Power Conversion Device Current Estimation via Control Unit
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Solution Overview
Problem
Existing power conversion devices in electric vehicles face challenges in accurately estimating input and output currents due to non-linear duty ratio effects and temperature variations, leading to errors in current measurement, especially when using methods that require special circuits and sensors.
Innovation Solution
A power conversion device with an inverter, transformer, rectifying circuit, smoothing reactor, and control unit, which includes an input current detecting circuit with a current-to-voltage conversion circuit to estimate input and output currents without a special circuit, using a control unit to compute these values based on AD conversion data and accounting for temperature effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sensor is provided on the secondary side to accurately measure output current, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces a current sensor on the primary side as an intermediary device to indirectly measure the secondary side output current. Instead of placing a sensor directly on the high-current secondary side, the system uses a transformer relationship where the primary side current sensor measures input current, and the control unit calculates output current based on the known transformer turn ratio and duty cycle, thereby avoiding the need for a complex secondary side sensor
Solution Approach 2:
The patent replaces the direct electrical measurement approach (mechanical/electrical sensor on secondary side) with a computational approach. The control unit uses arithmetic calculations based on primary current detection, transformer parameters, and switching duty cycle to derive the output current, substituting a complex physical sensing system with a simpler detection and calculation system
2Device complexity
If estimation method from primary side is used to avoid special circuits, then device complexity is reduced, but measurement precision deteriorates due to non-linear duty ratio effects
Solution Approach 1:
The control unit continuously monitors the primary side current detection values and uses feedback control to estimate the input current. By repeatedly acquiring detection values during the switching period and using the known duty ratio, the system refines its current estimation through iterative calculation, improving accuracy while maintaining circuit simplicity
Solution Approach 2:
The patent accounts for the non-linear duty ratio effect by introducing correction based on the duty cycle parameter. The control unit adjusts the current estimation calculation to compensate for the non-linear relationship between duty ratio and current/voltage conversion, thereby improving measurement precision without adding complex hardware
3Stability of the object's composition
If temperature correction is applied to restrict temperature change effects, then stability is improved, but device complexity increases
Solution Approach 1:
The control unit implements temperature compensation through feedback control by continuously monitoring temperature changes and adjusting the current estimation calculations accordingly. The system uses the detected temperature to correct the duty ratio and current/voltage conversion parameters, maintaining stability without requiring complex external correction circuits
Solution Approach 2:
The control unit performs self-correction for temperature effects by using its own processing capabilities to calculate compensation based on temperature detection. Rather than requiring external correction circuits or additional hardware, the system uses its built-in computational resources to automatically adjust for temperature variations, maintaining stability while avoiding additional device complexity
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
Enables accurate estimation of input and output currents, reducing errors and costs associated with special circuits and sensors, while improving temperature stability and efficiency in power conversion.
Implementation Method 1
a current-to-voltage conversion circuit connected to the second winding of the input current detecting circuit
Implementation Method 2
a transformer that has a primary winding and a secondary winding, converts a voltage applied across the primary winding by the inverter device into a differing voltage
Implementation Method 3
a smoothing capacitor that smoothes a voltage waveform of a current flowing through the smoothing reactor
Data Source
AI summary
The present application provides a power conversion device such that input current and output current can be accurately estimated without providing a special circuit. A DC-DC converter including a control unit and semiconductor switching elements is such that a current detecting current transformer is connected in series between a high voltage battery and the semiconductor switching elements, in addition to which the DC-DC converter includes a current-to-voltage conversion circuit on a secondary side of the current transformer, and the control unit estimates an input current from an AD conversion value input from the current-to-voltage conversion circuit.