The cause of the leakage problem of Sunland inverter

1. The cause of inverter leakage

According to the inverter to control the operation of the motor, the three-phase electricity is supplied to the inverter bridge (IGBT) through the filter capacitor through the rectification, and then the operation of the motor is controlled by the three-phase electricity with adjustable output frequency and voltage of the inverter.

We all know that the three-phase stator winding of the motor flows through the current to produce a rotating magnetic field, according to the principle of magnetoelectric induction, the shell of the motor will induce electromotive force, the size of the electromotive force depends on the size of the switching frequency of the inverter IGBT, because the high-performance control requires a high switching frequency, the switching speed is very fast, then the DV/DT is large, and the induced electromotive force is large, and the person will have the feeling of electric shock on contact. Theoretically, the faster the switching speed of IGBT, the higher the induced electromotive force on the motor shell, and the higher the control accuracy and response of the inverter to the motor, the higher the feeling of being charged after contact, on the contrary, the switching frequency of IGBT is slow, the induction electricity is small, and the feeling of human contact is small, so the switching frequency of the domestic low-end inverter is low, and the induction electricity is small after controlling the motor, and the person does not feel anything when he touches, but its handling is poor, and the dynamic response is slower. Our inverter performance and dynamic response are better, so the switching frequency and speed of our IGBT are higher, and the induced electromotive force will be larger accordingly. Because the frequency of the power frequency operation motor is only 50HZ, there will be no feeling of leakage on one side, and when the frequency conversion is controlled, the switching frequency is very high, and the motor shell will have a feeling of leakage.

The cause of the leakage problem of Sunland inverter

The cause of the leakage problem of Sunland inverter

2. The solution plan for the leakage problem

In order to avoid the occurrence of this problem, in the hardware planning, the induction surge filter circuit is added, and the grounding end of the surge filter is connected to the shell of the inverter, and in the wiring description of the inverter, the grounding terminal of the motor is required to be connected with the grounding B of the inverter, and the ground (earth) of the input power supply is connected to the grounding A of the inverter, so that the induction electricity of the motor forms a loop through the grounding of the motor and the inverter and the grounding wire of the inverter and the power supply. The ground of the ground inverter of the motor and the ground of the power supply are at the same potential, and the potential difference between them is 0 volt voltage, so that people standing on the ground and touching the shell of the motor, the rack of the equipment, and the shell of the inverter will not have the feeling of being electrified.

However, in some factories for the convenience of wiring, the high-voltage power distribution room did not pull the ground wire into the workshop, and even the fault that the earth is the ground wire, this idea is wrong, we might as well think about it, if the earth can be on the ground, then why do we have to pull the N line box ground wire in our daily days? The N line in the power station is also connected to the ground wire. We don't have to pull the N wire box ground wire, doesn't it save a lot of wires? Why waste manpower, material resources, and time? However, in reality, there are many factories that do not pull the power ground wire, and the equipment cannot find the grounding point, but the motor has induction leakage in use.

Plan 1: Connect the ground end of the motor, the frame housing, and the ground end of the inverter

After the motor, inverter and frame are connected together, so that they are at the same potential, and through the surge absorption and discharge inside the inverter, the induced voltage is greatly reduced, so that people will not feel electrocuted, that is, there is no ground wire and no connection, as long as a few ground are connected together, so that the surge filter inside the inverter can play a role.

Plan 2: Under normal circumstances, through the treatment of plan 1, there will be no phenomenon of electric person, but because of special reasons, the induced voltage is still relatively high, and it can still be used to electric person, then under the premise of plan 1, an inductive surge filter will be added to the input power supply end of the inverter.

And the ground of the induction surge filter is connected with the ground of the motor and the ground of the inverter, so that the induction surge filter absorbs and discharges the induced electricity of the motor again, further reduces the induced voltage, and achieves the current goal of preventing leakage. The circuit principle of the added inductive surge filter is the same as that of the inverter, but it is too large to be planned to be installed in the internal circuit of the inverter, so it is made an external connection method.

We have proved through many tests that through the on-site rectification of the connection method of plan 2, the induced voltage of the motor can be reduced to below 20V in the use of the ground wire without the power supply, so as to ensure the safety of the on-site operators and no longer have the feeling of being leaked. However, if the ground wire with the power cord is connected to the second plan, then there is no need to connect an external induction surge filter.

In addition, if there are multiple inverters on the site to control the motor to work, and it is not convenient to install a plurality of inductive surge filters, it is not necessarily required that each inverter is equipped with an inductive surge filter, but also can only connect one or two inductive surge filters, and connect the grounding end of the filter with the grounding terminal of several inverters on the site, the grounding terminal of the field motor, and the equipment rack together: because each inverter has an inductive surge filter circuit inside, However, if the grounding wire of the motor is not connected back to the grounding terminal of the inverter, the induced surge filter will not work, so the grounding end of the motor in field use must be connected to the grounding terminal of the inverter. Of course, some equipment in some occasions the motor does not connect to the ground wire and will not have the feeling of leakage, which is the same as the principle of "although the earth is also a conductor, but the earth has a resistance value after all, and according to the soil composition of different lands, the resistance value is also very small". However, according to the correct electrical safety specifications, it is required that the motor is excellently grounded, but the conditions do not allow it (such as there is no power grounding terminal), the ground of the motor, the electrical cabinet shell and the ground of the inverter can always be connected together.

The cause of the leakage problem of Sunland inverter

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