Unbalanced Voltage Compensation via Centroid Vector Operation
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Solution Overview
Problem
Conventional methods for compensating unbalanced three-phase AC voltages during voltage sag events require large electric storage devices and periodic maintenance, and they struggle to quickly respond to instantaneous voltage drops, especially in delta-connected power distribution systems where wye-phase voltages are unmeasurable.
Innovation Solution
A method that uses centroid vector operations to derive instantaneous wye-phase voltages from line voltages at a single measurement point, allowing for the calculation of positive-phase-sequence, negative-phase-sequence, and zero-phase-sequence voltages, which are then used to control a three-phase PWM converter for unbalanced voltage compensation without the need for electric storage devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional voltage sag compensators using electric storage devices are installed, then voltage fluctuations can be compensated, but the system requires large-sized storage devices and periodic maintenance
Solution Approach 1:
The invention extracts and eliminates the electric storage device component from the voltage sag compensator system. By using a three-phase PWM converter with controlled switching elements, the patent achieves voltage sag compensation through power electronic conversion rather than energy storage, completely removing the need for capacitors or batteries while maintaining the compensation function.
Solution Approach 2:
The invention replaces the mechanical/physical energy storage system (capacitors, batteries) with an electronic control system based on PWM conversion. The voltage sag compensation is achieved through controlled switching of power electronic devices and modulation techniques, substituting the passive storage mechanism with an active electronic conversion process.
2Measurement precision
If wye-phase voltages are measured for control in delta-connected systems, then accurate voltage compensation can be achieved, but wye-phase voltages are unmeasurable in delta connections
Solution Approach 1:
The invention introduces line voltages as an intermediary measurement that can be obtained in delta-connected systems. By measuring the easily accessible line voltages and using mathematical transformation (centroid vector operation), the system derives the necessary phase voltage information without requiring direct measurement of unmeasurable wye-phase voltages.
Solution Approach 2:
The invention changes the measurement parameter from unmeasurable wye-phase voltages to measurable line voltages. Through mathematical transformation of the measured line voltage parameters, the system obtains the equivalent phase voltage information needed for control, effectively converting an unmeasurable parameter into a measurable one.
3Measurement precision
If multiple measurement points are used to derive instantaneous voltages, then accurate voltage derivation can be achieved, but the response time to instantaneous voltage drops increases
Solution Approach 1:
The invention performs preliminary establishment of the centroid vector relationship between line voltages and phase voltages. By pre-defining the mathematical transformation based on instantaneous line voltage measurements, the system can immediately calculate phase voltage information without waiting for multiple measurement points, achieving both accuracy and fast response.
Data Source
AI summary
In compensating for unbalanced voltages of three-phase AC, instantaneous values of wye-phase voltages 120° out of phase with each other are obtained from line voltages using a centroid vector operation, symmetrical component voltages of three-phase balanced system are obtained from the instantaneous values of wye-phase voltages, a compensation signal to compensate unbalanced voltages of three-phase AC is generated from zero-phase-sequence voltage of symmetrical component voltages is generated, wye-phase voltages 120° out of phase, the unbalanced voltages of which are compensated, are obtained from the compensation signal and the symmetrical component voltages, a control signal of a PWM conversion is generated based on the compensated wye-phase voltage compensated, and the unbalanced voltages of three-phase AC are compensated. The amount of time to compensate the three-phase unbalanced voltages required for detecting an unbalance of voltages and generating a control signal can be shortened.