Converter Circuit Oscillation Damping via Low-Pass Filtering
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Solution Overview
Problem
Conventional converter circuits connected to electrical AC voltage networks experience undesirable oscillations above the fundamental frequency, which cannot be damped or reduced, especially in networks with weakly damped resonance points.
Innovation Solution
The method involves filtering the mains current, transformer inductance voltage, and mains voltage using low-pass characteristics to form a control signal that regulates the controllable power semiconductor switches, thereby damping oscillations above the fundamental frequency without affecting the fundamental frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional converter circuits are used with standard control methods, then the converter can operate and regulate mains current, but oscillations above the fundamental frequency occur in the mains voltage that cannot be damped or reduced
Solution Approach 1:
The invention applies preliminary action by filtering the mains current, transformer inductance voltage, and mains voltage through low-pass filters before they are used in the control signal generation. This pre-filtering removes oscillations above the fundamental frequency in advance, preventing them from affecting the converter operation and causing harmful voltage oscillations in the mains.
Solution Approach 2:
The invention introduces an intermediary element - the low-pass filter - between the measured electrical quantities and the control signal generation. This intermediary filters out harmful oscillations while preserving the fundamental frequency components, allowing the control system to operate with clean, filtered signals that do not excite resonant oscillations in the mains voltage.
2Object-affected harmful factors
If filtering according to low-pass characteristic is applied to mains current and voltages, then oscillations above fundamental frequency are damped, but the control process becomes more complex
Solution Approach 1:
The invention merges the filtering function into the existing control circuitry by applying low-pass characteristics to the measurement and control signal generation processes. Rather than adding separate filtering stages, the filtering is integrated into the control device's signal processing path, combining measurement, filtering, and control signal generation into a unified control process.
3Object-affected harmful factors
If multiple filtering operations are performed on mains current and voltages, then oscillations are reduced, but the number of components increases
Solution Approach 1:
The invention makes the control device multi-functional by enabling it to perform both filtering and control signal generation functions. The control device processes mains current and voltage signals, applies low-pass filtering, and generates control signals for the power semiconductor switches all within a single integrated system, eliminating the need for separate filtering components.
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 effectively reduces unwanted oscillations in the mains voltage above the fundamental frequency, simplifying the control process and reducing circuit complexity while requiring a minimal number of components.
Implementation Method 1
a filtered mains current is formed by filtering according to a low-pass characteristic of a mains current, a filtered transformer inductance voltage is formed by filtering according to a low-pass characteristic
Implementation Method 2
the control signal is formed by summing a regulator voltage, the filtered transformer inductance voltage and the filtered mains voltage
Data Source
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AI summary
A method for operating a converter circuit is specified, wherein the converter circuit has a converter unit (2) with a plurality of drivable power semiconductor switches and is connected to a three-phase electrical AC voltage network (1) by means of a transformer, in which method the drivable power semiconductor switches are driven by means of a drive signal (SA) formed from a control signal (SR). In order to attenuate oscillations of a network voltage (UG) above the fundamental frequency, a filtered network current (iGTP) is formed by means of filtering according to a low-pass characteristic of a network current (iG), a filtered transformer inductance voltage (ULTTP) is formed by means of filtering according to a low-pass characteristic of a transformer inductance voltage (uLT) formed from the network current (iG), a filtered network voltage (UGTP) is formed by means of filtering according to a low-pass characteristic of a network voltage (uG), and the control signal (SR) is formed by adding a controller voltage (uR), the filtered transformer inductance voltage (ULTTP) and the filtered network voltage (UGTP), wherein the controller voltage (uR) is formed by adjusting the filtered network current (iGTP) to a desired network current value (iGref). An apparatus for carrying out the method is also specified.