Inverter Control for Transient Heavy Load Management
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Solution Overview
Problem
Power converter systems, such as UPS, face challenges in managing high-load transient states during mode transitions or cold-boots, which can lead to excessive current draw, triggering safety features and potential damage due to the inability to effectively regulate output current.
Innovation Solution
A power converter system with a DC bus, DC/DC converter, and inverter, controlled by a controller that reduces the peak output current by lowering the DC bus voltage and increasing the inverter's duty cycle during impending high-load transient states, thereby preventing battery safety features from tripping and maintaining constant RMS output current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the inverter operates at high duty cycle during transient load, then the output current capability is improved, but the DC bus voltage drops excessively causing instability
Solution Approach 1:
The DC/DC converter acts as an intermediary between the battery and the inverter. During transient load conditions, it provides additional current to the DC bus, preventing voltage drops while allowing the inverter to maintain high output current capability. This mediator approach resolves the contradiction by decoupling the inverter's current delivery from direct battery dependence.
Solution Approach 2:
The controller predicts impending transient load conditions and proactively adjusts the DC/DC converter operation before the voltage drop occurs. By anticipating the load transient and pre-positioning the DC bus voltage and converter duty cycle, the system maintains stability while preparing to deliver the required current surge.
2Productivity
If the DC/DC converter increases duty cycle to boost output current, then the current delivery capability is improved, but the battery current limit is exceeded triggering safety shutdown
Solution Approach 1:
The current delivery function is segmented between two sources: the battery and the DC/DC converter. During transient conditions, the DC/DC converter handles the peak current demand while the battery provides steady-state current within its safe operating limits. This segmentation allows the system to achieve high current delivery capability without exceeding battery current ratings.
Solution Approach 2:
The controller dynamically changes operating parameters by adjusting the DC/DC converter duty cycle in response to detected transient conditions. When a transient is anticipated, the converter duty cycle increases to provide additional current, while the battery current is simultaneously managed to stay within safe limits. This parameter adjustment resolves the contradiction between current capability and safety limits.
3Power
If the system responds to voltage drop by increasing inverter duty cycle, then the output power is maintained, but the peak current exceeds safe limits causing shutdown
Solution Approach 1:
The DC/DC converter serves as a mediator that prevents the harmful feedback loop between voltage drop and excessive current. Instead of directly increasing inverter duty cycle in response to voltage drop (which would cause peak current damage), the DC/DC converter compensates for voltage drops by providing current support, allowing the inverter to maintain output power within safe current limits.
Solution Approach 2:
The controller implements feedback control by continuously monitoring DC bus voltage and adjusting the DC/DC converter duty cycle in response to voltage variations. This feedback mechanism prevents excessive peak currents by modulating the converter operation to maintain voltage within acceptable ranges while supporting the required output power delivery.
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
This solution effectively manages high-load transient states by reducing peak output current, preventing battery overloads and maintaining stable power delivery, thus avoiding unintended shutdowns and component damage while supporting loads during critical operational transitions.
Implementation Method 1
operate, in response to identifying the impending high-load transient state, the DC/DC converter to reduce a voltage level on the DC bus
Implementation Method 2
an inverter coupled to the DC bus and configured to convert DC power from the DC bus into output AC power having an output current
Data Source
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AI summary
A power converter system including a DC bus, a DC/DC converter coupled to the DC bus, an inverter coupled to the DC bus and configured to convert DC power from the DC bus into output AC power having an output current, an output coupled to the inverter and configured to provide the output AC power to a load, and at least one controller configured to identify an impending high-load transient state at the output, and in response to identifying the impending high-load transient state, reduce a peak value of the output current of the output AC power by operating the DC/DC converter to reduce a voltage level on the DC bus and increasing a duty cycle of the inverter.