IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. IA-22, NO. 4, JULY/AUGUST 1986 Microcomputer Control of Switched Reluctance Motor BIMAL K. BOSE, SENIOR MEMBER, IEEE, TIMOTHY J. E. MILLER, SENIOR MEMBER, IEEE, PAUL M. SZCZESNY, AND WILLIAM H. BICKNELL Abstract-A microcomputer-based four-quadrant control system of a switched reluctance motor is described. The control was implemented with a speed feedback loop, a torque feedback loop, and both the torque and speed feedback loops combined. In addition the controller incorpo- rates a startup operation, sequencing, and synchronized angle steering control. The angle controller was designed using dedicated digital hardware, whereas the other functions were implemented using an Intel 8751 single-chip microcomputer. The complete control system was tested in the laboratory with a 5-hp drive, and the test results were found to be excellent. INTRODUCTION INTEREST in switched reluctance motor (SRM) drives has revived during the last five to ten years. The points in favor of SRM drives are that the machine is simple in construction and economical compared to induction and synchronous types of machines [6]. In addition, the converter which supplies power to the machine requires fewer power devices and, therefore, is more economical and reliable [7]. The SRM drives have received wide attention in Europe, and serious attempts are being made to commercialize them. The literature on SRM drives concentrates mainly on the analysis of the machine and the configuration of the power converters, but very few papers discuss the control a'spects. The control requirements of the SRM drive are so unique that the concepts of induction- and synchronous-type machines can hardly be extrapolated to the SRM. The SRM drives discussed in the literature are mainly open-loop control with angle and current amplitude regulation and have usually been designed with discrete components and dedicated hardware. This paper describes a microcomputer-based control of the SRM drive system which is capable of operating in all four quadrants. The microcomputer functions include feedback speed and torque controls, computation of the feedback speed and torque, starting, sequencing control, computation of the switching angles, and a phase-locked loop for the angle Paper IPCSD 86-1, approved by the Industrial Drives Committee of the IEEE Industry Applications Society for presentation at the 1985 Industry Applications Society Annual Meeting, Toronto, ON, Canada, October 6-1 1. Manuscript released for publication February 5, 1986. B. K. Bose is with the General Electric Research and Development Center, Building 37-380, 1 River Road, Schenectady, NY 12345. T. J. E. Miller and P. M. Szczesny are with the General Electric Company, Corporate Research and Development Center, Building 37-380, P.O. Box 43, Schenectady, NY 12301. W. H. Bicknell is with the General Electric Company, Corporate Research and Development Center, Building 37-478, P.O. Box 43, Schenectady, NY 12301. IEEE Log Number 8608632. controller. The angle controller, which interfaces to the microcomputer, has been designed using dedicated hardware. The complete control system has been designed and tested in the laboratory with a prototype drive system. POWER CIRCUIT OPERATION The control system was developed for a four-phase machine which has four stator pole pairs and three rotor pole pairs. The power converter with a cross section of the machine is shown in Fig. 1. The opposite stator poles are supplied by a converter phase, and the phase current is switched on and off in synchronism with the rotor position. The bifilar winding in series with the diode returns stored energy to the source when the transistor turns off. The transistors conduct in sequence, and the order of conduction depends on the direction of the rotation. A dynamic brake exists in the dc link (not shown) which absorbs energy during regeneration. The inductance profile of the stator pole pair with respect to the rotor angular position is shown in Fig. 2, which also indicates typical stator phase current waves. In a forward motoring mode, for example, the current pulse is established where the inductance profile has a positive slope. This is because the instantaneous motor torque is given by the relation I Te(j) = i2M 2 (1) where i is the instantaneous current and m is the inductance slope. The current i is switched on at an advance angle 06, and it rises linearly to the magnitude I at the corner point (00) by the relation (2) 00 = ILmr 0 Vd where Lm is the minimum inductance; wr is the rotor speed, and Vd is the dc link voltage. The current I is maintained constant by the chopping control and then turned off at a Op angle so that the current zero angle Oq does not extend much into the negative inductance slope region. At high speed the machine counter EMF dominates, and chopping control is lost as indicated by the pulse B, which also indicates the saturation effect. The current pulse, during forward braking, is nearly identical to that of forward motoring at low speed, except that it is established where the inductance slope m is negative. Since here the Oq angle can freely extend into the minimum 0093-9994/8610700-0708$01 .00 © 1986 IEEE 708