Dual-DC Bus Midpoint Grounding via Impedance Circuit
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Solution Overview
Problem
Directly connecting the midpoint of a dual-DC bus in an active rectifier system to system ground can result in high third harmonic current flow, especially during transient periods when the active rectifier is inactive or not yet in steady-state, causing issues due to the short-circuit path to ground.
Innovation Solution
A high-frequency impedance circuit, comprising a capacitor in parallel with a resistor-capacitor (RC) circuit, is used to connect the midpoint of the dual-DC bus to system ground, providing impedance for third harmonic common-mode current and reducing its amplitude to acceptable levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the midpoint of the dual-DC bus is directly connected to system ground, then the connection is simple and direct, but high third harmonic common-mode current flows causing operational disruptions
Solution Approach 1:
An impedance circuit is introduced as an intermediary element between the midpoint of the dual-DC bus and system ground. This impedance circuit blocks high-frequency third harmonic common-mode current while allowing the ground connection to be established, thus resolving the contradiction between connection simplicity and harmful current suppression
Solution Approach 2:
The impedance circuit changes the electrical parameter (impedance) at the ground connection point. By introducing frequency-dependent impedance, the circuit allows low-frequency fundamental currents to pass while blocking high-frequency third harmonic currents, thus eliminating the harmful effect while maintaining the ground connection
2Object-affected harmful factors
If the midpoint is connected to ground through an impedance circuit, then third harmonic current is reduced, but the connection becomes more complex
Solution Approach 1:
The impedance circuit is applied locally only at the midpoint ground connection point where third harmonic current suppression is needed. This localized application achieves the desired current suppression without requiring complex modifications throughout the entire power conversion system
Solution Approach 2:
A relatively simple impedance circuit (comprising passive components) is used as an intermediary to achieve third harmonic suppression. This intermediate solution is simpler than alternative approaches such as complex active filtering or modifying the rectifier control strategy
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
The impedance circuit effectively manages third harmonic common-mode current, ensuring safe and efficient operation by reducing high-frequency current flow, thus allowing the midpoint to be connected to system ground without causing operational disruptions.
Implementation Method 1
The impedance circuit comprises a capacitor in parallel with a resistor-capacitor (RC) circuit
Implementation Method 2
The impedance circuit comprises a capacitor in parallel with a resistor-capacitor (RC) circuit
Implementation Method 3
provides impedance for third harmonic common-mode current
Data Source
Figure 1
Figure 2A~2B
AI summary
A system includes a power source 12 that provides alternating current (AC) power and is connected to system ground; a dual-DC bus that provides direct current (DC) power to a load, and comprises a positive line, a negative line, load, and a midpoint line; an active rectifier 16 that converts AC power from the power source to DC power for the dual-DC bus; and an impedance circuit 22 connected between the midpoint of the dual-DC bus and the system ground that provides impedance for third harmonic common-mode current.