变频器控制方式特点：

其特点是控制电路结构简单、成本较低，机械特性硬度也较好，能够满足一般传动的平滑调速要求，已在产业的各个域得到广泛应用。但是，这种控制方式在低频时，由于输出电压较低，转矩受定子电阻压降的影响比较显著，使输出大转矩减小。另外，其机械特性终究没有直流电动机硬，动态转矩能力和静态调速性能都还不尽如人意，且系统性能不高、控制曲线会随负载的变化而变化，转矩响应慢、电机转矩利用率不高，低速时因定子电阻和逆变器死区效应的存在而性能下降，稳定性变差等。因此人们又研究出矢量控制变频调速。

S7-1200通信和程序的特点：

S7-1200是西门子的新一代的控制器，在串口通信方面在硬件与软件方面都与S7-200不同：通讯方面：作为200的升产品，1200不支持DP等应用比较广泛的通讯协议，但保留了强大的自由口通讯功能；程序方面：引入块概念，更接近于300，编程方便，尤其是通讯方面的编程（自由口、MODBUS等，一个块可以控制多个驱动器，不同电机的数据存储在不同的数据库中；硬件方面：S7-1200现有的几款PLC都可以扩展3个串口通信模板（即可以全部是RS232接口，也可以全部是RS485接口，也可以是两种接口的组合），而S7-200这不可以进行扩展，只能用本体上的RS485口，在这一点上功能强了。软件方面：S7-1200，在编程上与S7-300的编程方法类似，组态完硬件接口，直接调用功能块就可以，非常简单，不像S7-200需要对SM进行操作。S7-1200与S7-300在串口通信比较起来基本上一样，但在作Modbus的通信时不需要额外的Dongle来支持。

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