| Electric power is the pillar of the national economy. Electric power safety has been a major issue that can not be ignored. Relay protection is one of the important means to ensure the safety of electric power. For now, the microcomputer relay protection has developed to the dominant position. Further, self-powered microcomputer protection device, which obtains power from electric line, represents the latest development result. Following the current development direction of microcomputer relay protection, a low power consumption and self-powered microcomputer protection device is designed. The power for the device can be obtained from electric line and external auxiliary power supply. Besides, backup battery is used to keep device working while power off.The device can obtain power from electric line. Input current is converted to DC voltage source by using the capacitor charging booster circuit and MOS tube discharge circuit. Then, the voltage source is converted to stable DC power. The ultra low power 16-bit microcontroller MSP430F149 is used as the main control chip to implement the protection function. The input current signal is transformed to voltage signal that can be sampled by A/D by gain variable signal conditioning circuit which consists of additive circuit and analog switch circuit. All circuits are designed follow the law of low power consumption. Effective value of fundamental current is calculated using fullwave Fourier algorithm and floating point operations are replaced by the 32-bit fixedpoint decimal operations.Each module of the device is tested. The self-power system and current protection works properly. Power consumption of the device is low and current is 2μA while device stays in sleep mode and power is provided by the backup battery. Rest modules of the device function perfect. Based on the test results, it can be concluded that the device meets the design expectations and the design goals have been completed. |
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