One of the first power converter circuits three phase motor was published in the magazine “Radio” No. 11 1999. The developer of the scheme, M. Mukhin, was a 10th grade student at that time and was involved in a radio club.

The converter was intended to power a miniature three-phase motor DID-5TA, which was used in a machine for drilling printed circuit boards. It should be noted that the operating frequency of this motor is 400Hz, and the supply voltage is 27V. In addition, the middle point of the motor (when connecting the windings in a star) is brought out, which made it possible to simplify the circuit extremely: only three output signals were needed, and only one output switch was required for each phase. The generator circuit is shown in Figure 1.

As can be seen from the diagram, the converter consists of three parts: a three-phase sequence pulse generator on DD1...DD3 microcircuits, three switches on composite transistors (VT1...VT6) and the electric motor M1 itself.

Figure 2 shows the timing diagrams of the pulses generated by the generator-shaper. The master oscillator is made on the DD1 chip. Using resistor R2, you can set the required engine speed, and also change it within certain limits. More detailed information You can find out about the scheme in the above magazine. It should be noted that according to modern terminology, such generator-shapers are called controllers.

Picture 1.

Figure 2. Generator pulse timing diagrams.

Based on the considered controller by A. Dubrovsky from Novopolotsk, Vitebsk region. a variable frequency drive design was developed for a mains powered motor alternating current voltage 220V. The device diagram was published in Radio magazine in 2001. No. 4.

In this circuit, practically without changes, the controller just discussed according to M. Mukhin’s circuit is used. The output signals from elements DD3.2, DD3.3 and DD3.4 are used to control the output switches A1, A2, and A3, to which the electric motor is connected. The diagram shows key A1 in full, the rest are identical. The complete diagram of the device is shown in Figure 3.

Figure 3.

To familiarize yourself with connecting the motor to the output switches, it is worth considering the simplified diagram shown in Figure 4.

Figure 4.

The figure shows an electric motor M controlled by keys V1...V6. To simplify the circuit, semiconductor elements are shown as mechanical contacts. The electric motor is powered by a constant voltage Ud received from the rectifier (not shown in the figure). In this case, the keys V1, V3, V5 are called upper, and the keys V2, V4, V6 are called lower.

It is quite obvious that opening the upper and lower keys at the same time, namely in pairs V1&V6, V3&V6, V5&V2 is completely unacceptable: a short circuit will occur. Therefore, for normal operation such a key scheme, it is necessary that by the time the lower key is opened, the upper key has already been closed. For this purpose, control controllers create a pause, often called a “dead zone”.

The length of this pause is such as to ensure guaranteed closure of the power transistors. If this pause is not sufficient, then it is possible to briefly open the upper and lower keys simultaneously. This causes the output transistors to heat up, often leading to their failure. This situation is called through currents.

Let's return to the circuit shown in Figure 3. In this case, the upper keys are 1VT3 transistors, and the lower ones are 1VT6. It is easy to see that the lower keys are galvanically connected to the control device and to each other. Therefore, the control signal from output 3 of element DD3.2 through resistors 1R1 and 1R3 is supplied directly to the base of the composite transistor 1VT4…1VT5. This composite transistor is nothing more than a lower switch driver. In exactly the same way, elements DD3, DD4 control the composite transistors of the lower key drivers of channels A2 and A3. All three channels are powered by the same rectifier VD2.

The upper keys of galvanic connection with common wire and do not have a control device, so to control them, in addition to the driver on the composite transistor 1VT1...1VT2, it was necessary to install an additional 1U1 optocoupler in each channel. The output transistor of the optocoupler in this circuit also performs the function of an additional inverter: when the output of element 3 of DD3.2 is high, the transistor of the upper switch 1VT3 is open.

To power each upper switch driver, a separate rectifier 1VD1, 1C1 is used. Each rectifier is powered by an individual winding of the transformer, which can be considered as a disadvantage of the circuit.

Capacitor 1C2 provides a switching delay of about 100 microseconds, the same amount is provided by optocoupler 1U1, thereby forming the above-mentioned “dead zone”.

Is frequency regulation enough?

As the frequency of the AC supply voltage decreases, the inductive reactance of the motor windings decreases (just remember the formula for inductive reactance), which leads to an increase in the current through the windings, and, as a consequence, to overheating of the windings. The stator magnetic circuit is also saturated. To avoid these negative consequences, when the frequency decreases, the effective value of the voltage on the motor windings must also be reduced.

One of the ways to solve the problem in amateur frequency generators was to regulate this most effective value using a LATR, the moving contact of which had a mechanical connection with variable resistor frequency regulator. This method was recommended in the article by S. Kalugin “Refinement of the speed controller of three-phase asynchronous motors" Radio magazine 2002, no. 3, p. 31.

In amateur conditions, the mechanical unit turned out to be difficult to manufacture and, most importantly, unreliable. Simpler and reliable way the use of an autotransformer was proposed by E. Muradkhanyan from Yerevan in the magazine “Radio” No. 12 2004. The diagram of this device is shown in Figures 5 and 6.

The 220V network voltage is supplied to the autotransformer T1, and from its moving contact to the rectifier bridge VD1 with filter C1, L1, C2. The filter output produces a variable constant pressure Ureg, used to power the engine itself.

Figure 5.

The voltage Ureg through resistor R1 is also supplied to the master oscillator DA1, made on the KR1006VI1 microcircuit (imported version). This connection turns a conventional square wave generator into a VCO (voltage controlled oscillator). Therefore, as the voltage Ureg increases, the frequency of generator DA1 also increases, which leads to an increase in engine speed. As the voltage Ureg decreases, the frequency of the master generator also decreases proportionally, which avoids overheating of the windings and oversaturation of the stator magnetic circuit.

Figure 6.

Figure 7.

The generator is made on the second trigger of the DD3 chip, designated in the diagram as DD3.2. The frequency is set by capacitor C1, frequency adjustment is carried out by variable resistor R2. Along with the frequency adjustment, the pulse duration at the generator output also changes: as the frequency decreases, the duration decreases, so the voltage on the motor windings drops. This control principle is called latitudinal pulse modulation(PWM).

In the amateur circuit under consideration, the motor power is low, the motor is powered by rectangular pulses, so the PWM is quite primitive. In real high-power applications, PWM is designed to generate almost sinusoidal voltages at the output, as shown in Figure 8, and to operate with various loads: at constant torque, at constant power and at fan load.

Figure 8. Output voltage waveform of one phase of a three-phase PWM inverter.

Power part of the circuit

Modern branded frequency generators have outputs specifically designed for operation in frequency converters. In some cases, these transistors are combined into modules, which generally improves the performance of the entire design. These transistors are controlled using specialized driver chips. In some models, drivers are produced built into transistor modules.

The most common microcircuits and transistors of the company are currently International Rectifier. In the described circuit, it is quite possible to use IR2130 or IR2132 drivers. One package of such a microcircuit contains six drivers at once: three for the lower switch and three for the upper, which makes it easy to assemble a three-phase bridge output stage. In addition to the main function, these drivers also contain several additional ones, such as overload protection and short circuits. More information about these drivers can be found in technical descriptions Data Sheet for the corresponding chips.

With all the advantages, the only drawback of these microcircuits is their high price, so the author of the design took a different, simpler, cheaper, and at the same time workable path: specialized driver chips were replaced with integrated timer chips KR1006VI1 (NE555).

Output switches on integral timers

If you return to Figure 6, you will notice that the circuit has output signals for each of the three phases, designated as “H” and “B”. The presence of these signals allows you to control the upper and lower keys separately. This separation allows a pause to be formed between switching the upper and lower keys using the control unit, and not the keys themselves, as was shown in the diagram in Figure 3.

The diagram of output switches using KR1006VI1 (NE555) microcircuits is shown in Figure 9. Naturally, for a three-phase converter you will need three copies of such switches.

Figure 9.

KR1006VI1 microcircuits connected according to the Schmidt trigger circuit are used as drivers for the upper (VT1) and lower (VT2) keys. With their help, it is possible to obtain a gate pulse current of at least 200 mA, which allows for fairly reliable and fast control of output transistors.

The microcircuits of the lower DA2 switches have a galvanic connection with the +12V power source and, accordingly, with the control unit, so they are powered from this source. The upper switch chips can be powered in the same way as shown in Figure 3 using additional rectifiers and separate windings on the transformer. But this scheme uses a different, so-called “booster” method of nutrition, the meaning of which is as follows. The DA1 microcircuit receives power from the electrolytic capacitor C1, the charge of which occurs through the circuit: +12V, VD1, C1, open transistor VT2 (through drain - source electrodes), “common”.

In other words, the charge of capacitor C1 occurs while the lower switch transistor is open. At this moment, the negative terminal of capacitor C1 is practically short-circuited to the common wire (the resistance of the open “drain-source” section in powerful field effect transistors is thousandths of an Ohm!), which makes it possible to charge it.

When transistor VT2 is closed, diode VD1 will also close, the charging of capacitor C1 will stop until the next opening of transistor VT2. But the charge of capacitor C1 is sufficient to power the DA1 chip for as long as transistor VT2 is closed. Naturally, at this moment the upper switch transistor is in the closed state. This scheme power switches turned out to be so good that they are used without changes in other amateur designs.

This article discusses only the simplest circuits of amateur three-phase inverters on microcircuits with a low and medium degree of integration, from which it all began, and where you can even look at everything “from the inside” using the circuit diagram. More modern designs have been made, the diagrams of which have also been repeatedly published in Radio magazines.

Microcontroller control units are simpler in design than those based on medium-integrated microcircuits; they have such necessary functions as protection against overloads and short circuits, and some others. In these blocks, everything is implemented using control programs or, as they are commonly called, “firmware”. It is these programs that determine how well or poorly the control unit of a three-phase inverter will work.

Quite simple circuits of three-phase inverter controllers were published in the magazine “Radio” 2008 No. 12. The article is called “Master generator for a three-phase inverter.” The author of the article, A. Dolgiy, is also the author of a series of articles on microcontrollers and many other designs. The article shows two simple circuits on the PIC12F629 and PIC16F628 microcontrollers.

The rotation speed in both circuits is changed in steps using single-pole switches, which is quite sufficient in many practical cases. There is also a link where you can download ready-made firmware, and, moreover, special program, with which you can change the firmware parameters at your discretion. It is also possible to operate the generators in “demo” mode. In this mode, the generator frequency is reduced by 32 times, which allows you to visually observe the operation of the generators using LEDs. Recommendations for connecting the power section are also given.

But, if you don’t want to program a microcontroller, Motorola has released a specialized intelligent controller MC3PHAC, designed for 3-phase motor control systems. On its basis, it is possible to create inexpensive three-phase adjustable drive systems containing all the necessary functions for control and protection. Such microcontrollers are increasingly used in various household appliances, for example, in dishwashers or refrigerators.

Complete with the MC3PHAC controller, it is possible to use ready-made power modules, for example IRAMS10UP60A developed by International Rectifier. The modules contain six power switches and a control circuit. More details about these elements can be found in their Data Sheet documentation, which is quite easy to find on the Internet.

The generator, the diagram of which is shown in Fig. 1, can find application in various converters single-phase voltage to three-phase. It is simpler than those described in.

Rice. 1 Three-phase pulse generator circuit

The device consists of generator clock pulses DD1.1...DD1.3, shaper DD2 and inverters DD1.4...DD1.6. Clock frequency generator choose 6 times higher frequency than required three-phase voltage and calculated using the approximate formula

The shaper is made on shift register, connected according to the counter-frequency divider circuit by 6. At outputs 1, 3 and 5 (pins 5, 6, 13)

Rice. 2 Output signals of three-phase pulse generator

DD2 are formed square pulses, shifted by 1/3 of a period with a duty cycle of 2. Inverters DD1.4...DD1.6 are connected to the outputs of DD2 for decoupling. The output signals of the generator are shown in Fig. 2.

A. ROMANCHUK

Literature

1. Shilo V.L Popular digital chips. - Radio and communications, 1989, p.60.

2. Ilyin A. Connecting three-phase consumers to a single-phase circuit. - Radio Amateur, 1998, N10, P.26.

3. Kroer Yu. Three-phase 200 Hz from 50 Hz. - Radio Amateur, 1999, N10, P.21.

4. Pyshkin V. Three-phase inverter. - Radio, 2000, N2, P.35.

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Master generator for a three-phase inverter.

The topic of powering a three-phase electric motor from a single-phase network is not new, but still remains relevant. Today we bring to our readers another technical solution Problems. To simplify the master generator - the basis of a three-phase inverter that provides power to such a motor - the author of the article suggests using the PIC12F629 (PIC12F675) or PIC16F628 (PIC16F628A, PIC16F648A) microcontroller. The frequency of the generated oscillations can be changed from the nominal (50 Hz) both downwards (33 and 25 Hz) and up (67 Hz). A description of the program is given that allows you to change the frequency of the generated pulses and their duty cycle. In addition, this program, when loaded into the memory of the PIC12F629 (PIC12F675) microcontroller, is capable of controlling the operation of a six-LED display that simulates the rotation of the rotor of a three-phase electric motor. The microcontroller program files and the “Setting up a three-phase generator” program will be placed on our FTP server at .

The topic of powering a three-phase electric motor from a single-phase network is not new, but still remains relevant. Today we bring to our readers another technical solution to the problem. To simplify the master generator - the basis of a three-phase inverter that provides power to such a motor - the author of the article suggests using a microcontroller.
In recent years, the magazine "Radio" has described many three-phase inverters - converters of direct or alternating single-phase voltage into three-phase. These devices are designed, as a rule, to power asynchronous three-phase electric motors in the absence of a three-phase network. Many of them allow you to regulate the speed of the motor shaft by changing the frequency of the supply voltage.
In addition to powerful output nodes directly connected to the engine, all inverters contain a master generator that generates the multiphase pulse sequences necessary for the operation of these nodes. Assembled on standard logic chips, such a generator is a rather complex device. Particularly complicating it is the need, when adjusting the pulse frequency, to change their duty cycle according to a certain law (to maintain the current in the windings of the electric motor fed from the inverter within acceptable limits). The often used simultaneous adjustment of these parameters with a conventional dual variable resistor does not allow maintaining the desired relationship with a sufficient degree of accuracy.
All these problems can be easily solved using a microcontroller (MK). The master oscillator circuit (Fig. 1) is simplified to the limit, and all its properties are implemented in software. Here elements U1.1-U6.1 are emitting diodes of transistor optocouplers connecting the generator with powerful inverter units. Current flows through diodes U1.1, U3.1 and U5.1 in the time intervals when the “upper” (according to the diagram) switches of phases A, B and C should be open, respectively, and through diodes U2.1, U4.1, U6.1, when the “lower” switches of these phases should be opened. The values ​​of the current flowing through the emitting diodes can be changed by selecting resistors R3-R5, but they should not exceed the permissible 25 mA for the MK.
In the powerful part of the inverter, which is opto-isolated from the master oscillator, pulses of the required polarity for controlling the keys are generated using units made according to the circuits shown in Fig. 2 (a - positive, b - negative). Here Up.2 are phototransistors of optocouplers U1-U6 (see Fig. 1). The supply voltage Upit and the value of resistor R1 are selected depending on the type of powerful switches and their drivers used in the inverter.

Switch SA1 (see Fig. 1) selects one of four frequency values ​​of three-phase voltage. In the version of the program attached to the article (file G3F629.HEX) two of them are lower than nominal (50 Hz), and one is higher. The duration of the generated pulses at nominal and increased frequencies is slightly less than the half-cycle of their repetition, which eliminates the simultaneous opening of the “upper” and “lower” switches of the same phase. A decrease in frequency relative to the nominal one is achieved by increasing pauses between pulses, the duration of which remains the same as at the nominal frequency. This ensures the constant amplitude of the current pulses in the motor windings and prevents saturation of its magnetic circuit. If there is no need to change the frequency, switch SA1 and diodes VD1, VD2 are excluded (the device will generate pulses with a repetition frequency of 50 Hz). Instead of the PIC12F629 MK, you can use the PIC12F675.
The circuit of a similar generator on the PIC16F628 MK is shown in Fig. 3. Its main advantage over the one discussed earlier is the ability to connect an external quartz resonator ZQ1 to the MK and increase the frequency of the generated signals in proportion to the ratio of the frequencies of the resonator and the internal oscillator of the MK (4 MHz). For example, with a resonator frequency of 20 MHz, the maximum frequency of the three-phase voltage will reach 88.5x20/4 = 442.5 Hz (here 88.5 Hz is the maximum frequency that can be set at the frequency of the MK clock generator - built-in or with an external quartz resonator - 4 MHz). If you don't need to increase the frequency, quartz resonator ZQ1 and capacitors C1, C2 (shown in dashed lines in Fig. 3) are not installed, and the MK is configured to operate from the built-in RC oscillator. It is for this device configuration that the version of the G3F628.HEX program attached to the article is designed. Without changes in the circuit and program, it is possible to replace PIC16F628 with PIC16F628A or PIC16F648A.

Optical isolation of the master oscillator and the powerful components of the three-phase inverter is not provided in this case, but it is easy to organize by connecting emitting diodes of optocouplers to a pair of outputs of each phase according to the circuit shown in Fig. 4. In addition to decoupling, such a circuit design additionally guarantees that the “upper” and “lower” switches of each phase will not be open simultaneously (at the same voltage levels at the MC outputs, there is no current through the emitting diodes, and at different voltage levels, only one of them flows) .
If the default pulse frequency and duty cycle values ​​recorded in the MK program are not suitable for some reason, they can be changed (and in the version for the PIC16F628 MK, you can also change the polarity of the output pulses). For this purpose it is intended computer program“Setting up a three-phase generator” (G3F.exe), after running which the window shown in Fig. is displayed on the monitor screen. 5.

The setup begins by selecting the MK for which the adjusted program is intended. Then, if necessary, change the frequency values ​​of the generated pulses and their duty cycle indicated in the table (the reciprocal of the duty cycle, called “duty cycle” in English literature). This is done using the arrow buttons available in the corresponding columns of the table. The values ​​are “non-round”; they change with the discreteness provided in the MK program. The limits of frequency change in each position of switch SA1 are limited by the values ​​​​set for its positions with lower and higher numbers. The highest frequency that can be set at a 4 MHz MK clock generator frequency is, as already mentioned, 88.5 Hz, the lowest is 8.02 Hz.
The duty cycle value can be changed manually ranging from zero (no pulses) to 98.33% (the pause between the pulses that open the “upper” and “lower” keys is minimal). If you click on the "Automatic" screen button, the duty cycle for the position of switch SA1 corresponding to the nominal frequency (it is designated "nom.") will be taken as a basis. For a frequency above the nominal frequency, the coefficient will be set the same, and below it it will be reduced in proportion to the frequency. Note that any switch position can be taken as nominal - just “click” with the mouse next to its number.

The fields "Clock generator" and "Pulse polarity", located below the table of generator operating modes, are active only when the PIC16F628 microcontroller is selected. In the first of them, the type of clock generator is selected and, if necessary, its frequency is specified. In the second, the polarity of the output pulses is set separately for the control channels of the “upper” and “lower” keys. Please note that when using optical isolation according to the scheme shown in Fig. 4, the polarity of the pulses can be any, but must be the same. In other cases it is chosen depending on the characteristics of the powerful components of the inverter.
When you have finished setting all the required values, click on the “Create HEX file” softkey. A window will open in which you should specify the name of this file (the program suggests G3F.HEX), the location on the computer’s hard drive where it will be written, and then click on the “Save” on-screen button. All that remains is to load the created file into the program memory of the MK.

In conclusion, let’s talk about the “Demo” item available in the generator configuration program window. If you check it, a version of the program will be generated with the frequency values ​​of the generated pulses reduced by 32 times relative to those indicated in the table. If in a generator assembled according to the diagram in Fig. 1, load it in the MK, to which the DLA/6GD LED assembly is connected instead of the emitting diodes of the optocouplers (Fig. 6), you can see alternating flashes of six LEDs located in it around the circumference, which simulates the rotation of the rotor of a three-phase motor. This design can be used as a toy or souvenir. The LED assembly can be replaced with six single LEDs, including those of different glow colors, by mounting them on a board of suitable dimensions.
LITERATURE
1. Dubrovsky A. Speed ​​controller of three-phase asynchronous motors. - Radio, 2001, No. 4, S. 42, 43.
2. Kalugin S. Refinement of the speed controller of three-phase asynchronous motors. - Radio, 2002, N9 3, p. 31.
3. Naryzhny V. Power supply for a three-phase electric motor from a single-phase network with speed control. - Radio, 2003, No. 12, p. 35-37.
4. Muradkhanyan E. Controlled inverter for powering a three-phase motor. - Radio, 2004, No. 12, p. 37, 38.
Material taken from: Radio Magazine 2008 No. 12

In the archive Program, Firmware and Source

(downloads: 2447)

To power various household and industrial devices, a three-phase alternating current network with a frequency of 200 or 400 Hz is required. To obtain such voltage, in most cases, an appropriate electromechanical three-phase generator is used, the rotor of which is driven by a single-phase electric motor powered from a 220V network.

The proposed electronic generator allows us to solve this problem with a better efficiency.

If you examine the three-phase voltage diagram, you can see three sinusoidal signals shifted in series by 1/3 of the cycle. If a frequency of 200 Hz is assumed, then the period is 5 mS. Therefore, 1/3 of the period is equal to 1.666... ​​mS. Thus, it turns out that if we have an initial single-phase voltage of 200 Hz, passing it through two delay lines connected in series, each of which introduces a delay of 1.666.. mS, we will obtain a three-phase voltage, one phase is the original voltage, and two phases of voltage with outputs of the corresponding delay lines.

A schematic diagram of a device operating on this principle is shown in the figure. All source signals are rectangular, their conversion to sinusoidal occurs in the inductances of the output transformers T1-T3.

The multivibrator on chip D1 produces rectangular pulses with a frequency of 200 Hz. These pulses are supplied to the input of an electronic high-voltage switch on transistors VT1 and VT4, at the output of which the primary winding of transformer T1 is switched on. As a result, the winding receives impulse voltage 300V. The self-induction EMF smoothes these pulses to a shape close to sinusoidal and an alternating voltage with a frequency of 200 Hz is formed on the secondary winding T1. Thus, phase “A” is formed.

To form phase “B”, pulses with a frequency of 200 Hz from output D1 are supplied to a delay circuit having a time constant equal to 1.666 mS. From output D1.2, a pulse voltage shifted by 1/3 phase compared to the voltage at output D1.3 is supplied to the second switch on transistors VT2 and VT5, which operates similarly to the previous one. On the secondary winding T1 there is phase "B".

Then, from the output of element D2.2, the pulse voltage, already shifted by 1/3 phase, is supplied to the second delay line on elements D2.3 and D2.4, in which another shift by 1/3 phase occurs. Pulses from the output of element D2.4 are supplied to the third switch on transistors VT3 and VT6, in the collector circuit of which the primary winding of transformer T3 is switched on, and an alternating voltage of the third phase is released on its secondary winding.

Microcircuits: D1 - K561LE5, D2 -K561LP2. The microcircuits may be from the K176 series, but in this case the supply voltage must be lowered to 9V (instead of 12V). KT604 transistors can be replaced with KT940, KT848 transistors with KT841. Transformers T1-T3 are identical transformers, designed to obtain the required voltage when a voltage of 220V is applied to their primary winding. For example, if you need to obtain a three-phase voltage of 36V, you need to take 220V/36V transformers for the required power. Used to power microcircuits

constant stabilized voltage source 12V. The +300V voltage is obtained by rectifying the 220V mains voltage using a diode bridge, for example on D242 diodes or other powerful diodes with a voltage of at least 300V. Ripple smoothing is carried out by a 100 µF/360V capacitor (as in the power supply of an USCT TV). This constant voltage is applied to the “+300V” point. You can also apply a lower voltage, and the output voltages will change accordingly.

During the setup process, you need to select resistance R1, use a frequency meter to set the frequency at pin 10 D1 equal to 200 Hz, and then select R2 and R3, use a phase meter to set the phase shift to 120°.

If a three-phase voltage with a frequency of 400 Hz is required, the values ​​of the elements change to the following: R1 = 178 kohms, R2 = 60 kohms, R3 = 60 kohms. All parts, except output transistors and transformers, are mounted on one printed circuit board made of single-sided fiberglass. The output transistors must be installed on heat sinks with a surface area of ​​at least 100 cm2.

View printed circuit board three-phase voltage source