loss 3phase3level inverter help

8/10/2019 Loss 3Phase3Level Inverter Help

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Loss Calculation in a 3-Phase 3-Level Inverter

Using SimPowerSystems and Simscape

Pierre Giroux, Gilbert Sybille, Olivier Tremblay

Hydro-Quebec Research Institute (IREQ)

General

From a +/- 1800 volts DC source, a 400-kW, 3-phase 3-level inverter delivers variable power to adistribution power system. The inverter output is connected to the 25-kV, 40 MVA, 50-Hz systemthrough a 2200 V / 25 kV transformer. The inverter topology is based on the following document:

Raffael Schnell, Manager Application, ABB Switzerland, "High-Voltage Phase-Leg Modules forMedium Voltage Drives and Inverters", www.abb.com/semiconductors PCIM 12-408.

Each 3-level leg of the inverter comprises three commercial half-bridge IGBT modules. Phase-Aleg is implemented using three SimPowerSystems blocks Half-bridge IGBT with LossCalculation. This block has been used and documented in a previous demonstration: Loss

Calculation in a Buck Converter Using SimPowerSystems and Simscape.Both switching andconduction losses are calculated and injected into a thermal network.

The simulation illustrates the achievable output power versus switching frequency for the 3-phase, 3-level inverter. The circuit is simulated using a fixed-step solver (discrete sample time of

5 s) and the Simulink Accelerator mode.

Half-bridge IGBT ModelDescription (phase A on ly)

If you go inside Module 1 (using Edit -> Look Under Mask from the main menu), you will see foursections:

1) PowerThe half-bridge is built using standard SPS power electronics elements (IGBT/Diode block).The upper and lower IGBT/Diode blocks are pulsed from the external pulse generator (inside

the Inverter Control block).

2) Loss CalculationOne Simulink subsystem is used to calculate the IGBT losses and another one for the diodelosses. The losses are calculated as follows:

For the IGBTs:- Turn-on loss: Pre-switching value of the voltage across the device, post-switching value

of the current flowing into the device, and the junction temperature are used to determinethe energy losses with the help of a 3-D lookup table. This energy is converted into apower pulse which is injected into the thermal network.

- Turn-off loss: Pre-switching value of the current flowing into the device, post-switchingvalue of the voltage across the device, and the junction temperature are used to

determine the energy losses with the help of a 3-D lookup table. This energy is convertedinto a power pulse which is injected into the thermal network.

- Conduction loss: Value of the current (Ic) flowing in the device and its junctiontemperature determine what would be the saturation voltage (Vce) across the IGBT usinga 2-D look-up table. This Vce is then multiplied by Ic to obtain the losses which areinjected into the thermal network.

For the diodes:- Reverse recovery loss: Pre-switching value of the current flowing into the device, post-

switching value of the voltage across the device, and the junction temperature are used


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to determine the energy losses with the help of a 3-D lookup table. This energy isconverted into a power pulse which is injected into the thermal network.

- Conduction loss: Value of the current (If) flowing in the device and its junctiontemperature determine what would be the on-state voltage (Vf) across the diode using a2-D look-up table. This Vf is then multiplied by If to obtain the losses which are injectedinto the thermal network.

3) Thermal modelA Simulink state-space block is used to build a one-cell Cauer network modeling the thermalcapacitance of the device junction as well as its junction-to-case thermal resistance. ASimscape physical modeling connection port is built using an Ideal Heat Flow Source block.

4) MeasurementsA bus creator is used to output all relevant signals to a Simulink outport.

Note:

For module 3, IGBT pulsing is not required since only the anti-parallel diodes areoperating as neutral clamping diodes.

The loss calculation is based on the specifications found on the manufacturers datasheets. In our demonstration, we provide a choice of 3 different commercial components.

Using the IGBT type and Diode type pop-up menus of the mask, you can chooseamong these three IGBT modules. (The thermal specifications are saved on two .matfiles). However, you could create your own thermal library by modifying the 2 following.m files: LossSpec_IGBT_LibCreateand LossSpec_Diode_LibCreate.

Simscape Thermal ModelDescription

This Simscape subsystem contains a two-cell Cauer network based on the thermal capacitances(case and heat sink) and resistances (case-to-sink and sink-to-ambient) specified in the maskmenu. If you go inside the model, you will see various Simscape blocks (from the thermalfoundation library) used to build the thermal network. Of course, a far more complex thermalrepresentation can be done with Simscape. For the sake of simplicity, we have used this two-cellCauer network with arbitrary values for the thermal capacitances in order to reduce the timerequired to simulate the thermal phenomena.

Inverter Contro l

The control system (sample time of 50 s) uses two PI controllers (one PQ regulator and oneCurrent regulator) to generate the pulses to the inverter in order to get the desired output power.To see the various components of the control system, you can go inside the system by clicking onthe block and using Edit -> Look Under Mask from the main menu.

Demonstration

Open the Half-Bridge IGBT with Loss Calculation (Module 1 to 3) mask parameters and verifythat the following component has been selected for both IGBT and diode type: ABB: Half-bridgeIGBT 3300V/250A. Run the simulation for 12 seconds and observe the following operating pointson the Scope1 and displays:

From t=0 sec to t= 5 sec, the inverter outputs 372 kW (power factor= 0.85) using aswitching frequency of 850 Hz. The converter total losses are 2.7 kW and the highest

junction temperature (125 C) is observed on IGBT1 of Module 1 (or IGBT2 of Module 2).See Scope Tj (Celsius)insideAdditional Scopes & Measurementsblock.

From t=5 sec to t= 12 sec, the inverter outputs 210 kW (power factor= 0.85) using aswitching frequency of 1850 Hz. The converter total losses are 2.7 kW and the highest

junction temperature (125 C) is still observed on IGBT1 of Module 1.


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You can run additional simulation using various switching frequencies and inverter power outputs:

To modify the PWM switching frequency, double-click on the Fsw (Hz)step blockconnected to the Inverter Control and change the value of the Initial or Final valueparameters.

To modify the inverter output power, double-click on the Pref_kW and Qref_kvarstepblocks connected to the Inverter Control and change the value of the Initial or Final value

parameters.

If you double-click on the green block Plot Output Power vs. Switching Frequency, you will seesimulation results saved from a previous simulation (Achievable 3-phase output power at amaximum junction temperature of 125 C) compared to the manufacturer data for six switchingfrequencies.

By double-clicking on the green block Plot FFT Comparison, you can observe the difference inpower quality of the injected current at bus B1 for two switching frequencies. You can also usethe FFT Analysis Tool of the Powergui to analyze the injected current for other switchingfrequencies. The signal to analyze, Phase A current at bus B1 is included in the structureVIabc_B1, Input= Iabc, Signal number=1.

loss 3phase3level inverter help

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