WO1995034946A1

WO1995034946A1 - Speed control and bootstrap technique for high voltage motor control

Info

Publication number: WO1995034946A1
Application number: PCT/US1995/006912
Authority: WO
Inventors: David Lloyd Schantz, Jr.
Original assignee: Westinghouse Electric Corporation
Priority date: 1994-06-10
Filing date: 1995-06-01
Publication date: 1995-12-21
Also published as: TW269069B

Abstract

A circuit for controlling a high voltage pump motor in an electric vehicle is efficiently provided and provides for the use of a bootstrap circuit that functions regardless of the desired rotor speed for the pump motor. A first converting circuit (162) converts a pulse width modulated signal having a pulse width proportional to the actual rotor speed of the pump motor (108) into a first signal having a frequency proportional to the actual rotor speed. A second converting circuit (172) converts the first signal into a second signal having a voltage proportional to the actual rotor speed. Part of the circuit compares the signal whose voltage is proportional to the actual rotor speed with a signal whose voltage is proportional to the desired rotor speed, and generates an error signal having a voltage proportional to the difference between the actual rotor speed and the desired rotor speed. A comparator (200) compares the signal having a voltage proportional to the desired rotor speed with a predetermined fixed signal corresponding to a predetermined fraction of a maximum motor speed. The circuit closes the low-side switches of the bootstrap circuit when the desired motor speed is less than the predetermined fraction of the maximum motor speed, and thereby allows the bootstraps' high-side capacitors (128) to recharge regardless of the desired speed of the rotor.

Description

SPEED CONTROL AND BOOTSTRAP TECHNIQUE FOR HIGH VOLTAGE MOTOR CONTROL

RELATED APPLICATIONS The following identified U.S. patent applications are filed on the same date as the instant application and are relied upon and incorporated by reference in this application.

U.S. patent application entitled "Flat Topping Concept" bearing attorney docket No. 58,295, and filed on the same date herewith;

U.S. patent application entitled "Electric Induction Motor And Related Method Of Cooling" bearing attorney docket No. 58,332, and filed on the same date herewith;

U.S. patent application entitled "Automotive 12 Volt System For Electric Vehicles" bearing attorney docket No. 58,333, and filed on the same date herewith;

U.S. patent application entitled "Direct Cooled Switching Module For Electric Vehicle Propulsion System" bearing attorney docket No. 58,334, and filed on the same date herewith; U.S. patent application entitled "Electric

Vehicle Propulsion System" bearing attorney docket No. 58,335, and filed on the same date herewith;

U.S. patent application entitled "Vector Control Board For An Electric Vehicle Propulsion System Motor

SUBSTITUTESHEET(RULT26)

M I S S I N G P A G E

U.S. patent application entitled "Electric Vehicle System Control Unit Housing" bearing attorney docket No. 58,348, and filed on the same date herewith;

U.S. patent application entitled "Low Cost Fluid Cooled Housing For Electric Vehicle System Control Unit" bearing attorney docket No. 58,349, and filed on the same date herewith;

U.S. patent application entitled "Electric Vehicle Coolant Pump Assembly" bearing attorney docket No. 58,350, and filed on the same date herewith;

U.S. patent application entitled "Heat Dissipating Transformer Coil" bearing attorney docket No.

58.351, and filed on the same date herewith;

U.S. patent application entitled "Electric Vehicle Battery Charger" bearing attorney docket No.

58.352, and filed on the same date herewith.

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a controller for controlling a high voltage motor. More particularly, the present invention relates to a controller for controlling a high voltage motor for use in electric vehicles. Even more particularly, the present invention relates to a controller for controlling a high voltage oil pump motor for use in electric vehicles. While the invention is subject to a wide range of applications, it is especially suited for use in electric vehicles that utilize batteries or a combination of batteries and other sources, e.g., a heat engine coupled to an alternator, as a source of power, and will be particularly described in that connection.

Description of the Related Art Due to the importance currently placed on conserving petroleum reserves, achieving energy efficiency, and reducing air pollution, development of electric vehicles has become a priority. Ultimately, to be successful, these vehicles must be safe, inexpensive, efficient, and acceptable to consumers who are used to driving gasoline-powered vehicles.

For an electric vehicle to be commercially viable, its cost and performance should be competitive with that of its gasoline-powered counterparts.

Typically, the vehicle's propulsion system and battery are the main factors which contribute to the vehicle's cost and performance competitiveness.

Generally, to achieve commercial acceptance, an electric vehicle propulsion system should provide the following features: (1) vehicle performance equivalent to typical gasoline-powered propulsion systems; (2) smooth control of vehicle propulsion; (3) regenerative braking; (4) high efficiency; (5) low cost; (6) self-cooling; (7) electro-magnetic interference (EMI) containment;

(8) fault detection and self-protection; (9) self-test and diagnostics capability; (10) control and status interfaces with external systems; (11) safe operation and maintenance; (12) flexible battery charging capability; and (13) auxiliary 12 volt power from the main battery. In prior practice, however, electric vehicle propulsion system design consisted largely of matching a motor and controller with a set of vehicle performance goals, such that performance was often sacrificed to permit a practical motor and controller design. Further, little attention was given to the foregoing features that enhance commercial acceptance.

Conventional coolant systems are unable to meet the special requirements for use in electric vehicles. For example, in electric vehicles, it is desirable to drive the pump of the coolant system from the main vehicle battery. This avoids either overloading the 12 volt system or requiring that more power be consumed by the 12 volt system. It is also desirable to drive the pump of the coolant system to provide full performance over a widely varying terminal voltage, typically 230 to 400 VDC. The pump should also have a variable speed (flow) operation to conserve battery energy when full cooling capability is not needed. The coolant system should also have high efficiency for battery energy conservation and higher reliability with a useful life of approximately 10,000 hours. The coolant system should also be compact in size, lightweight, low-cost, and should have electrical isolation between its controller and power supply and provide self-protection from overloads. Conventional coolant system controllers cannot meet these special requirements.

Conventional oil pump systems in particular do not meet these special requirements. High voltage oil pumps do not have the compact size, efficient operation parameters, and low cost needed for a coolant system in an electric vehicle propulsion system. For example, an oil pump generally requires some kind of a feedback loop from the oil pump motor to the oil pump motor controller to insure that the oil pump's rotor speed is at a desired level. Conventionally, this feedback is accomplished by a combination of an actual rotor speed detector, a device setting forth a fixed desired rotor speed, and a circuit for correcting the actual rotor speed based on the actual and desired rotor speeds. Typically, commercially available frequency to voltage converters used in conventional oil pumps are not suited for use in an electric vehicle propulsion system. These circuits are complex, often including elements to provide a.level of performance deviating from the requirements of a coolant motor in an electrical vehicle application. As a result, these conver ors are too expensive, consume too much power, and take up too much space. Furthermore, the controls for feedback correction are typically not flexible enough for use on an electric car.

In conventional oil pumps the desired rotor speed is set manually by adjusting a potentiometer in the controller. If the desired rotor speed changes, then the potentiometer indicating that desired rotor speed must be changed manually. This use of a fixed desired speed is unacceptable in an electrical vehicle propulsion system where the desired rotor speed for a coolant pump may vary. As noted above, a coolant system for an electric vehicle propulsion system must minimize power consumption as well as the power supply complexity. Bootstrapping is one common method of minimizing power supply complexity that is well known in the art, as shown in "HV Floating MOS-Gate Driver IC," by Steve Clemente and Ajit Dubhasi, Application Notes (International Rectifier 1990). This passage from the Application Notes shows that bootstrapping can provide a way to minimize power supply complexity for a high-side and low-side transistor switch combination by providing a high-side capacitor that can transfer its charge to the base-emitter capacitance of the transistor in the high-side switch thereby turning on the high-side switch. In the operation of a bootstrap circuit, the high-side capacitor is charged by a low-side capacitor when the low-side switch is on, and then transfers its charge to the base-emitter capacitance of the transistor in the high-side switch to turn on the the high-side switch. In this way, although the low-side switch must be driven by the power supply directly and the low-side capacitor must be charged by the power supply, the high-side switch can be driven by the high-side capacitor, rather than directly by the power supply. This bootstrapping method requires that the high-side switch be periodically shut off and the low-side switch regularly turned on, however, so that the high-side capacitor may be recharged. This means that if a conventional bootstrap circuit is used, the motor must be continually run above a particular speed. Therefore, although bootstrapping is well accepted as a means for reducing the complexity of the power supply realization, it is infeasible for use in an electric vehicle propulsion system which must run a coolant pump at a variable speed and even periodically shut it down. Conventional bootstrapping requires continuous operation of the power bridge and therefore continuous rotation of the motor. An electric vehicle propulsion system may not provide continuous rotation of the motor.

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a high voltage motor controller that substantially obviates one or more of the problems due to the limitations and disadvantages of the related art.

Features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the method and apparatus particularly pointed out in the written description and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention provides for a circuit for controlling a high voltage pump motor in a vehicle powered at least partially by electricity, comprising a rotational position sensor for outputting a variable frequency square wave signal having a frequency proportional to the actual rotor speed; a first converting circuit for converting the variable frequency signal into a first signal having a fixed pulse width and frequency proportional to the actual rotor speed; a second converting circuit for converting the first signal into a second signal having a voltage proportional to the actual rotor speed; means for determining a desired rotor speed and outputting a third signal having a voltage proportional to the desired rotor speed; an error generating circuit for comparing the second signal with the third signal and generating an error signal having a voltage proportional to the difference between the actual rotor speed and the desired rotor speed; and means, responsive to the error signal, for correcting the actual rotor speed.

In another aspect, the invention further provides that the high voltage pump motor includes a bootstrap circuit having high and low-side switches, and the circuit for controlling the pump further comprises a comparator circuit for comparing the third signal to a predetermined fixed signal, the predetermined fixed signal corresponding to a predetermined fraction of a maximum motor speed; and means, responsive to the comparing means, for closing the low-side switches of the bootstrap circuit when the desired motor speed is less than the predetermined fraction of the maximum motor speed.

In yet another aspect, the invention provides a method for controlling a high voltage pump motor unit in a vehicle powered at least partially by electricity, wherein the high voltage pump motor unit includes a bootstrap circuit having high-side and low-side switches, comprising the steps of determining a desired rotor speed; outputting a desired speed signal having a voltage proportional to the desired rotor speed; comparing the desired speed signal to a predetermined fixed signal, the predetermined fixed signal corresponding to a predetermined fraction of a maximum motor speed; and closing the low-side switches of the bootstrap circuit when the desired motor speed is less than the predetermined fraction of the maximum motor speed.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate a presently preferred embodiment of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:

Fig. 1 is a block diagram of an electric vehicle propulsion system in accordance with a preferred embodiment of the invention;

Fig. 2 is a power distribution diagram of the electric vehicle propulsion system of Fig. 1;

Fig. 3 is a functional diagram of the electric vehicle propulsion system of Fig. 1;

Fig. 4 is a cooling diagram of the electric vehicle propulsion system of Fig. 1;

Fig. 5 is a diagram, partially schematic and partially in block form, of the oil pump unit shown in Figs. 1-4;

Fig. 6 is an electrical schematic diagram of one of the bootstrap circuits shown in Fig. 5; and

Fig. 7 is an electrical schematic diagram of the speed control loop shown in Fig. 5. DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to a present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. As shown in Fig. 1, there is provided an electric vehicle propulsion system 10 comprising a system control unit 12, a motor assembly 24, a cooling system 32, a battery 40, and a DC/DC converter 38. The system control unit 12 includes a cold plate 14, a battery charger 16, a motor controller 18, a power distribution module 20, and a chassis controller 22. The motor assembly 24 includes a resolver 26, a motor 28, and a filter 30. The cooling system 32 includes an oil pump unit 34 and a radiator/fan 36.

Fig. 2 is a power distribution diagram of the electric vehicle propulsion system 10. As shown in Fig.' 2, the battery 40 serves as the primary source of power for the electric propulsion system 10. The battery 40 comprises, for example, a sealed lead acid battery, a monopolar lithium metal sulfide battery, a bipolar lithium metal sulfide battery, or the like, for providing a 320 volt output. Preferably, the electric propulsion system 10 works over a wide voltage range, e.g., 120 volts to 400 volts, to accommodate changes in the output voltage of the battery 40 due to load or depth of discharge. However, the electric vehicle propulsion system 10 is preferably optimized for nominal battery voltages of about 320 volts. The power distribution module 20 is coupled to the output of the battery 40 and includes, among other things, fuses, wiring, and connectors for distributing the 320 volt output from the battery 40 to various components of the electric vehicle propulsion system 10. For example, the power distribution module 20 distributes the 320 volt output from the battery 40 to the motor controller 18, the DC/DC converter 38, the oil pump unit 34, and the battery charger 16. The power distribution module 20 also distributes the 320 volt output from the battery 40 to various vehicle accessories, which are external to the electric vehicle propulsion system 10. These vehicle accessories include, for example, an air conditioning system, a heating system, a power steering system, and any other accessories that may require a 320 volt power supply.

The DC/DC converter 38, which, as described above, is coupled to the 320 volt output of the power distribution module 20, converts the 320 volt output of the power distribution module 20 to 12 volts. The DC/DC converter 38 then supplies its 12 volt output as operating power to the battery charger 16, the motor controller 18, the chassis controller 22, the oil pump unit 34, and the radiator/fan 36. The DC/DC converter 38 also supplies its 12 volt output as operating power to various vehicle accessories, which are external to the electric vehicle propulsion system 10. These vehicle accessories include, for example, vehicle lighting, an audio system, and any other accessories that may require a 12 volt power supply. It should be appreciated that the DC/DC converter 38 eliminates the need for a separate 12 volt storage battery.

As shown in Fig. 3, the components of the electric vehicle propulsion system 10 are interconnected via various data busses. The data busses can be of the electrical, optical, or electro-optical type as is known in the art. Operation of the electric vehicle propulsion system 10 will now be described with reference to Fig. 3. The battery charger 16 receives command signals from and sends status signals to the motor controller 18 for charging the battery 40. The battery charger 16 provides a controlled battery charging current from an external AC power source (not shown). Preferably, AC current is drawn from the external source at near-unity power factor and low harmonic distortion in compliance with expected future power quality standards. Further, the battery charger 16 is preferably designed to be compatible with standard.ground fault current interrupters and single-phase power normally found at residential locations.

The oil pump unit 34 and radiator/fan 36 also receive command signals from and send status signals to the motor controller 18. As will be described in more detail below, the oil pump unit 34 and radiator/fan 36 are part of a closed loop oil cooling system for the electric vehicle propulsion system 10. Additional details concerning the oil pump unit 34 and radiator/fan 36 are disclosed in copending U.S. Patent Application Serial No. 08/258296 (Westinghouse Case 58,350) entitled "ELECTRIC VEHICLE COOLANT OIL PUMP" filed on the same day as this application and which has been expressly incorporated by reference.

The chassis controller 22 and the motor controller 18 receive signals from a vehicle communication bus. Generally, the vehicle communication bus serves as a communication pathway for interfacing various vehicle sensors and controllers to the chassis controller 22 and the motor controller 18, as will be explained in more detail below.

The chassis controller 22 comprises a microprocessor-based digital and analog electronics system and provides control and status interfacing to the vehicle's sensors and controllers and to the motor controller 18. For example, the chassis controller 22 is connected, via the vehicle communication bus, to the vehicle key switch, accelerator, brake, and drive selector switches. The chassis controller 22 interprets signals from these switches to provide the motor controller 18 with start-up, drive mode (e.g., forward, reverse, and neutral), motor torque, regenerative braking, shutdown, and built-in test (BIT) commands. Preferably, the chassis controller 22 communicates with the motor controller 18 via an opto-coupled serial data interface and receives status signals from the motor controller 18 of all the commands sent to verify the communication links between the chassis controller 22, the vehicle, and the motor controller 18 and to verify that the vehicle is operating properly. It should be appreciated that because the chassis controller 22 provides the control and status interfacing to the vehicle's sensors and controllers and to the motor controller 18, the electric vehicle propulsion system 10 can be modified for use with any number of different vehicles simply by modifying the chassis controller 22 for a particular vehicle.

The chassis controller 22 also provides battery management capabilities by using signals received over the vehicle communication bus from a battery current sensor located in the power distribution module 20. The chassis controller 22 interprets signals from the battery current sensor, provides charging commands to the motor controller 18, and sends a state-of-charge value to a "fuel" gauge on the vehicle dashboard. The chassis controller 22 further connects, via the vehicle communication bus, to vehicle controllers including odometer, speedometer, lighting, diagnostic and emissions controllers, as well as to an RS-232 interface for system development.

As shown in Fig. 4, the electric vehicle propulsion system 10 utilizes a closed loop cooling system including the cold plate 14, the filter 30, the motor 28, the oil pump unit 34, and the radiator/fan 36. Preferably, the cold plate 14 is a hollow body having a double-sided surface on which the battery charger 16, the motor controller 18, and the power distribution module 20 are mounted in thermal contact. The oil pump unit 34 circulates oil, e.g., aircraft turbine oil, from the oil reservoir of the motor 28 through the radiator/fan 36, the cold plate 14, the filter 30, and back through the motor 28 as shown in Fig. 4. Heat is removed from the oil by the radiator/fan 36 and the oil is filtered by the filter 30, which can comprise a commercially available oil filter known in the art. Preferably, the oil pump unit 34 is controlled by the motor controller 18 to provide a variable rate of oil flow.

It should be appreciated that the closed loop oil cooling system of Fig. 4 protects the electric vehicle propulsion system 10 from the harsh automotive operating environment, thus increasing reliability and reducing maintenance. Further, because the same oil used for lubricating the motor 28 is also used for cooling of the system control unit 12, the cooling system can have a simplified design.

As shown in Fig. 5, a preferred embodiment of the oil pump unit 34 includes an oil pump motor controller 14

100, a speed control loop 102, a gate drive and level shifter 104, a 3-phase power bridge 106, an oil pump motor 108 with a rotor 112, and a rotational position sensor 110. The gate drive and level shifter 104 and the 3-phase power bridge together contain three bootstrap circuits 114, 116, and 118.

The oil pump motor controller 100 preferably comprises a brushless DC motor controller for controlling the operation of the gate drive and level shifter 104 which in turn drives the 3-phase power bridge 106 and the oil pump motor 108. The brushless DC motor controller accepts input signals from the motor controller 18, the speed control loop 102, the gate drive and level shifter 104, and the rotational position sensor 110. The brushless DC motor controller sends signals to the gate drive and level shifter 104 to control the operation of the oil pump motor 108. In the preferred embodiment, the oil pump motor controller 100 uses a brushless DC motor controller device, such as a LS7362 brushless DC motor commutator/controller commercially available from LSI Computer Systems, Inc., for example. The brushless DC motor controller device has its outputs connected to the gate drive and level shifter 104 through simple inverters, the inverters having pull down resistors connected to their inputs.

The speed control loop 102 accepts as inputs a low voltage signal from the motor controller 18 corresponding to the desired rotor speed for the oil pump motor and a high voltage signal from the rotational position sensor 110 corresponding to the actual rotor speed of the rotor 112 in the oil pump motor 108. The low voltage is preferably the low voltage output from the DC/DC converter 38, which in the preferred embodiment is 12 volts. The high voltage is preferably the high voltage supplied from the power distribution module 20, which in the preferred embodiment is 320 volts. Preferably the signal from the motor controller 18 is a low voltage fixed frequency pulse width modulated signal whose pulse width corresponds to the desired rotor speed, and the signal from the rotational position sensor 110 is a signal referenced to high voltage whose pulse frequency corresponds to the actual rotor speed of the rotor 112. The speed control loop 102 outputs an error signal whose voltage is proportional to the difference between the actual rotor speed and the desired rotor speed, and a brake signal that is logical high when the desired rotor speed is less than a predetermined percentage of the maximum rotor speed. In the preferred embodiment, this chosen percentage of the maximum rotor speed is 10%, but the predetermined percentage may be chosen to be any reasonable value without departing from the scope of this invention.

Preferably the gate drive and level shifter 104 conditions the amplitude of the pulse width modulated (PWM) control signals from the oil pump motor controller 100 to a high voltage level and conditions the level of the PWM control signals so that they will be appropriate for the insulated gate bipolar transistors (IGBTs) in the 3-phase power bridge 106. This high voltage level is preferably the high voltage level of the voltage supplied from the power distribution module 20, which in the preferred embodiment is 320 volts. In the preferred embodiment, the gate drive and level shifter 104 comprises a high voltage gate driver, such as an IR2130 high voltage 3-phase MOS gate driver, commercially available from International Rectifier Corporation, for example. The 3-phase power bridge takes the high shifted signals from the gate drive and converts the high shifted signals into control signals for the three windings. A, B, and C, of the rotor 112 in the oil pump motor 108. The 3-phase power bridge comprises six IGBT switches,- two switches for each of the three windings A, B, and C, one high-side switch and one low-side switch. In the preferred embodiment, the 3-phase power bridge uses a type CPV362MF IGBT SIP module, commercially available from the International Rectifier Corporation, to provide the six IGBT switches.

In addition to the functions described above, certain elements of the gate drive and level shifter 104 and the 3-phase power bridge 106 preferably perform the function of a bootstrap circuit to conserve power and minimize circuit complexity in the gate drive and level shifter 104. Together the gate drive and level shifter 104 and the 3-phase power bridge contain three bootstrap circuits 114, 116, and 118, one for each winding A, B, and C of the oil pump motor 108.

The oil pump motor 108 is preferably a high voltage 3-phase DC brushless motor used for driving the oil pump and has a rotor 112 and three windings A, B, and C, one on each of three shafts connected to the rotor 112. As shown in Fig. 2, the oil pump motor 108 receives its high voltage power from the power distribution module 20, for example, and its low voltage power from the DC/DC converter 38.

The rotational position sensor 110 is preferably positioned proximate to the motor 108 for detecting the angular motion of each of the three shafts. In the preferred embodiment the rotational position sensor 110 is a series of three Hall Effect sensors which are placed in positions proximate the oil pump motor 108 such that the presence of a particular winding can always be detected by at least one of the Hall Effect sensors. Each Hall Effect sensor detects whether a given winding is within its particular area of detection and outputs a signal, for example, with a variable frequence square wave indicating this information. The combination of the three signals, one from each Hall Effect sensor, allows the oil pump motor controller to determine the position of the rotor 112. In the preferred embodiment. All three signals from the rotational position sensor are then sent to the oil pump motor controller 100, and one of the output signals 17 is sent to the speed control loop 102 to provide the speed control loop 102 with a signal indicating the speed of the rotor 112. Only one of the three Hall Effect signals is required to indicate the rotor speed since the frequency of the signal output from the Hall effect sensors is proportional to the rotational speed of one winding on the rotor 112, and each winding of the rotor is moving at the same speed.

Although in the preferred embodiment the rotational position sensor 110 comprises a series of Hall Effect sensors, it is not limited to this device and may be any commercially available rotational position sensor or other rotational position sensor known in the art.

Fig. 6 shows the elements that combine to form the preferred embodiment of one of the bootstrap circuits 114, 116, and 118 for a single winding of the oil pump motor 108. In the preferred embodiment, the bootstrap circuits for all three windings are identical. Each bootstrap circuit includes, for example, a high-side switch 140 and a low-side switch 142 in the 3-phase power bridge; and a high-side driver 130, a low-side driver 126, a high-side capacitor 128, and a diode 122 in the gate drive and level shifter 104. The three bootstrap circuits preferably have a common low-side capacitor 124. The high-side and low-side switches 140 and 142 are preferably IGBT switches comprised of an IGBT and a diode. In these IGBT switches, the cathode of the diode is connected to the collector of the IGBT and the anode of the diode is connected to the emitter of the IGBT. High-side switch 140 is comprised of IGBT 132 and diode

136; and low-side switch 142 is comprised of IGBT 134 and diode 138. The emitter of IGBT 132 in the high-side switch is connected to the collector of IGBT 134 in the low-side switch. The collector of IGBT 132 in the high-side switch 140 is connected to the positive high voltage V^ which in the preferred embodiment is +160 volts. The emitter of the IGBT 134 in the low-side switch 142 is connected to the negative high voltage V^,., which in the preferred embodiment is -120 volts. The high-side and low-side switches, in combination with the high-side and low-side switches of the other two bootstraps, are used to run the oil pump motor. While running the oil pump motor 108 the high-side and low-side switches 140 and 142 will never be on at the same time.

The low-side driver 126 and the low-side capacitor 124 have applied to them, for example, a low voltage V_LV+ referenced to the negative high voltage V^..

Thus, in the preferred embodiment, the low-side driver 126 and the low-side capacitor receive 12 volts referenced to -160 volts, that is, they receive -148 volts.

In the preferred embodiment of the bootstrap circuit shown in Fig. 6, when the low-side driver 126 switches the low-side switch 142 on (the high-side switch 140 being off) , the voltage from the low-side capacitor 124 passes through the diode 122 and charges the high-side capacitor 128. When the high-side driver 130 switches the high-side switch on (the low-side switch 142 being off) , the voltage from the high-side capacitor 128 is transferred to the base-emitter capacitance of the IGBT 132 in the high-side switch 140. Then, when the low-side switch 142 is again turned on (the high-side switch 140 again being off) , the high-side capacitor is charged by the low-side capacitor 124 again.

Fig. 7 shows the specific structure of the preferred embodiment of the speed control loop 102. The power voltage V^ in the speed control loop 102 may be any suitable power voltage, but it is chosen by way of example to be 12 volts referenced to the negative high voltage line. Thus, in the preferred embodiment the power voltage V^ is -148 volts and the ground voltage V^ is -160 volts. One of the outputs from the rotational position sensor 110 preferably serves as an input to the circuit hat forms the speed control loop 102. This input is applied to the positive input of a operational amplifier 152. Resistor 150 serves as a pull up resistor for the one output signal of the rotational position sensor 110 sent to the speed control loop 102. The output of the operational amplifier 152 is connected to the negative input of the operational amplifier 152, making the operational amplifier 152 function as a buffer between the output signal of the rotational position sensor 110 and the speed control loop 102.

The output of the operational amplifier 152 is passed, for example, through a differentiator 162 formed by capacitor 154 and resistor 160. The capacitor 154 has one end connected to the output of the operational amplifier 152 and the other end connected to the resistor 160. The resistor 160 has one end connected to the capacitor 154 and the other end connected to a reference voltage V^.

Preferably the reference voltage V_nf is placed at the one half the voltage drop from the power voltage to the ground voltage. Thus, in the preferred embodiment the reference voltage is placed at one half the drop from -148 volts to -160 volts, or -154 volts. This can also be seen as one half of the unreferenced power voltage of 12 volts, referenced to the negative high voltage line, i.e., 6 volts referenced to -160 volts. In the preferred embodiment, diodes 156 and 158 serve as clamp diodes and keep the voltage in the differentiator from going higher than the power voltage, V_pαw, or lower than the reference voltage, V^. Diode 156 has its cathode connected to the junction of the capacitor 154 and the resistor 160, and has its anode connected to the reference voltage V_ra£. Diode 158 has its anode connected to the junction of the capacitor 154 and the resistor 160, and its cathode connected to the power voltage. The output of the differentiator 162, formed at the junction of the capacitor 154 and the resistor 160, is preferably supplied to resistor 164 which serves as one input to a first low pass filter with gain 172. The first low pass filter with gain 172 is preferably comprised of resistor 164 connected to the negative input of operational amplifier 170 and resistor 168 and capacitor 166 connected in parallel between the output of the operational amplifier 170 and the negative input of the operational amplifier 170. The positive input of the operational amplifier 170 is connected, for example, to the reference voltage V_{nt '} The low voltage control signal received by the speed control loop 102 is input, for example, to an optical isolator 176. This low voltage signal is preferably received from the motor controller 18 in the form of a two wire interface and corresponds to the desired rotor speed. In the preferred embodiment, the optical isolator 176 converts the low voltage signal into a high voltage signal for use in the speed control loop 102. Resistor 178, connected between the output of the optical isolator 176 and the reference voltage V_n£, serves as a pull up resistor for the transistor output of the optical isolator. The high voltage output of the optical isolator 176 is applied, for example, to the resistor 180 which serves as one input of a second low pass filter with gain 188. The second low pass filter with gain 188 is preferably comprised of resistor 180 connected to the negative input of operational amplifier 186 and resistor 184 and capacitor 182 connected in parallel between the output of the operational amplifier 186 and the negative input of the operational amplifier 186. The positive input of the operational amplifier 186 is connected, for example, to the reference voltage V_nf.

In the preferred embodiment, the outputs of the first low pass filter with gain 172 and the output of the second low pass filter with gain 188 are each applied to inputs of integrator 196, which is preferably comprised of operational amplifier 194, resistors 192 and 174 connected to the negative input to the operational amplifier 194, and capacitor 190 connected between the output and the negative input of the operational amplifier 194. The output of the first low pass filter with gain 172 is applied to resistor 174 which serves as one input to integrator 196. The output of the second low pass filter with gain 188 is applied to resistor 192 which serves as another input to integrator 196. The reference voltage is applied to the positive input of the operational amplifier 194. The values of resistors 174 and 192 are preferably chosen to be equal so that the integrator 196 considers equally the signals from the first and second low pass filters with gain. The output of the integrator 196 is supplied to the oil pump motor controller 100 as an error signal.

The output of the second low pass filter with gain 188 is also attached to one end of resistor 198. The other end of resistor 198 is attached to the negative input of operational amplifier 200. Resistors 202 and 204 are each connected at one end to the positive input of operational amplifier 200. The other end of resistor 202 is connected to the power voltage V.^, and the other end of resistor 204 is connected to the ground voltage ^. In the preferred embodiment, resistors 202 and 204 are chosen to set up a reference-cutoff voltage at the positive input of operational amplifier 200 that is proportional to the desired percentage of full power below which the oil pump motor controller 100 will turn on the low-side switches 142 in the bootstrap circuit shown in Fig. 6. Resistor 198 is chosen for impedance matching with resistors 202 and 204. Resistor 206 serves as a pull up resistor for the output of operational amplifier 200. Operational amplifier 200 preferably serves as a straight comparator and, with the pull up resistor 206, outputs a signal that is logical high when the input from the second low pass filter with gain is less than the fixed voltage applied to the input connected to resistors 202 and 204. The output signal of the operational amplifier 200 is output to the oil pump motor controller 100 as the brake signal.

The operation of the preferred embodiment of the oil pump unit 34 will now be described. The motor controller 18 will output a desired rotor speed for the oil pump motor 108 to the speed control loop 102 in the oil pump unit 34. This signal will preferably have a fixed frequency and a pulse width that is proportional to the desired rotor speed. The rotational position sensor 110 will provide a signal to the speed control loop 102 whose pulse frequency is preferably proportional to the actual rotational speed of the rotor 112.

The speed control loop 102 will then perform two functions: it will determine the difference between the actual rotor speed and the desired rotor speed; and it will determine if the desired rotor speed is less than a predetermined percentage of the maximum rotor speed, 10% in the preferred embodiment. The speed control loop 102 will send to the oil pump motor control 100 an error signal that is proportional to the difference between the actual rotor speed and the desired rotor speed and a brake signal that is logical high when the desired rotor speed is less than the predetermined percentage of the maximum rotor speed.

The oil pump motor controller 100 will use the error signal, for example, to correct the actual rotor speed to the desired rotor speed in a manner that is well known in the art. The oil pump motor controller 100 will use the brake signal, for example, to control the bootstrap circuit present in the gate drive and level shifter 104 and the 3-phase power bridge 106. In the preferred embodiment, when the brake signal is logical high, the oil pump motor controller will order the low-side switches 142 in the three bootstrap circuits 114, 116, and 118 to turn on, thereby shutting off the oil pump motor 108. This will insure that the high-side capacitor 128 in each bootstrap circuit in the three bootstrap circuits 114, 116, and 118 will have a chance to recharge.

In order to start the oil pump motor, the desired motor speed need only be raised above the predetermined percentage of the maxi um rotor speed.

Then, the brake signal will turn logical low and the oil pump motor controller 100 will continue with the regular running of the oil pump.

The operation of the preferred embodiment of the speed control loop 102 will now be described with reference to Fig. 7. The differentiator 162 accepts as an input one of the high voltage outputs of the rotational position sensor 110. This signal, which is buffered by operational amplifier 152, preferably has a 50% duty and a variable frequency that is proportional to the speed of the rotor 112. The differentiator 162 converts the variable frequency, 50% duty actual speed signal into a signal with a fixed pulse width at the same frequency that is proportional to the actual speed of the rotor 112. The variable frequency, fixed pulse width actual speed signal output from the differentiator 162 is then supplied to the input of the first low pass filter with gain 172.

The first low pass filter with gain 172 then converts the variable frequency, fixed pulse width actual speed signal into a signal with a constant frequency and a voltage proportional to the actual speed of the rotor 112. This variable voltage actual speed signal is then supplied to one input of the integrator 196, as shown in Fig. 7. Meanwhile, the low voltage desired rotor speed signal, whose pulse width is preferably proportional to the desired rotor speed, is brought up to high voltage, 12 volts referenced to the negative high voltage line of -160 volts in the preferred embodiment, through the optical isolator 176 and is supplied to the input of the second low pass filter with gain 188. The second low pass filter with gain 188 then converts the fixed frequency, variable pulse width desired speed signal into a signal with a constant voltage proportional to the desired speed of the rotor 112. This voltage-dependent desired speed signal is then supplied to another input of the integrator 196. The integrator 196 determines a difference between the voltage-dependent actual speed signal, representing the actual speed of the rotor 112, and the voltage-dependent desired rotor speed signal, representing the desired rotor speed of the rotor 112. The integrator 196 then supplies to the oil pump motor controller 100 an error signal whose voltage is proportional to the difference between the actual rotor speed and the desired rotor speed.

The voltage-dependent desired rotor speed, output from the second low pass filter with gain 188, is also supplied to the negative input of operational amplifier 200 through resistor 198. Operational amplifier 200 preferably serves as a pure comparator and outputs to the oil pump motor controller 100 a brake signal that is logical high when the desired rotor speed is less than the predetermined percentage of the maximum rotor speed set by the resistors 202 and 204.

This invention includes the advantage of providing a simple circuit for controlling the speed of a pump motor. A rotational position sensor outputs a 50% duty variable frequency signal having a frequency proportional to the actual rotor speed. A first converting circuit converts the 50% duty, variable frequency signal into a first signal having a fixed pulse width and a frequency proportional to the actual rotor speed. A second converting circuit then converts the first signal into a second signal having a voltage proportional to the actual rotor speed. An error generating circuit compares the second signal with a third signal having a voltage proportional to the desired rotor speed. This error generating circuit generates an error signal having a voltage proportional to the difference between the actual rotor speed and the desired rotor speed.

In the preferred embodiment, the speed control loop 102 converts the signal from the rotational position sensor 110 into the signal applied to the integrator 196. In the speed control loop 102, the output from the rotational position sensor 110 is converted from a 50% duty, variable frequency signal in which the frequency corresponds to an actual rotor speed into a constant voltage that corresponds to the actual rotor speed. The circuit such as the one shown in Fig. 7, for example, performs this conversion with a minimum of circuitry and avoids the complexity, cost, and inefficiency of methods used in the prior art to effect such conversions. The present invention also provides an advantage in controlling a high voltage pump motor unit in a vehicle powered at least partially by electricity, which includes a bootstrap circuit having high-side and low-side switches. The invention determines a desired rotor speed; outputs a desired speed signal having a voltage proportional to the desired rotor speed; compares the desired speed signal to a predetermined fixed signal corresponding to a predetermined fraction of a maximum motor speed; and closes the low-side switches of the bootstrap circuit when the desired motor speed is less than the predetermined fraction of the maximum motor speed.

In the preferred embodiment, the speed control loop 110 and the oil pump motor controller 100 determine when the desired rotor speed is less than a predetermined fraction of the maximum rotor speed and turn the low-side switches in the bootstrap circuit on when this condition occurs. This bootstrap control function allows the bootstrap circuit to function in the oil pump unit by insuring that no matter how low the desired rotor speed is, the high-side capacitors 128 in the bootstrap circuits 114, 116, and 118, will always have a chance to recharge. If the speed control loop 102 and the oil pump motor controller 100 did not perform the unique bootstrap control set forth in the description above, then the oil pump unit 34 would not be able to take advantage of the power saving benefits offered by a bootstrap circuit.

Therefore, the oil pump unit as broadly described above provides an advantage over any other oil pump in the prior art by first minimizing the number of control components, and thus the cost, and by then including a bootstrap circuit that can be used even when the oil pump motor 108 is set to run at a low speed or is turned off for a time.

It should be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

27CLAIMS:

1. A circuit for controlling a high voltage pump motor in a vehicle powered at least partially by electricity, comprising: a rotational position sensor for outputting a 50% duty, variable frequency signal having a frequency proportional to the actual rotor speed; a first converting circuit for converting the 50% duty, variable frequency signal into a first signal having a fixed pulse width and a frequency proportional to the actual rotor speed; a second converting circuit for converting the first signal into a second signal having a voltage proportional to the actual rotor speed; means for determining a desired rotor speed and outputting a third signal having a voltage proportional to the desired rotor speed; an error generating circuit for comparing the second signal with the third signal and generating an error signal having a voltage proportional to the difference between the actual rotor speed and the desired rotor speed; and means, responsive to the error signal, for correcting the actual rotor speed.

2. The circuit according to claim 1, wherein the converting circuit comprises a low pass filter with gain.

3. The circuit according to claim 2, wherein the low pass filter with gain comprises a single operational amplifier.

4. The circuit according to claim 3, wherein the low pass filter with gain further comprises a resistor connected to the negative input of the operational amplifier, and a capacitor and a resistor connected in parallel between the output of the operational amplifier and the negative input of the operational amplifier.

5. The circuit of claim 1, further comprising an oil pump operatively coupled to the high voltage pump motor.

6. The circuit according to claim 1, wherein the high voltage pump motor includes a bootstrap circuit having high-side and low-side switches, further comprising: a comparator circuit for comparing the third signal to a predetermined fixed signal, the predetermined fixed signal corresponding to a predetermined fraction of a maximum motor speed; and means, responsive to the comparing means, for closing the low-side switches of the bootstrap circuit when the desired motor speed is less than the predetermined fraction of the maximum motor speed.

7. The circuit according to claim 6, wherein the comparator circuit comprises a single operational amplifier.

8. The circuit of claim 6, further comprising an oil pump operatively coupled to the high voltage pump motor.

9. A method for controlling a high voltage pump motor unit in a vehicle powered at least partially by electricity, wherein the high voltage pump motor unit 29 includes a bootstrap circuit having high-side and low-side switches, comprising the steps of: determining a desired rotor speed; outputting a desired speed signal having a voltage proportional to the desired rotor speed; comparing the desired speed signal to a predetermined fixed signal, the predetermined fixed signal corresponding to a predetermined fraction of a maximum motor speed; and closing the low-side switches of the bootstrap circuit when the desired motor speed is less than the predetermined fraction of the maximum motor speed.