AC Drive Common Mode Voltage Reduction via Active Vector PWM
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Solution Overview
Problem
Existing AC motor drives face challenges in reducing common mode voltages, which can lead to adverse effects such as motor bearing damage and insulation issues, due to issues like deadtime and zero vector usage in power conversion systems.
Innovation Solution
The implementation of a pulse width modulation technique that employs active vector-only switching sequences, deadtime compensation, and reflected wave mitigation, using a switch control system that generates switching control signals based on feedback signals and a space vector modulation diagram, avoiding zero vectors and selectively adjusting feedback signals to minimize common mode voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If zero vectors are used in PWM switching sequence, then the control simplicity is maintained, but common mode voltages increase causing motor bearing damage and insulation issues
Solution Approach 1:
The patent extracts and removes zero vectors from the PWM switching sequence, using only active vectors (non-zero vectors) to generate the control signals. This extraction eliminates the source of common mode voltage while maintaining the space vector modulation framework, directly resolving the contradiction between control simplicity and common mode voltage reduction
Solution Approach 2:
Instead of using the conventional approach that includes zero vectors for simplicity, the patent inverts the approach by deliberately excluding them. The switching sequence is designed to cycle through only active vectors in a specific order, thereby achieving common mode voltage reduction while maintaining adequate control through the active vector sequence
2Reliability
If deadtime is introduced in switching devices, then device protection and reliable operation are achieved, but common mode voltage distortion and phase distortion occur
Solution Approach 1:
The patent introduces deadtime as a preliminary protective action in the switching sequence, inserting brief intervals where all switches are off before transitioning between states. This preliminary action prevents device damage from shoot-through currents while the active vector-only sequencing minimizes the resulting distortion effects
Solution Approach 2:
The patent optimizes the deadtime parameter to be as short as possible while still providing adequate protection, and positions it strategically within the active vector sequence. By changing the timing parameters and sequence arrangement, the system achieves device protection with minimized phase distortion and common mode voltage effects
Data Source
Figure 1A
Figure 1B
Figure 1C~1D
AI summary
Control systems, methods and power conversion systems (110) are presented for controlling common mode voltages in AC motor loads driven by inverter PWM control using switching sequences (162) with only active vectors where a first vector of each switching sequence differs by one phase switching state from a last vector of a switching sequence of an adjacent sector, along with enhanced deadtime compensation and reflected wave reduction techniques in providing pulse width modulated switching signals (142b) to a switching inverter (110b).