Dijital kontrollü LLC rezonans güç dönüştürücüsü tasarımı ve uygulaması
Digitally controlled LLC resonant converter design and implementation
Yazar: BURAK GÖKÇEN
Danışman: DOÇ. DR. ÖZGÜR ÜSTÜN
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Elektrik Mühendisliği Ana Bilim Dalı / Elektrik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Elektrik ve Elektronik Mühendisliği = Electrical and Electronics Engineering
Dizin: Anahtarlamalı güç kaynağı = Switched mode power supply ; Darbe genişliği modülasyonu = Pulse width modulation ; Elektronik devreler = Electronic circuits ; Etkinlik = Efficiency ; Güç kaynakları = Power sources ; Rezonans çevirici teknoloji = Resonant converter technology

Özet:
Hem endüstride hem de son kullanıcıda çeşitli yüklerin beslenmesinde DC gerilime ihtiyaç duyulmaktadır. Endüstride haberleşme sistemleri, ağ sistemleri, PV sistemler, elektrikli araçlar, DC güç kaynakları, batarya şarjı gibi uygulamalarda; son kullanıcıda ise küçük ev aletlerinde sıklıkla görülen adaptörlerde bu ihtiyaç gözlemlenebilir. Günümüzde ise bu ihtiyacın yanında DC güç kaynağı olarak kullanılan cihazların verim ve hacim isterleri hem teknolojinin buna el vermesinden hem de son kullanıcının taleplerinden dolayı kritik hale gelmiştir.
Bu bağlamda bu tez çalışmanın konusu olan yarım köprü LLC rezonans dönüştürücüsü, klasik anahtarlamalı güç kaynaklarından verim, güç yoğunluğu ve maliyet olarak avantajlı konumdadır.
Tezin asıl amacı 240W anma gücünde, 24V çıkış gerilimde 10A çıkış akımına sahip izoleli bir topoloji olan yarım köprü LLC rezonans dönüştürücü güç katı ve kontrol katı tasarımının yapılması ve uygulanmasıdır. Tasarım yapılırken LLC rezonans dönüştürücü devresinin durum-uzay analizi yapılarak topoloji analiz edilmiştir. Rezonans tank elemanlarının değerlerini hesaplamak ve frekansa göre kazanç grafiğini çıkartmak için temel harmonik yaklaşım yöntemi kullanılmıştır. Bu yöntem ile isterlere göre rezonans tank elemanları değerleri belirlenmiştir. Uygulama devresinde kontrol kartı olarak ise ST firmasına ait NUCLEO-F303RE model geliştirme kiti kullanılmış olup kitte bulunan STM32F103 mikrodenetleyicisi C dilinde programlanmıştır. Uygulama devresinin PSIM ve MATLAB SIMULINK programlarında simülasyonları yapılarak yine bu programlarda bulunan PI tuner modülü kullanılarak PI kontrolör katsayıları hesaplanmıştır. Mikrodenetleyici ile sayısal olarak devre kontrolünün yapılmasının yanında düşük ve yüksek gerilim koruma fonksiyonları eklenerek kodlanmıştır. Rezonans tank eleman değerleri, kontrolör tasarımı ve simülasyon çalışmalarının ardından devrenin şematik ve PCB tasarımı Altium Designer programında yapılmıştır. Mikrodenetleyici ve opamp gibi muhtelif elemanların besleme gerilimlerinin üretilmesi için devrenin giriş kısmında düşük güçlü izolesiz bir güç entegresi kullanılmıştır. Devrenin çıkış geri besleme sinyali ise diferansiyel analog çıkışa sahip bir analog izolatör entegresi ile okunmuştur.
Devre uygulaması yapıldıktan sonra test düzeneği kurularak çeşitli giriş gerilimi ve yük değerlerinde ölçümler alınmış olup bu koşullara göre verim ölçümleri, çıkış gerilim dalgalanması ölçümleri yapılmıştır. Uygulaması yapılan devre ile hesaplanan değerler kıyaslanmış ve yorumlanmıştır.

Abstract:
Because of increased use of electronic devices and increasing power consumption, power sources are critical for both industry and consumer electronics. DC power sources are used in industry applications such as computer systems, network systems, telecommunication systems, PV systems, electric vehicles, battery charger; in the consumer electronics, adapters which are frequently used at small household appliances. Nowadays, the efficiency and size requirements of these devices have become essential due to development of the technology, standards, the demands of the industry and consumer electronics. 
In power electronics, especially with the development of semiconductor technology, the development of DC-DC converters continues with increasing efficiency over time. When DC-DC converter topologies are examined, categorization can be made with various approaches. For example, DC-DC converters according to the operating method; can be divided into linear converters, hard switching converters and soft switching converters. When the developments of DC-DC converters in the literature are examined, it can be seen that these three topologies have evolved, respectively. 
Although linear converters are inefficient, they are cheap, have fast response to load changes and low output voltage ripple. Therefore, it is generally used in industry at low power applications such as to provide the supply voltages of opamps, microcontrollers, LEDs and other integrated circuits on the complex circuits. In addition, it is frequently used at the output of the switched mode power supplies for filtering output and obtain even smoother output voltages. 
Switch mode power supplies, on the other hand, are more efficient power supplies than linear converters. The most important reason for this is that the power switch element used in switch mode power supplies, compared to linear converters, is either working at completely turn on or turn off state, in this context, the losses on the switch elements are dramatically less than linear converters due to the fact that the switch element does not work in the linear region. 
Switch mode power supplies utilize the energy storage properties of passive elements such as inductors and capacitors to derive the desired output voltage from the input voltage with switching phenomenon. In conventional hard switching DC-DC converters, at the moment of switching, for a while, either current or voltage on the switching element are not zero instantaneously. This situation creates a power loss on the power switch in every switching period which is called switching loss. These losses are minimized in soft switching converters. In the design stage of resonant converters zero voltage switching or zero current switching conditions are taking into consideration.
Resonant power converters and quasi resonant power converters can reach higher efficiency values than conventional hard switching converters due to their operation modes at zero voltage switching and zero current switching with high switching frequencies. Unlike the pulse width modulation method used in conventional converters, resonant converters are controlled by changing the frequency value of the switching signal with constant duty cycle which is called frequency modulation method. 
In this context, the resonant power converters, have more advantageous in terms of efficiency and power density compared to classical switch mode power supplies. There are many types of resonant power converter topologies in the literature. In the introduction chapter of this thesis these topologies are mentioned and investigated as a result half-bridge LLC resonant power converter topology chosen for this application circuit.
The main purpose of the thesis is to design and implement the power stage and digital stage of the half bridge LLC resonance power converter, an isolated topology with 24V output voltage at 240W rated power. While designing, the topology of the LLC resonance converter circuit was examined by analyzing the state space model of converter. First harmonic approach method was used to calculate the values of resonance tank elements and to obtain the gain versus frequency graph. With the first harmonic approach method a power stage design diagram for the half bridge LLC resonance converter has been created. With this design diagram, the values of resonance tank elements are determined according to the requirements. With the determined values, the resonance tank transformer is designed for various magnetic cores. Among the various transformer designs, E42 core was chosen. After the transformer design made other resonant tank elements and power switches and diodes were chosen.
For the output voltage feedback signal AMC1311 IC which is a precision, isolated, low offset error amplifier used. Output voltage measurement circuit was combined with a sallen-key low-pass filter. Feedback signals accuracies are critical for transient responses and low output voltage ripple thus the low-pass filter's cutoff frequency is designed to be take into account with the PI controller.
NUCLEO-F303RE model development kit of ST was used as a control card in the application circuit and the STM32F103 microcontroller included in the kit was programmed in the C programing language for operating the power circuit. The PI control coefficients were calculated by simulating the application circuits with actual circuit parameters in PSIM and MATLAB SIMULINK programs using the PI tuner tools in these programs. A software operation algorithm for the half bridge LLC resonance converter has been created. Microcontroller was coded by adding soft start, undervoltage-lockout out protection and high voltage protection functions as well as digitally control algorithm of power circuit. After the resonance tank element values determined, according to the simulations and obtained transfer function, controller parameters were determined and controller design were made. A low power non-isolated SMPS IC is used at the input side of the circuit to produce the supply voltages of various elements such as microcontroller and opamps. For the mosfet gate driver IRS2304SPBF half bridge driver IC was used with bootstrap operation mode. Bootstrap operation also investigated and bootstrap capacitance value was determined. Circuit schematic and PCB designs were made in Altium Designer program. With the software and interface created with CUBEMX and CUBEIDE programs, the circuit values like output voltage switching frequency etc. were monitored live by the measurements taken by the microcontroller.
After obtaining the circuit, the test setup was established and measurements were taken at various input voltages and load values. Zero voltage switching was achieved with wide operating regions. Efficiency measurements, output voltage ripple measurements and dynamic load responses were taken according to various requirements. The application circuit test results and simulation results were compared and evaluated. Suggestions were made for the development of the circuit for obtaining better efficiency values and possible usage areas.