Patent Application
20170327002
Embodiments are related to electric vehicles, drivetrains, power electronics, and pulse width modulation.
Current technology electric and hybrid vehicles use drive systems and power systems that switch between different distinct driving modes. While being driven, many all-electric vehicles simply stay in drive mode. Their batteries supply power to the wheels. More and more all-electric vehicles also have a regenerative braking mode. The vehicle generates power when the driver presses the brake pedal. The two modes are distinctly different. Hybrid vehicles have more modes that are distinctly different. For example, the vehicle's fossil fuel engine can charge the battery while also powering the wheels. For rapid acceleration, the vehicle can power the wheels with both the engine and the electric motor. In all of these cases, the vehicle switches between the different modes.
The current methods of switching between driving modes do not provide for fine grained transitions between different applications of vehicle and battery power. Systems and methods for fine grained transitions between different applications of vehicle and battery power are needed.
The following summary is provided to facilitate an understanding of some of the innovative features unique to the disclosed embodiments and is not intended to be a full description. A full appreciation of the various aspects of the embodiments disclosed herein can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
The embodiments have at least one electric motor, at least one electric energy storage device, and at least one electric energy producing device. The energy storage device can be a battery, group of batteries, capacitor bank, or some other device or combination of devices that store electrical energy. Without losing generality, the energy storage device will hereinafter be referred to as a battery or batteries. The electric energy producing device is a transducer that accepts kinetic energy on an input shaft and produces electrical energy that can be used to charge the battery. Examples of such transducers are generators and rectified alternators. Without losing generality, the electric energy producing device will hereinafter be referred to as a generator. The motor can be a simple DC motor having a power connection and a ground connection or can be a more complicated motor having two or more power inputs to various windings. For ease of presentation, a simple DC motor will be assumed with the realization that one skilled in the art of electric motors can apply the teachings to power the more complicated motors.
The embodiments employ pulse modulation techniques. In pulse modulation, a signal is rapidly turned on and off over a period of time. The value of the signal, or the amount of power transmitted by the signal, is a function of how much time the signal spends turned on in relation to how much time it is turned off. This is called the duty cycle. Some modulation techniques use lots of pulse having the same length. For example, all the pulses can be about 0.05 seconds long. Eighteen pulses per second is a 90% duty cycle. Other techniques use pulse width modulation where the signal can stay high for different lengths of time. For example, a signal can stay high for 0.8 seconds for every second. Such a signal would have an 80% duty cycle.
The embodiments switch direct current (DC) electrical power on and off. Drive power signals have powered states and non-powered states. A powered state occurs when the wire carrying the signal is connected to the battery, perhaps by way of some transistors. The non-powered state occurs when the wire carrying the signal is not connected to the battery or to ground. It is floating. Charging signals are similar. The charging state occurs when the generator's power lead is electrically connected to the battery. The non-charging state occurs when the generator's power lead is not connected to the battery. The power lead should also float when not powering the battery.
Aspects of the embodiments address limitations and flaws in the prior art by pulse modulating the supply of electric power to motors and to batteries. The batteries supply electric power to the motor. A generator supplies electric power to the batteries. The motor and the generator can be mechanically linked so that turning one causes the other to turn. In other words, powering the motor causes both the generator and the motor to spin. The generator does not work against the motor because the charging power signal is always in the non-charging state when the drive power signal is in the powered state. The pulse width modulation techniques provide for connecting the generator to the battery whenever it is appropriate to do so and perhaps for just a moment or two. It is in this manner that the generator can sip energy back into the batteries without otherwise interrupting the vehicles operation.
It is a further aspect of embodiments that a modulating system or subsystem switches the drive power signals between the powered and non-powered states. The modulation subsystem also switches the charge power signal between the charging and non-charging states. The modulation subsystem has a battery connection, one or more drive connections, a charging connection, and a control input. Wires carrying drive power signals to the motor can be connected to drive connections. Wires carrying the charge power signal can be connected to the battery connection. The generator can be connected to the charging connection. The control input guides the modulation subsystem in producing the various duty cycles of the drive power signals and charge power signals. For example, a brake control can cause the charging power signal to have a very high duty cycle and the drive power signals to have very low duty cycles. An acceleration or speed control can cause the duty cycle of charging power signal to drop while that of the drive power signal increases.
A key aspect of the embodiments is that the voltage level of the drive power signals can be drastically different from those of the charging power signal. Pulse modulation ensures that the drive signals and the charge signal will never be present on the same wire at the same time. This is another advantage over the prior art in which motors and generators must be matched. In some embodiments, the batteries can be switched between being connected in serial to being connected in parallel depending on the charging or drive power signals. For example, the batteries can be switched to parallel connections when being charged and to series when powering the motor.
The accompanying figures, in which like reference numerals refer to identical or functionally similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the present invention and, together with the background of the invention, brief summary of the invention, and detailed description of the invention, serve to explain the principles of the present invention.
The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate embodiments and are not intended to limit the scope thereof.
The embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. The embodiments disclosed herein can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
A vehicle with electric drive can employ a pulse width modulation technique to govern the amount of drive power provided to the vehicles wheels while also governing the charging power supplied to the storage device. For example, an electric motor, generator, and a drive shaft can all be linked such that when one spins, they all spin. The disclosed technique provides for rapidly switching from powering a wheel to charging the battery. In fact, the switching can be done rapidly enough that the battery can be charged between every pulse provided to the motor. This rapid switching provides for advanced capabilities in energy harvesting and vehicle weight distribution.
During the powered state 202, the batteries are connected to the motor via a switching device. A switching device is a device such as a power transistor, bank of power transistors, or other device that can turn the flow of energy off and on. The charge power signal 206 is in the non-charging state 204 while the drive power signal 205 is in the powered state 202. During the non-charging state 204, the generator is not connected to the batteries and the generator spins freely and, in many embodiments, powers nothing during the non-powered state.
During the charging state 203, the generator 103 is connected to the batteries 107, 108 via a switching device in the switching/modulating subsystem 105. Some embodiments can have a conditioning circuit that adjusts the charging voltage that is supplied to the batteries 107, 108. The generator 103 can power the conditioning circuit at all times or can be disconnected from the conditioning circuit when charge power signal 206 is in the non-charging state 204. The drive power signal 205 is in the non-powered state 201 while the charge power signal 206 is in the charging state 203. During the non-powered state 201, the motor 102 is not connected to the batteries 107, 108 and the motor 102 spins freely.
Embodiments can have a cruise mode. In cruise mode, the drive power signal 205 and the charge power signal 206 are held in the non-powered state 201 and non-charging state 204, respectively. During cruise mode the vehicle moves forward under its momentum and the drive wheel 101 spins. The motor 102 and the generator 103 also spin unless they are mechanically disengaged by a clutch or other disengagement device.
The charging control signal 616 can also drive transistors 612 to thereby cause the generator 103 to be connected or disconnected from the batteries. The relationship between the charge control signal 616 and a charge power signal 312 is the charge control signal 616 can operate switches, such as transistors 612, to thereby produce the charge power signal. In a similar manner, first power control signal 617 can operate transistors 612 to thereby produce drive power signal 309, second power control signal 614 can operate transistors 612 to thereby produce second drive power signal 310, and third power control signal 615 can operate transistors 612 to thereby produce third drive power signal 311. The drive power signals are passed from the modulating subsystem 107 to the motor 605. Connection 609 can pass a drive power signal to connection 606, connection 610 can pass a drive power signal to connection 607, and connection 611 can pass a drive power signal to connection 608.
Traction motor drive control 708 can control the flow of current from battery 707, through motor 701, and then to ground 711. As discussed above, a PWM scheme drives the motor with longer pulses allowing more current to flow through traction motor drive control 708 and then to ground 711. An accelerator sensor 709 can inform the traction motor drive control 708 as to how wide to make the PWM pulses. In general, when the PWM pulse is “on” the motor current pass through traction motor drive control 708 and then to ground 711, but when the PWM pulse is “off” the motor drive current is unable to flow through traction motor drive control 708 to ground 711. Current fault sensor 718 can monitor the amount of current flowing through traction motor drive control 708, can read the charging current flowing through ammeter 717, and can cut off the current flowing through traction motor drive control 708 or can reduce the PWM pulse widths when the motor drive current is above a threshold value.
A charging circuit 706 can be energized by motor 701 when certain conditions exist such as the vehicle's brakes being applied or a cruising speed being reached. The current passing through motor 701 preferentially passes through traction motor drive control 708 whenever traction motor drive control 708 allows such a flow. Whenever the traction motor drive control does not allow such a current flow, motor 701 can instead drive current through charging circuit 706 which then charges the battery 707.
In certain conditions, the traction motor drive control 708 can trigger charging circuit bypass control 710 such that the charging circuit 706 does not charge the battery 707. For example, the charging circuit bypass control can be triggered when the duty cycle of the motor drive PWM signal is above a certain threshold such as 85%. Duty cycle sensor 719 is shown passing a duty cycle measurement to charging circuit bypass control 710.
Current fault detector 808 can compare the current flow to a trigger point and, when the trigger point is exceeded, informs the traction motor PWM generator 802 to reduce the pulse widths, thereby reducing the current flow, or to shut off, thereby stopping the current flow. Potentiometer 801 is illustrated as providing a trigger point input to traction motor PWM control 802. Those practiced in the arts of circuitry or electronics know of a plethora of means for providing a set point or trigger and it is therefore stressed that potentiometers are illustrated here only as non-limiting examples.
Potentiometer 811 is illustrated as providing a set point or trigger point to duty cycle sensor 810. The duty cycle sensor can measure the duty cycle using any of a number of well-known means such as integrating with a capacitor, counting, and comparing time periods, or some other means to measure the duty cycle. An alternative is for the traction motor PWM control to directly output a duty cycle value. Such capabilities exist for certain types of PWM generators such as those implemented with microcontrollers. Note that it is known in the art for a single microcontroller to concurrently generate multiple PWM signals while also measuring analog values on A/D input pins, outputting analog value on D/A output pins, and handling digital I/O functions. In any case, duty cycle sensor 810 can control a charging circuit bypass. As illustrated here, duty cycle sensor 810 can control switch 1901 of
In a first state, switch 21103 and switch 2B 1101 are closed and switch 2A 1102 is open. In the first state, the circuit of
Transformer 902 has been used in the examples discussed herein for clarity. The charging circuit can instead be an isolated switch mode power converter, also known as an isolated switched power converter, which is a well-known technology that is commonly used instead of transformers in many applications such as in power supplies that convert AC power into DC power.
Having described the embodiments in the figures, a higher level overview can be understood. When a vehicle is being driven, counter electromotive force (CEMF) is PWM switched and generated magnetic fields generated during PWM binary one (such as that of traction motor PWM generator 802) in the motor's magnetic core mass and temporarily stored in the core as magnetic inductive energy due to PWM switching are released during PWM binary zero as CEMF through the freewheeling diode (illustrated as element 908), through the primary winding 903 of transformer 902, through switch 21103, and through the H-bridge elements (switches 3-6, elements 702-705) that are connected to the armature of traction motor 701.
Kinetic energy can be harvested when the armature of traction motor 701 is freewheeling due to vehicle inertia. For example, when traction motor PWM generator 802 produces no pulses, IGBT 804 is thereby held off. No CEMF is generated and therefore all generated EMF from motor 701 is the same polarity as provided by battery 707 through switch 2B 1101, and through the H bridge elements (switches 3-6, elements 702-705) that are connected to the armature of traction motor 701. Battery charging while freewheeling is discussed above where
It should be noted that the sensors, triggers, set points, and signal generators discussed herein can be implemented using a wide range of technologies ranging for analog potentiometers and relays to solid state sensors and microcontrollers. Those practiced in the arts of electronics realize that such implantations are simply variations on a theme. It should also be noted that the embodiments disclosed herein provide novel circuitry for using PWM signals to switch circuit elements that can carry high currents for powering motors and for harvesting energy from the motors to charge batteries.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
