TO SHEARERS, AND NOT ONLY
MSU200 shearers with three-phase asynchronous electric motor built into the handle (200 Hz, 36 V, 100 W, 12OO rpm) are not uncommon in our countryside. True, slightly modified, with a hardening sleeve on the power cable. This technique is also popular in neighboring territories, where it is used by sheep and camel shearers, as well as by specialists involved in post-conservation cleansing of caracoule smoothies. As a regular power source for it is three-phase network of 380 V, to which the MS200 is connected through electric machines converters ÈE9401À and ÈE9403.
The first unit can power 12 shearers at the same time, the second unit can power six shearers at the same time. But unfortunately they both become uneconomical with a small load.
Recently transistor frequency converters designed to provide power to one shearing machine have also become widespread. Designed for small farms, these compact, quiet, highly efficient machines are connected to a 220 V single-phase household power supply. But they have two significant, in the opinion of pro-professional practitioners, drawbacks: excessive complexity of circuit solutions, underlying the design, and low reliability, explained by short-lived output cascades, which often have to work in very stressful modes.
The frequency converter I offer for MSU200 or any other load requiring similar power supply is free from the above drawbacks. It is based on T273A synchronous alternator, which has long been successfully used in the 24-volt power supply systems of KAMAZ and MAZ trucks. Of course, modified: by disconnecting (for example, with wire cutters) the reverse polarity diodes from the negative bus (heat sink) in the standard rectifier, which immediately transforms from a push-pull to a single-stroke three-phase device
negative terminal strip (heat sink); 2. insulating bush (2 pcs.); 3. negative terminal strip (heat sink).); 3. diode BA20 of direct polarity (3 pcs.); 4. bushing (3 pcs.); 5. generator phase clamp (3 pcs.); 6. positive busbar; 7. reverse polarity diode BA20 (3 pcs.)
During such modernization the power supply of the rotating field winding inevitably changes: the voltage comes not from “zero” point of stator winding connection and “minus” terminal of the former rectifier, but from “zero” and “stabilized plus” of the updated unit. As a result it is possible to get from Т273А the necessary 36 V instead of regular 24,3 V.
In order to stabilize the alternator voltage (and it has to be unshakeable in case of any load change) a voltage regulator made on the base of common РР362B was introduced into the circuit of excitation winding power supply. But since a serial device is designed for connection to 14 V, and now it needs to operate at another, much higher rating, I had to correct slightly the circuit by including in series with the relay coil K2 “quenching” resistor J7 type MLT-0,5 resistance of 25 Ohm At that working currents and voltages in the test points have been saved at the level of quite permissible values, and this ensured high reliability of the whole converter.
I. control gear (magnetic starter type with “Mains” and “Work” indicators); II. Electric drive motor (50 Hz, 220 V, 500 W, 2850 rpm; single- or three-phase, the latter requires a phase-shifting capacitor); III. V-belt drive (1 = 1,38); IV. finalized generator G273A; V. finalized voltage regulator РР362B;
stator coils winding, 2. stator; 3. rotor; 4. excitation winding; 5. brush (2 pcs).); 6. contact ring (2 pcs.); 7. dismountable diode of reverse polarity (3 pcs.); 8. yoke; 9. spring; 10. thermo-metal plate; 11. core; 12. armature
As before the modification, the finalized РР362B contains a voltage regulator PH (in Fig. 2 with through numbering of parts and assemblies this is K2) and protection relay PZ (K1), transistor \. And PH and PZ are placed on the panel in the sealing compartment of the device, all resistors. under the panel, and the transistor with diodes. in the vented compartment. The air for cooling them flows through the slots in the cover of the housing.
Electromagnetic vibrating PH is a sensing element that responds to an increase in alternator voltage. Regulator contacts open or close the transistor VT 1, which conducts or does not conduct current into the field winding of the mating G273A. The PH consists of a yoke, a core with a winding, an armature with a spring and a thermo-metal plate, normally closed by K2.1 and normally open K2.2 contacts. The protection relay, in fact, has a similar design. The only difference here is probably the number of working contacts. There is one pair of relays (K1.1).
The PH and PZ windings have 1224 turns of PETV-0,27 wire each. Resistance of each DC
17,1 Ohm. Gap between pins of voltage regulator must be 0,2-0,3 mm. At relays of protection this parameter from 0,7 to 0,8 mm. Adjustment is done by moving the contact holder and the armature stroke limiter.
A 500 watt single-phase motor is needed to drive the generator. If a V-belt is not available, a more common three-phase electric motor with slightly higher power can be used. For operation in a domestic power grid, it is connected with starting and working capacitors (see. “Modelist-constructor” ’86, 11’90, 12’91, 8’99).
Dimensions of the pulley to obtain the required 200 Hz from the generator considered above, the rotor of which (in relation to the motor shaft) is slave, are specified according to the proportion:
(n1/n2)=(D2/D1); where n1. rotor speed of the electric motor, rpm; n2. rotor speed of the generator, rpm; D1. pulley diameter of the electric motor, mm; D2. pulley diameter of the generator, mm.
In particular, with standard D2 = 105 mm, n2- 2000 rpm and n1 = 2850 rpm, master D1 must be 74 mm. It is better to take a V-belt (for example, from a washing machine).
As a rigid basis for assembling all kinematics it is desirable to use a box frame made of 2525 mm steel angle. Dimensions and other parameters of such a device greatly depend on the motor used.
The housing must be enclosed to prevent accidental contact with the V-belt drive and live parts of the structure. The walls are mesh, for better ventilation of the converter. And the cover, made of solid insulating material (for example, from 3 mm thick textolite), serves at the same time as the electrical board with the located on it starting and controlling device of the magnetic starter type, three-phase connector “Load”, the indicator lights “Network” and “Operation.
Frequency drive 5-200Hz (10-400Hz) with their own hands
In this article we will talk about the frequency converter, in common parlance, the frequency converter. This frequency controller, and later the frequency drive, is able to control a 3-phase asynchronous motor. In this frequency drive (FD) I use a smart power module by International Rectifier, specifically the IRAMS10UP60B (from AliExpress). The only thing I did with it was to bend the legs, so in fact the module turned out to be IRAMS10UP60B-2. I chose this module mainly because of the built-in driver. The main feature of the inline driver is the ability to use 3 PWM channels instead of 6 PWM channels. over I use ATmega48 as a controller.
When developing this drive I focused on the efficiency of the design, the minimum cost, the availability of the necessary protections, the flexibility of design. As a result a frequency drive with the following characteristics (functions) turned out:
- Output frequency 5-200Hz
- The typing speed is 5-50Hz per second
- Frequency dropping speed 5-50Hz per second
- 4 fixed speeds (each from 5-200Hz)
- Volt add 0-20%
- Two “factory” settings that can always be activated
- Magnetizing motor function
- Full motor stop function
- Reverse input (as without it)
- Ability to change U/F characteristic
- Possibility of setting the frequency with a variable resistor
- IGBT module temperature control (alarm in case of overheating and drive stop)
- DC link voltage control (over-under-voltage DC link, alarm and stop of the drive)
- DC link precharge
- Maximum power with this module 750w, but also turns 1.1kV on my CNC
- All this on one 8 x 13 cm board.
At the moment, protection against overcurrent or short circuits are not implemented (I think there is no point, although, I left a free leg in the MCU with an interrupt to change)
The printed circuit board of this device (available in the lay under the iron)
In this photo completely working model, tested and run-in (has no panel located on the left). The second one is for the test of the atmega 48 before shipment (on the right side).
The one on this picture is the same irams (I made it with reserve, it should fit iramx16up60b)
Algorithm of operation of the device
Initially the MC (microcontroller) is configured to work with an electric motor with a nominal voltage of 220V at a rotating field frequency of 50Hz (t.е. normal induction motor with 220v 50Hz written on it). The sampling rate is set to 15Hz/sec.(т.е. Acceleration to 50 Hz takes just over 3 seconds., to 150 Hz 10 sec). Volt additive is set at 10%, the magnetization duration is 1 sec. (Constant value unchanged), constant current braking duration 1 sec. (the constant is unchanged). It should be noted that the magnetizing voltage, as well as the braking voltage, is the volt additive voltage and changes at the same time. By the way, the frequency converter is a scalar one, i.e.е. as the output frequency increases the output voltage increases.
After energizing, the capacitance of the dc link is charged. As soon as the voltage reaches 220V (constant), the pre-charging relay switches on with a certain delay and the only LED I have lit up L1. From now on the drive is ready to start. There are 6 inputs to control the frequency converter:
- On (if you supply only this input, the PD will rotate the motor with a frequency of 5Hz)
- On/reverse (if only this input is given the PD will rotate the motor at 5Hz, but in the other direction)
- 1 fixed frequency (set by R1)
- 2 fixed frequency (set by R2)
- 3 fixed frequency (set by R3)
- 4 fixed frequency (set by R4)
There is one BUT in this control. If the set point on the resistor is changed while the motor is rotating, it will change only after the command is given again (on/off).) or (on/off).). In other words, the data from the resistors is read as long as these two signals are missing. If you plan to adjust the speed with the resistor during operation, it is necessary to set the jumper J1.In this mode only the first resistor is active and the resistor R4 limits the maximum frequency, that is if it is set to 50% (2.5v-4 “pin”. in the photo below 5 ground), then the frequency of R1 will be controlled by a resistor from 5 to 100Hz.
To set the rotational speed it is necessary to remember, that 5v on the input of MC corresponds to 200Hz., 1v-40Hz, 1.25v-50Hz and t.д. To measure the voltage there are pins 1-5, where 1-4 correspond to the numbers of resistors, 5. common minus (in the photo below). The resistor R5 serves for adjustment of the DC-link voltage scale of 1v.100v (R30 in the schematic).
The arrangement of the elements
Note! The board is under voltage dangerous to life. The control inputs are isolated by optocouplers.
Setting of drive before first switching on is reduced to checking of assembling of electronic components and setting of voltage divider for DC-link (R2).
100 volts DC link must correspond to 1 volt on 23 (leg of the MC). this is IMPORTANT. This completes the setup process.
Before applying the mains voltage it is necessary to wash the board (remove the remains of rosin) on the soldering side with solvent or alcohol, preferably with a varnish.
The drive is preset to suit both 220V 50Hz) and 380V 50Hz motors. These settings can always be set if you do not dare to tune the drive yourself. In order to set the “factory” settings for the motor (220V 50Hz) :
- Run the thrust actuator
- Waiting for readiness (if only the MC is powered). Simply wait for 2-3 seconds)
- Press and hold down button B1 until the LED L1 starts to flash, release button B1
- Give 1st speed selection command. As soon as the LED stops flashing, clear the command
- Drive adjusted. Depending on. LED lit (if not lit, the drive is waiting for DC link voltage).
With this setting, the following parameters are automatically recorded:
- Rated motor frequency at 220V. 50Hz
- Volt additive (magnetizing, braking voltage ). 10%
- Acceleration rate 15Hz./sec
- 15 Hz braking intensity./sec
If the second speed selection signal is given, the following parameters will be written to the EEPROM (the only difference is the frequency):
- Rated motor frequency at 220V-30Hz
- Volt additive (Magnetizing, braking voltage ) 10%
- Acceleration intensity 15Hz./sec
- 15Hz braking intensity./sec
- Press and hold button B1
- Wait until the LED starts to blink
- Release button B1
- Do not apply any voltage to the 1st or 2nd speed selection inputs
- To set the parameters with the trimmers
- Press and hold button B1 until the LED starts to blink
Thus, as long as the LED is blinking, the drive is in tuning mode. In this mode, when the 1st or 2nd speed input is applied, the parameters are written to the EEPROM. If you don’t supply voltage to the 1st or 2nd speed input, then the fixed parameters will not be written into the EEPROM, but will be set with the trim resistors.
- The resistor sets the nominal frequency of the motor at 220V (So, for example if it says 200Hz / 220V the resistor has to be turned up to the maximum; if it says 100Hz / 220V it has to be 2.5 Volt on the 1st contact. (1 Volt on the first contact corresponds to 40 Hz); if it is written on the motor that it is 50Hz/400V then you have to set 27Hz/0,68V (for example:(50/400)220=27Hz), because we have to know the motor frequency at 220V supply. Variation range of the parameter 25Hz. 200Hz.(1 Volt on the 1st pin represents 40 Hz)
- Resistor is responsible for volt addition. 1 Volt on the 2nd contact corresponds to 4% of the voltage volt additive (my opinion is to choose at 10% i.e. 2.5 volts increase with caution) Adjustment range 0-20% of line voltage (1 volt on pin 2 corresponds to 4%)
- The acceleration value of 1 V equals 10Hz/sec (in my opinion the optimal value is 15.25 Hz/sec) Setting range 5Hz/sec. 50Hz/sec. (1 volt on pin 3 corresponds to 10 Hz/sec)
- Braking intensity of 1 Volt equals 10Hz/s (10 is optimal in my opinion).15 Hz/sec) Tuning range 5Hz/sec. 50Hz/sec. (1 Volt on pin 4 corresponds to 10 Hz/sec)
After all the resistors are set, press and hold button B1 until the LED does not flash any more. If the LED blinked and turned on, the drive is ready to start.If the LED was blinking and did NOT light, then wait 5 seconds and only then disconnect power from the controller.
Below is the volt/frequency response of the device for a 220v 50Hz motor with a volt additive of 10%.
преобразователь 220 на 36 вольт 200 герц для МСУ100
- Umax is the maximum voltage the inverter is capable of delivering
- Uv.д.- Volt additive voltage as a percentage of the mains voltage
- Fn.д.- rated motor speed at 220V. IMPORTANT
- Fmax is the maximum output frequency of the inverter.
Another example of tuning
Suppose you have a motor that has a rated frequency of 50Hz. The nominal voltage is 80V, To find out what the nominal frequency will be at 220V you need: 220V divided by the nominal voltage and multiplied by the nominal frequency (220/8050=137Hz). Thus we get that voltage on 1 contact (resistor) must be set to 137/40 = 3,45V.
Simulation in Proteus 0-50Hz one phase (on 3 phases, the computer hangs)
As you can see from the screenshot, as the frequency increases, the amplitude of the sine increases. Acceleration takes about 3.1 sec.
I recommend using a transformer as this is the most reliable option. On my test boards there are no diode bridges and stabilizer for igbt module 7812. Two printed circuit boards are available for download. The first one is the one presented in the review. The second has minor changes, a diode bridge and a regulator are added. The protecting diode must be P6KE18A or 1.You must use a 5KE18A.
An example of transformer placement, as it turned out, is not difficult to find.
Which motor can be connected to this frequency inverter?
It depends on the module. Basically any motor can be connected, as long as its resistance for the irams10up60 module is greater than 9 ohms. Note that the irams10up60 module is designed for small surge currents and has a built in protection at 15A This is very low. But for a 50Hz 220V 750W motor, that’s good enough. If you have a high speed spindle, it probably has a small winding resistance. This module can pulse current. When using the IRAMX16UP60B module (you have to bend the legs yourself), the motor power according to the datasheet increases from 0.75 to 2.2KW.
The great thing about this module: the short circuit current is 140A vs 47A, the protection is set at 25A. Which module to use is up to you. Remember that for 1 kW you need 1000mcf of capacitance dc link.
As for the short circuit protection. If you do not add a smoothing choke (it limits the rate of current buildup) right after the output and short-circuit the output of the module, then the module will be doomed. If you have an iramX module, chances are. But with IRAMS there is no chance, it has been tested.
The program takes 4096 kB of 4098 memory. Everything is compressed and optimized to the maximum program size. The cycle time is a fixed value of 10ms.
At the moment all of the above works and has been tested.
If I use a 20MHz crystal the drive will achieve 10-400Hz; the ramp rate is 10-100Hz/sec; the PWM frequency will go up to 10kHz; the cycle time will drop to 5ms.
Looking ahead the next frequency converter will be implemented on the ATmegа64, have a PWM bit depth not 8, but 10 bits, have a display and many parameters.
Below you can see the video of setting up the drive, checking the overheat protection, demonstration of operation (I use a 380V 50Hz motor, and the settings for 220V 50Hz). I did this on purpose to check how the PWM works with the minimum setting.)
There will not be any firmware in free access, BUT a programmed ATmega48-10pu or ATmega48-20pu controller will be cheaper than mc3phac. Ready to answer all your questions.