变频调速器能否实现节电，是由其负载的调速特性决定的。对于离心风机、离心水泵这类负载，转矩与转速的平方成正比，功率与转速的立方成正比。只要原来采用阀门控制流量，且不是满负荷工作，改为调速运行，均能实现节电。当转速下降为原来的80%时，功率只有原来的51.2%。可见，变频调速器在这类负载中的应用，节电效果最为明显。对于罗茨风机这类负载，转矩与转速的大小无关，即恒转矩负载。若原来采用放风阀放走多余风量的方法调节风量，改为调速运行，也能实现节电。当转速下降为原来的80%时，功率为原来的80%。比在离心风机、离心水泵中的应用节电效果要小得多。对于恒功率负载，功率与转速的大小无关。水泥厂恒功率负载，如配料皮带秤，在设定流量一定的条件下，当料层厚时，皮带速度减慢；当料层薄时，皮带速度加快。变频调速器在这类负载中的应用，不能节电。
Whether the VVVF can save electricity is determined by the speed governing characteristics of its load. For such loads as centrifugal fans and pumps, the torque is proportional to the square of the rotational speed and the power is proportional to the cube of the rotational speed. As long as the original use of valve control flow, and not full load work, to speed operation, can achieve power saving. When the speed decreases to 80%, the power is only 51.2%. It can be seen that the application of frequency converter in this kind of load has the most obvious effect of saving electricity. For the load of Roots blower, torque has nothing to do with speed, that is, constant torque load. If the original method of releasing excess air volume by air release valve is used to regulate air volume and speed regulation operation is changed, power saving can also be realized. When the speed decreases to 80%, the power is 80%. The power saving effect is much smaller than that in centrifugal fans and centrifugal pumps. For constant power load, power has nothing to do with the speed. Constant power load in cement plant, such as batching belt weigher, will slow down the belt speed when the material layer is thick, and accelerate the belt speed when the material layer is thin. The application of frequency converter in this kind of load can not save electricity.
与直流调速系统比较，直流电动机比交流电动机效率高、功率因数高，数字直流调速器与变频调速器效率不相上下，甚至数字直流调速器比变频调速器效率略高。所以，宣称使用交流异步电动机和变频调速器比使用直流电动机和直流调速器要节电，理论和实践证明，这是不正确的。
Compared with DC speed control system, DC motor has higher efficiency and power factor than AC motor, and the efficiency of digital DC speed governor and frequency converter is equal, even the efficiency of digital DC speed governor is slightly higher than frequency converter speed governor. Therefore, the claim that the use of AC asynchronous motor and inverter governor than the use of DC motor and DC governor to save electricity, theory and practice has proved that this is not correct.