离网逆变器为什么能过载几倍

从上图看出，采用高频隔离技术的离网逆变器，峰值功率可以达到额定功率的两倍；采用工频隔离技术的离网逆变器，峰值功率可以达到额定功率的三倍。 那么，一台3kW的高频离网逆变器，可以带动一台1P的空调（启动功率约5.5kVA），一台12kW的工频离网逆变器，可以带动一台6P的空调（启动功率约33kVA）。逆变器给负载提供启动能量，一部分来自于蓄电池或者光伏组件，超出的部分也是靠逆变器自己（内部的储能元件—电容和电感）来提供。

高频 

SPF3000-5000TL HVM

工频 

SPF 4000-12000T HVM

电容和电感都是一种储能元件 ，不同的是电容是以电场的形式储存电能，电容的容量越大，储存的电量越多。 而电感则是以磁场的形式存储能量，电感器磁芯的磁导率越大，电感量也越大，则能够储存的能量也越多。  

电容的原理 从其结构便可以看出，如上图，两边各有一块金属板引出两个电极，中间由绝缘物质隔开，在电容两端未施加外部电场的情况下，两个极板上所带的正负电荷处于一种平衡状态。 

如上图，当在电容两端施加外电场时，一端极板上开始聚集正电荷，另一端极板则聚集负电荷，随着电容两端的电压不断升高至电源电压，电容充电停止，此时就算断开外电路，电容上的能量也不会消失，原因是正负电荷具有“同性相斥，异性相吸”的特性，两端的电荷相吸引就形成了储存能量的作用。  

工频隔离变压器 ，是指频率为工频(50HZ)的变压器，变压器初级和次级都有电感，与逆变器里面的滤波电感，都可以储存一定的电能。而当电感流过电流时，由于电流会存在磁场，当电流的磁场经过磁芯时，电流磁场会打破“磁畴”的平衡状态，使“磁畴”同时趋向于外部磁场的方向， 进而导致磁芯此时会对外表现出磁场。而这个磁芯磁场从无到有的过程，其实就是电感储存磁场的过程。

电感 是由漆包线绕制在绝缘骨架或磁芯上形成的元器件。当线圈中有电流通过时，会在周围产生一定的磁场，而当通过的电流含有交流成分时，产生的磁场会不断变化，根据电磁感应原理，变化的磁力线又会在线圈两端产生感应电动势，但此电动势的方向和原来产生的电动势方向相反，并以此来阻碍电流的变化。  

由此可以看出，电感的主要作用是阻碍电流的变化。电流增加时，它会阻碍电流的增加，同时通过磁场储存一部分能量； 而当电流减小时，它又会阻碍电路中电流的减小，并释放出储存的能量来维持电流。正因为电感有储存能量的特性，所以才有滤波和延迟等功能。

总结

光伏离网系统，输出功率是由负载决定。当有电动机等感性负载启动时，短时间需要非常大的电流，而这些能量，光伏无法提供，蓄电池也不能提供，锂电池短时间如果过载输出，会引起爆炸。但是，逆变器里的电容、电感、变压器可以储能电量，还可短时间放大几倍输出而不会损坏。

As can be seen from the figure above, the peak power of the off-grid inverter using high-frequency isolation technology can reach twice the rated power; Off-grid inverter with power frequency isolation technology, the peak power can reach three times the rated power. Then, a 3kW high-frequency off-grid inverter can drive a 1P air conditioner (starting power about 5.5kVA), and a 12kW power-frequency off-grid inverter can drive a 6P air conditioner (starting power about 33kVA). The inverter provides starting energy for the load, partly from the battery or photovoltaic modules, and the excess is also provided by the inverter itself (internal energy storage components -- capacitors and inductors).

The picture

High frequency

SPF3000-5000TL HVM

The picture

Power frequency

SPF 4000-12000T HVM

Capacitors and inductors are both energy storage components. The difference is that capacitors store electric energy in the form of electric fields. The larger the capacity of capacitors, the more electricity they store. Inductors store energy in the form of magnetic fields. The larger the permeability of the inductor's magnetic core, the larger the inductance, and the more energy can be stored.

The picture

The principle of the capacitor can be seen from its structure. As shown in the figure above, there is a metal plate on each side leading to two electrodes separated by insulating material. In the case that no external electric field is applied to both ends of the capacitor, the positive and negative charges on the two plates are in a state of equilibrium.

The picture

As shown above, when both ends of an electric field applied in capacitance, end plate began to gather on the positive, the other end of the plate is gathered negative charge, as at the ends of the capacitor voltage rising to power supply voltage, capacitance charging to stop, if disconnect external circuit, capacitance on energy will not disappear, the reason is that with positive and negative charge on the characteristic of "the same, opposites attract", The charges at both ends attract and store energy.

Power frequency isolation transformer, refers to the frequency of power frequency (50HZ) transformer, transformer primary and secondary have inductance, and inverter inside the filter inductance, can store a certain amount of electric energy. When the inductor flows through the current, there will be a magnetic field. When the magnetic field of the current passes through the magnetic core, the current magnetic field will break the equilibrium state of the "magnetic domain" and make the "magnetic domain" tend to the direction of the external magnetic field, resulting in the magnetic field of the core at this time. The process of the core magnetic field from scratch is actually the process of inductive storage of magnetic field.

The picture

Inductance is a component formed by enameled wire wound on an insulating skeleton or magnetic core. When the coil is energized, can produce a magnetic field in the surrounding, when through the current communication ingredients, fields changing, according to the principle of electromagnetic induction, the change of magnetic field lines and can produce inductive electromotive force on both ends of the coil, but the direction of the electromotive force and the original electromotive force in the opposite direction, and to hinder the current changes.

The picture

It can be seen that the main function of inductance is to hinder the change of current. As the current increases, it blocks the increase and stores some of the energy through the magnetic field. When the current is reduced, it blocks the reduction of the current in the circuit and releases the stored energy to maintain the current. Because the inductor has the property of storing energy, it has the function of filtering and delay.

conclusion

The picture

Photovoltaic off-grid system, the output power is determined by the load. When a motor and other inductive load is started, a very large current is needed in a short time, and these energies cannot be provided by photovoltaic and battery. If the overload output of lithium battery is carried out in a short time, it will cause an explosion. However, the capacitor, inductor, transformer in the inverter can store power, but also a short time to magnify several times the output without damage.