MFC710/AcR - Section: 1. General description of the MFC710/AcR frequency converter
1. General description of the MFC710/AcR frequency converter
The MFC710/AcR frequency converter was developed by extending the MFC710 frequency converter with an
AcR (Active Rectifier) reversible rectifier module replacing the conventional diode input circuit. This eliminates
the problems arising from the use of diode rectifiers:
• power supply current and voltage distortions caused by the non-linear load,
• no possibility of returning electricity to the mains.
Fig. 1.1 shows block diagrams of both types of converters.
MFC710
Asynchro-
nous motor
AC/DC
rectifier
DC-link
circuit
DC/AC
inverter
Directions of electricity
flow
Electrical
grid
C
mfc710acr-05.1-en
MFC710/AcR
C
AC/DC
rectifier
DC-link
circuit
DC/AC
inverter
Electrical
grid
Directions of electricity
flow
mfc710acr-06.1-en
Asynchro-
nous motor
Fig. 1.1: Block diagrams of MFC710 and MFC710/AcR converters
Using the MFC710/AcR converter, we obtain:
1. FC power factor correction, limitation of THDi current distortion factor and THDu voltage.
The AcR module allows to obtain a sinusoidal waveform of the consumed current, eliminating the
negative impact of higher harmonics introduced into the power supply network when using
conventional power supply systems.
2. Bidirectional power flow, four-quadrant operation.
In converter drives, there is often a situation in which the energy accumulated in the load must be
transferred back to the source or lost in the form of heat on an additional resistor. If this process is
intense or repeated often, the use of an additional braking resistor may be unprofitable or impossible.
The AcR module allows bidirectional power flow, so that it can transfer the stored energy to the
mains for recycling. Such a solution is justified not only from the point of view of the energy balance
but also from the point of view of operating costs. The module is used, among others in drive
applications for centrifuges, cranes and the processing of energy obtained from renewable sources.
3. Voltage stabilization in the intermediate circuit.
The AcR module is a three phase AC / DC boost converter. This means that the voltage in the
intermediate circuit of the inverter may be higher than the mains voltage. The use of the AcR module
in the frequency converter allows for higher voltage than the supply voltage at the inverter output
(e.g. 400VAC 50Hz input voltage, 0-500VAC 0-400Hz output voltage).
TWERD POWER ELECTRONICS
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