Güç elektroniği ve motor sürücü devrelerinde verim artırma yöntemleri
Methods for increasing the efficiency of power electronics and motor drive circuits
Yazar: AHMET BERKANT ECEVİT
Danışman: DOÇ. DR. GÜVEN KÖMÜRGÖZ KIRIŞ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Elektrik Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Elektrik ve Elektronik Mühendisliği = Electrical and Electronics Engineering

Özet:
Bu tez kapsamında öncelikle temel güç elektroniği elemanları, devreleri ve bunların sürüşü için gerekli devreler incelenmektedir. Sonrasında bir adet yeni yarı iletken teknolojili elemanın güç elektroniği devrelerindeki kayıplara etkisi gösterilmekte ve verimi artırdığı bilinen paralel anahtarlama yöntemine yeni bir bakış getirilmektedir. 
Yeni yarı iletken teknolojisi olarak günümüzde yavaş yavaş seri üretimine başlanan Galyum Nitrit tabanlı anahtarlama elemanları kullanılmıştır. Bir motor kontrol devresinde Silikon ve GaN elemanlar kullanılarak karşılaştırılmıştır. Yük olarak bir fan yükü kullanılmıştır. Ortam şartları eşitlenerek şebekeden çekilen güç ölçümü yapılmış ve ölçümler alınmıştır. Sonuç olarak GaN tabanlı anahtarların verim avantajı açıkça görülmüştür. 
Paralel anahtarlama için ise anahtarlama işaretlerinin değiştirilmesi için bir yöntem geliştirilmiştir. Yapı gereği verimin artması için yavaş anahtar elemanın sonra açılıp önce kapanması gerekmektedir. Dolayısıyla anahtarlama işaretinde bir takım manipülasyonların yapılması gerekmektedir. Konu hakkında detaylı bir literatür taraması yapılmıştır. Literatür taraması sonucu, açma ve kapama işaretini aynı anda değiştiren devrelerin ya oldukça pahalı olduğu ya da fazladan mikorişlemci çıkışı gerektirdiği görülmüştür. Bu sorunun çözümü için, basit yapılı bir devre tasarımı yapılmıştır. Temel olarak RC devresinin zaman sabiti hesabıyla çalışan bir tasarım yapılarak simülasyon ve uygulaması yapılarak sonuçları verilmiştir. Devre ile ilgili hesaplamalar yapılmış ve ölçüm sonuçlarıyla karşılaştırılmıştır.

Abstract:
Power electronics is one of the most popular topics in electrical engineering. Today's world, power converters, motor drivers, voltage regulators are have a very wide usage. From defence industry to home appliances, from automative to medical electronics, power electronic circuits are everywhere.
Since power electronic devices have this popularity, their parameters like lifetime or efficiency become more important. Most of the people working on this field try to focus on improving the lifetime or efficiency of the power electronic circuits rather than inventing a new topology. Especially for home appliances industry, lifetime and efficiency of the system is very important because of the government regulations. For example, compressor motor and motor control circuit for a refridgator should have a very hig efficiency like  more than 90%  to classify the system as a high-end product. 
For the reasons above, brushless DC motors or permanent magnet synchronous motors are getting popular everyday. Since they have a good efficiency-torque-speed relationship, their usage in all industries are increasing rapidly. Although this motors are very efficient, they can not work directly with the AC mains. These kind of motors need a motor control circuit to operate and efficiency of this controller is also becomes important. Usually, BLDC or PMSM motors are producted as 3-phase motors and so, they are controlled with a 3-phase inverter circuit.
A 3-phase inverter circuit for controlling a motor usually has a harmonic eliminating circuit to obey the regulations. Then an AC to DC converter is used for gathering DC voltage from mains. After that, a six switch inverter is used for controlling the motor. Also there is a low voltage side for the microcontroller, integrated circuits and other peripheral components which is needed to gather the information from the motor and decide the next signal for inverter.
 It is important to know the basic power electronics circuits topologies to understand how a six switch inverter controlls the motor in terms of speed or torque or both of them. Everything starts with a buck converter, which is used for decreasing the voltage value of the input and gives to the output. Buck circuit is a very simple circuit, just has one switch, one diode, one inductance and one capacitor. 
Also boost converter is a main converter type, which increases the voltage of the input for the output. Boost converter is again very simple, has the same components with buck, just connected in a different way. 
In todays power electronics world, most of the circuits derived from buck converter and boost converter. The most obvious example of that is the buc-boost converter. This converter type is used to increase or decrease the voltage, which is needed.
Bridge type converters are the basics of motor control circuits. Simply, one can use a buck converter to drive a brushed DC motor, but only operates in one direction since the current flows only one direction. But in a bridge converter, current path can be changed so the direction of the rotation can be changed. That is the reason why the bridge type converters are important in motor control. These converters are based on buck converter, which means they decrease the input voltaage for the output.
A half bridge converter includes two switches and two capacitors, whereas a full bridge converter includes four switches to have a perfect control on the current direction.
A six switch inverter is based on the half bridge topology. Actually, it is nothing more than three half bridge converters. The middle points of the half brigde converters are connected to the load. 
In a six switch inverter circuit which is used for a motor control, switches are the most important elements in terms of efficiency. Basicly, one can say that switches decide the efficiency level of the circuit. That is the reason why most of the scientists are working to increase the switching elements performance. There are a few ways to increase the switching performance, like using a new semiconductor technology or parallel switching.
Superior semiconductors are the new era for electronics. Silicon Carbide (SiC) and Galium Nitride (GaN) are the most important technologies for today. Most of the semiconductor companies are trying to product a new, cheap and better superior semiconductors. 
GaN is the main focus point of the companies. SiC technologies are complicated and expensive, but GaN production is easy and cheap. People in the industry says that procedure for production of the GaN may be cheaper than standard Silicone.  Many of the market predicters state that by the end of 2010's GaN will replace the Si in semiconductors.
A GaN switch has very good switching and conducting performance. To show this in this thesis, a Si based circuit and a GaN based circuit compared in terms of losses in calculation. After that, a motor control circuit is modified for GaN and new switches implemented. Than comparison re-done in the same load conditions, in terms of heating and losses. Results are given.
Parallel switching is another way for increasing the efficiency of the circuit. Researchers are working on this technology since the early 90's. Yirming Jiang, Guichao Hua and Fred C. Lee are the founders of the concept with their publication" which shows that it is possible to work with parallel switches. After this work, a lot of researchers worked on this topic and publicated their job.
Sakhon Woothipatanapan, Anuwat Jangwanitlert and Phop Cancharoensook, show that a parallel switching method increases the efficiency on motor drives in their publication. This publication is the first in this field for 3-phase implementation of the parallel switching method. 
Parallel switching needs a very good gate driving circuit in terms of timing. Since a bad gate signal may cause a short circuit, designer must be very careful. For gate driving of parallel switches, there are not many offers.  People usually uses two microcontroller outputs for this. Bu it is not an efficient way for gate driving. 
An ASIC can be a solution for gate drive timing. H.P.Yee, and Dean Liu published "An ASIC to Control the Paralleling of an IGBT with a MOSFET" article and designed an IC for closing time delay.
There are some other methods like FPGA based design. But common problem is the high costs of new gate driving circuits. Cheap solutions can not provide opening delay which is important for switching losses.
In this thesis, two RC based delay circuits are offered for opening delay and closing delay. Opening delay is for IGBT opening signal and closing delay is for MOSFET closing signal. By this way, IGBT never produces a switching loss ideally since it is under soft switching conditions. Also MOSFET never produces a conduction loss if it is selected correctly.
At first, concept design of the circuits are made and explained. After that, switching elements are selected and delay times are desired. Than some calculation for delay times are done and values of the components are given. 
Simulations are done on these designs via PSpice. It is shown that calculations and simulations are supporting each other. After that, a schematicof the circuit has designded and PCB has drawn. 
With the real circuit, timing tests are done. A 200 kHz PWM is generated from a microcontroller and given to the delay circuits. Results are measured with a high speed-high resolution ossiloscope.
In the end, it can be stated that, future of the power electronics lies in superior semiconductors. But since that time, parallel switching method is a good alternative for increasing the efficiency.