1. CAN bus and ship power station With the development of shipping industry and the requirements of ship power station, bus technology is gradually used in ship control technology, and distributed system has gradually become the protagonist in the new design system. The Controller Area Network (CAN) module is a serial interface that can be used to communicate with other peripherals or microcontrollers. This interface/protocol is designed to allow communication in noisy environments. This article is based on the CAN bus, combined with single-chip microcomputer (MCU) technology,
The power supply station system consisting of three engines, three generators and three main power distribution panels in the ship power station realizes automatic control without remote control and can realize remote monitoring.
CAN has several important features: First, the bus protocol is completely open, and the relevant control words and registers can be directly obtained from the relevant CAN chip or MCU. As long as the relevant registers are effectively set, the CAN bus module can automatically communicate. The MCU can directly process the CAN communication information by reading or writing; the second is that the CAN is the underlying protocol, and the user can completely carry out the user-customized high-level protocol on the basis; the third is that the bus has mature market use and reliable resistance. Interference characteristics. Therefore, the CAN bus is also increasingly used in ship control systems.
The ship power station can be divided into the following parts according to the control function:
1) Starting and stopping control of the engine
2) Generator voltage control and reactive power distribution control
3) Generator signal detection and protection control
4) Generator automatic parallel control
5) The power management of the generator controls each of the above-mentioned controls, and the signal transmitter and the execution controller are matched with it. The system implements each link or component with a single-chip microcomputer with CAN bus. The system structure is specific. As shown in Figure 2, the system is divided into three layers. The upper layer is a power management controller (PMU) of the power grid. It detects the power usage of the power grid and sends a start or stop to the corresponding controller in the middle layer according to the situation. Signal, or send load increase and decrease signal, the middle layer is the controller required by each generator, adjust and control the respective power signal, such as voltage or current, as needed, the lower layer is the sensor and actuator layer, One or several sensors or actuators form a CAN bus unit, all of which are hung on a CAN bus network. To ensure system reliability, each unit physically has a dual CAN interface, and the entire network constitutes two CAN networks, ie The CAN bus implements redundant control. In theory, any controller can control any sensor or actuator to achieve redundant control of the controller. In fact, the controllers of the three generators are made redundant, and the controllers of different natures are not redundant, but the upper level controller (PMU) has the function of the middle and all controllers. Downward redundancy control can be achieved.
The digital input transmitter 1 detects some basic signals of the fuel engine and converts them into CAN bus interface signals. These basic signals include: cooling water pressure, oil temperature, oil sump oil level, engine standby state, engine automatic Control position, fuel pressure, starting air pressure, etc.; CAN bus 2 is the network bus of the whole system communication, shown as a bus, in order to ensure the system is reliable, using two bus modes, each unit has two bus interfaces, Double bus redundancy is realized; the start and stop output actuator 3 is a relay output with a CAN interface to control the start, stop and emergency stop solenoid valves of the engine; the engine start stop and protection controller 4 is a control core for controlling the engine to run or stop. On the one hand, accept the control button and other signals, on the one hand accept the CAN bus signal, and according to these command signals to control the engine; add and subtract output actuator 5 is a CAN output relay controller with local manual output, its role Is to control the input of the governor inside the engine, to adjust the speed or load The fuel engine 6 operates according to the start or stop solenoid valve control, and adjusts the running speed or output power according to the governor; the analog input transducer 7 such as the rotational speed detects the engine speed, the cooling water temperature, the lubricating oil pressure, the exhaust temperature, and the like. Some important parameters of the sensor and the signal is converted into a signal of the CAN bus interface; the power management controller 8 of the power station is the dispatch control unit of the entire control system, detecting the state of the power grid and each engine, realizing the automatic control of the frequency modulation and load transfer, or realizing Automatic start, or control automatic unloading and unloading; pressure regulating actuator 9 is a phase compound excitation automatic voltage regulator controller with CAN bus control, adjusting its bypass thyristor according to the command from CAN bus or its own adjustment knob signal The trigger angle is used to realize the voltage regulation control of the engine; the generator 10 accepts the excitation adjustment of 9, and the prime mover 6 drives the output power to the power distribution device; the automatic voltage regulation and reactive power controller 11 according to the voltage and current signal of the generator At the same time, it is necessary to judge its reactive power and power factor values ​​to adjust its output to unit 9 to achieve constant voltage and reactive power. The voltage and current signal input transmitter 12 detects the voltage and current signals output by the generator and the phase difference between the two, and calculates the power value, reactive power value, power factor value, etc., which need to be used. And converted into digital signal through the CAN interface to provide other links needed; the main switch protection controller 13 mainly achieves the generator over current, under voltage, reverse power protection, the input signal is provided by the link 12, the main switch and power distribution The screen status signal is input as an auxiliary signal, which controls the breaking control of the main switch; the input transducer 14 such as an on-screen button converts all operating signals such as buttons on the power distribution panel into standard CAN interface signals and provides them to the CAN. The relevant part of the network is used; the main distribution panel 15 is equipped with a main switch, the relevant relay circuit, the relevant equipment is installed with its internal power distribution device; the main switch parallel vehicle controller 16 will detect the power between the generator and the grid The difference is that the generator is synchronized by the adjustment of the generator and automatically parallel; the main switch closing/opening actuator 17 is a relay output link with a CAN interface. It is matched with the main switch to realize the energy storage, closing or opening control of the main switch; the power supply bus 18 is the power supply of the three generators of the ship power station, and all external electrical equipment is powered by the power grid.
2. MCU unit with CAN bus interface
It can be seen from Figure 2 that the relevant links of the control system need to be equipped with CAN bus interface, including sensor signal input and control output. Some of the signal transmission links need to be calculated and analyzed. Basically, the units with CAN bus need to be equipped. The MCU of the single-chip microcomputer acquires the required signal or output control signal through the MCU, and realizes the bus interface by the MCU and CAN. To facilitate the realization of this function, the MCU with the CAN bus interface is selected. The system uses the control of the PIC30 series of the MICROCHIP company. The chip is implemented, and the main features of its built-in CAN module are as follows:
Implement CAN protocol: CAN 1.2, CAN 2.0A and CAN 2.0B
Standard and extended data frames
? Data length is 0 to 8 bytes
? Programmable bit rate up to 1 Mb/s
? Support remote data frames
Double buffered receiver with two prioritized receive message store buffers
According to the above description of the MCU with CAN communication interface, combined with the use of the circuit, a variety of transmitters and actuators with dual CAN interfaces can be realized. The MCU adopts dsPIC30f5011 and has two CAN interfaces. MCU and CAN interface circuit shown in Figure 3, C1Tx is the transmission signal of No. 1 CAN bus, C1Rx is the acceptance signal of No. 1 CAN bus, C2Tx is the transmission signal of No. 2 CAN bus, C2Tx is the receiving signal of No. 2 CAN bus The peripheral switch quantity can realize 48 channels of input or output, and the analog quantity can realize 16 channels of input. The MCU and the periphery are optically isolated by the high-speed chip 6N137. The CAN bus transceiver uses the standard PCA82C250, and its output is a differential signal, defined as a pair of CANH and CANL, which is connected to the CAN bus network of the whole system by twisted pair. The small parallel capacitor between CANH and CANL can filter the high frequency interference on the bus and the ability to prevent electromagnetic radiation. In addition, a 120 ohm is connected in parallel between the two lines CANH and CANL at the terminal of the CAN bus. Resistance to eliminate reflection of the signal.
MCU has powerful functions, 16-bit CPU, program memory up to 66K, 4K RAM, 1K EEPROM, 16 × 16bit working register, high clock can use 16M crystal multiplier 16 times, so the general application can adapt, due to its own The DSP core can also be used for data processing that requires fast response. Generally, it does not need to be extended to meet the needs. The specific signal input and output that needs to be realized can be realized by using a suitable peripheral interface circuit; the control function that needs to be implemented can also be realized. Programming implementation. In addition to the complex requirements of the power management controller of the power station in this system, it is necessary to further enhance the system configuration. Other controllers and signal interfaces or transmitters are implemented by the above circuit. The transmitter or actuator with CAN interface has one end. Figure 3 shows the CAN bus interface, and the other end is equipped with a peripheral circuit corresponding to the MCU, which can realize the input and output of different functions with the CAN bus. details as follows:
2.1 Common signal transmitter with CAN bus
Commonly used signals are divided into digital input, 0-5V, 4-20mA, thermal resistance, thermocouple, etc., wherein the switch signal input uses optocoupler isolation input, analog input uses high-performance instrument operational amplifier, thermal resistance, Thermocouples and the like all use standard signal conditioning circuits, so for the MCU, the input is a standard 0-5V signal, corresponding to the sensor's large range. After the signal-conditioned 16-channel analog input is connected to the RB0-15 of the MCU, the MCU can sample the 16-channel analog input. The digital input signal transmitter isolates the input signal and sends it to the PORTB-G port of the MCU. It can realize 48 inputs, and no other circuit is needed except the optocoupler isolation circuit.
2.2 Coded Signal Transmitter with CAN Bus Orthogonal pulse code input, with A and B quadrature 2-phase inputs, that is, the phase difference is 90 degrees, and the frequency is up to 20KHz. Due to the high frequency, the optical isolation should be sampled by high-speed optocoupler. The MCU signal capture interface RD8-11 can be used to realize two sets of four orthogonal pulse code inputs. The corresponding registers of the MCU can be used to realize the counting of orthogonal pulse codes. And positive and negative judgment.
2.3 Power signal transmitter with CAN bus
The sampling of the power signal needs to collect the voltage and current signals and convert them into effective values, and adjust them to the 0-5V signals required by the MCU. At the same time, the sine-square wave conversion is needed and sent to the interrupt interface of the MCU to facilitate phase calculation. The voltage signal conditioning circuit is shown in Figure 4. The current-type voltage transformer converts the sampled voltage signal into a mA current signal and is amplified into a voltage signal by the operational amplifier U2. The U1A comparison circuit obtains the detection signal of the AC voltage zero-crossing square wave for the detection signal. For frequency conversion and phase calculation, the U1B and U1C circuits form the rectifier circuit, and the U1D circuit is the filter circuit. The output is the 0-5V voltage signal required by the MCU. The voltage signal sampling takes into account the limited variation range. The 1.5 times rated voltage corresponds to the MCU's large input 5V, and the current signal changes relatively large. Especially when the large motor starts, the current can reach 6-8 times its rated current. The current protection control It is also necessary to effectively achieve 8-10 times of protection control, so the sampling of the same current is divided into three levels. One is that 2 times the rated current corresponds to 5V of the MCU answering input, and the other is 4 times the rated current corresponding to the 5V input of the MCU. The other is 10 times the rated current corresponding to the 5V input. The circuit principle is similar to that shown in Figure 4. Thus, the sampling of the three-phase voltage and current output by one generator requires 12 analog inputs, three voltage zero-crossing interrupt inputs, and three current zero-crossing interrupt inputs. According to the above signal, the MCU will not only obtain the corresponding voltage value and current value, but also calculate the phase difference, power factor, active power, reactive power, apparent power, active energy statistics, etc., and it is necessary to determine whether it has been based on the rated value. Voltage, undervoltage, long delay overcurrent, short delay overcurrent, transient overcurrent, reverse power and other fault signals, so this power transmitter contains multiple functions.
2.4 Actuator with CAN bus
The I/O port of the MCU can be configured as an output. After the corresponding I/O is configured as an output, it is connected to the optocoupler unit, and its output is then driven by a triode to drive the relay. The control of the actuator is sent to the actuator after the control power is passed through the contact of the relay, and the forward and reverse operation is controlled to achieve corresponding adjustment, or the solenoid valve circuit is controlled to be turned on and off. In some special cases, the output of the MCU can be optically coupled to the MOSFET through the triode to achieve PWM regulation control, or related actuator operation adjustment.
3. Various controllers with CAN bus interface
The CAN interface of the controller with CAN bus is the same as that of the above MCU. In the controller, the input and output are not the main ones. The main ones are the computing power, storage capacity, control capability, display driver, etc. of the MCU, so consider the MCU used as the PIC. The higher-end MCUs in the series have similar hardware circuits. Except for the CAN interface circuit shown in Figure 3, in addition, some expansion circuits with I 2 C, such as EEPROM and clock circuits, are used as shown in Figure 5. SCL, SDA is the I 2 C interface in the MCU, defined as the clock line and data line, A0, A1, A2 are the selection signals when the same device is used at the same time, controlled by the MCU, U3 is the clock chip DS1307, and For the clock source crystal, 24C08 is the I 2 C interface EEPROM. If other functions are required, it can be extended on the original I 2 C bus interface circuit. On the basis of this hardware, the information on the bus is accepted by CAN, each controller compiles the corresponding software according to its required function, and sends the corresponding output signal to the corresponding output CAN interface module through CAN. The controller is divided into engine controller, automatic voltage regulation and reactive power regulation controller, power distribution protection controller, synchronous parallel vehicle controller, and power management controller according to specific positions and functions.
4. Redundant control technology In addition to the main power management controller PMU, the hardware circuits of several other controllers designed are close to each other, and the functions are different, but the control redundancy can be realized by software, so in the actual design, each The controller is designed into two sets of control programs. Under normal circumstances, one set of its own main program is working, and the other set is used as a backup for other controllers to read data on the CAN bus, but the standby program does not perform output actions. When a controller failure occurs in the system, the heartbeat signal of the controller does not work normally on the CAN bus network, and its standby controller wakes up its standby program and outputs it to replace the faulty controller. A corresponding display appears on the working controller. The relationship between each control redundancy and standby in the system design is shown in Table 1, where the power management controller can be used as a backup for other controllers.
In addition to the redundancy provided by the controller, the aforementioned CAN bus uses a dual CAN interface, and the actual line is also a corresponding dual CAN network. After one CAN bus fails, the system can automatically enable the standby CAN network to realize the redundancy of the CAN bus. control.
5. Conclusion The ship power station control system adopts distributed structure, hardware design standardization and software design modularization, which makes the whole system design combination more flexible. This design method also has certain reference value for the development of other projects. The actual operation of the system is good and the work is reliable. It shows that the use of CAN bus technology in the ship power station is successful and can be promoted.
The innovation of this paper: The CAN protocol developed by the company was applied to the field of automobile manufacturing. Now the CAN technology is transplanted to the control of the ship power station, and the unmanned operation, automatic process control and remote monitoring of the ship power station are realized, and the degree of ship automation is improved. , improved system performance.
(This article is from the world of electronic engineering: http://)
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The control valve function as follow:
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(5) negative flow control, give the main pump a negative flow signal, so that the stem in the middle, the main pump displacement to the minimum.
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(7) the electric sensor can be configured to meet the needs of electronic control.
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