As we all know, in the field of industrial control, frequency converter is a kind of application of frequency conversion technology and microelectronics technology, through the change of AC motor power supply frequency and voltage to accurately control the motor speed of the power control equipment, which can not only indirectly improve the energy efficiency ratio of the motor, to achieve energy saving and emission reduction, but also integrated overcurrent, overvoltage, overload and other protection functions, is a widely used in modern industry, one of the indispensable and important equipment.
Schematic diagram of the main circuit of a general-purpose inverter
As shown in the above figure, the inverter is a complete electrical device integrating rectification, filtering, inversion and other functions, and its working principle is to rectify the industrial frequency alternating current (e.g., 380V/220V, 50Hz) into direct current (DC), and then smoothen the rectified DC through the filtering circuit, and then invert the smooth DC through the inverter circuit into adjustable frequency alternating current (AC) to change the AC motor speed regulation and realize the motor speed regulation. frequency of the power supply to realize the speed regulation of the motor.
Why do I need electrical isolation in a frequency converter?
It is worth mentioning that the MOSFET/IGBT power tubes in the frequency converter will carry out high-speed switching action during the working process (DC-AC inverter), and generate high-frequency harmonics, electromagnetic radiation and common mode noise and other undesirable interference phenomena, which will lead to a series of problems such as malfunctioning of the control system, distortion of signals, interruption of communication and inaccuracy of the measuring instruments.
Therefore, in order to suppress the undesirable interference phenomenon, ensure the accurate transmission of signals, and at the same time block the main circuit of the inverter (rectifier, inverter) in hundreds to thousands of volts of high-voltage current conduction to the low-voltage control circuit, to avoid the occurrence of potential safety hazards, to take effective electrical isolation measures has become the inevitable choice of the design of high-end, reliable, stable inverter.
As a key device that can realize stable signal transmission under electrical isolation, digital isolator can not only block the electrical conduction path between high and low voltage circuits, but also isolate the electromagnetic radiation and common mode noise interference on signal transmission, which has become one of the core devices in the current market to enhance the stability of the frequency converter system and electrical safety.
Digital isolator, how to guard the safe operation of the inverter?
With the continuous development of modern industry in the direction of high precision and high energy efficiency, digital isolator has become a key bridge connecting "weak control" and "strong power" in inverter, which solves the problem of system instability caused by electromagnetic interference by electrical isolation, noise suppression and signal fidelity, and also solves the problem of system instability caused by electromagnetic radiation and common mode noise interference on signal transmission. The system instability caused by electromagnetic interference can be solved through electrical isolation, noise suppression and signal fidelity, and at the same time, it can also guarantee the safety of sensitive components and operators.
Schematic diagram of a typical inverter circuit electrical isolation scheme
As shown in the above figure, in the electrical isolation scheme provided by HOPERF for inverter, CMT860XX and other isolation driver chips can be applied between the system master MCU and power tubes (MOSFET/IGBT), which can effectively prevent the high voltage from running into the control side and damaging the sensitive components, and at the same time, amplify the PWM control signals to provide sufficient drive current to meet the needs of the wide bandwidth semiconductors of the high-frequency switching requirements, and also integrates a failure protection mechanism, which can protect sensitive components and operator safety. It also integrates a failure protection mechanism to ensure the efficient and reliable operation of the inverter circuit.
Isolated sampling chips such as CMT130X can be applied between the MCU and the high-voltage bus, which can block the risk of the high voltage of the bus from running into the control circuit, and at the same time can effectively suppress noise interference, sample analog signals such as bus voltage and current, and provide high-precision digital sampling data for the MCU, which can significantly improve system reliability.
Standard digital isolation chips such as CMT812X and CMT804X can be applied between the master MCU and the serial bus (RS485/SPI/IIC), effectively eliminating ground loops and blocking noise from coupling to the communication link through the ground or signal line to ensure the stability of data communication.
Looking ahead, with the acceleration of industrial automation and green manufacturing, digital isolator as a core device to ensure the safe operation of power electronic equipment, its development will deeply meet the needs of the industrial field of change and iteration, to the integration, low power consumption, high performance and other directions continue to breakthrough for the safe and efficient operation of industrial equipment to build a solid foundation to help the manufacturing industry to high-quality, sustainable direction.
