Insulation monitoring in the AC aircraft power district
A method for monitoring insulation in a power system comprising a motor drive circuit configured to provide AC power from a power source to power a motor. The method includes: boosting a DC link voltage of an inverter of the motor drive by an active rectifier, the active rectifier converting the AC power from the power source to DC power for the inverter; isolating the motor drive circuit from the power source; performing at least one isolation test by providing a current path through components of the motor drive and optionally a motor connected to the output of the inverter to be tested; monitoring the current during each isolation test to detect partial discharge or excessive leakage from the current path, thereby indicating that there exist one or more defect(s) in the insulation in the current path.
1 . A method for monitoring insulation in a power system comprising a motor drive configured to provide AC power from a power source to power a motor, the method comprising:
boosting a DC link voltage of an inverter of the motor drive by an active rectifier, the active rectifier converting the AC power from the power source to DC power for the inverter;
isolating the motor drive from the power source;
performing at least one isolation test by providing a current path through components of the motor drive; and
monitoring the current during each isolation test to detect partial discharge or excessive leakage from the current path, thereby indicating that there exist one or more defect in the insulation in the current path;
wherein the step of isolating the motor drive from the power source comprises:
turning off bidirectional switches on each leg of the active rectifier during a zero current demand resulting from the boosting of the DC link voltage.
2 . The method of claim 1 , wherein the step of boosting the DC link voltage comprises:
controlling the active rectifier to perform a boost operation, thereby converting the AC power from the power source at its input to high voltage DC power at its output, thereby providing a boosted DC link voltage for the inverter of the motor drive.
3 . The method of claim 1 , further comprising:
storing the monitored current during each isolation test; and
using the stored current to predict the remaining life or present state of the insulation of the current path associated with each isolation test.
4 . The method of claim 1 , wherein the step of monitoring the current during each isolation test comprises:
measuring the current on a low voltage DC rail, HVDC−, by closing a first switch thereby allowing current to pass through a first current monitoring circuit, and
measuring the current on a high voltage DC rail, HVDC+, by closing a second switch thereby allowing current to pass through a second current monitoring circuit.
5 . The method of claim 1 , wherein the step of performing at least one isolation test comprises at least one of:
testing the insulation of the inverter top switches and the active rectifier;
testing the insulation of inverter bottom switches, windings of the motor and the harness of the winding; and
testing the insulation of the active rectifier.
6 . The method of claim 1 , wherein the motor drive is a first motor drive of a plurality of motor drives, and each of the plurality of motor drives is connected at least one of a plurality of motors via a reconfiguration matrix, and wherein the reconfiguration matrix connects a desired motor drive of the plurality of motor drives to the output of the first motor drive such that the insulation of the desired motor drive may be tested.
7 . A motor drive for performing the method of claim 1 , the motor drive comprising:
the active rectifier, wherein the active rectifier is configured to connect to the power source at its input, and provide DC power along a high voltage DC rail, HVDC+, and a low voltage DC rail, HVDC−, at its output;
the inverter, wherein the inverter is configured to convert DC power across HVDC+ and HVDC− to an AC power output;
an output capacitor network circuit connected to the output of the active rectifier, the capacitor network circuit being configured to operate as local energy storage and voltage balancing for the inverter;
a first current monitoring circuit connected to HVDC−; and
a second current monitoring circuit connected to HVDC+.
8 . The motor drive of claim 7 , wherein the inverter module is based on IGBTs, Mosfet SiC, Si devices or relays.
9 . The motor drive of claim 7 , further comprising:
an EMC filter configured to filter input DC power.
10 . The motor drive of claim 7 , further comprising:
a first switch in series with the first current monitoring circuit, and a second switch in series with the second current monitoring circuit.
11 . The motor drive of claim 7 , further comprising:
at least one boost inductor connected to the input of each phase of the active rectifier.
12 . A system comprising:
a power source configured to provide AC power;
the motor drive of claim 7 connected to the power source to receive the AC power; and
a motor connect to the motor drive.
13 . A system comprising
a plurality of motor drives, wherein at least one of the motor drives is a first motor drive, and is a motor drive as claimed in claim 7 ;
a plurality of motors;
wherein each of the plurality of motor drives is connected at least one of the plurality of motors via a reconfiguration matrix.
14 . The system of claim 13 , wherein the reconfiguration matrix is further configured such that one of the plurality of motor drives may be connected to the output of the first motor drive, such that the first motor drive can test the insulation of any of the plurality of motor drives.