Converter Pulse Sequencing for Overvoltage Mitigation
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Solution Overview
Problem
Existing methods for controlling electrical machines using DC/AC converters face issues with voltage variations (dv/dt) leading to leakage currents, losses, and overvoltages, particularly when connected via long cables, and existing solutions either require energy-dissipating resistors or are difficult to implement with two-level converters.
Innovation Solution
A method and system that use an LC filter with inductors and capacitors connected to each cable conductor to generate a sequence of voltage pulses, optimizing switching transitions to minimize overvoltages and switching losses by determining the number and width of pulses based on cable impedance and filter characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a dv/dt type filter with passive components is placed at the output of the inverter, then overvoltages and leakage currents are reduced, but energy is dissipated through the damping resistor
Solution Approach 1:
The patent extracts and eliminates the damping resistor from the traditional dv/dt filter, keeping only the reactive components (inductor and capacitor). This removes the energy dissipation element while retaining the voltage smoothing function through optimized pulse sequencing that prevents resonance and overvoltages without requiring resistive damping.
Solution Approach 2:
The patent applies periodic voltage pulses with specifically timed intervals to the cable. By controlling the frequency and timing of these pulses to match or counteract the cable's natural resonance frequency, the system achieves dv/dt control and overvoltage prevention through constructive and destructive interference patterns, eliminating the need for energy-dissipating components.
2Device complexity
If a two-level converter is used, then device complexity is reduced, but control of voltage variations (dv/dt) becomes more difficult
Solution Approach 1:
The patent segments each voltage transition into multiple discrete pulses rather than applying a single step change. By dividing the voltage transition into a sequence of smaller steps with controlled timing, the two-level converter achieves fine-grained dv/dt control capability while maintaining its simple two-switch structure per phase.
Solution Approach 2:
The patent introduces dynamic pulse width and timing control to the two-level converter. By dynamically adjusting the width and spacing of voltage pulses based on operating conditions, the simple two-level converter gains adaptive dv/dt control capability, transforming a static switching scheme into a dynamic control system that compensates for the lack of intermediate voltage levels.
3Speed
If the rise time of voltage pulses is reduced, then switching speed is improved, but overvoltages at the machine terminals increase
Solution Approach 1:
The patent uses periodic pulse sequences with controlled rise times that are optimized to avoid exciting cable resonance. By repeating pulses at frequencies that do not match the cable's natural frequency, the system maintains fast switching while preventing the buildup of resonant overvoltages that would occur with single sharp transitions.
Solution Approach 2:
The patent applies preliminary voltage pulses before the main switching event. By pre-charging or pre-discharging the cable through controlled preliminary pulses, the system reduces the magnitude of subsequent voltage transients, allowing faster main switching without generating excessive overvoltages at the machine terminals.
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
Effectively reduces overvoltages and switching losses at the electrical machine terminals while maintaining efficient operation, even with two-level converters, by generating an optimal sequence of pulses that adapts to the cable and filter parameters.
Implementation Method 1
said filter being of the type LC and comprising at least one inductor and one capacitor for each conductor of the cable
Implementation Method 2
said filter being of the type LC and comprising at least one inductor and one capacitor for each conductor of the cable
Implementation Method 3
a voltage pulse being able to be of the increasing type and comprising a rising vertical voltage front with a plateau of duration non-zero at the value E or of the decreasing type with a plateau of non-zero duration at the value 0V and comprising a vertical voltage edge descending
Data Source
Figure 1~2B
Figure 3~4
Figure 5A~5B
AI summary
The invention relates to a method of controlling a converter connected to an electrical machine by a cable (Cx) via a filter (F), said method consisting of determining at least one sequence of several voltage pulses forming a square signal to be applied to each conductor to minimize an overvoltage level, said sequence comprising a number 2N of successive pulses, N being greater than or equal to 1, each pulse being defined by a distinct rank n, said sequence being generated so that each increasing voltage pulse of rank n has a pulse width identical to that of a decreasing voltage pulse of rank equal to 2N+1-n, and the method includes in particular the following steps: - Determining the number of successive pulses of said sequence, - Determining the width of each pulse of the sequence adapted to minimize the overvoltage level at the terminals of the electrical machine (M).