Turbocharger control system for reducing speed fluctuations

Abstract

A turbocharger control system includes a turbocharger having an exhaust turbine and a centrifugal compressor mechanically coupled by a shaft; a pressure sensor for detecting boost pressure; a motor configured to apply a rotational pressure to the shaft in response to an electric current; and a processor that determines an expected rotational speed in response to the boost pressure, determines a current value in response to a difference between the expected rotational speed and the expected rotational speed, and generates a control signal indicative of the current value to control a current applied to the motor.

Description

Technical Field

[0001] The present invention generally relates to a turbocharger system with an electric motor, and more specifically, to using an electric motor to provide power and damping to the turbocharger shaft between the turbine and the compressor to regulate speed fluctuations. Background Technology

[0002] An internal combustion engine requires air, fuel, and a spark to operate. Typically, an internal combustion engine rotates a crankshaft, which is attached to pistons inside cylinders. In response to the rotation of the crankshaft, the pistons compress the fuel-air mixture within the cylinders. This compressed mixture is then ignited by a spark, causing combustion and forcing the piston downwards into the cylinder, thus rotating the crankshaft. The rotation of the crankshaft is used to turn the transmission, which moves the vehicle. Higher compression within the cylinders before ignition results in better combustion efficiency, leading to greater power, less fuel consumption, and fewer exhaust gases. Furthermore, increasing engine compression can be an effective way to achieve higher horsepower.

[0003] A turbocharger is a method used to increase the compression of an internal combustion engine to improve fuel economy, reduce emissions, and increase horsepower. A turbocharger uses a pump to compress the intake air before it is introduced into the cylinders. A specific type of turbocharger is the turbocharger, which uses exhaust gases from the internal combustion engine to rotate a turbine (such as a radial-flow turbine). This turbine is mechanically coupled to a compressor, such as a centrifugal compressor, which compresses the intake air for use by the compression engine.

[0004] To ensure a sufficient air supply to the engine, it is desirable for the turbocharger to operate at a constant speed. Speed ​​fluctuations can cause bearing wear and potentially premature journal bearing failure due to time-varying thrust and radial loads. When turbochargers are used in internal combustion engines, turbine shaft speed fluctuations can be observed due to the number of intermittent ignitions during a full engine rotation, especially in engines with three or even two cylinders. The lower the number of cylinders, the fewer the number of intermittent ignitions, and the greater the shaft speed fluctuations on the turbocharger. Furthermore, speed variations can cause exhaust valves to open when cylinder pressures are higher than exhaust manifold pressures. Therefore, it is desirable to reduce turbocharger speed fluctuations to increase operating efficiency and reduce premature bearing wear. Other desirable features and characteristics of this disclosure will become apparent from the following detailed description and appended claims, taken in conjunction with the accompanying drawings and this background discussion. Summary of the Invention

[0005] In one embodiment, a turbocharger control system includes: a turbocharger having an exhaust turbine and a centrifugal compressor mechanically coupled via a shaft; a pressure sensor for detecting exhaust pressure; an electric motor configured to apply rotational pressure to the shaft in response to an electric current; and a processor that determines a desired rotational speed in response to the exhaust pressure, determines a current value in response to the difference between the desired and expected rotational speeds, and generates a control signal indicating the current value to control the current applied to the electric motor.

[0006] In another embodiment, a method for controlling a turbocharger system includes: detecting exhaust pressure using a pressure sensor; determining a predicted turbocharger speed in response to the exhaust pressure; determining a current value by a processor in response to the difference between the predicted speed and the desired turbocharger speed; and applying a current corresponding to the current value to an electric motor by a turbo controller to generate a rotational force on the turbocharger shaft.

[0007] Furthermore, a turbocharger control system includes: a pressure sensor for measuring exhaust pressure; a rotation sensor for measuring the measured rotational speed of the turbocharger shaft; an electric motor configured to apply a rotational force to the turbocharger shaft and a damping force to the turbocharger shaft in response to a control signal; and a processor operable to generate a control signal indicating an indicative current value in response to the exhaust pressure, the measured rotational speed, and the desired rotational speed. Attached Figure Description

[0008] This disclosure will be described below in conjunction with the accompanying drawings, wherein like reference numerals denote like elements, and wherein: Figure 1 An exemplary turbocharger configuration according to an exemplary embodiment of the present disclosure is illustrated; Figure 2 An exemplary system for regulating turbocharger speed is illustrated according to an exemplary embodiment of the present disclosure; Figure 3 An exemplary method for adjusting turbocharger speed according to an exemplary embodiment of the present disclosure is illustrated; Figure 4 The illustration shows another exemplary system for regulating turbocharger speed according to an exemplary embodiment of the present disclosure; Figure 5 The illustration shows another exemplary method for adjusting the speed of a turbocharger according to an exemplary embodiment of the present disclosure. Detailed Implementation

[0009] The following specific embodiments are merely exemplary in nature and are not intended to limit this disclosure or its application and use. Furthermore, they are not intended to be construed as being limited by the foregoing background information or any theory presented in the following specific embodiments.

[0010] Now turning Figure 1 An exemplary system 100 for reducing speed variations in a turbocharger is shown. The exemplary system 100 includes an internal combustion engine 110, a pressure sensor 120, a centrifugal compressor 130, a speed sensor 140, an electric motor 150, an exhaust turbine 160, a shaft 170, a turbine controller 180, and a battery 190.

[0011] Generally, system 100 is operable to use the exhaust gas produced by internal combustion engine 110 to rotate exhaust turbine 160. Shaft 170 is coupled between exhaust turbine 160 and centrifugal compressor 130 such that rotation of exhaust turbine 160 causes a corresponding 1:1 rotation of centrifugal compressor 130. Centrifugal compressor 130 is configured to draw in air from the ambient environment (typically through an air filter) and compress that air to generate compressed air. This compressed air is then coupled to the inlet of internal combustion engine 110 to increase the compression of the ignited air / fuel mixture, thereby driving the internal combustion engine to rotate.

[0012] A drawback of conventional turbocharger configurations is turbo lag. Turbo lag occurs when the accelerator is depressed until sufficient pressure is built up in the exhaust system to rotate the exhaust turbine 160 to generate compressed intake air for the internal combustion engine 110, thus providing additional compression and power to the engine. To address turbo lag, an electric motor 150 has been added to the turbocharger configuration to immediately rotate the centrifugal compressor 160 in response to accelerator depressing, thereby supplying compressed intake air more quickly and minimizing the effects of turbo lag. The electric motor 150 can be directly coupled to shaft 170 to rotate the centrifugal compressor 130 and the exhaust turbine in response to current applied to the electric motor 150. In some exemplary embodiments, current may be supplied from battery 190 to the electric motor 150 and controlled by turbo controller 180. Alternatively, current may be supplied to a vehicle power supply network, etc.

[0013] Turbocharger speed fluctuations can reduce the expected lifespan of the turbocharger due to premature bearing wear. Furthermore, speed fluctuations reduce turbine efficiency, and consequently, fuel economy and engine power. To address these issues, system 100 is configured to regulate the rotation of shaft 170 using electric motor 150. Electric motor 150 can be used to drive shaft 170 to increase its speed or to dampen the shaft to decrease its speed. Electric motor 150 can drive shaft 170 by applying current from battery 190 to electric motor 150 in response to a control signal generated by turbo controller 180. Alternatively, electric motor 150 can also dampen the speed of shaft 170 by acting as a generator to extract rotational energy from shaft 170 and generate current that can be used to recharge battery 190. In some exemplary embodiments, the shaft speed is stabilized when and after exhaust pulses strike the turbine in generator mode.

[0014] In some exemplary embodiments, system 100 may include: a pressure sensor 120 for monitoring exhaust pressure output from internal combustion engine 110; and a speed sensor 140 for monitoring the rotational speed of shaft 170. In some exemplary embodiments, the speed sensor may include a magnet on the stator shaft of a turbocharger that can sense changes in voltage on the stator circumference to determine the rotational speed. Turbo controller 180 may generate control signals to control electric motor 150 such that a rotational force or damping force is applied to the shaft in response to changes in exhaust pressure detected by pressure sensor 120 and / or changes in rotational speed of shaft 170 detected by speed sensor 140. In some exemplary embodiments, speed sensor 140, electric motor 150, and turbo controller 180 may be juxtaposed in a common component.

[0015] In some exemplary embodiments, the turbo controller 180 may use a machine learning algorithm to predict the rotational speed of the shaft 170 for a corresponding exhaust pressure detected by the pressure sensor 120. Furthermore, the machine learning algorithm may also determine, using machine learning training data, the required electric motor boost or damping for rotating the shaft 170 to obtain the desired rotational speed for the detected exhaust pressure measured by the pressure sensor 120. The speed sensor 140 may monitor the obtained rotational speed of the shaft 170. If the obtained rotational speed deviates from the predicted speed, this data may be used as additional training data for the machine learning algorithm. In some exemplary embodiments, changes in rotational speed may occur over a period of time as a result of the detected exhaust pressure. The turbo controller 180 may delay the application of the electric motor 150 to compensate for this time-varying change. Ideally, the turbo controller 180 will control the electric motor 150 in response to the exhaust pressure detected by the pressure sensor 120, such that the rotational speed of the shaft 170 remains constant.

[0016] For reference Figure 2This illustration shows a system for regulating turbocharger speed according to exemplary embodiments of the present disclosure. Exemplary system 200 may include an electric motor 210, a pressure sensor 220, a controller 230, a battery 240, and a memory 250. Exemplary system 200 is operable to maintain a constant speed of the turbocharger assembly to compensate for fluctuating exhaust pressure detected from internal combustion engine exhaust. Such fluctuating exhaust pressure may be a result of discontinuous firing of internal combustion engine cylinders during the internal combustion engine's rotational cycle, thereby generating deviations in the exhaust gas pressure applied to the turbocharger exhaust turbine. The lower the number of engine cylinders in the internal combustion engine, the lower the number of discontinuous firings, and the greater the fluctuation in exhaust pressure.

[0017] The exemplary system 200 may utilize a pressure sensor 220 to detect the pressure of exhaust gas from an internal combustion engine. Data indicating the detected pressure is then coupled from the pressure sensor 220 to a controller 230. This detected pressure can then be used to estimate the turbocharger speed. The turbine speed can be adjusted to achieve a desired intake manifold pressure. In some exemplary embodiments, the pressure sensor 220 may perform a series of pressure detections at regular time intervals. This series of pressure detections may be coupled to the controller 230. In response, the controller 230 may generate a pressure profile of the exhaust pressure. This pressure profile can be used to predict the turbocharger speed.

[0018] The controller 230 is configured to receive data indicating exhaust pressure from the pressure sensor 220 to generate a control signal to control the rotational speed of the electric motor 210. The rotational speed of the electric motor 210 can be increased by applying current to the motor, causing the motor 210 to apply rotational force on the turbocharger shaft. Alternatively, the rotational speed of the electric motor 210 can be reduced by using it as a generator, causing the motor 210 to apply rotational force along the turbocharger shaft, generating current that can be coupled to the battery 240 to recharge it.

[0019] In some exemplary embodiments, data may be stored in memory, such as lookup tables, formulas, etc., to determine the required current to be drawn from or applied to the electric motor 210 based on the detected internal combustion engine exhaust pressure in order to maintain the desired speed of the turbocharger. In some exemplary embodiments, data may be generated in response to a machine learning algorithm, wherein various exhaust pressures are applied to a training system to determine the obtained speed and the current required to maintain the desired speed. The machine learning algorithm may use pressure curves to predict the obtained speed at a given time, and the machine learning algorithm may generate current curves to control the current applied to or drawn from the electric motor 210 to maintain the desired speed of the turbocharger. If the predicted speed deviates from the actual speed after the calculated current level is applied to the electric motor 210, the actual speed may be used as additional training input to the machine learning algorithm.

[0020] Now turning Figure 3 This illustration shows an exemplary method 300 for adjusting turbocharger speed according to an exemplary embodiment of the present disclosure. The exemplary method 300 first operates in a machine learning training mode 310 to detect exhaust pressure from an internal combustion engine employing a turbocharger. This exhaust pressure can be detected using a pressure sensor between the exhaust of the internal combustion engine and the exhaust turbine of the turbocharger. Alternatively, the exhaust pressure can be estimated in response to internal combustion engine revolutions per minute, coolant temperature, and other engine parameters.

[0021] Next, in training mode, the rotational speed of the 315 turbocharger is determined using a rotation sensor. Next, the current value to be applied to the electric motor (320) is determined to achieve the desired speed. This current value can be calculated using the electric motor's parameters or determined experimentally. The current value can be positive to generate torque through the electric motor, which is then applied to the turbocharger's rotating shaft to increase the speed. Alternatively, the current value can be negative, indicating that the current is generated by the electric motor acting as a damping force to reduce the speed on the turbocharger's rotating shaft. The estimated and / or detected exhaust pressure and current values ​​are stored in memory. Furthermore, the turbocharger's speed at exhaust pressure can also be stored along with the current and pressure values.

[0022] In operating mode, exhaust pressure is detected at the exhaust outlet of the internal combustion engine 330. The method is then operable to retrieve, 335, a current value corresponding to the exhaust pressure from a memory. A current corresponding to this current value is then applied, 345, to the electric motor to increase the turbocharger speed in response to a positive current value, or decrease the turbocharger speed in response to a negative current value. In some exemplary embodiments, the method next determines, 350, the actual speed of the turbocharger after the current is applied to the electric motor. The method compares the desired speed with the actual speed, 355. If the desired speed is not equal to the actual speed, the actual speed, current value, and exhaust pressure value are stored, 360, in memory as additional training data for a machine learning algorithm. The method continues to detect the next exhaust pressure, 330. If the desired speed equals the actual speed, the method continues to detect the next exhaust pressure, 330.

[0023] Now turning Figure 4 An exemplary system 400 for controlling the rotational speed of a turbocharger is shown. The exemplary turbocharger control system 400 may include a rotational sensor 420, an electric motor 410, a battery 440, and a controller 430. This exemplary system is configured to maintain a constant rotational speed of a turbocharger assembly including a turbine, compressor, and shaft.

[0024] The controller 430 can be configured to monitor the rotational speed of the turbocharger assembly using a rotation sensor 420. The rotation sensor can provide data indicating the number of revolutions per minute (RPM) of the turbocharger assembly shaft. In some exemplary embodiments, the rotation sensor 420 can be integrated with the electric motor 410. The controller 430 is configured to regulate the rotational speed of the turbocharger assembly to prevent premature bearing wear, etc., due to speed fluctuations. The controller 430 can control the current from the vehicle board net or battery 440 to the electric motor 410 such that current is applied to the electric motor when the turbocharger assembly's rotational speed is less than a desired speed, and current is generated by the electric motor 410 when the speed is greater than the desired speed. In some exemplary embodiments, the controller 430 provides a boost pressure target for the intake manifold pressure and controls the turbine shaft speed in response to the boost pressure target.

[0025] In some exemplary embodiments, controller 430 may determine a desired engine speed in response to internal combustion engine throttle setting or other engine parameters. Controller 430 may then determine a current value in response to the difference between the desired speed and the measured speed. Controller 430 may generate a control signal indicating the current value to control the current applied to the electric motor. The control signal may be coupled to a battery controller, or it may be coupled to the electric motor 410 or an associated motor controller. In some exemplary embodiments, the current value may be determined in response to the desired speed, the measured speed, and an estimated speed, the estimated speed being estimated in response to internal combustion engine load, engine speed, environmental conditions, and other performance characteristics.

[0026] In some exemplary embodiments, the current value may be stored in a memory communicatively coupled to the controller 430, wherein the current value is associated with the desired rotational speed, the measured rotational speed, and the difference between the two. Furthermore, the rate of change of the measured rotational speed may also be used to determine the current value. These current values ​​may be determined in response to a machine learning model generated by a machine learning algorithm. In some exemplary embodiments, the current value and its change may be stored in memory. These stored values ​​may be updated and associated with the desired rotational speed, the measured rotational speed, and the difference between the two.

[0027] The electric motor 410 can be used to apply a rotational force to the shaft of the turbocharger assembly or a damping force to the rotating shaft of the turbocharger. The rotational force is generated by applying a positive current to the electric motor 410 to induce a positive rotational force, thereby increasing the rotational speed of the turbocharger assembly. Furthermore, when the electric motor 410 is used as a generator to generate current that can be used to recharge the battery 440, a damping force or a negative rotational force can be applied to reduce the shaft speed. In some exemplary embodiments, the measured rotational speed can be determined based on multiple rotational speed measurements at periodic time intervals to generate a rotational speed profile. This rotational speed profile can then be used to determine periodic pressure fluctuations in the exhaust pressure. The current values ​​can be periodic current profiles generated in response to these periodic pressure fluctuations. These current values ​​associated with the exhaust pressure fluctuations can be stored in a memory. The controller 430 can then be configured to retrieve these current values ​​from the memory in response to exhaust pressure fluctuations and / or rotational speed fluctuations. The memory can further store information related to crankshaft position, engine load, valve phase, and other system attributes that can be received from the engine controller, etc.

[0028] In some exemplary embodiments, in addition to the rotational sensor 420 for measuring the measured rotational speed of the turbocharger shaft, system 400 may further include a pressure sensor for measuring exhaust pressure. In some exemplary embodiments, the exhaust pressure may be estimated in response to throttle setting, vehicle speed, and other vehicle performance characteristics. Controller 430 may then be operable to generate a control signal indicating a current value in response to exhaust pressure, the measured rotational speed, and a desired rotational speed. Electric motor 410 is then configured to apply a rotational force and a damping force to the turbocharger shaft in response to the control signal. Furthermore, system 400 may include a battery 440, an onboard network, or a direct connection to a vehicle alternator / generator electrically coupled to electric motor 410, such that electric motor 410 is configured to control the drive current from battery 440 in response to a control signal indicating a desired rotational speed greater than the measured rotational speed. Electric motor 410 may be further configured to control the recharging current from electric motor 410 to battery 440 in response to a control signal indicating a desired rotational speed less than the measured rotational speed. In some exemplary embodiments, the rotational speed is determined by boost demand. The turbo controller can then control the consumption of electrical power or the supply of electrical power to the battery 440 to change the wastegate or VNT position. This will then result in a change in the cycle-average electrical power, exceeding the range that the high-frequency variations of the damping / electric motor can adjust. This allows the electric motor's power to be limited to avoid overheating.

[0029] Now turning Figure 5 An exemplary method 500 for controlling turbocharger speed is illustrated. The method is first configured to determine the rotational speed of a turbocharger assembly 510. The rotational speed of the turbocharger assembly may be determined by a rotation sensor coupled to the turbocharger assembly, or may be estimated in response to exhaust pressure between the exhaust turbine and the internal combustion engine of the turbocharger assembly. The actual rotational speed of the turbocharger shaft may be determined in response to detection by a speed sensor, exhaust pressure, throttle level, engine temperature, and one or more other internal combustion engine performance parameters.

[0030] The method can then be operated to determine a 520 current value by a processor or turbo controller in response to the difference between the predicted speed and the desired turbocharger speed. In some exemplary embodiments, the current value can be determined in response to the actual speed detected by a rotational sensor, the expected speed in response to exhaust pressure estimation, and the desired speed used to maintain a constant speed. The current value can be determined in response to a machine learning algorithm trained by detecting multiple measured speeds in response to multiple exhaust pressures. Different current levels can then be applied to the electric motor until the desired speed is achieved for different combinations of the measured speed and the desired speed.

[0031] The method is then operable to control a current at 530 corresponding to the current value destined for the electric motor to generate a rotational force on the turbocharger shaft. This current can be controlled by a turbo controller or a battery controller configured to control the current applied to the electric motor to apply force to the shaft of the turbocharger assembly. In some exemplary embodiments, the current is coupled from the battery to the electric motor in response to a control signal from the turbo controller. The electric motor can be configured to apply damping pressure, damping force, or damping torque to the turbocharger shaft in response to a desired speed being lower than a expected speed. Furthermore, the electric motor can be configured to generate current to charge the battery in response to a desired speed being lower than a expected speed. The power generation mode will induce a damping force on the turbocharger assembly to reduce the rotational speed. Additionally, changes to the exhaust valve (such as closing it) can be used to prevent the average turbine shaft speed from dropping below a desired value.

[0032] While at least one exemplary embodiment has been presented in the foregoing detailed descriptions, it should be understood that numerous variations exist. It should also be understood that one or more exemplary embodiments are merely examples and are not intended to limit the scope, applicability, or configuration of this disclosure in any way. Rather, the foregoing detailed descriptions will provide those skilled in the art with a convenient roadmap for implementing exemplary embodiments of this disclosure. It will be understood that various changes may be made to the function and arrangement of the elements described in the exemplary embodiments without departing from the scope of this disclosure as set forth in the appended claims.

Claims

1. A turbocharger control system, comprising: A turbocharger having an exhaust turbine and a centrifugal compressor mechanically coupled via a shaft; Pressure sensor used to detect boost pressure; An electric motor, configured to apply a rotational force to a shaft in response to an electric current; and The processor determines the expected speed in response to the boost pressure, determines the current value in response to the difference between the expected speed and the desired speed, and generates a control signal indicating the current value to control the current applied to the motor.

2. The turbocharger control system of claim 1, further comprising a battery for generating a current to be applied to the electric motor in response to a control signal.

3. The turbocharger control system according to claim 1 or claim 2, further comprising a rotational sensor for detecting the actual rotational speed of the shaft, wherein the current value is determined in response to the actual rotational speed, the expected rotational speed, and the desired rotational speed.

4. The turbocharger control system according to any of the preceding claims, wherein the current value is determined in response to a machine learning model generated by a machine learning algorithm.

5. The turbocharger control system according to any of the preceding claims, wherein the boost pressure is a pressure curve generated in response to a plurality of intake pressure detections performed at periodic time intervals, and the current value is a current curve generated in response to the pressure curve, and wherein the current applied to the electric motor varies in response to the current curve.

6. The turbocharger control system according to any of the preceding claims, wherein the current is coupled to the electric motor after a first time delay.

7. The turbocharger control system according to any of the preceding claims, wherein the electric motor is further configured to apply a damping force to the shaft in response to a desired rotational speed being less than a expected rotational speed.

8. The turbocharger control system according to any of the preceding claims, wherein the electric motor is further configured to apply a damping force to the shaft, such that the electric motor generates a recharging current to recharge the battery.

9. The turbocharger control system according to any of the preceding claims, wherein the boost pressure is a pressure profile generated in response to a plurality of intake pressure detections performed at periodic time intervals, and wherein the processor is configured to determine periodic pressure fluctuations of the boost pressure in response to the pressure profiles, and wherein the current value is a periodic current profile generated in response to the periodic pressure fluctuations.

10. The turbocharger control system according to any of the preceding claims, further comprising a memory for storing current values ​​associated with boost pressure, wherein a processor is configured to retrieve the current values ​​from the memory in response to boost pressure.

11. A method for controlling a turbocharger system, comprising: Use a pressure sensor to detect exhaust pressure; The predicted rotational speed is determined in response to the exhaust pressure; The current value is determined by the processor's response to the difference between the predicted and desired rotational speeds; and The turbo controller applies a current corresponding to the current value to the electric motor to generate rotational force on the turbocharger shaft.

12. The method for controlling a turbocharger system according to claim 11, wherein current is coupled from the battery to the electric motor in response to a control signal from the turbo controller.

13. The method for controlling a turbocharger system according to claim 11 or 12, further comprising detecting the actual rotational speed of the turbocharger shaft by a rotation sensor, wherein the current value is determined in response to the actual rotational speed, the predicted rotational speed, and the desired rotational speed.

14. The method for controlling a turbocharger system according to claim 11, 12 or 13, wherein the exhaust pressure is a pressure curve generated in response to a plurality of exhaust pressure detections performed at periodic time intervals, and the current value is a current curve generated in response to the pressure curve, and wherein the current value varies in response to the current curve.

15. The method for controlling a turbocharger system according to claim 11, 12, 13 or 14, wherein the electric motor is further configured to apply a damping force to the turbocharger shaft in response to a desired rotational speed being less than a expected rotational speed.

16. The method for controlling a turbocharger system according to claim 11, 12, 13, 14 or 15, further comprising: In response to a desired speed being lower than the predicted speed, the battery is charged using the current generated from the electric motor.

17. The method for controlling a turbocharger system according to claim 11, 12, 13, 14, 15 or 16, wherein the current is coupled to the electric motor after a first time delay.

18. The method for controlling a turbocharger system according to claim 11, 12, 13, 14, 15, 16 or 17, wherein the current value is determined in response to a machine learning algorithm trained by detecting a plurality of measured speeds in response to a plurality of exhaust pressures.

19. A turbocharger control system, comprising: A rotary sensor is used to measure the rotational speed of the turbocharger shaft. An electric motor is configured to apply a rotational force to the turbocharger shaft and a damping force to the turbocharger shaft in response to a control signal; and A processor operable to generate a control signal indicating a current value in response to the measured rotational speed and the desired rotational speed.

20. The turbocharger control system of claim 19, further comprising a battery electrically coupled to an electric motor, wherein the electric motor is configured to control a drive current from the battery in response to a control signal indicating a desired rotational speed greater than a measured rotational speed, and the electric motor is further configured to control a recharge current from the electric motor to the battery in response to a control signal indicating a desired rotational speed less than a measured rotational speed.

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