Abstract This paper introduces a method for soft starting and energy-saving control of asynchronous motors using an 8098 microcontroller. Keywords Microcontroller Energy-saving control Soft starting 1 Introduction The power factor of a three-phase asynchronous motor is related to the load. The power factor is highest at rated load, and therefore the efficiency is highest. As the load decreases, the power factor decreases, and the power also decreases. To prevent the power factor from decreasing significantly under light load, an effective method is to reduce the stator supply voltage accordingly as the load decreases. This paper uses the HSO.0, HSO.1, and zHSO.2 of the 8098 high-speed input port to control the conduction angle of three bidirectional thyristors in the three-phase main circuit to complete three-phase AC voltage regulation. The power factor is measured using HSI.1 of its high-speed input port and used as the controlled variable to realize closed-loop control of the power factor. 2 Three-phase AC voltage regulation [sup][2][/sup] Figure 1 shows the three-phase AC voltage regulation principle applicable to bidirectional thyristors used in this paper. Since there is a strict interrelationship between the three-phase trigger signals, only the pulse signal formed by the zero-crossing point of the X-phase voltage needs to be used as the synchronization signal of the three-phase trigger signals HSO.0, HSO.1, and HSO.2, and it will also be used as the interrupt request signal for its high-speed input HSI.0. The main task of its interrupt service program is to load the nature and occurrence time of the 6 events as shown in Figure 1, where the ignition time τ is calculated by the closed-loop control algorithm. [align=center] Figure 1 Three-phase AC voltage regulation principle[/align] T Three-phase voltage period TP Trigger pulse width τ Ignition time 3 Soft start Since this device has a three-phase AC voltage regulation function, it is very easy to realize the soft start of the asynchronous motor. Soft start can be realized in three ways: manual, open loop (according to the pre-given τ curve), and closed loop (according to the given starting current). Here, the second soft start method is adopted. 4 Power Factor Measurement [sup][3][/sup] The voltage and current of phase X are shaped into corresponding square waves and used as inputs to an XOR gate. The pulse width of its output u[sub]o[/sub] represents the power factor, as shown in Figure 2. u[sub]o[/sub] is sent to the high-speed input terminal HSI.1. The rising edge time t[sub]r[/sub] of u[sub]o[/sub] has been measured in the HSI.0 interrupt service routine, and the falling edge time td has been measured in the HSI.1 interrupt service routine. The pulse width T[sub]c[/sub] = t[sub]r[/sub] - t[sub]d[/sub] is calculated. [align=center]Figure 2 Power Factor Measurement[/align] 5 Closed-Loop Control of Power Factor [sup][2][/sup] The sampling time T[sub]S[/sub] of the closed-loop control is determined by a software timer of the 8098, and interruption is allowed. The PI algorithm calculation is completed in the interrupt service routine. The algorithm's input is T[sub]c[/sub], representing the actual power factor (implicit error signal), and its output is the thyristor ignition delay time τ. 6. Fault Handling and Protection The overvoltage, overcurrent, and phase loss fault signals are ORed together and sent to the external interrupt input EXTINT. The interrupt service routine's function is to disable the thyristor trigger signal, cut off the three-phase power supply, and issue an alarm signal. 7. Main Program Flowchart The main program flowchart is shown in Figure 3. After receiving the start command, the system performs a soft start on the motor according to the pre-set program. After startup, it enters the closed-loop automatic adjustment state of the power factor. When a stop command is received, the trigger pulse is disabled, thereby cutting off the three-phase power supply and stopping the motor. [align=center]Figure 3 Main Program Flowchart[/align] 8 Simplified Hardware Diagram The simplified hardware diagram is shown in Figure 4. Since the 8098 chip has no internal program memory, an external EPROM must be used, and pin EA must be grounded. This paper uses a 27128 chip with an address space of 2000H-5FFFH. To convert the wide pulse trigger signal output by HSO into a pulse train, the PWM output within the 8098 chip is used. To disable the output of the trigger pulse, P2.0 is used as a gating signal; when low, the output is disabled. The start and stop control signals are input by P0.0 and P0.1 respectively, and are active low. Two reset functions are used: power-on and manual. 9 Conclusion In summary, the AC motor soft-start and energy-saving control method introduced in this paper is simple and easy to implement. Furthermore, with slight hardware modifications and different programs, it can be used in other applications related to AC voltage regulation. Examples include soft starting and local power factor compensation for large electric motors (using switching compensation capacitors instead of voltage regulation), and it can also be used for voltage regulation and speed control of DC motors. [align=center]Figure 4 Simplified Hardware Diagram[/align]