Chapter 18 Utility Interface

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Chapter 18
Utility Interface
• Power quality has become an important issue
18-1
Various Loads Supplied by the Utility Source
• PCC is the point of common coupling
Chapter 18 Utility Interface
18-2
Diode-Rectifier Bridge
• Bock diagram
Chapter 18 Utility Interface
18-3
Typical Harmonics in the Input Current
• Single-phase diode-rectifier bridge
Chapter 18 Utility Interface
18-4
Harmonic Guidelines: IEEE 519
• commonly used for specifying limits on the input
current distortion
Chapter 18 Utility Interface
18-5
Harmonic Guidelines: IEEE 519
• Limits on distortion in the input voltage supplied
by the utility
Chapter 18 Utility Interface
18-6
Reducing the Input Current Distortion
• use of passive filters
Chapter 18 Utility Interface
18-7
Power-Factor-Correction (PFC) Circuit
• For meeting the harmonic guidelines
Chapter 18 Utility Interface
18-8
Dc current
• No losses and current sinusoidal in input side
pin  2U s sin t
2 I s sin t  U s I s  U s I s cos 2t
• Dc voltage ud can be assumed constant
pd  U d id
• Large switching frequency
– Ld can be assumed small
– Instantaneous powers are equal, pin = pd
Us Is Us Is
id  I d  iC 

cos 2t
Ud
Ud
18-9
Voltage ripple
Us Is Us Is
id  I d  iC 

cos 2t
Ud
Ud
I d  I load
Us Is

Ud
• Capacitor current
Us Is
iC  
cos 2t   I d cos 2t
Ud
• Capacitor voltage ripple
ud ,ripple
Id
1

iC dt  
cos 2t

Cd
2Cd
18-10
Power-Factor-Correction (PFC) Circuit
Control
• generating the switch on/off signals
Chapter 18 Utility Interface
18-11
Power-Factor-Correction (PFC) Circuit
• Operation during each half-cycle
Chapter 18 Utility Interface
18-12
Current ripple
• Both dc voltage Ud and supply voltage
assumed constant during switch conduction
– times
ton 
Ld I hys
us
toff 
Ld I hys
U d  us
U d  us  us

1
fs 

ton  toff
Ld I hysU d
• Switching frequency
• Switching frequency is constant, current ripple
and its maximum value
I hys
U d  us  us


f s LdU d
I hys,max 
Ud
4 f s Ld
kun
U
us  d
2
18-13
Thyristor Converters for 4-Quadrant
Operation
• Two back-to-back connected 2-quadrant converters
Chapter 18 Utility Interface
18-14
Switch-Mode Converter Interface
• Bi-directional power flow; unity PF is possible
Chapter 18 Utility Interface
18-15
Switch-Mode Converter Interface
• Rectifier and Inverter modes based on the
direction of power flow
Chapter 18 Utility Interface
18-16
Switch-Mode Converter Control
• DC bus voltage is maintained at the reference
value
Chapter 18 Utility Interface
18-17
Switch-Mode Converter Interface
• Waveforms in the rectifier mode
Chapter 18 Utility Interface
18-18
3-Phase Switch-Mode Converter Interface
• Rectifier and Inverter modes based on the
direction of power flow
Chapter 18 Utility Interface
18-19
EMI: Conducted Interefence
• Common and differential modes
Chapter 18 Utility Interface
18-20
Switching Waveforms
• Typical rise and fall times
Chapter 18 Utility Interface
18-21
Conducted EMI
• Various Standards
Chapter 18 Utility Interface
18-22
Conducted EMI
• Filter arrangement
Chapter 18 Utility Interface
18-23
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