Independent ground fault detection using current transformer

Abstract

A fault detection system for a system having a single DC input and a plurality of A/C loads such as an electric or hybrid electric vehicle. A plurality of inverters convert DC to 3-phase A/C and supply A/C power to a corresponding individual A/C load. Each inverter includes a common mode current transformer and a controller. An individual corresponding common mode current transformer is coupled to the 3-phase A/C output of the inverter. An individual corresponding controller is coupled to the output of an individual corresponding common mode current transformer and is coupled to an individual corresponding A/C load. Each controller is configured to detect a fault at the individual corresponding A/C load and in the case of detection of a fault at an individual corresponding A/C load, the corresponding controller disables the A/C load.

What is claimed is: 
     
         1 . A fault detection system comprising:
 a DC power source;   a plurality of inverters coupled to the DC power source, the plurality of inverters converting DC to 3-phase A/C, the plurality of inverters each supplying A/C power to a corresponding individual A/C load;   a plurality of common mode current transformers, an individual corresponding one of the plurality of common mode current transformers being coupled to the 3-phase A/C output of each of the plurality of inverters; and   a plurality of controllers, an individual corresponding one of the plurality of controllers being coupled to the output of an individual corresponding one of the plurality of common mode current transformers and being coupled to an individual corresponding A/C load, each of the plurality of controllers being configured to detect a fault at the individual corresponding A/C load,   wherein in the case of detection of a fault at an individual corresponding A/C load, the corresponding controller disables the A/C load.   
     
     
         2 . The fault detection system of  claim 1 , wherein each of the common mode current transformers is configured with a primary coil coupled to the 3-phase A/C output of the corresponding inverter and a secondary coil coupled to an imbalance detection circuit of the corresponding controller, wherein a current on the secondary of the common mode current transformer is input to the imbalance detection circuit for fault threshold comparison. 
     
     
         3 . The fault detection system of  claim 2 , wherein each of the common mode current transformers has a separate primary coil for each phase of the 3-phase A/C output of the corresponding inverter. 
     
     
         4 . The fault detection system of  claim 2 , wherein the current on the secondary of the common mode current transformer is measured as voltage across a high precision resistor using an op amp to input a low voltage to the corresponding controller. 
     
     
         5 . The fault detection system of  claim 1 , each of the plurality of inverters includes a dV/dT filter circuit coupled to the corresponding common mode current transformer. 
     
     
         6 . A line replaceable unit comprising:
 a DC link input configured to be coupled to DC power source;   a plurality of DC drive modules coupled to the DC link input; and   a plurality of DC-AC drive modules coupled to the DC link input, each DC-AC drive module comprising:
 an inverter coupled to the DC link input, the inverter converting DC to 3-phase A/C to supply A/C power to a corresponding individual A/C load; 
 a common mode current transformer coupled to the 3-phase A/C output of the inverter; and 
 a controller coupled to the output of the common mode current transformer and coupled to the corresponding A/C load, the plurality of controller being configured to detect a fault at the individual corresponding A/C load, 
   wherein in the case of detection of a fault at the individual corresponding A/C load, the controller disables the corresponding A/C load.   
     
     
         7 . The line replaceable unit of  claim 6 , wherein the common mode current transformer is configured with a primary coil coupled to the 3-phase A/C output of the inverter and a secondary coil coupled to an imbalance detection circuit of the controller, wherein a current on the secondary of the common mode current transformer is input to the imbalance detection circuit for fault threshold comparison. 
     
     
         8 . The line replaceable unit of  claim 7 , wherein the common mode current transformer has a separate primary coil for each phase of the 3-phase A/C output of the inverter. 
     
     
         9 . A fault detection method comprising:
 converting DC to 3-phase A/C output to supply A/C power to a corresponding individual A/C load;   providing a common mode current transformer coupled to the 3-phase A/C output;   detecting an imbalance between the phases as a fault; and   disabling the corresponding individual A/C load in response to the detection of a fault.   
     
     
         10 . The method of  claim 9 , wherein the common mode current transformer is configured with a primary coil coupled to the 3-phase A/C output and a secondary coil coupled to an imbalance detection circuit of a controller, wherein a current on the secondary of the common mode current transformer is input to the imbalance detection circuit for fault threshold comparison. 
     
     
         11 . The method of  claim 10 , wherein a current from the secondary of the common mode current transformer is detected as a voltage on a shunt resistor by the controller as a fault. 
     
     
         12 . A computer system for detecting a fault, comprising:
 one or more computer processors;   one or more non-transitory computer-readable storage media;   program instructions, stored on the one or more non-transitory computer-readable storage media, which when implemented by the one or more processors, cause the computer system to perform the steps of:
 converting DC to 3-phase A/C to supply A/C power to a corresponding individual A/C load; 
 providing a common mode current transformer coupled to the 3-phase A/C output of the inverter; 
 detecting an imbalance between the phases as a fault; and 
 disabling the corresponding individual A/C load in response to the detection of a fault. 
   
     
     
         13 . The computer system of  claim 12 , wherein the common mode current transformer is configured with a primary coil coupled to the 3-phase A/C output of the inverter and a secondary coil coupled to an imbalance detection circuit of a controller, wherein a current on the secondary of the common mode current transformer is input to the imbalance detection circuit for fault threshold comparison. 
     
     
         14 . A computer program product comprising:
 program instructions on a computer-readable storage medium, where execution of the program instructions using a computer causes the computer to perform a method for detecting a fault, comprising:
 converting DC to 3-phase A/C to supply A/C power to a corresponding individual A/C load; 
 providing a common mode current transformer coupled to the 3-phase A/C output of the inverter; 
 detecting an imbalance between the phases as a fault; and 
 disabling the corresponding individual A/C load in response to the detection of a fault. 
   
     
     
         15 . The computer program product of  claim 14 , wherein the common mode current transformer is configured with a primary coil coupled to the 3-phase A/C output of the inverter and a secondary coil coupled to an imbalance detection circuit of a controller, wherein a current on the secondary of the common mode current transformer is input to the imbalance detection circuit for fault threshold comparison.