Rotary Machine Control via Dynamic Switching Frequency
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Solution Overview
Problem
Rotary machines experience reduced control ability due to high-level harmonic currents caused by harmonic voltage components, which are exacerbated by lower switching frequencies in rectangular-control and over-modulation control modes.
Innovation Solution
An apparatus that includes a generator for creating a drive signal with an on-off pattern for switching elements, a driver to execute this pattern, a parameter monitor to detect harmonic current changes, and a limiter to restrict the drive signal generation based on monitored parameters, thereby controlling the harmonic current levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If rectangular-control mode or over-modulation control mode is used to increase voltage utilization factor, then voltage utilization factor is improved, but harmonic voltage components are generated causing high-level harmonic currents
Solution Approach 1:
The patent changes the switching frequency parameter dynamically based on rotational velocity. When rotational velocity decreases, the switching frequency is increased to suppress harmonic currents. This parameter adaptation allows the system to maintain high voltage utilization factor while compensating for harmonic generation under varying operating conditions.
Solution Approach 2:
The patent implements dynamic adjustment of switching frequency according to rotational velocity. The switching frequency is not fixed but varies with the operating state of the rotary machine, allowing optimal performance across different speed ranges while suppressing harmonic currents when needed.
2Use of energy by moving object
If switching frequency is reduced in rectangular-control mode or over-modulation control mode, then voltage utilization factor is improved, but control ability is reduced due to high-level harmonic currents
Solution Approach 1:
The patent dynamically changes the switching frequency parameter based on rotational velocity to maintain control ability. When rotational velocity decreases and harmonic currents increase, the switching frequency is increased to suppress harmonics and maintain stable control, thus preserving control ability while still benefiting from over-modulation or rectangular control modes.
3Use of energy by moving object
If switching frequency is reduced to increase voltage utilization factor, then voltage utilization factor is improved, but harmonic current levels increase causing control instability
Solution Approach 1:
The patent implements dynamic parameter adjustment where switching frequency is increased in response to decreasing rotational velocity. This compensates for the instability caused by harmonic currents and maintains control stability across the operating range, allowing the system to operate in high voltage utilization modes without sacrificing stability.
Data Source
AI summary
In an apparatus for controlling a variable of a rotary machine based on an AC voltage supplied to the rotary machine via a switching element of a power converter, a generator generates a drive signal including an on-off pattern of the switching element. A driver drives, based on the on-off pattern of the drive signal, the switching element. A parameter monitor monitors a parameter indicative of change of a harmonic current flowing in the rotary machine based on a harmonic voltage included in the AC voltage. A limiter limits, based on the parameter monitored by the parameter detector, generation of the drive signal by the generator to limit an increase of a level of the harmonic current.