Calculation and Checking of Diode Parameters in Uncontrollable Rectification Circuit
Due to the transition stage of automotive and aerospace power systems to more electric and all-electric power systems, traditional engines are gradually replaced by motors and motor controllers.
As a transitional stage and a new situation of new energy power, the development trend of hybrid electric power is unstoppable.
Let's briefly talk about the uncontrollable rectification principle and the calculation, verification and selection of rectifier diode parameters in the rectification process of the motor controller from the engine power generation to the energy storage stage.
Author: Xiou
1. The principle of uncontrolled rectification
1.1 Principle of uncontrolled rectification
The uncontrollable rectification circuit uses a rectifier diode, so this type of circuit is also called a diode rectifier circuit.
Currently commonly used are one-way bridge and three-phase bridge connection.
1.2 Features
Although the completely uncontrolled rectification circuit based on the diode device has a simple and reliable structure and low loss.
The output voltage of the uncontrollable rectification circuit composed of rectifier diodes cannot be adjusted, and the power quality of the AC side is poor.
The key component of uncontrolled rectification is the diode.
2. Calibration and calculation of rectifier diode parameters
To evaluate the parameters of a rectifier bridge or diode, it is necessary to obtain its corresponding data sheet. Take Infineon's DDB6U180N16RRPB37BPSA1 rectifier bridge as an example.
2.1 Calculation of rectifier bridge loss and efficiency
Assume that our generator power factor cosθ=0.8, the effective value of the generator output line voltage is 800V, and the calculation formula of the output voltage of the three-phase rectifier bridge: Ud=1.2*Uab=700V (the coefficient is calculated according to 1.2 under full load, and Uab is the output rated line voltage of the generator).
According to the generator rated output power of 60kW, the rectifier bridge output rated current: Id=P/1.05Ud=81A;
according to the diode loss calculation formula:
Where:
Pv: diode conduction loss;
IAV: average conduction current;
VT0: diode threshold voltage;
rT: diode slope resistance;
F: form factor (IRMS/IAV)
According to the DDB6U180N16RRPB37BPSA1 manual, rT=2.3mΩ, VT0=0.83V, without considering the influence of current sharing, the three-phase phase is calculated at 120°, and F²=3.
Assuming the power factor cosθ=0.8, the average conduction current:
For a single diode in a three-phase rectifier:
Single Diode Loss:
The total loss of the entire rectifier bridge is 135W, and the output power of the controller is 60kW, so the power generation efficiency of the controller is 99.8%.
2.2 I2t calculation and verification
The parameter "I2t" reflects the ability of the rectifier diode to be subjected to short-term thermal shock. When the line is overloaded or short-circuited, a large current will flow through the device in a short time and its junction temperature will rise suddenly, even exceeding the maximum allowable operating junction temperature Tj. As long as the device is within the specified value of the parameter "I2t", the device will not be damaged.
Inrush current squared time product I²t, calculated according to motor speed 8000rpm (frequency 1000Hz):
This value is much lower than the manual 9800A²s.
2.3 Frequency calibration
The maximum electrical frequency of power generation is 1000Hz (1ms). According to engineering experience, the power module DDB6U180N16RRPB37BPSA1 diode, the working frequency range meets the application requirements.
