Photovoltaic Inverter Time Base Calibration for Grid Frequency Accuracy
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Solution Overview
Problem
Photovoltaic inverters experience inaccuracies in grid frequency measurement due to aging of timing components, leading to premature or delayed disconnection of AC current, which affects the efficiency and stability of the power supply grid.
Innovation Solution
A method and apparatus for calibrating the time base signal in photovoltaic inverters by receiving a reference signal, determining deviations, and correcting the time base signal using a calibration unit, which adjusts nominal values based on the reference signal and operating parameters such as temperature and supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If conventional time signal generators with millihertz tolerances are used, then the inverter can operate for years without replacement, but the measurement accuracy of grid frequency deteriorates over time due to aging of timing components
Solution Approach 1:
The patent applies preliminary action by performing calibration of the time base signal at predetermined time intervals (e.g., every 6 months or 1000 operating hours) before significant measurement errors accumulate. The calibration unit proactively adjusts the time base signal using stored reference values and temperature compensation data, preventing degradation of measurement accuracy rather than reacting to it after it occurs.
Solution Approach 2:
The patent implements feedback through the calibration unit that continuously monitors the time base signal generated by the time signal generator and compares it against stored reference values. The calibration unit automatically adjusts the time base signal based on detected deviations and temperature measurements, creating a closed-loop system that maintains measurement accuracy over the inverter's operational lifetime.
2Reliability
If the inverter switches off AC current feed-in early due to inaccurate frequency measurement, then grid stability protection is maintained, but the operator loses productive output time
Solution Approach 1:
The patent replaces the mechanical/physical aging process of timing components with an electronic/software-based calibration system. Instead of relying on the physical stability of quartz crystals or oscillators, the system uses a calibration unit that digitally adjusts the time base signal based on temperature compensation and stored reference values, substituting physical component reliability with computational accuracy.
3Productivity
If the inverter delays switch-off due to inaccurate frequency measurement, then productive output time is maximized, but the inverter cannot make its due contribution to grid stability
Solution Approach 1:
The patent applies parameter changes by adjusting the time base signal parameters (frequency, period) based on measured temperature variations and stored reference data. The calibration unit dynamically modifies the time base signal parameters to compensate for thermal drift and aging effects, ensuring that frequency measurements remain accurate across different operating conditions and time periods.
4Measurement precision
If calibration is performed continuously using reference signals, then measurement accuracy is maintained, but the device complexity and dependency on external signals increase
Solution Approach 1:
The patent applies preliminary action by pre-storing reference calibration values and temperature compensation data in memory during manufacturing or initial operation. These reference values are captured when the inverter is known to be operating accurately, and then used later for calibration without requiring continuous connection to external reference signal sources, reducing system complexity while maintaining accuracy.
Data Source
AI summary
A method and device is provided for calibrating a time base signal in a photovoltaic inverter, which has a conversion circuit configured to convert a DC current into an AC current. The method comprises the steps of: receiving a reference signal by a receiving unit from an external reference signal source; determining a deviation between the received reference signal and a time base signal which is generated by a local time signal generator; correcting the generated time base signal to minimize the determined deviation or calculating a correction factor, wherein the calibration unit automatically corrects the time base signal obtained from the time signal generator, even when a reference signal is temporarily unavailable, depending on at least one operating parameter which is stored in a data memory and which is formed by an internal temperature inside the housing of the photovoltaic inverter and/or by a measured supply voltage; and adapting predetermined values for components of the conversion circuit depending on the corrected time base signal or depending on the calculated correction factor.