Motor Control Apparatus Rotor Position Detection Voltage Ripple Reduction
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Solution Overview
Problem
Existing motor control techniques for sensorless DC brushless motors face challenges in detecting rotor position during low-speed rotation and stopping, leading to voltage fluctuations and ripples in the output voltage of the switching power supply, which are difficult to manage due to rapid changes in coil current and load-dependent impedance.
Innovation Solution
A motor control apparatus that includes a switching power supply and a control unit, where the control unit supplies power to a load other than the motor before detecting the initial rotor position using a current flowing through the motor, allowing for reduced ripples in the output voltage by stabilizing the switching frequency through hold excitation of a stepping motor before position determination excitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the amount of change per unit time in the current flowing through the coil is increased to enable rotor position detection, then the rotor position can be detected during stoppage and low-speed rotation, but voltage drop and ripples occur in the output voltage of the switching power supply
Solution Approach 1:
The patent applies preliminary action by performing hold excitation of a stepping motor before position determination excitation of the DC brushless motor. This preliminary action stabilizes the switching frequency of the power supply in advance, preventing voltage ripples and drop when the large current change for rotor position detection begins. The hold excitation creates a buffer state that prepares the power supply system to handle the subsequent load change smoothly.
2Stability of the object's composition
If the capacity of the smoothing capacitor of the switching power supply is increased to reduce voltage drop and ripples, then the output voltage stability is improved, but the substrate area is increased leading to increased costs
Solution Approach 1:
The patent replaces the mechanical/electrical solution of increasing capacitor capacity with a control system solution. Instead of physically enlarging the smoothing capacitor to handle voltage stability, the invention uses a control unit to coordinate hold excitation and position determination excitation timing. This substitution of control logic for physical component scaling reduces substrate area while maintaining voltage stability.
3Stability of the object's composition
If the on-time of the switching element of the switching power supply is increased to suppress voltage fluctuations, then the output voltage stability is improved, but power becomes excessive when the load is small causing the output voltage to become temporarily higher than steady state
Solution Approach 1:
The patent applies dynamics by making the switching element on-time variable rather than fixed. The control unit dynamically adjusts the on-time based on operational conditions: during hold excitation when the stepping motor is active, the on-time is set to suppress voltage fluctuations; during position determination excitation of the DC brushless motor, the on-time is adjusted to accommodate the large current change. This dynamic adjustment prevents both voltage instability and excessive power consumption under different load conditions.
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 effectively reduces voltage ripples in the switching power supply by minimizing changes in switching frequency, thereby maintaining a stable output voltage during rotor position detection, without increasing the substrate area or costs.
Implementation Method 1
allowing for reduced ripples in the output voltage by stabilizing the switching frequency through hold excitation of a stepping motor before position determination excitation
Implementation Method 2
a switching power supply that supplies operating power to the motor performs feedback control in order to make the output DC voltage constant
Implementation Method 3
the rotor position is detected by measuring the coil impedance, which changes depending on the rotor position
Data Source
AI summary
A motor control apparatus includes: a switching power supply; a first motor configured to operate with a voltage from the switching power supply; and a control unit configured to control the first motor, wherein the control unit is further configured to cause the switching power supply to supply power of the switching power supply to a load other than the first motor before detecting an initial position of a rotor of the first motor using a current flowing through the first motor.