DC Bus Precharge Circuit for UPS Inrush Current Reduction
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Solution Overview
Problem
Conventional power conversion systems, such as UPSs, face challenges with large inrush currents when using boost rectifiers with storage capacitance, and existing precharge techniques are either slow, costly, or require bulky components.
Innovation Solution
A power conversion apparatus with a DC link including first and second DC busses and a reference bus, utilizing a precharge circuit and a DC generator circuit, where the precharge circuit charges a capacitance and transfers charge to another capacitance using a balancer circuit, allowing the DC generator to commence voltage generation after precharging, and the balancer circuit can operate as a rectifier or balancer depending on the mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a boost rectifier with large storage capacitance is used to generate DC voltage greater than peak AC input voltage, then the DC voltage level is improved, but large inrush currents are produced when coupled to AC source
Solution Approach 1:
The patent applies preliminary action by pre-charging the storage capacitors before connecting the boost rectifier to the AC source. The precharge circuit charges the capacitors to a voltage close to or above the utility peak voltage prior to closure of the utility disconnect device, preventing large inrush currents while enabling the boost rectifier to achieve DC voltages greater than peak AC input voltage.
Solution Approach 2:
The patent uses an intermediary precharge circuit as a mediator between the AC source and the boost rectifier. This precharge circuit includes a precharge converter and balancer that temporarily charge the storage capacitors before the main rectifier connects to the AC source, thus eliminating the harmful inrush current effect while preserving the voltage boosting capability.
2Object-generated harmful factors
If a power resistor with series control device is used to precharge the DC bus, then the inrush current is reduced, but the precharge time becomes long and the components become bulky and expensive
Solution Approach 1:
The patent applies universality by designing a precharge circuit that uses the same power conversion components (switches, inductors, capacitors) as the main boost rectifier circuit. The precharge converter and balancer share circuitry with the main power conversion function, eliminating the need for separate bulky precharge resistors and control devices while achieving both inrush current reduction and voltage precharging.
Solution Approach 2:
The patent changes the operating parameters of the power conversion circuit by controlling the duty cycle and switching frequency of the precharge converter to achieve precharging function. Instead of using fixed resistive precharging, the system dynamically adjusts conversion parameters to transfer energy from the AC source to charge storage capacitors before main operation begins.
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 approach efficiently precharges DC busses, reducing inrush currents and eliminating the need for separate precharge circuits, while utilizing the boost capability of the rectifier to achieve desired voltage levels, thus enhancing the scalability and cost-effectiveness of the power conversion process.
Implementation Method 1
The precharge circuit is operative to charge a first capacitance between the first DC bus and the reference bus and to transfer charge from the charged first capacitance to a second capacitance between the second DC bus and the reference bus
Implementation Method 2
The balancer circuit is operative to transfer charge between the first and second capacitances
Implementation Method 3
a rectifier or other circuit that is used to generate a DC voltage at a DC output or link
Implementation Method 4
an input rectifier circuit that receives an AC voltage from an AC power supply and that generates positive and negative DC voltages on a DC link
Implementation Method 5
Some on-line UPSs use a boost rectifier, which allows the DC voltage on the DC link to be boosted to levels greater than the peak AC input voltage
Data Source
AI summary
A power conversion apparatus, such as a UPS, includes a DC link including first and second DC busses and a reference bus and a DC generator circuit coupled to the DC link and operative to generate first and second DC voltages with respect to the reference bus on respective ones of the first and second DC busses. The apparatus further includes a precharge circuit coupled to the DC link and operative to charge a first capacitance between the first DC bus and the reference bus and to transfer charge from the charged first capacitance to a second capacitance between the second DC bus and the reference bus. The DC generator circuit may be operative to commence generation of the first and second DC voltages on the first and second DC busses after the precharge circuit precharges the first and second DC busses. Related operating methods are also discussed.