UPS Bus Capacitor Precharge for Safe Grid Reconnection
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Solution Overview
Problem
Uninterruptible power supplies (UPS) face challenges in safely starting due to voltage differences between bus capacitors and AC power supplies, leading to potential damage and failure, especially when reconnecting after grid faults or initial connection.
Innovation Solution
The implementation of a charge-discharge circuit that boosts the voltage of the bus capacitor, combined with a first and second rectification circuit, allows for controlled pre-charging, reducing voltage differences and ensuring safe startup by regulating the voltage difference between the AC power supply and the bus capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bus capacitor is pre-charged using an uncontrollable switch device through the first rectification circuit, then the pre-charge voltage is limited by the grid voltage amplitude, but this may result in insufficient voltage to compensate for grid voltage fluctuation and load power supply, causing startup failure or switch device damage
Solution Approach 1:
The charge-discharge circuit performs preliminary voltage boosting action before the uninterruptible power supply connects to the grid. The bus capacitor is pre-charged to a first voltage that is greater than or equal to the peak voltage of the alternating current power supply through the charge-discharge circuit's voltage boosting function. This preliminary action ensures that when the switch device connects the bus capacitor to the grid, the voltage difference is minimized, preventing switch device contact conglutination and startup failure.
Solution Approach 2:
The charge-discharge circuit changes the voltage parameter of the bus capacitor from a standard charging voltage (limited by grid amplitude) to a boosted voltage (greater than or equal to peak grid voltage). By adjusting the charging voltage parameter upward through voltage boosting, the system compensates for grid voltage fluctuations and load power supply requirements, ensuring reliable startup without damaging the switch device.
2Object-affected harmful factors
If the bus capacitor voltage is kept low to match grid voltage, then switch device safety is improved, but the uninterruptible power supply cannot compensate for voltage drops caused by load operation and grid fluctuation
Solution Approach 1:
The system performs preliminary voltage boosting through the charge-discharge circuit before grid connection. The bus capacitor is charged to a voltage level that provides both safety margin for switch device protection and sufficient headroom for voltage compensation during operation. This preliminary action resolves the contradiction by establishing an optimal initial voltage state.
Solution Approach 2:
The charge-discharge circuit provides beforehand cushioning by pre-charging the bus capacitor to a voltage level that cushions against future voltage drops. The boosted voltage creates a voltage reserve that compensates for load operation and grid fluctuation, while still maintaining switch device safety through controlled charging protocols.
3Device complexity
If the first rectification circuit charges the bus capacitor directly without voltage boosting, then the circuit structure is simplified, but the charging voltage is insufficient to ensure safe startup under grid voltage fluctuation
Solution Approach 1:
The charge-discharge circuit acts as an intermediary between the first rectification circuit and the bus capacitor. Instead of direct charging, the rectification circuit charges the charge-discharge circuit, which then boosts the voltage to charge the bus capacitor. This intermediary component enables voltage boosting while maintaining a relatively simple overall structure by reusing existing circuit elements.
Solution Approach 2:
The charge-discharge circuit serves multiple functions: it acts as a voltage booster during startup, functions as a battery charge-discharge interface, and provides voltage regulation. By making the charge-discharge circuit multi-functional, the system avoids adding separate dedicated boosting circuitry, thus maintaining structural simplicity while achieving reliable voltage boosting for safe startup.
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 enables the uninterruptible power supply to start safely and securely, protecting switch devices and maintaining continuous power to loads by compensating for voltage fluctuations and drops, thereby reducing the risk of component damage.
Implementation Method 1
a charge-discharge circuit, configured to charge the bus capacitor after boosting a voltage, until the voltage across the bus capacitor reaches the first voltage
Data Source
AI summary
An uninterruptible power supply, a control method and a power supply system for normally starting the uninterruptible power supply and securing switch devices are provided. The uninterruptible power supply includes a first rectification circuit, a charge-discharge circuit, a bus capacitor, a first switch circuit and a second rectification circuit. The first rectification circuit is connected to the charge-discharge circuit, and is configured to rectify a voltage outputted by the alternating current power supply. The charge-discharge circuit is connected to the bus capacitor, and is configured to charge the bus capacitor after boosting the voltage outputted by the first rectification circuit, until the voltage across the bus capacitor reaches a first voltage. The first switch circuit is connected to the second rectification circuit, and is configured to connect the alternating current power supply to the second rectification circuit. The uninterruptible power supply boosts the voltage through the charge-discharge circuit to reduce the voltage difference between the alternating current power supply and the bus capacitor. Then, the first switch circuit is switched on to normally start the uninterruptible power supply and secure the first switch circuit.