A Study on the Power Loss Simulation of IGBT for HVDC Power Conversion System

Abstract

In this study, IGBT_Total_Loss and DIODE_Total_Loss were used to analyze the slope of the junction temperature for each section for temperature and duty variables in order to simply calculate the junction temperature of the power semiconductor (IGBT). As a result of the calculation, IGBT_Max_Junction_Temp and DIODE_Max_Junction_Temp form a proportional relationship with temperature for each duty. This simulation data shows that the power loss of a power semiconductor is calculated in a complex manner according to the current dependence index, voltage dependence index, and temperature coefficient. By applying the slope for each condition and section, the junction temperature of the power semiconductor can be calculated simply.

1. Introduction

A power semiconductor is configured in an electronic component circuit such as a power converter. However, power semiconductors that are generally composed of power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors),IPDs (Intelligent Power Devices), DIODEs, IGBTs (Insulated Gate Bipolar Transistors), power modules, bipolar transistors, and SiC (silicon carbide) drive Since the loss of function due to heat generation is large and the service life is also reduced due to self-deterioration, a cooling mechanism for cooling the driving heat generation should be configured in the corresponding electronic component. There is a need to introduce and develop a technology capable of predicting and diagnosing the driving life of electronic components in advance and replacing them, and also efficiently and economically performing the prediction and diagnosis made during facility operation. For this purpose, it is necessary to calculate the loss of the power conversion device. However, there is a difficulty in calculating the loss under various conditions such as current and voltage, switching frequency, duty, and temperature. Therefore, the applicability of the proposed method was checked by varying the duty and temperature in order to calculate it in a simple look-up table format.

2. Main subject

2.1 Power Loss of IGBT

The power loss of the power semiconductor (IGBT) is expressed as the sum of the conduction loss and the switching loss in equation 1. Conduction loss is represented by IGBT Forward Characteristics (Static) in Figure 1, and is represented by the slope of temperature and r_ce in equation 2. Switching loss is expressed as the product of switching frequency and switching power loss consumption according to current, voltage, and temperature in equation 3. In equation 4, the switching energy consumption is calculated differently according to Ki (current dependence index), Kv (voltage dependence index), TC_sw(temperature coefficient), and measurement rating of current, voltage, and temperature, which are makes calculation of junction temperature difficult.

Power loss = P_cond + P_sw       (1)

P_cond : conduction loss, P_sw : switching loss

V_CE(sat) = f(I_c) = V_CEO + r_ce × I_c ,

V_CEO = V_CEO-25^℃ + TC_V × (T_j - 25^℃),

r_ce = r_{ce - 25^℃} + TC_r × (T_j - 25^℃)       (2)

Switching loss = f_sw × E_sw (I : V_CC : T_J)       (3)

\(\begin{align}\begin{aligned} &E_{s w}=E_{s w r e f} \times\left(\frac{I_{o u t}}{I_{r e f}}\right)^{K i} \times\left(\frac{V_{\in}}{V_{r e f}}\right)^{K v} \\ &\times\left(1+T C_{s w}\left(T_{j}-T_{j r e f}\right)\right) \end{aligned}\end{align}\)       (4)

Ki : Exponent of current dependency, Kv : Exponent of voltage dependency, TC_sw: Temperature coefficient, I_ref, V_ref, T_jref : Measurement rating of current, voltage, and temperature

Fig. 1 IGBT forward characteristics(Static)

2.2 Thermal Equivalent Model of Power Semiconductor (IGBT)

The mathematical thermal equivalent circuit shown in figure 3 is called the natural or physical equivalent circuit of heat conduction and accurately depicts the internal heat distribution. Through this equivalent circuit, it is possible to accurately know the correlation between the equivalent element and the actual structural element. The thermal equivalent network in figure 2 is often used to accurately represent the thermal behavior at the input terminals of a black box. The thermal equivalent network in figure 2 is often used to accurately represent the thermal behavior at the input terminals of a black box. Each RC element represents the partial fraction terms of the heat transfer function of the system. Using the partial fractional expression, the step response of the thermal impedance can be expressed as equation 5. The equivalent input impedance of the input terminal can be expressed as equation 6. A curve fitting algorithm in a computer software tool such as Matlab is derived from the transient thermal impedance curve to determine the individual R_th and C_th components. Transient thermal impedance curves are usually provided in the device’s data sheet. This simple model was based on the parameterization of equivalent circuit elements using curve fittings related to the measurement data. In practice, the usual procedure for a cooling curve is to first heat up with a component of a given power dissipation P_k until a fixed temperature T_jk is assumed. If the exact temperature dependence of a parameter of the chip is known, such as the forward voltage drop, the T_j(t) curve, known as the cooling curve, can be determined by gradually reducing the power dissipation P_k to zero. This cooling curve is used to find the transient thermal impedance of the device.

Fig. 2 Combination of electrical and thermal components for IGBT

Fig. 3 Thermal equivalent factors for modeling heat conduction of IGBT

This cooling curve is used to find the transient thermal impedance of the device.

\(\begin{align}Z_{\text {th }}(t)=\sum_{i=1}^{n} R_{i}\left(1-e^{\frac{t}{R_{i} C_{i}}}\right)\end{align}\)       (5)

\(\begin{align}Z_{t h}=\frac{1}{s C_{t h, 1}+\frac{1}{s R_{t h, 1}+\frac{1}{s C_{t h, 2}+\cdots+\frac{1}{s R_{t h, n}}}}}\end{align}\)       (6)

\(\begin{align}Z_{t h}=\frac{T_{j k}-T_{j}(t)}{P_{k}}\end{align}\)       (7)

2.3 Power loss simulation of power semiconductor (IGBT) for HVDC

To calculate the lifespan of the IGBT of the SM (Sub Module) for MMC (Modular Multi Level Converter) Type HVDC (High Voltage Direct Current), Ki (current dependence index), Kv (voltage dependence index), TC_sw(temperature coefficient), The IGBT junction temperature should be calculated according to I_ref, V_ref, T_jref(rating of current, voltage, and temperature). For this purpose, IGBT_Total_Loss and DIODE_Total_Loss were calculated for temperature variable and P_F variable. The simulation conditions are (switching frequency: 180[hz], rated current: 1010[Arms], rated voltage: 2400[V]), and the duty is varied (D = 0.5,0.6,0.7,0.8,0.9,0.95) for correlation analysis between IGBT and DIODE. For temperature correlation analysis, the ambient temperature (Ta) was varied as 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120[℃].

As a result of the calculation, in figures 4, 5, 6, 7, 8, and 9, IGBT_Max_Junction_Temp and DIODE_Max_Junction_Temp form a proportional relationship with the temperature for each duty. In figures 10, 11, 12, 13, 14, 15, 16, 17, and 18, IGBT_Switching_Loss, DIODE_Switching_Loss, IGBT_Conduction_Loss, etc. show that it can be expressed as a temperature gradient for each constant temperature section.

Fig. 4 IGBT_Max_Junction_Temp

Fig. 5 DIODE_Max_Junction_Temp

Fig. 6 IGBT_Switching_Loss

Fig. 7 DIODE_Switching_Loss

Fig. 8 IGBT_Conduction_Loss

Fig. 9 DIODE_Conduction_Loss

Fig. 10 Junction temperature distribution of IGBT and DIODE according to ambient temperature

Fig. 11 Slope of IGBT_Max_Junction_Temp. according to ambient temperature by power factor

Fig. 12 Slope of DIODE_Max_Junction_Temp. according to ambient temperature by power factor

Fig. 13 Slope of IGBT_Switching_Loss according to ambient temperature by power factor

Fig. 14 Slope of DIODE_Switching_Loss according to ambient temperature by power factor

Fig. 15 Slope of IGBT_Conduction_Loss according to ambient temperature by power factor

Fig. 16 Slope of DIODE_Conduction_Loss according to ambient temperature by power factor

Fig. 17 Slope of IGBT_Total_Loss acording to ambient temperature by power factor

Fig. 18 Slope of DIODE_Total_Loss acording to ambient temperature by power factor

3. Conclusion

In this study, in order to simply calculate the junction temperature of the power semiconductor (IGBT), the slope of the junction temperature was analyzed for each section for the temperature variable IGBT_Total_Loss and DIODE_Total_Loss and the P_F variable.

As a result of the calculation, in figures 4, 5, 6, 7, 8, and 9, IGBT_Max_Junction_Temp and DIODE_Max_Junction_Temp form a proportional relationship with the temperature for each duty.

In figures 10, 11, 12, 13, 14, 15, 16, 17, and 18, IGBT_Switching_Loss, DIODE_Switching_Loss, IGBT_Conduction_ Loss, etc. show that it can be expressed as a temperature gradient for each constant temperature section. The power loss of a power semiconductor is complicatedly calculated according to Ki, Kv, and TC_sw of equations 2 and 4. This simulation data makes it possible to calculate the junction temperature of the power semiconductor simply and easily by applying the slope for each condition and section. The proposed method is that can dramatically reduce the calculation time when estimating the thermal resistance of the HVDC MMC type power converter. In the future, in order to more precisely and easily calculate and measure the junction temperature of power semiconductors, it is necessary to conduct an experiment on the proposed method and further analyze the errors of calculation and measurement.