Multi-Slope Output Impedance Control for Parallel Converter Load Sharing
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Solution Overview
Problem
In masterless configurations of parallel-connected power supplies, current imbalances occur due to variations in reference voltages and non-linear effects, leading to inefficiencies and potential shutdowns, especially at low load currents where one converter dominates or circulating currents flow between converters.
Innovation Solution
A multi slope output impedance controller that dynamically varies the effective impedance of power converters to reduce current imbalances by commanding a high impedance at low load currents for sharing and a low impedance at higher load currents to improve regulation, using a coefficient generator controller to adjust the output impedance based on sensed currents and voltage references.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed output impedance is used in parallel-connected power converters, then the device complexity is reduced, but current imbalance occurs between converters leading to inefficiencies and potential shutdowns
Solution Approach 1:
The patent implements dynamic output impedance adjustment by switching between multiple impedance values (first, second, and third impedance values) based on operating conditions such as load current levels and converter status. This allows the system to adapt to varying conditions while maintaining current balance, resolving the contradiction between fixed simplicity and dynamic reliability.
Solution Approach 2:
The controller changes the output impedance parameter dynamically by selecting from multiple predefined impedance values. When a converter starts up or when load conditions change, the controller adjusts the impedance to specific values to ensure proper current sharing, thereby maintaining reliability without requiring complex continuous control mechanisms.
2Reliability
If the output impedance is increased to reduce current imbalance at low load currents, then current sharing improves, but load regulation deteriorates at higher load currents
Solution Approach 1:
The system dynamically adjusts output impedance based on load current levels. At low load currents, a higher impedance (first or second impedance value) is applied to improve current sharing. At higher load currents, the impedance is reduced (third impedance value) to maintain proper voltage regulation, thus resolving the contradiction between current sharing and voltage regulation across different operating conditions.
Solution Approach 2:
The controller changes the output impedance parameter based on sensed operating conditions. By switching between different impedance values, the system optimizes current sharing at low loads while maintaining voltage regulation at high loads, effectively resolving the performance trade-off across the full operating range.
3Device complexity
If a single impedance value is used for all operating conditions, then the control mechanism is simplified, but current imbalance occurs during start-up and steady-state operations
Solution Approach 1:
The control mechanism dynamically selects from multiple impedance values based on the operational state of the power converters. During start-up, a first impedance value is applied to ensure proper current sharing. During steady-state operation, the controller switches to appropriate impedance values based on load conditions, maintaining current balance without requiring overly complex continuous adjustment mechanisms.
Solution Approach 2:
The impedance control is segmented into discrete operating modes, each with a predefined impedance value. This segmentation allows the system to handle different operational scenarios (start-up, steady-state, low load, high load) with appropriate impedance settings, maintaining reliability while keeping the control mechanism manageable through discrete state transitions rather than continuous complex control.
4Measurement precision
If the output impedance is decreased to improve load regulation, then voltage stability improves, but current imbalance increases between parallel converters
Solution Approach 1:
The system dynamically adjusts output impedance based on operational needs. When load regulation is the priority (higher load currents), a lower impedance (third impedance value) is applied to maintain voltage stability. When current balance is the priority (low load currents or start-up conditions), higher impedance values (first or second impedance values) are applied, thus resolving the contradiction by adapting to the dominant requirement at each operating point.
Solution Approach 2:
The controller changes the output impedance parameter based on sensed operating conditions and control objectives. By adjusting the impedance value, the system prioritizes either voltage regulation or current balance depending on the operational context, effectively resolving the performance trade-off through conditional parameter modification.
Data Source
AI summary
A multi slope output impedance controller is configured to vary the effective impedance Zeff_n of a power converter to reduce a current imbalance between power supplies in a masterless configuration of N parallel-connected power supplies while maintaining load regulation during start-up and steady-state operation. Generally speaking, the controller commands a high value of Zeff_n when Iout_n is low to facilitate current sharing and reduce current imbalance Ib between the power supplies and commands a low value of Zeff_n when Iout_n is high to improve load regulation.