Bidirectional Chopper Neutral Point Isolation
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Solution Overview
Problem
In three-phase four-wire uninterruptible power supply systems, the bidirectional chopper connected to the neutral point can cause short-circuiting, leading to current flow from the battery to the load and other uninterruptible power supply devices, resulting in system failure.
Innovation Solution
The uninterruptible power supply device configures a three-phase four-wire system with a bidirectional chopper not connected to the third DC bus, and a controller manages the ON periods of transistors to equalize the terminal-to-terminal voltages of capacitors, preventing excessive voltage and potential short-circuiting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bidirectional chopper is connected to the neutral point to enable battery power storage and discharge, then the uninterruptible power supply can function during outages, but the bidirectional chopper may fail causing short-circuiting and current flow from battery to load through neutral point
Solution Approach 1:
The patent extracts the bidirectional chopper from the neutral point connection and relocates it between the first and second DC buses. This separation removes the harmful short-circuit path through the neutral point while preserving the battery's power storage and discharge functionality through the relocated chopper configuration.
Solution Approach 2:
The patent introduces the third DC bus as an intermediary element between the neutral point and the bidirectional chopper circuit. The third DC bus, connected to the neutral point through capacitors, acts as a mediator that provides the necessary electrical connection without creating a direct short-circuit path, thus eliminating the harmful current flow while maintaining system functionality.
2Adaptability or versatility
If the bidirectional chopper is connected to the neutral point, then the system can share battery among multiple devices, but capacitor voltage may become unbalanced causing excessive terminal-to-terminal voltage
Solution Approach 1:
The patent implements voltage detection circuits that continuously monitor the terminal-to-terminal voltages of the third and fourth capacitors. The controller uses this feedback information to detect voltage imbalances and adjust the switching timing of the bidirectional chopper accordingly, ensuring that capacitor voltages remain balanced and preventing excessive voltage conditions.
Solution Approach 2:
The patent makes the bidirectional chopper's switching operation dynamic by adjusting the ON periods of switching elements based on real-time capacitor voltage conditions. This dynamic control allows the system to adapt to varying voltage states and maintain capacitor voltage balance, preventing excessive terminal-to-terminal voltage while preserving battery sharing capability.
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 configuration prevents current flow from the battery to the load and other devices during a short-circuit failure, ensuring the system's reliability and preventing capacitor overvoltage.
Implementation Method 1
a converter configured to convert a three-phase AC voltage supplied from a commercial AC power supply into a first DC voltage
Implementation Method 2
an inverter configured to convert the first, second, and third DC voltages supplied through the first, second, and third DC buses into a three-phase AC voltage
Implementation Method 3
a bidirectional chopper connected between the first and second DC buses and a power storage device
Data Source
AI summary
An uninterruptible power supply device (60) does not have a wire connecting a bidirectional chopper (24) to a neutral point (NP). The bidirectional chopper (24) includes first and second capacitors (C11, C12), first to fourth transistors (Q11-Q14), and a normal mode reactor (50). In a discharging mode, a controller (63) causes the second and third transistors (Q12, Q13) to be complementarily turned on and controls the ON period of each of the second and third transistors (Q12, Q13) so that terminal-to-terminal voltages (V11, V12) of the first and second capacitors (C11, C12) are equal to each other.