I am working on a simulation in Simscape involving a three-phase rectifier fed by a three-phase synchronous machine (alternator with round rotor).

I have successfully modeled both components, but I am facing a significant issue. When I replace the three-phase voltage source with the alternator, the input voltage to the three-phase rectifier becomes nearly zero, despite the alternator producing a stable three-phase voltage.

Here are the details of my setup:

1. Rectifier Configuration:

• Using a Universal Bridge block in Simulink and a Converter (Three-Phase) block in Simscape.
• Parameters for Universal Bridge:
• Number of bridge arms: 3
• Snubber resistance Rs: 1e5 Ohms
• Snubber capacitance Cs: inf
• Power electronic device: IGBT / Diodes
• Ron: 1e-3 Ohms
• Forward voltages [Device Vf(V), Diode Vfd(V)]: [0 0]
• Parameters for Converter (Three-Phase):
• Forward voltage, Vf: 0.00000001 V
• On-state resistance: 0.001 Ohm
• Off-state conductance: 1e-6 1/Ohm
• Threshold voltage, Vth: 0.1 V
• Integral protection diode: Diode with no dynamics
• Forward voltage: 0.00000001 V
• On resistance: 0.001 Ohm
• Off conductance: 1e-5 1/Ohm
• Snubber: RC snubber
• Snubber capacitance: 1e-7 F
• Snubber resistance: 1e5 Ohms

1. Alternator Parameters:

• Three-phase synchronous machine with a round rotor.
• Proper initialization and verified output: stable three-phase voltage and current.

1. Simulation Settings:

• Solver: ode23t
• Proper machine initialization.

Problem Description:

• The output of the alternator is a good three-phase voltage and current when checked independently.
• When the alternator is connected to the rectifier, the input voltage to the rectifier is distorted and significantly diminished.
• No connection issues were found, and the simulation settings were adjusted, including changing the solver to ode23t, but the problem persists.

Questions:

1. What could be causing the input voltage to the rectifier to be nearly zero when using the three-phase synchronous machine as the source?
2. Are there specific snubber values or configurations that could resolve this issue?
3. Could there be any interaction or parameter mismatch between the alternator and the rectifier that I need to address?
4. What are the best practices for setting snubber parameters in such a setup?

Any insights or suggestions to resolve this issue would be greatly appreciated. Thank you for your help!

Answer 1

[Umar]

Hi Omar,

When encountering issues with the input voltage to the rectifier being distorted or significantly diminished, despite a stable output from the alternator, several factors need to be considered for troubleshooting. Let's delve into possible causes and solutions for this problem:

1. Interaction and Parameter Mismatch:

Check for any interaction or parameter mismatch between the alternator and the rectifier. Ensure that the electrical characteristics of the alternator match the input requirements of the rectifier. Verify that the voltage levels and frequencies are compatible between the two components.

2. Snubber Configuration:

Review the snubber values and configurations in both the rectifier and the alternator circuits. Adjusting the snubber capacitance and resistance values can sometimes help in reducing voltage distortions and ensuring smoother operation. Experiment with different snubber configurations to find the optimal settings for your setup.

3. Snubber Best Practices:

When setting snubber parameters, consider the following best practices:

Snubber Capacitance: Adjust the snubber capacitance to dampen voltage spikes and reduce noise in the circuit.

Snubber Resistance: Proper snubber resistance helps in dissipating energy and protecting the components from voltage transients.

Snubber Type: Choose the appropriate snubber type (e.g., RC snubber) based on the circuit requirements and characteristics.

4. Simulation Settings:

Ensure that the simulation settings are accurately configured. Check the initialization of the alternator and rectifier components to guarantee proper operation when connected. Verify that the solver settings, such as ode23t, are suitable for the dynamic behavior of the system.

5. Troubleshooting Steps:

Validate the connections between the alternator and the rectifier to rule out any wiring issues. Monitor the voltage and current waveforms at different points in the circuit to pinpoint the exact location of the voltage drop. Gradually modify parameters and configurations while observing the impact on the input voltage to identify the root cause of the issue.

By systematically analyzing the interaction between the alternator and the rectifier, adjusting snubber configurations, and ensuring proper simulation settings, you can troubleshoot and resolve the input voltage issue effectively. Experimentation and careful observation of the system behavior will be key in diagnosing and rectifying the problem.

[Omar Mahmood]

Thanks a lot for your answer, Umar. I actually used the model with a three-phase source, and the model worked properly. However, when I switched to the alternator, the problem of diminished voltage came into the picture.