The "usqref" and "usdref" components permit so-called overmodulation of the DC link voltage (limitation to hexagon instead of circle).
The maximum output voltage which can be set for each phase angle results from the circle which fits in the voltage hexagon (diagram below). By setting the hexagon modulation (3) "Hex Phase", the length of the vector for the output voltage can be placed in the area of the DC link voltage (red). As a result only two of the three half-bridges are switched in each switching interval. The third remains at the upper or lower potential of the DC link voltage for a period of 60° of the output frequency.
This method has only two third of the switching losses of modulation with all three phases. Disadvantages are higher harmonics of the motor currents and thus less smooth running at high motor speeds.
UN = rated voltage
Ul = voltage at inductor
Uu = inverter voltage
Uzk = DC link voltage
α = phase angle
Setting of the output amplitude and phase of the drive controller
Representation of the 8 vectors of the three-phase voltage system (3 half-bridges each with 2 states [23]) The vectors correspond to the DC link voltage UZK and form a voltage hexagon.
Bild: Circle and hexagon voltages
Parameters
| P. no. | Parameter name | Function |
|---|---|---|
| P 0431 |
CON_CCON_VLimit |
Voltage limit of the current controller |
| P 0432 | CON_CCONMode | Selector for the mode of voltage limitation of "usqref" and "usdref". |
| (0), (1) | PRIO(0.1) | Hard switch from d-priority (motorized) to q-priority (regenerative). A portion of the voltage is held in reserve; the amount can be specified via parameter P 0431 CON_CCON_VLimit. |
| (2) | Phase(2) | Phase-correct limitation |
| (3) | HEX, Phase (3) | Hexagon modulation with phase-correct limitation. More voltage is available for the motor. The current exhibits a higher ripple at high voltages however (see diagram). |
| (4) | D_PRIO(4) | Pure priority of the d-current controller |
Tabelle: Parameters for setting the voltage limit
Copyright © LTi DRiVES GmbH, Januar 2013, ID-Nr.: 0842.26B.1-00 DE