Sensorless Motor Drive Voltage Correction During Current Limit
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Solution Overview
Problem
Existing motor drive devices that control brushless motors without using a position sensor face challenges in maintaining accurate position estimation during current limit conditions, leading to potential decreases in estimation accuracy and motor performance.
Innovation Solution
A motor drive device is designed with a power conversion circuit, a controller for PWM control, a current detection unit, a current limit unit, and a position estimation unit that corrects the motor voltage used for position estimation during current limit conditions, ensuring accurate rotational position estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate signal is cut off during current limit to protect the motor, then motor current is limited and safety is improved, but output voltage falls below command and position estimation accuracy deteriorates
Solution Approach 1:
The system performs preliminary actions by storing the duty ratio before current limit occurs and preparing correction data in advance. When current limit happens, the stored duty ratio is immediately retrieved and used to correct the output voltage command, avoiding the delay that would occur if correction had to be calculated from scratch during the limit condition.
Solution Approach 2:
The system uses feedback by detecting the actual output voltage during current limit and comparing it with the command voltage. Based on this comparison and the stored duty ratio, the system calculates and applies a correction value to the output voltage command, creating a closed-loop control that actively compensates for the voltage drop caused by current limiting.
2Ease of manufacture
If single-shunt current detection system is used to reduce costs, then system cost is reduced, but accurate motor current detection becomes difficult when gate signal is cut off
Solution Approach 1:
The system uses the duty ratio as an intermediary parameter to indirectly determine the output voltage during current limit. Instead of directly measuring current through complex sensing, the duty ratio (which is already stored and represents the intended voltage level) serves as a mediator to calculate the correction value, enabling accurate voltage reconstruction without requiring additional current sensors.
3Ease of operation
If 120-degree square-wave driving is used to enable electromotive voltage detection, then position detection without sensor is enabled, but noise and vibration increase compared to 180-degree sinewave driving
Solution Approach 1:
The system dynamically adapts its control strategy based on operating conditions. During normal operation, it uses smooth control methods, but during current limit conditions, it dynamically switches to a correction mode that accounts for the abrupt gate signal termination. This dynamic adaptation allows the system to maintain accuracy across different operating states without being constrained to a single control approach.
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 effectively prevents a decrease in rotational position estimation accuracy during current limit conditions, allowing for continued accurate motor control and operation.
Implementation Method 1
each of the semiconductor switching elements is driven by PWM (Pulse Width Modulation) control. Thus, a DC power supplied from the DC power supply line is converted into three-phase AC power
Implementation Method 2
detecting a rotational position using an electromotive voltage generated in motor coils, instead of detecting the rotational position of a motor with a magnetic-pole sensor
Data Source
AI summary
An embodiment provides a motor drive device including: a power conversion circuit having a configuration in which a plurality of arms including a series circuit of positive and negative semiconductor switching elements are connected in parallel to each other and configured to drive a motor; a controller configured to generate and output on/off signals for each of the semiconductor switching elements constituting the power conversion circuit by PWM control; a current detection unit configured to detect a current flowing through the power conversion circuit; a current limit unit configured to stop an operation of the controller when the current reaches a threshold; and a position estimation unit configured to estimate a rotational position of the motor using a motor current and a motor voltage, the position estimation unit being configured to correct the motor voltage used for estimation of the rotational position in a carrier cycle of the PWM control in which the operation of the controller is stopped.