T. YOSHIDA , J. OYAMA, T. HIGUCHI, T. ABE and T. HIRAYAMA

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

2. 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.

3. In this presentation On the characteristics improvement of Linear Synchronous Motorwith Half-Wave Rectified Self Excitation 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 Control3. 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

4. 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 isalmost zero.

5. Basic Principle of Half-Wave Rectified Self Excitation 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 isalmost constant. Coil 2 is short circuitedthrough a Diode Off On

6. 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.

7. Special Merits DC power supply for field excitation is not neededbecause 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.

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

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

10. 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 wb much greater than the mechanical resonance frequency.

11. Control method of high speed operation A control method of high speed operation for the novel LSM with half-wave rectified self excitation we proposed. 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 If. We derive the condition of the excitation current If for the field weakening operation.

12. Control method of high speed operation In the field weakening operation, the maximum velocity is limited by the field flux limit, because the excitation current If decreases with increase in velocity and finally becomes zero. Maximum Thrust-per-Voltage Control 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”. the excitation current If and thrust current It become;

13. Operation characteristics Table 1. Rated values, winding resistances and inductances high speed region Fig. 5 shows simulation results of the operation characteristics. The simulation conditions are as follows; If at constant thrust region is 2.0A, bias frequency wb = 50Hz, voltage limit Vm = 131.4V. The input voltage of the inverter is 200V. The field weakening operation is applied at vs = 1.69m/s. The voltage V is equal to voltage limit Vm = 131.4V.In case of applying the maximum thrust-per-voltage control, the control method is switched to the maximum thrust-per-voltage at vs = 1.95m/s.

14. Operation characteristics In the maximum thrust-per-voltage control, the excitation current If and the thrust current It 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.

15. The novel LSM with short-stator type system Long-stator type system (Number of poles：4poles) secondary side Specification of the basic model primary side Short-stator type system (Number of poles：16poles) primary side secondary side

16. The coupled analysis Fig. 6. Circuit analytical model 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.

17. 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. Analytical condition Efficiency

18. 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.

19. Effect by the number of field pole The number of the series-connected field poles was selected for average thrust and efficiency characteristics. (a) 8 poles (b) 4 poles

20. Effect by the number of field pole The number of the series-connected field poles was selected for average thrust and efficiency characteristics. (c) 2 poles (d) 1 pole

21. Effect by the number of field pole Analytical condition (If : It = 1:1)

22. 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. Analytical result The number of the series-connected field poles was selected for average thrust and efficiency characteristics. (If : It = 1:1)

23. 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.

24. At the end Thank you for listening !!

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