三相模块级联型固态变压器及其控制策略研究
发布时间：2018-09-14 18:14
【摘要】：近年来,能源问题和环境问题愈加严重,解决好这两大问题关系到人类能否实现可持续发展。在此背景下分布式发电系统得到了迅速的发展,智能电网的建设成了电网发展必然趋势。智能电网能够灵活的分配能量,改善电能质量,更加安全可靠。固态变压器就是智能电网的核心设备之一。固态变压器主要功能有:管理系统能量,使能量分布更加合理;对输入交流侧进行功率因数校正;隔离电网和用户,提高用电安全;为分布式发电系统和储能设备提供直流接口。本文研究的固态变压器主电路拓扑为三相三级式模块级联型结构,三级式拓扑主要包括输入级、中间级和输出级。输入整流级把输入的工频交流电压转换为直流电压。为了提高输入电压等级,整流级采用模块级联型结构,每相由三个PWM整流桥级联而成。中间隔离级实现整流输出电压的电压等级的转换和隔离。每个整流模块后接一个双有源桥(Dual active bridge,DAB)DC-DC变换器。DAB模块由一个高频变压器和两个对称的全桥电路组成,DAB输出电压并联,为分布式发电系统和储能设备提供直流接口。逆变级把DAB输出的直流电压逆变为工频交流电压供用户使用。通过对主电路拓扑结构的分析,确定了输入级采用载波移相的调制方法、DAB级采用单移相控制的控制方式。载波移相控制下,整流级级联H桥输入电压为七电平,更接近于正弦波;单移相控制下DAB级高频变压器漏感电流在一个周期内有六种工作状态,通过分析各工作状态,得出传输功率与各电气量之间的关系。建立电路的小信号模型,推导出电路传递函数。提出了整流级采用基于三相dq变换的共同占空比控制和DAB级采用电压跟随的控制策略。共同占空比控制下,各整流级输出平均电压稳定在设定值上。电压跟随控制使DAB输出电压按一定比例跟随输入电压。为了解决系统各模块电路参数不匹配引起的整流级输出电压不均衡和DAB级传输功率不均衡的问题,论文提出了功率均衡控制的控制策略。该功率均衡控制策略不需要电流传感器,降低了成本。为了验证理论的正确性,在PSIM软件中对整个系统进行了仿真,并搭建硬件平台进行实验验证。仿真结果和实验结果都验证了所提出理论的正确性。
[Abstract]:In recent years, energy and environment problems become more and more serious. In this context, the distributed generation system has been developed rapidly, and the construction of smart grid has become an inevitable trend of grid development. Smart grid can distribute energy flexibly, improve power quality, and be more safe and reliable. Solid state transformer is one of the core equipments of smart grid. The main functions of solid-state transformer are as follows: managing system energy, making energy distribution more reasonable, correcting input AC side power factor, isolating power grid and users, improving power safety; Provide DC interface for distributed generation system and energy storage equipment. The main circuit topology of solid-state transformer in this paper is three-phase three-stage modular cascade structure. The three-stage topology mainly includes input stage, intermediate stage and output stage. Input rectifier level converts input power frequency AC voltage to DC voltage. In order to improve the input voltage level, the rectifier stage adopts a modular cascade structure, each phase is cascaded by three PWM rectifier bridges. The intermediate isolation stage realizes the conversion and isolation of the voltage level of the rectified output voltage. Each rectifier module is followed by a dual-active bridge (Dual active bridge,DAB) DC-DC converter. The dab module consists of a high-frequency transformer and two symmetrical full-bridge circuits, which provide a DC interface for distributed generation system and energy storage equipment. The inverter stage converts DC voltage output from DAB to power frequency AC voltage for user's use. Based on the analysis of the topology of the main circuit, the modulation method of input stage using carrier phase shift and the control mode of DAB stage adopting single phase shift control are determined. Under carrier phase shift control, the input voltage of rectifier cascaded H bridge is seven levels, which is closer to sine wave, and the leakage inductance current of DAB high frequency transformer has six working states in one cycle. The relation between transmission power and electrical quantity is obtained. The small signal model of the circuit is established and the circuit transfer function is derived. A common duty cycle control based on three-phase dq transform and a voltage following control strategy for DAB stage are proposed. Under the common duty cycle control, the average output voltage of each rectifier stage is stable on the set value. The voltage following control causes the DAB output voltage to follow the input voltage in a certain proportion. In order to solve the problems of unbalanced output voltage of rectifier stage and unbalanced transmission power of DAB stage caused by the mismatch of circuit parameters in each module of the system, the control strategy of power equalization control is proposed in this paper. The proposed power equalization control strategy does not require current sensors and reduces the cost. In order to verify the correctness of the theory, the whole system is simulated in PSIM software, and the hardware platform is built for experimental verification. Simulation results and experimental results verify the correctness of the proposed theory.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM41
[Abstract]:In recent years, energy and environment problems become more and more serious. In this context, the distributed generation system has been developed rapidly, and the construction of smart grid has become an inevitable trend of grid development. Smart grid can distribute energy flexibly, improve power quality, and be more safe and reliable. Solid state transformer is one of the core equipments of smart grid. The main functions of solid-state transformer are as follows: managing system energy, making energy distribution more reasonable, correcting input AC side power factor, isolating power grid and users, improving power safety; Provide DC interface for distributed generation system and energy storage equipment. The main circuit topology of solid-state transformer in this paper is three-phase three-stage modular cascade structure. The three-stage topology mainly includes input stage, intermediate stage and output stage. Input rectifier level converts input power frequency AC voltage to DC voltage. In order to improve the input voltage level, the rectifier stage adopts a modular cascade structure, each phase is cascaded by three PWM rectifier bridges. The intermediate isolation stage realizes the conversion and isolation of the voltage level of the rectified output voltage. Each rectifier module is followed by a dual-active bridge (Dual active bridge,DAB) DC-DC converter. The dab module consists of a high-frequency transformer and two symmetrical full-bridge circuits, which provide a DC interface for distributed generation system and energy storage equipment. The inverter stage converts DC voltage output from DAB to power frequency AC voltage for user's use. Based on the analysis of the topology of the main circuit, the modulation method of input stage using carrier phase shift and the control mode of DAB stage adopting single phase shift control are determined. Under carrier phase shift control, the input voltage of rectifier cascaded H bridge is seven levels, which is closer to sine wave, and the leakage inductance current of DAB high frequency transformer has six working states in one cycle. The relation between transmission power and electrical quantity is obtained. The small signal model of the circuit is established and the circuit transfer function is derived. A common duty cycle control based on three-phase dq transform and a voltage following control strategy for DAB stage are proposed. Under the common duty cycle control, the average output voltage of each rectifier stage is stable on the set value. The voltage following control causes the DAB output voltage to follow the input voltage in a certain proportion. In order to solve the problems of unbalanced output voltage of rectifier stage and unbalanced transmission power of DAB stage caused by the mismatch of circuit parameters in each module of the system, the control strategy of power equalization control is proposed in this paper. The proposed power equalization control strategy does not require current sensors and reduces the cost. In order to verify the correctness of the theory, the whole system is simulated in PSIM software, and the hardware platform is built for experimental verification. Simulation results and experimental results verify the correctness of the proposed theory.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM41
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