I. Introduction Since the birth of the world's first IC in 1959, microelectronics technology has developed rapidly. Integrated circuits, printed circuit boards (PCBs), and programmable logic controllers (PLCs) have been increasingly applied to intelligent instruments and automated control. Integrated circuits (ICs) are characterized by a wide variety of system chips, large size, long design cycles, and high costs. The overlapping and intersecting wiring between components on printed circuit boards (PCBs) not only complicates the manufacturing process but also increases the distributed capacitance of electrical connections, increasing the load on upstream circuits and raising system interference. Furthermore, the multiple solder points and double-sided wiring holes on PCBs reduce system reliability. In contrast, programmable logic controllers (PLCs), based on microprocessors and integrating computer and communication technologies, are a new type of general-purpose automatic control device. They offer advantages such as simple structure, superior performance, high reliability, flexibility, ease of programming, and convenient use. In recent years, they have been widely used in industrial automatic control, mechatronics, and the transformation of traditional industries. PLC control of emergency generator sets offers numerous advantages. Primarily software-controlled, it eliminates the need for hardware development, requires minimal external circuitry, and significantly improves system reliability and anti-interference capabilities. Its simple and easy-to-use programmable functionality allows for changes to system control requirements without altering external hardware wiring, greatly enhancing system flexibility. II. Main Design Functions Offshore drilling platforms typically have a separate power station. If the main station experiences a sudden power outage during production, the lack of a backup power source could lead to accidents. In emergency situations, the emergency power station should be capable of supplying power to at least the following equipment: 1. Radio communication and navigation signaling equipment. 2. Lighting in critical areas, such as escape routes, control rooms, and radio rooms. 3. Fire and toxic gas alarm devices. 4. Wellhead blowout preventers. 5. Emergency fire pumps and bilge pumps. The prime mover of an emergency power station generally uses a diesel engine with an independent cooling and fuel supply system, and is equipped with an automatic starting device to ensure startup within 0-45 seconds after the main station loses power. The emergency power grid is usually part of the main power grid. Under normal circumstances, these electrical devices are powered by the main distribution board, but are powered by the emergency generator set in emergency situations. Therefore, there is an electrical interlock between the main switch of the emergency generator on the emergency distribution board and the switch that supplies power to the emergency distribution board from the main switch to ensure safety. The power distribution system of the Shengli No. 7 platform is shown in Figure 1: Under normal power supply conditions, K13 closes to allow the emergency load and emergency lighting circuits to operate normally as part of the normal circuit. Under normal power failure conditions, KT1-KT4 and K13 trip, and after the emergency generator EG starts, KE closes to supply power to the emergency load and emergency lighting. As an emergency power source for the platform, the emergency generator set should meet the following basic requirements: 1. Automatic start-up: When a fault occurs in the normal power supply (power outage), the unit can automatically start, automatically increase speed, and automatically close the circuit to supply power to the emergency load. 2. Automatic Shutdown: When normal power supply is restored and the system is deemed normal, the system controls the switching switch to automatically switch from emergency power to normal power, then controls the unit to slow down to idle speed and shuts down. 3. Automatic Protection: During operation, if the unit experiences low oil pressure (less than 0.3 MPa), high cooling water temperature (greater than 95 degrees Celsius), or abnormal voltage, it will shut down immediately and issue an audible and visual alarm. If high water temperature (greater than 90 degrees Celsius) or high oil temperature occurs, an audible and visual alarm will be issued to alert maintenance personnel for intervention. 4. Three-Start Function: The unit has a three-start function. If the first start fails, it will attempt to start again after a 10-second delay. If the second start fails, it will attempt to start a third time after a delay. If any one of the three starts is successful, the system will continue running according to the pre-set program. If all three starts fail, it is considered a startup failure and an audible and visual alarm will be issued (it can also simultaneously control the start of another unit). 5. Automatic Maintenance of Pre-Start Status: The unit can automatically maintain a pre-start status. At this time, the unit's automatic periodic pre-fuel supply system, automatic oil and water heating system, and automatic battery charging device are put into operation. 6. It has both manual and automatic operation modes. [b]III. Hardware Design of Control System[/b] The emergency power supply of offshore oil equipment built in my country mostly uses 135 series diesel engine units. The following is an example of using PLC to control the automatic start of the diesel engine. The circuit design is shown in Figure 2: 2. Circuit Analysis and Design Description: The control panel has a "manual/automatic" selection knob, a "stop/idle/rated speed" selection knob, and "start", "close", and "open" buttons. Motor A drives the cam switch ZK to rotate in 3 positions A, B, and C, which correspond to the 3 positions of stop/idle/rated speed, that is, the 3 positions of the throttle. The speed relay, voltage detection, water temperature, and oil pressure are all external switch signals. Original state: The diesel engine throttle lever control motor is in the "stop" state, cam switch A is closed, and B and C are both open. One-time start-up process: After a normal power failure, a 5-second confirmation period is completed. The throttle controller activates, and motor A rotates forward, pulling the throttle to the "low speed" position. Simultaneously, cam switch ZK activates, disconnecting A and closing B. Motor B starts for 4 seconds. If the diesel engine ignites and runs, the sensor activates when the speed reaches 600-700 RPM. Motor A activates again, pulling the throttle to "full speed." At this point, cams B and A disconnect, while C closes, and the generator starts generating electricity. After the voltage returns to normal, the main switch KE is closed to supply power to the load. Three-time start-up process: If the first start-up fails, the speed relay remains in its original position. The PLC's internal timer controls the restart, with a 10-second cycle. The three start-ups take approximately 30 seconds. An alarm is output after 32 seconds. Start-up failure and diesel generator shutdown: After a start-up failure, the system processes for 50 seconds. Motor A reverses, pulling the throttle back to the "stop" position. When normal power is restored, motor A reverses again, pulling the throttle back to the "stop" position, and the diesel engine shuts down due to lack of fuel. 3. Select PLC Model Based on Required Input/Output Points: According to the control requirements of the automated unit, the required PLC has 14 input points and 6 output points. The system's control quantities are primarily switching quantities; only voltage and speed are analog quantities. To reduce costs, analog quantities can be converted to switching quantities using detection circuits. For example, voltage monitoring can be replaced by a voltage protector. Therefore, a PLC without analog inputs can be selected. This system uses the Siemens S7-200 small programmable controller, which is highly reliable, compact, and has 14 input points and 10 output points. The power supply, input, and output voltages are all 24VDC. 4. Allocate PLC Inputs and Outputs: Based on the control requirements and electrical schematic of the automated unit, the PLC input and output signal allocation table is shown in Table 1. [b]IV. Conclusion[/b] The automated diesel generator set controlled by PLC has simple hardware, good technical and economic indicators, and high reliability after use in different units. With slight program modifications, it can meet different user control requirements. References: 1. *Marine Oil & Gas Electrical* 2. *Jiahua PLC User Manual* 3. *Siemens PLC User Manual* 4. *PLC Programming Manual*