referring to fig1 , a patient 10 is shown in fragmentary front elevational view . surgically implanted either into the patient &# 39 ; s abdominal cavity or pericardium 11 is the pumping unit 12 of a ventricular assist device . an inflow conduit 13 conveys blood from the patient &# 39 ; s left ventricle into pumping unit 12 , and an outflow conduit 14 conveys blood from pumping unit 12 to the patient &# 39 ; s ascending thoracic aorta . a power cable 15 extends from pumping unit 12 outwardly of the patient &# 39 ; s body via an incision to a compact controller 16 . a power source , such as a battery pack 17 worn on a belt about the patient &# 39 ; s waist , is connected with controller 16 . cable 15 is flexible in order to allow freedom of movement of the patient . such movement , however , causes stresses to cable 15 and to its connections with pumping unit 12 and controller 16 . to increase reliability and fault tolerance , the present invention uses redundant conductors in cable 15 to supply each of the phase currents that drive the pump motor . a conventional inverter and cabling for an lvad system is shown in fig2 . a dc motor in pump unit 12 has phases 20 - 22 connected by cable 15 to an h - bridge inverter 23 . a controller 24 , such as a general purpose microcontroller , implements a vector control or other algorithm to determine proper energization of phases 20 - 22 to obtain the desired motor operation . controller 24 is connected to a driver 25 for generating drive signals coupled to the control inputs of individual switches ( e . g ., transistors ) in inverter 23 . controller 24 has an input / output 26 for sending messages or generating fault alarms directed at the user or a physician , for example . inverter 23 has an h - bridge configuration with a first phase leg 30 , a second phase leg 31 , and a third phase leg 32 . phase leg 30 has an upper switch 33 and a lower switch 34 which are turned on and off by controller 24 via driver 25 as known in the art . a current sensor 35 in series with phase leg 30 provides a measured current to controller 24 as an input to the vector control algorithm . similarly , phase leg 31 includes switches 36 and 37 and a current sensor 38 . phase leg 32 includes switches 40 and 41 , but a current sensor may not be required since the vector control algorithm can infer a third current based on measured currents from sensors 35 and 38 . fig3 shows an improved ventricular assist system having higher reliability and fault tolerance as a result of redundant cable conductors and redundant phase legs . thus , an inverter 45 is coupled by a redundant cable 46 to motor 47 in pump unit 12 . inverter 45 has a first phase 50 , a second phase 51 , and a third phase 52 . first phase 50 has a first phase leg 55 and a second phase leg 56 . the upper and lower power switches in legs 55 and 56 are respectively coupled together to provide synchronous operation of the legs . respective conductors 57 and 58 connect phase legs 55 and 56 to a connector terminal 60 . cable 46 includes conductors 61 and 62 connected at terminal 60 to conductors 57 and 58 , respectively . conductors 61 and 62 are coupled to motor 47 via a terminal connector 63 in pump unit 12 . redundant conductors 61 and 62 become interconnected within pump unit 12 in order to drive a respective phase of motor 47 . legs 55 and 56 include respective current sensors 64 and 65 measuring the separate current magnitudes flowing in each of legs 55 and 56 . the measured currents are coupled to the controller for monitoring and motor control purposes as explained below . phases 51 and 52 of inverter 45 have an identical configuration . thus , phase 51 includes redundant phase legs 66 and 67 , which are independently connected to terminal 60 by conductors 68 and 69 . corresponding conductors 70 and 71 are provided in cable 46 . current sensors 72 and 73 provide measured currents for phase leg 66 and 67 to the controller . phase 52 includes legs 74 and 75 having their outputs connected to terminal 60 by conductors 76 and 77 . cable 46 includes conductors 78 and 79 which connect conductors 76 and 77 to pump unit terminal 63 . phase 52 includes current sensors 80 and 81 in legs 74 and 75 , respectively , which provide measured currents for legs 74 and 75 to the controller . the redundancy of the cable conductors , phase leg switches , and phase leg conductors provide fault tolerance whereby damage such as loss of continuity in one conductor or failure of one switch does not prevent operation of the ventricle assist system . upon failure of one of these , the redundant conductor or phase leg carries the full current load instead of being distributed between the redundant elements , thereby providing continuous operation of the pump . fault monitoring is performed by comparing measured currents within redundant phase legs . specifically , if the currents are substantially equal ( indicating that operation of electrical components is the same in each redundant leg ) then conditions are nominal and no fault is detected . if the measured currents are substantially unequal , on the other hand , then a fault is detected . the fault occurrence may trigger an alarm to inform a user that steps should be taken to remedy the fault . however , regular pump operation is maintained by virtue of the redundant element continuing to supply the proper current to the motor . in a preferred embodiment , measured currents from redundant legs of the same phase are compared by forming a ratio of the measured currents . assuming no fault is present , then the currents are about equal and the ratio has a value near 1 . thus , the ratio may be compared to a range centered on 1 ( e . g ., from 0 . 8 to 1 . 2 ) such that no fault is present when the ratio is within the range , and a fault is detected when the ratio falls outside the range . in controlling the motor based on the phase currents , the controller sums the two measured currents from the redundant legs corresponding to each phase and uses each summed current as an input to the vector control algorithm . thus , the present invention does not necessitate any changes in the motor control algorithm itself . however , it may be possible to simplify the algorithm since the invention provides actual measurements of the currents in all three phases instead of just two . the controller may preferably perform fault monitoring using the logic shown in fig4 . respective phase currents i a1 and i a2 from current sensors in the respective phase legs of a single phase a may be converted to digital values in analog - to - digital converters 85 and 86 . a ratio block 87 determines the ratio of the currents which is then provided to inputs of comparators 88 and 89 . comparator 88 compares the ratio with an upper threshold t 1 and generates a high - level logic output signal when the ratio is greater than t 1 . comparator 89 compares the ratio with a lower threshold t 2 . when the ratio is below threshold t 2 , then a low - level logic output is generated by comparator 89 . an or - gate 90 has its inputs coupled to the respective outputs of comparators 88 and 89 , whereby when the ratio is outside the range defined by thresholds t 1 and t 2 , then a high - level logic signal is provided at output 91 of or - gate 90 . in response to the detected fault , the controller may preferably generate an alarm to signify the need to take corrective action .
a implantable pump system comprises an implantable pump motor and an external unit . an inverter comprises respective phases with redundant legs connected in parallel , and respective current sensors in series with each leg generating a respective measured current . a cable redundantly couples the inverter to the motor . the cable includes a respective conductor coupling each redundant leg to a respective phase of the motor . the controller receives the measured currents , monitors for a fault in the conductors by comparing the measured currents in the respective redundant legs . a fault in a pair of redundant conductors is detected if a ratio of the respective measured currents is not within a predetermined range .