The use of inverters is an effective method of adjusting the speed of rotation of an asynchronous motor with a squirrel-cage rotor. In practice, the method of changing the amplitude of the supply voltage is more often implemented. Suitable for any type of asynchronous motors. For a long time they did not think about the possibility of the approach: if only it worked, what other inverter compressor in the refrigerator! Bykov's well-known reference book on refrigeration compressors of 1992 does not give a word about variable frequency pulse generators. Today equipment is called inverters.
Asynchronous motors, control methods
Almost all generators are built according to the scheme of synchronous motors. In fact, you can rotate the permanent magnet inside the coil, EMF will be induced. It is enough to position the coils correctly in order to remove alternating current at the output. The beauty is that in a synchronous motor, the shaft speed and the voltage removed are the same. It is able to withstand the parameters. Otherwise, it would be necessary to rectify the current, to install inverters in order to give power to the consumers( cities, villages).We will lose the accuracy of the parameters, most household appliances will be able to work. Stability will fall, the equipment will begin to fail.
In most everyday, industrial situations, asynchronous motors are good, including a refrigerator compressor circuit. Just manage. Synchronous motors gave way to generators. Rotating magnetic field is used in devices. The rotor of an asynchronous motor is short-circuited or phase. In the latter case, the rotor windings are connected to the starting resistor. In our opinion, asynchronous motors with a phase-rotor are used not for the ability to change the rotational speed, for a large starting torque. Actually, a starting rheostat is introduced, the resistance of which after start-up gradually decreases in steps. Difficult adjustment method, but used in trams, lifts.
Let's talk another time, it is not customary to turn on the compressors of the refrigerators in series, reducing the starting current, therefore, this topic is not relevant. Asynchronous motors with a squirrel cage rotor are simple in design. Equipped with slip rings over time. The advantage leads to different ways of regulation.
For phase rotors, additional resistance is applied to the winding circuit, powered by rotating coils with alternating current, and the amplitude of the voltage applied to the stator changes. Suitable for short-circuited motors only the latter method. It is possible to control the rotational speed by varying the clocking frequency of the supply voltage.
Inverters are used in household appliances. Generate pulses of variable frequency, as appropriate affecting the speed of rotation of the rotor of the induction motor. To understand the principle of action, let us briefly consider what is happening inside. An alternating voltage is applied to the stator, the number of phases is not considered. Due to the power supply, an alternating rotating magnetic field is generated inside, acting on the rotor. As a result, EMF is induced on the coils, electromagnets with poles are created inside. Each sign begins to be captured by the magnetic field, the asynchronous motor starts to move. The starting period consumes a significant starting current( 3-7 nominal).
The rotor rotates faster, the frequency of the induced EMF is lower. Gradually, the system reaches equilibrium, as if permanent magnets rotated inside. The rotor speeds and the alternating current of the stator cannot be compared, the EMF will disappear, the engine will begin to slow down. Again there will be a difference.
EMF is induced, the rotor of the engine is again captured by the field. Turns will be lower than frequency of the feeding pressure. The feature is used to manipulate the rotation speed. The inverter smoothly changes the parameter, the asynchronous motor immediately obeys.
Why it was impossible to put permanent magnets on the shaft, they would rotate, practicing the frequency of the field. In synchronous engines do. Is it possible to control by varying the frequency of the voltage. Why are synchronous motors not used in combination with inverters? We do not know the answer, presumably, it concerns the inertia of the rotor. From reading it becomes clear: when disconnecting the starting rheostat, closing the rings, an analogue of a short-circuited rotor is obtained. Why the method of changing the frequency of the supply voltage is unsuitable for phase motors remains a mystery.
Back to the inverters. Today, refrigeration compressors are controlled, where no significant starting torque is needed. Therefore, we see grounds to assume that there are no rotors with double squirrel cages or deep grooves under the copper plates connected in the form of a drum inside.
The two windings simply create a field, the fan blades begin to rotate slowly, moving the freon. Soon the asynchronous motor enters the mode, the starting circuit is switched off by the command of the corresponding relay. How does he understand: the momentum reached the given? There are several ways.
- Induction. Starting current of great value closes the contacts with the help of the anchor of the starting coil. Then consumption decreases, the chain is gradually disconnected from the supply.
- Thermal. The working substance of the conductor of the starting coil circuit gradually heats up, expanding, breaking the electrical contact.
It remains to add, almost every refrigerator compressor is supplemented with a protective relay to prevent overheating. As a result, the device operates controlled by thermostats and protection devices.
Inverter compressors in refrigerators
Now it is easy to understand how the inverter compressor of the refrigerator works. At the initial moment of time, the asynchronous motor starts up, leaving the mode. Gradually, the temperature of the chambers decreases, reaching the set point, here the motor does not stop, it just reduces the speed to a minimum. As a result, the cooling rate drops sharply, does not become zero. Gradually begins to balance the heat loss due to imperfect insulation. If you open the door of the refrigerator, the warm air will rush inwards, causing a slight increase in the speed of the inverter compressor. Fully rarely stops, works on benign modes.
That's why Samsung gives 10 years warranty for inverter compressors in its own refrigerators. Refrigerators with a linear compressor exclude from the design of the usual engine with a rotating rotor. Compressor - there is an engine! The piston moves linearly due to a change in the electromagnetic field. Inverter control circuit God has prescribed. The power supply frequency will be higher, the piston will more often knock, driving the freon. Consequently, the cooling rate will increase.
The supporter of LG linear compressors is slow to give 10 years warranty. Let's discuss the inverter linear compressor. Linear compressor - piston moves in a straight line - equipped with inverter control. We believe that the future is behind frequency regulation, high engine efficiency is promising. It becomes obvious: the method is universal. Not surprising. Asynchronous motors operate in Russia and abroad. Work from 50, 60 Hz. .. Why not adjust the frequency.
Replacing the compressor of the refrigerator
Freon will need to be filled with a new one; replacement of the compressor of the refrigerator requires knowledge of the service information: type of start-up relay. Of course, it is better to put a native spare part, in most cases others will do. Sure, the linear compressor can be replaced by a crankshaft, in older models there is a thermostat, the voltage is 230 volts at 50 Hz. No modulation of the power supply. It is worth worrying about the start-up relay because those compressor engines do not burn out due to improper regulation. Another thing if you change the tandem immediately. Big chance that the device will work.
By the way, do not rush to throw out old household appliances, pay for recycling. An old refrigerator compressor Atlant will serve in the garage, pumping up the wheels. Read the section! Refrigerator compressor is a worthwhile thing. They are becoming safer, more reliable, you can not say about the adsorption, abused by fishermen. In the near future, a small chance, they will come up with something new, effective, cheap, the problem of buying a compressor for a refrigerator will alarm many generations of people on the planet.
We want to say goodbye, please do not judge the weak knowledge of electrical engineering. The standing textbooks did not translate into electronic form. Other do not use! Reply with strong comments.