LCL Filter Parameter Estimation via PRBS Signal Injection
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Solution Overview
Problem
Existing methods for identifying LCL filter parameters in grid-connected converters are inefficient, often requiring additional equipment and sensors, and do not enable automatic control tuning, leading to poor control performance due to incorrect data sheet values and neglecting grid inductance, especially in weak grid connections.
Innovation Solution
The method estimates discrete-time model parameters using a PRBS voltage signal and a discrete-time Box and Jenkins model structure, allowing for the calculation of physical parameters of the LCL filter, including grid impedance, without additional sensors, enabling automatic control tuning and accounting for grid inductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurement methods are used to obtain LCL filter parameters, then parameter accuracy is improved, but additional equipment including sensors are required which increases cost and complexity
Solution Approach 1:
The converter itself serves as the measurement device by utilizing its existing current sensor and control system. The parameter identification is performed using the converter's own operational data during normal grid-connected operation, eliminating the need for external measurement equipment.
Solution Approach 2:
The patent replaces physical measurement equipment (external sensors and test devices) with a computational identification method based on electrical signal processing and parameter estimation algorithms, substituting mechanical/physical measurement systems with information-processing approaches.
2Device complexity
If data sheet values are used for LCL filter parameters, then device complexity is reduced, but control performance deteriorates due to incorrect values and neglect of grid inductance
Solution Approach 1:
The patent performs preliminary parameter identification during the commissioning phase or initial operation, storing the identified parameters for use in control applications. This preliminary action ensures accurate parameters are available before control tuning is performed, avoiding the need for trial-and-error adjustments.
Solution Approach 2:
The identification method uses feedback from the converter's actual operational behavior and measured currents to determine the true LCL parameters. The system continuously monitors its own performance and uses this information to accurately identify parameters that reflect the actual operating conditions rather than relying on nominal values.
3Ease of operation
If parametric estimation methods are used, then control tuning capability is improved, but the connection to physical world parameters remains unclear
Solution Approach 1:
The patent transforms discrete-time model parameters into continuous-time physical parameters through mathematical relationships. By establishing the connection between the Z-domain parameters (from discrete-time modeling) and s-domain physical parameters (inductance L, capacitance C, resistance R), the method enables both control tuning and physical interpretation.
Data Source
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AI summary
A model-based method of estimating physical parameters of a LCL filter connected between a converter and electrical power network and a converter. The method comprising forming an analytical discrete-time model of the LCL filter and the converter, forming a discrete-time pulse-transfer function of the analytical discrete-time model having discrete time parameters, injecting a voltage signal superimposed on the reference voltage to the converter, determining output current of the converter, based on the injected voltage signal and output current of the converter, estimating the discrete-time parameters, and based on the estimated discrete-time parameters solving the estimated physical parameters using the analytical discrete-time model.