1 Introduction
The development of integrated automation devices for hydropower stations has mainly focused on large and medium-sized hydropower stations, while the automation level of small hydropower stations is relatively backward, with a considerable number of small hydropower stations still using traditional control methods. Simply copying the integrated automation system design of large and medium-sized hydropower stations would be too costly. This paper presents an integrated automation system designed based on the actual conditions of a hydropower station. This system has a short design and development cycle, powerful functions, reliable operation, a user-friendly interface, simple operation, and low cost.
2 System Hardware Design
2.1 Overall Design
This paper adopts a unit-based control approach, using a simple architecture and design method to integrate sequential control, speed measurement, frequency measurement, temperature monitoring, excitation control, synchronization control, power acquisition, switch power acquisition, and communication in a small hydropower station. Simultaneously, it can display and query the forebay (or reservoir) water level, sump well water level, and tailrace water level, and monitor the operating status of the unit and auxiliary equipment in real time, improving the reliability of the comprehensive automation of the small hydropower station. The core controllers are a Siemens PLC7-200 and a Texas Instruments (TI) high-performance digital signal processor (TMS320F2812), with a touchscreen as the human-machine interface. The system hardware structure is shown in Figure 1.
The PLC is the core component of the monitoring system, consisting of a Siemens S7-200 CPU226, one EM223 digital expansion module, and one EM235 analog expansion module. The CPU226 itself has 24 input points and 16 output points, with a maximum expansion capacity of 7 modules. The EM223 digital expansion module has 16 input points and 16 output points. The EM235 analog expansion module has 4 analog inputs and 1 analog output. In this system design, the PLC mainly handles the normal start-up and shutdown of the generator set, accident and emergency shutdown, and monitoring of auxiliary equipment. This PLC configuration fully meets the requirements of the automation design.
Digital signal processors (DSPs) are the core controllers for speed control, excitation control, synchronization control, integrated protection, and communication. This paper uses the fixed-point 32-bit DSP chip TMS320F2812 from Texas Instruments (TI). The chip is rich in resources, with up to 128k words of on-chip flash program memory and up to 18k bytes of single-port RAM (SARAM); two event manager modules, EVA and EVB, each including: four 16-bit general-purpose timers; 16 16-bit pulse width modulation (PWM) channels; a 12-bit 16-channel A/D converter with a minimum conversion time of 80ns per channel, which can be triggered by two 8-channel input A/D converters or one 16-channel input A/D converter; an enhanced control local area network (ECAN) module; up to 56 individually programmable or multiplexed input/output ports (GPIO); and rich peripheral interfaces including one SPI serial peripheral interface, two SCI serial communication interfaces, one UART standard universal asynchronous transceiver interface, one CAN bus interface, and one MCBSP multi-channel buffered serial interface [2], which can fully meet the requirements of system design.
The touch screen uses the MT506 touch screen, which is a 256-color 5.6" TFT four-wire resistive touch screen. It is designed specifically for PLC applications and can display the unit's data information, graphics, strings, alarm information, historical records, trend charts, etc. in real time. The touch button can generate corresponding switch signals or input values and characters to exchange data with the PLC [5].
2.2 Monitoring Principle
The TMS320F2812 DSP in this system receives control signals from the PLC, rapidly acquires generator and system voltage and current values, calculates the current, voltage, phase, and frequency using the Fast Fourier Transform algorithm, automatically adjusts the speed governor and excitation unit, quickly tracks changes in the system grid's voltage, frequency, and phase, automatically connects to the grid, and automatically loads according to unit load requirements. It also reflects the status information of speed regulation, excitation, synchronization, and protection on the PLC. The DSP development environment is Texas Instruments' DSP integrated development environment CCS (Code Composer Studio), developed by TI specifically for designing TMS320 series DSP software. It uses a Windows-style interface and integrates editing, compiling, linking, software simulation, hardware debugging, and real-time tracking functions. The program is written in C language with a well-modular structure, featuring flexibility, ease of use, good readability, and high reliability. The entire software program consists of several major modules, including self-testing, communication, excitation regulation, speed regulation, and grid connection.
The programming environment for the MT506 touchscreen is EViewMT500. The system comprises three modules: EasyLoad (upload and download), EasyWindow (online and offline simulation), and EasyBuilder. The EasyBuilder configuration software allows for convenient configuration design of the MT506 touchscreen. This system includes initial screens, power-on process screens, power-off (emergency stop) process screens, alarm screens, common parameter setting screens, input/output switch monitoring screens, operation statistics screens, password verification screens, alarm prompts, and a message board. Its user-friendly interface and prompts simplify the system operation and effectively prevent accidental operation.
3. Modular Software Design
The PLC in this system is responsible for the start-up and shutdown control of the generator set and the monitoring of auxiliary equipment. This mainly includes system initialization, automatic start-up and shutdown, emergency shutdown, and control of oil, gas, and water. These functions are implemented through programming; this paper uses ladder logic to program the PLC [1].
To standardize the program while maintaining scalability and facilitating future improvements and modifications, the PLC program design employs a modular structure. The entire program consists of an initialization module, an automatic power-on control module, an automatic power-off control module (including fault and emergency stop mechanisms), a touchscreen communication module, a remote signaling and alarm control module, and a protection module.
3.1 Initialization Module
The initialization process is completed for all used intermediate relays (m), timers (t), and data registers (d), and values are assigned to some parameters that require initial values.
3.2 Automatic power-on control module
After the unit's self-test meets the start-up conditions, when the operator issues the start-up command, the unit automatically follows the normal safe start-up procedure. The PLC sends control signals to the DSP and auxiliary equipment, the DSP starts automatic speed regulation, excitation, and quasi-synchronous grid connection, and all auxiliary equipment is put into normal working condition, completing the entire process from safe start-up to grid connection of the hydro-generator unit. The automatic start-up flowchart is shown in Figure 2.
3.3 Automatic Shutdown Control Module
When the unit is generating electricity, after the staff issues a normal shutdown order, or in the event of an emergency, the unit will be disconnected from the power system. Then, the turbine generator unit will be safely shut down in sequence, and all auxiliary equipment will be safely decommissioned from the power generation state. The automatic shutdown flowchart of the unit is shown in Figure 3.
3.4 Communication and Alarm Control Module
It handles communication between the PLC, the touch screen, and the host computer monitoring unit, processes control commands from the touch screen and the host computer monitoring unit in real time, and collects some unit operating parameters (such as unit speed, oil temperature, oil pressure, etc.) for real-time display on the touch screen and host computer monitoring software. It also provides real-time alerts for system remote signaling and telemetry alarms and immediately pops up alarm windows.
3.5 Protection Module
The system monitors the operating status of generator sets and auxiliary equipment in real time. When an abnormality occurs, it quickly reflects the information on the touch screen and the monitoring host, and simultaneously initiates an emergency shutdown to disconnect the generator set from the power grid, thereby protecting the safety of the generator set and the stability of the power grid.
4. Conclusion
This system simplifies the operation process, enabling "one-click power-on" and "one-click power-off" on both the touchscreen and the host computer. Its highly automated design is suitable for the operation and management of small hydropower stations, effectively preventing human error, improving operational safety, and enabling unmanned or minimally staffed operation.
