在离网光伏发电系统中，逆变器的效率将直接影响到整个系统的效率，因此，太阳能光伏发电系统逆变器的控制技术具有重要的研究意义。在逆变器的设计中，通常采用模拟控制方法，然而，模拟控制系统中存在很多缺陷，如元器件的老化及温漂效应，对电磁干扰较为敏感，使用的元器件数目较多等。典型的模拟PWM逆变器控制系统采用自然采样法将正弦调制波与三角载波比较，从而控制触发脉冲，但三角波发生电路在高频（20kHz）时容易被温度、器件特性等因素干扰，从而导致输出电压中出现直流偏移，谐波含量增加，死区时间变化等不利影响。高速数字信号处理器（DSP）的发展使太阳能光伏发电系统中逆变器的数字化控制成为可能。因其大部分指令可在一个指令周期内完成，因此可以实现较为复杂的先进的控制算法，进一步改善输出波形的动态性能、稳态性能，并且可以简化整个系统的设计，使系统具有良好的一致性。

逆变器是一种功率电子电路，能把太阳能电池阵列发出的直流电转换为交流电为交流负载供电，是整个太阳能发电系统的关键组件。离网光伏逆变器有两个基本功能：一方面是为完成DC/AC转换为交流负载提供电能，另一方面是找出最佳的工作点以优化太阳能光伏系统的效率。对于特定的太阳光辐射、温度及太阳能电池类型，太阳能光伏系统都相应有唯一的最佳电压及电流，从而使光伏发电系统发出最大功率的电能。因此，在离网太阳能光伏发电系统中对逆变器提出以下基本要求：

1）逆变器要具有合理的电路结构，严格的元器件筛选，并要求逆变器具备各种保护功能，如输入直流极性接反保护，交流输出短路保护，过热，过载保护等。

2）具有较宽的直流输入电压适应范围，由于太阳能太阳能电池阵列的端电压随负载和日照强度而变化，蓄电池虽然对太阳能电池的电压具有钳位作用，但由于蓄电池的电压随蓄电池剩余容量和内阻的变化而波动，特别是当蓄电池老化时其端电压的变化范围很大，如12V蓄电池，其端电压可在10V～16V之间变化，这就要求逆变器必须在较宽的直流输入电压范围内保证正常工作，并保证交流输出电压稳定在负载要求的电压范围内。

3）逆变器尽量减少电能变换的中间环节，以节约成本、提高效率。

4）逆变器应具有较高的效率，由于目前太阳能电池的价格偏高，为了最大限度地利用太阳能电池，提高系统效率，必须提高逆变器的效率。

5）逆变器应具有较高的可靠性，目前离网太阳能光伏发电系统主要用于边远地区，许多离网太阳能光伏发电系统无人值守和维护。这就要求逆变器具有高的可靠性。

6）逆变器的输出电压与国内市电电压同频、同幅值，以适用于通用电器负载。

7）在中、大容量的离网太阳能光伏发电系统中，逆变器的输出应为失真度较小的正弦波。因在中、大容量系统中，若采用方波供电，输出将含有较多的谐波分量，高次谐波将产生附加损耗，许多离网太阳能光伏发电系统的负载为通信或仪表设备，这些设备对电源品质有较高的要求。对于离网太阳能光伏发电系统的逆变器而言，高质量的输出波形有两方面的指标要求：一是稳态精度高，包括THD值小，基波分量相对参考波形在相位和幅度上无静差；二是动态性能好，即在外界扰动下调节快，输出波形变化小。

In off-grid photovoltaic power generation system, the efficiency of the inverter will directly affect the efficiency of the whole system, so the control technology of solar photovoltaic power generation system inverter has important research significance. In the design of inverter, the analog control method is usually adopted. However, there are many defects in the analog control system, such as the aging of components and temperature drift effect, more sensitive to electromagnetic interference, and the number of components used is too large. Typical analog PWM inverter control system adopts the natural sampling method will be compared with the triangle carrier wave, sine wave modulation to control the trigger pulse, but triangle wave occurred in high frequency circuit (20 KHZ) are easy to be interference factors such as temperature, the device features, which leads to the output voltage in the dc offset, harmonic content increase, the dead band time change, etc. The development of high speed digital signal processor (DSP) makes the digital control of inverter in solar photovoltaic power generation system possible. Because most of its instructions can be completed within one instruction cycle, more complex and advanced control algorithms can be realized to further improve the dynamic performance and steady-state performance of the output waveform, and the design of the whole system can be simplified, so that the system has a good consistency.

Inverter is a kind of power electronic circuit, which can convert the DC current from solar array to AC power supply for AC load. It is the key component of the whole solar power system. Off-grid PV inverters have two basic functions: one is to provide power for the conversion of DC/AC to AC load, and the other is to find the best operating point to optimize the efficiency of the solar PV system. For specific solar radiation, temperature and solar cell types, the solar photovoltaic system has a unique optimal voltage and current, so that the photovoltaic system can emit the maximum power of electricity. Therefore, the following basic requirements are put forward for inverters in off-grid solar photovoltaic power generation systems:

1) The inverter should have a reasonable circuit structure, strict component screening, and the inverter is required to provide a variety of protection functions, such as input DC polarity connection reverse protection, AC output short-circuit protection, overheating, overload protection.

2) dc input voltage is wider than the range, due to the voltage of the solar solar arrays with load and sunshine intensity, although battery for solar battery voltage has a clamping function, but because of the battery voltage fluctuates according to the battery residual capacity and the change of the internal resistance, especially when the voltage of battery aging change range is very large, For example, the terminal voltage of a 12V battery can vary from 10V to 16V, which requires that the inverter must work normally in a wide DC input voltage range and ensure that the AC output voltage is stable within the voltage range required by the load.

3) Inverter to minimize the intermediate link of power conversion, in order to save costs and improve efficiency.

4) The inverter should have a high efficiency. Due to the high price of solar cells at present, in order to maximize the use of solar cells and improve the efficiency of the system, the efficiency of the inverter must be improved.

5) The inverter should have high reliability. Currently, off-grid solar photovoltaic power generation systems are mainly used in remote areas, and many off-grid solar photovoltaic power generation systems are unattended and maintained. This requires the inverter to have high reliability.

6) The output voltage of the inverter is the same frequency and amplitude as the domestic mains voltage, so as to be suitable for the load of general electrical appliances.

7) In the medium and large capacity off-grid solar photovoltaic power generation system, the output of the inverter should be sine wave with small distortion degree. Because in the medium and large capacity system, if the square wave power supply, the output will contain more harmonic components, high harmonic will produce additional loss, many off-grid solar photovoltaic power generation system load for communication or instrument equipment, these equipment have higher requirements for power quality. For the inverter of off-grid solar photovoltaic power generation system, high-quality output waveform has two requirements: first, high steady-state accuracy, including small THD value, and no static difference between the fundamental wave component and the reference waveform in phase and amplitude; Second, the dynamic performance is good, that is, the adjustment is fast under the external disturbance, the output waveform change is small.