DESC:FIELD OF INVENTION
The present invention relates to a speed control system for a synchronous motor. More particularly the present invention relates to a method for the control of permanent magnet synchronous motor using a cost-effective electronic controller and a single hall sensor, suitable for use in applications such as E-vehicles, traction motor, etc., where high starting torque is required and are sensitive to reverse rotation.

BACKGROUND OF INVENTION
It is known that a Permanent Magnet Synchronous Motors (PMSM) has stator comprising windings of copper wire and a permanent-magnet rotor. When the stator windings are connected to the power supply rotating magnetic field is produced. If a permanent magnet is present in this rotating magnetic field, the permanent magnet is magnetically locked with this rotating magnetic field and rotates with the same speed of the rotating field.

The Permanent Magnet Synchronous Motors (PMSM) has considerable problems during starting, owing to the fact that the rotor passes from a condition in which
speed is zero to a condition in which it is frequency-locked with the electric power supply source.

The Permanent Magnet Synchronous Motors (PMSM) has a variety of advantages such as superior torque-to-weight ratio, higher efficiency, lower cost, electronic-based commutation. The field-oriented control is used to get the lower torque ripples and better dynamic running performance of the motor. However, the field-oriented control cannot work at a standstill to the startup of the motor. The control requires position signals of the motor to do the commutation process of the motor by providing control signals to the inverter.

The position signals are sensed either by three Hall Effect sensors embedded in motor or estimated using back EMF signals of the motor. The PMSM requires an initial rotor position of the motor from where it can accelerate slowly and run to higher speeds. The initial rotor position can be identified by using three hall sensor signals or the motor can be aligned to a certain position and from there the motor will start its rotation.

The motor can be started with Variable Voltage and Variable Frequency (V/F) method at a slower speed and then switched over to the field-oriented control, but this method cannot work in such applications like on-load starting of the motor.

So it will be advantageous to provide a start-up method suitable for permanent magnet synchronous motors using a cost-effective electronic controller and a single hall sensor to estimate the initial rotor position of the motor in standstill condition and accelerating the motor in gradual speed that avoids reverse rotation of motor, the condition which is essential for the applications like E-vehicles, traction motor where high starting torque is required.

OBJECTS OF INVENTION
It is one of the objectives of the present invention to provide reliable and cost-effective system and method for the determination of initial rotor position of Permanent Magnet Synchronous Motors (PMSM) at standstill condition with single hall sensor instead of three hall sensors using a microcontroller and firmware.

It is one of the objectives of the present invention to eliminate the cost and effort of aligning the additional sensors to back EMF in Permanent Magnet Synchronous Motors (PMSM).

It is one of the objectives of the present invention, wherein the initial rotor position of Permanent Magnet Synchronous Motors (PMSM) is determined by measuring the variation in amplitude of the current required for the generation of predetermined flux with respect to the position of rotor magnetic pole to the stator winding.

It is one of the objectives of the present invention to provide a system and method for smooth starting of Permanent Magnet Synchronous Motors (PMSM) with a full load and also for starting the motors without reversing. These are done by making the transition from open loop to closed loop within 3 electrical cycles.

It is one of the objectives of the present invention wherein position estimation of the rotor of Permanent Magnet Synchronous Motors (PMSM) at standstill condition is achieved by using a single hall sensor.

SUMMARY OF INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the present invention.

It is the primary aspect of the present invention to provide a system for controlling permanent magnet synchronous motor (PMSM) comprising a voltage divider, a microcontroller, a six transistor inverter stage, a current sensing circuit and a single hall sensor.

It is another aspect of the present invention, wherein the microcontroller preprogrammed with firmware logic determines the initial rotor position of Permanent Magnet Synchronous Motors (PMSM) by twelve-step commutation method and starts the Permanent Magnet Synchronous Motors (PMSM) by correcting estimated angle from back Electromotive force (EMF) observers during startup with actual angle measured from hall sensor output.

It is another aspect of the present invention, wherein the initial rotor position of the Permanent Magnet Synchronous Motors (PMSM) is determined by measuring the variation in amplitude of the current required for the generation of predetermined flux with respect to the position of rotor magnetic pole to the stator winding and the motor is started with full load and transition is performed from open to closed loop within three electrical cycles.

It is another aspect of the present invention, wherein the amplitude of feedback current of the Permanent Magnet Synchronous Motors (PMSM) in the sectors of stator is measured by using the current sensing circuit.

It is another aspect of the present invention, wherein the speed and rotor angle position of Permanent Magnet Synchronous Motors (PMSM) is estimated using the current feedback signal from a current sensor.

It is another aspect of the present invention to provide a method for detecting the initial rotor position of the Permanent Magnet Synchronous Motors (PMSM), comprising of steps determining the electrical half-cycle by reading a hall sensor output; initializing the counter of buffer with zero value and dividing one electrical cycle into six sectors namely 1, 2, 3, 4, 5 & 6; checking whether the hall sensor signal is high or low; wherein if the hall sensor signal is high, apply the short DC voltage pulses for the predetermined period to the three sectors of stator namely 1, 2 and 3, wherein if hall sensor signal is low, apply the short DC voltage pulses for the predetermined period to the other three sectors of stator namely 4, 5 and 6, measuring the amplitude of feedback current of the Permanent Magnet Synchronous Motors (PMSM) in the sectors of stator using current sensor circuit; determining the sector value that provides maximum amplitude of current among three; saving of corresponding sector value in the buffer in the microcontroller and increment counter of buffer value by 1; checking consecutive buffer values for same sector value; wherein if the consecutive buffer contains same sector values, then save the sector value in the microcontroller, wherein if the consecutive buffer contains different sector values, then the microcontroller checks the counter value, wherein if the counter value is less than four, repeat the above steps, and wherein if the counter value is greater than or equal to four, the microcontroller gives a fault message as position detection failure.

It is another aspect of the present invention, wherein the predetermined period is in the range 130µs to 160 µs preferably 150µs.

It is another aspect of the present invention to provide a method for starting the Permanent Magnet Synchronous Motors (PMSM), comprising of steps getting the initial rotor position of the Permanent Magnet Synchronous Motors (PMSM); applying voltage to stator winding with 60-degree in advance; performing the six step commutation process; checking whether six step commutations are completed; running of back EMF observers in the background and estimate the angle of the rotor; detecting for the falling edge of a hall sensor; calculating the actual angle of the rotor based on the hall sensor output by measuring the angle corresponding to the falling edge; comparing the actual angle and estimated angle from the observer then reinitializing the observer angle with the actual angle measured from the hall sensor output; checking whether twelve-step commutations are completed; and switching over to closed loop field oriented control.

It is another aspect of the present invention, wherein the back EMF observers used is a luenberger type back EMF observer.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1: Schematically illustrates the Permanent magnet synchronous motor drive system according to the present invention.
Figure 2: Is the flow chart illustrating the method for detecting the initial rotor position of the motor according to the present invention.
Figure 3: Is the flow chart illustrating the method for starting the motor according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES
The present invention provides a reliable and cost-effective system and method for the determination of initial rotor position estimation of Permanent Magnet Synchronous Motors (PMSM) at standstill condition from where it can accelerate slowly and run to higher speeds with a single hall sensor instead of three hall sensor using a microcontroller and firmware.

According to the present invention, system for controlling three-phase [104 - 106] permanent magnet synchronous motor (PMSM) [109] comprising of a voltage divider [101], a microcontroller [102], a six transistor inverter stage [103], a current sensing circuit [107] and a single hall sensor [108] as shown in Figure 1. The microcontroller [102] loaded with firmware algorithm is placed in an electronic controller. The microcontroller [102] used for the detection of the initial rotor position of the permanent magnet synchronous motor (PMSM) [109] and for starting the same.

To control the permanent magnet synchronous motor (PMSM) [109] according to the present invention, the control is done in the firmware loaded in the microcontroller [102]. This control logic is implemented by pre-programming the 8-bit microcontroller of the electronic controller for,
1) Detection of the initial rotor position of the permanent magnet synchronous motor (PMSM) [109] at standstill condition using a single hall sensor [108] and
2) Start the permanent magnet synchronous motor (PMSM) [109] by using the six-step commutation method

Referring to Figures 1 to 3, a startup method of permanent magnet synchronous motor (PMSM) [109] with a single hall sensor [108] is illustrated. The logic shown in figure 2 is implemented by the microcontroller [102] to detect the initial rotor position of permanent magnet synchronous motor (PMSM) [109] at standstill condition using the single hall sensor [108].

The following twelve step commutation methods are used to detect the initial rotor position of permanent magnet synchronous motor (PMSM) [109] at standstill condition as illustrated in figure 2. The electrical half cycle is determined by reading the hall sensor [108] output. Initializing the counter of buffer with zero value and one electrical cycle is divided into six sectors namely 1, 2, 3, 4, 5 & 6 in the permanent magnet synchronous motor (PMSM) [109]. The microcontroller [102] monitors the hall sensor [108] signal. As one electrical cycle is divided into six sectors, the short DC voltages impulses are applied for a predetermined period to the determined three sectors of stator winding based on the first step. In the preferred embodiment of the invention, if the hall sensor [108] signal is high, apply the short DC voltage pulses for the period of about 150µs to the three sectors of stator namely 1, 2 and 3.If hall sensor [108] signal is low, apply the short DC voltage pulses for the period of about 150µs to the other three sectors of stator namely 4, 5 and 6.

When the DC voltage pulses are applied to stator winding, it produces a current and induces magnetic field. This results in the occurrence of saturation effect and thereby reducing the inductance further. To overcome this saturation effect, more current is required to generate the same flux. The amplitude of the current depends on how far the rotor magnetic pole is away from stator winding. Thus, this variation in current amplitude is measured using the current sensor circuit [107].

After measuring on the three sectors of stator, detect the sector value that provides maximum amplitude of current among three. Based on maximum amplitude of current, the corresponding sector value in the buffer is saved in the microcontroller [102] and the counter of buffer value is increased by 1. After incrementing the counter of buffer value, the microcontroller [102] checks the buffer (buffer successive to the one saved with sector value) for same value of sector. If the consecutive buffer contains same sector values, then the sector value saves in the microcontroller [102]. If the consecutive buffer contains different sector values, then the microcontroller [102] checks the counter value. If the counter value is less than 4, repeat the steps from 3 to 11. If the counter value is greater than or equal to 4, then the microcontroller [102] gives a fault message as position detection failure.
The method of initial rotor position estimation of the motor at standstill condition with a single hall sensor comprises the steps of
determining the rotor position in which electrical half-cycle is first determined by reading the hall sensor output;
dividing one electrical cycle into six sectors;
applying the short dc voltages impulses for a predetermined period of time to the three sectors of stator winding based on the first step; and
applying DC voltage to stator winding to produce current for the induction of magnetic field.

The twelve-step commutation method is used and luenberger type back EMF observer is executed in the background for starting the rotor of Permanent Magnet Synchronous Motors (PMSM). The speed and rotor angle position of Permanent Magnet Synchronous Motors (PMSM) is estimated using the current feedback signal from a current sensor. Once six commutation steps are completed, the estimated angle from the observer is compared with the absolute angle measured from hall sensor output and the observer angle is reinitialized with a new corrected angle.

The cost-effective system and method for starting the rotor of Permanent Magnet Synchronous Motors (PMSM) from standstill with twelve-step commutation method and correction of estimated angle from back EMF observers during startup with absolute angle from hall sensor to have the better convergence of estimated and actual position of motor.

The method [200] for detecting the initial rotor position of the Permanent Magnet Synchronous Motors (PMSM) [109], comprising of steps:
determining the electrical half-cycle by reading a hall sensor [108] output;
initializing [201] the counter of buffer with zero value and dividing one electrical cycle into six sectors namely 1, 2, 3, 4, 5 & 6;
checking [202] whether the hall sensor [108] signal is high or low;
wherein if the hall sensor [108] signal is high, apply [203] the short DC voltage pulses for the predetermined period to the three sectors of stator namely 1, 2 and 3,
wherein if hall sensor [108] signal is low, apply [204] the short DC voltage pulses for the predetermined period to the other three sectors of stator namely 4, 5 and 6,
measuring [205] the amplitude of feedback current of the Permanent Magnet Synchronous Motors (PMSM) [109] in the sectors of stator using current sensor circuit [107];
determining [206] the sector value that provides maximum amplitude of current among three;
saving [207] of corresponding sector value in the buffer in the microcontroller [102] and increment [208] counter of buffer value by 1;
checking [209] consecutive buffer values for same sector value;
wherein if the consecutive buffer contains same sector values, then save [210] the sector value in the microcontroller [102],
wherein if the consecutive buffer contains different sector values, then the microcontroller [102] checks [211] the counter value,
wherein if the counter value is less than four, repeat the above steps, and
if the counter value is greater than or equal to four, the microcontroller [102] gives [212] a fault message as position detection failure.

The predetermined period is in the range 130µs to 160 µs preferably 150µs.

The method [300] for starting the Permanent Magnet Synchronous Motors (PMSM) [109], comprising of steps:
getting [301] the initial rotor position of the Permanent Magnet Synchronous Motors (PMSM) [109];
applying [302] voltage to stator winding with 60-degree in advance;
performing [303] the six step commutation process;
checking [304] whether six step commutations are completed;
running [305] of back EMF observers in the background and estimate the angle of the rotor;
detecting [306] for the falling edge of a hall sensor[108];
calculating [307] the actual angle of the rotor based on the hall sensor [108] output by measuring the angle corresponding to the falling edge;
comparing [308] the actual angle and estimated angle from the observer then reinitializing the observer angle with the actual angle measured from the hall sensor [108] output;
checking [309] whether twelve-step commutations are completed; and
switching [310] over to closed loop field oriented control.

In the preferred embodiment of the invention, after detecting of the initial rotor position of the Permanent Magnet Synchronous Motors (PMSM) [109] at standstill condition by above twelve-step commutation method, the method of starting the motor is done by using the existing method namely six-step commutation method with luenberger type back EMF observer executed in background. It estimates the speed and rotor angle using the current feedback signal from the current sensor circuit [107]. The flow chart 2 illustrates this logic of starting the motor with full load. Referring to figure 3, the microcontroller [102] applies voltage to stator winding sector with 60 degree in advance then executes the six step commutation process. Once six commutation steps are completed, the estimated angle from the observer is compared with the actual angle measured from hall sensor [108] output as shown in table 1.

Table 1: Actual angle measurement using hall sensor output signal
Motor Starting- Clock Wise Direction Motor Starting- Counter Clock Wise Direction
Signal of Hall sensor A Actual angle Signal of Hall sensor A Actual angle
0 32 0 32
0 96 0 96(actual angle)
1 160 1 160
1 224 1 224
1 288 1 288
0 352(actual angle) 0 352

The microcontroller [102] checks for the falling edge of hall sensor [108] signal in the hall sensor [108] output and then measures the angle corresponding to the falling edge. It is called the actual angle measured from hall sensor [108] output. After measuring the actual angle, reads the angle measured from back EMF observer and then reinitializes the observer angle with actual angle measured from hall sensor [108] output. The above process will be repeated after the completion of nex12 commutations. By giving better convergence of observer angle, the transition will happen smoothly from open loop to closed loop.

Thus, the Permanent Magnet Synchronous Motors (PMSM) [109] can be started with full load and transition can happen from open to closed loop within three electrical cycles. The present invention also avoids the reverse rotation of the Permanent Magnet Synchronous Motors (PMSM) [109] by correcting the observer value with actual angle for 2 commutations.

The present invention eliminates the difficulties in precisely aligning the three hall sensors in the motor as this invention uses only one hall sensor feedback. In case of three hall sensor based control, if any of the hall sensors is misaligned, it will lead to wrong commutation and thereby causes more stator current, less torque, more torque ripple and erroneous speed feedback

Although, the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. It is therefore, contemplated that the claims will cover any such modifications or embodiments that fall within the true scope of the invention. ,CLAIMS:WE CLAIM:
1. A system [100] for controlling permanent magnet synchronous motor (PMSM) [109] comprising:
a voltage divider [101];
a microcontroller [102];
a six-transistor inverter stage [103];
a current sensing circuit [107]; and
a single hall sensor [108],
characterized in that the microcontroller [102] preprogrammed with firmware logic determines the initial rotor position of Permanent Magnet Synchronous Motors (PMSM) [109] by twelve-step commutation method and starts the Permanent Magnet Synchronous Motors (PMSM) [109] by correcting estimated angle from back Electromotive force (EMF) observers during startup with actual angle measured from hall sensor [108] output,
wherein the initial rotor position of the Permanent Magnet Synchronous Motors (PMSM) [109] is determined by measuring the variation in amplitude of the current required for the generation of predetermined flux with respect to the position of rotor magnetic pole to the stator winding, and
the motor is started with full load and transition is performed from open to closed loop within three electrical cycles.
2. The system [100] for controlling permanent magnet synchronous motor (PMSM) [109] as claimed in claim 1, wherein the amplitude of feedback current of the Permanent Magnet Synchronous Motors (PMSM) [109] in the sectors of stator is measured by using the current sensing circuit [107].

3. The system [100] for controlling permanent magnet synchronous motor (PMSM) [109] as claimed in claim 1, wherein the speed and rotor angle position of Permanent Magnet Synchronous Motors (PMSM) [109] is estimated using the current feedback signal from a current sensor.

4. A method [200] for detecting the initial rotor position of the Permanent Magnet Synchronous Motors (PMSM) [109], comprising of steps:
determining the electrical half-cycle by reading a hall sensor [108] output;
initializing [201] the counter of buffer with zero value and dividing one electrical cycle into six sectors namely 1, 2, 3, 4, 5 & 6;
checking [202] whether the hall sensor [108] signal is high or low;
wherein if the hall sensor [108] signal is high, apply [203] the short DC voltage pulses for the predetermined period to the three sectors of stator namely 1, 2 and 3,
wherein if hall sensor [108] signal is low, apply [204] the short DC voltage pulses for the predetermined period to the other three sectors of stator namely 4, 5 and 6,
measuring [205] the amplitude of feedback current of the Permanent Magnet Synchronous Motors (PMSM) [109] in the sectors of stator using current sensor circuit [107];
determining [206] the sector value that provides maximum amplitude of current among three;
saving [207] of corresponding sector value in the buffer in the microcontroller [102] and increment [208] counter of buffer value by 1; and
checking [209] consecutive buffer values for same sector value,
wherein if the consecutive buffer contains same sector values, then save [210] the sector value in the microcontroller [102],
wherein if the consecutive buffer contains different sector values, then the microcontroller [102] checks [211] the counter value,
wherein if the counter value is less than four, repeat the above steps, and
wherein if the counter value is greater than or equal to four, the microcontroller [102] gives [212] a fault message as position detection failure.

5. The method [200] for detecting the initial rotor position of the Permanent Magnet Synchronous Motors (PMSM) [109] as claimed in claim 4, wherein the predetermined period is in the range 130µs to 160 µs preferably 150µs.

6. A method [300] for starting the Permanent Magnet Synchronous Motors (PMSM) [109], comprising of steps:
getting [301] the initial rotor position of the Permanent Magnet Synchronous Motors (PMSM) [109];
applying [302] voltage to stator winding with 60-degree in advance;
performing [303] the six step commutation process;
checking [304] whether six step commutations are completed;
running [305] of back EMF observers in the background and estimate the angle of the rotor;
detecting [306] for the falling edge of a hall sensor [108];
calculating [307] the actual angle of the rotor based on the hall sensor [108] output by measuring the angle corresponding to the falling edge;
comparing [308] the actual angle and estimated angle from the observer then reinitializing the observer angle with the actual angle measured from the hall sensor [108] output;
checking [309] whether twelve-step commutations are completed; and
switching [310] over to closed loop field oriented control.

7. The method [300] for starting the Permanent Magnet Synchronous Motors (PMSM) [109] as claimed in claim 6, wherein the back EMF observers used is a luenberger type back EMF observer.