Patent Application
20180302019
An Electric Vehicle (EV) uses one or more electric motors or traction motors for its mean of propulsion. An EV's propulsion system can use various regulators and inverters to regulate and transform a direct current (DC) from a battery to an alternating current (AC) required by the EV's induction motor. The speed of the electric motors or traction motors can be regulated by controlling the frequency and phase of the inverter.
However, electric motors in EVs can draw as much as 1,000 amps requiring expensive discrete components to achieve the regulation and inversion. These expensive discrete components require complex heatsinks to dissipate the heat they produce when switching the DC to the pulse width modulated (PWM) voltage. Various circuits and control strategies have been developed in order to address the cost and heat issues, but these prior approaches are often complex and difficult to implement. Therefore, improved circuits and methods to improve an EV drive efficiency and operation are needed.
With reference to the Figures, wherein like numerals indicate like parts throughout the several views,
An inductor motor is an AC electric motor in which an electric current in the motor's rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. Therefore, an induction motor can be made without electrical connections to the rotor. An induction motor's rotor can be either a wound type or a squirrel-cage type.
A synchronous motor is an AC motor in which, at steady state, the rotation of the shaft is synchronized with the frequency of the supply current. In other words, the rotation period is exactly equal to an integral number of AC cycles. Synchronous motors contain multiphase AC electromagnets on the stator of the motor that create a magnetic field which rotates in time with the oscillations of the line current. The rotor with permanent magnets or electromagnets turn in step with a stator field at the same rate, and as a result provides the second synchronized rotating magnet field of the AC motor.
In a merging onto a highway scenario, the EV requires obtaining a maximum amount of torque from the electric drive system in the quickest possible time. With a high performance electric vehicle, it is not unforeseeable for the electric drive system to draw as much as 1000 amperes from the HV battery.
One technique to deliver high currents to the motors from the ISC is to connect multiple power devices of the ISC in parallel. One example of the aforementioned power device is an insulated-gate bipolar transistor (IGBT) 22 as shown in
In one such configuration, an ISC may use four power devices in parallel for each of the three phases of voltages and their associated currents fed to the motor to achieve the high current capability of the high current power device. In this configuration, each power device only needs to carry ¼ of the total current. Deploying power devices in parallel permits, by adding-on an additional power devices in parallel will achieve an even a higher maximum current. For example, three power devices with a current rating of 100 amps each can be combined in parallel to produce a total rating of 300 amps. Four power devices with a current rating of 100 amps each can be combined in parallel to produce a total rating of 400 amps.
The designer of an ISC can use lower current, less expensive power devices, obtain the power devices in larger quantities, and thus receive a discount on the cost of the part form the manufacture of the power device. However, a problem for utilizing power devices in parallel is the current sharing between the paralleled power devices. Any current unbalance will cause the power devices to become inefficient, and therefore decrease the power device's output current capability.
To reduce the number of paralleled power devices, the number of the motor's parallel windings can be increased. An example being, to twelve windings with four ISCs that eliminate having to have the power devices in parallel, but rather create a series configuration. As a result, the current sharing problem is eliminated. However, this solution will make designing and implementation of motor design and motor control extremely difficult and will require more current sensors. In other words, the twelve windings will require twelve current sensors increasing the costs and complexity of the system.
An advantage this embodiment this embodiment has over other inverter circuits that a filter capacitor 20 which may be placed across the DC power source 16 to reduce any ripple currents can have smaller capacitance value, thus reducing the size and the cost of the capacitor 20.
The four inverter circuit 21232527 are controlled by a controller unit (not shown) or a motor control unit (not shown) to determine such parameters as an inverter frequency value and an inverter frequency phase value which the inverter 21232527 outputs to the motor as a motor control signal. In some embodiments, the controller unit and the motor control unit can be combined into a single unit. The inverter 21232527 are made up of a series and parallel IGBT 22. The motor control signal may be for example, a pulse width modulated (PWM) signal applied to the IBGTs of the inverter 21232527. As a result, the inverter outputs a winding control signal to the motor windings to produce a motor speed and a motor torque of the EV motor 28.
The ISC controller can be communicatively coupled to a controller area network (CAN) bus (not shown), e.g., in a known arrangement to a plurality of electronic control units (ECUs) (not shown), as is known. An ISC controller, such as for systems or controllers mentioned above, typically contains a processor and a memory, each memory storing instructions executable by the respective processor of the controller. Each controller memory may also store various data, e.g., data collected from other controllers or sensors in the EV, such as may be available over the CAN bus, parameters for operations of the controller, etc.
The present embodiment permits the ISC controller to control the phase shift between any two separate windings. The phase shift can be any value from zero to +/−180 degrees. Since the ISC controller has independent control of the four inverter circuit 21232527, allows the system 11 to be optimized. An example being inverter 21, inverter 23, inverter 25 and inverter 27 may be set to have different phase shift for their PWM motor control signals in order to reduce the capacitor ripple current, which as discussed above reduces the capacitor 20 size and cost.
For example, if the DC bus voltage from the DC power source 16 is 375 V with a power factor of 0.75, a modulation index is 0.86, and a total load current is 900 Amps rms. The resultant DC bus ripple current rms value is 172 Amps. A ripple ratio is the DC bus ripple current rms value divided by the total load current or 172 Amps/900 Amps=0.19. For comparison, if a single inverter is employed to achieve the same current of 900 Amps with the same power factor, modulation index, the DC bus ripple current rms will be 495 Amps, so the ripple ratio is 495 Amps/900 Amps=0.55. The single inverter would require a larger more expensive high voltage DC capacitor to handle the high ripple current.
As used herein, the adverb “substantially” modifying an adjective means that a shape, structure, measurement, value, calculation, etc. may deviate from an exact described geometry, distance, measurement, value, calculation, etc., because of imperfections in the materials, machining, manufacturing, sensor measurements, computations, processing time, communications time, etc.
Computing devices such as those discussed herein generally each include instructions executable by one or more computing devices such as those identified above, and for carrying out blocks or steps of processes described above. Computer executable instructions may be compiled or interpreted from computer programs created using a variety of programming languages and/or technologies, including, without limitation, and either alone or in combination, Java′, C, C++, C#, Visual Basic, Python, Java Script, Perl, HTML, PHP, etc. In general, a processor (e.g., a microprocessor) receives instructions, e.g., from a memory, a computer readable medium, etc., and executes these instructions, thereby performing one or more processes, including one or more of the processes described herein. Such instructions and other data may be stored and transmitted using a variety of computer readable media. A file in a computing device is generally a collection of data stored on a computer readable medium, such as a storage medium, a random access memory, etc.
A computer readable medium includes any medium that participates in providing data (e.g., instructions), which may be read by a computer. Such a medium may take many forms, including, but not limited to, non-volatile media, volatile media, etc. Non-volatile media include, for example, optical or magnetic disks and other persistent memory. Volatile media include dynamic random access memory (DRAM), which typically constitutes a main memory. Common forms of computer readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH EEPROM, any other memory chip or cartridge, or any other medium from which a computer can read.
With regard to the media, processes, systems, methods, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of systems and/or processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the disclosed subject matter.
Accordingly, it is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent to those of skill in the art upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to claims appended hereto and/or included in a non-provisional patent application based hereon, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the arts discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the disclosed subject matter is capable of modification and variation.
