Environmental Engineering Reference
In-Depth Information
Quantization error
. Sample, hold and quantization are studied by adjusting the
sample period to a fixed value and by setting the resolution to 10 A/2,048 or
0.0049 A/bit. Now, the
i
qds
signals contain high frequency distortion and also
mixing of
i
ds
and
i
qs
as for balanced delay error. This latter effect is under-
standable since the sample and hold operation adds a one-half sample delay
that is balanced, hence the mixing action. The presence of a high frequency
content in the controller is very objectionable.
●
This section concludes with a summary of available current sensor types and
their salient characteristics (Table 6.9). Current sensors can be classified as ac and
dc sensors. The dc types can be further classified as double ended or single ended
depending on whether or not a balanced power source is required. All current
sensors operate at 5 or 10 V logic levels.
Table 6.9 Current sensors for hybrid propulsion ac drives
Manufacturer
Supply
voltage
(V)
Sensitivity
(V/A)
Peak
current
(A)
Low
frequency
(3 dB Hz)
High
frequency
(3 dB Hz)
Ion Physics
CT
1
500
35
15 million
Pearson Electronics
CT
1
500
140
35 million
Power Electronics
Measurements Ltd.
CT
1 M Rogowski
coil
1
7 million
F.W. Bell
12
0.05
100
dc
150, 000
Nana
5
0.0043
400
dc
25, 000
LEM
15
0.025
400
dc
100, 000
Honeywell
6-12
0.0058
400
dc
50, 000
CT, current transformer or current monitor
Current sensors are vital components in power electronic systems. The Hall
effect, control current types available from F.W. Bell, Nana Electronics, LEM,
Honeywell, and others are the primary types in use because sensing to dc is afforded.
Some manufacturers are investigating magnetoresistive current sensors for improved
temperature performance, but these are still not in the market. Other manufacturers
have developed prototype, digital, high accuracy current sensor, based on a tem-
perature stable manganin shunt and all digital signal conditioning and impedance
correction for dc to 100 kHz bandwidth [23]. As the quest for fully digital ac traction
drives progresses, the approach given in Reference 23 may find renewed interest.
6.11
Interleaved PWM for minimum ripple
There have been periodic attempts to use various power electronic systems to
minimize the rms ripple current in the dc link capacitor of a hard switched inverter.
Bose and Kastha [24] describe the use of active filters to eliminate the dc link
