# US 7,746,038 B2 · System and method for suppressing DC link voltage buildup due to generator armature reaction > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,746,038 B2 - Document ID: US7746038B2 - Status: Granted - Kind: B2 - Application number: 12/006,430 - Filed: 2008-01-02 - Published: 2009-07-02 - Granted: 2010-06-29 - Earliest claimed: 2008-01-02 - Assignees: Hamilton Sundstrand Corporation - Inventors: Vijay K. Maddali; John F. Defenbaugh - Web page: https://patentgrep.com/patent/US7746038B2 ## CPC - H02P 9/10: Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load - H02H 7/065: {against excitation faults} - H02P 9/30: using semiconductor devices - H02P 9/305: {controlling voltage (H02P9/302 takes precedence)} - G01R 31/343: {in operation} - G01R 31/52: Testing for short-circuits, leakage current or ground faults - H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS - H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H) - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract A controller employed in conjunction with a synchronous generator monitors the output voltage of the generator. The controller employs the monitored output voltage as feedback that is used to control the excitation provided to an exciter field winding. In addition, the controller applies a control loop to the monitored output voltage that detects and modifies voltage ripple signals within the monitored output voltage to generate a compensated signal that is used to control the excitation to the exciter field winding. In particular, by detecting and modifying voltage ripple signals within the monitored output voltage, the controller is able to counteract armature reaction voltage ripples caused by unbalanced short-circuit faults, thereby preventing the build-up of voltage on the DC link. ## Claims ### Claim 1 A controller for use in a synchronous generator that includes an exciter field winding, an exciter armature winding, a main field winding and a main armature winding, the controller comprising: a first input-operably connected to monitor output voltages of the generator; a voltage calculator operably connected to the first input for calculating an average voltage value based on the monitored output voltages; a control loop operably connected to the voltage calculator for generating a compensated signal based on the average voltage value, wherein in response to an unbalanced short-circuit condition the control loop identifies and modifies a voltage ripple component within the average voltage value to generate a compensated signal; and an output operably connected to control excitation provided to the exciter field winding based on the compensated signal provided to the control loop, wherein the compensated signal counteracts armature reaction voltage ripples generated as a result of an unbalanced short-circuit fault. ### Claim 2 (depends on 1) The controller of claim 1, further including: a second input operably connected to monitor output currents of the generator; a detector that detects unbalanced short-circuit fault based on the monitored output currents of the generator, wherein the detection circuit selectively applies the control loop to the monitored output voltage when an unbalanced short-circuit fault is detected. ### Claim 3 (depends on 2) The detection circuit of claim 2, wherein the detection circuit compares each phase of the monitored output currents to a threshold value to detect short-circuit conditions. ### Claim 4 (depends on 3) The detection circuit of claim 3, wherein the detection circuit determines that a short-circuit condition is unbalanced when one or more, but not all, of the monitored output currents indicate a short-circuit condition. ### Claim 5 (depends on 1) The controller of claim 1, further including a voltage calculator operably connected to the first inputs to calculate an average value representative of the monitored output voltage. ### Claim 6 (depends on 5) The controller of claim 5, wherein the control loop includes a filter for isolating alternating current (AC) content from the average voltage value to obtain a voltage ripple signal caused by the unbalanced short-circuit fault condition. ### Claim 7 (depends on 6) The controller of claim 6, wherein the control loop includes a phase compensator for applying a phase shift to the voltage ripple signal. ### Claim 8 (depends on 7) The controller of claim 7, wherein the control loop includes a gain compensator for applying a gain to the phase-shifted voltage ripple signal to generate the compensated signal. ### Claim 9 A method of preventing a build-up of voltage on a DC link connected to an exciter field winding of a generator as a result of an unbalanced short-circuit fault at an output of the generator, the method comprising: monitoring each phase of output voltage generated by the generator; calculating an average voltage value based on the monitored output voltage; applying a control loop that detects and modifies a voltage ripple component detected within the average voltage value to generate a compensated signal; and applying the compensated signal to the exciter field winding to counteract an armature reaction voltage ripple generated in response to the unbalanced short-circuit fault. ### Claim 10 (depends on 9) The method of claim 9, wherein applying the control loop includes: monitoring each phase of output current generated by the generator; and detecting an unbalanced short-circuit condition based on the monitored output current of the generator, wherein the control loop is selectively applied to the average voltage value in response to a detected unbalanced short-circuit condition. ### Claim 11 (depends on 10) The method of claim 10, wherein detecting an unbalanced short-circuit condition includes: comparing each phase of the monitored output currents to a threshold value to detect whether a short-circuit condition exists on the monitored phase; determining that an unbalanced short-circuit condition exists when a short-circuit condition exists on one or more, but not all, of the monitored output currents. ### Claim 12 (depends on 9) The method of claim 9, further including converting the monitored output voltage to an averaged voltage value based on the monitored output voltage. ### Claim 13 (depends on 12) The method of claim 12, wherein applying the control loop to the monitored output voltage includes: detecting a voltage ripple signal in the average voltage value; applying a phase shift to the voltage ripple signal; and applying a gain to the phase-shifted voltage ripple signal to generate the compensated signal. ### Claim 14 A synchronous generator comprising: an input for receiving direct current (DC) voltage from a DC source; an exciter field winding; exciter armature windings mounted on a rotatable shaft that is magnetically coupled to the exciter field winding such that the DC current provided to the exciter field winding induces an alternating current (AC) voltage in the exciter armature windings; a rotating rectifier mounted on the rotatable shaft and operably connected to the exciter armature windings to convert the AC voltage generated on the exciter armature windings to a DC voltage; a main field winding mounted on the rotatable shaft and operably connected to receive the DC voltage generated by the rotating rectifier; main armature windings magnetically coupled to the main field winding such that the DC voltage provided to the main field winding induces an AC output voltage in the main armature windings; a controller having a first input operably connected to monitor the AC output voltage generated by the main armature windings and to apply a control loop to the monitored output voltage that detects and modifies the monitored output voltage to generate a compensated signal; wherein the controller employs the compensated signal to control the excitation provided to the exciter field winding to minimize armature reaction ripple voltage caused by unbalanced short-circuit conditions. ### Claim 15 (depends on 14) The synchronous generator of claim 14, wherein the controller includes: a second input operably connected to monitored the AC output current generated by the main armature windings; and a detector operably connected to the second input that detects unbalanced short-circuit faults based on the monitored output currents of the generator, wherein the detector causes the control loop to be selectively applied in response to a detected unbalanced short-circuit fault. ### Claim 16 (depends on 15) The synchronous generator of claim 15, wherein the detector detects an unbalanced short-circuit condition when one or more, but not all, of the monitored currents exceed the threshold value. ### Claim 17 (depends on 14) The synchronous generator of claim 14, wherein the controller computes an average voltage value representative of the monitored AC output voltage and provides the average voltage signal as an input to the control loop. ### Claim 18 (depends on 17) The synchronous generator of claim 17, wherein the control loop includes a filter that is applied to the average voltage signal to isolate a voltage ripple caused by an unbalanced short-circuit fault. ### Claim 19 (depends on 18) The synchronous generator of claim 18, wherein the control loop includes a phase compensator for applying a phase shift to the voltage ripple signal. ### Claim 20 (depends on 19) The synchronous generator of claim 19, wherein the control loop includes a gain compensator for applying a gain to the phased shifted voltage ripple signal to generate the compensated signal. ### Claim 21 A computer readable storage medium encoded with a machine-readable computer program code for generating thereof a compensated signal in response to a detected unbalanced fault condition, the computer readable storage medium including instructions for causing a controller to implement a method comprising: acquiring input from one or more sensors positioned to monitor output voltage and output current of a generator; detecting an unbalanced fault condition based on the monitored output current; calculating an average mean squared voltage signal based on the monitored output voltage; detecting a voltage ripple signal in the average mean squared voltage signal; applying a phase shift to the voltage ripple signal; applying a gain to the phase-shifted voltage ripple signal to generate the compensated signal; and providing as an output to a current loop controller for generating a desired current on an exciter field winding the compensated signal.