Inverter Impedance Matching for Motor Drive Reflection
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Solution Overview
Problem
Existing motor driving devices with inverters face challenges in achieving stable impedance matching to prevent current and voltage reflection, especially when influenced by surrounding conductors, magnetic materials, or dielectric materials, due to variations in characteristic impedance values caused by these external factors.
Innovation Solution
The motor driving device incorporates a configuration with paired U-phase, V-phase, and W-phase lines, each with an impedance-matched circuit, and a rejection or bypass filter, connected via insulators, to ensure stable impedance matching and prevent reflection, even in the presence of external influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impedance matching is attempted using conventional single wire cable configuration, then leakage current can be reduced, but characteristic impedance values become indeterminate due to influence of surrounding conductors, magnetic materials, or dielectric materials
Solution Approach 1:
The invention divides the cable system into multiple independent phase lines (U-phase, V-phase, W-phase lines) with distinct conductors. Each phase line is treated as a separate transmission line with its own characteristic impedance, allowing individual impedance matching without interference from surrounding materials that would affect a single wire configuration.
Solution Approach 2:
The invention applies different impedance matching values to different phase lines based on their specific characteristics. Each phase line can have its own surge suppressing circuit with tailored resistance and capacitance values, allowing precise local impedance matching that accounts for variations in cable layout and surrounding materials affecting each phase differently.
2Reliability
If surge suppressing circuit is added to achieve impedance matching, then current and voltage reflection can be prevented, but device complexity increases
Solution Approach 1:
The invention combines the surge suppressing circuit functionality directly into the motor driving device architecture. The surge suppressing circuits for each phase are integrated with the inverter output stages, merging impedance matching functions with the existing power conversion and distribution system, thereby preventing reflection without adding separate standalone surge protection devices.
Solution Approach 2:
The surge suppressing circuits serve multiple functions simultaneously: they provide impedance matching to prevent voltage and current reflection, suppress electromagnetic interference, protect against overvoltage transients, and enable accurate current sensing. This multi-functionality reduces the need for separate dedicated circuits for each function.
3Ease of manufacture
If characteristic impedance is determined based on cable parameters alone, then calculation is simplified, but accuracy deteriorates due to unaccounted influence of surrounding materials
Solution Approach 1:
The invention determines characteristic impedance values through empirical measurement and adjustment rather than relying solely on theoretical calculations from cable parameters. The resistance and capacitance values in the surge suppressing circuits are tuned based on actual measured impedance characteristics of each phase line, accounting for the real-world influence of surrounding conductors, magnetic materials, and dielectric materials that cannot be captured by simple cable specifications.
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
An object of the present invention is to provide a motor driving device including an inverter that can achieve impedance matching to prevent reflection of current and voltage even when being influenced by a surrounding conductor, magnetic material, or dielectric material. The motor driving device of the present invention includes: a first motor (3A) and a second motor (3B); a first power line (41) for supplying driving power to the first motor (3A); a second power line (42) for supplying driving power to the second motor (3B); a first inverter circuit (15A) configured to supply the driving power to the first power line (41); a second inverter circuit (15B) configured to supply the driving power to the second power line (42); transmission lines (44u, 44v, 44w) including a pair of a U-phase line (41u) and a U'-phase line (42u), a pair of a V-phase line (41v) and a V'-phase line (42v), and a pair of a W-phase line (41w) and a W'-phase line (42w); and an impedance circuit (51) impedance-matched to the transmission lines (44u, 44v, 44w). Each of the transmission lines (44u, 44v, 44w) is arranged via an insulator.