Comparing Phase Converter and VFD Applications

相位转换器的类型

一个相位转换器通过采用两条单相线路并通过一条额外的支路补充它们来促进三相转换，从而产生真正的三相电源。相转换器已经存在了相当长的一段时间，并且在正确维护的情况下平均寿命为30年。

相位转换器的类型：

• 静态相位转换器：  适用于小功率电机; 无法在三条不同的路线上平衡电流。在大多数情况下，承载大部分负载的绕组在铭牌马力的50％至80％范围内最大化。因此，连接的电机不能以全功率运行。它包括一个电容器（产生磁场）和一个电压敏感继电器（当电动机起动时断开电容器）。
• 旋转相位转换器：  能够满足所连接电机的铭牌所设定的严格的马力要求，功率损失极低。非常适用于启动负载较重的大型机器。使用感应电机（惰轮）来产生三相转换过程的第三段。作为一种高效的电压转换工具，这些设备可提供高达95％的转换效率，损耗通常为单位数字（低于10％）。
• 数字相位转换器：  这种类型的相位转换器是固态的，并使用数字信号处理器（DSP）产生第三相电源。与静态和旋转相位转换器相比，该装置安静，更准确地运行。它不使用闲人。

变频器的特点和用途

The way a VFD facilitates phase conversion differs, compared to phase converters. During installation, the device is wired to the supply line and motor. Compared to a phase converter, controls take place on the VFD interface – not a set of switches or using starters. Common applications include drill presses, large mills and pumps, CNC, cranes, automation and lathes. It’s important to highlight that when sizing a VFD, one must check for the Full-load Amps (FLA) rating on the nameplate, not the horsepower rating.

During operation, the unit converts the single-phase AC supply line (input) into DC, which is converted to three-phase AC on the output side. To start, a bridge rectifier (consisting of 4 or 6 semiconductor diodes) is used to facilitate the initial conversion from AC to DC voltage. At this stage, the DC voltage generated is ‘dirty’ or filled with ripples in its waveform. Next, a capacitator bank acts as a filter to smoothen out the DC voltage. In the next section of the VFD, DC voltage is converted to AC three-phase, via an inverter. Switches in the inverter manages positive and negative voltages that are needed to generate the desired phase and frequency.

The wave produced by the VFD on the output side is rectangular, as the units are unable to generate a sinusoidal wave.

Which One is Better?

Both devices can facilitate phase conversion, from single phase to three phase. Choosing one over the other depends on a handful of factors, such as the number of machines connected to the unit, motor power requirements and costs. All of these variables will be addressed in this section of the article.

For operators who need to simultaneously run more than one three-phase machine from a single-phase supply line, a phase converter is highly recommended. VFDs are more applicable to running one connected machine at a time, as well as for highly accurate control of starting and stopping connected motors, such as an industrial conveyor belt in a manufacturing plant.

As for specific types of phase converters, a static phase converter is suitable for light loads and machines with minimal starting loads. With this in mind, if you’re operating large saws and air compressors at the facility, it would be more advisable to consider a rotary phase converter because the units are more capable of handling large starting loads.

Compared to phase converters, which cannot adjust frequency or motor speed, VFDs provide more control over several aspects of power regulation and distribution. Such factors include motor speed, frequency, direction and soft starting (great for preserving the lifespan of large machines and reducing inrush currents).

值得注意的是，由于所产生的波形没有平滑的正弦曲线特性，VFD可能会导致无线电频率干扰。与VFD相关的一般缺点通常可以通过重新连线连接的机器来纠正，以使其与设备更加兼容。

最后，对快速设置和安装感兴趣的人可能会从使用相位转换器中受益。电子变频器需要一些编程来满足连接机器的要求，并包含更复杂的配置设置。该单元比带有惰轮的标准相位转换器更紧凑。这为企业提供了更多节省空间的优势。