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

英国研究理事会已经建立了一个RCUK能源计划，投资超过5.3亿英镑的研究和技能，以开创低碳未来。能源也是TSB资助的一个主要应用领域。包括BP、卡特彼勒、EDF Energy、E.On、罗尔斯·罗伊斯和壳牌在内的几家主要全球公司已与英国政府联手成立了能源技术研究所，为新能源技术创建了一个潜在的10亿英镑投资基金。正在进行的研究方案涵盖能源从发电、传输到最终使用的各个方面，以创造负担得起、可靠和可持续的热能、电力和运输能源。增加风能、太阳能、海洋能和生物量等可再生能源的份额，以及提高能源效率，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，优选地，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装置。然而，单个功率逆变器的容量是有限的，并且需要多个逆变器并联操作以实现所需的功率容量。对于5GW海上风电场，需要1000台5 MW逆变器。如何确保逆变器将按比例/均匀地分担负载是一个挑战。不应假定逆变器可以自动并联。如果没有适当的机制，可能会出现环流，一些逆变器可能会过载，这可能会导致损坏。系统甚至可能变得不稳定，导致不必要的行为。逆变器的并联运行一直是工业中的一个主要问题，这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有确保共享精度对数值计算误差、参数漂移和组件失配具有鲁棒性的机制。然后，提出了一种鲁棒下垂控制器，它能够保持准确的共享真实的功率和无功功率在同一时间，也保持良好的电压调节时，逆变器是相同的类型。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理解，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开发通用的控制策略，允许不同类型的输出阻抗的逆变器并联运行，并开发一个基本的理论，以保证电力系统的稳定运行与并联运行的逆变器。

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.