Electrolytic Capacitor-Free PMSM Drive Resonance Suppression
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Solution Overview
Problem
Current electrolytic capacitor-free variable frequency driving systems for permanent magnet synchronous motors suffer from increased current harmonics and decreased power factor due to unaddressed bus voltage pumping during motor braking in active damping control methods, leading to LC resonance and poor grid-side current quality.
Innovation Solution
A resonance suppression method that involves a pre-designed high-pass filter to extract bus voltage harmonics, calculating damping current based on feedback gain, converting it to equivalent damping power, and injecting damping voltages into the motor current to absorb resonance components, thereby improving power factor and reducing harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active damping control is applied to suppress LC resonance, then resonance is suppressed, but bus voltage pumping during motor braking is not addressed causing grid current harmonics to increase and power factor to decrease
Solution Approach 1:
The patent introduces a feedback mechanism where the bus voltage is detected and processed through a high-pass filter to extract resonance components. The damping voltage is calculated based on the resonance frequency and injected into the motor terminal through coordinate transformation. This closed-loop feedback control dynamically adjusts the damping voltage to suppress LC resonance while preventing bus voltage pumping during motor braking, thereby eliminating grid current harmonics and improving power factor without sacrificing resonance suppression effectiveness
Solution Approach 2:
The patent uses the motor as an intermediary element to suppress LC resonance. Instead of directly damping the resonance at the grid side, the damping voltage is injected into the motor terminal where it absorbs the resonance energy. The motor acts as a buffer that converts the LC resonance oscillation into motor current, preventing the resonance from propagating back to the grid and causing harmonics and power factor degradation
2Reliability
If film capacitor or ceramic capacitor replaces electrolytic capacitor to eliminate electrolytic capacitor-free system, then service life is improved and reliability increased, but LC resonance occurs due to weak damping ability and low input line resistance
Solution Approach 1:
The patent replaces passive mechanical damping components (resistors, inductors, capacitors) with an active electronic control system. Instead of adding physical damping elements to suppress LC resonance, the system uses software-based active damping control that calculates and injects damping voltage through coordinate transformation. This electronic substitution eliminates the need for additional passive components while effectively suppressing resonance in the electrolytic capacitor-free system
Solution Approach 2:
The patent changes the control parameters by introducing damping voltage injection based on resonance frequency detection. The system dynamically adjusts the damping voltage magnitude and phase through coordinate transformation parameters (damping ratio ξ and natural frequency ωn) to match the LC resonance characteristics. This parameter adjustment allows the system to suppress resonance without modifying the physical capacitor configuration or adding damping components
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
Effectively suppresses LC resonance, improves the power factor, and reduces grid current harmonics, ensuring better grid-side current quality and digital implementation simplicity.
Implementation Method 1
a pre-designed high-pass filter extracts a bus voltage harmonic component
Implementation Method 2
the active damping control may suppress the rise of the bus voltage
Data Source
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AI summary
The present invention relates to the field of permanent magnet synchronous motor drive control, and disclosed thereby are a resonance suppression method and system for an electrolytic capacitor-free variable frequency driving system. The method comprises: extracting a bus voltage harmonic component; multiplying a bus voltage resonance component by a feedback proportional gain so as to obtain a damping current of the system; multiplying the damping current by a current bus voltage so as to obtain equivalent damping power at an input side of an inverter, and converting LC oscillation at an input side of the driving system to an output side of the inverter; dividing the equivalent damping power at the input side of the inverter by a current output current of the inverter so as to obtain an equivalent damping output voltage of the inverter; and superimposing the equivalent damping output voltage onto the damping voltage of the α axis and the damping voltage of the β axis according to currents of the α axis and the β axis of the motor, so that the resonance component is absorbed by the motor current, achieving LC resonance suppression. In the present invention, not only can the LC resonance in a driving system be effectively suppressed, but a power factor of an electrolytic capacitor-free driving system can also be improved, calculations are simple, and digital implementation is easy.