修正波与正弦波

逆变器输出波形主要分两类，一类是正弦波，另一类是修正波 。修正弦波逆变器，采用PWM脉宽调制方式生成修正波输出，由于存在20%左右的谐波失真，不能带空调等感性负载，但可以带电灯等阻性负载。修正弦波逆变器采用非隔离耦合电路，器件简单，效率高。 纯正弦波逆变器采用隔离耦合电路设计，电路较复杂，成本较高，可以连接任何常见的电器设备（包括电视机、液晶显示器等，特别是冰箱等感性负载）而没有干扰。

工频隔离和高频隔离

纯正弦波离网逆变器的输入端和输出端有电气隔离，按照电气结构分为高频隔离和工频隔离，高频隔离变压器放在直流升压端，采用的方案是先把直流电逆变器高频率的交流电，通过高频变压器升压，然后整流为直流电，最后又逆变为工频交流电，高频逆变器采用的是体积小，重量轻的高频磁芯材料，可以降低逆变器的重量，减少逆变器的体积，提高逆变器的效率，但电路较为复杂。工频隔离变压器放在交流端出端，逆变器电路较简单，抗冲击能力较强，但体积较大，重量比较重。

高频逆变器应用场景

工频逆变器应用场景

古瑞瓦特高频隔离逆变器

古瑞瓦特工频隔离逆变器

分体式与一体式

离网系统由于多了一个蓄电池，因此必须要配置控制器，用于组件给蓄电池充电，控制器和逆变器分开，做成两个设备，就是分体式。把控制器和逆变器集成在一起，就是一体式，也称为控制逆变一体式。分体式系统，控制器和逆变器可以分别选型，但接线比较复杂，适应于组件和逆变器功率相差比较大的系统，以及系统功率很大的系统。控制逆变一体式系统结构简单，用户接线方便，适应于组件和逆变器功率相差比较小的系统。

离网逆变器的重要技术参数

在选择离网逆变器时，除了注意逆变器的输出波形，隔离类型外，还有几个技术参数也非常重要，如系统电压、输出功率、峰值功率、转换效率、切换时间等等，这些参数的选择对负载的用电需求影响较大。

1）系统电压：就是蓄电池组的电压，离网逆变器的输入电压和控制器的输出电压是一致的，在设计选型时，要注意和控制器保持一致。

2）输出功率：离网逆变器的输出功率表述有两种，一种是视在功率表示法，单位是VA，这是参考UPS标记，实际输出有功功率还需乘以功率因素，如500VA的离网逆变器，功率因素是0.8，实际输出有功功率就是400W，也就是说能带动400W的阻性负载，如电灯，电磁炉等；第二种是有功功率表示法，单位是W，如5000W离网逆变器，实际输出有功功率就是5000W。

3）峰值功率：在光伏离网系统中，组件、蓄电池、逆变器、负载构成电气系统，逆变器的输出功率，是由负载决定的，有些感性负载，如空调、水泵等，里面的电动机，启动功率是额定功率的3-5倍，所以离网逆变器对过载有特别要求。峰值功率就是离网逆变器的过载能力。

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，超出的部分由逆变器内部的储能元件—电容和电感来提供 。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。 

4）转换效率：离网系统转换效率包括两方面，一是机器本身的效率，离网逆变器电路复杂，要经过多级变换，因此整体效率比并网逆变器稍低，一般在80-90%之间，逆变器整机功率越大效率越高，高频隔离比工频隔离效率要高，系统电压越高效率也越高。二是蓄电池充放电的效率，这个是蓄电池的类型有关系，当光伏发电和负载用电同步时，光伏可以直接供给负载使用，不需要经过蓄电池转换。

5）切换时间：离网系统带负载，有光伏、蓄电池、市电三种模式，当蓄电池能量不足，切换到市电模式时，存在切换时间，有的离网逆变器采用电子开关切换，时间在10毫秒内，台式电脑不会关机，照明灯也不会闪烁。有的离网逆变器采用继电器切换，时间可能超过20毫秒，台式电脑可能会关机或者重启。

Modified wave and sine wave

Inverter output waveform is mainly divided into two categories, one is sine wave, the other is the correction wave. Repair sine wave inverter, using PWM pulse-width modulation to generate corrected wave output, due to the existence of about 20% harmonic distortion, can not take inductive load such as air conditioning, but can take resistive load such as lights. The repair sine wave inverter adopts the non - isolated coupling circuit, the device is simple and the efficiency is high. Pure sine wave inverter adopts isolated coupling circuit design, the circuit is more complex, high cost, can be connected to any common electrical equipment (including TV, LCD, especially the inductive load such as refrigerator) without interference.

The picture

Power frequency isolation and high frequency isolation

Pure sine wave off-grid inverter input and output end has electrical isolation, according to the electrical structure is divided into high frequency isolation and power frequency isolation, high frequency isolation transformer in the DC boost end, the scheme is to first put the DC inverter high frequency alternating current, through the high frequency transformer boost, and then rectifier to DC, and finally inverter for power frequency alternating current, High frequency inverter is small volume, light weight of high frequency magnetic core material, can reduce the weight of the inverter, reduce the volume of the inverter, improve the efficiency of the inverter, but the circuit is more complex. The power frequency isolation transformer is placed in the AC end out of the end, the inverter circuit is simple, strong impact resistance, but the volume is larger, the weight is heavier.

The picture

Application scenarios of high-frequency inverters

The picture

Application scenario of power frequency inverter

The picture

Guruwatt high frequency isolation inverter

The picture

Agent Gureva has a frequency isolation inverter

The picture

Split asanas versus uniasanas

Off-grid system due to more than a battery, so it must be configured with a controller, used for battery charging components, controller and inverter separate, make two devices, is split. The controller and inverter integrated together, is the integral, also known as the control inverter integral. Split system, controller and inverter can be selected separately, but the wiring is more complex, suitable for the component and inverter power difference is relatively large system, as well as the system power is very large. The integrated control inverter system has the advantages of simple structure, convenient connection, and is suitable for the system where the power difference between the component and the inverter is relatively small.

Important technical parameters of off-grid inverter

The picture

The picture

In the selection of off-grid inverter, in addition to pay attention to the output waveform of the inverter, isolation type, there are several technical parameters are also very important, such as system voltage, output power, peak power, conversion efficiency, switching time and so on. The selection of these parameters has a greater impact on the power demand of the load.

1) System voltage: is the voltage of the battery. The input voltage of the off-grid inverter is consistent with the output voltage of the controller. In the design and selection, attention should be paid to keeping consistent with the controller.

2) Output power: The output power of off-grid inverter is expressed in two ways, one is apparent power representation, the unit is VA, this is a reference to the UPS label, the actual output active power needs to be multiplied by the power factor, such as 500VA off-grid inverter, the power factor is 0.8, the actual output active power is 400W, that is to say, can drive 400W resistance load, such as lights, Induction cooker, etc.; The second is active power representation, the unit is W, such as 5000W off-grid inverter, the actual output active power is 5000W.

3) Peak power: in the photovoltaic off-grid system, components, batteries, inverters and loads constitute the electrical system. The output power of the inverters is determined by the load. For some inductive loads, such as air conditioners and water pumps, the motor inside has a starting power 3-5 times of the rated power, so the off-grid inverters have special requirements for over-loading. Peak power is the overload capacity of the off-grid inverter.

The inverter provides the load with starting energy, part of which comes from the battery or photovoltaic module, and the excess part is provided by the energy storage components inside the inverter -- capacitors and inductors. 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.

4) Conversion efficiency: off-grid system conversion efficiency includes two aspects, one is the efficiency of the machine itself, the off-grid inverter circuit is complex, after multistage transformation, so the overall efficiency is slightly lower than the grid-connected inverter, generally between 80-90%, the greater the inverter power efficiency is higher, high frequency isolation efficiency is higher than the power frequency isolation efficiency is higher, the higher the system voltage efficiency is higher. The second is the efficiency of battery charging and discharging. This is related to the type of battery. When photovoltaic power generation and load power consumption are synchronized, photovoltaic can directly supply the load, without the need for battery conversion.

5) Switching time: off-grid system with load, there are three modes of photovoltaic, battery, mains, when the battery energy is insufficient, switch to the mains mode, there is a switching time, some off-grid inverter using electronic switch, time within 10 milliseconds, desktop computer will not shut down, lights will not blink. Some off-grid inverters use relay switches that may take longer than 20 milliseconds, and the desktop computer may shut down or restart.