双向半桥LLC谐振变换器及MPPT控制策略研究
发布时间：2018-09-04 08:27
【摘要】：随着化石能源的不断消耗,人类正在面临严重的能源危机,为了改善能源供应结构,可再生能源的开发利用得到了更多的重视。太阳能被认为最清洁的可再生能源,但是光伏发电具有间歇性,通过增加储能单元可保证电能的持续供应。双向DC/DC变换器可实现能量的双向流动,在储能单元控制中起着关键的作用。LLC谐振变换器因其高功率密度,高转换效率得到了广泛应用。本文主要研究了具有LLC谐振特性的双向DC/DC变换器,并对基于频率调制的最大功率跟踪算法做了研究。本文以带储能单元的户用光伏发电系统应用为背景,以双向半桥LLC谐振变换器做研究对象。通过基波分析法分析了变换器稳态的正、反向工作原理与特性,归纳出变换器正、反向不对称工作的异同点,为变换器设计提供了基础,并通过仿真分析了变换器不同工作方向下的主要波形。为了满足双向半桥LLC谐振变换器低电压环境工作要求,分析了变换器交错并联控制原理,研究了LLC谐振状态下驱动信号占空比变化对变换器电压增益的影响,提出了基于占空比与频率混合调制的均流控制策略,通过频率调制调节变换器输出电压,同时以变换器各模块谐振电流均值之差作为变量通过占空比调制实现电流平衡。仿真分析表明,混合调制可有效解决变换器交错并联回流问题,实现变换器模块间的等功率输出。为了使光伏电池时刻以最大功率输出,分析了光伏电池输出特性与变换器谐振特性的关系,采用了中值变频最大功率跟踪算法,通过等分变换器开关频率区间,比较中值开关频率点光伏电池输出功率,确定下一个等分区间,最终实现光伏电池最大功率输出。仿真分析表明,中值变频调制MPPT响应速度快,跟踪误差小,可实现光伏电池最大功率有效跟踪。根据课题指标要求,设计了交错并联双向半桥LLC谐振变换器样机,实验结果表明变换器工作原理与特性分析的正确性,实现了变换器模块间电流平衡,验证了中值变频调制MPPT的仿真与实验结果的一致性。
[Abstract]:With the continuous consumption of fossil energy, mankind is facing a serious energy crisis. In order to improve the structure of energy supply, more attention has been paid to the development and utilization of renewable energy. Solar energy is considered to be the cleanest renewable energy, but photovoltaic power generation is intermittent, by adding energy storage units to ensure the continued supply of electricity. Two-way DC/DC converter can realize bidirectional flow of energy, which plays a key role in energy storage unit control. LLC resonant converter is widely used because of its high power density and high conversion efficiency. In this paper, the bidirectional DC/DC converter with LLC resonance is studied, and the maximum power tracking algorithm based on frequency modulation is studied. In this paper, the application of household photovoltaic power generation system with energy storage unit is taken as the background, and the bi-directional half-bridge LLC resonant converter is taken as the research object. The principle and characteristics of steady-state forward and reverse operation of the converter are analyzed by the fundamental analysis method, and the similarities and differences of the forward and reverse asymmetric operation of the converter are summarized, which provide the basis for the design of the converter. The main waveforms of the converter in different working directions are analyzed by simulation. In order to meet the requirements of low voltage environment of bi-directional half-bridge LLC resonant converter, the principle of interleaved parallel control is analyzed, and the effect of the duty cycle of driving signal on the voltage gain of LLC resonant converter is studied. A current-sharing control strategy based on mixed modulation of duty cycle and frequency is proposed. The output voltage of the converter is regulated by frequency modulation, and the difference of resonant current mean of each module of the converter is taken as the variable to achieve current balance through duty cycle modulation. The simulation results show that the hybrid modulation can effectively solve the problem of interlaced parallel reflux and realize the equal power output between the converter modules. In order to make the photovoltaic cell output with maximum power at all times, the relationship between the output characteristic of photovoltaic cell and the resonant characteristic of the converter is analyzed. The median variable frequency maximum power tracking algorithm is adopted, and the switching frequency range of the equilateral converter is adopted. The output power of photovoltaic cell at median switching frequency point is compared and the next equipartition interval is determined to realize the maximum power output of photovoltaic cell. The simulation results show that the median frequency modulation (MPPT) has high response speed and low tracking error, and it can effectively track the maximum power of photovoltaic cells. According to the requirements of the project, the prototype of the interleaved bi-directional half-bridge LLC resonant converter is designed. The experimental results show that the principle and characteristic analysis of the converter are correct, and the current balance between the converter modules is realized. The simulation and experimental results of median frequency conversion modulation (MPPT) are verified.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM46
本文编号：2221545
[Abstract]:With the continuous consumption of fossil energy, mankind is facing a serious energy crisis. In order to improve the structure of energy supply, more attention has been paid to the development and utilization of renewable energy. Solar energy is considered to be the cleanest renewable energy, but photovoltaic power generation is intermittent, by adding energy storage units to ensure the continued supply of electricity. Two-way DC/DC converter can realize bidirectional flow of energy, which plays a key role in energy storage unit control. LLC resonant converter is widely used because of its high power density and high conversion efficiency. In this paper, the bidirectional DC/DC converter with LLC resonance is studied, and the maximum power tracking algorithm based on frequency modulation is studied. In this paper, the application of household photovoltaic power generation system with energy storage unit is taken as the background, and the bi-directional half-bridge LLC resonant converter is taken as the research object. The principle and characteristics of steady-state forward and reverse operation of the converter are analyzed by the fundamental analysis method, and the similarities and differences of the forward and reverse asymmetric operation of the converter are summarized, which provide the basis for the design of the converter. The main waveforms of the converter in different working directions are analyzed by simulation. In order to meet the requirements of low voltage environment of bi-directional half-bridge LLC resonant converter, the principle of interleaved parallel control is analyzed, and the effect of the duty cycle of driving signal on the voltage gain of LLC resonant converter is studied. A current-sharing control strategy based on mixed modulation of duty cycle and frequency is proposed. The output voltage of the converter is regulated by frequency modulation, and the difference of resonant current mean of each module of the converter is taken as the variable to achieve current balance through duty cycle modulation. The simulation results show that the hybrid modulation can effectively solve the problem of interlaced parallel reflux and realize the equal power output between the converter modules. In order to make the photovoltaic cell output with maximum power at all times, the relationship between the output characteristic of photovoltaic cell and the resonant characteristic of the converter is analyzed. The median variable frequency maximum power tracking algorithm is adopted, and the switching frequency range of the equilateral converter is adopted. The output power of photovoltaic cell at median switching frequency point is compared and the next equipartition interval is determined to realize the maximum power output of photovoltaic cell. The simulation results show that the median frequency modulation (MPPT) has high response speed and low tracking error, and it can effectively track the maximum power of photovoltaic cells. According to the requirements of the project, the prototype of the interleaved bi-directional half-bridge LLC resonant converter is designed. The experimental results show that the principle and characteristic analysis of the converter are correct, and the current balance between the converter modules is realized. The simulation and experimental results of median frequency conversion modulation (MPPT) are verified.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM46
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