太阳能并网发电系统关键技术研究
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摘要
并网逆变器是太阳能发电系统中最重要的能量转换设备。本文对单相太阳能并网逆变器的电压和电流闭环控制、最大功率点跟踪控制以及抗孤岛效应保护功能等关键技术进行研究，有助于提高系统的性能和可靠性。
介绍了并网逆变器的基本电路结构和控制方法，给出了产品设计例证。针对单级逆变器的直流输入电压范围非常宽、控制系统优化设计困难这个问题，提出采用脉宽调制器载波和比例-积分控制器随工作电压变化而同步改变的变参数控制方法，保证输出电流闭环控制在整个输入电压工作范围内都稳定可靠的工作。对于两级逆变器，在分析前级Boost变换器工作模式和电路模型基础上，研究了输入电压-电流双闭环控制系统的设计和实现方法。
最大功率点跟踪是太阳能逆变器的基本功能。第三章首先介绍太阳能电池等效电路模型和电压-电流特性以及相关标准中指定的最大功率跟踪效率的评估方法，得出了扰动-观察法的电压扰动步长、扰动周期的设计要求，给出设计结果并分析跟踪的精度。电池电压的调节是通过基于并网功率最大化的电压闭环跟踪控制实现的。根据电池电压控制环路的动态响应特性，提出电压扰动周期的设计方法及功率计量时段选择方法，具有稳态好和跟踪精度高的优点。单级并网逆变器的母线电压存在两倍于电网频率的电压纹波，这会带来一定的功率损失，给出了该功率损失与直流工作电压和纹波电压的关系。
抗孤岛效应保护是小型并网逆变器最重要的保护功能之一。第四章首先分析了测试采用的谐振负载的阻抗特性和频率保护孤岛检测方法失效的原因，给出频率保护方法的检测盲区计算和仿真方法。介绍常规频率扰动和相位扰动方法的工作原理，计算频率上下限和扰动策略对检测盲区的影响，在此基础上分析负载阻抗频率特性、锁相控制误差和电流环相位跟踪误差等因素对孤岛频率的影响，提出孤岛频率的计算方法，并给出仿真和实验验证结果。根据孤岛系统的相位关系，提出采用间歇性相位或频率扰动、双向相位或频率扰动以及加大频率扰动周期三种办法，可以减小孤岛检测的盲区，并减小扰动对电流波形质量的影响。
随着太阳能并网发电应用的扩大，同一电网并列点会有多个发电系统。本文给出了多个电流型逆变器并网系统的数学分析方法，分析各逆变器相位（或频率）扰动策略和同步关系对孤岛检测的影响，在此基础上给出一种多逆变器并网系统的抗孤岛效应保护策略，并进行了仿真和实验验证。
Grid connected inverter is the most important power conversion unit in a photovoltaic electricpower generation system. This paper mainly deals with the key techniques such as voltage and currentcontrol, maximum power point tracking and anti-islanding protection of small scale single phasephotovoltaic grid connected inverter, which contributes to the performance and reliability of thesystem.
It gives the basic electric circuits, control methods and product design examples in chapter2.Aiming at the problem that the dc input voltage range of the single-stage inverter is very wide and theoptimum design of the control system is difficult, this dissertation put forward that pulse widthmodulating carrier or proportional-integral controller parameters of current loop vary with DC inputvoltage, and the inverter can work well in the full voltage range. The transient voltage overshoot ofthe ac output when the grid is suddenly gone is also solved by this method. Double-close loop of inputvoltage and current control system is analyzed based on the work mode and circuit model of thefront-stage Boost converter of a two-stage inverter.
Maximum power point tracking is a basic function of the solar inverter. The equivalent circuitmodel, voltage-current characteristic of solar module and static and dynamic maximum power pointtracking efficiency evaluation in related standard are introduced in chapter3. The Disturb-Observemethod is designed, and the realization and efficiency analysis are given out to meet the requirementsof voltage step and period of cycle. The regulation of PV voltage is achieved by closed loop controlbased on maximum of the power sent to the grid. The cycle of voltage disturb and power estimationwith good stablilty and high efficiency is designed according to the dynamic performance of theclosed voltage control. For the single-stage inverter, there is a power loss because of the voltage rippleof double line frequency with the dc-bus voltage. The relationship between the power loss and thedc-voltage and ac voltage ripple is given out.
Anti-islanding is one of the most important protective functions of small scale grid connectedinverter. The calculation and simulation method of none detection zone of frequency protection arepresented in chapter4, which are analyzed based on the load impedance characteristic and the failurereason of frequency detection method. It introduces the working principle of regular frequency driftand phase shift method for islanding detection, and sets forth the effects of over and under frequencylimits and frequency or phase interference strategy on the none detection zone. Furthermore, thisdissertation illuminates the effects of the load impedance characteristic, the tracking error of phaselock loop and phase error of closed current control loop on islanding frequency, and the result isverified with simulations and experiments. According to the phase formula of islanding system, three methods of intermittently frequency or phase interference, bi-directional frequency drift or phase shiftand increasing of frequency interference cycle are presented to decrease none detection zone ofanti-islanding protection and to improve waveform of current injected into the grid.
There may be many power generation systems at one common power point with the applicationenlargement of photovoltaic grid connected system. This dissertation gives the math model of currentcontrolled multi-inverter grid connected power system. It also analyzes synchronization strategy offrequency or phase interference and the effects on the islanding detection. Based on this, thisdissertation also illustrates an anti-islanding protection strategy of multi inverter grid connectedsystem and verifies the result by simulation and experiments.
介绍了并网逆变器的基本电路结构和控制方法，给出了产品设计例证。针对单级逆变器的直流输入电压范围非常宽、控制系统优化设计困难这个问题，提出采用脉宽调制器载波和比例-积分控制器随工作电压变化而同步改变的变参数控制方法，保证输出电流闭环控制在整个输入电压工作范围内都稳定可靠的工作。对于两级逆变器，在分析前级Boost变换器工作模式和电路模型基础上，研究了输入电压-电流双闭环控制系统的设计和实现方法。
最大功率点跟踪是太阳能逆变器的基本功能。第三章首先介绍太阳能电池等效电路模型和电压-电流特性以及相关标准中指定的最大功率跟踪效率的评估方法，得出了扰动-观察法的电压扰动步长、扰动周期的设计要求，给出设计结果并分析跟踪的精度。电池电压的调节是通过基于并网功率最大化的电压闭环跟踪控制实现的。根据电池电压控制环路的动态响应特性，提出电压扰动周期的设计方法及功率计量时段选择方法，具有稳态好和跟踪精度高的优点。单级并网逆变器的母线电压存在两倍于电网频率的电压纹波，这会带来一定的功率损失，给出了该功率损失与直流工作电压和纹波电压的关系。
抗孤岛效应保护是小型并网逆变器最重要的保护功能之一。第四章首先分析了测试采用的谐振负载的阻抗特性和频率保护孤岛检测方法失效的原因，给出频率保护方法的检测盲区计算和仿真方法。介绍常规频率扰动和相位扰动方法的工作原理，计算频率上下限和扰动策略对检测盲区的影响，在此基础上分析负载阻抗频率特性、锁相控制误差和电流环相位跟踪误差等因素对孤岛频率的影响，提出孤岛频率的计算方法，并给出仿真和实验验证结果。根据孤岛系统的相位关系，提出采用间歇性相位或频率扰动、双向相位或频率扰动以及加大频率扰动周期三种办法，可以减小孤岛检测的盲区，并减小扰动对电流波形质量的影响。
随着太阳能并网发电应用的扩大，同一电网并列点会有多个发电系统。本文给出了多个电流型逆变器并网系统的数学分析方法，分析各逆变器相位（或频率）扰动策略和同步关系对孤岛检测的影响，在此基础上给出一种多逆变器并网系统的抗孤岛效应保护策略，并进行了仿真和实验验证。
Grid connected inverter is the most important power conversion unit in a photovoltaic electricpower generation system. This paper mainly deals with the key techniques such as voltage and currentcontrol, maximum power point tracking and anti-islanding protection of small scale single phasephotovoltaic grid connected inverter, which contributes to the performance and reliability of thesystem.
It gives the basic electric circuits, control methods and product design examples in chapter2.Aiming at the problem that the dc input voltage range of the single-stage inverter is very wide and theoptimum design of the control system is difficult, this dissertation put forward that pulse widthmodulating carrier or proportional-integral controller parameters of current loop vary with DC inputvoltage, and the inverter can work well in the full voltage range. The transient voltage overshoot ofthe ac output when the grid is suddenly gone is also solved by this method. Double-close loop of inputvoltage and current control system is analyzed based on the work mode and circuit model of thefront-stage Boost converter of a two-stage inverter.
Maximum power point tracking is a basic function of the solar inverter. The equivalent circuitmodel, voltage-current characteristic of solar module and static and dynamic maximum power pointtracking efficiency evaluation in related standard are introduced in chapter3. The Disturb-Observemethod is designed, and the realization and efficiency analysis are given out to meet the requirementsof voltage step and period of cycle. The regulation of PV voltage is achieved by closed loop controlbased on maximum of the power sent to the grid. The cycle of voltage disturb and power estimationwith good stablilty and high efficiency is designed according to the dynamic performance of theclosed voltage control. For the single-stage inverter, there is a power loss because of the voltage rippleof double line frequency with the dc-bus voltage. The relationship between the power loss and thedc-voltage and ac voltage ripple is given out.
Anti-islanding is one of the most important protective functions of small scale grid connectedinverter. The calculation and simulation method of none detection zone of frequency protection arepresented in chapter4, which are analyzed based on the load impedance characteristic and the failurereason of frequency detection method. It introduces the working principle of regular frequency driftand phase shift method for islanding detection, and sets forth the effects of over and under frequencylimits and frequency or phase interference strategy on the none detection zone. Furthermore, thisdissertation illuminates the effects of the load impedance characteristic, the tracking error of phaselock loop and phase error of closed current control loop on islanding frequency, and the result isverified with simulations and experiments. According to the phase formula of islanding system, three methods of intermittently frequency or phase interference, bi-directional frequency drift or phase shiftand increasing of frequency interference cycle are presented to decrease none detection zone ofanti-islanding protection and to improve waveform of current injected into the grid.
There may be many power generation systems at one common power point with the applicationenlargement of photovoltaic grid connected system. This dissertation gives the math model of currentcontrolled multi-inverter grid connected power system. It also analyzes synchronization strategy offrequency or phase interference and the effects on the islanding detection. Based on this, thisdissertation also illustrates an anti-islanding protection strategy of multi inverter grid connectedsystem and verifies the result by simulation and experiments.
引文
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