在離網(wǎng)光伏發(fā)電系統(tǒng)中，逆變器的效率將直接影響到整個(gè)系統(tǒng)的效率，因此，太陽(yáng)能光伏發(fā)電系統(tǒng)逆變器的控制技術(shù)具有重要的研究意義。在逆變器的設(shè)計(jì)中，通常采用模擬控制方法，然而，模擬控制系統(tǒng)中存在很多缺陷，如元器件的老化及溫漂效應(yīng)，對(duì)電磁干擾較為敏感，使用的元器件數(shù)目較多等。典型的模擬PWM逆變器控制系統(tǒng)采用自然采樣法將正弦調(diào)制波與三角載波比較，從而控制觸發(fā)脈沖，但三角波發(fā)生電路在高頻（20kHz）時(shí)容易被溫度、器件特性等因素干擾，從而導(dǎo)致輸出電壓中出現(xiàn)直流偏移，諧波含量增加，死區(qū)時(shí)間變化等不利影響。高速數(shù)字信號(hào)處理器（DSP）的發(fā)展使太陽(yáng)能光伏發(fā)電系統(tǒng)中逆變器的數(shù)字化控制成為可能。因其大部分指令可在一個(gè)指令周期內(nèi)完成，因此可以實(shí)現(xiàn)較為復(fù)雜的先進(jìn)的控制算法，進(jìn)一步改善輸出波形的動(dòng)態(tài)性能、穩(wěn)態(tài)性能，并且可以簡(jiǎn)化整個(gè)系統(tǒng)的設(shè)計(jì)，使系統(tǒng)具有良好的一致性。

逆變器是一種功率電子電路，能把太陽(yáng)能電池陣列發(fā)出的直流電轉(zhuǎn)換為交流電為交流負(fù)載供電，是整個(gè)太陽(yáng)能發(fā)電系統(tǒng)的關(guān)鍵組件。離網(wǎng)光伏逆變器有兩個(gè)基本功能：一方面是為完成DC/AC轉(zhuǎn)換為交流負(fù)載提供電能，另一方面是找出最佳的工作點(diǎn)以優(yōu)化太陽(yáng)能光伏系統(tǒng)的效率。對(duì)于特定的太陽(yáng)光輻射、溫度及太陽(yáng)能電池類型，太陽(yáng)能光伏系統(tǒng)都相應(yīng)有唯一的最佳電壓及電流，從而使光伏發(fā)電系統(tǒng)發(fā)出最大功率的電能。因此，在離網(wǎng)太陽(yáng)能光伏發(fā)電系統(tǒng)中對(duì)逆變器提出以下基本要求：

1）逆變器要具有合理的電路結(jié)構(gòu)，嚴(yán)格的元器件篩選，并要求逆變器具備各種保護(hù)功能，如輸入直流極性接反保護(hù)，交流輸出短路保護(hù)，過(guò)熱，過(guò)載保護(hù)等。

2）具有較寬的直流輸入電壓適應(yīng)范圍，由于太陽(yáng)能太陽(yáng)能電池陣列的端電壓隨負(fù)載和日照強(qiáng)度而變化，蓄電池雖然對(duì)太陽(yáng)能電池的電壓具有鉗位作用，但由于蓄電池的電壓隨蓄電池剩余容量和內(nèi)阻的變化而波動(dòng)，特別是當(dāng)蓄電池老化時(shí)其端電壓的變化范圍很大，如12V蓄電池，其端電壓可在10V～16V之間變化，這就要求逆變器必須在較寬的直流輸入電壓范圍內(nèi)保證正常工作，并保證交流輸出電壓穩(wěn)定在負(fù)載要求的電壓范圍內(nèi)。

3）逆變器盡量減少電能變換的中間環(huán)節(jié)，以節(jié)約成本、提高效率。

4）逆變器應(yīng)具有較高的效率，由于目前太陽(yáng)能電池的價(jià)格偏高，為了最大限度地利用太陽(yáng)能電池，提高系統(tǒng)效率，必須提高逆變器的效率。

5）逆變器應(yīng)具有較高的可靠性，目前離網(wǎng)太陽(yáng)能光伏發(fā)電系統(tǒng)主要用于邊遠(yuǎn)地區(qū)，許多離網(wǎng)太陽(yáng)能光伏發(fā)電系統(tǒng)無(wú)人值守和維護(hù)。這就要求逆變器具有高的可靠性。

6）逆變器的輸出電壓與國(guó)內(nèi)市電電壓同頻、同幅值，以適用于通用電器負(fù)載。

7）在中、大容量的離網(wǎng)太陽(yáng)能光伏發(fā)電系統(tǒng)中，逆變器的輸出應(yīng)為失真度較小的正弦波。因在中、大容量系統(tǒng)中，若采用方波供電，輸出將含有較多的諧波分量，高次諧波將產(chǎn)生附加損耗，許多離網(wǎng)太陽(yáng)能光伏發(fā)電系統(tǒng)的負(fù)載為通信或儀表設(shè)備，這些設(shè)備對(duì)電源品質(zhì)有較高的要求。對(duì)于離網(wǎng)太陽(yáng)能光伏發(fā)電系統(tǒng)的逆變器而言，高質(zhì)量的輸出波形有兩方面的指標(biāo)要求：一是穩(wěn)態(tài)精度高，包括THD值小，基波分量相對(duì)參考波形在相位和幅度上無(wú)靜差；二是動(dòng)態(tài)性能好，即在外界擾動(dòng)下調(diào)節(jié)快，輸出波形變化小。

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.