1. Introduction
Given the enormous market potential and significant energy-saving benefits, achieving rapid development, cost reduction, increased reliability, and large-scale automated production of power electronic products is of great practical importance. However, the power electronics industry is currently both labor-intensive and technology-intensive, a characteristic that severely hinders the realization of these goals. Many scholars predict that the only way to achieve this goal is through power electronic system integration, standardization, and modularization. Power electronic system integration is a novel research topic. In 1995, the U.S. Navy first proposed the concept of Power Electronic Blocks (PEBBs) for ship propulsion electrification. In 1998, the U.S. government approved funding from the National Science Foundation to establish the Center for Power Electronic Systems (CPES), dedicated to system integration research. In January 2003, the National Natural Science Foundation of China officially approved the key project "Research on Basic Theory and Several Key Technologies of Power Electronic System Integration," marking the official launch of power electronic integration technology research in my country. Power electronic system integration is a long-term, complex, and arduous research task that requires phased and hierarchical approaches. At present, system integration research mainly focuses on the following directions {7-10]: (1) power device integration; (2) passive component integration; (3) circuit topology optimization suitable for power electronic system integration; (4) packaging and thermal technology; (5) sensor integration; (6) communication integration. The above research mainly focuses on power electronic power circuits and is the foundation of power electronic system integration. The content involving power circuit integration can be called power level integration. Closely related to power level integration is system control integration. Although digital control technology has been widely used in high-power application systems or complex power electronic devices, research on control integration of power electronic systems is not common, especially research on digital control integration. However, digital control has many advantages such as high reliability, strong computing power and good versatility. It has shown unparalleled superiority of analog controllers in medium and high power applications. At the same time, in small and medium power applications, digital power supply is also an important trend in the future development of power supply. Therefore, the study of power electronic digital control integration has important practical significance. The power electronic digital control platform was proposed in the context of system integration. It is not only a continuation and improvement of the previous stage of system integration, but also the basic content required for the next stage of system integration.
2. Basic Types of Digital Controllers and Their Control Chips
The emergence and development of embedded digital control systems are inseparable from the development of microelectronics technology, directly leading to the diversity of controller implementation methods. Currently, based on the control execution method, they can be broadly divided into three types: (1) sequential execution control method;
(2) Parallel execution control mode; (3) Hybrid mode.
Due to the advantages of DSP architecture, most current power electronic digital controllers based on sequential control are designed with DSP as the core. Parallel execution controllers offer excellent real-time performance, making them particularly suitable for handling fast-process control systems. In the field of high-frequency DC-DC digital control, these controllers have become a research hotspot and focus. Hybrid approaches combine the advantages of both.
Given the advantages of DSPs, many researchers have adopted DSP controllers to develop corresponding power electronics application systems. The most typical example is the ezDSP development board provided by TI, as shown in the figure:
Figure 1 Single-chip motion control DSP controller
The advantages of hardware parallelism in CPLD/FPGA (Fieldprogrammable Gate Array) devices are gradually being accepted and valued by power electronics workers and researchers. General DSP processors struggle to meet their control requirements; although they may be able to achieve this, they spend most of their time on the core algorithm, neglecting other functionalities and thus wasting a significant portion of the DSP's hardware and software resources. For this reason, implementing PFC control using an FPGA and employing digital charge control methods to achieve simpler and faster control of the current loop is more convenient.
Figure 2. FPGA-based servo controller
3. Current Status of Power Electronics Software System Design
With the widespread application of digital control in power electronic systems, some digital control chip manufacturers have established various types of software packages to accelerate the user development process. At the same time, some rapid prototyping companies such as dSPACE and RTLAB have collaborated with Matlab to develop graphical control software implementation methods.
3.1 Structured Programming Method
Structured programming is the most mature and widely used design method among the three software implementation methods. It is used to write corresponding control software according to specific topology and control requirements. In the early stages of power electronic digital control applications, in order to improve code efficiency, save hardware resources, and reduce the software's runtime in each control cycle, control software was often implemented using assembly language.
As the performance of digital processors continues to improve, various DSP manufacturers have launched high-efficiency C language compilers to meet the real-time requirements of control systems.
In order to make the program more readable and maintainable, many software engineers have started to write power electronic control software in C language. Its programming advantages are: (1) the software is universal and has good portability; (2) the program is readable and easier to maintain; (3) software engineers do not need to master assembly language for different processors.
3.2 Embedded Design Method
A real-time operating system (RTOS) acts as a bridge between system software and hardware. Applications only need to control hardware devices through the operating system and do not have a direct relationship with the hardware system itself. Software developers can focus on developing core control software based on the ROS, reducing software development time and thus improving system development efficiency.
Figure 3 Hierarchical structure of uCOS-based control software
4. Structure of the Power Electronic Digital Control Platform
4.1 DSP Minimum System
Common power electronic control platforms typically use motion control-specific DSPs as processors. Apart from input/output buffer circuits, analog conditioning circuits, and communication interface circuits, these systems have no other peripheral circuits. Since the DSP itself integrates some basic components required for power electronics and motor drives, the entire circuit structure is very simple.
4.2 Control Platform Based on General-Purpose DSP and FPGA
To address some of the shortcomings of DSP minimum systems, many scholars and companies have dedicated themselves to developing digital control platforms with powerful computing capabilities and good scalability. A common feature of these platforms is the use of floating-point DSPs. However, this significantly reduces the integration of hardware resources across the platform. Currently, no floating-point DSP integrates the basic hardware circuits required for power electronics, yet these functional circuits are essential for controlling power electronic systems. Therefore, additional hardware circuits must be added to compensate for the limitations of the floating-point DSP's inherent hardware resources.
Figure 4. Numerical control platform based on floating-point DSP and FPGA
4.3 Communication capabilities
As a power electronics digital control platform, in addition to providing independent control capabilities for power electronic devices, it also needs the ability to exchange information with other digital controllers. Communication technology is the fundamental way for power electronics digital control platforms to achieve information exchange. Real-time distributed control systems based on fieldbus technology have been widely used in factory automation and motion control. Therefore, using fieldbus technology in a power electronics control platform will facilitate communication connections with other industrial digital controllers. Commonly used fieldbuses include Foundation Fieldbus (FF), LonWrk, PROFIBUS, and CAN (Control Area Network).
When selecting a fieldbus, four issues need to be considered: (1) the bus's anti-interference capability, which directly affects the accuracy of data transmission; (2) isolation issues. Due to the difference in ground potential between different controllers, communication reliability is affected, and even damage to the controller may occur; (3) real-time requirements. Especially in the field of power electronics applications, real-time performance is particularly important, requiring not only fast transmission speed but also short response time; (4) ease of integration into the control platform.
Table 1 Fieldbus Parameters
5. Software Design
The development level of power electronics software is at a stage equivalent to the early development stage in the computer field. Software reuse technology will help improve software development efficiency and quality. After completing the design of reusable software modules, users can interact through interfaces, just as users use the internal functions of a hardware IC through its interface circuitry.
Typically, the design of CNC power electronics application systems revolves around a series of technical indicators, including the system's dynamic and steady-state characteristics and input-output relationships. The corresponding application system design can be carried out from the power level and the control level. The size of the software code is only one aspect of the software complexity; the content of the software code can reflect the software complexity. Based on reusable software programming methods, it is only necessary to select the corresponding software modules from the software library and then assemble these software modules in a certain order using simple assignment statements. The writing of software code is very simple and concise. In addition, these software modules have been rigorously tested, so the overall software reliability is very high.
After completing the design of reusable software modules, these modules can be used to "assemble" corresponding control software for different application scenarios. The software module bus is a common node for data transmission and exchange between modules. It is responsible for the management and allocation of input and output data of each software module, similar to the bus function in communication. Therefore, this paper calls it a software bus.
The entire control software can be designed by referring to the following steps.
1. Select the appropriate software module from the library based on the specific application;
2. Determine the calibration value for each software module based on simulation or calculation;
3. Control system hardware initialization;
4. Software module parameter initialization;
5. Software module connection, i.e., the exchange and transfer of data between modules;
6. Summary
Power electronic system integration is a crucial research topic in power electronics technology today, guiding the technology towards integration, standardization, and modularization. However, it is also a long-term, complex, and arduous research task, requiring phased and hierarchical approaches. As the integration technology of power electronic power levels matures and improves, the integration and refinement of power electronic control systems need further strengthening. Research on power electronic digital control platforms unfolds within this broader context of system integration research. Its main objective is to change the current design status of power electronic digital control systems, shorten their development cycle, and make them more suitable for the needs of power electronic system integration development. Therefore, it possesses significant academic value and promising application prospects.
About the author:
Contact person for manuscript fee: Wang Naixu (1986-), male (Han nationality), from Yantai City, Shandong Province, Master's degree, whose main research areas are intelligent control and pattern recognition.
Email: [email protected] Phone: 13070899172
Postal code: 266042
Address: No. 53 Zhengzhou Road, Sifang District, Qingdao City, Shandong Province
