notepad | ||||
| Tr2 | Transformer | 220/380 V - 15 V | 1 | To notepad | |||
| Bipolar transistor | KT3102 | 6 | To notepad | ||||
| Optocoupler | AOT101AC | 3 | To notepad | ||||
| VDS4-VDS6 | Diode bridge | 3 | For a voltage of at least 800 V | To notepad | |||
| VD4-VD6 | Rectifier diode | 1N4007 | 3 | To notepad | |||
| C4-C6 | Capacitor | 0.22 µF | 3 | To notepad | |||
| R29, R30, R36, R37, R43, R44 | Resistor | 300 kOhm | 6 | To notepad | |||
| R31, R32, R38, R39, R45, R46 | Resistor | 120 kOhm | 6 | To notepad | |||
| R33, R40, R47, R50-R52 | Resistor | 22 kOhm | 6 | To notepad | |||
| R34, R41, R48 | Resistor | 100 kOhm | 3 | To notepad | |||
| R35, R42, R49 | Resistor | 300 Ohm | 3 | To notepad | |||
| R53-R55 | Resistor | 5.1 kOhm | 3 | To notepad | |||
| Fuse | 100 mA | 6 | To notepad | ||||
| A, B, C | Terminal clamp | 3 | To notepad | ||||
| Control and display unit. | |||||||
| DD1 | MK AVR 8-bit | ATmega8 | 1 | To notepad | |||
| DD2 | Shift register | SN74LS595 | 1 | To notepad | |||
| T1-T3 | Bipolar transistor | ||||||
Such a simple, but at the same time very effective regulator can be assembled by almost anyone who can hold a soldering iron in their hands and even slightly read the diagrams. Well, this site will help you fulfill your desire. The presented regulator regulates power very smoothly without surges or dips.
Circuit of a simple triac regulator
Such a regulator can be used to regulate lighting with incandescent lamps, but also with LED lamps if you buy dimmable ones. It is easy to regulate the temperature of the soldering iron. You can continuously adjust the heating, change the rotation speed of electric motors with a wound rotor, and much more where there is a place for such a useful thing. If you have an old electric drill that does not have speed control, then by using this regulator you will improve such a useful thing.The article, with the help of photographs, descriptions and the attached video, describes in great detail the entire manufacturing process, from collecting parts to testing the finished product.
I’ll say right away that if you are not friends with your neighbors, then you don’t have to collect the C3 - R4 chain. (Joke) It serves to protect against radio interference.
All parts can be bought in China on Aliexpress. Prices are two to ten times less than in our stores.
To make this device you will need:
- R1 – resistor approximately 20 Kom, power 0.25 W;
- R2 – potentiometer approximately 500 Kom, 300 Kom to 1 Mohm is possible, but 470 Kom is better;
- R3 - resistor approximately 3 Kom, 0.25 W;
- R4 - resistor 200-300 Ohm, 0.5 W;
- C1 and C2 – capacitors 0.05 μF, 400 V;
- C3 – 0.1 μF, 400 V;
- DB3 – dinistor, found in every energy-saving lamp;
- BT139-600, regulates a current of 18 A or BT138-800, regulates a current of 12 A - triacs, but you can take any others, depending on what kind of load you need to regulate. A dinistor is also called a diac, a triac is a triac.
- The cooling radiator is selected based on the planned regulation power, but the more, the better. Without a radiator, you can regulate no more than 300 watts.
- Any terminal blocks can be installed;
- Use the breadboard as you wish, as long as everything fits in.
- Well, without a device it’s like without hands. But it’s better to use our solder. Although it is more expensive, it is much better. I haven't seen any good Chinese solder.
Let's start assembling the regulator
First, you need to think about the arrangement of parts so as to install as few jumpers as possible and do less soldering, then we very carefully check the compliance with the diagram, and then solder all the connections.
After making sure that there are no errors and placing the product in a plastic case, you can test it by connecting it to the network.
The power regulators presented on this page are designed for switching 3-phase loads in automation systems, in production, and at home. A three-phase power regulator is a complete device containing power thyristors, fuses, a radiator, a fan, and a control circuit in one housing. The three-phase regulator is designed to switch the load simultaneously across all 3 phases. Switching voltage is variable ~200…480VAC 50 Hz. The control signal can be of different types - voltage 0-10VDC, current 4-20mA and is selected by hardware with a jumper. The designation 60 Amps means that the power regulator can switch this current in each phase. Based on the type of switching, there are models with switching when the voltage crosses zero (ZZ series) and with phase control (TP series). All power regulators can operate with a 3-phase network without a neutral.
Features of the functioning of a three-phase power regulator
The regulator becomes hot during operation. Models with 30 and 45 Amps use natural cooling; models with 60 Amps or more use a fan. The regulators have a built-in overheating protection system. When the protection is triggered, the output voltage is turned off. Three-phase voltage is connected to the terminals on top of the device, below the terminals for connecting the load power cable. The power regulator is mounted vertically on the wall with screws in the grooves of the radiator.
For any questions, please contact the managers of the online store “Delta-kip” in Moscow; you can contact us by the multi-channel phone number listed on our website.
The digital power controller for a 3-phase AC motor is made using a special MC3PHAC chip from NXP Semiconductor. It generates 6 PWM signals for a 3 phase AC motor. The unit is easily combined with a powerful 3-phase IGBT/MOSFET key drive. The board provides 6 PWM signals for the IPM or IGBT inverter, as well as a brake signal. The circuit operates offline and does not require programming or coding.
Regulator circuit
Controls
- PR1: Potentiometer for setting acceleration
- PR2: Potentiometer for speed regulation
- SW1: DIPX4 switch for setting frequencies 60Hz/50Hz and setting output active low / active high
- SW2: Reset switch
- SW3: Start/stop motor
- SW4: change motor direction
Main settings
- Driver Power 7-15VDC
- Potentiometer for motor speed control
- Default PWM frequency 10.582 kHz (5.291 kHz - 164 kHz)
M/s MC3PHAC is a monolithic intelligent controller designed specifically to meet the need for low cost 3-phase variable speed AC motor control systems. The device adapts and configures depending on its parameters. It contains all the active functions required to implement the open loop part of the control. This makes the MC3PHAC ideal for applications requiring AC motor control support.
The MC3PHAC includes protection functions consisting of DC bus voltage monitoring and system fault input, which will immediately disable the PWM module when a system fault is detected.
All output signals are TTL level. The input for the power supply is 5-15 VDC, the constant voltage on the bus should be in the range of 1.75 - 4.75 volts, a DIP switch is provided on the board for installation with motors with a frequency of 60 or 50 Hz, jumpers help set the polarity of the output PWM - signal, that is, active low or active high, which allows this board to be used in any module, since the output can be set to active low or high. Potentiometer PR2 helps regulate the motor speed. To change the base frequency, PWM shutdown time, and other possible parameters, study the datasheet. Board files - archived
Speed control. The synchronous frequency of the electric motor can be set in real time to any value from 1 Hz to 128 Hz by adjusting potentiometer PR2. The scaling factor is 25.6 Hz per volt. Processed with a 24-bit digital filter to increase speed stability.
Acceleration control. The motor acceleration can be set in real time in the range from 0.5 Hz/sec to 128 Hz/sec by adjusting potentiometer PR1. The scaling factor is 25.6 Hz/second per volt.
Protection. When a fault occurs, the MC3PHAC immediately disables the PWM and waits until the fault condition is cleared before starting a timer to re-enable. In standalone mode, this timeout interval is set during the initialization phase by applying voltage to the MUX_IN pin while the RETRY_TxD pin is driven low. Thus, repeat times can be specified from 1 to 60 seconds with a scaling factor of 12 seconds per volt.
External fault monitoring. The FAULTIN pin accepts a digital signal indicating a fault detected by external monitoring circuits. A high level on this input causes PWM to be turned off immediately. Once this input returns to logic low, the fault retry timer starts running and the PWM is re-enabled after reaching the programmed timeout value. Input pin 9 of the CN3 FLTIN connector must be at high potential.
Voltage integrity monitoring(input signal pin 10 in cn3) in DC_BUS is monitored at 5.3 kHz (4.0 kHz if the PWM frequency is set to 15.9 kHz). In standalone mode, the thresholds are fixed at 4.47 volts (128% of nominal), and 1.75 volts (50% of nominal), where the nominal value is determined to be 3.5 volts. As soon as the DC_BUS signal level returns to a value within the permissible limit, the fault repeat timer begins to run, and the PWM is turned on again after reaching the programmed timeout value.
Regeneration. The saving process by which stored mechanical energy in the motor and load is transferred back to the drive electronics usually occurs as a result of forced deceleration. In special cases where this process occurs frequently (e.g., elevator motor control systems), it includes special functions to allow this energy to flow back into the AC grid. However, for most low-cost AC drives, this energy is stored in the DC bus capacitor by increasing its voltage. If this process is not installed, the DC bus voltage can rise to dangerous levels, which can damage the bus capacitor or the transistors in the power inverter. MC3PHAC allows you to automate and stabilize this process.
Resistive braking. The DC_BUS pin is monitored at 5.3 kHz (4.0 kHz if the PWM frequency is set to 15.9 kHz), and when the voltage reaches a certain threshold, the RBRAKE pin will go high. This signal can be used to control a resistor brake placed across a DC bus capacitor so that mechanical energy from the motor is dissipated as heat in the resistor. In standalone mode, the DC_BUS threshold required to acknowledge the RBRAKE signal is fixed at 3.85 volts (110% of nominal), where nominal is defined as 3.5 volts.
PWM frequency selection. The MC3PHAC has four discrete switching frequencies that can be dynamically changed as the motor rotates. This resistor can be a potentiometer or a fixed resistor within the range shown in the table. The PWM frequency is determined by applying voltage to the MUX_IN pin while the FREQ_RxD PWM pin is driven low potential.
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