Lecture Notes. Introduction to Power Electronics

Transcription

1 Lecture Notes 1 Introduction to Power Electronics Prepared by Dr. Oday A Ahmed Website: @uotechnology.edu.iq Scan QR

2 Contents of this Lecture: What is Power Electronics Power Electronic System Structure Power Electronic Converters Power Semiconductor Devices Examples for Power Electronic Applications What is Power Electronics? The field of power electronics is concerned with the processing and control of electrical power using high efficiency electronic circuits. 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 Power Electronic System Structure Figure 1.1 Shows the basic structure of the power electronics system: Source Power Processer Load Control System Electronic Circuits Fig.1.1 Power Electronics System Structure Source: is an electrical source which is be either DC or AC Power Processor: is a device that used to change the energy form between the source and the load. 1

3 Electronics Circuit: is a low power electronic circuits used to measure the voltage/current and to drives the power processor Control System: is a system used to control the power processor so that maintain different parameters such as voltage, current and power. Load: is an Electrical load which is be either DC or AC load Power Electronic Converters Power electronic converter is a device that can convert of the electric power from one to another form. The main forms of power conversion are as follows: 1. Rectification (conversion from ac to dc) The corresponding converter is known as a rectifier or an ac/dc converter for rectification. 2. Inversion (conversion from dc to ac) The corresponding converter is known as an inverter or an ac/dc converter for inversion. 3. Conversion from dc to dc The corresponding converter is known as a dc converter or DC Chopper 4. Conversion from ac to ac The corresponding converter is known as an ac converter. two types exist: AC chopper: convert the fixed voltage and frequency to the fixed frequency and variable voltage Frequency Converter: convert the fixed voltage and frequency to the variable frequency and voltage. Note: A. All the above converters can be transferred the energy in unidirectional from or in bidirectional form. 2

4 B. The PEs converters can be connected in series or parallel connection to either increase voltage or current and reduce the ripple. C. Connection of two different converters types is very common in PE system. D. Changing the output voltage in the PE converter on the account of current magnitude. Fig.1.2 shows some types of the power electronic converter connections Fig.1.2 Functional diagrams of converters connections Depending on the properties of the power source, we may distinguish the voltage and current converters. At the input of a voltage converter, the properties of the power source V resemble those of an emf source. As a 3

5 rule, a capacitor C is connected in parallel to the source (Figure 1.3a). At the input of a current converter, the properties of the power source I resemble those of a current source. A choke L is connected in series with the source (Figure 1.3b). Fig.1.3 (a) Voltage converter and (b) current converter. Question will be solved in the class: 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. Differences between PE circuits and Electronic Circuits In PE circuits the focus is on power conversion at the highest possible efficiency using very small control signals. In Electronic circuits the focus is on information processing with minimum loss of information How can this converter be realized? DC-DC conversion can be obtained using electronics/power electronic circuits as shown in Fig

6 (a) (b) (c) Fig.1.4 How to build DC-DC converters In Fig.1.4.a voltage divider is used to obtain 50V from 100V input source. to regulate the output DC voltage a series pass regulator circuit is used as shown in fig.1.4.b. Both circuits have high losses (Why?). To reduce the loses the third circuit in Fig.1.4b is much efficient. 5

7 Power Electronics Applications 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%. Some of the PE applications are listed below: 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; 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 spacecraft, satellites, planes; Communication: sources, RF amplifiers, audio-amplifiers. Figures below show various PE converters applications: Laptop computer power supply 6

8 Typical wind power system Typical configuration of photovoltaic system Typical configuration of Electronic Light 7