Rezonans çeviricileri
Resonant converters
- Tez No: 39136
- Danışmanlar: PROF.DR. R. NEJAT TUNCAY
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1993
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 83
Özet
ÖZET Bu çalışmada rezonans çeviricilerinin anahtar modunda çalışan çeviricilere olan avantajları ve dezavantajları incelenmiştir. Bir güç elektroniği devresindeki güç kaynaklarının boyutlarını küçültmek için reaktif elemanların boyutunu küçültecek çalışma frekansını arttırmak gerekmektedir. Bu esnada yüksek çalışma frekanslarından dolayı ortaya çıkan yüksek anahtarlama kayıplarım da azaltmak gereklidir. Bu amaçla rezonans devreleri kullanılmaktadır. Darbe genişlik modülasyonunu kullanan bütün çeviriciler, her anahtarlama esnasında bütün yük üzerlerindeyken açma veya kapama yapması gereken bir modda çalıştıklarından büyük anahtarlama kayıplarına sebep olurlar. Bu yüzden eğer her anahtarın üzerindeki gerilim veya içinden geçen akım sıfırken o anahtarı iletime veya kesime götürürsek bu anahtarlama kayıplarının üstesinden gelinebilir. Bu çalışmada birinci ve ikinci bölümlerde renosans çeviricilerine niçin gereksinim duyulduğundan ve çeşitlerinden bahsedilmiş olup üçüncü bölümde en basit yapıdaki renosans çeviricileri incelenmiştir. Çalışmanın esas kısmım oluşturan dördüncü bölümünde ise bu tip çeviriciler farklı çalışma frekansları için detaylı olarak incelenmiştir. -v-
Özet (Çeviri)
SUMMARY RESONANT CONVERTERS In this study advantages and disadvantages of resonant converters versus switch-mode converters are discussed.In all the pulse-width-modulated dc-to-dc and dc-to-ac converter topologies, the controllable switches are operated in a switch-mode where they are required to turn on and turn off the entire load current during each switching. In this switch mode operation, the switches are subjected to high switching power loss that increases linearily with the switching frequency of the pulse- width-modulation. An other significant drawback of the switch mode operation is the electromagnetic interference [EMI] produced due to large di/dt and dv/dt caused by a switch-mode operation [1]. These shortcomings of switch-mode converters are exacerbated if the switching frequency is increased in order to reduce the converter size and weight, and hence to increase the power density. Therefore, to realize high switching frequencies in converters, the aforementioned shortcomings are minimized if each switch in a converter changes its status (from on to off or vice versa) when the voltage across it and/or the current through it is zero at the switching instant. To illustrate further the problems associated with switch-mode operation, consider one of the legs of a full bridge dc-dc converter or a dc-ac inverter as shown in Fig.l. TT / t, Ad, vd + ul/ \\ I A D, '. Fig. 1. One inverter leg.The output current can be in either direction and can be assumed to have a constant magnitude Io due to the load inductance, during the very brief switching interval. The linearized voltage and current vaweforms, for example, for the lower switch T2 are shown in Fig.2.a. \- Turn off - i la) SOA (safe-operating area) j» Turn- Fig. 2. Switch-mode inductive current switchings. Here, the average value the switching loss P^, being proportional to the switching frequency, limits how high the switching frequency can be pushed, without significantly degrading the system efficiency. With the availability of fast switches, the present limit seems to be up to approximately 500 kHz with a resonable energy efficiency. Another significant disadvantage of the switch-mode operation, is that it results in large di/dt and dv/dt due to fast switching transition required to keep the switching losses in the switch as low as possible. Diodes with poor reverse recovery characteristics significantly add to this phenomenon, which produces electromagnetic interference[EMT|. -Vll-Zero Voltage And Zero Current Switchings Switching frequencies in the megahertz range, even tens of megahertz, are being contemplated to reduce the size and the weight of transformers and filter components and, hence, to reduce the cost as well as the size and the weight of power electronics converters. The switch stresses can be reduced by connecting simple dissipative snubber circuits(consisting of diodes and passive components) in series and in parallel with the switch-mode converters. Such snubber circuits are shown in Fig. 3. a and the switching loci that result in reduced switch stresses are shown in Fig. 3.b. However, these dissipative snubbers shift the switching power loss from the switch to the snubber circuit, and therefore do not provide a reduction in the overall switching power loss. «T2 Vy Turn-on \ /C Turn-< - v-n lb) r" ı i 5 D, 1 1 -Turn-on snubber (at Fig. 3. Dissipative snubbers: (a) snubber circuits, (b) switching loci with snubbers. -Vlll-In contrast to dissipative snubbers in switch-mode convertes, the combination of proper converter topologies and switching strategies can overcome if the problems of switching stresses, switching power losses, and the EMI by turning on and off each of the converter switches when either the switch voltage or the switch current is zero. Ideally, both the switch voltage and current should be zero when the switching transition occurs. Classification Of Resonant Converters The resonant converters are defined here as the combination of converter topologies and switching strategies that result in zero-voltage and/or zero-current switchings. One way to categorize these converters is as follows: 1. Load-Resonant converters 2. Resonant-Switch converters 3. Resonant-dc-Link converters 4. High-frequency-link Integral-half-cycle converters Load Resonant Converters These converters consist of an L-C resonant tank circuit. Oscillating voltage and current, due to L-C resonance in the tank, are applied to the load, and the converter switches can be switched at zero voltage and/or zero current. Either a series L-C or a parallel L-C circuit can be used. In these converter circuits, the power flow to the load is controlled by the resonant tank impedance, which in turn is controlled by the switching frequency fs in comparison to the resonant frequency f0 of the tank. These dc-to-dc and dc-to- ac converters can be subclassified as follows: 1. Voltage-source series-resonant converters a. Series-loaded resonant(SLR) converters b. Parallel-loaded resonant(PLR) converters c. Hybrid-resonant converters 2. Class-E resonant converters Resonant Switch Converters In certain switch-mode converter topologies, an L-C resonance can be utilized primarily to shape the switch voltage and current to provide zero- voltage and/or zero-current switchings. In such resonant switch converters, during one switching frequency time period, there are resonant as well as non- resonant operating intervals. A majority of such converters can be divided into three switching categories: 1. Zero-Current-Switching(ZCS) topology where the switch turns on and off at zero current. The peak resonant current flows through the switch voltage remains the same as in its switch-mode counterpart. -IX-2. Zero-Voltage-Switching(ZVS) topology where the switch turns on and off at zero voltage. The peak resonant voltage appears across the switch, but the peak switch current remains the same as in its switch-mode counterpart. 3. Zero- Voltage-Switching, clamped-voltage(ZVS-CV) topology where the switch turns on and off at zero voltage. However, a converter of this topology consists of at least one converter leg made up of two such switches. The peak switch voltage remains the same as in its switch-mode counterpart, but the switch current is generally higher. Resonant-dc-link Converters In the conventional switch-mode PWM dc-to-ac inverters, the input Vd to the inverter is a fixed magnitude dc, and the sinusoidal output(single-phase or three-phase) is obtained by switch-mode PWM switchings. However, in the resonant-dc-link converters, the input voltage is made to oscillate around Vd by means of an L-C resonance so that the input voltage remains zero for a finite duration during which the status of the inverter switches can be changed, thus resulting in zero-voltage switching. High-Frequency-Link Integral-Half-Cycle Converters If the input to a single-phase or three-phase inverter is a high-frequency sinusoidal ac, then by using bidirectional switches it is possible to synthesize a low-frequency ac of adjustable magnitude and frequency or an adjustable magnitude dc, where the switches are turned on and off at the zero-crossings of the voltage. -x-
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