Inverter PWM Timing Control for Fast Load Variation Response
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional inverter control devices have low responsiveness due to calculation times being shorter than half of the carrier period, leading to difficulties in following load variations during high-speed rotation, resulting in step-out or overcurrent issues.
Innovation Solution
An inverter control device with a configuration that includes semiconductor switching elements, current detectors, voltage detectors, and an inverter control unit, which sets a calculation period twice as long as the pulse width modulation (PWM) signal generation period, detects DC current half a calculation period before starting, and calculates output voltage vectors to reflect PWM signals from half to three-quarters of the calculation period, improving control responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the conventional inverter control device uses the detected current in a next carrier period and calculates PWM modulation for a carrier period after the next, then the control structure is simple, but the responsiveness of control is low and cannot follow load variation at high-speed rotation
Solution Approach 1:
The patent performs current detection in advance during a 1/2 calculation period before the calculation start timing, and pre-calculates the output voltage vector based on this detected current. This preliminary action allows the PWM modulation to be generated with higher responsiveness without increasing the overall control cycle complexity, as the detection and calculation are optimized to occur within the available time window.
Solution Approach 2:
The patent dynamically adjusts the timing of current detection and PWM signal generation by setting the calculation period to be twice longer than the calculation time, and setting the carrier period to be 1/N times as long as the calculation period. This dynamic timing adjustment enables the system to adapt to high-speed rotation conditions while maintaining manageable control structure complexity.
2Speed
If the calculation period is set to be twice longer than the calculation time, then the responsiveness is improved, but the control cycle duration increases
Solution Approach 1:
The patent employs periodic action by setting the carrier period to be 1/N times as long as the calculation period, where N is an integral number equal to or larger than 1. This creates multiple carrier cycles within one calculation period, allowing the system to maintain improved responsiveness through the extended calculation period while the periodic carrier action ensures that control updates occur frequently enough to manage the overall cycle duration effectively.
3Speed
If the carrier period is set to be 1/N times as long as the calculation period, then the PWM signal frequency is increased for better control, but the calculation burden increases
Solution Approach 1:
The patent performs current detection and output voltage vector calculation in advance during the 1/2 calculation period before the calculation start timing. This preliminary action reduces the real-time calculation burden during the active PWM generation phase, allowing for higher PWM frequencies without proportionally increasing the calculation power consumption, as the heavy computational tasks are distributed across the extended calculation period.
Data Source
AI summary
An inverter control device includes an inverter main circuit, a current detector, a voltage detector that detects a DC voltage between DC bus lines, and an inverter control unit that generates PWM signals to perform on/off control of a plurality of semiconductor switching elements respectively with a DC current and a DC voltage. The unit sets a carrier period of PWM signals to be 1/N times a calculation period in which the PWM signals are generated, performs detection of a DC current detected by the current detector in a 1/2 calculation period immediately before a calculation start timing for generating PWM signals, calculates an output voltage vector based on the detected DC current, and reflects PWM signals generated from the output voltage vector in one calculation period from a 1/2 calculation period after the calculation start timing to 3/2 control calculation periods after the same.