??Inverters have taken a prominent role in the modern technological world due to the sudden rise of electric cars and renewable energy technologies.

 由于电动汽车和可再生能源技术的突然兴起，逆变器在现代技术世界中扮演了重要角色。

?? Inverters convert DC power to AC power, they are also used uninterrupted power supplies, control all of electrical machines and active power filtering. This video will explain how to get a pure Sinusoidal electric power output from DC power input, in a step by step logical manner.

  逆变器将直流电转换为交流电，这一过程可以为电机工作和有功功率的转换提供不间断的电源。这个视频将逐步讲解如何从DC电源输入中获得纯正弦电源的输出。

??Alternating current periodically reverses its direction.  For this reason,  the average value of an alternating current over a cycle will be zero.  Before proceeding to sine wave production, let's see how a square wave alternating current is produced.  In fact, the old type inverter is used to produce simple square wave as their output.

 交流电会周期性地反转其方向。因此，整个周期内交流电的平均值为零。在进行正弦波介绍之前，让我们看看如何产生方波交流电。 实际上，旧式逆变器通过产生简单的方波作为其输出的。

?? Let's build an interesting circuit as shown with four switches and one input voltage. This circuit is known as full bridge inverter. 

 让我们构建一个有趣的电路，如图所示，其中包含四个开关和一个输入电压，该电路称为全桥逆变器。

?? The output is drawn between points A and B. To make this circuit analysis easier, let's replace this actual load with a hypothetical load. Just note the current flow when switches S1 and S4 are on, and S2 and S3 are off.  

输出在点A和点B之间绘制，为了简化此电路分析，让我们用一个假设负载替换此实际负载。当开关S1和S4接通，而S2和S3关断时，注意此时电流流向。

?? Now just do the reverse and observe the current flow. It is clear that the current flow is the opposite in this case, as is the output voltage across the load. This is the basic technique that produces a square wave alternating current.

现在，只需进行相反的操作并观察电流。显然，在这种情况下，电流流动是相反的，负载两端的输出电压也是如此。以上，就是产生方波交流电的基本原理。

?? We all know that the frequency of the AC supply available in our homes is 60 Hz. This means that we need to turn the switch on and off 120 times in a second, which is not possible when manually or by using mechanical switches. 

 我们都知道，我们家中可用的交流电源的频率为60 Hz。这意味着我们需要在一秒钟内将开关打开和关闭120次，这在手动或使用机械开关时是不可能的。

?? We introduce semiconductor switches, such as Mosfet for this purpose. They can turn on and turn off thousands of times per second. With the help of control signals, we can turn transistors on or off very easily. 

 为此，我们引入了半导体开关，例如MOSFET。它们每秒可以打开和关闭数千次。借助控制信号，我们可以非常轻松地打开或关闭晶体管。

?? The square wave output is a high approximation of sine wave output. Old inverter is used to produce them. That's why you hear a humming noise when you run your electric fan or other appliances using square wave power. They also heat up electric equipment. 

方波输出是正弦波输出的高度近似，而老的控制器一般产生的是方波电流。这就是为什么在使用方波电源运行电风扇或其他设备时听到嗡嗡声的原因，此外，它们还会加热电气设备。

?? Modern inverters produce pure sinusoidal output. Let's see how they achieve it. 

 然而，现代的逆变器输出的是正弦电流，下面让我们看看他们是如何实现的？

?? A technique called Pulse Width Modulation is used for this purpose. 

 为此，使用了一种称为脉冲宽度调制的技术。

?? The logic of Pulse Width Modulation is simple. Generate the DC voltage in the form of pulses of different widths. In regions where you need higher amplitude, it will generate pulses of larger width. The pulses for the sine wave look like this.

 脉冲宽度调制的逻辑很简单。以不同宽度的脉冲形式产生直流电压，在需要更高幅度的区域中，它将生成更大宽度的脉冲。正弦波的脉冲看起来像这样：

?? Now here is the tricky part, what will happen if you average these pulses in a small time interval.  You will be surprised to see that the shape of the average pulses looks very similar to the sine curve. The finer the pulses used, the better shape the sine curve will be. 

 这里面最有技巧的一部分是：如果在较短的时间间隔内，对这些脉冲求平均，会发生什么？你会惊讶地发现平均脉冲的形状看起来与正弦曲线非常相似。使用的脉冲越精细。正弦曲线的就形状越好。

?? Now, the real question is how to make these pulses and how do we average them in a practical way? Let's see how they are implemented in an actual inverter.

现在真正的问题是：如何产生这些脉冲，以及如何以将其在实际中应用? 让我们看看如何在实际的逆变器中实现它们。

?? Two comparators are used for this purpose. Comparators compare a sine wave with triangular waves.  One comparator uses a normal sine wave,  and the other comparator uses an invertion sine wave.  

为此使用了两个比较器。比较器将正弦波与三角波进行比较。一个比较器使用正常的正弦波；另一个比较器使用反向正弦波。

?? The first comparator controls S1 and S2 switches. And the secondcomparator controls S3 and S4.  

第一比较器控制S1和S2开关，第二比较器控制S3和S4。

?? S1 and S2 switches determined voltage level at point A and the other two switches determined voltage level at point B. 

S1和S2的切换，决定了A点的电压电平；其他两个的切换决定了B点的电压电平。

?? You can see that the one branch of comparative output is fitted with a logic not gate.  This will make sure that when S1 is on S2 will be off . This also means that we can never turn on S1 and S2 at the same time, which will cause the DC circuit to short circuit. 

可以看到比较器输出的一个分支装有逻辑非门。这将确保当S1打开时S2将关闭，这也意味着我们永远不能同时打开S1和S2，这将导致DC电路短路。

?? The switching logic of PWM is simple. When the sine way value is more than the triangular wave, comparator produces 1 signal, otherwise zero signal. 

PWM的开关逻辑很简单：当正弦波值大于三角波时，比较器将置1，否则置0。

?? Now observe voltage variation at first comparator according to this logic. 

现在，根据此逻辑在第一个比较器处观察电压变化：

?? Control signal of 1 turns on the MOSFET. The voltage pulse is produced at point A are shown. 

MOSFET上控制信号置1，A点处产生的电压脉冲如下图：

?? Apply the same switching logic and observe the voltage pulses generated at point B. 

采用相同的开关逻辑，观察B点处的电压脉冲如下图：

?? Since we are drawing output voltage between point A and B, the net voltage will be the difference between A and B. This is the exact pulse train we need to create the sine wave. The finer the triangular wave, the more accurate the pulse train will be.

由此，我们可以在点A和点B之间绘制输出电压，因此净电压将是点A和点B之间的差，这正是我们需要产生正弦波的确切脉冲序列。三角波越精细，脉冲序列将越精确。

?? Now the next question is how do we practically implement the averaging. 

 现在，下一个问题是我们如何实际中实现平均化。

?? To make it exactly sinusoidal, energy storage elements such as inductors and capacitors are used to smoother power flow. They are called passive filters. Inductors are used to smoothen the current. And capacitors are used to smooth in the voltage.

 为了使其精确地呈正弦形，使用了诸如电感和电容之类的能量存储元件来平滑功率流。它们称为无源滤波器。电感用于平滑电流。电容用来平滑电压。

??  All in all, with an inverter bridge, a good PWM technique, and a passive filter, you can generate sinusoidal voltage and operate all of your appliances without any fuss. 

 总而言之，借助逆变器电桥、良好的PWM技术和无源滤波器，您可以产生正弦电压，并且可以轻松操作所有设备。

??  The inverter technology we have explained so far has only two levels of voltage.  What if we introduce one more voltage level. This will give better approximation of the sine wave and can reduce instantaneous error.

 到目前为止，我们解释的逆变器技术只有两个电压电平，如果再引入一个电压电平该怎么办。这样可以更好地近似正弦波，并可以减少瞬时误差。

?? Such Multilevel Inverter Technology is used in high precision applications like wind turbines and electric cars.

 这种多电平逆变器技术用于风力涡轮机和电动汽车等高精度应用中。

??  Inverters are used in the electric cars have intelligent frequency and amplitude control. In fact, frequency controls the speed of an electric car and amplitude controls the power of it. This way inverters act as the brain of electric cars by producing electric power ideal for driving conditions.

 电动汽车中使用的逆变器具有智能的频率和幅度控制。实际上，频率控制电动汽车的速度，振幅控制电动汽车的功率。通过这种方式，逆变器通过产生理想的驾驶条件电力来充当电动汽车的大脑。

总结

以上就是关于逆变器工作原理的介绍，三句话简单总结下：

1). 通过MOSFET开关，我们在全桥逆变电路上产生高频变化的方波

2). 通过比较器的应用，产生正弦波所需要的脉冲序列

3). 通过电容、电感等储能元件，获得精确的交流电，实现电机的控制和功率的转换。