METHOD FOR CONVERTING WIDE VARYING AC VOLTAGE FROM PMA TO REGULATED DC VOLTAGE
Publication Date: 2017-Jun-02
The IP.com Prior Art Database
A shunt regulated PMA voltage source consists of a PMA, a shunt regulator and a PWM controller, to create regulated DC bus, for powering all the downstream electronics in an aircraft engine control system. The two different shunt regulator topologies proposed herein are efficient and requires a reduced number of components compared to the conventional topologies. One of the proposed topologies generates a regulated bipolar voltage, which simplifies the design of downstream point of load power converters powering different electronic loads in aircraft engine control system.
The present disclosure relates generally to electrical systems used in aircrafts, and more particularly to conversion of AC voltage to DC voltage.
Permanent Magnet Alternator (PMA) generates a widely varying output voltage, from as low as 48VAC to as high as 700VAC. Conventionally, shunt regulators are used as converters to derive a regulated voltage of 28VDC. The PMA during normal operation generates a 400VAC output voltage. Several shunt regulator topologies are available to convert 400VAC to 20VDC. However, the PMA current flows through the diode bridge rectifier, due to which the existing topologies are not efficient.
Therefore, there exists a need for improving the efficiency in the AC to DC voltage conversions in aircraft electrical systems.
BRIEF DESCRIPTION OF DRAWINGS
FIGS. 1 is a schematic illustration of Topology 1.
FIG. 2 depicts a possible implementation of bidirectional controlled switches as shown in FIG. 1.
FIG. 3 depicts gate signals for switches S1 and S2 with same triangular carrier signals.
FIG. 4 depicts gate signals for switches S1 and S2 with phase shifted carrier signals.
Figure 5 is a schematic illustration of Topology 2.
The present disclosure proposes two topologies, described herein as Topology 1 and Topology 2, to solve the issue of low efficiency by reducing the part count. Topology 2 enables an additional feature of bipolar voltage, which optimizes the design of downstream converters in engine control systems, improving the efficiency of the entire system.
FIG. 1: Topology 1
FIG. 1 shows Topology 1 of the shunt regulated PMA voltage source. The PMA generates a 3‑phase AC voltage with magnitude and frequency determined by the speed of PMA. Switches S1 and S2 are used to regulate the output voltage Vo. The current circulates in the windings of PMA when the switches S1 and S2 are closed. The magnitude and phase of winding currents depends on the winding inductance and resistance of PMA. When the switches S1 and S2 are open, current flows to the output load resistance through the diode bridge rectifier.
Switches S1 and S2 are bidirectional controlled switches. One of the several ways to realize S1 and S2 is by connecting the MOSFETs or IGBTs in a back-to-back configuration as shown in FIG. 2. Another way to realize switches S1 and S2 is to use HEMTs (such as GaN) which do not have freewheeling or body diodes.
FIG. 2: Bidirectional controlled switches
One of the ways to operate switches S1 and S2 is to turn the switches S1 and S2 ON or OFF simultaneously, by using the same triangular carrier for comparing the control command given by the closed loop controller for controlling the output voltage. The gate signal for switches is high when carrier signal is greater than, or equal to the modulation signal as shown in FIG. 3.
FIG. 3: Gate signals for switches S1 and S2 with same triangular carri...