Conventional ac induction motors are universal in application to the point that you would be hard pressed to find an industrial facility or even a residence without one. However, in this energy conscious age, manufacturers are hitting the limits of efficiency in this design. On the other hand, permanent magnet (PM) motors can offer higher efficiency levels than induction motors since they have no I2R losses in the rotor.
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sp;   In spite of this and other advantages, wider adoption of PM motors has been hobbled by the expense and trouble of having to include a speed encoder for Control. This problem has been mitigated thanks to developments of more sophisticated strategies that use an open-loop vector control method, eliminating the encoder. With that problem out of the way, users have discovered that ac PM motors offer some

        Rotor construction of ac PM motors is much different from traditional induction designswww.cechina.cn, but eliminating the rotor copper losses gives PM motors a big efficiency boost.

        attractive packages with smaller frame sizes and weight for a given horsepower rating weighed against conventional induction designs. On the other hand, induction motors are still generally less expensive and more able to withstand rough applications.
        Two rotor types
        Like their induction motor counterparts控制工程网版权所有, ac PM motors use a wound stator, but that's where the similarity ends. PM motors have the magnets attached to the rotor控制工程网版权所有, either on the surface or embedded inside. Consequentlywww.cechina.cn, there is no rotor currentwww.cechina.cn, which reduces copper losses. This is the main source of the efficiency gain.
        The differences between surface mounted permanent magnet (SPM) and interior