Active Rectifier Controller Phase Compensation for Variable-Frequency Generators
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Solution Overview
Problem
Existing active rectifier controllers for variable frequency synchronous generators (VFSG) suffer from reduced efficiency due to phase shifts between the back-electromotive force (BEMF) and current, caused by high-frequency switching, especially in aerospace applications where output impedance is significant, leading to suboptimal power factor.
Innovation Solution
An active rectifier controller that decouples the control algorithm from relying on monitored AC output voltages by using independent position information from the rotor position, such as PMG voltages or a resolver, to generate PWM signals ensuring AC currents remain in-phase with the rotor position, thereby avoiding phase shifts and maximizing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If prior art active rectifier control methods are used that maintain current in-phase with monitored output voltage, then the control is simple to implement, but the power factor becomes suboptimal due to phase shifts between BEMF and current caused by output impedance
Solution Approach 1:
The patent introduces an intermediary phase compensation network that mediates between the monitored output voltage and the control signals. This network compensates for the phase shift caused by output impedance, allowing the rectifier current to remain in-phase with the BEMF voltage rather than the distorted output voltage, thereby improving power factor while maintaining control simplicity
Solution Approach 2:
The patent replaces the direct voltage-monitoring control method with an alternative approach using current sensors and phase compensation networks. This substitution allows the system to indirectly account for phase shifts without requiring complex real-time calculations, maintaining ease of operation while improving efficiency
2Speed
If high-frequency switching is applied in the active rectifier, then the power conversion speed is improved, but phase shifts between BEMF and current increase due to output impedance effects
Solution Approach 1:
The patent applies preliminary anti-action by introducing a phase compensation network that pre-corrects for the expected phase shifts before they affect the control signals. The compensation network is designed to counteract the phase lag introduced by output impedance at high switching frequencies, allowing fast power conversion without energy losses from phase misalignment
3Device complexity
If the active rectifier draws current in-phase with output voltage, then the control algorithm is simple, but the BEMF voltage becomes out of phase with the current provided by the VFSG
Solution Approach 1:
The phase compensation network serves as an intermediary that decouples the simplicity of voltage-based control from the requirement of BEMF alignment. By introducing this intermediate compensation stage, the system maintains simple control logic while achieving proper phase alignment with BEMF through the compensated signal rather than the raw output voltage
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 maintains AC currents in-phase with the rotor position, enhancing the power factor and overall efficiency of the VFSG by isolating noise and phase delay issues from AC output voltages, thus improving power conversion efficiency.
Implementation Method 1
the back-electromotive force (BEMF) of the VFSG
Implementation Method 2
switches that are rapidly turned ON and OFF to ensure the current drawn by the active rectifier is sinusoidal
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
An active rectifier controller (22) decouples measurements of the phase and speed of a variable frequency synchronous generator (14) from measurements of the AC output voltage. The active rectifier controller receives position information representative of the rotor position of the VFSG independent of a load connected to the VFSG that is used to determine the phase position and speed of the VFSG. Based on measurements of the generator speed and phase, the active rectifier controller controls the active rectifier (18) to draw AC currents in-phase with the back-electromotive force (BEMF) voltage of the VFSG.