Unified Power Flow Controller MMC Control Strategy
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Solution Overview
Problem
Existing unified power flow controllers have complex structures, high maintenance costs, and poor reliability, making them unsuitable for efficient power flow control in modern smart grids due to high switching frequencies and harmonic losses.
Innovation Solution
A dual-loop control strategy for unified power flow controllers based on Modular Multilevel Converters (MMC) is implemented, where an outer loop generates a valve side current reference value and an inner loop calculates a converter output voltage reference value to control line power, enabling independent control of active and reactive power with reduced switching frequency and losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional GTO-based series connection converters are used in UPFC, then the device can implement power flow control functions, but the structure becomes complex and reliability decreases
Solution Approach 1:
The patent changes the key parameter of switching frequency and adopts MMC topology with lower switching frequency operation, which simplifies the converter structure and improves reliability while maintaining power flow control capability. The MMC structure with modular design reduces system complexity compared to traditional series connection of GTO devices.
2Speed
If low-level converter bridges with high switching frequency are used, then power flow control response is fast, but losses increase and harmonics are generated
Solution Approach 1:
The patent changes the switching frequency parameter to a lower value and adopts MMC topology, which reduces converter losses and harmonic generation while maintaining adequate response speed for power flow control applications. The modular structure allows for optimized switching strategies that balance response speed and loss reduction.
3Adaptability or versatility
If complex control strategies with multiple loops are implemented, then active and reactive power can be controlled independently, but the control system complexity increases
Solution Approach 1:
The patent segments the control system into distinct functional modules within the MMC framework, where each module handles specific control tasks. This modular control approach enables independent active and reactive power control while keeping the overall system manageable through standardized control blocks and clear functional separation.
Data Source
AI summary
A line power control method and system for a unified power flow controller includes outer loop line power control, inner loop valve side current control, and converter valve control. Series-side converter valve side current reference values Isedref and Iseqref are calculated by means of the outer loop line power control according to line power instructions Pref and Qref that are input, a measured line power UL, and measured line power Pline and Qline; a converter output voltage reference value Ucref is calculated by means of the inner valve side current control according to the valve side current reference values that are output by means of the outer loop power control, a measured valve side current, and a measured valve side voltage; and finally, a converter outputs, according to the voltage reference value, a corresponding voltage to control line power to achieve a reference value.