In recent years, DC inverter air conditioner is becoming more popular compared to the conventional air conditioner due to its many advantages. As the compressor takes the most power in any air conditioning system, the change in the compressor technology has enabled better and more efficient air conditioner or heatpump to be deployed. In a 3-phase AC induction motor, the stator of the motor has windings that are designed in such as way that a rotating magnetic field is produced when a 3-phase AC voltages are applied to the windings.The rotor usually has windings that is embedded within iron laminates. As power is supplied to the windings, the magnetic field is produced in the rotor that causes it react with the magnetic field in the stator. The rotating magnetic field of the stator pulls the rotor around with the rotor trying to keep up with the rotating field. The falling behind or slips is about a few percent. This design is one of the conventional ways of driving a 3-phase motor in a compressor.

In a DC brushless motor used in the DC inverter air conditioner or heatpump, the rotor of the motor is constructed using permanent magnets with windings on the stator. There are no brushes and commutator compared to typical DC motor hence eliminating concerns such as sparks, brush life, brush residue and electrical noise. The windings of the motor are connected to the power electronics control that determine the speed of the motor by the use of micro controller. Various protection and monitoring circuits are built into the electronic controls to ensure efficiency and reliability. This type of motor is being used in more design due to its better reliability and energy efficiency. Hence, the main advantages of a DC brushless motor compressor is its quiet operation, compact, longer life time, energy saving and better capacity control which translates to a more comfortable environment for the peoples using the equipment. Its usage is no longer confined to air conditioner equipment but also in refrigerators, washing machines, pumps and fans.

In many ductless split DC inverter design, the indoor fan used is DC fan instead of AC fan. install ac unit wallSimilarly, the outdoor fan used is DC fan instead of the conventional AC fan. portable heat ac combo unitWhen purchasing your unit, check with the personnel whether the compressor and fans used are DC type before making a decision of buying the air conditioner or heatpump.cost of central air for 2000 sq.ft. home The electronics control is the most complicated part of a DC inverter system hence making it one of the most costly component of the air conditioner, the other part being the compressor.Let us look at the control circuity for the DC compressor that takes its supply from a single phase power supply. There are many variation of design and we will look at a design that uses power factor correction that gives better power factor. 

The first section consists of a DC converterThe DC converter converts the incoming power supply from AC to DC using four diodes connected like a bridge. Inductors and capacitors are connected before the converter to reduce the electrical noise being introduced into the power supply due to the switching of the transistors.In the simplified diagram below, the single phase power supply is used. If 3-phase supply is used, six diodes will be needed to convert the AC power to DC power. The second section being PFC or power factor correctionBeing an active power converter means that the power factor correction for this design is able to correct the power factor of the equipment to more than 98% compared to the other solution based on LC (inductor and capacitor) filter. It also helps to reduce the harmonic current emission to a low level which is acceptable to the standards being imposed by the Electromagnetic Compatibility technical committee. The only setback with this method is the higher cost needed for its implementation. 

The third section is the INVERTER consisting of IGBT transistorsThis section generates 3 phase voltage supply to the DC compressor motor. In the initial design, the designers used six discrete IGBT transistors which are controlled by the microcomputer.The software is written in such a way that proper signals are being used to power ON or OFF each transistors at a correct timing depending on the feedback such as the position of the rotors in relation to the stator motor and the voltage levels detected.The brushless DC motor of the compressor will receive close to a 3 phase sinusoidal voltage that turns the motor ON. The speed of the motor can be controlled from low to high by varying the power supplied to the motor through the switching of the transistors. In this way,  capacity controlled HVAC can be achieved. When cooling or heating is needed immediately, the motor will turn at the highest speed. When the temperature of the room has stabilized, the motor will turn at a lower speed.

Newer design makes use of power modules known as IPM or Intelligent Power Modules where the 6 IGBT transistors, detection circuit, overload conditions and other parameters are being built in an encapsulated casing. It looks like an integrated circuit except that it is very much bigger in size.See also the advantages & challenges of developing the inverter technology. Back To DC Inverter Air Conditioner Home PageCompressor Overheating Troubleshooting | Air Conditioner RepairWhat you will learn from Compressor Overheating Troubleshooting article: 1) Avoiding the problem of compressor overheating 2) how does compressor overheating effect the refrigeration system? 3) diagnosing compressor overheating 4) repairing the problem of compressor overheating and future prevention 5) lots of related links to help you learn Compressor Overheating Troubleshooting | Air Conditioner Repair – There are some problems with air conditioner or heat pump compressors that can be avoided with proper maintenance.

Other problems result in a mechanical or electrical problem with the systems that need to be resolved. Compressor overheating is an issue that can cause serious problems with your air conditioner or heat pump system. A compressor that overheats can still operate and provide cooling or heating but if the temperature inside the compressor rises too high then the oil in the compressor can break down and reduce the lubrication and cooling effect the oil has inside the compressor for proper and necessary lubrication. This leads to possible mechanical failure and other problems that will occur to the compressor and in the refrigeration system that results from compressor overheating. When the oil becomes overheated it changes chemically. Through a lack of lubricating and cooling it becomes like an acid when the oil overheats. This eats away at the windings and will cause compressor failure.pressor Overheating Troubleshooting | Air Conditioner RepairThe check for excessively high temperatures is to take a discharge temperature on the discharge line at least 6 inches from where it leaves the compressor.

Temperatures over 300° Fahrenheit inside the discharge port of the compressor means there is a serious problem that needs to be addressed.Related Link: Air Conditioner Compressor Troubleshooting - Diagnosis and Repair (opens in a new window) What are the causes of compressor overheating and how to fix it:High Head Pressure - This can be caused by dirty condenser coils, a bad condenser fan motor, a recirculation of air back into the coils, improper rotation of the condenser fan, non-condensibles (air, nitrogen or other gas), and an overcharge of the refrigeration system. Another thing found that can cause this is any extra heat source near the condenser such as a drier vent which can introduce extra heat into the system.I have a customer who called me for a bid to install a new system. The customer received 3 different bids from 3 different contractors. My competition got the contract and installed the new split system air conditioner. The next summer I got a call from that same customer asking me to check out their air conditioner.

It seems my competitor had installed the condenser under a deck and near many bushes. The condenser could not breathe and the air and heat was simply recirculated back into the unit. Once the recirculated heat rises about outdoor ambient temperature you lose effective cooling because the condenser was no longer rejecting the latent heat picked up in the evaporator, suction line, and the heat from compression. I moved the unit to a better location and the customer called me later and told me the difference was like night and day.It wasn’t difficult to figure out this problem for anyone and who knows why the competition chose that location but I used the experience to teach a few junior technicians about heat rejection and compressor overheating. I had them take temperatures and pressures and let them come to the conclusion of the main problem. Once the line was cut to move the unit I also had them test the oil to make sure it was acid-free. After all, when everything was said and done I did not want to have any warranty issues replacing a compressor because I did not do my homework.

Improper Voltage - This can be a power company issue that needs to be corrected by the power company especially high voltage but low-voltage can be a problem in the circuits providing power to the compressor. Lose connections and corroded wires or terminal connections can cause low voltage and high amperage problems that result in compressor overheating. This can also be the result of a power company transformer issue along with the high voltage problem.High Superheat - this can result from a low refrigerant charge, a restriction in the refrigerant piping or a faulty metering device. It can also result in a liquid line too close to a heat source such as hot water piping loops. In that case the liquid line needs to be insulated from the hot water piping or relocated.Short Cycling of Compressor - this can be caused by a low charge or faulty metering device. Air flow across the evaporator coil can also result in this issue and can be from a dirty or clogged air filter or frozen evaporator coil.

A bad capacitor can also cause the problem.Other Possible Causes - A failure of the internal overloads inside the compressor or bad compressor valves can cause issues with overheating. These problems can be difficult to resolve in hermetic compressors without replacing the compressor. pressor Overheating Troubleshooting Additional TestingBoth hermetic and semi-hermetic compressors are difficult to troubleshoot sometimes and many times the problem is external to the compressor or a result of poor installation skills by the installation technician if the compressor was recently replaced or it is a split system where the system was evacuated by an HVAC technician. It is recommended when any type of refrigeration system is put into service that a refrigeration triple evacuation be performed to ensure all moisture is removed from the system. Moisture leads to bad windings in the compressor and can be a cause of overheating. The only real way to tell if the windings are healthy is to use a megaohmmeter or a megger to test the windings to make sure they are not damaged from moisture in the system.