Parallel Active Filter Enhancing DC Voltage
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Solution Overview
Problem
Existing active filter technologies require boost choppers and transformers for harmonic current compensation, and often result in insufficient DC voltage, leading to inadequate harmonic current compensation.
Innovation Solution
A parallel active filter configuration is implemented, connecting a rectifier circuit between AC input lines and DC buses, with a capacitor and current limiting elements, including diodes or resistors, to enhance DC voltage and suppress harmonic currents without the need for boost choppers or transformers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a boost chopper and transformer are used for harmonic current compensation, then the compensation performance is improved, but the device complexity and cost increase
Solution Approach 1:
The invention extracts and eliminates the boost chopper and transformer from the active filter system. By using a capacitor connected directly to the DC bus with current limiting elements, the patent achieves harmonic current compensation without these complex components, thereby reducing device complexity while maintaining compensation functionality.
Solution Approach 2:
The capacitor in the invention serves multiple functions: it acts as both the DC link capacitor and the active filter capacitor, eliminating the need for separate boost chopper and transformer components. This multi-functionality reduces the overall device complexity while maintaining harmonic current compensation capability.
2Device complexity
If capacitors are connected in parallel with one diode protection, then the device complexity is reduced, but the DC voltage becomes insufficient for appropriate compensating current
Solution Approach 1:
The invention introduces current limiting elements (diodes or resistors) as intermediary components between the capacitor and DC bus. These elements enable the capacitor to operate at a higher voltage than the DC bus by limiting the current flow, thereby providing sufficient voltage for appropriate compensating current while maintaining a simple parallel connection structure.
Solution Approach 2:
The invention changes the voltage parameter of the capacitor by connecting it through current limiting elements. This allows the capacitor voltage to exceed the DC bus voltage, providing the necessary voltage headroom for generating appropriate compensating current while keeping the overall device structure simple.
3Reliability
If the DC voltage is increased to improve compensating current, then the harmonic current compensation performance is improved, but the power capacity of clamping capacitors increases
Solution Approach 1:
The capacitor in the invention serves dual purposes: it provides both the DC link function and the active filter function. By operating at a higher voltage than the DC bus through the current limiting elements, it generates appropriate compensating current without requiring additional high-capacity clamping capacitors, thereby improving harmonic current compensation while avoiding increased power capacity requirements.
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 achieves a higher DC voltage, effectively suppresses harmonic currents, and reduces the power capacity required for clamping capacitors, while maintaining sinusoidal waveforms of compensating currents.
Implementation Method 1
a rectifier circuit (2) between a set of AC input lines (W) and a pair of DC buses (LH, LL)... the rectifier circuit rectifying AC voltages (Vr, Vs, Vt) inputted from the set of AC input lines and outputting a DC voltage (Vdc) to the pair of DC buses
Implementation Method 2
a pair of current limiting elements (D1, D2, R2), each of which connects each of a pair of ends of the first capacitor to each of the pair of DC buses, and at least one of which is a diode (D1) disposed in an orientation to be forward with respect to the DC voltage
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
By a simple configuration, a series voltage given to an active filter is enhanced. The active filter is connected in parallel to a rectifier circuit (2) between a set of AC input lines (W) and a pair of DC buses (LH, LL). The active filter includes a capacitor (C2), diodes (D1, D2) and an inverter (5). The diode (D1) is disposed between one end of the capacitor (C2) and the DC bus (LH). The diode (D2) is disposed between other end of the capacitor (C2) and the DC bus (LL). The diodes (D1, D2) are disposed in an orientation to be forward with respect to a DC voltage (Vdc) outputted by the rectifier circuit (2). The inverter (5) includes: a set of AC-side terminals (51, 52, 53) connected to the AC input lines (W); and a pair of DC-side terminals (54, 55) connected to both ends of the capacitor (C2).