Inverter Phase Current Detection Using PWM Threshold Compensation
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Solution Overview
Problem
Existing methods for detecting phase currents in inverters face challenges such as high costs, complex circuitry, and insufficient detection of three-phase currents due to minimal pulse width requirements, leading to potential overcurrent damage to loads and inverter components.
Innovation Solution
An apparatus and method that set a threshold voltage to determine the minimal pulse width of PWM signals, allowing detection of three-phase currents by varying the reference voltage and compensating for voltage differences to ensure accurate current detection without influencing load drive, using current detecting resistors, analog/digital converters, and a current detection controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sensors are inserted between inverter output terminal and load to detect three-phase currents, then current detection accuracy is improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent replaces expensive current sensors with inexpensive current detecting resistors that can be easily manufactured and replaced. The resistors are inserted in series with each phase line between the inverter output terminal and the load, providing accurate current detection through voltage measurement across the resistors without the high cost of traditional current sensors.
Solution Approach 2:
The patent substitutes the mechanical/electromagnetic current sensor system with an electrical measurement system using resistors and voltage detection. Instead of using complex current sensing mechanisms, the invention measures the voltage drop across known resistance values to calculate current, simplifying the detection mechanism while maintaining accuracy.
2Measurement precision
If current detecting resistors are inserted between inverter output terminal and load to detect three-phase currents, then current detection capability is improved, but circuit complexity and insulation requirements increase
Solution Approach 1:
The patent merges the current detection function with the existing power transmission circuit by inserting resistors directly into the phase lines. The same resistors that are part of the power delivery path also serve as sensing elements, eliminating the need for separate detection circuits and reducing overall system complexity.
Solution Approach 2:
The current detecting resistors serve multiple functions: they are part of the power transmission path and simultaneously act as sensing elements for current detection. This multi-functionality reduces the number of separate components needed and simplifies the overall circuit architecture while maintaining detection capability.
3Device complexity
If one current detecting resistor is inserted between DC power negative terminal and ground to detect three-phase currents, then circuit simplicity is improved, but detection accuracy and control complexity increase
Solution Approach 1:
The patent divides the single-resistor detection approach into three separate detection paths by inserting resistors in each phase line independently. This segmentation allows accurate measurement of each phase current individually, enabling precise detection of unbalanced loads and improving overall detection accuracy while maintaining relatively simple circuit implementation.
4Speed
If minimal pulse width PWM signals are used for switching, then switching speed and efficiency are improved, but current detection capability deteriorates due to insufficient time for current flow
Solution Approach 1:
The patent performs preliminary measurement of the minimal pulse width of PWM signals and uses this information to determine the timing window for current detection. By knowing the exact duration of the PWM pulse in advance, the system can accurately sample the current at the appropriate moment, ensuring detection capability is maintained even with minimal pulse widths.
Solution Approach 2:
The patent implements a feedback mechanism where the detected current information is used to adjust and optimize the PWM control. The system continuously monitors the current through the detecting resistors and uses this feedback to maintain accurate detection while operating with minimal pulse widths, ensuring both switching efficiency and detection accuracy.
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 precise detection of three-phase currents with minimal pulse width PWM signals, preventing overcurrent damage and ensuring continuous, normal operation of the load by adjusting PWM signal widths and compensating sine wave voltages.
Implementation Method 1
a plurality of current detecting resistors coupled between a plurality of lower switching elements and a ground, respectively; a plurality of analog/digital converters for converting voltages of the plurality of current detecting resistors into digital signals
Data Source
AI summary
The present invention previously sets a threshold voltage, compares the set threshold voltage with a reference voltage, and judges whether a minimal pulse width of a PWM signal is obtained. When a pulse width of one PWM signal is equal to or greater than the minimal pulse width, but each pulse width of two PWM signals is less than the minimal pulse width, a sine wave voltage corresponding to one of the two PWM signals less than the minimal pulse width is varied to a threshold voltage to detect two phase currents, and a remaining one phase current is calculated based on the two detected phase currents. After the phase current was detected by varying the threshold voltage, a level difference between an original sine wave voltage and the threshold voltage is set as a compensation voltage, and the sine wave voltage is compensated by the compensation voltage.