Link Circuit Capacitor Current Sensing for Sensorless Motor Drives
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Solution Overview
Problem
Current methods for determining currents in electrical machines of drive systems are costly and space-intensive, particularly due to the need for multiple current sensors, which can be problematic with tape-wound toroidal cores and are expensive and structurally intensive.
Innovation Solution
A method that uses a link circuit capacitor to detect electromechanical feedback signals based on predefined carrier frequencies, allowing for the identification and determination of currents without the need for current sensors by detecting signal components associated with these frequencies, using a control device to regulate and determine phase and excitation currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sensors are used to detect currents in electrical machines, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The link circuit capacitor serves dual functions: its primary function of smoothing voltage ripple and its secondary function of generating detectable electromechanical feedback signals through current-induced electromagnetic forces. This self-service approach eliminates the need for separate current sensors, as the capacitor inherently provides the measurement function through its mechanical response to current variations.
Solution Approach 2:
The patent replaces electronic current sensors with a mechanical detection approach. Electromechanical feedback signals are generated through electromagnetic forces acting on the link circuit capacitor, and these mechanical vibrations or position changes are detected to infer current information, substituting electronic sensing with mechanical transduction.
2Reliability
If multiple current sensors are installed for three-phase electrical machines, then complete current monitoring is achieved, but cost and installation space increase
Solution Approach 1:
The link circuit capacitor is designed to perform multiple functions simultaneously: voltage smoothing, energy storage, and current sensing through electromechanical feedback. This multi-functionality reduces the total component count in the drive system, as the capacitor replaces what would traditionally require separate current sensors for each phase.
Solution Approach 2:
The patent merges the current sensing function with the existing link circuit capacitor, combining two previously separate functions (voltage smoothing and current detection) into a single component. This consolidation reduces the number of discrete parts, simplifies the circuit board layout, and decreases overall system cost.
3Measurement precision
If Hall sensors with tape-wound toroidal cores are used, then current detection precision is improved, but structural space and cost increase
Solution Approach 1:
The patent extracts the current detection function from separate physical sensors and relocates it to the link circuit capacitor. By taking out the sensing function from dedicated sensor assemblies and embedding it in the capacitor's electromagnetic interaction, the system eliminates the need for bulky toroidal cores and sensor housings.
Solution Approach 2:
Instead of using physical current sensors that directly measure current, the system creates a copy of the current information through electromechanical feedback signals. The mechanical response of the capacitor to current-induced electromagnetic forces provides a replicable signal that contains current information without requiring direct electrical contact or physical current measurement.
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 the need for cost-intensive and space-consuming current sensors, enabling efficient and accurate determination of currents fed to electrical machines, thereby improving drive system regulation and reducing structural complexity.
Implementation Method 1
excitations with the carrier frequencies or with a multiple of the carrier frequencies of the currents are effected at the link circuit capacitor on account of the feedback
Data Source
AI summary
A method for determining at least one current fed to an electrical machine of a drive system includes predefining a carrier frequency of the at least one current fed to the electrical machine, detecting an electromechanical feedback signal dependent on the at least one current, at a link circuit capacitor of the drive system, identifying a signal component associated with the at least one current in the feedback signal on the basis of the predefined carrier frequency, and determining the at least one current fed to the electrical machine on the basis of the signal component.