Motor based on PWM inverter output (Pulse width modulation, similar high speed switch)Methods to manipulate, thus produces high frequency leakage current. The following factors can determine the size of the system leakage current, and selected the appropriate leakage circuit breakers and necessary measures to improve the phenomenon of leakage circuit breaker tripping after sending. First of all, three level before the inverter, power supply transformer, motor transmission device of PE point must be together, and consistent to the ground. Inverter is high frequency square wave voltage output, because inside the motor coil and motor shell equivalent capacitance between exist, then the leakage current. If no grounding or bad, there will be a leakage phenomenon. Leakage current size of the elements are: (1)Cable leakage current (There are two parts)The leakage circuit breakers, filter the leakage current of cable length. The leakage current of frequency converter, motor cable length. （2)The leakage current of filter (Including frequency converter)。 （3)The leakage current of the motor. Some site using inverter control motor, can present leakage problem, dozens of creepage voltage v to two hundred v voltage range. Aiming at this problem, especially for analysis of this kind of phenomenon the reason is as follows: on the basis of the function of the inverter control motor working diagram, three-phase power supply after the converter rectifier bridge rectifier, the capacitor filter to inverter bridge (IGBT）To through the inverter bridge, three phase output frequency and voltage adjustable alternating current to control the motor work. Three mutually sent 120 degrees alternating current flowing in the three-phase stator coil winding of the motor, a rotating magnetic field, make the rotor on the stator winding of the motor rotating magnetic field under the effect of active spin. Happened after the three-phase motor stator winding through the current rotating magnetic field, and based on the principle of electromagnetic induction, the shell of the motor can produce inductive electromotive force. The induced electromotive force size, depends on the size of the switch frequency of inverter IGBT and C× DV / DT (Related to the speed of IGBT switch)。 If the induction electromotive force is bigger, so people touch will feel being shocked. In theory of the IGBT switching frequency is higher, the effective value of motor shell induced electromotive force (The induced voltage)The higher, and the frequency converter for motor control precision and dynamic echo is higher, after the body touch the greater is the feeling of electric; On the other hand, the IGBT switching frequency is lower, the effective value of motor shell of induction electromotive force (Induced voltage)After the lower, and from the body touch is the feeling of power. For asynchronous motor, motor shell will be induced voltage (The so-called leakage), so, motor manufacturers will be in the motor factory, in the junction box inside install earthing terminal, convenience in bridging the earth when it is applied to eliminate the induced electromotive force (Eliminate voltage induced leakage)To deal with the human touch is the feeling of electric motor. When work motor, power frequency switching frequency is approximately 50 hz, power frequency is very low, so usually can't have the feeling of leakage (Unless the motor insulation is very poor)。 And the inverter control, because its switching frequency is much higher than the work frequency, so the inverter in the rolling control motor, motor shell will have the feeling of the leakage.
