Parallel Converter Synchronization for Common Mode Current Reduction
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Solution Overview
Problem
Existing electric motor control installations with multiple converters connected in parallel to a DC power bus face challenges in minimizing common mode voltage, leading to oversized filtering needs and increased costs, as previous solutions are not effectively applicable to these architectures.
Innovation Solution
A control method that synchronizes the switching of voltage pulses between two converters using intersective pulse width modulation, ensuring that rising and falling edges of one converter coincide with opposite edges of the other, thereby reducing common mode currents and the need for large filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a filter is used to reduce common mode voltage disturbances, then electromagnetic disturbances are attenuated, but the filter must be oversized to prevent saturation of the magnetic core
Solution Approach 1:
The invention applies preliminary action by synchronizing the switching of voltage pulses between converters before the common mode voltage disturbances occur. By coordinating the rising and falling edges of voltage pulses across multiple converters, the method prevents the accumulation of common mode voltages that would otherwise require oversized filtering capacity.
Solution Approach 2:
The invention converts the harmful effect of common mode voltage generation into a beneficial outcome by using the same switching mechanisms that generate these voltages to cancel them out. By synchronizing opposite edges (rising with falling) of voltage pulses from different converters, the method transforms individual harmful disturbances into mutually compensating effects, reducing the need for large filters.
2Manufacturing precision
If the switching frequency of converters is increased, then control precision is improved, but common mode current increases
Solution Approach 1:
The invention converts the harmful common mode current generated by high-frequency switching into a beneficial effect by synchronizing opposite edges of voltage pulses from different converters. This coordination causes the common mode currents to cancel each other out, allowing high switching frequencies to be used for precise motor control without the penalty of excessive common mode current.
3Adaptability or versatility
If multiple converters are connected in parallel to control separate motors, then system versatility is improved, but total common mode voltage increases
Solution Approach 1:
The invention merges the switching operations of multiple parallel converters by synchronizing their voltage pulse edges. Instead of allowing each converter to operate independently and contribute additively to common mode voltage, the method combines their switching actions协调ly, where the rising edge of one converter coincides with the falling edge of another, causing their common mode voltages to cancel rather than accumulate.
Data Source
Figure 1A
Figure 1B~3B
Figure 4A~5
AI summary
Control method implemented for an electric motor control installation, said control installation comprising: - A first converter (CONV1) having controlled switching arms to apply first voltage edges to a first electric motor (M1) connected to said first converter by first output phases, - A second converter (CONV2) having controlled switching arms to apply second voltage edges to a second electric motor (M2) connected to said second converter by second output phases, - said control method comprising a step of synchronizing the first voltage edges with the second voltage edges in order to minimize the common mode currents generated by said installation.