Claims:We Claim:
1. A method of controlling an inverter (14) in a vehicle (10), said method comprising :
- detecting at least one vehicle parameter for every predefined time interval by corresponding sensing element (18);
- generating pulse width signals by a pulse generator (15) based on said detected at least one vehicle parameter;
- regulating at least one switching strategy of said inverter (14) by a control unit (12), in dependence with said generated pulse width signal for said detected at least one vehicle parameter , to achieve a maximum rotating flux in said vehicle (10).
2. The method as claimed in claim 1, wherein regulating at least one switching strategy of said inverter (14) by a control unit (12) , in dependence with said generated pulse width signal for said detected at least one vehicle parameter, to achieve a maximum efficiency of said vehicle (10)

3. The method as claimed in claim 1, said at least one vehicle parameter is chosen from a group of parameters comprising an motor speed, a torque developed, an input voltage, a vibration on a motor shaft, harmonics generated on the stator lines, an audible frequency ranges for the switching frequencies , an amount of heat generated or the like.

4. The method as claimed in claim 1, wherein regulating of said at least one switching strategy of said inverter (14) comprises providing multiple pulse width signals with different duty cycles and pulse positioning to said inverter (14) based on at least one detected vehicle parameter.

5. The method as claimed in claim 1, wherein values of said duty cycle , pulse pattern and a supplied frequency of at least one said pulse width signal that generated said maximum rotating flux in said hybrid vehicle (10), when fed to said inverter (14), is stored in said control unit (12).

6. A control unit (12) in a vehicle (10), said control unit (12) adapted to :

- detect at least one vehicle parameter for every predefined time interval;
- generate a pulse width signal based on said detected at least one vehicle parameter;
- regulate at least one switching strategy of an inverter (14) of said hybrid vehicle (10) , in dependence with said generated pulse width signal for said detected at least one vehicle parameter , to achieve a maximum rotating flux in said hybrid vehicle (10).
, Description:Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of the invention
[0001] This invention relates to a method of controlling and calibrating an inverter in a vehicle.

Background of the invention
[0002] Electric motors used in hybrid/electric cars have varied efficiency curves and a major part of the efficiency is controlled by the inverter for different torque ,speed and high voltage battery profiles. Current state of the art uses theoretical formulas to fix the efficiency of the inverter , electric motor and the switching strategy for inverter in different torque/speed profiles. This method is not very accurate and not efficient. Various parameters of inverter used for controlling electric motors like permanent magnet synchronous motor that are used in Hybrid Electric cars needs to be calibrated with respect to multiple current and voltage vector values to give accurate torque values. One such parameter is the inductance values of the stator coils of the electric motor. Manually calibrating the inductance parameters of the electric motor in a test Bench for different ranges axis currents is a time consuming activity and prone to errors and also has lack of accuracy.
[0003] A Prior art document US 6046554 discloses a motor, which has a first motor winding that provides a motor back EMF during operation of the motor, and which is operable by a supply current. The first motor develops, at a predetermined nominal rotational speed, a predetermined nominal torque corresponding to a predetermined operating current and a predetermined nominal back EMF. The above parameters are calibrated by applying a supply current to the motor. The motor operates at a known rotational speed, disconnecting the supply current from the motor such that the motor decelerates from the known rotational speed, and obtaining an EMF indication of motor back EMF.

Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[0005] Fig.1 illustrates a control unit in a vehicle in accordance with one embodiment of the invention;
[0006] Fig.2 illustrates a flowchart of a method of calibrating the inverter in the hybrid vehicle.

Detailed description of the embodiments
[0007] Fig.1 illustrates a control unit 12 in a vehicle 10 according to one embodiment of the vehicle. The control unit 12 detects at least one vehicle parameter for every predefined time interval and generates pulse width signals based on the detected at least one vehicle parameter. The control unit 12 regulates at least one switching strategy of an inverter 14 of the vehicle 10, in dependence with the generated pulse width signal for the detected at least one vehicle parameter, to achieve a maximum rotating flux in the hybrid vehicle 10. The vehicle 10 is chosen from a group of vehicles comprising a hybrid vehicle, an electric vehicle or the like. The control unit 12 regulates the switching strategy of the inverter 14 of the vehicle 10, to achieve maximum efficiency during the development of the maximum rotating flux. The control and calibration functions on the inverter 14 is performed in a vehicle or on an electric motor test bench.

[0008] Further the construction of the inverter 14 in the hybrid vehicle 10 and the components of the inverter 14 is explained as follows. The inverter 14 provides power to the electric motor 20 from a battery 22. The inverter 14 comprises at least six switches 16 connected as shown in the figure1. According to one embodiment of the invention, the switches 16 are insulated-gate bipolar transistors. The electric motor 20 according to one embodiment of the invention is a permanent magnet synchronous motor. However, it is not restricted to the above-disclosed one, but can be any electric motor 20, which is used for various applications. At least one sensing element 18 adapted to sense at least one vehicle parameter, is placed in proximity connecting to the electric motor 20 or it is integrated into the electric motor 20 based on the requirement. At least one sensing element 18 is chosen from a group of sensing elements comprising a torque sensor, a speed sensor , shaft vibration sensor or the like.

[0009] The control unit 12 is chosen from a group of control units comprising a microcontroller, a microprocessor, an ASCII chip, an IC chip or the like. At least one vehicle parameter is chosen from a group of parameters comprising an motor speed, a torque developed, an input voltage, a vibration on a motor shaft, harmonics generated on the stator current lines, an audible frequency ranges for the switching frequencies , an amount of heat generated or the like. The control unit 12 comprises a pulse width generator 15 to generate a series of pulses, which are provided to the switches 16 of the inverter 14. The control unit 12 provides a multiple switching strategies to the switches of the inverter 14 based on at least one detected vehicle parameter. The control unit 12 regulates at least one switching strategy that is provided to the inverter 14 comprises providing multiple pulse width signals with different duty cycles to the inverter based on at least one detected vehicle parameter. The control unit 12 adapted to provide the pulse width signal to at least three switches 16 of the inverter 14 in at least one switching strategy.

[0010] Figure 2 illustrates a flowchart of a method of calibrating an inverter in a hybrid vehicle 10. In step S1, at least one vehicle parameter for every predefined time interval is detected by corresponding sensing element 18. In step S2, pulse width signals are generated by a pulse generator 15, based on the detected at least one vehicle parameter. In step S3, at least one switching strategy of the inverter 14 is regulated by a control unit 12, in dependence with the generated pulse width signal for the detected at least one vehicle parameter, to achieve a maximum rotating flux with highest efficiency in the hybrid vehicle/electric motor test bench 10.

[0011] The control unit 12 receives the current torque ,the speed and high voltage line values under which the hybrid vehicle 10 is operating. The control unit 12 changes the demanded speed, torque and input high voltage supply to the inverter and test bench system based on a predefined motor torque vs speed vs high voltage profile stored in the control unit 12. Based on the received speed and the torque values, the control unit 12 determines the pulse width signals that is to be provided to the switches 16 of the inverter 14 to achieve a maximum rotating flux. The control unit 12 provides a series of pulse width signals comprising different duty cycle, pulse width and frequency values. The control unit 12 changes the switching strategy, by changing the above-mentioned parameters of the pulse width signals. The control unit 12 alters the pulse width signal parameters like the duty cycle, pulse width and the frequency values and different combination of the above-mentioned parameters are given to the switches 16 of the inverter 14 so that a rotating magnetic flux is achieved for every switching strategy

[0012] For each of switching strategy, the control unit 12 compares the torque generated in the vehicle 10 to the desired torque. For instance, if the torque generated is equal to the desired torque value (that is stored in the control unit 12), then a mechanical power developed is calculated using the torque and the speed values. The inverter efficiency is calculated based on an input power provided to the inverter 14 from the battery 22 using inverter voltage and current values obtained from the voltage and the current sensors 18 and the calculated mechanical power. In addition to the inverter efficiency, the vehicle parameters as mentioned above (like a vibration on a motor shaft, harmonics generated on the stator lines, an audible frequency ranges for the switching frequencies , an amount of heat generated or the like) are calculated. Upon detection of the completion of the combination of the switching strategy(which give a full rotating flux) provided to the inverter 14, the control unit 12 determines one switching strategy, where the above-mentioned vehicle parameters are not much deviated from the predefined values. The determined switching strategy is stored in the control unit 12 for further usage.

[0013] For example, the control unit 12 provides a pulse width signal frequency to 6KHz and the duty cycle is initialized to 50%. Since, the inverter 14 comprises six switches, the pulse width signal is provided to three switches 16 at different wave form positioning like first switch T1 =0ms, T2 = 4ms, and T3 = 8ms. Upon providing the above switching strategy to the inverter 14, the control unit 12 determines at least one vehicle parameter and the variation of the vehicle parameter with the predefined value. For instance, the control unit 12 determines the rotating flux generated for the above provided switching strategy and based on the amount of the rotating flux generated, the control unit 12 stores the switching strategy.

[0014] If the rotating flux generated is not maximum or equal to the predetermined value, then the control unit 12 alters the parameters of the pulse width signal to frequency (6KHz) , duty cycle (60%) , and the wave form positioning to T1 = 3ms, T2 = 5ms and T3 = 7ms and the above disclosed process is continued. The control unit 12 alters one or more parameters of the pulse width, to provide to the switches of the inverter 14, to attain a maximum rotating flux. Upon detecting the completion of the all the combinations of the pulse width signal parameters, the control unit 12 detects, the switching strategy that provided a maximum rotating flux for a corresponding torque , speed and high voltage values of the vehicle/test bench 10, and is stored in the control unit 12. The control unit 12 continues this process for multiple torque , speed and high voltage values of the vehicle 10 and multiple switching strategies are stored in the control unit 12 based on the variation of at least one vehicle parameter of the vehicle 12 from the predefined values.

[0015] With the above-disclosed method, the efficiency of the electric motor 20 is improved by using automatic calibration and learning of switching strategy technique. Usage of power used by the electric motor 20 in the hybrid vehicle 10 is minimized. More mileage is achieved with the improved efficiency with the same power input provided to the electric motor 20. Manual intervention is reduced, by making the calibration process more accurate. The harmonics , vibration, audible frequencies for different speed,torque and high voltage ranges are optimized automatically.

[0016] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.