Sensorless Oil-Pump Motor Drive Using Dynamic D-Axis Current
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Solution Overview
Problem
Existing vector-control-type sensor-less methods for oil-pump brushless motors face challenges in accurately estimating rotor position at low speeds, leading to potential instability and vibrations due to complex control modes and rotor deformation.
Innovation Solution
A drive apparatus with a current detection unit and control unit that converts multi-phase currents into d-axis and q-axis currents, calculates phase errors, and adjusts d-axis current command values to ensure accurate position estimation and stable operation even at low speeds by increasing induced voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If 180-degree energized sine-wave driving is performed over the entire speed range to estimate rotor position based on induced voltage, then the control method remains simple, but the accuracy for estimating the position of the rotor deteriorates in low-speed operations
Solution Approach 1:
The patent applies dynamics by making the d-axis current command value dynamic based on motor rotation speed. When the motor rotates at low speed, the control unit sets the d-axis current command value to a value greater than zero to enhance induced voltage and improve rotor position estimation accuracy. When the motor rotates at high speed, the control unit sets the d-axis current command value to zero to maintain simple sine-wave driving control. This dynamic adjustment resolves the contradiction between control simplicity and position estimation accuracy.
2Use of energy by moving object
If the d-axis current command value is set to zero for high-speed operation, then power consumption is reduced and control efficiency is improved, but rotor position estimation accuracy deteriorates in low-speed operation
Solution Approach 1:
The patent applies parameter changes by adjusting the d-axis current command value parameter based on motor rotation speed. At low speeds, the d-axis current command value is changed to a positive value to increase induced voltage for accurate position estimation. At high speeds, the parameter is changed to zero to reduce power consumption and improve control efficiency. This parameter adjustment strategy resolves the contradiction between power consumption and position estimation accuracy.
3Measurement precision
If control mode is changed between high-speed and low-speed ranges, then rotor position estimation accuracy is maintained across all speeds, but the control becomes complicated
Solution Approach 1:
The patent applies universality by making the d-axis current command value serve multiple functions based on operating conditions. The same control unit and control algorithm handle both high-speed and low-speed operations, automatically adjusting the d-axis current command value to achieve accurate position estimation at low speeds while maintaining simple control at high speeds. This multi-functional approach avoids the need for separate control modes and reduces overall control complexity.
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
Enables stable vector-control sensor-less operation of oil-pump brushless motors across all speed ranges without sensor usage, reducing the risk of vibrations and improving speed response.
Implementation Method 1
a vector-control-type sensor-less method for estimating a position of a rotor of a brushless motor based on an induced voltage of the motor calculated from a motor constant such as a current, a voltage, and a winding resistance
Data Source
AI summary
A drive apparatus for a motor having a stator and a rotor, the drive apparatus including a current detection unit configured to detect, when the motor is rotating, each of multi-phase currents flowing through coils of the stator, and a control unit for controlling the motor by sensor-less control configured to convert the detected multi-phase currents into a d-axis current Id and a q-axis current Iq in a d-q coordinate system, calculate a phase error between an actual rotational position of the rotor and an imaginary rotational position thereof by comparing the d-axis current Id with a d-axis current command value Idref and comparing the q-axis current Iq with the d-axis current command value Idref, perform control so that the phase error gets closer to zero, and output voltage command values to a motor drive circuit.