Inverter Controller Reference Voltage Adaptation
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Solution Overview
Problem
Conventional voltage regulators face instability and failure in regulating AC voltage due to unfeasible reference signals when the DC link voltage sags, leading to modulation index saturation, unwanted harmonics, and system destabilization.
Innovation Solution
An inverter controller with a realizable reference generator that determines a feasible reference voltage (Vpor_REF) based on measured or estimated DC voltage (Vdc), ensuring the modulation index signal M_abc is regulated at a selectable frequency, allowing the inverter to output AC voltage that satisfies load requirements even during voltage sags.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverter uses a fixed reference voltage Vpor_REF to regulate AC voltage, then the regulation is simple and stable under normal conditions, but the system becomes unstable and fails when DC link voltage sags below nominal value
Solution Approach 1:
The reference voltage Vpor_REF is changed from a fixed value to a dynamic value that varies with the DC link voltage Vdc. The controller continuously adjusts Vpor_REF based on the measured or estimated Vdc, ensuring the modulation index remains within feasible limits across all operating conditions. This dynamic adaptation prevents saturation and instability while maintaining effective voltage regulation.
Solution Approach 2:
The patent changes the parameter Vpor_REF from a constant nominal value to a variable value that depends on the DC link voltage Vdc. By establishing a functional relationship between Vpor_REF and Vdc, the system adapts to varying DC voltage conditions, preventing modulation index saturation and ensuring stable operation across the full range of DC voltage variations.
2Manufacturing precision
If the inverter attempts to maintain nominal Vpor using a fixed Vpor_REF during DC voltage sag, then the regulation target remains constant, but the modulation index saturates and causes windup of the integrator
Solution Approach 1:
The controller proactively adjusts the reference voltage Vpor_REF before the modulation index can saturate. By monitoring the DC link voltage Vdc and preemptively modifying Vpor_REF to reflect the reduced available voltage, the system prevents the integrator windup condition from occurring in the first place, maintaining both precision and stability.
Solution Approach 2:
The system implements feedback by continuously monitoring the DC link voltage Vdc and using this information to adjust the reference voltage Vpor_REF. This closed-loop approach ensures that the modulation index remains within feasible limits by adapting the reference to actual operating conditions, preventing saturation and integrator windup while maintaining regulation precision.
3Reliability
If the inverter uses an unfeasible reference Vpor_REF when Vdc is low, then the regulation target remains ambitious, but the system produces unwanted harmonics and may trip due to over-voltage or over-current
Solution Approach 1:
The reference voltage Vpor_REF is changed from a fixed nominal value to a variable value that scales with the DC link voltage Vdc. This parameter change ensures that the modulation index remains within feasible limits, preventing the generation of unwanted harmonics and avoiding over-voltage or over-current conditions that could cause system tripping.
Data Source
AI summary
A system and method is provided for controlling conversion of a received DC voltage (Vdc) into an AC inverter voltage. The method includes determining a reference Vpor (Vpor_REF) based on measured or estimated Vdc such that Vpor_REF is feasible at all values of Vdc for regulating a modulation index signal M_abc at a selectable frequency ω as a function of a measured or estimated voltage at the point of reference (Vpor), wherein M_abc is regulated by Vpor_REF to regulate the inverter hardware circuit to output the AC inverter voltage in order for Vpor to satisfy a requirement appropriate for the load.