His current research interests include development and modeling of power converters, design and development of Direct Digital Control with D–∑ processes for single‐phase and three‐phase converters with grid connection, rectification, APF, power balancing and UPS functions, and design of resonant converters for ultrasonic cutter, ozone generator, remote‐plasma‐source, and electrical surgery unit applications.
Yu‐Kai Chen is a professor in the Department of Aeronautical Engineering, National Formosa University, Taiwan, ROC where he is the director of Innovative Design and Energy Application Lab. (IDEAL). In 2015, he received the outstanding industry collaboration award from National Formosa University. His research interests include modeling and control of power converters, design of solar panel‐supplied inverters for grid connection, and DSP‐ and microprocessor‐based application systems with fuzzy and robust controls.
1 Introduction
Electrical energy has been widely applied, and its growth rate has been increasing dramatically over the past two decades. In particular, renewable energy coming to play has driven electricity utilization and processing needs to reach another growth peak. Additionally, machine electrification and factory automation have also increased the demand of electricity. With increasing use of sophisticated equipment and instruments, high power quality becomes just essential. To supply sufficient, of high quality, and stable electrical power in desired voltage or current forms, power processing systems are indispensable. Meanwhile, they also play an important role in supporting continuous growth of human beings' civilization, environmental conservation, and energy harvesting. In designing a power processing system, the first step needs to select a power converter topology since the converter topology mainly governs the fundamental properties, such as step‐up, step‐down, bipolar operation, component stresses, etc. Converters come out with very diversified configurations. How to derive or develop them systematically without trial and error is an interesting topic. Thus, many researchers have devoted in developing power converter topologies for various types of applications.
In this chapter, configuration of a power processing system is first addressed. Fundamental two types of power converter classifications, general pulse‐width modulated (PWM) converters and non‐PWM ones, are presented. Then, the well‐known PWM converters are introduced for later comparison and illustration. In literature, there are many approaches to developing power converters, and their fundamental principles will be described briefly. In addition, an evolution concept is presented for illustrating later converter derivation. A section introducing the overall organization of this book will be included in the end of this chapter.
1.1 Power Processing Systems
Configuration of a power processing system can be illustrated in Figure 1.1, which mainly includes input filter, power converter, feedback/feedforward circuits, controller, gate driver, and protection circuit. The input source can be obtained from utility outlet/grid or renewable energy generators, such as photovoltaic panel, wind turbine, geothermal heat pump, etc. Its voltages and currents can be any form, and their amplitudes might vary with time or fluctuate frequently. At the output side, the load may require various voltage and current forms, too. Thus, a proper power converter topology along with a promising controller is usually required to realize a power processing system.
Conventionally, the conceptual block diagram of a power processing system shown in Figure 1.1 can be realized by the circuit shown in Figure 1.2, which, as an example, is a linear regulator. In the circuit, semiconductor switch QN is operated in linear region to act as a variable resistor, which can absorb the voltage difference between input voltage Vi and output voltage Vo and in turn regulate Vo under load variation. The primary merits of a linear regulator include low output voltage ripple and low noise interference. However, it has many drawbacks, such as the transformer with low operating frequency results in bulky size and heavy weight, semiconductor QN operating in linear region results in high power loss and low efficiency, and the low efficiency requires a large, heavy heat sink and even needs forced ventilation. These drawbacks have limited its wide applications to compact electronic products, renewable power generators, and energy harvesters, where efficiency and size are the essential concerns.
Figure 1.1 Configuration of a power processing system.
Figure 1.2 Block diagram of a linear regulator.
To improve efficiency and release the aforementioned limitations, switching power regulators were developed. A typical configuration of the switching regulators is shown in Figure 1.3, where in the power converter, switch M1 is operated in saturation region (if using BJT as a switch) or in ohmic region (if using MOSFET as a switch), reducing conduction loss dramatically. At the input side, the corner frequency of the filter is close to switching frequency, and its size and weight can be also reduced significantly. If isolation is required, high frequency transformer will be introduced to the converter, and its size and weight are relatively small as compared with a low‐frequency one (operating at 50/60 Hz). In general, a switching regulator has the merits of high power density, small volume, low weight, improved efficiency, and cost and component reduction. There still exist several limitations, such as resulting in high switching noise, increasing analysis and design complexity, and requiring sophisticated control. Although switching regulators have the limitations, thanks to recent advances in high efficiency and high frequency component development, nanoscale integrated circuit (IC) fabrication technique, and analysis tool, they have been widely applied to electronic products, energy harvesting, and power quality improvement. For further discussion, we will focus on switching regulators only.
For a switching regulator or a more general term, switching power converter, the input source can be either AC or DC form, and the output load can be also supplied by either AC or DC form. Thus, there are four types of combinational forms in classifying power converter topologies, which are AC to DC, AC to AC, DC to AC, and DC to DC. In Figure 1.3, the rectifier converts AC to DC, and the power converter converts DC to DC. Typically, a power processing system may need multiple power converters to collaborate each other, but they might be integrated into a single power stage for certain applications, such as a notebook adapter consisting of a rectifier (AC to DC), a power factor corrector (DC to DC), and an isolated regulator (DC to DC), which can be integrated into a bridgeless isolated regulator. A power converter requires at least a control gear or switch to control power flow between source and load, and it might need some buffers or filters to smooth and hold up voltage and current, which can be illustrated in Figure 1.4. The switch can be realized with BJT, MOSFET, IGBT, GTO, etc. along with freewheeling diodes. It is worth noting that recent advances in wide‐bandgap switching device development, such as SiC and GaN, have merited to switching power converters because their switching losses
