Dual-Sensor Current Sensing for Low-Loss Switched-Mode Converters
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Solution Overview
Problem
Current current measuring devices for switched-mode power converters face challenges in minimizing losses and achieving high resolution due to the high AC current components and discontinuous nature of measured currents, leading to increased measurement losses and poor utilization of components.
Innovation Solution
A current measuring device with a filter inserted into the power path, utilizing two independent sensors connected in series, where one resistor measures the average current value and another measures the instantaneous value without low-pass filtering, allowing AC current components to flow with minimal loss and providing separate measurement voltages for evaluation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a filter is inserted into the power path to measure current, then measurement precision is improved, but measurement losses increase due to the filter resistance
Solution Approach 1:
The current measuring device is segmented into two independent sensors connected in series: a first sensor (resistor) for measuring average current values and a second sensor (resistor with parallel capacitor) for measuring instantaneous current values. This segmentation allows each sensor to be optimized for its specific measurement function, with the second sensor's parallel capacitor filtering high-frequency AC components locally without requiring a series filter that would cause power losses.
Solution Approach 2:
A parallel capacitor is introduced as an intermediary element connected to the second sensor. This capacitor acts as a local filter for high-frequency AC current components, allowing the second sensor to measure instantaneous values accurately while the capacitor shunts the harmful AC components away from the measurement path, thereby reducing measurement losses while maintaining precision.
2Measurement precision
If high resistance is used in the current measuring resistor to achieve higher resolution, then measurement precision is improved, but measurement losses increase
Solution Approach 1:
The patent changes the configuration parameters of the measuring circuit by introducing a parallel capacitor with the second sensor. This allows the second sensor to use higher resistance for better resolution of instantaneous current measurements, while the parallel capacitor provides an alternative low-impedance path for high-frequency AC components, thereby reducing the power losses that would otherwise result from the high resistance.
3Measurement precision
If low-pass filtering is applied to measured current signals, then measurement precision is improved by removing AC components, but the response speed deteriorates
Solution Approach 1:
The measurement system is segmented into two independent measurement paths: one for average current values and another for instantaneous current values. The instantaneous measurement path includes a parallel capacitor that selectively filters high-frequency AC components while preserving the transient response capability, thus achieving both precision and fast response without the severe time constant constraints of a traditional series low-pass filter.
Solution Approach 2:
The parallel capacitor serves as an intermediary filtering element that selectively removes high-frequency AC components from the instantaneous current measurement path. Unlike a series low-pass filter that would slow down the response, the parallel capacitor provides a shunt path for AC components while allowing the measurement circuit to respond quickly to changes in current, thereby maintaining both precision and response speed.
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 approach reduces measurement losses by carrying AC current components without loss and enables higher resolution by allowing a higher resistance for the parallel current measuring resistor, while maintaining accurate determination of average current values, thus improving the utilization of power converter components.
Implementation Method 1
a filter which is inserted into the power path and comprises a conductance and an admittance, wherein the admittance comprises an average value capacitor which is configured to carry AC current components of the current to be measured approximately without losses
Implementation Method 2
two mutually independent sensors, that is to say e.g. two different resistors or two purely resistively equipped branches, which are connected in series with one another and thus considered together touch three nodes, that is to say at least two independent current measuring resistors
Data Source
AI summary
A current measuring device for switched-mode electronic power converters includes two independent sensors connected in series for the current to be measured, one of said sensors providing an admittance and the other providing a conductance. The current measuring device further includes a parallel current measuring resistor and an average value capacitor which are connected in parallel contribute to the provided admittance. The conductance is provided by a serial current measuring resistor as one of the sensors. The current to be measured has both DC and AC current components. The current measuring device further includes a filter is transferred back into the power path or merged with the current measuring sensors.