Developing Fundamental Theory and Enabling Technologies for Parallel Operation of Inverters to Facilitate Large-scale Utilisation of Renewable Energy

英国研究委员会已经建立了一个RCUK能源计划，投资超过5.3亿英镑用于研究和技术，开创低碳的未来。能源也是TSB资助的一个主要应用领域。包括英国石油公司、卡特彼勒、法国电力能源公司、意昂、劳斯莱斯和壳牌在内的几家主要的全球公司已经与英国政府联手建立了能源技术研究所，为新能源技术创造了一个潜在的10亿英镑的投资基金。正在进行的研究方案涵盖能源从产生、传输到最终使用的各个方面，以便为热能、电力和运输创造负担得起、可靠和可持续的能源。增加风能、太阳能、海洋和生物质能等可再生能源的份额和提高能源效率是所有与能源有关的方案的两个最重要的最终目标。可再生能源需要连接到电网，最好是通过逆变器，以便它们参与电网调节，特别是对于大型可再生能源装置。然而，单个逆变器的容量有限，需要多个逆变器并联运行才能实现所需的功率容量。对于一个5GW的海上风力发电站，需要1000个5MW的逆变器。如何确保逆变器按比例/均匀地分担负载是一个挑战。不应该假设逆变器可以自动并联。如果没有适当的机制，可能会出现循环电流，一些逆变器可能会过载，这可能会造成损坏。该系统甚至可能变得不稳定，并导致不必要的行为。逆变器的并联运行一直是工业上的一个主要问题，阻碍了可再生能源的大规模利用。这是一个简单的问题，多年来一直没有得到妥善解决。传统的下垂控制策略是一种很有前途的技术，但不能保证共享精度。最近，PI揭示了传统的下垂控制方案及其变体不具备一种机制来确保共享精度对数值计算误差，参数漂移和组件不匹配具有鲁棒性。在此基础上，提出了一种鲁棒下垂控制器，既能保证实功和无功同时准确共享，又能在同一类型逆变器下保持良好的电压调节。当逆变器不同时，问题仍然没有解决。该项目的主要目标是发展对并联逆变器的基本了解，并开发使能控制技术，以促进可再生能源和分布式发电的大规模利用。该项目的最终目标是制定通用控制策略，允许不同类型输出阻抗的逆变器并联运行，并发展一个基本理论，以保证并联逆变器电力系统的稳定运行。

UK Research Councils have set up a RCUK Energy Programme, investing more than £530 million in research and skills to pioneer a low carbon future. Energy is also a major application area funded by TSB. Several major global companies, including BP, Caterpillar, EDF Energy, E.On, Rolls-Royce and Shell, have joined their forces with the UK government to establish the Energy Technologies Institute, creating a potential £1billion investment fund for new energy technologies. The ongoing research programmes cover various aspects of energy from generation, transmission to end use, in order to create affordable, reliable and sustainable energy for heat, power and transport. Increasing the share of renewable energy, e.g. wind, solar, marine and biomass, and improving energy efficiency are the two most important ultimate goals for all energy-related programmes. The renewable energy needs to be connected to the grid, preferably, via inverters in order for them to take part in the grid regulation, in particular, for large-scale renewable installations. However, the capacity of individual power inverters is limited and multiple inverters are needed to be operated in parallel to achieve the power capacity needed. For a 5GW offshore wind power site, 1000 of 5MW inverters are needed. How to make sure that the inverters will share the load proportionally/evenly is a challenge. It should not be assumed that inverters could be connected in parallel automatically. Without proper mechanisms in place, circulating currents may appear and some inverters may be overloaded, which may cause damage. The system may even become unstable and lead to unwanted behaviours. The parallel operation of inverters has been a major problem in industry that prevents the large-scale utilisation of renewable energy sources. This is a simple problem which has not been solved properly for many years. The conventional droop control strategy is a promising technology but the sharing accuracy cannot be guaranteed. Very recently, the PI has revealed that the conventional droop control scheme and its variants do not possess a mechanism to make sure that the sharing accuracy is robust against numerical computational errors, parameter drifts and component mismatches. A robust droop controller is then proposed, which is able to maintain accurate sharing of real power and reactive power at the same time and also to maintain good voltage regulation when the inverters are of the same type. The problem is still unsolved when the inverters are different. The major aims of the project are to develop fundamental understanding about parallel-operated inverters and to develop enabling contorl technologies to facilitate the large-scale utilisation of renewable energy and distributed generation. The ultimate goals of the project are to develop universal control strategies that allow the parallel operation of inverters with different types of output impedances and to develop a fundamental theory to guarantee the stable operation of power systems with parallel-operated inverters.