Active Bridge Arms for Three-Phase Brushless DC Motor Power Factor Correction
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Solution Overview
Problem
Existing three-phase fed EC motors with passive B6 bridge rectifier circuits suffer from low mains-side power factor and high harmonic content, leading to inefficiencies and increased costs due to the need for additional components like PFC chokes and inverters.
Innovation Solution
The system replaces passive bridge arms and large-volume linear chokes with active bridge arms and integrates a shunt resistor for current measurement, along with a mains-side filter structure and cascade control to optimize power factor correction, eliminating the need for passive components and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If passive B6 bridge rectifier circuit with linear chokes is used, then power factor correction is achieved, but device complexity and installation space increase due to additional PFC chokes and inverters
Solution Approach 1:
The invention extracts and eliminates the unnecessary passive PFC chokes and inverter components from the traditional circuit structure. By using active bridge arms with controllable switches instead of passive linear chokes, the system removes redundant components while maintaining power factor correction functionality, thereby reducing device complexity and installation space requirements
Solution Approach 2:
The invention replaces the passive mechanical/electrical system (linear chokes and passive rectifier diodes) with an active electronic control system. The active bridge arms use controllable semiconductor switches (IGBTs or MOSFETs) that can be electronically controlled to achieve power factor correction, substituting passive component-based power factor correction with active electronic control
2Device complexity
If passive bridge arms with rectifier diodes are used, then circuit simplicity is maintained, but power factor and harmonic distortion performance deteriorate
Solution Approach 1:
The invention transforms the static passive bridge arms into dynamic active bridge arms. The controllable switches in each active bridge arm can be dynamically controlled based on circuit conditions to optimize current waveform and achieve power factor correction. This dynamic control capability allows the system to actively manage power flow and harmonic content, improving power factor while maintaining controlled complexity
Solution Approach 2:
The invention implements feedback control through the controllable switches in the active bridge arms. The control system monitors circuit parameters and adjusts the switching states of the active bridge arms to maintain optimal power factor and minimize harmonics. This feedback mechanism enables the system to adapt to varying load conditions and maintain high power factor performance
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 configuration significantly increases the mains-side power factor to near-ideal values, reducing energy losses and costs while minimizing common mode interference and harmonic distortion.
Implementation Method 1
Each active bridge arm comprises two anti-parallel connected diodes, an active switch, and a shunt resistor for measuring a current in the bridge arm
Implementation Method 2
Each active bridge arm comprises two anti-parallel connected diodes, an active switch, and a shunt resistor
Data Source
AI summary
The present invention relates to a control system and a method for raising the mains-side power factor λ of three-phase fed EC motors having a dc voltage intermediate circuit (2) with an intermediate center tap (DCM) for generating a positive and a negative intermediate circuit potential (DC+, DC−), comprising three active bridge arms (Ia, IIa, IIIa), each of which are connected to a subordinate two-point current control (ZPR1, ZPR2, ZPR3) and, in each case, via said current control to a superimposed intermediate circuit voltage control (3), which controls the potential difference between the middle circuit potentials (DC+, DC−) via set point settings for the subordinate two-point current controllers (ZPR1, ZPR2, ZPR3).