8-6 | MVW3000
88
Special Functions
F1
F2
R
S
T
D2
D4
D6
R1
R2
D1
D3
D5
C1
FA
NE
By
pas
s
Figure 8.6:
Power cell with bypass system active
Figure 8.6 on page 8-6
exemplifies the power cell operation with the bypass system active. The current of the
respective phase passes through the bypass system, and the cell no longer processes any energy. Therefore,
the inverter current capacity, when in bypass mode, is not reduced. That occurs due to the connection in series
of the power cells.
8.4 ANGLE ADJUSTMENT
During the operation of the MVW3000 in bypass mode, the inverter current capacity is preserved, because of
the connection is series of the power cells. Differently, the maximum voltage available at the motor terminals will
smaller, due to the connection in series. Such effect is not desired, since the motor torque is directly related to
the voltage and current applied to its terminals. In addition to the smaller voltage available for the load, the inverter
output also becomes unbalanced, jeopardizing the motor operation. Those problems can be circumvented by
using the technique of angle adjustment between the converter phases.
This technique consists in modifying the phase voltage angles so as to keep the balance between the line
voltages. Thus it is possible to maximize the line voltages and have a smaller impact of the cell bypass on
the application voltage. In order to exemplifies how the technique works, it is possible to represent an 18-cell
MVW3000 (6 per phase) for 18 power supplies (6 in series per phase, connected in Y to the neutral point). Under
normal operation of the inverter, with all the cells operating, the phase voltages are shifted 120° between each
other, and the line voltages have the same amplitude, as shown in
Figure 8.7 on page 8-7
(a).
In bypass, without the angle adjustment technique, the line voltages are unbalanced, since the shift between
the phases is still 120°. This process can be seen in
Figure 8.7 on page 8-7
(b). In practice, this case is not
compatible with the operation of the application; therefore, as soon as the cell bypass occurs, the inverter applies
the angle adjustment method to balance the line voltages.
For such situation, where 3 cells of phase W are out of operation and without the angle adjustment, Vvw and
Vwu voltages would fall down to 76 % (0.76 p.u.) of the inverter rated operating voltage, even having 15 cells
in operation (approximately 83.3 % of the cells). As the inverter neutral point is not connected to the motor, its
relative position can be easily changed by the angles of the phase voltages. Thus, even with the phase voltages
unbalanced, it is possible to obtain balanced line voltages with the best use of the available voltage.
With the angle adjustment, presented in
Figure 8.7 on page 8-7
(c), it is possible to observe that the line voltages
remain balanced. The phase voltages have different shifts now. The voltage available at the motor terminals is
now 80% (0.80 p.u.) of the inverter rated voltage.
Summary of Contents for MVW3000 A0040 V023
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Page 5: ...User s Manual Series MVW3000 Language English Document 10004823674 00 Publication Date 03 2017...
Page 6: ...Summary of Reviews Version Review Description R00 First edition...
Page 12: ...1 4 MVW3000 1 Safety Notices...
Page 58: ...6 18 MVW3000 6 Installation Connection and Energization...