UPS Inverter Voltage Matching for Low-Inrush Bypass Transfer
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Solution Overview
Problem
Existing uninterruptible power supplies (UPS) face issues with high inrush currents during transitions from bypass to online modes due to delays in adjusting inverter reference voltages, potentially damaging silicon-controlled rectifiers (SCRs) from sudden voltage changes.
Innovation Solution
A hybrid control system in UPSs uses a controller to rapidly adjust the inverter reference voltage by measuring and matching the input and inverter output voltages within a threshold, employing both digital and analog controls to minimize inrush currents and protect SCRs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverter reference voltage is adjusted rapidly during mode transition, then the inrush current is reduced and SCR protection is improved, but the control system complexity increases
Solution Approach 1:
The controller pre-adjusts the inverter reference voltage before the bypass-to-online mode transition by detecting the input voltage and setting the reference voltage to match it. This preliminary action ensures that when the inverter switch closes, there is minimal voltage difference, preventing inrush current and protecting the SCR without requiring complex real-time control during the transition itself.
Solution Approach 2:
The control system continuously monitors the input voltage and uses this feedback to dynamically adjust the inverter reference voltage. During mode transition, the controller compares the detected input voltage with the current inverter output voltage and modifies the reference voltage accordingly, creating a closed-loop control mechanism that reduces inrush current while maintaining system reliability.
2Device complexity
If the inverter reference voltage is adjusted slowly during mode transition, then the control system remains simple, but high inrush currents damage SCRs
Solution Approach 1:
The controller performs the voltage adjustment action before the actual mode transition occurs. By detecting the input voltage early and pre-setting the inverter reference voltage to match it, the system eliminates the need for rapid voltage changes during the transition itself, thereby protecting the SCR from inrush current while keeping the control logic relatively simple.
Solution Approach 2:
The control system takes preliminary action to counteract the potential harmful effect of inrush current. By pre-adjusting the reference voltage to match the input voltage before the inverter switch closes, the system prevents the voltage difference that would cause inrush current, thereby protecting the SCR without requiring complex mitigation measures during the transition.
3Reliability
If the inverter output voltage is quickly aligned with input voltage during transition, then inrush current is minimized, but measurement and control precision requirements increase
Solution Approach 1:
The controller uses feedback from voltage sensors to continuously monitor both the input voltage and inverter output voltage. During mode transition, this feedback information is used to dynamically adjust the reference voltage, ensuring precise alignment between input and output voltages. The closed-loop control mechanism maintains voltage matching within acceptable tolerances, ensuring smooth transition while managing measurement precision requirements.
Data Source
AI summary
An uninterruptable power supply (UPS) is disclosed. The UPS includes an input configured to be coupled to a power source, a backup interface configured to be coupled to a backup power source, a backup interface configured to be coupled to a backup power source and to receive backup power from the backup power source, an output configured to be coupled to a load and to provide output power to the load, a bypass line coupled between the input and the output and configured to provide the input power to the output in a bypass mode of operation, an inverter coupled to the output and configured to provide the output power to the output derived from the input power in an online mode of operation, and a controller. Non-transitory computer readable medium for operating the controller and methods of providing output power to a load from a UPS are also disclosed.