N-Channel IGBT

N-Channel insulated gate bipolar transistor

Library:
Simscape / Electrical / Semiconductors & Converters

Description

The N-Channel IGBT block models an Insulated Gate Bipolar Transistor (IGBT). The block provides two main modeling variants, accessible by right-clicking the block in your block diagram and then selecting the appropriate option from the context menu, under Simscape > Block choices:

Full I-V and capacitance characteristics — This variant is a detailed component model suitable for simulating detailed switching characteristics and predicting component losses. This variant, in turn, provides two ways of modeling an IGBT:
- As an equivalent circuit based on a PNP bipolar transistor and N-channel MOSFET. For more information on using this model, see Representation by Equivalent Circuit, Fine-Tuning the Current-Voltage Characteristics, and Modeling Temperature Dependence.
- By a 2-D lookup table approximation to the I-V (current-voltage) curve. For details, see Representation by 2-D Lookup Table.
- By a 3-D lookup table approximation to the I-V (current-voltage) curve that includes temperature data. For details, see Representation by 3-D Lookup Table.
The gate junction capacitance in the detailed model is represented as a fixed gate-emitter capacitance C_GE and either a fixed or a nonlinear gate-collector capacitance C_GC. For details, see Charge Model.
Simplified I-V characteristics and event-based timing — This variant models the IGBT more simply by using just the on-state I-V data as a function of the collector-emitter voltage. In the off state (gate-emitter voltage less than Threshold voltage, Vth), the IGBT is modeled by a constant Off-state conductance. This simplified model is suitable when approximate dynamic characteristics are sufficient, and simulation speed is of paramount importance. For details, see Event-Based IGBT Variant.

Together with the thermal port variants (see Thermal Port), the block therefore provides you with four choices. To select the desired variant, right-click the block in your model. From the context menu, select Simscape > Block choices, and then one of the following options:

Full I-V and capacitance characteristics | No thermal port — Detailed model that does not simulate the effects of generated heat and device temperature. This is the default.
Full I-V and capacitance characteristics | Show thermal port — Detailed model with exposed thermal port.
Simplified I-V characteristics and event-based timing | No thermal port — Simplified event-based model, which also does not simulate the effects of generated heat and device temperature.
Simplified I-V characteristics and event-based timing | Show thermal port — Simplified event-based model with exposed thermal port.

Representation by Equivalent Circuit

The equivalent circuit of the detailed block variant consists of a PNP Bipolar Transistor block driven by an N-Channel MOSFET block, as shown in the following figure:

The MOSFET source is connected to the bipolar transistor collector, and the MOSFET drain is connected to the bipolar transistor base. The MOSFET uses the threshold-based equations shown in the N-Channel MOSFET block reference page. The bipolar transistor uses the equations shown in the PNP Bipolar Transistor block reference page, but with the addition of an emission coefficient parameter N that scales kT/q.

The N-Channel IGBT block uses the on and off characteristics you specify in the block dialog box to estimate the parameter values for the underlying N-Channel MOSFET and PNP bipolar transistor.

The block uses the off characteristics to calculate the base-emitter voltage, V_be, and the saturation current, I_S.

When the transistor is off, the gate-emitter voltage is zero and the IGBT base-collector voltage is large, so the PNP base and collector current equations simplify to:

$\begin{array}{l} I_{b} = 0 = - I_{s} [\frac{1}{β_{F}} (e^{- q V_{b e} / (N k T)} - 1) - \frac{1}{β_{R}}] \\ I_{c} = - I_{s} [e^{- q V_{b e} / (N k T)} (1 + \frac{V_{b c}}{V_{A F}}) + \frac{1}{β_{R}}] \end{array}$

where N is the Emission coefficient, N parameter value, V_AF is the forward Early voltage, and I_c and I_b are defined as positive flowing into the collector and base, respectively. See the PNP Bipolar Transistor reference page for definitions of the remaining variables. The first equation can be solved for V_be.

The base current is zero in the off-condition, and hence I_c = –I_ces, where I_ces is the Zero gate voltage collector current. The base-collector voltage, V_bc, is given by V_bc = V_ces + V_ces, where V_ces is the voltage at which I_ces is measured. Hence we can rewrite the second equation as follows:

$I_{c e s} = I_{s} [e^{- q V_{b e} / (N k T)} (1 + \frac{V_{c e s} + V_{b e}}{V_{A F}}) + \frac{1}{β_{R}}]$

The block sets β_R and β_F to typical values of 1 and 50, so these two equations can be used to solve for V_be and I_S:

$\begin{array}{l} V_{b e} = \frac{- N k T}{q} \log (1 + \frac{β_{F}}{β_{R}}) \\ I_{s} = \frac{I_{c}}{e^{- q V_{b e} / (N k T)} + \frac{1}{β_{R}}} \end{array}$

Note

The block does not require an exact value for β_F because it can adjust the MOSFET gain K to ensure the overall device gain is correct.

The block parameters Collector-emitter saturation voltage, Vce(sat) and Collector current at which Vce(sat) is defined are used to determine V_be(sat) by solving the following equation:

$I_{c e (s a t)} = I_{s} [e^{- q V_{b e (s a t)} / (N k T)} (1 + \frac{V_{c e (s a t)} + V_{b e (s a t)}}{V_{A F}}) + \frac{1}{β_{R}}]$

Given this value, the block calculates the MOSFET gain, K, using the following equation:

$I_{d s} = I_{b} = K [(V_{G E (s a t)} - V_{t h}) V_{d s} - \frac{V_{d s}^{2}}{2}]$

where V_th is the Gate-emitter threshold voltage, Vge(th) parameter value and V_GE(sat) is the Gate-emitter voltage at which Vce(sat) is defined parameter value.

V_ds is related to the transistor voltages as V_ds = V_ce – V_be. The block substitutes this relationship for V_ds, sets the base-emitter voltage and base current to their saturated values, and rearranges the MOSFET equation to give

$K = \frac{I_{b (s a t)}}{[(V_{G E (s a t)} - V_{t h}) (V_{b e (s a t)} + V_{c e (s a t)}) - \frac{{(V_{b e (s a t)} + V_{c e (s a t)})}^{2}}{2}]}$

where V_ce(sat) is the Collector-emitter saturation voltage, Vce(sat) parameter value.

These calculations ensure the zero gate voltage collector current and collector-emitter saturation voltage are exactly met at these two specified conditions. However, the current-voltage plots are very sensitive to the emission coefficient N and the precise value of V_th. If the manufacturer datasheet gives current-voltage plots for different V_GE values, then the N and V_th can be tuned by hand to improve the match.

Representation by 2-D Lookup Table

For the lookup table representation of the detailed block variant, you provide tabulated values for collector current as a function of gate-emitter voltage and collector-emitter voltage. The main advantage of using this option is simulation speed. It also lets you parameterize the device from either measured data or from data obtained from another simulation environment. To generate your own data from the equivalent circuit representation, you can use a test harness, such as shown in the IGBT Characteristics example.

The lookup table representation combines all of the equivalent circuit components (PNP transistor, N-channel MOSFET, collector resistor and emitter resistor) into one equivalent lookup table.

Representation by 3-D Lookup Table

For the temperature-dependent lookup table representation of the detailed block variant, you provide tabulated values for collector current as a function of gate-emitter voltage, collector-emitter voltage, and temperature.

The lookup table representation combines all of the equivalent circuit components (PNP transistor, N-channel MOSFET, collector resistor and emitter resistor) into one equivalent lookup table.

If the block thermal port is not exposed, then the Device simulation temperature parameter on the Temperature Dependence tab lets you specify the simulation temperature.

Charge Model

The detailed variant of the block models junction capacitances either by fixed capacitance values, or by tabulated values as a function of the collector-emitter voltage. In either case, you can either directly specify the gate-emitter and gate-collector junction capacitance values, or let the block derive them from the input and reverse transfer capacitance values. Therefore, the Parameterization options for charge model on the Junction Capacitance tab are:

Specify fixed input, reverse transfer and output capacitance — Provide fixed parameter values from datasheet and let the block convert the input and reverse transfer capacitance values to junction capacitance values, as described below. This is the default method.
Specify fixed gate-emitter, gate-collector and collector-emitter capacitance — Provide fixed values for junction capacitance parameters directly.
Specify tabulated input, reverse transfer and output capacitance — Provide tabulated capacitance and collector-emitter voltage values based on datasheet plots. The block converts the input and reverse transfer capacitance values to junction capacitance values, as described below.
Specify tabulated gate-emitter, gate-collector and collector-emitter capacitance — Provide tabulated values for junction capacitances and collector-emitter voltage.

Use one of the tabulated capacitance options (Specify tabulated input, reverse transfer and output capacitance or Specify tabulated gate-emitter, gate-collector and collector-emitter capacitance) when the datasheet provides a plot of junction capacitances as a function of collector-emitter voltage. Using tabulated capacitance values will give more accurate dynamic characteristics, and avoids the need to iteratively tune parameters to fit the dynamics.

If you use the Specify fixed gate-emitter, gate-collector and collector-emitter capacitance or Specify tabulated gate-emitter, gate-collector and collector-emitter capacitance option, the Junction Capacitance tab lets you specify the Gate-emitter junction capacitance, Gate-collector junction capacitance, and Collector-emitter junction capacitance parameter values (fixed or tabulated) directly. Otherwise, the block derives them from the Input capacitance, Cies, Reverse transfer capacitance, Cres, and Output capacitance, Coes parameter values. These two parameterization methods are related as follows:

C_GC = Cres
C_GE = Cies – Cres
C_CE = Coes – Cres

The two fixed capacitance options (Specify fixed input, reverse transfer and output capacitance or Specify fixed gate-emitter, gate-collector and collector-emitter capacitance) let you model gate junction capacitance as a fixed gate-emitter capacitance C_GE and either a fixed or a nonlinear gate-collector capacitance C_GC. If you select the Gate-collector charge function is nonlinear option for the Charge-voltage linearity parameter, then the gate-collector charge relationship is defined by the piecewise-linear function shown in the following figure.

With this nonlinear capacitance, the gate-emitter and collector-emitter voltage profiles take the form shown in the next figure, where the collector-emitter voltage fall has two regions (labeled 2 and 3) and the gate-emitter voltage has two time-constants (before and after the threshold voltage V_th):

You can determine the capacitor values for Cies, Cres, and C_ox as follows, assuming that the IGBT gate is driven through an external resistance R_G:

Set Cies to get correct time-constant for V_GE in Region 1. The time constant is defined by the product of Cies and R_G. Alternatively, you can use a datasheet value for Cies.
Set Cres so as to achieve the correct V_CE gradient in Region 2. The gradient is given by (V_GE – V_th)/(Cres · R_G).
Set V_Cox to the voltage at which the V_CE gradient changes minus the threshold voltage Vth.
Set C_ox to get correct Miller length and time constant in Region 4.

Because the underlying model is a simplification of an actual charge distribution, some iteration of these four steps may be required to get a best overall fit to measured data. The collector current tail when the IGBT is turned off is determined by the Total forward transit time parameter.

Note

Because this block implementation includes a charge model, you must model the impedance of the circuit driving the gate to obtain representative turn-on and turn-off dynamics. Therefore, if you are simplifying the gate drive circuit by representing it as a controlled voltage source, you must include a suitable series resistor between the voltage source and the gate.

Fine-Tuning the Current-Voltage Characteristics

For the equivalent circuit representation of the detailed model, use the parameters on the Advanced tab to fine-tune the current-voltage characteristics of the modeled device. To use these additional parameters effectively, you will need a manufacturer datasheet that provides plots of the collector current versus collector-emitter voltage for different values of gate-emitter voltage. The parameters on the Advanced tab have the following effects:

The Emission coefficient, N parameter controls the shape of the current-voltage curves around the origin.
The Collector resistance, RC and Emitter resistance, RE parameters affect the slope of the current-voltage curve at higher currents, and when fully turned on by a high gate-emitter voltage.
The Forward Early voltage, VAF parameter affects the shape of the current-voltage curves for gate-emitter voltages around the Gate-emitter threshold voltage, Vge(th).

Modeling Temperature Dependence

For the 2-D lookup table representation, the electrical equations do not depend on temperature. However, you can model temperature dependence by either using the 3-D lookup table representation, or by using the equivalent circuit representation of the detailed model.

For the equivalent circuit representation, temperature dependence is modeled by the temperature dependence of the constituent components. See the N-Channel MOSFET and PNP Bipolar Transistor block reference pages for further information on the defining equations.

Some datasheets do not provide information on the zero gate voltage collector current, Ices, at a higher measurement temperature. In this case, you can alternatively specify the energy gap, EG, for the device, using a typical value for the semiconductor type. For silicon, the energy gap is usually 1.11 eV.

Event-Based IGBT Variant

This implementation has much simpler equations than that with full I-V and capacitance characteristics. Use the event-based variant when the focus of the analysis is to understand overall circuit behavior rather than to verify the precise IGBT timing or losses characteristics.

The device is always in one of the following four states:

Off
Turning on
On
Turning off

In the off state, the relationship between collector current (i_c) and collector-emitter voltage (v_ce) is

i_c = G_offv_ce

(1)

In the on state, the relationship between collector current (i_c) and collector-emitter voltage (v_ce) is

v_ce = tablelookup(i_c)

(2)

When turning on, the collector-emitter voltage is ramped down to zero over the rise time, the device moving into the on state when the voltage falls below the tabulated on-state value. Similarly when turning off, the collector-emitter voltage is ramped up over the (current) fall time to the specified blocking voltage value.

The following figure shows the resulting voltage and current profiles when driving a resistive load.

Thermal Port

The block has an optional thermal port, hidden by default. To expose the thermal port, right-click the block in your model, and select the appropriate block variant:

For a detailed model, select Simscape > Block choices > Full I-V and capacitance characteristics | Show thermal port. This action displays the thermal port H on the block icon, and exposes the Thermal Port parameters.
For a simplified event-based model, select Simscape > Block choices > Simplified I-V characteristics and event-based timing | Show thermal port. This action displays the thermal port H on the block icon, exposes Thermal Port parameters and additional Main parameters. To simulate thermal effects, you must provide additional tabulated data for turn-on and turn-off losses and define the collector-emitter on-state voltage as a function of both current and temperature.

Use the thermal port to simulate the effects of generated heat and device temperature. For more information on using thermal ports and on the Thermal Port parameters, see Simulating Thermal Effects in Semiconductors.

Assumptions and Limitations

The detailed model is based on the following assumptions:

This block does not allow you to specify initial conditions on the junction capacitances. If you select the Start simulation from steady state option in the Solver Configuration block, the block solves the initial voltages to be consistent with the calculated steady state. Otherwise, voltages are zero at the start of the simulation.
You may need to use nonzero junction capacitance values to prevent numerical simulation issues, but the simulation may run faster with these values set to zero.
The block does not account for temperature-dependent effects on the junction capacitances.

The simplified, event-based model is based on the following assumptions:

When you use a pair of IGBTs in a bridge arm, normally the gate drive circuitry will prevent a device turning on until the corresponding device has turned off, thereby implementing a minimum dead band. If you need to simulate the case where there is no minimum dead band and both devices are momentarily partially on, use the detailed IGBT model variant (Full I-V and capacitance characteristics). The assumption used by the event-based variant that the collector-emitter voltages can be ramped between on and off states is not valid for such cases.
A minimum pulse width is applied when turning on or off; at the point where the gate-collector voltage rises above the threshold, any subsequent gate voltage changes are ignored for a time equal to the sum of the turn-on delay and current rise time. Similarly at the point where the gate collector voltage falls below the threshold, any subsequent gate voltage changes are ignored for a time equal to the sum of the turn-off delay and current fall time. This feature is normally implemented in the gate drive circuitry.
This model does not account for charge. Hence there is no current tail when turning off an inductive load.
Representative modeling of the current spike during turn-on of an inductive load with preexisting freewheeling current requires tuning of the Miller resistance parameter.
The tabulated turn-on switching loss uses the previous on-state current, not the current value (which is not known until the device reaches the final on state).
Due to high model stiffness that can arise from the simplified equations, you may get minimum step size violation warnings when using this block. Open the Solver pane of the Configuration Parameters dialog box and increase the Number of consecutive min steps parameter value as necessary to remove these warnings.

Ports

Conserving

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`C` — Collector terminal
electrical

Electrical conserving port associated with the PNP emitter terminal

`G` — Gate terminal
electrical

Electrical conserving port associated with the IGBT gate terminal

`E` — Emitter terminal
electrical

Electrical conserving port associated with the PNP collector terminal

Parameters

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Main (Default Block Variant)

This configuration of the Main tab corresponds to the detailed block variant, which is the default. If you are using the simplified, event-based variant of the block, see Main (Event-Based Block Variant).

`I-V characteristics defined by` — IGBT representation
`Fundamental nonlinear equations` (default) | `Lookup table (2-D, temperature independent)` | `Lookup table (3-D, temperature dependent)`

Select the IGBT representation:

Fundamental nonlinear equations — Use an equivalent circuit based on a PNP bipolar transistor and N-channel MOSFET. This is the default.
Lookup table (2-D, temperature independent) — Use 2-D table lookup for collector current as a function of gate-emitter voltage and collector-emitter voltage.
Lookup table (3-D, temperature dependent) — Use 3-D table lookup for collector current as a function of gate-emitter voltage, collector-emitter voltage, and temperature.

`Zero gate voltage collector current, Ices` — Zero gate voltage collector current
`2` `mA` (default)

The collector current that flows when the gate-emitter voltage is set to zero, and a large collector-emitter voltage is applied, that is, the device is in the off-state. The value of the large collector-emitter voltage is defined by the parameter Voltage at which Ices is defined.