DC/DC Converter Current Estimation via Transformer
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Solution Overview
Problem
Conventional current sensing methods for DC/DC converters, such as using current sensing resistors or Hall effect sensors, face issues like power dissipation, bandwidth limitations, and measurement distortion, especially when dealing with DC currents in discontinuous conduction modes.
Innovation Solution
An apparatus comprising a current sensing unit, signal sampling unit, and current estimator that utilizes a current transformer and resistor to sense and estimate inductor current, synchronized with the driving signal, and calculates the estimated magnitude based on the sampled signal, scale factor, duty ratio, input, and output voltages, applicable to various DC/DC converters like buck, boost, and buck-boost converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sensing resistor and current sensing shunt are employed, then inductor current can be sensed, but power dissipation increases due to large current flowing through the sensing resistor
Solution Approach 1:
The patent introduces a current transformer as an intermediary device to sense the inductor current indirectly. The current transformer couples magnetically to the inductor and provides an isolated, scaled version of the current signal, eliminating the need for direct current flow through sensing resistors and thereby reducing power dissipation while maintaining measurement capability
Solution Approach 2:
The patent replaces the direct electrical connection method (current sensing resistor) with a magnetic coupling method (current transformer). This substitution allows current measurement without direct electrical contact, eliminating the power loss associated with resistive sensing while preserving the measurement function
2Measurement precision
If a Hall effect sensor is used, then inductor current can be sensed, but bandwidth is limited and switching signals cannot be sensed
Solution Approach 1:
The patent employs a current transformer, which is a simpler and more bandwidth-capable device compared to Hall effect sensors. The current transformer can accurately sense high-frequency switching signals without the bandwidth limitations that plague Hall effect sensors, making it suitable for high-speed DC/DC converter applications
3Loss of energy
If a current transformer is applied, then power loss is reduced and bandwidth is improved, but measurement distortion occurs due to DC component saturation
Solution Approach 1:
The patent applies preliminary action by intentionally introducing an AC component to the inductor current before it reaches the current transformer. This is achieved by adding a series capacitor and resistor network that superimposes an AC signal on the DC current, preventing DC saturation of the current transformer while preserving the ability to measure the original current through the AC component
Solution Approach 2:
The patent changes the parameter of the current signal by adding an AC component to the DC current. This parameter change transforms the current from purely DC (which would saturate the transformer) to a composite signal with AC content, enabling the current transformer to operate within its linear range while still providing accurate measurement information
4Measurement precision
If current sensing is conducted in discontinuous conduction mode, then current can be sensed with current transformer, but the inductor current is asymmetrical compared to continuous conduction mode
Solution Approach 1:
The patent applies dynamics by making the current sensing system adaptable to different conduction modes. The control circuit dynamically adjusts the AC component injection and processes the transformer output to compensate for the asymmetry in discontinuous conduction mode, maintaining measurement accuracy across varying operating conditions rather than requiring fixed symmetric waveforms
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 enables accurate current estimation and control in both continuous and discontinuous conduction modes, reducing power loss and measurement distortion, while maintaining circuit simplicity and cost-effectiveness.
Implementation Method 1
The current sensing unit is for sensing a current passing through a switch of the DC/DC converter and converting the current into a voltage signal. In an embodiment, the current sensing unit includes: a current transformer and a resistor; the current transformer has a primary coil connected to the switch of the DC/DC converter and a secondary coil coupled to the resistor
Data Source
AI summary
An apparatus for current estimation of a DC/DC converter includes a current sensing unit, a signal sampling unit, and a current estimator. The current sensing unit is for sensing a current passing through a switch of the DC/DC converter and converting the current into a voltage signal. The signal sampling unit, coupled to the current sensing unit, is for sampling the voltage signal so as to output a sampled signal. The current estimator, coupled to the signal sampling unit, is for determining a signal indicating estimated magnitude of an inductor current of the DC/DC converter, based on the sampled signal, a scale factor of the current sensing unit, a duty ratio of a driving signal for controlling the switch, an input voltage and an output voltage of the DC/DC converter. An apparatus for current estimation that can further control an averaged current of a DC/DC converter.