Motor Current Filtering for Accurate PWM Power Control
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Solution Overview
Problem
Existing electric motor control devices struggle to accurately control power supplied to electric motors when the load current changes during the on-period of the switching element, leading to inappropriate power control.
Innovation Solution
An electric motor control device is designed with a switching unit, a current detection unit, an interface unit with multiple filters of different time constants, and an arithmetic processing unit. The interface unit performs filtering on the detection signal, and the arithmetic processing unit selects an appropriate filter based on the control pulse length to ensure accurate current detection and power control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed filtering time constant is used for current detection, then the filtering processing is simple, but the detected current value deviates when load current changes during switching element on-period
Solution Approach 1:
The patent applies dynamics by making the filtering time constant variable rather than fixed. The arithmetic processing unit dynamically selects different time constants based on the PWM duty ratio range, adapting the filtering characteristics to match the switching element's on-period characteristics. This resolves the contradiction by allowing accurate current detection across varying load conditions without requiring a complex multi-filter system.
Solution Approach 2:
The patent changes the parameter of filtering time constant based on operating conditions. By dividing the PWM duty ratio into ranges and assigning different time constants to each range, the system optimizes current detection accuracy for different load current scenarios. This parameter adaptation resolves the measurement precision issue while maintaining relatively simple filtering processing.
2Ease of operation
If A/D conversion timing is set based on fixed delay amounts and stable state start time, then the control timing is simple, but power control becomes inappropriate when load current changes during on-period
Solution Approach 1:
The patent makes the A/D conversion timing dynamic by linking it to the PWM duty ratio. The arithmetic processing unit determines optimal conversion timing based on the current duty ratio range, ensuring that conversion occurs when the current value is stable and representative. This dynamic timing adjustment maintains power control accuracy under varying load conditions while preserving ease of operation through automated timing selection.
Solution Approach 2:
The system uses feedback by continuously monitoring the PWM duty ratio and adjusting the A/D conversion timing accordingly. The arithmetic processing unit receives feedback about the current operating point and adapts the conversion timing to ensure accurate current sampling. This feedback mechanism ensures reliable power control without complicating the overall control structure.
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 device effectively controls power supplied to the electric motor even when the load current changes, ensuring accurate detection and correction of current values, thus maintaining appropriate power control.
Implementation Method 1
an interface unit configured to perform filtering processing on the detection signal; The interface unit includes a plurality of filters having time constants different from one another
Data Source
AI summary
An electric motor control device includes a current detection unit, an interface unit, a switching unit, and an arithmetic processing unit. A detection signal of a current detected by the current detection unit is input to the interface unit. The interface unit includes a plurality of filters having time constants different from one another, and performs filtering processing on the detection signal. The switching unit controls power supplied to an electric motor. The arithmetic processing unit uses, as a selected filter, a filter selected from among the plurality of filters based on the length of a control pulse. The arithmetic processing unit uses, as a detected current value, a value obtained by A/D conversion of a processed signal that is the detection signal on which the filtering processing has been performed with the selected filter.