Inverter Current Allocation During Asymmetrical LVRT
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Solution Overview
Problem
Existing inverter-based resources (IBRs) face challenges in efficiently utilizing their current capacity during asymmetrical low-voltage ride-through (LVRT) conditions, particularly in meeting the requirements for positive-sequence and negative-sequence reactive currents while ensuring phase current limits are not exceeded, leading to underutilization and potential violations of grid codes.
Innovation Solution
A method and system for determining active and reactive currents during asymmetrical LVRT conditions, involving a controller or processing unit that receives LVRT indications, scales reactive currents to maintain phase current limits, and optimizes active current generation based on voltage angles and sequence reactive currents, using quadratic relationships and non-uniform scaling to maximize active power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverter prioritizes reactive current injection to meet grid code requirements during LVRT, then grid code compliance is improved, but the inverter's current capacity is reduced leading to lower active power generation
Solution Approach 1:
The patent changes the parameters of reactive current injection by introducing sequence-dependent scaling factors (K+ for positive sequence, K- for negative sequence) that modify the magnitude of reactive currents based on voltage sags. This allows optimization of the balance between reactive power support and active power generation by adjusting these scaling parameters within grid code constraints.
Solution Approach 2:
The patent applies asymmetry by treating positive-sequence and negative-sequence reactive currents differently through distinct scaling factors and calculation methods. The positive-sequence reactive current uses one scaling approach while the negative-sequence uses another, allowing asymmetric optimization of current utilization to maximize active power while meeting grid requirements.
2Productivity
If the inverter increases positive-sequence active current to maximize power output, then active power generation is improved, but phase current limits are exceeded
Solution Approach 1:
The patent implements dynamic current allocation by continuously adjusting the active and reactive current components based on real-time voltage conditions and inverter capacity. The control system dynamically recalculates the optimal current distribution during LVRT events, allowing the inverter to operate at maximum capacity without exceeding phase current limits.
Solution Approach 2:
The patent introduces a new dimension of control by using sequence components (positive and negative sequences) as independent control variables. This transforms the traditional single-dimensional current control into a multi-dimensional control space, enabling independent optimization of active and reactive power while maintaining phase current constraints.
3Object-affected harmful factors
If the inverter uniformly scales down reactive currents to limit phase current, then phase current limit compliance is improved, but the utilization of inverter current capacity is reduced
Solution Approach 1:
The patent applies local quality by allowing different scaling treatments for different sequence components and phases. Instead of uniform scaling, the system applies specific scaling factors to positive-sequence and negative-sequence currents independently, and can apply phase-specific adjustments to maximize current capacity utilization while ensuring all phases remain within limits.
Data Source
AI summary
There is provided a system and method for determining active and reactive currents during asymmetrical low-voltage ride through (LVRT) conditions at an inverter. The method including: receiving an indication of an LVRT condition; and where the largest phase current magnitude does not exceed a phase current limit, determining a maximum active current for associated positive-sequence and negative-sequence reactive currents by determining a largest active current magnitude and outputting the largest active current and associated positive-sequence and negative-sequence reactive currents to the inverter, otherwise: scaling down each of the positive-sequence and negative-sequence reactive currents, or superimposed positive-sequence and negative-sequence reactive currents, uniformly or non-uniformly to determine revised positive-sequence and negative-sequence reactive currents; where the magnitudes of all of the phase currents are below the phase current limit, determining a non-zero positive-sequence revised active current; and outputting the revised active current and the revised positive-sequence and negative-sequence reactive currents to the inverter.