Inverter Voltage Command Correction for DC Link Pulsation Control
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Solution Overview
Problem
Conventional power conversion devices experience significant pulsation and distortion in power supply current and DC link voltage due to LC resonance, particularly when using small-capacity film capacitors, which are difficult to suppress effectively.
Innovation Solution
A power conversion device that includes a control unit capable of deriving pulsation voltage prediction and actual measured values, correcting D-axis and Q-axis voltage commands to reduce deviations, and performing feedback control using gains proportional to DC bus voltage and inversely proportional to current, thereby suppressing pulsation in the power supply current and DC link section.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a small-capacity film capacitor is used as the smoothing capacitor to reduce device size, then device size is reduced, but great pulsation of DC voltage and distortion of power supply current occur
Solution Approach 1:
The control unit detects DC link voltage and power supply current, compares them with reference values, and generates feedback signals to adjust the inverter's switching timing. This closed-loop feedback mechanism dynamically compensates for voltage pulsation and current distortion, enabling stable operation with small-capacity capacitors.
Solution Approach 2:
The invention changes the operating parameters of the inverter by adjusting switching timing and pulse width based on detected voltage and current conditions. This dynamic parameter adjustment allows the system to maintain performance with reduced capacitor capacity by optimizing power transfer timing.
2Object-affected harmful factors
If conventional correction method based on detected voltage across inductor is used, then pulsation suppression effect is achieved, but the effect becomes smaller when impedance on power supply side is greater
Solution Approach 1:
The control unit implements feedback control by detecting actual DC link voltage and power supply current, comparing them with reference values, and adjusting inverter switching timing accordingly. This feedback mechanism adapts to varying power supply impedance conditions, maintaining effective pulsation suppression across different grid environments.
Solution Approach 2:
The invention uses dynamic switching timing adjustment based on real-time voltage and current detection. The inverter's switching pattern is continuously modified to match actual operating conditions, enabling the system to maintain pulsation suppression effectiveness regardless of power supply impedance variations.
3Object-affected harmful factors
If current command correction is used to reduce pulsation, then pulsation suppression is achieved, but extremely high response current control system is required
Solution Approach 1:
The control unit detects DC link voltage and power supply current, compares them with reference values, and generates feedback signals to adjust inverter switching timing. This feedback approach suppresses pulsation by modifying voltage output timing rather than relying on high-response current control, reducing system complexity.
Solution Approach 2:
The invention replaces the need for high-response mechanical/electrical current control systems with a control strategy based on voltage timing adjustment and feedback. By controlling the timing of voltage application rather than directly controlling current with extreme precision, the system achieves pulsation suppression with simpler control requirements.
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 pulsation and distortion in power supply current and DC link voltage, ensuring stable operation of the inverter even under varying conditions and high-order noise, without requiring high response in the current control system.
Implementation Method 1
a rectification unit which converts inputted three-phase AC voltages to DC voltage
Implementation Method 2
derives, as a pulsation voltage prediction value, pulsation contained in the DC voltage obtained through full-wave rectification of the three-phase AC voltages
Implementation Method 3
corrects at least one of the D-axis voltage command or the Q-axis voltage command by a voltage correction command generated so as to reduce a deviation between the pulsation voltage prediction value and the pulsation voltage actual measured value
Data Source
AI summary
A power conversion device includes a rectifier which converts three-phase AC voltages to DC voltage, a power converter which converts the DC voltage to AC voltage, to control an electric motor, and a controlling circuitry. The controlling circuitry derives, as a pulsation voltage prediction value, pulsation contained in DC voltage obtained through full-wave rectification of the three-phase AC voltages, using a detected value of the three-phase AC voltages, and derives pulsation contained in the DC voltage, as a pulsation voltage actual measured value, using a detected value of the DC voltage. The controlling circuitry corrects at least one of a D-axis voltage command or a Q-axis voltage command by a voltage correction command generated so as to reduce a deviation between the pulsation voltage prediction value and the pulsation voltage actual measured value.