Importance of Inverter Conversion Efficiency

It is very important to improve the conversion efficiency of the inverter. For example, if we increase the conversion efficiency by 1%, the inverter of 500KW is an average of 4 hours a day, and the inverter can generate nearly 20 kWh more electricity every day. It can generate nearly 7300 kWh more electricity, and 73000 kWh more electricity in ten years, which is equivalent to the power generation of a 5KW inverter, so that customers can save a 5KW inverter power station, so in order to improve the customer's maximum interest, we need to improve the conversion efficiency of the inverter as much as possible.

Influence factors of inverter efficiency

The only measure to improve the efficiency of the inverter is to reduce losses. The main losses of the inverter come from power switches such as IGBTs and MOSFETs, as well as magnetic devices such as transformers and inductors. There are relationships.

The loss of IGBT is mainly conduction loss and switching loss, among which conduction loss is related to the internal resistance of the device and the current passing through it, and the switching loss is related to the switching frequency of the device and the DC voltage that the device withstands.

The loss of inductance mainly includes copper loss and iron loss. Copper loss refers to the loss caused by the coil resistance of the inductance. When the current passes through the coil resistance to heat up, a part of the electric energy will be converted into heat energy and lost, because the coil is generally made of insulated copper wire. Winding, so called copper loss, copper loss can be calculated by measuring the short-circuit impedance of the transformer. The iron loss includes two aspects: one is the hysteresis loss, and the other is the eddy current loss. The iron loss can be calculated by measuring the no-load current of the transformer.

How to improve inverter efficiency

There are currently three technical routes: one is to use control methods such as space vector pulse width modulation to reduce losses; the other is to use components made of silicon carbide materials to reduce the internal resistance of power devices; the third is to use three-level, five-level and other multi-level power The flat electrical topology and soft switching technology can reduce the voltage across the power device and reduce the switching frequency of the power device.

1. Voltage space vector pulse width modulation

It is an all-digital control method with the advantages of high DC voltage utilization and easy control, and is widely used in inverters. The utilization rate of DC voltage is high, and a lower DC bus voltage can be used under the same output voltage, thereby reducing the voltage stress of the power switching device, reducing the switching loss on the device, and improving the conversion efficiency of the inverter. improvement. In the space vector synthesis, there are a variety of vector sequence combination methods. Through different combinations and sorting, the effect of reducing the switching times of the power device can be obtained, thereby further reducing the switching loss of the inverter power device.

2. Components using silicon carbide materials

The impedance per unit area of silicon carbide devices is only one percent of that of silicon devices. For power devices such as IGBTs made of silicon carbide materials, the on-state impedance is reduced to one-tenth of that of ordinary silicon devices. Silicon carbide technology can effectively reduce The small diode reverse recovery current can reduce the switching loss on the power device, and the current capacity required by the main switch can also be reduced accordingly. Therefore, using the silicon carbide diode as the inverse diode of the main switch is to improve the inverter efficiency. way. Compared with the traditional fast recovery silicon anti-parallel diode, after adopting the silicon carbide anti-parallel diode, the diode reverse recovery current is significantly reduced, and the total conversion efficiency can be improved by 1%. After adopting the fast IGBT, the conversion efficiency of the whole machine can be improved by 2% due to the accelerated switching speed. When combining SiC inverse parallel diodes with fast IGBTs, the efficiency of the inverter will be further improved.

3. Soft switching and multi-level technology

Soft switching technology uses the resonance principle to make the current or voltage in the switching device change according to a sinusoidal or quasi-sinusoidal law. When the current naturally crosses zero, the device is turned off; when the voltage naturally crosses zero, the device is turned on. Thereby, the switching loss is reduced, and at the same time, the problems of inductive turn-off and capacitive turn-on are greatly solved. When the voltage across the switch tube or the current flowing through the switch tube is zero, it is turned on or off, so that there is no switching loss in the switch tube. The three-level inverter topology is mainly used in high-voltage and high-power applications. Compared with the traditional two-level structure, the three-level inverter output increases the zero level, and the voltage stress of the power device is halved. Because of this advantage, at the same switching frequency, the three-level inverter can use a smaller output filter inductor than the two-level structure, and the inductance loss, cost and volume can be effectively reduced; and at the same output harmonics The three-level inverter can use a lower switching frequency than the two-level structure, the switching loss of the device is smaller, and the conversion efficiency of the inverter is improved.