SIMULATION OF SENSORLESS CONTROL OF PERMANENT MAGNET SYNCHORONOUS

MOTOR

Sensor less drives In Sensor less drives the speed and position is

obtained by monitored voltage/current and by utilizing mathematical models or artificial intelligence based systems.

The performance of the sensor less drives is based on the torque control capabilities and also on the speed estimation accuracy and bandwidth.

MAIN TECHNIQUES OF SENSORLESS CONTROL OF PMSM

Open loop estimator using monitored stator voltage/current

Estimator using spatial saturation stator phase third harmonic voltage.

Model reference adaptive system Observers Artificial intelligence Back emf based position estimators

Vector control The three phase stator currents are measured.

These measurement provides Ia and Ib . Ic can be calculated from the following relationship

Ia +Ib+Ic=0. The three phase current is then converted

into two axis system. The conversion provides the variables Iα and Iβ.

The two axis coordinate system is rotated to align with the rotor flux using a transformation angle calculated at the last iteration of the control loop. this conversion provides the Id and Iq from Iα and Iβ.

Vector control Error signals are formed using Id, Iq and

reference values for each. The error signal is then provided to PI

controller. The output of the controller provide Vd and Vq which is a voltage vector that will be sent to the motor .

A new transformation angle is estimated where Vα,Vβ,Iα and Iβ are the inputs. the new angle guides the FOC algorithm as to where to place the next voltage vector.

Vector control The Vd and Vq output values from the PI

controller are rotated back to the stationary reference frame using the new angle. This provides the next quadrature voltage values Vα and Vβ.

The Vα and Vβ values are transformed back to 3 phase values Va Vb and Vc. The 3 phase voltage values are used to calculate the new PWM duty cycle values that generate the desired voltage vector

Vector control block diagram

Clarke transformation

Park transformation

PI controller

Inverse park transformation

Inverse Clarke transformation

Parameters to be estimated Three phase current Ia, Ib,Ic Position θ Speed ω

Position and speed estimation methodI) Model based estimators

a) state observersb)back EMF methodc)flux linkage methods

II) Signal injection methoda)high frequency signal injectionb)low frequency signal injection

III) Phase loop lock technique

References DISADVANTAGE OF MODEL BASED ESTIMATOR

At zero speed the current ,voltage and back emf are zero, so this method is not suitable at low speeds.

DISADVANTAGE OF SIGNAL INJECTION TECHNIQUE Ripples at high speed When Saliency ratio close to unity error

signal is too small

PHASE LOCKED LOOP Combination of both back emf

method and high frequency injection technique.

At low speed high frequency injection technique is used and switched to back emf method at high speed.

REFERENCES Sensor less vector control of interior

permanent magnet synchronous motor drives at very low speed without signal injection,” IET ELECTRICAL APPLICATIONS 2009”.

Simple rotor position estimation using the current saturation at a standstill.

An improved back-EMF based initial rotor position estimation for IPMSM ,”ECCE Asia 2011”.

DANKEDANKE