Features of power electronic devices and the composition of power electronic control systems

Features of power electronic devices and the composition of power electronic control systems

Features of power electronic devices

Power electronic devices generally refer to power semiconductor devices. Like ordinary semiconductor devices, the main material currently used in power semiconductor devices is silicon.

Since power electronic devices are directly used in the main circuit for processing electrical energy, they generally have the following characteristics compared with electronic devices that process information:

1) The electric power that the power electronic device can handle is relatively large. Its ability to withstand voltage and current is its most important parameter. Its ability to handle electrical power is as small as milliwatts to as large as megawatts, and is generally far greater than electronic devices that process information.

2) Power electronic devices generally work in a switching state. Because the electric power processed by the power electronic device is relatively large, the switching state can reduce the loss of the device itself and improve the efficiency of electric energy conversion. In analog electronic circuits, electronic devices generally work in linear amplification. Although the electronic devices in the digital electronic circuit also work in the on-off state, their purpose is to use the on-off state to represent different information.

3) Power electronic devices need to be controlled and driven by information electronic circuits. In practical applications, since the electric power handled by power electronic devices is relatively large, information electronic circuits must be used to achieve weak current control over strong current.

4) Power electronic devices must be equipped with radiators. Although the power electronic device works in the switching state, the power loss of the power electronic device is usually much larger than that of the information electronic device. Therefore, in order to ensure that the device is not damaged due to excessive heat caused by the heat dissipated by the loss, not only the heat dissipation design is paid more attention to the device package, but also a heat sink is generally required to be installed during its work.

The composition of the power electronic control system

The composition of a power electronic control system is shown in Figure 1. In practical applications, power electronic devices generally consist of a control unit, a drive circuit, a detection circuit, and a main circuit centered on power electronic devices.

The control unit can be composed of computer, single-chip microcomputer, PLC, etc. and information electronic circuits. The control circuit forms control signals according to the working requirements of the system. The drive circuit controls the on and off of the power electronic devices in the main circuit to realize the functions of the entire system.

The detection circuit is composed of a sensor and an information electronic circuit. The sensor detects the main circuit or on-site signals. After these signals are processed by the information electronic circuit, they are provided to the control unit and form a closed-loop control signal according to the working requirements of the system.

The drive circuit is generally composed of information electronic circuits. In some occasions that require high-power drive and shutdown, the drive circuit can also be composed of power power electronic devices.

People tend to classify circuits other than the main circuit such as the detection circuit and the drive circuit as the control circuit, so the power electronic system can be regarded as composed of the main circuit and the control circuit. The voltage and current in the main circuit are generally large, while the components in the control circuit can only withstand small voltages and currents. Therefore, the connection between the main circuit and the control circuit, such as the connection between the drive circuit and the main circuit, or the connection between the drive circuit and the control signal, and the connection between the main circuit and the detection circuit, need to be electrically isolated. Generally, optical and magnetic signals are transmitted through photocouplers or transformers to achieve electrical isolation. In addition, power electronic devices based on semiconductor materials have poor withstand voltage and current overshoot. Therefore, some protection circuits must be added to the main circuit and control circuit to ensure the normal and reliable operation of the power electronic devices and the entire power electronic system.

Features of power electronic devices and the composition of power electronic control systems
Figure 1 – The composition of the power electronic control system