Non-ideal diode rectifier lecture note Nottingham Uni

A non-ideal diode rectifier is a rectifier circuit in which the diodes used are modeled with practical, non-ideal characteristics rather than assuming an ideal diode. In reality, semiconductor diodes deviate from the ideal model due to physical limitations, and these deviations directly affect the performance of rectifier circuits.
A non-ideal diode rectifier considers diode imperfections (forward drop, leakage, recovery time, capacitance, resistance) which reduce efficiency and alter the output characteristics compared to the ideal case. Accurate modeling of these effects is essential for practical rectifier design, especially in high-frequency or high-efficiency power electronic systems.

1. Non-ideal 
Diode Rectifier (1)
0
Neutral
A
B
C
Line A
Phase
voltage
V
xy
D1 D3 D5
D4 D6 D2
Id=constant
x
y
h
h
h
a’
b’
c’
Effect of supply inductance = this causes overlap since current
cannot transfer instantaneously from one device to another
VA VB VC
D1
a’
D3
b’
x
ia
0
a
a
di
i const h
dt
= = 0
a
a d
di
i I h
dt
= → =∞
Instant commutation between D1 and D3 is not possible !
ia
ib
2009/10
Lecture notes and much more@ http://webct.nottingha m.ac.uk
Commutation group “P”
D1
⇒D3

2. Non-ideal 
Diode Rectifier (2)
'
a
a AN
di
V V h
dt
= −
'
b
b BN
di
V V h
dt
= −
a b d
i i I const+ = =
a b
di di
dt dt
⇒ =−
Outgoing diode (D1) Incoming diode (D3)
Both diodes conduct simultaneously (overlap)
' 'a b
V V=
a a
AN BN
di di
V h V h
dt dt
− = +
2
a AN BN
di V V
h
dt
−
⇒ =
'
2 2
AN BN AN BN
a AN x
V V V V
V V V
− +
= − = =
y CN
V V=
μ
Loss in Volt-time area!! ⇒smaller V xy
2 2 2
AC BC BC AC BA
xy BC
V V V V V
V V
+ −
∆ = − = =
2 2
AN BN AC BC
xy CN
V V V V
V V
+ +
⇒ = − =
Voltage Loss
2009/10
Lecture notes and much more@ http://webct.nottingha m.ac.uk
Is half the commutating voltage B=(incoming D3) A=(outgoing D1)
VANVBN

3. Non-ideal 
Diode Rectifier (3)
The missing VTA in Vxyis required to commutate the load
current I
dfrom D1 to D3
Loss in mean V
xy
Total VTA lost from Vxin one cycle = 3*h*I d
a
L
di
V h
dt
=
6 3
2
d d
I h I h
= ⋅ ⋅ ⋅ = ⋅ ⋅ ⋅
ω ω
π π
Effect on the line current waveform
lost L a d
VTA V dt h i h I⇒ = = ⋅∆ = ⋅∫
Similar for Vy⇒hence total VTA loss in Vxy= 6*h*I d
3 3
3
xy d
E
V I h
⋅= − ⋅ ⋅ ⋅
ω
π π
Causes volt-drop with Id
known as “regulation”
Negligible effect on the
harmonics unless μis
very large
⇒Same Power Quality
measures (DPF, DF, PF)
as for ideal diode rectif.
ia ib
Id
0
μ
a b d
i i I+ =
2009/10
Lecture notes and much more@ http://webct.nottingha m.ac.uk
Only a small change of shape during commut.

4. Non-ideal 
Diode Rectifier (4)
Calculation of μμμμ
0
A
B
D1D3
Id=const
x
h
h
a’
b’
VBA
ia
ib
Easiest way to find it is by considering the following loop:
μ
3E⋅
VBA=commut.
voltage
( )3 cos0 cos 2
d
E h I μ⋅ − = ⋅
( )
3
1 cos
2
d
I h E⋅ = ⋅ ⋅ − μ
Area = 2 Id*h
twice of what’s lost
⇒Determine μ
During this time, Vbacauses the change of :
• i
afrom Idto 0 in phase A inductance
• i
bfrom 0 to Idin phase B inductance
Detrimental effect on other users
0
A
B
C
Id=const
L1 L2
L1 L2
To other users
Current in L2 is
distorted due to
overlap
Voltage in PCC =
partially distorted
PCC
1
1 2
L
L L+
⇒
2009/10
Lecture notes and much more@ http://webct.nottingha m.ac.uk