Bài giảng Electrical and electronic principles: Chương 5 - ThS. Ngô Quốc Cường

Bài giảng Electrical and electronic principles - Chương 5 trình bày những nội dung chính sau: Magnetically coupled circuits, transformer, resonance. Mời các bạn cùng tham khảo để biết thêm các nội dung chi tiết.

TRƯỜNG ĐẠI HỌC SƯ PHẠM KỸ THUẬT

TP HỒ CHÍ MINH

ELECTRICAL AND ELECTRONIC PRINCIPLES

WEEK 5

CONTENTS (Today)

• Magnetically coupled circuits

• Transformer

• Resonance

1.Magnetically coupled circuits

• Mutual inductance

– Mutual inductance is the ability of one inductor to induce a voltage across a neighboring inductor, measured in henrys (H)

– If a current enters the dotted terminal of one coil, the

reference polarity of the mutual voltage in the second coil

is positive at the dotted terminal of the second coil

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1.Magnetically coupled circuits

• If a current leaves the dotted terminal of one coil, the

reference polarity of the mutual voltage in the second coil is negative at the dotted terminal of the second coil

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1.Magnetically coupled circuits

• Model

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1.Magnetically coupled circuits

• Example 1

• Calculate the phasor currents I1 and I2

1.Magnetically coupled circuits

2 Transformer

Courtesy: Jensen Transformers

2 Transformer

• Ideal transformer

– Coils have very large reactances

– Coupling coefficient is equal to unity

– Primary and secondary coils are lossless

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2 Transformer

• Typical circuits illustrating proper voltage polarities and

current directions in an ideal transformer

2 Transformer

• Input impedance

• Complex power supplied by the source

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2 Transformer

• Example

Find Vo and complex power supplied by the source

2 Transformer

• Answer

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3 Resonant circuits Series resonance

• Resonance is a condition in an RLC circuit in which the

capacitive and inductive reactances are equal in magnitude, thereby resulting in a purely resistive impedance

• The value of 𝜔 that satisfies this condition is call resonant

frequency 𝜔𝑜

3 Resonant circuits

• Amplitude of current

– At 𝜔 = 𝜔𝑜

– At 𝜔 = 𝜔1

3 Resonant circuits

• The quality factor of a resonant circuit is the ratio of its

resonant frequency to its bandwidth

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3 Resonant circuits

• Example

• With R = 2 Ω, L = 1 mH, C = 0.4 µF

• Find the resonant frequency and half-power frequencies

• Calculate the quality factor and bandwidth

• Determine the amplitude of current at 𝜔𝑜, 𝜔1

3 Resonant circuits

• Answer

• 50 krad/s; 25; 2 krad/s; 10 A; 7.071 A

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3 Resonant circuits Parallel resonance

• Resonant frequency

3 Resonant circuits Parallel resonance

• Half-power frequencies, bandwidth, and quality factor

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