Patent Description:
Electric motor is an essential power source in an electric vehicle or hybrid vehicle. The performance of the motor affects the overall performance of the electric vehicle. An electric motor comprises of a rotor and a stator. The stator includes windings, permanent magnets or metal sheets called laminators. The stator in the electric motor provides a rotary magnetic field to drive the rotary armature.

The electric motor performance directly affects the overall performance of a vehicle or any machine running on electric motor. The electric motor windings heat up when operated under extreme load thereby reducing the efficiency of the vehicle. As such, the propulsion system requires cooling systems, not only for the electric motor but also for the battery banks in order to ensure efficient operation and maximizing the electric components and vehicle lifetime.

The same numbers are used throughout the drawings to reference like features and components.

It is always necessary that the temperature of the motor does not increase beyond a certain threshold which may affect the drivability of the vehicle. Various means have been used for this purpose such as thermistors or other temperature detectors placed on the motor windings to respond directly to the temperature, or current responsive devices for tripping the motor circuit breaker in response to excessive current which would produce overheating if allowed to continue.

There are resistance measuring devices such as multimeter type instrument which is able to measure the resistance up to <NUM> Ohms and hence the multimeter type instrument can be optimum for small size machine which may has the phase winding resistance in the range of <NUM> to <NUM> Ohm. Larger machines with lower winding resistance use four terminal bridge like Kevin bridge for achieving the accuracy. But Kevin bridge has problems related to high requirement of current for obtaining better sensivity, requirement of manual balancing and also the galvanometer to detect balance condition.

Another known method to measure temperature of the motor winding is by introducing a small direct current component into the motor current which can be done by connecting an asymmetrical resistance device in the motor circuit. The resistance of the motor winding can be determined from measuring the direct current component and the corresponding voltage. But these methods have their own short coming like limit in the range of measuring the resistance along with low precision due to the resistance measurement circuit which compresses the scale at a higher values of the resistance, error prone methods like balancing issues. But the common issue in all the above mentioned methods is the requirement of an additional component to measure the resistance which leads to increase in the cost and also at the same time making the overall system bulky. Also, introducing a new component leads to dependency on the introduced component which reduces the reliability of the motor.

The electric motor uses inbuilt sensor for performing vital function such as detection of phase current and phase voltage and some sensor provided in the electric motor used for measuring the power drawn from the battery to run the electric motor. In order to overcome the above mentioned disadvantages the present subject matter enables the sensors, provided in the electric motor, to measure the resistance in each of the winding by a controller and thereby controlling the operation of the electric motor by generating a high frequency sinusoidal signal and detecting the resistance of each winding. Depending on the resistance, a temperature of the winding is measured and the operation of the electric motor is controlled based on the temperature. The present subject matter, hence, provides an advantage of overcoming the problems mentioned in the prior art like using an extra element, packaging constraint etc..

Further cooling the electric motor in a saddle type two wheeled vehicle which is typically compact in layout, an additional challenge persists which is related to space and packaging constraint. Additionally, the means to provide cooling mechanism adds to the challenge of limited space. Therefore, there exists a challenge of designing a compact, low cost, high reliability electric machine which can safely operate at rated as well as over-rated loads without going into adverse thermal run-away or catastrophic failure. In a prior art document with application number <CIT>, a phase current comparison unit is disclosed. The phase current comparison unit diagnoses a fault of a current sensor on the basis of a comparison result between the estimation value of phase current by the phase current operation unit and the detection value of phase current by the current sensor. However, the prior art does not describe an apparatus or a method of detecting a temperature value of an electric machine. In another prior art document with application number <CIT>, a protection method for preventing a permanent magnet synchronous motor from being demagnetized is disclosed. The method comprising calculating a real time stator winding resistance, obtaining a current motor stator temperature value, comparing the obtained motor stator temperature value with a prestored temperature threshold. However, the prior art uses a Clarke transformation formula to determine a current motor stator temperature value. Through this method, receiving the inputs from various sensors and processing of the data becomes very complex to determine current motor stator temperature value. Further, it requires high performance processors to determine a simple parameter. Therefore, there is a requirement to provide a simple solution to determine the temperature value of electric machine. In yet another prior art document with application number <CIT>, a processor to receive the RMS current values from the plurality of sensors and compute a fault indicator based on the RMS current values, is disclosed. It further discloses a motor temperature being measured by a temperature sensor. However, the present invention aims at determining the temperature value of the electric machine without using any additional temperature sensor.

Hence, in order to overcome the above mentioned challenges the present subject matter provides an electric machine according to claim <NUM> and a method of controlling an electric machine according to claim <NUM>, wherein the electric machine can detect the temperature of the winding by eliminating the requirement of any additional components such as thermistors to determine the temperature and controlling the starting operation of the electric machine based on the detected temperature and thereby reducing additional cost by eliminating the need of an additional component e.g. a sensor to measure temperature and also providing a compact packaging. Also, if an additional sensor fails the system becomes highly vulnerable and may lead to catastrophic failure like fire, thermal runaway or the rider may get stranded in the middle of a road. Thus, the reliability requirement of the sensor is very high leading to high cost of sensor. Without using an additional component, the reliability of the electric machine operation increases as the electric machine is not dependent on any additional component. Further, the present subject matter enables the driver of the vehicle to know when the electric machine needs repair since over due course of time the resistance of the windings increases and the same would be indicated to the user by the diagnostic system in the controller of the electric machine.

Another aspect of the present subject matter provides a motor control unit to control a power supply to an electric motor. The motor control unit comprises a microcontroller that generates a high frequency sinusoidal current and transfers the high frequency sinusoidal current to one or more phase lines of the electric motor. The sinusoidal current of high frequency is adjusted in close proximity to a rated frequency of the electric machine to get a suitable sinusoidal current.

Still another aspect of the present subject matter provides a microcontroller which enables a plurality of first sensors provided in the electric machine to detect a direct voltage and direct current from a power source supplied to the electric motor. The microcontroller determines a direct current power from the detected values of the direct voltage and the direct current.

Yet another aspect of the subject matter is to provide a microcontroller which enables a plurality of second sensors provided in one or more phase lines of the electric machine to detect one or more phase currents.

Another aspect of the present subject matter is to provide a commutation device such as a MOSFET switching unit also called six pulse half bridge circuit or B6 bridge circuit functioning as a commutation device. The MOSFET switching unit receives the sinusoidal current from the microcontroller and performs the bridge operation. The MOSFET switching unit comprises of one or more bridges connected to said one or more phase lines of the electric motor. Each bridge of the MOSFET switching unit comprises two MOSFET switches to perform switching operation.

Another aspect of the present subject matter is to determine a resistance for said one or more phase lines of the electric motor by processing a root mean square value of one or more phase current of said one or more phase lines and the direct current power from the power source.

Still another aspect of the present subject matter is to determine a current temperature from said resistance and comparing said current temperature with a predetermined temperature (temperature value set by the manufacturer) and controlling the actuation- of the electric motor based on the current temperature of the phase lines.

The above aspects and the associated advantages of the present subject matter will be better understood through following description, appended claims and accompanying drawings.

<FIG> illustrates a block diagram of the present subject matter depicting an electric machine (<NUM>) comprising a power source (<NUM>) such as a battery to drive an electric motor (<NUM>). A motor control unit (<NUM>) controls the power supply to the electric motor (<NUM>).

<FIG> illustrates the architecture of the motor control unit (<NUM>) of the electric machine (<NUM>). The motor control unit (<NUM>) is electrically connecting the power source (<NUM>) to the electric motor (<NUM>). The motor control unit (<NUM>) comprises a plurality of first sensors (<NUM>,<NUM>) adapted to sense a DC voltage (Vdc) and a DC current (Idc). The plurality of first sensors (<NUM>,<NUM>) are DC voltage sensor (<NUM>) connected across the power source (<NUM>) to sense the voltage of the power source (<NUM>) and the DC current sensor (<NUM>) is connected to the positive terminal of the power source (<NUM>) to sense the current received from the power source (<NUM>) to the electric motor (<NUM>).

The plurality of first sensors (<NUM>,<NUM>) is connected to a microcontroller (<NUM>). The microcontroller (<NUM>) is adapted to receive input from said plurality of first sensors (<NUM>,<NUM>) and determines a direct power (P) received from the power source (<NUM>) [P=VdcIdc]. The plurality of first sensors (<NUM>,<NUM>) can be either halls based isolated sensors or shunt based sensors.

The microcontroller (<NUM>) is capable of generating a high frequency wave of sinusoidal currents. The microcontroller (<NUM>) is connected to a MOSFET switching unit (<NUM>) and the MOSFET switching unit (<NUM>) is controlled by the sinusoidal current generated by the microcontroller (<NUM>) to enable a bridge operation (or the MOSFET switching).

By generating and supplying a high frequency of the sinusoidal current, a torque is generated which provides a small movement in the electric motor. The high frequency sinusoidal current generated by the microcontroller (<NUM>) which is then supplied to one or more phase lines (Lr, Ly, Lb) of the electric motor (<NUM>) after the bridge operation of the MOSFET switching unit (<NUM>). Each of the phase lines (Lr, Ly, Lb) connecting the different phases of the electric motor (<NUM>) is provided with plurality of second sensors (<NUM>,<NUM>,<NUM>). The plurality of the second sensors (<NUM>,<NUM>,<NUM>) are adapted to sense the high frequency wave of sinusoidal currents (Ir, Iy, Ib) in the each of the phase lines (Lr, Ly, Lb). The sinusoidal current of high frequency is kept in close proximity to the rated frequency of the electric machine to get a high frequency sinusoidal current. The plurality of the second sensors (<NUM>,<NUM>,<NUM>) can be hall based isolated sensors or shunt based sensors.

<FIG> illustrates the circuit level diagram of the present subject matter. The three-phase excitation winding is disposed in the stator (not shown) of the electric motor (<NUM>). The sinusoidal current is provided to the electric motor (<NUM>) after the bridge operation of the MOSFET switching unit (<NUM>) and plurality of the second sensors (<NUM>,<NUM>,<NUM>) for each phase winding of the electric motor (<NUM>) sense the phase current (Ir, Iy, Ib) and sent it to the microcontroller (<NUM>) to determine root mean square (rms) value of the phase currents (Ir, Iy, Ib).

The phase windings are connected in a star pattern through one or more MOSFET switches (M1, M2, M3, M4, M5, M6) in the MOSFET switching unit (<NUM>). The MOSFET switching unit (<NUM>) is also called six pulse half bridge circuit or B6 bridge circuit functioning as a commutation device.

A first bridge (B1) of the MOSFET switching unit (<NUM>) comprises M1 and M4 MOSFETS. The central node of the first bridge (B1) connects to a red phase (R) of the electric motor (<NUM>). Similarly, a second bridge (B2) of the MOSFET switching unit (<NUM>) comprises M2 and M5 MOSFETS and the central node of the second bridge (B2) connects to a yellow phase (Y) of the electric motor (<NUM>). A third bridge (B3) of the MOSFET switching unit (<NUM>) comprises M3 and M6 MOSFETS and the central node of the third bridge (B3) connects to a blue phase (B) of the electric motor (<NUM>).

A gate driver (<NUM>) is provided which connects the MOSFET switches (M1, M2, M3, M4, M5, M6) in the MOSFET switching unit (<NUM>) to the microcontroller (<NUM>). The microcontroller (<NUM>) enables the gate driver (<NUM>) to actuate the switching of the MOSFET switches (M1, M2, M3, M4, M5, M6) by controlling one or more gate terminals of the MOSFET switches (M1, M2, M3, M4, M5, M6).

The phase current 'Ir' flows through the red phase (R) of the electric motor (<NUM>), phase current 'Iy' flow through the yellow phase (Y) of the electric motor (<NUM>) and the phase current 'Ib' flows through the blue phase (B) of the electric motor (<NUM>).

The microcontroller (<NUM>) is adapted to calculate the root means square current (Irms) of the phase current (Ir, Iy, Ib) in the plurality of phase lines (Lr, Ly, Lb). Through root mean square current in each phase, the resistance in the phase winding can be determined and based on the value of each phase winding resistance corresponding temperature can be determined based on the temperature co-efficient of the winding material as per following equations of physics. <MAT> <MAT> <MAT> <MAT> <MAT> <MAT>.

<FIG> illustrates the flow diagram of the method of controlling the electric machine (<NUM>). In step <NUM>, a power is determined from the direct voltage (Vdc) and direct current (Idc) detected by the plurality of first sensors (<NUM>,<NUM>). The direct voltage (Vdc) is detected across the power source (<NUM>) and the direct current (Idc) is received by the microcontroller (<NUM>) from the power source (<NUM>). In step <NUM>, the microcontroller (<NUM>) generates a high frequency sinusoidal current. In step <NUM>, the sinusoidal current is transferred to said one or more phase lines (Lr, Ly, Lb) of the electric motor (<NUM>) after the bridge operation of the MOSFET switching unit (<NUM>).

In step <NUM>, the plurality of the second sensors (<NUM>, <NUM>, <NUM>) sense the phase currents (Ir, Iy, Ib) in each phase line (Lr, Ly, Lb) of the electric motor (<NUM>). After sensing the phase current (Ir, Iy, Ib), in step <NUM>, the microcontroller (<NUM>) determines root mean square values of each phase current, in step 405a,and based on the root mean square current (Irms) of each phase and the direct power (P)determined based on the direct voltage (Vdc) and direct current (Idc) as stated in step <NUM>, corresponding resistance of each phase lines (Lr, Ly, Lb) is determined through calculated direct power (P) and root mean square current (Irms) values in step 405b.

Claim 1:
An electric machine (<NUM>) comprising:
an electric motor (<NUM>), said electric motor (<NUM>) being configured to receive a power supply from a power source (<NUM>);
a motor control unit (<NUM>), said motor control unit (<NUM>) being configured to control said power supply from said power source (<NUM>) to said electric motor (<NUM>);
a commutation device (<NUM>), said commutation device (<NUM>) being configured to receive a high frequency sinusoidal current from a microcontroller (<NUM>), said microcontroller (<NUM>) being configured to generate a sinusoidal current to enable excitation of said commutation device;
a plurality of first sensors (<NUM>,<NUM>), said plurality of first sensors (<NUM>,<NUM>) being adapted to sense a direct current (Idc) from said power source (<NUM>) and a direct voltage (Vdc) across said power source (<NUM>); and
a plurality of second sensors (<NUM>,<NUM>,<NUM>), said plurality of second sensors (<NUM>,<NUM>,<NUM>) being connected to one or more phase lines (Lr, Ly, Lb) of said electric motor (<NUM>), said plurality of second sensors (<NUM>,<NUM>,<NUM>) being adapted to sense one or more phase currents (Ir, Iy, Ib)
characterised in that
said microcontroller (<NUM>) determines a direct current power (P) through an input received from said plurality of first sensors (<NUM>,<NUM>),
said microcontroller (<NUM>) determines root mean square current (Irms) values for said one or more phase lines (Lr, Ly, Lb) after receiving said one or more phase currents (Ir, Iy, Ib) from said plurality of second sensors (<NUM>,<NUM>,<NUM>),
wherein,
said microcontroller (<NUM>) being configured to determine a current temperature based on said direct current power (P) and said root mean square current (Irms) values,
said microcontroller (<NUM>) being configured to disconnect a power supply to said electric motor (<NUM>), when said current temperature being greater than a predetermined temperature (To).