Focused Practice

I. Answer the following questions:

1. Where is a device called “4:2 hybrid” used?

2. What would an ideal hybrid do?

3. Where will some of the energy in the incoming line leak in a real device?

4. What is an adaptive filter used for?

5. When is the echo of the far end speech cancelled?

6. What misbehavior arises in certain situations?

7. What did the real time tests utilize?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: “4:2 hybrid”.

Unit 62 Grammar: The Future Simple Tense Word List:

1. fuel cell	топливный элемент, топливная батарея
2. photovoltaics	фотоэлектричество, фотоэлектрическая энергетика
3. renewable energy sources	возобновляемые источники энергии
4. static var compensation	компенсация статической реактивной мощности
5. a modular, scaleable power electronics technology	технология создания модульных блоков силовой электроники
6. real and reactive power flow	активная и реактивная составляющие мощности
7. medium voltage adjustable speed motor drives	запуск моторов с регулировкой скорости при среднем напряжении
8. multilevel converter	многоуровневый конвертор (преобразователь)
9. a high voltage dc back-to-back intertie	непосредственное соединение двух высоковольтных конверторов постоянного тока друг за другом
10. harmonic filtering	фильтрация гармоник
11. fast response	быстродействие
12. dynamic voltage restoration	восстановление (стабилизация) действующего напряжения
13. utility interface	промежуточное звено

Multilevel Converters as a Utility Interface for Renewable Energy Systems

Electric power production in the 21^st Century will see dramatic changes in both the physical infrastructure and the control and information infrastructure. A shift will take place from a relatively few large, concentrated generation centers and the transmission of electricity over mostly a high voltage ac grid to a more diverse and dispersed generation infrastructure that also has a higher percentage of dc transmission lines.

Some of the distributed generation power sources that are expected to increase greatly their market share of the total power produced in the US and abroad include renewable energy sources such as photovoltaics, wind, etc. Fuel cell technology is also nearing the development point where it could start to supply a significant share of the power needs. The advent of high power electronic modules has also encouraged the use of more dc transmission and made the prospects of interfacing dc power sources such as fuel cells and photovoltaics more easily attainable. A modular, scalable power electronics technology that is ideal for these types of utility applications is the transformerless multilevel converter.

The use of a multilevel converter to control the frequency, voltage output (including phase angle), and real and reactive power flow at a dc/ac interface provides significant opportunities in the control of distributed power system.

Additional applications of multilevel converters include such uses as medium voltage adjustable speed motor drives, static var compensation, dynamic voltage restoration, harmonic filtering, or for a high voltage dc back-to-back intertie.

Because distributed power sources are expected to become increasingly prevalent in the near future, the use of a multilevel converter to control the frequency and voltage output (including phase angle) from renewable energy sources will provide significant advantages because of its fast response and autonomous control. Additionally, multilevel converters can also control the real and reactive power flow from a utility connected renewable energy source. These power electronic topologies are attractive for continuous control of system dynamic behavior and to reduce power quality problems such as voltage harmonics, voltage imbalance, or sags.