The Implementation Of The Carrier-based Space Vector Modulation Schemes In Three-phase Two-and Three-level Converters

The continuous expansion of the scale of wind power and photovoltaic power generation has greatly changed the structure of the power system.As a link between the renewable energy and the power system,the power electronic converters will play an extremely important role in the future.For the power electronic converter,the modulation technology is an important technology to ensure the normal operation which affects many performance indicators of the converters at the same time.Space vector modulation and carrier modulation are two kinds of mostly used modulation technologies.Space vector modulation is based on the principle of vector synthesis,which is intuitive and clear.It is convenient to do accurate calculation for various performance indicators,but the implementation is often complex.Carrier modulation can directly get the control signals for each power switches by comparing the formulated modulation wave with carrier wave,which is easy to implement but difficult to get the performance indicators.Therefore,carrier-based space vector modulation technology can possess the advantages of two kinds of modulation technologies at the same time with the theoretical analysis based on vector modulation and the implementation based on carrier modulation,which is the inevitable development trend of modulation technology.For this reason,this paper studys the application of carrier-based space vector modulation technology in three topologies(two-level converter,Vienna rectifier and two parallelled converters)and analyzes many important issues of each technology.Two-level three-phase converter is the most widely used topology of power electronic converter.The study method for modulation techniques of two-level converters can be used for reference and applied to other topologies.So,this paper will discuss the carrier-based implementation and comprehensive assessment for many two-level space vector modulation strategies in order to find the general method and essence of the carrier-based space vector modulation technology and lay a theoretical foundation for other topology research.On the other hand,for the high-performance high-power AC drive system,in order to make full use of the DC bus voltage,increase the load capacity and improve the speed regulation range,the operation condition of the converter may exceed the linear modulation range and enter the over modulation range.As a result,the over-modulation technology must be studied,but the existing methods are still complicated.Therefore,this paper proposes a carrier-based space vector over-modulation strategy.With the unified expressions of three-phase modulation wave,the sector identification and calculation of various auxiliary variables and vector angles can be avoided,which greatly simplifies the implementation of the over-modulation strategy and ensures the normal operation under over modulation.For Vienna rectifier,the phase voltage output is determined by the switch state and the polarity of the phase current.When the polarity of the phase current and the phase reference voltage is different,the Vienna rectifier will not be able to synthesize the reference voltage normally,which will cause the output distortion.For this reason,this paper analyzes the working principle of Vienna rectifier,discusses the carrier implementation of normal space vector modulation,analyzes the causes of distortion through vector synthesis,and proposes a modified modulation strategy to suppress the output distortion and simplify the implementation process based on the carrier implementation.Two directly parallelled converters is an ideal current expansion topology.But the non-isolated DC side and the AC side lead the zero sequence circulating current.It is an important task to suppress the zero sequence circulating current and the high frequency circulating current can only be optimized through the modulation strategy.Therefore,this paper will analyze all kinds of zero sequence circulation optimization vector modulation strategies,discuss their carrier implementation methods,and comprehensively evaluate them through various performance indicators.On the other hand,the existing over-modulation strategies are most for two-level and three-level topologies,but over-modulation strategies for two parallelled converter topology are still lack.So this paper propose a unified over-modulation strategy which integrates the existing common linear modulation strategies.With the proposed method,the desired fundamental output is ensured and the smooth expansion to the over-modulation region of the existing methods is realized through simple mathematical operation and logical judgment.In this paper,the studies of modulation strategies of the three topologies is either to simplify and evaluate the existing modulation strategies comprehensively,or to put forward effective schemes for many important problems,which is helpful for the improvment of the corresponding modulation technology.And the research methods for carrier-based space vector modulation technology are unified and general,which can be used for reference to the study of other modulation strategies.There are 116 figures,41 tables and 122 references in this dissertation.