Electric Power Steering Control Circuit Duty Cycle Management
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Solution Overview
Problem
Electric power steering apparatuses face inefficiencies in energy usage due to excessive activation of auxiliary power supplies when power from the battery falls short, leading to unnecessary energy consumption and waste.
Innovation Solution
An electric power steering apparatus with a control circuit that manages the discharge from an auxiliary power supply by determining a command value for drive voltage based on actual and target currents, controlling the discharge duty to optimize voltage supply from both the battery and auxiliary power supply, and charging the auxiliary power supply only when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the auxiliary power supply is activated whenever battery power falls short, then the power supply reliability is improved, but the energy consumption of the auxiliary power supply increases excessively
Solution Approach 1:
The control circuit dynamically adjusts the discharge duty cycle of the auxiliary power supply based on the actual power shortage level. When the battery power is sufficient, the auxiliary power supply discharge duty is reduced to zero. When there is a moderate power shortage, the discharge duty is adjusted proportionally rather than activating at full capacity. This parameter adjustment resolves the contradiction by matching the auxiliary power supply output to the actual need, ensuring reliability while minimizing energy waste.
Solution Approach 2:
The control circuit continuously monitors the battery output power and the motor power demand, comparing the actual power supply capacity with the required power. Based on this feedback, the control circuit dynamically adjusts the discharge duty of the auxiliary power supply. This feedback mechanism ensures that the auxiliary power supply is activated only to the extent necessary, maintaining power supply reliability while preventing excessive energy consumption.
2Power
If the auxiliary power supply operates at full capacity whenever activated, then the power output is maximized, but the activation frequency increases leading to excessive energy waste
Solution Approach 1:
Instead of activating the auxiliary power supply at full capacity whenever there is any power shortage, the control circuit applies partial action by adjusting the discharge duty cycle proportionally to the power shortage level. The auxiliary power supply operates at a partial capacity that exactly matches the power deficit, rather than always operating at full capacity. This resolves the contradiction by providing sufficient power output while minimizing unnecessary energy consumption from excessive full-capacity activation.
Solution Approach 2:
The control circuit dynamically adjusts the discharge duty of the auxiliary power supply based on real-time power demand and battery capacity. The discharge duty is not fixed but varies continuously according to the power shortage level. This dynamic adjustment allows the system to maintain adequate power output when needed while reducing activation intensity and frequency when power shortage is moderate, thereby minimizing energy waste.
3Reliability
If the auxiliary power supply is charged frequently, then the readiness for high power operation is improved, but the control circuit load and charging time increase
Solution Approach 1:
The control circuit monitors the state of charge of the auxiliary power supply and autonomously decides when charging is necessary. The auxiliary power supply is charged only when its remaining energy falls below a predetermined threshold or when the battery power is sufficient to support charging without compromising motor operation. This self-service approach reduces unnecessary charging operations, lowering the control circuit load while maintaining readiness for high power operation when truly needed.
Solution Approach 2:
The control circuit adjusts the charging parameter (charging activation condition) based on the actual energy state of the auxiliary power supply and the battery capacity. Instead of charging at fixed intervals or whenever the auxiliary supply is depleted, the system changes the charging parameter to activate charging only when the auxiliary supply energy falls below a threshold and battery power is sufficient. This parameter-based control reduces unnecessary charging operations, lowering control complexity while maintaining operational readiness.
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 prevents undue voltage supply from the auxiliary power supply, ensures adequate voltage, and reduces energy waste by optimizing the use of both battery and auxiliary power, thereby efficiently using the auxiliary power supply.
Implementation Method 1
An electric double-layer capacitor, for example, may be used as the above auxiliary power supply
Implementation Method 2
a motor drive circuit for driving the motor; (b) a current detector for detecting an actual current supplied from the motor drive circuit to the motor
Data Source
Figure 1
Figure 2
Figure 3
AI summary
In an electric power steering apparatus of the invention, a control circuit (2) determines a command value of drive voltage supplied to a motor drive circuit (6) based on an actual current through a motor (5) and a target current. When the command value exceeds the previous value having a lower limit equivalent to a limit value representing the limit of the power supply from a battery (7), the control circuit (2) controls the amount of discharge from the auxiliary power supply (7) according to a difference between the command value and the previous value by increasing or decreasing a duty of switching devices (12, 13). Thus, the power steering apparatus can save the energy of the auxiliary power supply for efficiently using the auxiliary power supply.