Device, method, and program for controlling converter, and air conditioner
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Solution Overview
Problem
Conventional PWM rectifiers cannot control the power factor to unity across all load regions, limiting their effectiveness in maintaining optimal power conversion efficiency.
Innovation Solution
A converter control device that calculates reactive current using current detection values from two phases and a voltage phase, adjusts the voltage phase to zero reactive current, and generates driving signals for switch units to maintain a power factor of 1, regardless of load size, while also incorporating unbalance correction to stabilize phase currents and prevent harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional PWM rectifier control is used, then the power factor can be controlled to about 1 in a certain load region, but the power factor cannot be controlled to 1 in other load regions
Solution Approach 1:
The invention dynamically adjusts the voltage phase angle θ based on the detected power factor and reactive current, rather than using a fixed phase angle. The phase correction amount is continuously modified according to the actual load conditions, enabling the power factor to be maintained at unity across all load regions. This dynamic adaptation resolves the contradiction between ease of manufacture and load region adaptability.
Solution Approach 2:
The invention implements a feedback mechanism where the power factor or reactive current is continuously detected, and the voltage phase angle is adjusted based on this feedback. The phase correction amount is modified according to the detected reactive current, creating a closed-loop control system that maintains unity power factor under varying load conditions, thereby solving the adaptability issue.
2Ease of manufacture
If the voltage phase is adjusted to zero reactive current, then the power factor can be maintained at 1, but the control complexity increases
Solution Approach 1:
The invention changes the control parameter from a fixed voltage phase angle to a dynamically adjustable phase angle based on reactive current detection. By modifying the phase angle parameter according to actual operating conditions, the system achieves unity power factor control without requiring complex additional hardware, thus balancing control performance with system complexity.
3Measurement precision
If reactive current calculation uses current detection values from multiple phases, then accuracy improves, but the calculation complexity and processing time increase
Solution Approach 1:
The invention extracts and utilizes only the necessary current detection values from two phases (e.g., u-phase and w-phase) along with the voltage phase angle, rather than processing all three phases. This selective extraction maintains sufficient calculation accuracy for reactive current determination while reducing computational complexity and processing time, thus resolving the contradiction between precision and time loss.
Data Source
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AI summary
To control the power factor to about 1 irrespective of a load. A converter control device (4) includes: a reactive current calculation unit (21) that calculates a reactive current Iq by using current detection values Ir and It of R-phase and T-phase and an R-phase voltage phase θ, a correction amount calculation unit (22) that calculates a phase difference of the R-phase voltage phase for zeroing the reactive current Iq as a phase correction amount Φ, a phase correction unit (23) that corrects the R-phase voltage phase θ by using the phase correction amount calculated by the correction amount calculation unit (22), a three-phase voltage command determination unit (24) that determines phase voltage commands corresponding to the respective phases based on a predetermined voltage command value k and a corrected R-phase voltage phase θ', and a PWM signal generation unit (25) that generates driving signals for the switch units corresponding to the respective phases by using the phase voltage commands.