Full-Bridge Inverter Current Sensing via Alternating Integrator Capacitors
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Solution Overview
Problem
Existing current measurement devices are inadequate for high switching frequencies, such as 100kHz, as they are not quick enough to provide reliable measurements, leading to accuracy issues and high losses.
Innovation Solution
A current measurement device using two integrator capacitors in series, with reset switches to alternately reset each capacitor, reducing offset and drift, allowing for accurate and low-loss integration of voltage measurements at high frequencies, and processing the time integral for inverter control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current measurement devices (shunts, current sensors) are used, then the measurement is simple to implement, but they cannot provide reliable current measurements at high switching frequencies (100kHz)
Solution Approach 1:
The patent replaces conventional mechanical/electrical current measurement devices (shunts, current sensors, current transformers) with an integrator-based measurement system that uses voltage measurement across the choke and time integration to derive current. This substitution enables reliable high-frequency measurements by eliminating the bandwidth limitations of traditional sensors while avoiding their high-frequency losses.
2Device complexity
If a single integrator capacitor is used, then the device complexity is reduced, but offset errors and drift occur during continuous operation
Solution Approach 1:
The patent divides the single integrator capacitor into two separate capacitors (C1 and C2) that operate in alternating half-cycles. Each capacitor is reset during its non-active half-cycle, preventing offset accumulation and drift. This segmentation maintains measurement precision while keeping the overall device complexity manageable through the periodic reset mechanism.
3Speed
If current transformers are used for high switching frequencies, then the measurement speed is sufficient, but high losses are generated
Solution Approach 1:
The patent substitutes current transformers with an integrator-based voltage measurement system. By measuring voltage across the choke and integrating over time to obtain current information, the system achieves sufficient measurement speed for high switching frequencies without the core losses and copper losses inherent in current transformers operating at these frequencies.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables reliable and accurate current measurement at high frequencies, reducing offset errors and processing time, allowing for efficient control of inverters with minimal losses.
Implementation Method 1
uses an integrator for integrating the measured voltage at the choke over time, whereas the time integral of the voltage at the choke represents the current in the choke
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
To allow reliable current measurement of the output current of the switching stage of an inverter, especially at switching frequencies of the semiconductor switches in the 100kHz range, it is provided that a voltage (uLn) at the choke (L) is measured and integrated over time to be representative for the leg current (iLn) in the choke (L), and in that the time integral (∫uLn) is processed in a processing unit (14), whereas the processed time integral (∫uLn) is used in an inverter controller (10) for controlling the inverter, whereas the voltage (uLn) at the choke (L) is analogously integrated over time by two serially connected integrator capacitors (CI), whereas across each of the integrator capacitors (CI) a reset switch (SI) is provided, for alternately resetting the corresponding integrator capacitor (CI).