09-01-2012, 02:18 PM
DECENTRLISED ARCHITECTURE FOR POWER ELECTRONIC SYSTEM DESIGN BASED ON BIONICS
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INTRODUCTION
In Industrial fields such as avionic, space, military, telecommunications industry, the power electronic system requires high reliability. To meet such stringent requirement, a valid approach for enhancing power electronic system reliability is urgent and significant. Bionics is a promising scientific discipline, which is characterized by finding principles from biological objects that embody superior principles of previous technology and to which a technological exploitation can be assigned. Applying these principles to the power electronic system design can result in Power Electronics Bionics (PEB). PEB is fusion of Power Electronics and Biology but not mere sum of them, which involves innovation processes.
HIGH RELIABLE POWER ELECTRONIC SYSTEM DESIGN BASED ON PEB
The human body system is one of the most complicated system ever known; failures are not rare, but the overall function is high reliable. The high system reliability results from principles including autonomous decentralized architecture, redundancy, self diagnosis and self-repair, which can be a source of inspiration in designing power electronic system requiring high reliability.
A. Autonomous Decentralized Architecture:
Control of today’s power converters is based on a centralized digital controller. One of the main drawbacks of this approach is the large number of signal links that connect the controller and other parts. Furthermore, the signals in typical power electronic system come in variety of physical media. Thus it makes the standardization and modularization of system and subsystems very difficult. Moreover, performances of power converters based on centralized control including online maintenance, online expansion and fault tolerance are usually bad. As a result, some complicated power electronic systems based on centralized controller are usually low reliable.
A human body system and subsystems exhibit autonomous and spontaneous behaviors with hierarchically ordered relationships, which is a source of inspiration in designing Autonomous Decentralized Power Electronic System (ADPES). Structurally, the cell is the basic unit in all parts of a biological system. Cell acts as building blocks to make up the hierarchical layers in organisms. Thus, tissues (e.g., muscle tissue) are formed by cells with similar functions and shape. Different tissues combine to form organs with a particular function (e.g., heart). Organs, in turn, group together to form body systems and the systems make up the complex organisms. In such hierarchical structures, each layer in the same hierarchy communicates each other and is supported by the adjacent layers. The bottom layer such as cells exhibits low-level autonomous and spontaneous behavior (e.g., immunity to virus infection), thus adapting itself to changed environment. So the brain is librated from the many low-level tasks and perform the higher-level functions (e.g., reasoning). With this autonomous decentralized architecture, the organisms show enhanced reliability and adaptability.
Based on bionics, the principle of autonomous decentralized architecture can be applied to power electronic system requiring high reliability. Thus ADPES comes in. ADPES is homogeneous, i.e. ADPES is composed of identical units named Autonomous Power Electronic Building Cell (APEBC) here. Acting as a building unit like a biological cell, APEBC is essentially a subsystem which is characterized by automaticity.
Autonomous Controllability:
In case one APEBC fails, other APEBCs cooperate autonomously each other to achieve overall system function. As a standardized & integrated power electronic building block, APEBC is similar to Power Electronic Building Block (PEBB) in some degree. However, APEBC is not equal to PEBB. APEBC is characterized by autonomous controllability and cooperation. Compared to the conventional centralized architecture, the ADPES has several predominant operational features such as enhanced reliability, flexibility, online reparability, online expansion and fault tolerance.
B. Redundancy:
The concept of redundancy is well understood:
In case an element of a system fails, there is a spare element that is able to operate in the place of the failed one so that the operation of the overall system is uninterrupted. Redundancy is the addition of resource, information what is needed for normal system operation. The redundancy includes organs- redundancy (e.g., double lung), function-redundancy (e.g., neural network) and time-redundancy results in high reliability of human body system. The redundancy in biological system resembles redundancy in power electronic system.
1) Hardware Redundancy:
Any system, subsystem or component is replicated. Spare elements are used to replace the faulty ones. To increase system reliability, N-Modular redundant power electronic systems are designed. As applied to critical avionics on aircraft, illustration cost and weight savings in addition to improved power system reliability. However, redundant components usually add size, weight and cost of the whole equipment. So it is significant to find optimum configurations for N-Modular Redundant systems. To meet such requirement, further research must be carried out in order to determine to what extent the models proposed hold for any fault-tolerant systems with guidance of inspiration from optimum redundant biological systems.
2) Function-redundancy:
In function-redundancy the working modules perform the same function originally performed by the failed one. There being no spare modules or sub-systems, there is no increase in size, weight and cost arising from function-redundancy. So function-redundancy will be regarded as a novel approach for designing high reliable and economical power electronic system.
