Brushless Motor Control Using Induced Voltage at Low DC Link Voltage
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Solution Overview
Problem
The power limit of two-phase brushless motors is constrained by the intermediate circuit voltage, limiting their performance, especially in battery-operated devices where voltage drops reduce motor efficiency and capability.
Innovation Solution
The method involves determining a target phase voltage based on predetermined power or speed settings, adjusting phase voltage using PWM control, and modifying the commutation angle by regulating the induced voltage setpoint to exceed full modulation limits, thereby increasing actual power output even at low intermediate circuit voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If the intermediate circuit voltage is reduced (e.g., in battery-operated devices), then the device portability and cost are improved, but the motor power output and efficiency deteriorate
Solution Approach 1:
The patent changes the control parameter from conventional PWM duty cycle adjustment to induced voltage setpoint adjustment. By regulating the induced voltage setpoint instead of merely adjusting PWM frequency or duty cycle, the system can maintain motor power output even when intermediate circuit voltage drops, thereby resolving the contradiction between device portability and motor performance
Solution Approach 2:
The patent implements a feedback control mechanism where the actual induced voltage is continuously measured and compared with the setpoint induced voltage. The PWM frequency is adjusted based on the difference between these values, creating a closed-loop control system that maintains optimal motor performance despite variations in intermediate circuit voltage, thus preserving power output in portable devices
2Power
If the PWM duty cycle is increased to maintain power output at low voltages, then the motor power is improved, but the intermediate circuit voltage depletes faster and overheating risk increases
Solution Approach 1:
The patent changes the control approach from direct PWM duty cycle modulation to induced voltage setpoint regulation. This parameter change enables the system to maintain motor power output through more efficient voltage utilization, reducing the need for excessive duty cycle increases that would lead to energy waste and overheating
Solution Approach 2:
The feedback control mechanism continuously monitors the actual induced voltage and adjusts PWM frequency accordingly. This ensures optimal energy utilization by maintaining the motor operating point near the setpoint, preventing energy waste from excessive duty cycle adjustments and reducing thermal losses
3Device complexity
If conventional PWM control is used without induced voltage regulation, then the control simplicity is maintained, but the motor efficiency and power delivery capability deteriorate
Solution Approach 1:
The patent introduces induced voltage setpoint regulation as an additional control parameter. While this increases control complexity slightly, it dramatically improves motor power delivery capability and efficiency, especially in voltage-constrained applications. The added complexity is justified by the significant performance gains in power utilization
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 allows for increased motor performance and efficiency by synchronizing the PWM frequency with a setpoint induced voltage, enabling higher power delivery even at reduced battery voltages, and reducing costs and installation space requirements.
Implementation Method 1
adjusting phase voltage with PWM control
Implementation Method 2
measuring an induced voltage of a third, unenergized phase
Implementation Method 3
The rotor contains one or more permanent magnets. The interaction between the stator field and the rotor field generates an electric torque that can lead to rotation.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to a method for controlling a brushless motor (M) with at least two phases, preferably without a rotor position sensor, comprising at least the following steps: • Determining (100) a target phase voltage (UMotorRef) based on a predetermined target power (Pref) and an actual power (Pact), • Energizing (200) the two phases (U, V, W) with a phase voltage (UPhase) based on the target phase voltage (UMotorRef) and a detected actual phase voltage, wherein the phase voltage (UPhase) of the energizing (200) is set by means of PWM control, • Comparing (300) the determined target phase voltage (UMotorRef) with a detected DC link voltage (UDC), • in response to the comparison (300), if the determined target phase voltage (UMotorRef) corresponds to the detected DC link voltage (UDC): • Determining (400) an induced voltage (ΔU) of a non-energized phase (U, V, W),• Determine (500) a setpoint of the induced voltage (ΔUref) based on the predetermined setpoint power (Pref) and the actual power (Pact), • Compare (600) the determined induced voltage (ΔU) with the determined setpoint of the induced voltage (ΔUref), and • Adjust (700) the PWM frequency if the difference between the determined induced voltage (ΔU) and the determined setpoint of the induced voltage (ΔUref) is not zero.