Power Steering Control Apparatus Reducing Electromagnetic Noise
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Solution Overview
Problem
Existing power steering apparatuses face challenges in reducing electromagnetic noise and achieving stable motor control due to limitations in carrier frequency settings, which affect responsiveness and current control, leading to issues like current vibration and increased calculation load on microcomputers.
Innovation Solution
A control apparatus for power steering that dynamically sets the control period and carrier frequency, allowing for flexible frequency changes and improved motor control by calculating current and voltage instruction values and adjusting detection timings based on changing control periods, thereby reducing electromagnetic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the carrier frequency is set to a fixed value (around 20 kHz) to avoid audible noise and reduce switching loss, then electromagnetic noise falls outside human audible band and switching efficiency improves, but electromagnetic noise peak remains concentrated at a specific frequency and current control responsiveness is limited
Solution Approach 1:
The patent applies dynamics by making the control period variable rather than fixed. The control period is dynamically adjusted based on the absolute value of the fundamental wave voltage instruction value. When the fundamental wave voltage is low, the control period is extended to allow for spread spectrum noise reduction. When the fundamental wave voltage is high, the control period is shortened to improve current control responsiveness. This dynamic adjustment resolves the contradiction between noise reduction and responsiveness.
Solution Approach 2:
The patent changes the parameter of control period based on operating conditions. Specifically, the control period is set to a longer value when the absolute value of the fundamental wave voltage instruction value is below a threshold, and to a shorter value when it exceeds the threshold. This parameter change allows the system to adapt between noise reduction mode and responsiveness mode, resolving the technical contradiction.
2Object-affected harmful factors
If the control period is extended to reduce switching noise and spread electromagnetic spectrum, then electromagnetic noise peak is reduced, but current control responsiveness deteriorates and steering feel becomes unnatural
Solution Approach 1:
The patent changes the control period parameter dynamically based on the fundamental wave voltage instruction value. By setting the control period to a longer value only when the fundamental wave voltage is low (below threshold), the system reduces electromagnetic noise peak during low-demand conditions. When the fundamental wave voltage is high, the control period is shortened to maintain fast current control responsiveness, ensuring natural steering feel. This conditional parameter change resolves the contradiction.
3Object-affected harmful factors
If the carrier frequency is changed dynamically to spread electromagnetic spectrum, then electromagnetic noise peak is reduced, but calculation load on microcomputer increases and control stability becomes difficult to maintain
Solution Approach 1:
The patent implements parameter changes based on a simple threshold comparison of the fundamental wave voltage instruction value. This approach spreads the electromagnetic spectrum (reducing noise peak) while keeping the control logic simple and calculation load manageable. The microcomputer only needs to compare the absolute value of the fundamental wave voltage instruction value against a threshold and select between two predetermined control period values, avoiding complex real-time frequency modulation calculations.
4Speed
If the control period is shortened to improve current control responsiveness, then responsiveness improves, but electromagnetic noise concentration increases and switching loss increases
Solution Approach 1:
The patent applies dynamics by making the control period adaptable to operating conditions. The control period is set to a shorter value when the fundamental wave voltage is high to improve current control responsiveness. When the fundamental wave voltage is low, the control period is extended to reduce electromagnetic noise concentration and switching loss. This dynamic adaptation resolves the contradiction between responsiveness and noise reduction.
Data Source
AI summary
Provided is a control apparatus for a power steering apparatus, and a power steering apparatus using it that can reduce electromagnetic noise with the aid of a spread spectrum, thereby realizing stabilized motor control. The control apparatus for the power steering apparatus includes a PWM carrier period setting portion configured to set a natural number of PWM carrier periods within one period of a control period and also changeably set a length of the PWM carrier period, a motor current detection execution portion configured to detect a motor current during the control period, a motor rotational angle detection execution portion configured to detect a motor rotational angle during the control period, and an execution timing setting portion configured to set a timing at which the motor current is detected by the motor current detection execution portion or a timing at which the motor rotational angle is detected by the motor rotational angle detection execution portion, based on the control period set by the control period setting portion.