Brushless DC Machine Freewheeling Circuit Control
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Solution Overview
Problem
Existing brushless DC machines face inefficiencies in power loss and noise due to uncontrolled current reversals during freewheeling operations, particularly when the induced voltage exceeds the applied voltage, leading to reduced motor efficiency and undesirable noise.
Innovation Solution
The method involves operating semiconductor switches in a DC machine to form either an active or passive freewheeling circuit based on current direction, using a switching bridge with freewheeling diodes, where the first operating range utilizes an active freewheeling circuit when current flows in one direction and switches to a passive freewheeling circuit when direction changes are expected, preventing current reversal and minimizing power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passive freewheeling circuit is used continuously, then current reversal is prevented, but power loss increases and motor efficiency decreases
Solution Approach 1:
The patent applies dynamics by switching between two different freewheeling modes (active and passive) based on operating conditions. The control unit dynamically selects the appropriate mode: active freewheeling when induced voltage is lower than applied voltage, and passive freewheeling when induced voltage exceeds applied voltage. This dynamic adaptation resolves the contradiction by using the most efficient mode for each specific operating condition, preventing continuous power loss while maintaining current direction control when necessary.
Solution Approach 2:
The patent changes the operational parameters of the freewheeling circuit based on the relationship between induced voltage and applied voltage. By monitoring these voltage parameters and switching the freewheeling mode accordingly, the system optimizes power loss. This parameter-based control allows the system to transition from passive to active freewheeling when conditions change, resolving the contradiction between reliability and energy loss.
2Productivity
If semiconductor switches are clocked at high frequency, then power and speed control is improved, but noise and power loss increase
Solution Approach 1:
The patent applies periodic action by using pulse width modulation (PWM) to control the semiconductor switches. Instead of continuous high-frequency switching that generates noise, the system uses periodic PWM signals to control the switches, maintaining effective power and speed control while reducing noise. The active freewheeling mode further reduces noise by providing controlled current paths during switching transitions.
Solution Approach 2:
The patent introduces an intermediary control mechanism (the control unit that monitors voltage conditions and selects freewheeling modes) that mediates between the need for high-frequency switching control and noise reduction. This intermediary intelligence allows the system to achieve precise speed control while minimizing noise generation through appropriate mode selection.
3Loss of energy
If an active freewheeling circuit is used continuously, then power loss is reduced, but current reversal control is lost when induced voltage exceeds applied voltage
Solution Approach 1:
The patent applies dynamics by switching between two different freewheeling modes (active and passive) based on operating conditions. The control unit dynamically selects the appropriate mode: active freewheeling when induced voltage is lower than applied voltage, and passive freewheeling when induced voltage exceeds applied voltage. This dynamic adaptation resolves the contradiction by using the most efficient mode for each specific operating condition, preventing continuous power loss while maintaining current direction control when necessary.
Solution Approach 2:
The patent uses feedback by continuously monitoring the relationship between induced voltage and applied voltage. The control unit receives feedback about the voltage conditions and automatically adjusts the freewheeling mode accordingly. This feedback mechanism ensures that the system transitions from active to passive freewheeling when induced voltage exceeds applied voltage, maintaining current direction control while minimizing power loss during normal operation.
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 reduces power loss and prevents current reversal, maintaining motor efficiency and minimizing noise by dynamically switching between active and passive freewheeling modes based on operating conditions.
Implementation Method 1
each of which has a freewheeling diode connected in parallel... Due to the blocking effect of the freewheeling diode, the current can only flow through the freewheeling circuit in one direction
Implementation Method 2
In order to operate brushless DC machines, it is necessary to electrically commutate the currents of one or more phase windings
Implementation Method 3
the semiconductor switches being able to convert a DC voltage into an AC voltage of variable frequency and variable pulse width
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2~3
AI summary
The invention relates to a method for operating a brushless DC machine comprising at least one winding strand (3) to which a switching bridge (1) with at least two semi-conductor switches (4-7), respectively comprising a recovery diode which is connected in parallel, is associated. According to the invention, the semi-conductor switches (4-7) are controlled in a first operational area for forming an active free-wheeling circuit (16) and in a second operational area for forming a passive free-wheeling circuit (17). The invention also relates to a DC machine.