Power Conversion Device PWM Control for Capacitor Heat and Motor Noise
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Solution Overview
Problem
The existing power conversion devices using harmonic wave superposition systems face challenges in suppressing the increase in effective current flowing to smoothing capacitors, leading to increased heat and reduced reliability, while also generating motor noises due to insufficient current detection time and increased ripple waveforms.
Innovation Solution
A power conversion device with two power conversion units, each equipped with a bridge circuit and a smoothing capacitor, utilizes a control unit that generates PWM pulses based on output voltage vectors, correcting voltage command values to ensure sufficient detection time and intermittent harmonic wave superposition, reducing the effective current and motor noises by synchronizing current detection with PWM carrier periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a harmonic wave superposition system is used to synchronize PWM switching periods with current detection timing, then current detection time is secured, but the effective current flowing to the smoothing capacitor increases
Solution Approach 1:
The patent applies periodic action by intermittently performing harmonic wave superposition only during specific PWM periods when current detection is required, rather than continuously. The control unit selectively activates the harmonic wave superposition system based on whether current detection timing coincides with PWM switching periods, thereby reducing unnecessary effective current flow to the smoothing capacitor while ensuring adequate current detection time when needed.
2Loss of time
If harmonic wave superposition is continuously applied to secure current detection time, then current detection is achieved, but motor noises increase due to increased ripple waveforms
Solution Approach 1:
The patent reduces motor noises by applying harmonic wave superposition periodically rather than continuously. The control unit determines whether to apply harmonic wave superposition based on the specific PWM period and current detection requirements. This selective application minimizes the generation of ripple waveforms and associated motor noises while still ensuring current detection is achieved when necessary.
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
This configuration effectively suppresses the effective current and temperature rise of the smoothing capacitor, enhances reliability, and minimizes motor noises by using a single current detector and optimizing harmonic wave superposition timing, achieving silent operation and improved productivity.
Implementation Method 1
a smoothing capacitor that smooths the DC voltage
Implementation Method 2
a first power conversion unit that includes a bridge circuit to convert power; a second power conversion unit that includes a bridge circuit to convert power
Implementation Method 3
a control unit that generates a PWM pulse on the basis of an output voltage vector and a PWM carrier
Data Source
AI summary
An object of the invention is to simultaneously solve a miniaturization and an improvement of productivity of a power conversion device, a temperature rise suppression of a smoothing capacitor, and a reduction of motor noises. The power conversion device of the invention includes a smoothing capacitor, a first power conversion unit and a second power conversion unit which are connected in parallel, and a control unit which generates a PWM pulse on the basis of an output voltage vector and a PWM carrier. The control unit includes a correction unit which corrects a predetermined output voltage vector value to two or more different output voltage vector values such that an average value in one period of the PWM carrier becomes the predetermined output voltage vector value. The correction unit corrects a first output voltage vector value in a first period, and corrects a second output voltage vector value in a second period different from the first period.