Low-voltage circuit breakers are important components in the low-voltage power distribution system for the same segment control and protection. At present, foreign low-voltage circuit breakers are developing in the direction of high performance, miniaturization, intelligence and modularization, and are connected to the field bus system to achieve network. Some domestic manufacturers have also developed international type of circuit breaker controllers. The main disadvantage is that large-scale integrated devices are used, so the volume is large and easy to enter interference.
This paper describes the design of a new intelligent low voltage circuit breaker controller. The main features are: a focus on modular design, using large-scale integrated devices. Not only shortens the product development cycle, improves the product performance, but also reduces the product volume and reduces the cost; b increases the early warning function while implementing the basic protection function; c is the parameter measurement, except for the conventional parameters such as current and voltage. , increased power factor and power measurement, etc., and display parameters; d pay attention to product reliability design; e circuit breaker with communication interface, introduce CAN field bus technology.
2. Design of support low voltage circuit breaker controller
2.1 Introduction to the overall plan
The circuit breaker controller mainly includes a microprocessor, a signal acquisition circuit, a keyboard and a real circuit, an external expansion memory, a temperature detection circuit, an output execution circuit, and a power supply.
2.2 Microprocessor selection
The intelligent circuit breaker controller needs to realize various functions and better real-time and electromagnetic compatibility. In this issue, Dallas DS80C390 microprocessor is designed. Its main features are: backward compatible with 80C52, using 80C51 instruction set; high-speed architecture, only 4 clock cycles per machine cycle, maximum system clock frequency up to 40Mhz, compatible with 80C52 storage mode, containing 4KB of SRAM, Externally expands 4MB of program memory and 4MB of user data memory. It contains two CAN2.0B control ports with high integration.
The DS80C390 has two serial ports, three timer/counters, seven additional interrupts, one programmable dog timer, six 8-bit/O ports (two of which are interfaced to the memory), and a data pointer OPRT1. . The DS80C390 is available in two package styles: 68-pin PLCC and 64-pin LQFP. This design uses the former.
2.3 signal acquisition circuit
The design of the conventional signal input channel is generally filtered first in isolation, then A/D conversion, etc., but the design method is difficult to meet the real-time requirements. This design requires the acquisition of 3 route voltages and 4 phase current signals, and the range of signals to be collected is very wide. If a conventional design requires a lot of A/D conversion channels, the electronic device using Cirrus Logic is the energy meter chip CS5460. To design the signal input channel.
(1) Features of the CS5460. a high integration. The internal inherits a programmable gain amplifier, a voltage channel with a fixed gain amplifier, two optional high-pass filters, etc. b high precision. Conversion accuracy can reach 0.1%; c easy interface. The CS5460 is a high-speed A/D device. By default, the instantaneous A/D conversion frequency can reach 4 kHz. Its self-contained programmable gain amplifier can measure signals of 150mV and 30mV in two cities, which solves the problems of real-time, wide measurement range and low measurement accuracy.
(2) Hardware design of CS5460. The voltage and current mutual inductance secondary side induced voltage values ​​are divided and sent to the UIN+, UIN--, and IIN+, IIN- pins of the CS5460. The CS5460 has four serial ports: SDI is the serial data input port, SDO is the serial data output port, SCLK is the serial clock, and CS is the chip select control line. Because we want to collect 4 currents and 3 voltage values, we chose 4 CS5460 chips. Each pin CS5460 is strobed in turn with pins p4.0, p4.1, p4.2, and p4.3. When CS=1, SOD is in a high-impedance state, so the pins of the four CS5460s can be directly connected together. The DS80C390's I/O port can drive 4 gates, so the SDI and SCLK pins of the four CS5460s are directly connected in the form of a line.
(3) Software design of CS5460. The basic program of software design in this design is written in C51. The initialization and startup conversion of the CS5460 is done by the main program. The design requires a single point of three voltages and four currents every 1.25ms, using software timing interrupt mode. Every 1.25ms system starts an interrupt service program, completes the acquisition of the instantaneous value of each signal, and completes the acquisition of the effective value of each signal every 2s.
The DS80C390 interfaces to the CS5460 through SDI, SDO, SCLK, and CS signal lines. Use the write operation to set the internal registers of the CS5460; use the read operation to read the values ​​of the status registers and output result registers inside the CS5460.
2.4 External memory circuit
The traditional single-chip application system is generally composed of a microprocessor and a necessary chip. However, when a large number of additional chips are required, the resulting system structure will be complicated and difficult to update or modify. Therefore, this design uses the PSD934F2 chip.
(1) The main features of PSD934F2. The PSD934F2 chip introduced by WSI in the United States is specially designed for 8-bit microprocessors, which integrates multiple peripheral chips into one chip. Its main features are: easy to use multiplexed and non-multiplexed 8-bit microprocessor interface; built-in 2MB main FLASH memory and 256KB second FLASH memory; 64KB SRAM; 19 output general PLD (GPLD There is a decoding PLD (DPLD); there are 27 individually configurable I/O pins; the wait current can be reduced to 50μA; the JTAG-compliant serial port can be programmed into the whole chip; FLASH memory The number of erasing and erasing can be at least 100,000 times, and the number of erasing and writing of PLD can be at least 1,000 times.
(2) The hardware circuit of PSD934F2 and DS80C390. The system requires 256KB of FLASH, 125±8KB of SRAM and 16KB of auxiliary FLASH, as well as 31 I/O outputs and some peripheral chip select outputs, so the system also expands a 128KB SRAM. In this design, the DS80C390 operates in 22-bit continuous leaf addressing mode and is configured for 8-bit data/address multiplexing. The program strobe enable signal PSEN is used to access the program memory of the PSD934F2, and the data memory is accessed by WR and RD. The 27 I/O pins of the PSD934F2 are divided into 4 ports (PA, PB, PC, and PD), each of which can be individually configured for different functions.
(3) Software development of PSD934F2. PSD934F2 is supported by PSDsoft software. The system design does not require hardware description language (HDL) to define the pin function of the PSD934F2 and allocate memory addresses. The PSD934F2 supports the Flashl ink device programmer to program the PSD934F2. First, PSDsoft software is used to define the pin function of PSD934F2 and allocate the memory address, and then PSDsoft will combine the PSD934F2 configuration with the user HEX file to generate the target file. The HEX file is compiled and linked by the PSD-implanted application written in a high-level language, and then the target is written into the PSD934F2 through the FLASH1 ink.
2.5 Temperature detection circuit
The conventional temperature detecting circuit uses a temperature sensitive component such as a thermistor. Although the cost of the thermistor is low, a subsequent signal processing circuit is required, and the calibration of the measuring channel is troublesome, and the accuracy of the temperature measurement is relatively low. Therefore, this design uses the digital temperature sensor DS1620 produced by Dallas.
(1) Features of the DS1620. The digital temperature sensor DS1620 is a new temperature-sensitive device from Dallas. He outputs the temperature measurement value in digital quantity, which has the characteristics of wide measuring range, long transmission distance, reliability and stability. The DS1620 has a measurement range of -55 to 125 ° C and a resolution of 0.5 ° C. The temperature is output in 9 digits, and the value of the measured temperature can be converted in 1 second. It can work independently or be connected to the PC or MCU in serial mode.
(2) Software and hardware design of DS1620. The DS1620 controls the number of pulses of the low temperature coefficient oscillator through a high temperature coefficient oscillator to achieve a digital output of the measured temperature. The temperature counter and register are preset to a reference value of -55 ° C. If the temperature register and technology are 0 before the end of the pulse period, the temperature register is incremented to the measured temperature value.
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