Task 4.1. Which statements do you agree with? Give each item a number from l to 5 and compare your choices with your partner.
â•ã•ã ... ã.ãã•ããã•ã t.•••ããã.ã•. . . .... ã 1 = strongly disagree
® G 4 = disagree
2 = agree 3 = not sure 5 = strongly agree
What are the advantages of multiple-choice questions?
I. Multiple-choice questions require less time to grade.
2. Multiple-choice questions can limit variations in marking.
3. With multiple-choice questions, students may select the correct answer with a lucky guess.
4. Many content areas can be covered on a single exam.
5. The actual answer is visible.
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Task 4.2. Watch the video and decide whether the sentences T (True) or F (False).
Statements
There are six steps to do a multiple-choice question.
The first step is to read the question and predict the word form of the correct answer.
The third step is to scan the underlined keywords from the questions and locate the sentences containing the keywords in the reading passage.
Before choosing the answer, you don't need to read carefu1ly and thoroughly around the keywords.
Depending on the instruction, you may be required to choose more than one best answer out of the available options.
Task 4.3. Look at the provided patent, apply scanning, then answer the questions by circling one correct answer out of four options.
1. What is the number of this patent?
A. US 9,294,019 B2 C.US 9,673,539 B2
B. US 6,992,603 B 1 D. US 8,000,000 B2 2. What is the number of the application?
A. 13/458136 C. 12/252672
B. 12/401082 D. 18/159440 3. What is the date of the patent?
A. Jun. I 6, 2017 C. Oct. 19, 201 7 4. Who is the inventor?
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A. Leonardo Kelvin C. Lee Kang Vu
B. Sep.23, 2005 D. Feb.20, 2015
B. James Henderson D. Freddy Messi
5. The term of this patent can be reviewed under 36 U.S.C. 155 (b) by _ _ _ days.
A. 181 B.142 C.876 D.306
United States Patent And Trademark Office
James Henderson
CERTIFICATE OF CORRECTION
I nventor(s):
Notice:
the extended 36 U.S.C.
Appl. No.:
James Henderson Subject to any disclaimer, tenn of this patent is or adjusted under 155(b)by 181 days.
12/252672
Filed: Sep. 19, 2012
Int. CL 7 ... A65B 24/06 U.S CI. ...... 482/57; 482/5 Field of Search ... 482/1-9, 51, 5:
482/57-65, 900
(10) Patent No.: US 9,673,539 B2 ( 45) Date of Patent: Feb. 20, 2015
References Cited U.S. PATENT DOCUMENTS
3,689,194 A * 6/1972 Williams ....... 482/2 3,848,467 A * 11 /l 975 Johnson ... 482/4 3,869,121 A * 3/1976 Johnson ..... 482/2 5,919,125 A* 8/1999 Edwards et al. ... 482/6 2002/0019986 A 1 * 9/2002 Harris
* cited by examiner
Primary Examiner-Thomas R. Yu Assistant Examiner -Khang Nguyen
(74) Attorney, Agent, or Firm-Bacon & Jackson, PLLC
Task 4.4. Read parts of the introduction and choose the correct answer.
Introduction
1. For modern power electronic devices such as power supplies, adaptors, electronic ballasts and motor drives, a full-bridge rectifier is commonly required. Conventional approaches use bulky electrolytic filtering capacitors in the rectifier to reduce voltage ripple. However, they result in a very low power factor (around 0.5-0.7) and cause serious harmonic pollution. Since 1990, the International Electric Committee (IEC) has issued a regulation on the line current harmonic emission in its IEC I 000-3-2 for personal computers, lighting equipment, portable tools, and balanced three-phase equipment. To meet the IEC regulation, a common approach is to use a Power Factor Correction (PFC) circuit in power electronic devices to force the input current waveform to follow the sinusoidal input voltage waveform so that the Total Harmonics Distortion (THD) is nearly zero and the Power Factor (PF) is close to one.
2. In general, PFC circuits can be divided into two main categories-passive and active.
With attractive features such as continuous input current waveform and smaller 59
inductance, active PFC circuits such as boost converters with high switching frequency strategies have been commonly adopted in various power electronic appliances designed to achieve high PF and low THD. However, the use of high switching frequency carriers leads to several drawbacks such as Electromagnetic Interference (EMI) issues and significant switching losses. To overcome these problems, many approaches use soft-switching techniques and additional electromagnetic interference filters. However, this will increase the cost as well as the complexity of the circuit design. It is not surprising that the Passive Power Factor Correction (PPFC) circuit is still commonly used in many applications. In general, the PPFC circuit consisting of low-frequency inductors and capacitors is designed to control the high-order harmonics of the input current so that PF and THD can be improved and comply with the IEC regulations.
3. In addition to the PPFC circuit and the High-Frequency Active PFC (HF APFC) circuit, the Low-Frequency Active PFC (LF APFC) circuit can be viewed as a trade-off between the PPFC circuit and the HF APFC circuit. Compared with the standard PPFC circuit, the LFAPFC circuit has higher PF and smaller THD. Although its performance is not as good as that of the HF APFC circuit, the LF APFC circuit is cheaper and can comply with the harmonic limit regulations. In fact, in many applications the LF APFC circuit has been used as an alternative to the HF APFC circuit. However, in most existing literature, proper inductance and switching strategies of the LF APFC circuit are determined by either trial and error or through computer simulations. Both approaches are inefficient and difficult to understand. To simplify the design of the LFAPFC circuit, this paper proposes a new design method that is based on a symmetric trapezoidal current waveform. Using the proposed method, major performance indices such as PF and THD can be estimated. In particular, the proposed method simplifies the procedures for determining proper inductance and conduction parameters based on input conditions and output performance requirements.
4. Several experiments have been conducted to check the effectiveness of the proposed approaches. Experimental results show that the proposed approach for designing the LF APFC circuit based on the symmetric trapezoidal current waveform is feasible.
The remainder of the paper is organized as follows. Section 2 addresses the principle of the LFAPFC circuit. The proposed approach for designing the LFAPFC circuit based on the symmetric trapezoidal current waveform is introduced in Sect. 3. Experimental results and conclusions are given in Sects. 4 and 5.
Source: M. Hou, C. Chen and M. Cheng, (2016,) Design and analysis of a single-phase low-frequency active power factor correction circuit: A symmetric trapezoidal current waveform approach, Electrical Engineering, 257-270.
I. When has the IEC issued a regulation on the line current harmonic emission?
A. Since 1990
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B. Since 1992 C. Since 1882 D. Since 1909
2. How many main categories are there in PFC circuits?
A.3 B. 2 C. 4 D. 5
3. What are the solutions to overcome the EMI issues when using high switching frequency carriers?
A. To control the high-order harmonics of the input current
B. To increase the cost as well as the complexity of the circuit design C. High switching frequency strategies
D. To employ soft-switching techniques and additional electromagnetic interference filters
4. What are the differences between the LF APFC and the PPFC?
A. The LF APFC circuit has higher PF and smaller THD.
B. The THD circuit has higher PF and smaller LF APFC.
C. The THO circuit has shorter PF and smaller LF APFC.
D. The LF APFC circuit has shorter PF and smaller THD.
5. What has been checked by experiments?
A. Input conditions and output performance requirements B. The effectiveness of the proposed approaches