Loss and classification of power electronic devices

Loss and classification of power electronic devices

The development of power electronic technology is based on the production and development of various power electronic devices. Power electronic devices are the foundation of power electronic circuits. Mastering the characteristics of various commonly used power electronic devices and the correct use methods are the basis for learning power electronic technology.

Loss of power electronic devices

The losses of power electronic devices mainly include: on-state loss, off-state loss and switching loss.

The power electronic device is not ideal short circuit or open circuit in the conducting or blocking state. There is a certain on-state voltage drop on the device when it is turned on, and a small off-state leakage current flows through the device when it is blocked. Although their values are very small, they interact with the larger on-state current and off-state voltage to form the on-state loss and off-state loss of power electronic devices.

The loss generated during the conversion process of power electronic devices from off-state to on-state (on-through process) or from on-state to off-state (off-state) is called turn-on loss and turn-off loss, collectively referred to as switching loss. For some devices, the power injected into them by the drive circuit is also one of the reasons for the heating of the device. Except for some special devices, the on-state leakage current of power electronic devices is extremely small, so on-state loss is the main cause of power loss in power electronic devices. When the switching frequency of the device is high, the switching loss will increase and may become the main factor of the power loss of the device.

Classification of power electronic devices

There are many types of power electronic devices, which can be divided into uncontrolled devices, semi-controlled devices and fully controlled devices according to their switching control performance.

1) Uncontrolled devices are two-terminal devices without control terminals. For example, power diodes, the turn-on and turn-off of the device is completely determined by the voltage and current that it bears in the main circuit, and it does not have the controllable switching capability.

2) The semi-controlled device is a three-terminal device with a control terminal. But its control terminal can only control its turn-on but not its turn-off. The device’s turn-off is completely determined by the voltage and current it bears in the circuit. Thyristors and most derivative devices belong to this type of device.

3) The full-control device is a three-terminal device with a control terminal. It can be controlled to be turned on and turned off by a control signal, so it is also called a self-shutdown device. At present, the most commonly used insulated gate bipolar transistors (IGBT), field effect transistors (MOSFET) and gate turn off (GTO) thyristors are all of these devices.

According to the nature of the signal added by the drive circuit between the control terminal and the common terminal of the power electronic device, the power electronic device (except the power diode) can be divided into two types: current-driven and voltage-driven. If the turn-on or turn-off control is achieved by injecting or drawing current from the control terminal, this type of power electronic device is called a current-driven power electronic device, or a current-controlled power electronic device. If a certain voltage signal is applied between the control terminal and the common terminal to achieve turn-on or turn-off control, this type of power electronic device is called a voltage-driven power electronic device, or a voltage-controlled power electronic device.

In addition, power electronic devices can also be divided into unipolar devices, bipolar devices and composite devices according to the fact that the two carriers of electrons and holes inside the device participate in conduction. A device in which one type of carrier participates in conduction is called a unipolar device (also called a multi-child device); a device in which both electron and hole carriers participate in conduction is called a bipolar device (also called a minority carrier); a device composed of a polar device and a bipolar device is called a composite device.

Later articles will analyze these devices separately from the perspective of applications.

Loss and classification of power electronic devices
Figure 1 – The power semiconductor devices family
Loss and classification of power electronic devices
Figure 2 – Classification of Power Electronic Devices