State-Observer DC-AC Inverter Control Without Current Sensors
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Solution Overview
Problem
Existing DC-AC inverter systems face challenges with filter capacitor current ripples and reliance on hardware sensors, leading to signal distortion, delay, and increased costs and reliability issues due to temperature changes and component failures.
Innovation Solution
A state observer-based control method that estimates filter capacitor current and load current without hardware sensors, using DC link voltage and filter capacitor voltage to provide ripple-free average current values and reduce sampling time errors, applicable in on-grid, standalone, and transfer modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hardware sensors are used to detect filter capacitor current, then measurement accuracy is improved, but system cost and reliability deteriorate due to component failures and temperature sensitivity
Solution Approach 1:
The patent creates a virtual copy of the filter capacitor current signal through state observer calculation rather than using physical sensors. The state observer computes the filter capacitor current estimation value based on system model and measurable variables (DC link voltage, inductor current, filter capacitor voltage), eliminating the need for physical current sensors and their associated reliability issues.
Solution Approach 2:
The patent replaces the mechanical/electrical hardware sensor system with a computational/software-based state observer system. Instead of using physical components to detect current, the system uses mathematical models and digital calculations to estimate the current, thereby eliminating sensor-related failures and temperature sensitivity.
2Measurement precision
If hardware filter circuit is used to filter ripples from filter capacitor current, then signal quality is improved, but signal distortion and delay are introduced
Solution Approach 1:
The patent creates a clean virtual copy of the filter capacitor current signal through state observer calculation. The state observer inherently produces the average value without ripples by design of its mathematical model, eliminating the need for physical filter circuits that would introduce delay and distortion.
Solution Approach 2:
The patent replaces the physical filter circuit with a computational filtering approach. The state observer's mathematical model naturally filters out ripples and provides the average current value directly through calculation, avoiding the time delay and signal distortion inherent in analog filter circuits.
3Ease of operation
If traditional digital control with current sampling is used, then control implementation is simplified, but control time delay increases due to one sampling time lag
Solution Approach 1:
The patent performs preliminary calculation of the filter capacitor current estimation value at the next sampling time (k+1) based on current sampling data (k). This allows the control system to use the estimated future value directly for control decisions without waiting for the actual next sampling moment, effectively compensating for the one sampling time delay inherent in digital control systems.
Data Source
AI summary
A DC-AC inverter system using a state observer and a control method thereof are provided. The control method of the DC-AC inverter system includes the following steps. The state observer outputs a filter-capacitor-current estimation value at a next sampling time according to a DC link voltage at a current sampling time and a filter-capacitor-voltage actual value at the current sampling time. The filter-inductor-current estimation value at the next sampling time is compared with the filter-capacitor-current estimation value at the next sampling time to obtain a load current estimation value at the next sampling time. An inductor voltage estimator outputs a filter-inductor-voltage estimation value at the next sampling time according to the load current estimation value at the next sampling time. A feed-forward control is performed according to the filter-inductor-voltage estimation value at the next sampling time.