Electric-Power Conversion Apparatus Current Detection Circuit
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Solution Overview
Problem
Conventional electric-power conversion apparatuses face limitations in accurately detecting output current, particularly in three-phase AC rotating machines, due to restrictions on current detection methods, leading to torque ripples and noise, and are often expensive or require additional power sources.
Innovation Solution
An electric-power conversion apparatus with a chopper circuit, a current sense resistor, and a differential detection circuit that calculates the output current using a control signal, allowing accurate detection regardless of the upper or lower stage power semiconductor device's on/off state, and is designed to be cost-effective.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a current transformer is used to detect output current, then the detection method is simple, but it cannot detect DC current and is unsuitable for low rotation speed or stop mode operation
Solution Approach 1:
The patent combines the advantages of current transformer (simplicity) and hole current sensor (wide detection range including DC) by integrating a current transformer with a detection circuit that can process both AC and DC components, creating a unified detection system that operates across all rotation speeds and modes
Solution Approach 2:
The detection system is designed to perform multiple functions: detecting AC current components through the current transformer and DC current components through the integrated detection circuit, enabling it to operate effectively in stop mode, low rotation speed, and high rotation speed conditions without requiring separate detection methods
2Adaptability or versatility
If a hole current sensor is used to detect output current, then the detection range is wide including DC current, but the cost is high and robustness is reduced in harsh environments
Solution Approach 1:
The patent replaces the expensive hole current sensor with a more economical current transformer combined with a cost-effective detection circuit that achieves similar functional performance, reducing overall system cost while maintaining the ability to detect both AC and DC current components
Solution Approach 2:
The patent substitutes the physical hole structure of a hole current sensor with an electromagnetic field-based current transformer and electronic detection circuit, improving robustness against environmental factors such as temperature, humidity, and vibration while maintaining detection capabilities
3Device complexity
If current detection resistors are inserted in series into lower-arm switching devices, then the detection circuit is simple, but the upper-arm current cannot be detected and the on/off command is restricted
Solution Approach 1:
The patent introduces a detection circuit that uses the current transformer as an intermediary to detect current without requiring series insertion of resistors into the switching devices, enabling detection of both upper-arm and lower-arm currents while maintaining full switching control flexibility
Solution Approach 2:
The patent transitions from a one-dimensional detection approach (detecting only lower-arm current through series resistors) to a two-dimensional detection approach by using a current transformer that can detect current in both upper and lower arms simultaneously, providing comprehensive current information for optimized control
4Measurement precision
If additional power sources are added to improve detection accuracy, then the detection precision is improved, but the device complexity and cost increase
Solution Approach 1:
The patent designs a detection circuit that uses the existing power sources already present in the inverter system (DC power source and AC power source) to power the detection circuit itself, eliminating the need for additional dedicated power sources while maintaining detection accuracy
Solution Approach 2:
The detection circuit is designed to draw power from multiple existing sources in the system (both DC and AC power sources), making it adaptable to different operating conditions without requiring dedicated power supply infrastructure, thereby reducing overall system 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
The solution enables accurate and inexpensive detection of output current, reducing torque ripples and noise, and eliminating the need for additional power sources, while maintaining operational robustness in harsh environments.
Implementation Method 1
a current sense resistor that detects the output current of the chopper circuit
Implementation Method 2
a differential detection circuit that outputs, as a differential detection signal, the electric potential difference across the detection resistor
Data Source
AI summary
There is provided an electric-power conversion apparatus including a chopper circuit; a current sense resistor that detects the output current of the chopper circuit; a differential detection circuit that outputs, as a differential detection signal (vo), the electric potential difference across the current sense resistor; and a calculation means that corrects the differential detection signal (vo) from the differential detection circuit by use of a control signal (D1) for the chopper circuit so as to calculate the output current (i0) of the chopper circuit.