T. YOSHIDA, J. OYAMA, T. HIGUCHI, T. ABE and T. HIRAYAMA Department of Electrical and Electronic Engineering, Nagasaki University, Japan ON THE CHARACTERISTICS IMPROVEMENT OF LINEAR SYNCHRONOUS MOTOR WITH HALF-WAVE RECTIFIED SELF EXCITATION

Abstract We proposed a novel linear synchronous motor (LSM) with half-wave rectified self excitation. This paper presents a design and a control method of the novel LSM are proposed in order to improve the characteristics. A control method of high speed operation for the novel LSM with half-wave rectified self excitation we proposed. This paper proposes the novel LSM of the short-stator type system, in order to improve the efficiency characteristics in comparison with the long-stator type system.

In this presentation 1. The novel LSM with Half-Wave Rectified Self Excitation 1.1 Basic Principle 1.2 Structure and Special Merits 1.3 Principle of operation 2. The control method of high speed operation 2.1 Field weakening operation 2.2 Maximum Thrust-per-Voltage Control 3. The novel LSM with short-stator type system 3.1 Short-stator type system and Long-stator type system 3.2 Effect by the number of field pole On the characteristics improvement of Linear Synchronous Motor with Half-Wave Rectified Self Excitation

Basic Principle of Half-Wave Rectified Self Excitation Coil 2 is short circuited The magnetomotive force (MMF) produced by the AC current in the Coil 1 is canceled by the MMF by the short- circuit current in the Coil 2. The resultant flux along the axis is almost zero.

Coil 2 is short circuited through a Diode As the flux along the axis is increasing, electromotive force (EMF) in the Coil 2 negatively biases the diode. When the flux begins to decrease, the diode turns on and the secondary current starts to flow and compensates the flux decrease. The resultant flux along the axis is almost constant. Basic Principle of Half-Wave Rectified Self Excitation OnOff

Structure of the novel LSM The LSM consists of 1. A LSM mover whose field winding is short circuited through a diode. 2. A LSM stator with conventional 3-phase armature windings. 3. A control system that operates base on half-wave rectified self excitation principle. 4. A 3-phase PWM inverter.

DC power supply for field excitation is not needed because the field current is induced from the armature side. The novel LSM has merits of simple and robust structure and is more inexpensive than the PM type LSM. The field weakening operation is performed easily at high speed region, because the field flux of the novel LSM is controllable by varying amplitude of the armature current. Special Merits

Principle of operation A f (t) is a triangular wave function with the effective value of I f and bias frequency  b. ： synchronous angular velocity The following 3-phase currents are supplied to the 3-phase armature windings The dq-axis currents become; Were,

Flux linkage Equivalent Model on the dq-Axis The flux linkages are expressed in terms of self- and mutual- inductance as follows, Principle of operation

Thrust Then the thrust is obtained from the following equation. Though a pulsating thrust exists in this motor, it is not serious problem for practical usage by choosing the bias frequency  b much greater than the mechanical resonance frequency. Principle of operation

Control method of high speed operation Field weakening operation When the motor terminal voltage is confined to the limit of voltage source at high speed region. The field flux of the novel LSM is controllable by varying value of the excitation current I f. We derive the condition of the excitation current I f for the field weakening operation. A control method of high speed operation for the novel LSM with half-wave rectified self excitation we proposed.

Control method of high speed operation Maximum Thrust-per-Voltage Control In the field weakening operation, the maximum velocity is limited by the field flux limit, because the excitation current I f decreases with increase in velocity and finally becomes zero. the excitation current I f and thrust current I t become; In order to expand operation range, we propose a new control method for the novel LSM that maximizes the ratio of the thrust to the voltage. We call the new control method “maximum thrust-per-voltage control”.

Operation characteristics Rated current : I n = 4 A Rated voltage : V n = 200 V Armature winding resistance : r a = 9.9  Field winding resistance : r fd = 14.9  d-axis inductance : L d = H q-axis inductance : L q = H Mover self inductance : L fd = H Mutual inductance : M fd = H Table 1. Rated values, winding resistances and inductances Fig. 5 shows simulation results of the operation characteristics. The simulation conditions are as follows; I f at constant thrust region is 2.0A, bias frequency  b = 50Hz, voltage limit V m = 131.4V. The input voltage of the inverter is 200V. The field weakening operation is applied at v s = 1.69m/s. The voltage V is equal to voltage limit V m = 131.4V. In case of applying the maximum thrust-per-voltage control, the control method is switched to the maximum thrust-per-voltage at v s = 1.95m/s. high speed region

Operation characteristics In the maximum thrust-per-voltage control, the excitation current I f and the thrust current I t are controlled, and the armature current I decreases with increase in velocity. It is confirmed that the operating range is expanded by applying the maximum thrust-per-voltage control.

Long-stator type system Short-stator type system (Number of poles ： 16poles) (Number of poles ： 4poles) Stator length960 mm Pole pitch60 mm Air gap0.6 mm Stack height50 mm windings Double layer distribution pitch Armature windings 85 turns/phase Field windings 500 turns/pole Specification of the basic model The novel LSM with short-stator type system primary side secondary side primary side

Fig. 5. Field analytical model (Number of elements 37,324) The thrust characteristics are investigated by the electric and magnetic coupled analysis. The mesh model for transient finite element method (FEM) is shown in Fig. 5. Fig. 6 shows the equivalent circuit for the field winding short-circuited by diode. The coupled analysis is executed using the mesh model and the equivalent circuit. The coupled analysis Fig. 6. Circuit analytical model

Rated armature current4.0 A Bias frequency20 Hz Speed0.4 m/s Position0 ~ 240 mm Time step0.001 s Efficiency Analytical condition The analytical condition This paper proposes the novel LSM of the short-stator type system, in order to improve the efficiency characteristics in comparison with the long-stator type system.

Average thrust F xave [N] Core loss P i [W] Copper loss P c [W] Efficiency  [%] Long-stator Short-stator The analytical results The average thrust of the short-stator type system decreases in comparison with the long-stator type system but the efficiency increases. Because the armature winding resistance of the short-stator type system is lower than that of the long-stator type system, the copper loss decreases.

(a) 8 poles (b) 4 poles Effect by the number of field pole Number of series-connected field poles Field winding resistance r fd  The number of the series-connected field poles was selected for average thrust and efficiency characteristics. The number of the series-connected field poles was selected for average thrust and efficiency characteristics.

(c) 2 poles (d) 1 pole Number of series-connected field poles Field winding resistance r fd  The number of the series-connected field poles was selected for average thrust and efficiency characteristics. The number of the series-connected field poles was selected for average thrust and efficiency characteristics. Effect by the number of field pole

Rated armature current4.0 A Bias frequency20 Hz Speed0.4 m/s Position0 ~ 240 mm Time step0.001 s Analytical condition (I f : I t = 1:1) Effect by the number of field pole

Analytical result The number of the series-connected field poles was selected for average thrust and efficiency characteristics. The number of the series-connected field poles was selected for average thrust and efficiency characteristics. Effect by the number of field pole It is clarified to increase in thrust and normal force with reducing the number of series-connected field pole. It is confirmed that the efficiency characteristic is improved and the output power increases by the selection of the number of series- connected field pole. (I f : I t = 1:1)

Conclusions The control method of high speed operation for the novel LSM was proposed. The control method of field weakening operation was derived. The maximum thrust-per-voltage control method was proposed as the new control method for the novel LSM. The novel LSM of the short-stator type system was proposed. It was confirmed that the efficiency characteristics are improved. The number of the series-connected field poles was selected for average thrust and efficiency characteristics.

At the end Thank you for listening !!

“A novel linear synchronous motor with half-wave rectified self excitation” The field flux of the novel LSM is controllable by only varying amplitude of the armature current. Introduction Linear synchronous motor (LSM) have been widely used in various industry applications. Transportation system NC machine tools Home applications A permanent magnet (PM) type LSM shows higher efficiency but it is normally difficult to control the field flux.

Control method of high speed operation Field weakening operation For simplification, we derive the condition that the following terminal voltage V, which the winding resistance is assumed to be zero, is confined to voltage limit V m. the condition of the excitation current I f become;

Silicon steel band 50A470 Hysteresis coefficient Yoke 3.53 Teeth 5.88 Eddy coefficient Yoke 28.2 Teeth 49.4 Thickness of steel band 0.5 mm Core density 7.70 kg/dm 3 Efficiency Output power Copper loss Core loss  H ： hysteresis coefficient  E ： eddy coefficient d ： thickness of steel band [mm] F x ： thrust [N] v s ： speed [m/s] r a ： armature resistance  I ： armature current [A] hysteresis loss eddy current loss G i ： core weight [kg] B ： flux density [T] f ： frequency [Hz] [W] [%] Calculation of efficiency

the armature current I of the novel LSM is given as the following equation and limited to current limit I n