Method for regulating TETS power transfer

In an implanted medical device system, an internal controller, external power transmitter and methods for regulation of TETS power for an implanted medical device system are disclosed. According to one aspect, a method in an external power transmitter of an implanted medical device system includes determining a current in an external coil of the external power transmitter, multiplying the determined current by a supply voltage to determine a power delivered to the external coil, and controlling the power delivered to the external coil by adjusting the current in the external coil.

CROSS-REFERENCE TO RELATED APPLICATION

FIELD

The present technology is generally related to implantable medical devices such as a left ventricular assist device (LVAD), and more particularly to regulation of TETS power for an implanted medical device system.

BACKGROUND

Referring toFIG.1, an implantable LVAD system10has internal components (in the body of the patient) and external components. The LVAD system10may typically include an LVAD pump12, an implanted controller (i-controller)14having an internal battery15, an implanted internal transcutaneous energy transfer system (TETS) coil (i-coil)18, an external TETS coil (e-coil)20and an external power transmitter21with a detachable battery24. In operation, power is supplied from the external power transmitter21to the i-controller14via mutual coupling of the coils18and20, in order to charge the internal battery15of the i-controller14and to power the LVAD pump12. The coils18and20transfer power via electromagnetic energy over the air and through the body. The power supplied by the external power transmitter21may come from the detachable battery24or from a wall outlet, for example.

SUMMARY

The techniques of this disclosure generally relate to regulation of TETS power for an implanted medical device system.

The present disclosure provides an implanted medical device system, such as a left ventricular assist device (LVAD) system. The implanted medical device system includes at least an internal controller, an internal implanted device controlled by the internal controller and an external power transmitter in communication with the internal controller.

According to one aspect, an external power transmitter of an implanted medical device system is provided. The external power transmitter includes processing circuitry configured to determine a current in an external coil of the external power transmitter, multiply the determined current by a supply voltage to determine a power delivered to the external coil, and control the power delivered to the external coil by adjusting the current in the external coil.

According to this aspect, in some embodiments, the power is controlled by adjusting a duty cycle of a pulse-width-modulated bridge circuit. In some embodiments, the current is determined while the bridge circuit is active. In some embodiments, the current in the external coil is estimated based at least in part on peak coil current, a pulse width of the bridge circuit, and an assumption that the current is approximated by a sine wave. In some embodiments, the processing circuitry is further configured to adjust the power to account for resistive losses in the external coil. In some embodiments, the supply voltage is used to compensate a current proportional integral derivative (PID) controller to maintain a constant power over different supply voltages. In some embodiments, the current is determined by continuous measurement of a bridge circuit output. In some embodiments, determining the current includes measuring a peak current in the external coil.

According to another aspect, a method in an external power transmitter of an implanted medical device system is provided. The method includes determining a current in an external coil of the external power transmitter, multiplying the determined current by a supply voltage to determine a power delivered to the external coil, and controlling the power delivered to the external coil by adjusting the current in the external coil. In some embodiments, the power is controlled by adjusting a duty cycle of a pulse-width-modulated bridge circuit. In some embodiments, the current is determined while the bridge circuit is active. In some embodiments, the current in the external coil is estimated based at least in part on peak coil current, a pulse width of the bridge circuit, and an assumption that the current is approximated by a sine wave. In some embodiments, the method further includes adjusting the power to account for resistive losses in the external coil. In some embodiments, the supply voltage is used to compensate a current proportional integral derivative (PID) controller to maintain a constant power over different supply voltages. In some embodiments, the current is determined by continuous measurement of a bridge circuit output. In some embodiments, determining the current includes measuring a peak current in the external coil.

According to yet another aspect, a current control loop in an external device of an implanted medical device system is provided. The current control loop includes an H-bridge circuit configured to output a current to an external coil of the external device, and processing circuitry. The processing circuitry is configured to determine a current to the external coil based on the current output of the H-bridge circuit, multiply the determined current by a supply voltage applied to the external coil to determine a power delivered to the external coil, and control the power delivered to the external coil by adjusting the current in the external coil, the adjusting being by controlling a pulse width modulation (PWM) duty cycle of the H-bridge circuit in response to the determined current.

According to this aspect, in some embodiments, the current control loop also includes a current proportional integral derivative (PID) controller configured to control the PWM duty cycle of the H-bridge circuit. In some embodiments, the current control loop further includes a current sensor configured to measure the current of the external coil, the processing circuitry being configured to compare the measured current to a current that is based on a difference between a voltage across an internal coil of the implanted medical device system and a target voltage. In some embodiments, the H-bridge output current is based on a supply voltage provided by a power supply external to the external device.

DETAILED DESCRIPTION

Some embodiments described herein are related to regulation of TETS power for an implanted medical device system. In a TETS with resonant inductive-capacitive circuits for transmission and reception, alternating current (AC) power is introduced to a system for transfer using an H-bridge drive configuration from a DC power source. Control of the duty cycle or pulse width of the H-bridge drive is one method to control the power level delivered to the implanted circuitry of the implanted medical device system. However, the output power available and the current levels in the i-coil18and e-coil20are not directly controllable by control of the duty cycle or pulse with of the H-bridge drive. Measuring the peak or root-mean-squared (RMS) current level in the e-coil20and adjusting the duty cycle to maintain constant current can constrain the current level in the e-coil20, but may still allow delivery of an available power level that varies in response to changing operating conditions.

Thus, some embodiments provide for measuring and controlling the power delivered from the power supply to the primary coil to maintain nearly constant power available from the secondary coil. Further refinement of the controlled power level accounts for resistive losses in the primary coil. Measurement of the power delivered to the primary coil can be performed by measuring the current input to the primary coil while the H-bridge is active and multiplying the measured current by the DC voltage to obtain a measure of power. The current measurement can be a continuous measurement on the H-bridge drive. Alternatively, the current measurement can be an estimate based on RMS or peak primary coil current and knowledge of the H-bridge pulse width, further combined with knowledge that the current can be closely approximated by a sine wave.

FIG.2shows a block diagram of one example configuration of an implanted medical device system26having external components such as an external power transmitter22, and internal components such as an internal controller (i-controller)28configured to perform functions described herein. As used herein, the term “implanted medical device system26” refers to the system that includes both the implanted/implantable components as well as external components described herein.

The i-controller28may have processing circuitry30which may include a processor32and an internal memory34. The processor32may be configured to execute computer instructions stored in the internal memory34. Those instructions may include instructions to cause the processor to perform some of the processes described in more detail below.

A message or result from the i-controller28may be transferred from the i-controller28to an external display38of an external device40, which may include a processor42and a memory44within processing circuitry46, the external power transmitter22and the detachable battery24, as well as the e-coil20in some embodiments. The memory44may be configured to store computer instructions to be executed by the processor42. The external display38may be configured to display information received from the i-controller28. In some embodiments, an external power supply25may provide power to the external power transmitter22.

The processing circuitry30and/or46may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor32,42may be configured to access (e.g., write to and/or read from) the memory34,44, respectively, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).

The processing circuitry30and/or46may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed. Processors32,42each comprise multiple processors. The memory34,44is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software stored in the memory34,44, may include instructions that, when executed by the processor32,43, respectively, and/or processing circuitry30,46, respectively, causes the processor32,43and/or processing circuitry30,46to perform the processes described herein with respect to the i-controller28and the external power transmitter22.

Electrical communication of signals and power between the internal components of i-controller28may be via communication busses and individual electrical conductors not shown inFIG.2. For example, a multi-conductor address bus and data bus may connect processor32with internal memory34. In some embodiments, an i-coil interface19associated with i-coil18may be included in the set of internal components making up the implanted medical device system26. One purpose of i-coil interface19may be to modulate the alternating current applied to the i-coil18with signals from the i-controller28to be transmitted from the i-coil18to the e-coil20and/or to demodulate signals to be received by the i-coil18from the e-coil20. In some embodiments, a purpose of the i-coil interface19is to provide conversion between the alternating current (AC) of the i-coil18and direct current (DC) to charge the battery16.

The power supplied to the i-coil18may be adjusted by varying the AC electrical current in the e-coil20. Some or all functions of the i-coil interface19may be included in the i-controller28and/or the i-coil18. In some embodiments, the i-coil18and/or i-coil interface19may be internal to or considered part of the internal controller28. Similarly, electrical communication of signals and power between the internal components of external device may be by communication busses and individual electrical conductors not shown inFIG.2. For example, a multi-conductor address bus and data bus may connect processor42with memory44. In some embodiments, an e-coil interface23associated with e-coil20may be included in the set of external components making up the implanted medical device system26. The e-coil interface23may include a TETS interface configured to demodulate information signals from the processing circuitry30transmitted from the i-coil18to the e-coil20. The e-coil interface23may also be configured to couple power from the external power transmitter22to the e-coil20. In some embodiments, the e-coil interface23may be two distinct units, one unit for demodulation of signals from the i-controller that are uploaded via the coils18and20, and one unit for coupling power from the external power transmitter22to the e-coil20. In some embodiments, the i-controller28may upload information to the external power transmitter22via the coils18and20, but the power transmitter does not download information to the i-controller28via the coils18and20. In some embodiments, the e-coil interface23may include all or some of the components of a current control loop71that is configured to control power transfer from the e-coil20to the i-coil18.

In some embodiments, the internal components of the implanted medical device system26may include monitoring and control circuitry13. A purpose of monitoring and control circuitry13may include monitoring speed and temperature, for example, of the LVAD pump12. Another purpose of the monitoring and control circuitry13may include controlling the speed of the LVAD pump12. Another purpose of the monitoring and control circuitry13may include monitoring the temperature of the i-controller28, the i-coil18and/or the implanted battery16. In some embodiments, some or all of the monitoring and control circuitry13may be incorporated into the LVAD pump12and/or the i-controller28. In some embodiments, some or all of the functions performed by the monitoring and control circuitry13may be performed by the processing circuitry30. Thus, in some embodiments, the monitoring and control circuitry13may include one or more temperature sensors embedded in the LVAD pump12, the i-controller28, the i-coil18and/or implanted battery16. Information obtained from and/or about the LVAD pump12, such as speed and temperature, may be sent to the external device40to be displayed by external display38. Note that although an LVAD pump12is shown, other internal devices may be powered and controlled by the i-controller28instead of or in addition to an LVAD pump12.

The various internal components making up the LVAD system may be grouped into one or more separate housings. Similarly, the various external components making up the LVAD system may be grouped into one or more separate housings. Further, some of the components shown and described as being internal to the i-controller28may be instead, external to i-controller28in some embodiments. Similarly, some of the components shown and described as being internal to the external device40may be instead, external to external device40, in some embodiments. Note further that some of the functions performed by processor32may be performed instead by processor42.

Note that transfer of information from the external device40to the internal memory34, and vice versa, may be by wireless radio frequency (RF) transmission (over the air and through the body when the i-controller28is implanted). Accordingly, in some embodiments, the external device40includes an external radio interface50and the i-controller28includes an internal radio interface52. In some embodiments, the external radio interface50and the internal radio interface52are RF transceivers having both an RF receiver for receiving information wirelessly and an RF transmitter for transmitting information wirelessly. Such RF transceivers may be Bluetooth and/or Wi-Fi compliant, for example. In some embodiments, the RF receiver and RF transmitter within the external device40or within the i-controller28are integrated into one unit, whereas in some embodiments, they could be physically separate units.

Also, information may be communicated to the i-controller28from the external power transmitter22via the coils18and20, by modulating a parameter of power transmission, such as modulating the frequency of the transmitted power, or by modulating a parameter of the i-coil interface19, for example, by modulating a tuning capacitance of the i-coil interface19or by modulating the load level of the i-controller and/or the i-coil interface19.

The external device40could be a patient's external device that has an external interface54which provides an interface between the external device40and a clinician's device56. The clinician's device might, for example, have a USB port and interface54might include a USB port, so that a USB cable may connect the two ports. The clinician's device56may read data from the external device40and write information and control signaling to the external device40, in some embodiments. In the alternative to a wireline connection, the interface54could include or be a radio interface.

FIG.3is a block diagram of an implanted medical device system26that includes a mobile device58with a mobile application68in wireless communication with the i-controller28. The mobile device58may be a mobile phone or other mobile digital device that can process information and communicate wirelessly with the i-controller. Accordingly, the mobile device58has a display60, a mobile radio interface62, processing circuitry64, processor66which runs the mobile application68. The radio interfaces50,52and62may be Bluetooth Low Energy compatible radio interfaces, and the i-controller28may be a peripheral device responsible for advertising, while the mobile device58and the external power transmitter22may operate as master or central devices responsible for scanning and issuing connection requests.

Communication from the i-controller28to the external power transmitter22enables display on external display38of implanted device information such as pump data and alarm indications. The i-controller28may exchange, via the radio interfaces50and52, diagnostic and log file data with the external power transmitter22. The i-controller28may receive programming commands from an external device such as the clinician's device56or mobile device58. Further, communication from the i-controller28to the mobile device58, via the radio interfaces52and62, enables remote monitoring in cases where the mobile device58is connected to the Internet, and enables the display60to display information about the state of the implanted portion of the implanted medical device system26such as, for example, remaining battery runtime. In some embodiments, the internal radio interface52may only communicate with the external radio interface50and the mobile radio interface62one at a time. In some embodiments, when the i-controller28is not engaged in a communication session with an external device, such as external power transmitter22or mobile device58, the i-controller28may advertise continually to enable rapid reestablishment of the wireless connection between the i-controller28and the external power transmitter22or mobile device58. Conversely, either one or both of the external power transmitter22or mobile device58may scan for such advertisements. In some embodiments, the mobile device58may be configured with the mobile application68to perform some or all of the functions attributable herein to the power transmitter22.

FIG.4is a block diagram of closed loop power regulation of a TETS that supplies power to an implanted medical device. The closed loop70includes components of the processing circuitry30of the i-controller28and components of the processing circuitry46of the power transmitter22, as well as the internal coil18and external coil20. The closed loop70includes a current control loop71. The i-controller28includes the voltage difference message encoder36and the power transmitter22includes the voltage difference message decoder48.

An object of the closed loop power regulation provided by the closed loop70is to apply a predetermined constant voltage to the system load72of the implanted medical device of the implanted medical device system26. The system load72may be the load of the LVAD pump12or other implanted device, the load of the i-controller28(including the internal battery16), and optionally also the load of the i-coil interface19and the monitoring and control circuitry13. The system load72may be an electrical load at an input to a rectifier74. The rectifier74also has an input that is electrically coupled to the i-coil18. A purpose of the rectifier74is to rectify the voltage output of the i-coil18. The rectification by the rectifier74may be based at least in part on the load presented by the system load72. The rectified voltage output of the rectifier74is sensed by the voltage sensor76. The voltage sensor76produces an output that is stored in the internal memory34of the i-controller28as the TETS voltage78. The TETS voltage78is subtracted from a target voltage80by an adder82to produce the voltage difference84. The target voltage80may be stored in the internal memory34of the i-controller28and may be equal to or be based on a desired voltage across the internal battery16of the i-controller28. The voltage difference84is sent to the power transmitter22to be used to adjust the power transferred to the i-coil18in order to drive the voltage difference84to zero.

To send the voltage difference84to the power transmitter22, the voltage difference84may first be encoded by the voltage difference message encoder36by, for example, modulating a digital form of the voltage difference84onto an analog signal. The encoded voltage difference message may be modulated onto the alternating current (AC) passing through the i-coil18by the load modulator86. The load modulator86modulates the encoded voltage difference message onto the alternating current passing through the i-coil in such a way as to transmit the encoded voltage difference message to the power transmitter22via the mutual induction between the i-coil18and the e-coil20. For example, the encoding and/or modulating by the voltage difference message encoder36and the load modulator86may include on off keying (OOK) and/or binary phase shift keying (BPSK) to encode and/or modulate the voltage difference message. Other modulation schemes may be employed such as multilevel amplitude shift keying (ASK) or higher order phase shift keying such as quadrature phase shift keying (QPSK). For example, in some embodiments, OOK may be used to signal the encoded voltage difference84and BPSK may be used to signal secondary performance information such as charging rate of the internal battery16, power consumption by the LVAD pump12, temperature of the internal electronics and/or the LVAD pump12, as well as status of any of one or more processes implemented by the internal controller28.

Thus, power is transferred from the power transmitter22to the internal controller28via the coils18,20and, possibly simultaneously, the encoded voltage difference message is transferred from the internal controller28to the power transmitter22via the same two coils18and22. The voltage difference message may include the voltage difference84, as well as the secondary performance information as well as any other information to be sent with the voltage difference84.

In the power transmitter22, the current in the e-coil20is sensed by the current sensor88which outputs the e-coil current90. The e-coil current90carries the encoded voltage difference message that was encoded by the voltage difference message encoder36. The e-coil current90is filtered (and/or demodulated) by the digital signal processor (DSP) filter92. For example, the DSP filter92could be a finite impulse response (FIR) filter. In some embodiments, the DSP filter92extracts the encoded voltage difference message that is carried by the e-coil current90. The voltage difference message decoder48decodes the encoded voltage difference message to produce the decoded voltage difference94. This may equal or approximately equal the voltage difference84determined as a difference between the TETS voltage78and the target voltage80.

In some embodiments, there may be a delay between the time of determining a voltage difference84and the time of determining the corresponding decoded voltage difference94. This delay may affect how closely the closed loop70maintains the TETS voltage78at the target voltage80and may affect damping of the closed loop70.

A power proportional integral derivative (PID) controller96, in response to the decoded voltage difference94, generates a current adjustment signal that is subtracted from the coil current90by an adder98to produce current error signal. In response to the current error signal, a current PID controller100determines a pulse width modulation (PWM) duty cycle102to control the current in the e-coil20via a driver such as an H-bridge104. A purpose of one or both of the power PID controller96and the current PID controller100may be to dampen any overshoot without excessive damping of the control loop.

An objective of the closed loop70is to continually drive the voltage difference84,94toward zero so that the TETS voltage78is maintained at the target voltage80. When the voltage difference84,94is small, the current error signal input to the current PID controller100is small, resulting in a small change in the PWM duty cycle. When the change in the PWM duty cycle is small, the change in current driving the coil is small, which in turn results in only a small change in the TETS voltage78. This small change in the TETS voltage78should result in even a smaller voltage difference84. This causes the TETS voltage78to be maintained at or very close to the target voltage80.

Note that in some embodiments, the communication between the i-controller28and the power transmitter22may be synchronized. In some embodiments, the AC signal applied to the e-coil20is used as the synchronization clock. This reduces complexity. A low quantity of communication pulses per data bit such as one communication pulse per data bit may be transferred over 4 to 8 cycles of the AC signal applied to the e-coil20. This enables a fast enough update rate to drive the voltage difference to a negligible value. Note also that only the voltage difference84is fed back to the power transmitter, rather than the TETS voltage78. This reduces the amount of data to be transmitted for closed loop power regulation. Note that the external power supply25may provide input to the current PID controller100and/or to the e-coil20. In the alternative, or in addition, the battery24may supply input to the current PID controller100.

In some embodiments, the current control loop71measures the e-coil current90while the H-bridge104is active. The e-coil current90may be multiplied by the voltage supplied to the e-coil20to obtain a measure of power. The e-coil current90as measured by the current sensor88can be a continuous measurement on the H-bridge104output. Alternatively, the current measurement can be based on the peak e-coil20current and knowledge of the H-bridge104pulse width combined with an assumed sinusoidal form of the coil current90. Measuring and controlling the power delivered to the e-coil20may maintain a nearly constant power level available from the i-coil18. Further, extra power may be applied to the e-coil20to account for resistive losses in the e-coil18. By measuring current peaks in the e-coil20, the pulse width modulation duty cycle of the H-bridge104may be adjusted to maintain a constant power delivered to the i-coil18. The supply voltage across the e-coil20can be measured and used to compensate the gains of the current PID controller100to maintain consistent performance across multiple supply voltages.

Alternatives to regulating to achieve a constant power delivered to the e-coil20include regulating to achieve: constant peak voltage in the e-coil20, constant per cycle average current delivered to the e-coil20, and constant PWM pulse width applied by the H-bridge104to the e-coil20. Advantages to regulating to achieve a constant power delivered to the e-coil20include lower sensitivity of the power level to changes in e-coil20to i-coil18alignment and positioning. Another advantage in some embodiments is lower probability of shunting caused by fast changes in coil-to-coil coupling. Another advantage in some embodiments is reduced sensitivity to coil motion in the presence of poor communication, which can be caused by external factors such as electromagnetic interference or by rapid coil movement that degrades communication. Alternative methods for regulating the power delivered to the e-coil20may include measuring a power level on a cycle-by-cycle basis by measuring the average current of the H-bridge104and measuring the bridge supply voltage, where the power is the product of the average current and the bridge supply voltage. Another method for regulating the power delivered to the e-coil20includes measuring a power level on a cycle-by-cycle basis by measuring peak coil current and bridge supply voltage. The method includes computing the product of the peak coil current and bridge supply voltage, further times the H-bridge pulse width times a sine wave correction factor.

The current control loop71is a fast control loop compared to the slow control loop that includes the internal controller components, the DSP filter92, voltage difference message decoder48and power PID96. The slow control loop may set the target voltage for the fast control loop71.

As noted above, in some embodiments, the power is controlled by adjusting the duty cycle of the H-bridge104. Let V*I be the instantaneous applied power applied to the e-coil20. The average applied power is the average of V*I over a cycle. V is the supply voltage during the PWM “on” time, and 0 during the PWM “off” time. The supply voltage may be assumed to be constant during an individual PWM cycle, but may slowly change, as the battery24in the external power transmitter22is drained or as the external power transmitter22transitions from running untethered (from battery24) to running from wall power. The supply voltage change can be compensated.

In contrast to the assumption that the supply voltage is constant over an individual PWM cycle, the current in the coil is not constant during the PWM cycle. Rather, the current is assumed to be sinusoidal, peaking at the center of the PWM drive and dropping to zero at the points of maximum PWM drive width (and inverting for the opposing phase of PWM operation). This means that V*I during application of the PWM drive will not be constant, but will have a partial sine wave shape (peaking in the middle of the PWM drive).

In some embodiments, voltage may be directly measured by digitizing the supply voltage for the drive of the H-bridge104, as it changes slowly enough to be considered constant during individual bridge drive cycles.

The peak current in the e-coil20may be determined using the sine wave approximation for delivered power. The approximation includes the PWM pulse width, peak current and measured supply voltage. The measurements for this approximation will be available on each PWM drive cycle.

Another way to determine the current in the e-coil20involves measuring the average current input to the H-bridge104, which when multiplied by the bridge supply voltage will provide the average applied power. In order to obtain the average supply current, there may be a low pass filter applied to the measurement of the supply current, which means that the rate of “new” measurements of power will be related to the applied lowpass filter rather than the PWM update rate. This will be slower than the rate available from the peak current measurement and calculations. but will also not be subject to use of assumptions. Further, the update rate will still be faster than the rate of data being transmitted over the communication link, retaining some benefit of faster response time to changes in the positioning and orientation of the e-coil20with respect to the i-coil18.

FIG.5is a flowchart of a process implemented in an external device of an implantable medical device for regulation of TETS power for an implanted medical device system. The process includes determining a current in an external coil of the external power transmitter (Block S100). The process also includes multiplying the determined current by a supply voltage to determine a power delivered to the external coil (Block S102). The process further includes controlling the power delivered to the external coil by adjusting the current in the external coil (Block S104).