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(1) When positive current flows in the power supply (motor running)
By controlling two states a) and b) by turning on/off IGBT and IGTX, output voltage from U-phase is
controlled.
a) IGBTU is turned on (IGBTX off)
IGBTU turns on and IGBX turns off.
If the DC voltage is lower than the power supply voltage, the current flows into the DC capacitor through
the diode. On the other hand, even if the DC voltage is higher than the power supply voltage, when
IGBTX is turned off, IGBTU causes the current (that was flowing in the direction pointed by the arrow into
the power supply so far) to flow into the DC capacitor through FWD current of IGBTU.
Then the current flows through the loop that starts from virtual 0V of the converter and returns to the
neutral point of the power supply. (The neutral point is not connected actually but it can be assumed that
the current flows through the equivalent neutral point since V and W phases are provided).
b) IGBTX is turned on (IGBTU off)
IGBTX turns on and IGBTU turns off.
When IGBTX is turned on (gate signal is on), the positive current flows through IGBTX. In this mode, the
current becomes larger.
(2) When negative current flows in the power supply (regeneration)
For regeneration, two states a) and b) are controlled by turning on/off the IGBTU and IGBTX in the same
way as in motor running operation.
a) IGBTX is turned on (IGBTU off)
IGBTX turns on and IGBTU turns off.
In this case, since IGBTX is on, U-phase output becomes the negative potential (-340V output). Then the
current flows through the loop that starts from the virtual neutral point and returns to the virtual 0V of the
converter through the power supply.
b) IGBTU is turned on (IGBTX off)
IGBTU turns on and IGBTX turns off.
In this case, the current is controlled through IGBTU (340V output). Then the current flows the loop that
starts from the virtual neutral point and returns to the virtual 0V through the power supply.
Positive current and negative current may sometimes flow through IGBT and may sometimes flow
through diodes. However, the voltage is the same in both cases. That is, when IGBTU gate signal is on,
the voltage becomes 340V and when IGBTX gate signal is on, the voltage becomes –340V.
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