Marine power station is generally composed of fuel engine, generator and main distribution panel, as shown in the figure As shown in Fig. 1, each component has its own input and output signals. The traditional control method is to connect the respective input or output to the corresponding controller, and the corresponding controller can realize the control of a single equipment. If the power grid detects a large load, it will automatically generate a standby generator starting signal, and the standby engine controller will automatically start after receiving the signal, delay and After the voltage is established, the generator is connected to the power grid under the control of the automatic paralleling device. During the operation, the load is automatically adjusted by the load distribution device. If the load of the power grid is small and the load of each generator is too small after the load balance distribution, the system will automatically unload one of the original standby generators, and automatically shut down and return after the delay of running off the grid To the standby state, realize the automatic splitting of the power station.
1. Can bus and ship power station
With the development of shipping industry and the improvement of the requirements of ship power station, bus technology is gradually used in ship control technology, and distributed system has gradually become the leading role in the new design system. The controller area network (can) module is a serial interface, which can be used to communicate with other peripherals or microcontrollers. This interface / protocol is designed to allow communication in noisy environment. This paper is based on CAN bus, combined with single chip microcomputer (MCU) technology,
The power station system composed of three engines, three generators and three main distribution boards in the ship power station can realize unmanned automatic control and remote monitoring.
Can has several important characteristics: first, the bus protocol is completely open, and the related control words and registers can be directly obtained from the related can chip or MCU. As long as the relevant registers are set effectively, can bus module can communicate automatically, and MCU can directly read or write the can communication information; second, it can be used to read or write the can communication information Can is the bottom protocol, users can customize the high-level protocol on this basis; third, the bus has mature market use and reliable anti-interference characteristics. So can bus is used more and more in ship control system.
Ship power station can be divided into the following parts according to the control function:
1) Engine start and stop control
2) Voltage control and reactive power distribution control of generator
3) Signal detection and protection control of generator
4) Automatic parallel operation control of generator
5) Power management and control of generator
The above-mentioned control has corresponding sensors, signal transmitters and executive controllers. The system uses a single-chip microcomputer with CAN bus to realize each link or component. The system structure is shown in Figure 2. The system is divided into three layers, and the highest layer is a power management controller (PMU) of power grid, Detect the power consumption of the power grid, and send start or stop signals or load increase and decrease signals to the corresponding controller of the middle layer according to the situation. The middle layer is the controller required by each generator. According to the needs, it can adjust and control the respective power signals, such as voltage or current. The lowest level is the sensor and actuator layer, which is composed of one or more sensors or actuators In order to ensure the reliability of the system, each unit is equipped with dual can interfaces. The whole network forms two can networks, namely can In theory, any controller can control any sensor or actuator, which can realize the redundant control of the controller. In fact, the controller of the corresponding function of three generators is made into mutual redundancy, and the controllers of different properties do not do redundancy, but the controller of the highest level is not redundant（ PMU) has the function of middle and all controllers, which can realize down redundant control.
Switch input transmitter
1. Detect some basic signals of fuel engine and convert them into can bus interface signals. These basic signals include: cooling water pressure, lubricating oil temperature, oil pan oil level, engine standby state, engine automatic control position, fuel pressure, starting air pressure, etc;
2 is the network bus of the whole system communication. The diagram shows one bus. In fact, in order to ensure the reliability of the system, two bus modes are used. Each unit has two bus interfaces to realize dual bus redundancy;
Start stop output actuator
3 is the relay output with can interface to control the start, stop and emergency stop solenoid valve of the engine;
Engine start stop and protection controller
4 is the control core to control the engine running or stopping. On the one hand, it receives the signals such as the control button, on the other hand, it receives the signals from can bus, and controls the engine according to these command signals;
Add subtract output actuator
5 is a relay output controller with CAN bus and local manual output. Its function is to control the input of the governor in the engine to adjust the speed or load;
According to the start or stop solenoid valve control operation, according to the governor to adjust the operating speed or output power;
Analog input transmitter such as speed
7 is a sensor which can detect engine speed, cooling water temperature, oil pressure, exhaust temperature and other important parameters, and convert the signal into can bus interface signal;
Power management controller of power station
8 is the dispatching control unit of the whole control system, which can detect the state of the power grid and each engine, realize the automatic control of frequency modulation and load regulation, or realize the automatic starting, or control the automatic unloading and splitting;
Pressure regulating actuator
9 is a phase compound excitation automatic voltage regulator with CAN bus control. According to the command from can bus or the signal of self-contained adjusting knob, the trigger angle of the bypass thyristor is adjusted to realize the voltage regulation control of the engine;
According to the voltage and current signals of the generator, the automatic voltage regulator and reactive power controller 11 adjusts its output to unit 9 to achieve constant voltage and balanced reactive power distribution;
Voltage and current signal input transmitter
12 is to detect the output voltage and current signals of the generator as well as the phase difference between them, calculate the power value, reactive power value, power factor value, etc., and convert them into digital signals, which can be provided to other required links through the can interface;
Main switch protection controller
Its input signal is provided by link 12. The state signal of main switch and distribution panel is used as auxiliary signal input, which controls the breaking control of main switch;
Input transmitter such as button on screen
14 is to convert all operation signals such as buttons on the distribution panel into standard can interface signals and provide them to the relevant links on the can network; the main distribution panel 15 includes the main switch, relevant relay circuits, and relevant equipment to install its internal power distribution device;
Main switch parallel controller
The main switch closing / opening actuator 17 is a relay output link with can interface, which is matched with the main switch to realize energy storage, closing or opening control of the main switch;
18 is the power grid supplied by three generators of the ship power station, and all external electrical equipment is supplied by this grid.
2. MCU unit with CAN bus interface
As can be seen from Fig. 2, the relevant links of the control system need to be equipped with CAN bus interface, including sensor signal input and control output. Some signal transmission links also need to be calculated and analyzed. Basically, the unit with CAN bus needs to be equipped with a single-chip microcomputer MCU. The required signal or output control signal is collected by MCU, and the bus interface is realized by MCU and can To realize this function, MCU with CAN bus interface is selected. The system is implemented by pic30 series control chip of microchip company. The main characteristics of built-in can module are as follows:
Realize can protocol: can 1.2, can 2.0A and can 2.0B
· standard and extended data frames
The data length is 0 to 8 bytes
– programmable bit rate up to 1 MB / S
Support remote data frame
– double buffered receiver with two priority sensitive receiving message storage buffers
According to the characteristic description of MCU with can communication interface, combined with the application situation, various transmitters and actuators with dual can interface can be realized with relevant circuits. The MCU adopts dspic30f5011 and has two-way can interface. The interface circuit between MCU and can is shown in Figure 3. C1tx is the sending signal of can No.1, c1rx is the receiving signal of can No.1, c2tx is the sending signal of can No.2 bus, and c2tx is the receiving signal of can No.2 bus. The peripheral switching value can realize 48 input or output, and the maximum analog value can realize 16 input. MCU and periphery are separated by high-speed chip 6n137. Standard PCA82C250 is used for CAN bus transceiver. Its output is differential signal, which is defined as a pair of canh and canl. It is connected to the CAN bus network of the whole system by twisted pair. The parallel connection of small capacitance between canh and canl can filter out the high frequency interference on the bus and prevent certain electromagnetic radiation. In addition, a 120 ohm resistance is paralleled between the two lines of canh and canl at the terminal of CAN bus to eliminate the signal reflection.
MCU has a powerful function, 16 bit CPU, program memory up to 66K, 4K ram, 1K EEPROM, 16 × 16bit working register, maximum clock can use 10m crystal oscillator frequency doubling 16 times, so it can be used in general applications DSP core is also competent for data processing which requires fast response. Generally, it does not need to be expanded to meet the needs. The specific signal input and output can be realized by matching with appropriate peripheral interface circuit; the control function to be realized can also be realized by programming. In this system, in addition to the power station power management controller requirements are more complex, need to further enhance the system configuration, other controllers and signal interfaces or transmitters are implemented by the above circuit, transmitter or actuator with can interface as shown in Figure 3 to achieve can bus interface, the other end is equipped with The peripheral circuit corresponding to MCU can realize the input and output of different functions with CAN bus. The details are as follows:
2.1 common signal transmitter with CAN bus
The commonly used signals are divided into switch input, 0-5V, 4-20mA, thermal resistance, thermocouple, etc. among them, the switch signal input adopts the optocoupler isolated input, the analog input adopts the high-performance instrument operational amplifier, the thermal resistance, thermocouple, etc. all adopt the standard signal conditioning circuit For MCU, the input signals are standard 0-5V signals, corresponding to the maximum range of the sensor. The 16 channel analog input after signal conditioning is connected to rb0-15 of MCU to realize the sampling of the 16 channel analog input by MCU. The switch input signal transmitter can isolate the input signal and send it to the port B-G port of MCU. It can realize 48 inputs at most. There is no need for other circuits except optocoupler isolation circuit.
2.2 coded signal transmitter with CAN bus
The orthogonal pulse code input has two-phase input with a and B orthogonal, that is, the phase difference is 90 degrees, and the final frequency can reach 20kHz. Due to the high frequency, photoelectric isolation should adopt high-speed optocoupler for sampling. The signal capture interface rd8-11 of MCU can be used to realize two groups of four orthogonal pulse code input. Configuring the corresponding registers of MCU can realize the counting and positive and negative judgment of orthogonal pulse code.
2.3 power signal transmitter with CAN bus
At the same time, it is convenient to convert the required voltage and voltage into square wave in MCU. The voltage signal conditioning circuit is shown in Figure 4. The current type voltage transformer converts the sampling voltage signal into ma current signal, amplifies it into voltage signal through operational amplifier U2, and obtains the detection signal of AC voltage zero crossing square wave through U1A comparison circuit, which is used for frequency conversion and phase calculation. The rectifier circuit is composed of operational amplifier U1B and u1c, and the u1d circuit is a filter circuit 0-5V voltage signal required by MCU. Considering the limited variation range of voltage signal sampling, 1.5 times of rated voltage corresponds to the maximum input 5V of MCU, while the current signal changes greatly. Especially when the large motor is started, the current can reach 6-8 times of its rated current, and the protection and control of current also needs to be able to effectively realize 8-10 times of protection control. Therefore, the sampling of the same current is divided into three levels 2 times of rated current corresponds to 5 V input of MCU, one is 4 times of rated current corresponding to 5 V input of MCU, and the other is 10 times of rated current corresponding to 5 V input. The circuit principle is similar to that shown in Figure 4. In this way, 12 analog inputs, 3 voltage zero crossing interrupt inputs and 3 current zero crossing interrupt inputs are required for sampling the three-phase voltage and current output from a generator. According to the above signal MCU will not only get 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. at the same time, it is necessary to determine whether there are over-voltage, under voltage, long-time over-current, short-time over-current, instantaneous over-current, reverse power and other fault signals according to the rated value, so the electric quantity transmitter contains multiple Function.
2.4 actuator with CAN bus
The I / O port of MCU can be configured as output, and the corresponding I / O can be configured as output according to the needs, and then connected to the photoelectric coupling unit. The output of the relay is realized by driving the relay through the triode. The control of the actuator is that the control power is sent to the actuator through the contact of the relay to control its positive and negative operation to realize the corresponding regulation, or to control the on-off of the solenoid valve circuit. In some special occasions, the output of MCU can be coupled by photoelectricity and then driven by triode to realize the regulation and control of PWM, or the action regulation of related actuator.
3. Various controllers with CAN bus interface
The can interface of the controller with CAN bus is the same as the MCU mentioned above. In the controller, the input and output are not the main ones, but the operation ability, storage capacity, control ability, display and drive of MCU. Therefore, the MCU to be used is a high-end MCU in pic series, and its hardware circuit is similar, except for the one used in Fig. 3 In addition to the same can interface circuit, some expansion circuits with I2C are used for matching the needs, such as EEPROM, clock circuit, etc., as shown in Fig. 5. SCL and SDA are the interfaces of I2C in MCU, which are defined as clock line and data line. A0, A1 and A2 are the selection signals when the same devices are used at the same time Under the control of MCU, U3 is the clock chip DS1307, and 24C08 is the EEPROM of I2C interface. If other functions are needed, it can be extended on the original I 2C bus interface circuit. On the basis of this hardware, the information on the bus is received by can, and the corresponding software is programmed by each controller according to its required function, and the corresponding output signal is sent 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 operation controller, electric energy management controller, etc.
4. Redundancy control technology
In addition to the main power management controller In addition to PMU, the hardware circuits of other controllers designed are close to each other, and their functions are different. However, the control redundancy between them can be realized by software. Therefore, in the actual design, two sets of control programs are designed in each controller. Under normal circumstances, one set of main program is working, and the other is reading as standby of other controllers Can bus data, but the standby program does not output action. When a controller fault occurs in the system, when there is no heartbeat signal for the controller to work normally on the CAN bus network, the standby controller wakes up the standby program and outputs it to replace the faulty controller. At the same time, the corresponding display appears on the working controller. In the system design, the redundant standby relationship of each control is shown in Table 1, in which the power management controller can be used as the standby of other controllers.
In addition to the redundancy of the controller, the above-mentioned can bus uses dual can interfaces, and the actual circuit is also the corresponding dual can network. After one of the CAN buses fails, the system can automatically enable the standby can network, so as to realize the redundancy control of the CAN bus.
The control system of marine power station adopts distributed structure, standardized hardware design and modular software design, which makes the design combination of the whole system more flexible. This design method also has certain reference value for the development of other projects. The practical operation effect of the system is good and reliable, which shows that the application of CAN Bus Technology in marine power station is successful and can be popularized.
The innovation of this paper: the CAN protocol developed by Yun has been used in the field of automobile manufacturing. Now the can technology is transplanted to the control of ship power station, which realizes the unmanned operation, process automatic control and remote monitoring of ship power station, improves the degree of ship automation and improves the system performance.
Editor in charge: GT