Introduction Switched reluctance motors (SRMs) possess numerous significant advantages, such as simple structure, high starting torque, high efficiency, high reliability, and low cost, and are increasingly attracting attention from various industries. Figure 1(a) shows a typical 6/4 three-phase switched reluctance motor. The motor has a doubly salient pole structure, with the rotor having neither windings nor permanent magnets; the stator has concentrated windings wound on each pole, with the radially opposite pole windings connected in series to form a phase. The operation of a switched reluctance motor is based on the principle of "minimum reluctance"—magnetic flux always closes along the path of least reluctance, generating electromagnetic torque with reluctance properties due to magnetic field distortion. During motor operation, each phase winding is energized only when the inductance of that phase is increasing, and must be de-energized when the inductance is decreasing. Figure 2(b) shows the corresponding main circuit of this motor. The two semiconductor switching devices must be turned on simultaneously, and the two diodes are turned on simultaneously when the two semiconductor switching devices are turned off. The direction of rotor rotation is determined by the on/off sequence of the phase windings (commutation table), not the direction of the current. Clearly, the commutation timing of the motor is directly related to the specific position of the rotor. It must be specifically pointed out that positive torque (electric torque) can only be obtained when the motor inductance increases, while negative torque (braking torque) can only be obtained when the inductance decreases. Therefore, the magnitude of the phase current and the exact start and stop times are key factors determining the final operating performance of the switched reluctance motor. Regardless of the control strategy adopted by the system, the following two PWM modulation methods are required in the control of switched reluctance motors: • Voltage-type PWM modulation – Low-speed region: As shown in Figure 2, when the motor speed is low, the interval between two commutations is large enough. Common fixed-frequency voltage-type PWM modulation is used to control the current amplitude and its changes. • Single-pulse trigger mode – High-speed region: As the motor speed continuously increases, the commutation interval continuously decreases, and the influence of back EMF becomes increasingly significant, making phase current regulation increasingly difficult. Eventually, when the motor speed reaches a certain value, it is no longer possible to regulate the speed by controlling the amplitude and changes of the phase current. Instead, the motor speed can only be controlled by controlling the timing of phase current conduction and cutoff. At this time, the motor is in single-pulse trigger operation mode, as shown in Figure 2. In this mode, by continuously adjusting the on and off times of the current in each phase, it is possible to ensure that current is applied in time during the positive torque generation region and that current is cut off in time before the negative torque region arrives, thereby ensuring the normal operation of the motor. The C868 and CAPCOM6E: The C868 is a new member of Infineon's 8-bit microcontroller family, providing advanced control functions at low cost for various applications and systems. For R&D and mass production, the SRAM model offers high flexibility at the lowest system cost. The corresponding ROM model further reduces costs. With the powerful on-chip PWM generator CAPCOM6E, the C868 meets all the requirements for low-cost, high real-time power electronic control. Utilizing the flexible CAPCOM6E, all time-critical tasks are handled by hardware/software, while the CPU processes user commands and performs corresponding control calculations. The built-in 5-channel/8-bit ADC's synchronous characteristics facilitate the measurement of noise-free relevant system parameters. The CAPCOM6E is a powerful and flexible comparator capture unit that can drive various types of motors (AC asynchronous motors IM, DC brushless motors BLDC, and switched reluctance motors SRM, etc.). It is the latest achievement based on more than ten years of research and development of this type of PWM unit. The CAPCOM6E has the following features: • Two independent 16-bit timers with prescalers. • T12 has three capture/compare channels, each with two outputs, which can be used as capture or compare channels, and features dead-time control to prevent short circuits in the power circuit. • T12 has control modes such as center-aligned, edge-aligned, single-pulse triggered mode, and hysteresis control, and can be used to control induction motors IM, brushless DC motors BLDC, and switched reluctance motors SRM. For switched reluctance motors, its single-pulse triggered mode can be used for high-speed motor control. • T13 has an independent comparator channel and one output, which can generate a high-speed PWM signal and control the duty cycle. T13 also supports single-pulse triggered mode and can be synchronized with T12. • The PWM signal can be automatically superimposed onto the effective level of any (or all) of the six outputs of T12. For switched reluctance motors, in the low-speed range, the motor speed can be adjusted by controlling the phase current amplitude and its variation through the duty cycle of the T13 PWM. All timer output signals can be configured and modified within a single multi-channel control module. The CAPCOM6E also detects rotor position and features noise filtering. Another important feature of the CAPCOM6E is the emergency interrupt input CTRAP—this function ensures that the six outputs of T12 in the CAPCOM6E are in a user-defined state when the level is low. As shown in Figure 3, CC60-CC62 and COUT60-COUT62 are the six basic output signals used to drive the motor. For switched reluctance motor control, the rotor position feedback signal is input via CCPOS0-CCPOS2. The high-frequency PWM signal generated by T13 is applied to the effective level of any one of the CC60-CC62 and COUT60-COUT62 outputs of T12 with a resolution of up to 50ns. CTRAP is the emergency interrupt input. If the input is low, CC60-CC62 and COUT60-COUT62 will immediately switch to the predefined level to achieve overcurrent/overvoltage protection. Users can easily and quickly control the CAPCOM6E by simply setting the values ​​of various registers, such as the period register, compare register, offset register, etc. Figure 4 shows a block diagram of a switched reluctance motor system based on the C868. In the figure, the motor is the 6/4 three-phase switched reluctance motor shown in Figure 1(a). This motor has rotor position feedback (Hall sensor). The main circuit adopts a common (single-phase) dual-switch structure. Both switches are controlled by high-frequency PWM signals. The CAPCOM6E of the C868 initially operates in multi-channel mode, outputting a fixed-frequency voltage-type PWM control signal according to the rotor position feedback signal to control the current within a specified range. The DC bus current is input by an A/D converter. This A/D converter is synchronously triggered by T13 of the CAPCOM6E, avoiding current spikes and acquiring the true current signal. When the motor speed reaches a certain value, the CAPCOM6E switches to single-pulse trigger mode. At this time, the A/D converter is synchronously triggered by T12. Figure 5 shows the PWM output waveform and phase current waveform in the low-speed region. Conclusion This paper introduces a method for implementing a switched reluctance motor control system using Infineon's latest 8-bit microcontroller C868 and its powerful and flexible PWM generator CAPCOM6E. In addition to the common PWM control, the C868's CAPCOM6E features a dedicated single-pulse trigger mode, specifically designed for controlling the high-speed region of the switched reluctance motor. The synchronous function of the A/D converter integrated with the C868 enables accurate and noise-free current measurement, greatly contributing to the stable operation of the system.