Why do Motors Need Protection?
In general, a variety of types of protection are required for motor drive applications, such as safeguarding motors, power transistors, or any other component that is part of the. The protection against currents of the inverter is among the most essential components. It is not just a way to prevent possible harm to the transistor it also stops the demagnetization in the case of malfunction or when the control is unstable. OCP, as well as short circuit protection (SCP), can be described as two commonly used protection strategies, however, there are still some differences between them. This article explains the differences in OCP as well as SCP and other protection methods.
How do I How to Set OCP Points?
Whatever overcurrent scenario is encountered what method to set the protection current is crucial. To address this issue it is first necessary to identify the components that are vulnerable within the system. Most often the IGBT is more susceptible to damage than the diode that is freewheeling. If the inverter is transferring energy to the motor the motor, overcurrent conditions are more likely to develop. If you choose that OCP trip value is set to the maximum current the IGBT is able to handle is dependent on the control method used in the process. In Volt/Hertz control the value of the current can't be determined prior to the start of the system.
For instance, the permanent magnet motor in a refrigerator equipped with FOC is rated at a maximum current of one amp however, it is able to endure a 120% overload over 10 mins during its initial cooling phase. In this scenario, the maximum current is 1A 1200% Sqrt(2) equals 1.7 A peak. When considering the current control's overshoot margin +/-2 A could be set to set the range of feedback currently available within the control. This means that 2.5 A can be set as the OCP trip point. Even when the five A IGBT with the saturation maximum current of 30, A is utilized in the circuit of an inverter, this trip point doesn't have to be set at 10 A or greater. The trip point with a high current can cause the motor to demagnetize.
Summarize
This article explains the differences in OCP as well as SCP and the various schemes for protection. To ensure that you meet the standards, proper protection techniques must be selected with care.
One of the major drawbacks of these techniques is the inability to identify ground fault currents, as illustrated in Figure 2(a). So long as the sum does not reach zero, the software will determine three-phase currents, and also identify ground faults. The speed of its response may not be sufficient to protect against IGBT damages. Magnetic cores or a current detection resistor mounted on a negative DC bus rail, and desaturation protection is other options for grounding methods for protection.
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