Reliability of Power Electronic Converter Systems

Book Preface

Power electronic systems aim to best serve the needs of highly efficient generation and conversion of electrical energy. This section discusses the basic architecture of a power electronic system and its design objectives and performance factors.

Power electronic converter systems

Electrical energy conversion by power electronic systems can be classified into the following four categories [1]:

1. Voltage conversion and power conversion for both direct current (DC) and alternate current (AC).
2. Frequency conversion.
3. Wave-shape conversion.
4. Poly-phase conversion.

The above four kinds of conversions are used to meet needs in many industry sectors, such as automotive, telecommunications, portable equipment, smart grids, high-voltage DC, flexible AC transmission systems, traction, renewable energy, mining, electrical aircraft, adjustable speed drives, and aerospace. The power-level
ranges from sub-W to multi-MW and GW, processed by either a single power converter or multiple power converters.

Figure 1.1 shows the general architecture of a typical power electronic converter system. The electrical energy in the input and output is represented in the form of input voltage vin, input current iin, and input side frequency fin, and output 1Center of Reliable Power Electronics (CORPE), Department of Energy Technology, Aalborg University, Aalborg, Denmark 2Centre for Smart Energy Conversion and Utilization Research, Department of Electronic Engineering, City University of Hong Kong, Kowloon Tong, Hong Kong 3Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD, USA voltage vo, output current io, and output side frequency fo. The upper and lower blocks in Figure 1.1 show the power stage and control stage, respectively. The power stage is composed of switching devices and one or more kinds of passive components, connected by a specific circuit topology. The switching devices are turned on and off at a frequency in the range of hundreds of Hz to hundreds of MHz, depending on the capability of the devices and the application requirements. The capacitors and inductors are used for energy storage and filtering purposes. The transformers are usually of the high-frequency type and are used for galvanic isolation and step-up/down of voltage. Resistors are in fact not desirable in power electronic systems since they introduce power loss. However, in practical systems, there are parasitic resistances in components and resistors used for circuit snubbers, balancing circuits, filter damping, and so on. The control stage receives conditioned low-voltage signals from the power stage and sends back driven signals to control the on/off of the switching devices, including protection signals at the presence of abnormal operation. It can be implemented either in analog circuits, digital processors, or a hybrid way of both analog and digital parts typically implemented on print circuit boards.