Series Sub-Booster Circuit for EPS Voltage Stability
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Solution Overview
Problem
Conventional voltage booster circuits in electric power steering systems struggle to maintain high power output, leading to a reduction in booster output voltage and inadequate assist torque during rapid steering operations, especially in large-sized vehicles.
Innovation Solution
A motor drive apparatus with a booster circuit comprising multiple sub-booster circuits connected in series or parallel, controlled by a CPU using PID feedback control to maintain target output voltage, allowing for increased boosting ratios and preventing voltage output from falling below the target.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional chopping-type voltage booster circuit is used to reduce heat generation and suppress voltage overshooting, then the booster output voltage falls below the target voltage when high output power is required, but if the boosting duty is increased to maintain target voltage, then the switching elements may be damaged due to excessive current
Solution Approach 1:
The booster circuit is divided into multiple independent sub-booster circuits (first sub-booster circuit and second sub-booster circuit) connected in series. Each sub-booster circuit has its own switching elements and operates independently with separate PWM signals. This segmentation allows the current stress to be distributed across multiple switching elements, preventing any single element from being damaged by excessive current while maintaining the ability to generate high output power.
Solution Approach 2:
Multiple sub-booster circuits are combined in series connection to achieve the desired output voltage. The series combination of multiple voltage sources (sub-booster circuits) creates a higher output voltage capability without requiring a single switching element to handle the full voltage and current stress, thus improving reliability while preventing element damage.
2Power
If the boosting duty is increased to provide high output power for rapid steering operation, then the booster output voltage may fall below target voltage due to saturation duty limit, but if the boosting duty is limited to protect switching elements, then insufficient assist torque is provided
Solution Approach 1:
The booster circuit is segmented into multiple sub-booster circuits that operate in parallel or series configuration. This allows the system to distribute the power generation task across multiple independent units, enabling high output power delivery without requiring any single switching element to operate at excessive duty cycles that would cause saturation or damage.
Solution Approach 2:
The system changes the operational parameters by using multiple sub-booster circuits with independent PWM control. This allows flexible adjustment of duty cycles for each sub-circuit to optimize power output while staying within safe operating limits, preventing voltage saturation while maintaining reliable operation.
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 ensures a stable and sufficient booster output voltage is maintained, enabling the motor drive apparatus to provide required assist torque even during high power output conditions, enhancing steering operation in electric power steering systems, particularly for large-sized vehicles.
Implementation Method 1
The booster coil 71 induces voltage in response to charge and discharge of energy
Data Source
AI summary
A booster circuit of a motor drive apparatus has at least two sub-booster circuits connected in series. Each sub-booster circuit includes a booster coil, a boosting switching element, a reducing switching element and an output capacitor, and outputs, by boosting an input voltage, a boosted output voltage. The booster circuit 20 outputs from its final stage sub-booster circuit a booster output voltage, a total boosting ratio of which is a product of sub-boosting ratios of the series-connected sub-booster circuits. Thus, the booster output voltage supplied to a motor drive circuit is prevented from falling even when high power output is required.