Power Electronics in Smart Electrical Energy Networks
Power Electronics in Smart Electrical Energy Networks introduces a new viewpoint on power electronics, re-thinking the basic philosophy governing electricity distribution systems. The proposed concept fully exploits the potential advantages of renewable e
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1 Four-quadrant Frequency Converter The four-quadrant frequency converter is presently commonly applied in novel asynchronous drives, electric power generation using asynchronous variable speed generators and T&D systems [1]. The main circuit of this converter comprises two IGBT three-phase bridges and an intermediate circuit allowing two-way energy flow and four-quadrant operation. The operation of IGBT devices (high dv/dt) causes high level conducted and radiated electromagnetic emissions. We shall examine an asynchronous drive with the four-quadrant frequency converter in this section as a most interesting EMC case due to different impedance characteristics on the mains and load side. From the point of view of EMC analysis, the motoring and generating quadrants are quite the same. Figure 5.1 shows a four-quadrant asynchronous drive with elements that influence EMC behavior: heatsink-to-DC link capacitance and line reactors [2]. The limits for conducted emissions are contained in EN 61800-3 (EMC product standard for PDS). 4-quadrant Frequency Converter
M 3
3
Line-side Converter
Motor-side Converter Heatsink to DC link capacitance
Figure 5.1. Main circuit diagram of the four-quadrant inverter drive system
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A. Kempski and R. Smoleński
We have tested a two-pole, 10kW induction motor fed by a typical industrial four-quadrant frequency converter supplied via LISN (Line Impedance Stabilization Network). Figure 5.2 shows the results of measurements which have been carried out on the system consisting of LISN and EMI receiver ESCS-30, in the frequency range specified in EN 61800-3. We can observe oscillation modes of EMI current waveforms at frequencies 2.5 MHz, 3.8 MHz and 4.7 MHz. The limits are slightly exceeded at the frequency 2.5 MHz, and significantly at the beginning of the CISPR B band (150 kHz). The shape of the EMI envelope implies that its source could be located in a lower frequency range. Level [dBµV] 130 120x + x + xxx +++
100
x +
80 60 40
CISPR B
20
0
150k
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1M 2M 3M 4M Frequency [Hz]
6M
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Figure 5.2. Conducted EMI spectrum (drive without filters)
Figure 5.3 shows the results of additional measurements in CISPR A band (not required by the related Standard). Level [dBµV] 140
120
100
80
CISPR A
60
40
9k
20k
30k 40k Frequency [Hz]
50k 60k
80k 100k
150k
Figure 5.3. Conducted EMI spectrum (CISPR A)
In the low frequency part of the spectrum (CISPR A) we have observed repeatable changes at frequency 40 kHz, 80 kHz, … We have identified them with the time of the synchronized impulse of transistors switching (25 μs) and its harmonics. The envelope of this spectrum is characteristic for a damped sine wave pulse at a frequency of about 70 kHz.
EMC Cases in Distributed Electrical Power System
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In order to establish the nature of dominant oscillatory modes (CM or DM) measurements using a current probe have been made directly in the PE wires on the line and motor side (Figure 5.4). Level [dBµA]
Level [dBµA]
120
120
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100
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80
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