Christoph Haederli - Les thèses en ligne de l'INP - Institut National ...

NP Control with Carrier based PWM 103
5.2.3 Performance evaluation
For the performance analysis of the controllers, a NP voltage reference step has been
simulated. The Maximum dv/dt achieved is proportional to the maximum average NP current and
is a measure for NP control capacity and thus the performance of the control scheme.
TABLE 36, OPERATING POINT FOR THE SIMULATIONS IN TABLE 37 TO TABLE 38
m f out U DC U FC R load L load ϕ UI C DC C FC f sw
0.6 50 Hz 240 V 60 V 0.5 Ω 14.2
mH
1.53 990µF 1120µF 2000
Hz
All simulations in this paragraph are based on balanced undistorted systems. The controller
gain in the simulations has been chosen such that the controllers saturate at high voltage deviation
in the NP, but have a low impact close to the set point.
The dv/dt obtained with the real time NP current function is 800V/s (20V / 25ms in the
graph). With an effective capacitance of 4mF (upper and lower DC link capacitors in parallel), we
get a NP current of 3.2A during the transient corresponding with 18% of the peak phase current of
18A. The 6 th harmonic injection has a dv/dt of 600 V/s resulting in an NP current of 2.4A, which
corresponds with 13% of the peak phase current. This is a very good match with the values
obtained by calculation and shown in Figure 68.
The two schemes provide very similar currents during transients and the new set point is
reached after around 50ms. The phase output voltages in TABLE 37 show fundamentally different
behavior for the two schemes: The 6 th harmonic injection scheme has moderate 3 rd harmonic in
steady state; during transient operation, the 6 th harmonic is clearly visible. The real time NP current
function scheme applies a very high 3 rd harmonic content in steady states, which minimizes the NP
current ripple; in transient operation, a constrained DC is injected rather than a 6 th harmonic. The
6 th harmonic injection scheme results in a higher NP voltage ripple but yields smoother phase
voltage waveforms. Note that this results depends largely on the choice of underlying modulation
scheme and the controller gain.
The proposed modulation schemes keep the differential voltage and the resulting output
currents undistorted. There is a difference in the switching frequency on the device level (at a given
apparent output switching frequency) and the resulting losses. However the impact is relatively low
in the given operating point. The steady state switching losses can be reduced by only 2% through
the use of the 6 th harmonic injection scheme.
Experimental results comparing the NP control performance of these schemes with the more
powerful virtual vectors are given in paragraph 7.4.