Vienna Rectifier DC Bus Voltage Feedback for Harmonic Distortion
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Solution Overview
Problem
Vienna-type active rectifiers in aerospace applications experience significant input current harmonic distortion, exceeding power quality specifications within the 360 Hz to 800 Hz frequency range due to third-order harmonic voltages on the DC bus, which affects the efficiency of power conversion.
Innovation Solution
A modified pulse-width-modulation (PWM) modulator is introduced, where the voltages of the top and bottom halves of the DC bus are sensed and used to calculate scale factors, which are then applied to rescale reference signals from the controller, adjusting the PWM duty-cycle to minimize third-order harmonic distortion by scaling up or down the PWM command based on DC bus ripples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a Vienna-type active rectifier is used for power conversion in aerospace applications, then efficient AC to dual DC-bus voltage conversion is achieved, but input current harmonic distortion exceeds power quality specifications
Solution Approach 1:
The patent applies feedback control by sensing the actual DC bus voltages and using them to dynamically adjust the PWM reference signals. The controller continuously monitors the DC bus voltage and feeds this information back to modify the PWM duty cycle, thereby compensating for harmonic distortion in real-time while maintaining efficient power conversion.
Solution Approach 2:
The patent changes the PWM reference signal parameters dynamically based on the sensed DC bus voltage. By adjusting the amplitude and timing of the reference signals according to actual operating conditions, the system optimizes power conversion efficiency while minimizing harmonic distortion in the input current.
2Device complexity
If standard PWM modulation is used in the rectifier, then simple control implementation is achieved, but third-order harmonic voltages on the DC bus cause significant current distortion
Solution Approach 1:
The patent enhances standard PWM by incorporating feedback from the DC bus voltage sensing. This feedback mechanism allows the system to automatically compensate for third-order harmonic voltages without requiring complex control algorithms, maintaining relative simplicity while effectively reducing current distortion.
Solution Approach 2:
The patent introduces an intermediary processing stage between the standard PWM generator and the power switches. This intermediary stage modifies the PWM reference signals based on DC bus voltage feedback, acting as a mediator that eliminates third-order harmonics without significantly complicating the overall control structure.
3Object-generated harmful factors
If the PWM duty-cycle is adjusted to compensate for DC bus ripples, then input current power quality improves, but the control system complexity increases
Solution Approach 1:
The patent uses feedback control to automatically adjust the PWM duty-cycle based on sensed DC bus voltage ripples. This approach improves input current power quality by dynamically compensating for harmonics while keeping the control system relatively simple through the use of standard feedback control techniques.
Solution Approach 2:
The patent dynamically changes PWM duty-cycle parameters in response to DC bus voltage conditions. By adjusting these parameters based on real-time feedback, the system improves power quality without requiring overly complex control architecture, as the parameter adjustments follow straightforward control logic.
Data Source
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AI summary
A method is disclosed for reducing input current harmonic distortion in a Vienna-type active rectifier that includes the steps of sensing voltage values ([Vdc_p],[Vdc_n]) from upper and lower halves of a DC bus associated with the rectifier, determining an average of the sensed voltage values ([Vdc_p],[Vdc_n]), calculating upper and lower scale factors ([Vdc_px] and [Vdc_pn]) by dividing the sensed voltage values ([Vdc_p],[Vdc_n]) with the averaged sensed voltage value, rescaling a reference signal from a controller using the upper and lower calculated scale factors ([Vdc_px] and [Vdc_pn]), and forward feeding the rescaled reference signal from the controller to a pulse width modulator to obtain a gate driver signal for power semiconductor switches of the rectifier.