Lecture 1. Introduction to Power Electronics

Transcription

1 Lecture 1 Introduction to Power Electronics

2 Definition of Power Electronics Power Electronics (PE) is power processing It is an application of electronic circuits to control the power between the source and the load to change the characteristics (voltage and current magnitude and/or frequency) of electrical power to suit a particular application. Power electronics encompasses the use of electronic components, the application of circuit theory and design techniques, and the development of analytical tools toward efficient electronic conversion, control, and conditioning of electric power The primary task of power electronics is to process and control the flow of electric energy by supplying voltages and currents in a form that is optimally suited for user loads Goal of Power Electronics Efficient conversion, conditioning, or processing and control of electric power using solid-state semiconductor devices in order to supply high quality power to the load causing minimum pollution of environment and the utility supply circuit. Block Diagram of a Power Processor Figure below show the block diagram of the PE system Power Electronics can be spilt into: 2 P a g e

3 Power Circuit: convert input power and deliver to output Electronics Circuit: controls the converter by measuring the input and output voltage and or/current and generates for the power circuit. Converter has power switching semiconductor devices and energy storing elements like inductors and capacitors. Control is done using electronic switches, capacitors, magnetics, and control systems. Resistive elements are avoided in converters because they cause power loss and reduce efficiency. Controller switches on/off the switching devices present in the converter. Example of Power Processor is shown below: A power processor may have more than one stage of power conversion. This kind of electrical-to-electrical power conversion is normally effected using systems without moving parts. The systems that carry out these conversions are called electronic power converters or power electronics converters, or simply converters. Converters are classified by the relationship between input and output: Power electronic converter that can conversion of electric power from one to another. 3 P a g e

4 The Power Electronic Converter can be classified into five types as shown in the table below: Note: AC to AC conversion can be divided into three types: AC voltage controller: which can be used to change the input voltage only at the load demand. Cycloconverter: which can be used to change the input AC voltage and frequency to the desired level by the load. This converter consist from one stage. Frequency converter: which can be used to change the input AC voltage and frequency to the desired level by the load. This converter consist from two stages to give a wide voltage and frequency range. 4 P a g e

5 Rectifier AC voltage controller, Cycloconverter Chopper Inverter Power Electronics Vs Signal Processing In Power Electronics The focus is on power conversion at the highest possible efficiency using very small control signals. Semiconductor devices work as switches. 5 P a g e

6 Power handled may range from a few watts to several mega-watts. In Signal Processing Semiconductor devices generally work as controlled sources in the linear region of their characteristics. The focus is on information processing with minimum loss of information. Power handled will be of the order of few milli-watts or few watts. 6 P a g e

7 NOTE: In electronic circuits, it is difficult to include magnetic elements into integrated circuit as they are large in size compared to capacitors and resistors. In power circuits, resistors and power switches in linear mode are not used in power circuit due to significant losses generated by current via these components, which decreases the efficiency, and cause thermal problems. NOTE: Changing the output voltage in the PE converter on the account of current magnitude. Exercise: A 50Hz fixed AC input voltage is converted to fixed DC voltage and then is stepped up to a higher DC voltage level. This voltage is converted again to the same level of AC input voltage but with a higher output frequency. With the aid of block diagrams, show the power electronic conversion stages that required to satisfy the system above. Power Electronics Applications It should be mentioned here that power electronics technology has now gained significant maturity after several decades of the dynamic technology evolution of power semiconductor devices, converters, pulse width modulation (PWM) techniques, electrical machines, variable-frequency drives, advanced controls and computer simulation techniques. According to the estimate of the Electric Power Research Institute (EPRI) of the United States, roughly 70% of electrical energy in the United States is now processed through power electronics, which will eventually expand to 100%. 7 P a g e

8 In the present century, we expect to see the significant impact of power electronics not only in global industrialization and general energy systems, but also in energy conservation, renewable energy systems, bulk energy storage and electric vehicles (EVs) and hybrid electric vehicles (HEVs). The corresponding impact in solving or mitigating climate change problems is expected to be significant. With the changes that occurred in electrical power engineering has resulted in wide spread of PE in a large spectrum of applications. Figure below shows how electrical energy generation is distributed for the enduser, showing transmission, distribution, storage, renewable energy sources and users. In fact, nowadays PE is a key technology for all those sub-systems, and has spread in many applications, examples including: Residential: heaters, home appliances, electronic lighting, equipment sources; Commercial: heaters, fans, elevators, Uninterruptible Power Supply (UPS), AC and DC breakers, battery chargers; Industrial: pumps, blowers, robots, inductive heaters, welding, machine drive, portable sources; 8 P a g e

9 Transportation: electrical and hybrid vehicles, battery chargers, railroad electric system; Utility systems: high voltage direct current, generators, reactive compensators, interface for photovoltaic, wind, fuel cells systems, Flexible AC Transmission System (FACTS) equipment; Aerospace: sources for spacecrafts, satellites, planes; Communication: sources, RF amplifiers, audio-amplifiers. Global energy concerns will provoke a large interest in the increase of the conversion efficiency and more application of PE in power quality, distributed generation, energy conservation, and smart grids. The integration of power and control circuitry into functional modules will result in systems solutions that are highly integrated into packaged products that will be both more reliable and affordable. Some PE converters that used in various applications are shown in the figures below: 9 P a g e

10 Typical wind power system with two-sided PWM converters Typical configuration of photovoltaic system 10 P a g e

11 Typical configuration of Electric Elevator Typical configuration of Electric Vehicle 11 P a g e

12 Typical configuration of Electronic Lighting Elements of Power Electronics: Power Semiconductor Devices (PSD) Passive Components Control System 12 P a g e