Abstract: This paper takes the turbine governor independently developed by Chengdu Bayer Electric Equipment Co., Ltd., based on B&R PCC as the control core, as an example. It discusses how to realize the various functions of the governor through PCC technology, as well as its differences and advantages compared with traditional governors, from the perspectives of the governor's principle, hardware configuration and software structure.
Keywords: Programmable computer controller, turbine governor, frequency measurement, stepper motor drive
Abstract: The article takes the new generation of hydraulic turbine governo which based on PCC (programmable computer controller) and developed by ChengDu BaiEr electric power device limited corporation as example, with discribing the principle, hardware configuration and software structure of the hydraulic turbine governo, discussed how to carry out its functions with PCC, discussed its differences and advantages comparing to the traditional hydraulic turbine governo.
Key Words: programmable computer controller; hydraulic turbine governo; frequency measure; Stepping motor driver
1. Technical characteristics of programmable computer controllers (PCCs) [2]
Since the 1990s, Programmable Computer Controller (PCC) technology has entered my country's control field and has been increasingly widely applied in many industrial technology areas. With the widespread use of PCC in speed governors and excitation systems by some important domestic hydropower auxiliary equipment companies, its performance has gained increasing favor from manufacturers and recognition from users. PCC technology has gradually set off a trend of technological innovation.
The PCC (Programmable Computer Controller) was first proposed by B&R AG of Austria in 1994. It combines the advantages of traditional Programmable Logic Controllers (PLCs) and Industrial Control Computers (IPCs), possessing both the high reliability and scalability of PLCs and the powerful computing capabilities and real-time performance of IPCs. Therefore, it represents a new direction in PLC technology development. The use of PCCs as the core hardware control system is gradually becoming a new trend in the field of industrial automation control.
Compared with traditional PLCs, PCCs have the following significant advantages:
1) Qualitative Time-Sharing Multitasking Operating System: PCC borrows the concept of time-sharing multitasking operating systems from mainframe computers. Applications can be configured into different tasks and task levels according to different process functions and priorities, and the cycle time of tasks can be set as required. Higher priority tasks can have relatively shorter scan cycles. This makes the software structure more reasonable and scientific, while ensuring that the system has higher and more deterministic real-time performance.
2) Fast System Response Speed: The system's response speed is determined not only by the CPU but also by the I/O data transfer speed. The PCC's main CPU is extremely fast, and it also utilizes the architecture of a mainframe computer, employing a dedicated I/O Processor to handle I/O data transfer; a DPR Controller is used for network and system management. In other words, a PCC module has three processors that are both independent and interconnected, maximizing the overall system speed.
3) Fast frequency and phase measurement response: Traditional PLC stepper speed controllers still use microcontrollers or digital circuits for their frequency measurement units, resulting in low response frequencies and poor product consistency and reliability. However, by directly using a PCC for frequency measurement, no additional frequency measurement hardware is needed, thus ensuring very high reliability. This is because the PCC's main CPU contains an independent Time Processing Unit (TPU), capable of processing pulse signals up to 4MHz to 6MHz. Therefore, it cleverly solves the frequency and phase measurement problems of the speed controller, achieving rapid, automatic, quasi-synchronous grid connection. This is a function that traditional PLC-based speed controller solutions are inherently limited by and cannot achieve.
4) Advanced Programming Languages: PCC not only fully supports various languages specified in IEC 61131-1, such as ladder diagrams, instruction lists, and sequential function charts, but also supports high-level languages such as Automation Basic and standard C. Furthermore, it allows for mixed programming using multiple languages within the same project. This is particularly convenient for programming complex control algorithms and technological tasks. Due to its improved readability, it also makes it very easy for users to add or remove elements from the control program as needed.
5) High Portability: Programs written for different series and models of PCCs can be directly ported to other PCC series or models without modifying the source code. This is because all B&R PCC hardware platforms are based on the same operating system kernel and use a tag-variable-based programming method. Therefore, users do not need to worry about the actual hardware I/O mapping relationships when programming, but can focus on the process algorithm itself. After completing these tasks, it is only necessary to simply map each tag name to the actual I/O channel.
6) High reliability: PCC has extremely high reliability, with a mean time between failures (MTBF) of over 500,000 hours (equivalent to 57 years). It is a maintenance-free product, which is much higher than that of general PLCs or IPCs (the best PLC hardware on the market currently has an MTBF of 300,000 hours).
7) Integrated Software Development Environment: PCC's software configuration development environment uses the AUTOMATION STUDIO tool, adhering to the integrated automation concept of solving the entire automation project with a single software tool. This software integrates a wealth of functions, including touch screen configuration, PLC programming and debugging, servo drive programming and control, and offline and online simulation debugging. This greatly improves project development efficiency.
2. Principle and structure of PCC speed controller [3]
2.1 Basic Principles of the Regulation System
The PCC stepper turbine governor is a turbine governor that uses a programmable computer controller (PCC) and a stepper motor as its control core, and is equipped with a stepper hydraulic servo system. This governor device boasts a series of advantages, including novel hardware, simple structure, superior performance, high reliability, and low maintenance. It is a new generation product designed and developed by summarizing the latest technologies of domestic and international governors and the characteristics of modern hydraulic control technology. Its main functions are:
1) Control signals such as unit speed and load setpoint are converted into hydraulic signals to control the turbine's guide vane servo. The guide vane servo is connected to the turbine's control loop, thereby operating the guide vanes. This ensures that the turbine-generator unit's speed remains within the allowable deviation of the rated speed to meet the power grid's frequency quality requirements.
2) To achieve single-unit regulation and control of turbine speed to adapt to the increase or decrease of power grid load.
3) Enable the unit to perform normal automatic or manual start-up, no-load, load, and automatic shutdown according to the prescribed operating procedures. It should also be able to accept various fault signals and perform necessary unit protection operations up to an emergency shutdown to ensure the safe operation of the unit.
4) When the hydro-generator units are running in parallel in the power system, the governor can automatically undertake the predetermined load distribution, so that each unit can achieve economical operation. (See Figure 2.1-1 Governor principle block diagram [1])
Figure 2.1-1 Block diagram of speed controller principle
2.2 Hardware Configuration of the PCC Governor This turbine governor uses the B&R 2003 series programmable computer controller CP474 from B&R GmbH, Austria, as its hardware core. It is equipped with a power supply system, signal processing module, human-machine interface, relay displacement sensor, stepper motor driver, and relay operating circuit, forming a high-performance, highly reliable, and easy-to-operate electrical control system for the turbine governor. The main modules of the PCC controller include: CPU module, high-speed pulse input/output module, and hybrid module (switching and analog output/input). All components are mounted on a vertical mounting plate, making installation, debugging, and maintenance very convenient. Its system structure is shown in Figure 3.2-1.
The turbine governor mainly consists of an automatic-electric manual dual-channel system, enabling full automatic control. In case of a unit speed signal failure or PCC controller malfunction, it can automatically switch to pure mechanical manual control. In addition to automatic control, the guide vanes can also be controlled via the electric manual control unit. During automatic-manual switching, it can automatically track the guide vane opening. (See Figure 2.2-1 Electrical System Structure Diagram)
Figure 2.2-1 Electrical System Structure Diagram 2.2.1 Main PCC Modules Used in the System The PCC hardware system structure of this system includes: mounting rails, module base plate, CPU module, various I/O modules, communication module, LCD touch screen HMI, and other accessories. 1) CPU Module CP474 The CPU is installed at the far left of the base plate. The module has one RS232 and one CAN interface, status indicator lights, and four screw-in module slots. When expansion is needed, the screw-in modules are inserted into the slots and secured with screws. The screw-in modules can be analog or digital modules, or communication expansion modules. 2) High-Speed Counter Module DI135 The DI135 digital input module is a screw-in module suitable for the 2003 series PCC and PP41. It can perform the following tasks: TPU function, high-speed digital signal counting, gate measurement, frequency measurement, event counting, incremental encoder operation, µs-level input response, and local counter status monitoring with direct output control. 3) CM211 I/O Hybrid Module: A general-purpose input/output module with 8 digital inputs, 8 digital outputs, 2 analog inputs, 2 modular outputs, and special functions. 4) DO135 High-Speed Digital Output Module: The DO135 is a 4-channel output module. The operation type of each output can be individually set. Possible operation types include: output channel on/off switching, pulse width modulation (PWM), and TPU operation. 2.2.2 Power Supply System: The system uses two sets of high-power industrial-grade switching power supplies to convert the plant's 220V AC and 220V DC power supplies into 24V DC power supplies for the turbine regulator. This greatly improves the reliability of the power supply system. During normal operation, one power supply is the primary power supply, and the other is a hot standby. If either switching power supply fails, it will automatically and seamlessly switch to the other normal power supply without affecting the normal operation of the speed regulator. Voltage fluctuation range: 220V AC±20% (50Hz single phase) or 220V DC (180-260V). 2.2.3 Frequency Shaping Module (PT Signal) Two voltage transformer (PT) signals from the generating unit and one power grid PT signal are directly input to the frequency shaping module in the electrical cabinet. After passing through a signal isolation transformer, the signal is sent to the shaping circuit. After filtering and shaping, it is processed into a square wave signal with an amplitude of 24V and a frequency related to the actual frequency of the generating unit, and then sent to the PCC's high-speed pulse input module DI135. The PT signal amplitude range is 0.3V-180V, and the linear frequency range is 10-100Hz. The frequency measurement module is constructed using high-quality, low-power large-scale integrated circuits, and a channel redundancy structure ensures high reliability. 2.2.4 Human Machine Interface (HMI) The Human Machine Interface (HMI) uses an industrial color LCD touchscreen. The industrial touchscreen, equipped with a color LCD display, exchanges information with the PCC main controller via RS232. It offers a large information capacity and convenient operation. Through the HMI, users can display and modify various parameters and display fault information online. 2.2.5 The stepper motor lead screw displacement sensor uses a linear potentiometer with a working stroke of ±7.5mm. 2.2.6 The stepper motor driver employs excellent design and hybrid circuit technology, resulting in a compact structure and low noise; it uses a variable speed drive method, providing precise control without vibration and stable operation. 2.2.7 A DC24V relay operation circuit is set up to indicate manual/automatic, emergency stop/reset, and other signals, to complete manual/automatic, emergency stop/reset, and other operations, and to send relevant contact signals to the power station monitoring system. 3. Software Structure of the PCC Speed Controller Based on their functions and priorities, the PCC speed controller software is divided into several modules, including a frequency measurement program, a stepper motor driver program, an arithmetic program, a main control program, an alarm program, a communication function program, and a human-machine interface program. These modules are both independent and interconnected, and are uniformly scheduled by the main control program on a time-sharing multi-tasking operating system platform to complete the controller's various operations, control, display, and alarm functions. This program structure fully leverages the advantages of the PCC time-sharing multi-tasking operating system and optimizes the speed controller program. The main control program flowchart of this system is shown in Figure 4-1. Figure 3-1 Flowchart of the main control program . 4. Software implementation of various functions of the speed controller. 4.1 Frequency Measurement and Filtering The PCC has a counting reference frequency of up to 6 MHz, so it has higher frequency measurement accuracy than ordinary PLC. The machine frequency and network frequency signals after being shaped by the signal processing module are introduced into the TPU channels 1 and 2 of the PCC respectively. The time measurement function blocks LTXcpiC and LTXcpiD are used to measure the time between two adjacent rising edges of the machine frequency and network frequency pulse signals respectively. Then, the measured frequency can be calculated according to the calculation formula provided in the comments of the function block [4] , that is: f = f e / DifCnt f e is the internal crystal oscillator frequency of the PCC (the value is 6291667), and DifCnt is the count value between two adjacent rising edges. In addition, in order to improve the anti-interference capability of the frequency measurement circuit, we added a program segment with filtering function to this program module. The program judges and filters interference signals by comparing whether the frequency difference between two adjacent waveforms exceeds the normal frequency difference range (the difference can be set by the user). The part of the program segment of frequency measurement and filtering (taking machine frequency as an example) is as follows: 。 。 。 。 。 。 Speed1 FUB LTXcpi1() ; alias call TPU FBK Hz_real1=4000000.0/Speed0.DifCnt*Speed0.PCnt ; Calculate Hz delta1 = Hz_real1 - 50.0 ; Calculate the delta value PT1=Speed0.PRest 。 。 。 。 。 。 As shown in the program, we define the measured machine frequency as the temporary machine frequency (tempFj) and the machine frequency that actually participates in the calculation as the actual machine frequency (ActFj). The difference between the two is compared with the upper limit of the frequency difference (FilterFj_Diff). If it is within the frequency difference range, it means that the subsequent waveform is the actual machine frequency signal. Otherwise, it means that an interference signal has been encountered, and this waveform should be filtered. 4.2 Stepper Motor Drive and Control Stepper motors are high-precision digital components capable of rapid and accurate positioning, making them an excellent choice for controlling the actuators of speed controllers. Furthermore, stepper motors can form a closed-loop system with lead screw displacement sensors, allowing for zero-position correction of stepper motors that have lost steps due to frequent operation. 4.3 Calculation Program Undoubtedly, numerical calculation is the core of the PCC speed controller software. A good algorithm not only improves the speed and accuracy of calculations but also saves CPU resources. The PCC operating system provides both flexible and diverse programming languages and powerful floating-point arithmetic capabilities. Simple logic processing can still be done using ladder diagrams, but the application of high-level languages has changed the previously relatively difficult situation of writing calculation programs for PLCs. Complex calculations that previously required many ladder diagram statements can now be completed simply by defining variables and inputting formulas. In addition, while ordinary PLCs can only perform integer variable operations, PCCs can perform floating-point variable operations, greatly improving calculation accuracy. The following is an example of a calculation program: ... Fe=(Fc-F_x)/50.0 d_Yp=Kp*(Fe-Fe_1x) d_Yi=Ki*Ts*(Fe-bp*(Y_pid-Pc_1x)) d_Yd=(Kd*(Fe-2*Fe_1x+Fe_2x))/(T0+Ts)+((T0*d_Ydtem)/(T0+Ts)) Y_pid=(Y_tem+d_Yp+d_Yi)+d_Yd+Pc_1x-Pc_2x. . . . . . 5. Conclusion The new turbine governor developed by Chengdu Bayer Electric Equipment Co., Ltd., based on Programmable Computer Controller (PCC) technology, uses the 2003 series module from B&R (Austria) as its core control component. It boasts advantages such as high reliability, fast response speed, powerful computing capabilities, a user-friendly interface, and high regulation quality. All its static and dynamic indicators meet and in some aspects exceed the relevant technical requirements of the national standard GB/T9652-1997. After long-term practical application, it has demonstrated excellent stability and represents the future direction of technology development in the industry. References 1. Shen Zuyi, Turbine Regulation (3rd Edition). China Water Resources and Hydropower Press. 1998.5; 2. Qi Rong (Chief Editor), Programmable Computer Controller Principles and Applications. Northwestern Polytechnical University Press. 2002.7; 3. Nan Haipeng, PCC Control of Hydropower Generator Units. Northwestern Polytechnical University Press. 2002.9; 4. Kong Zhaonian, Proceedings of the 2004 China Hydropower Control Equipment Conference. Yellow River Conservancy Press. 2004.10.
