Power Converter Current Control at Low Carrier Frequency
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Solution Overview
Problem
Existing power converters face challenges in reducing loss and noise while maintaining constant reactor voltage, especially when the carrier frequency is decreased, due to pulsing input voltage from the rectifier, which complicates current control and increases harmonic components.
Innovation Solution
A power converter system that includes a rectifier, a transformation circuit with a reactor and switching element, a capacitor for smoothing, and a converter control unit that detects line voltage, reactor current, and output voltage to calculate and integrate current deviations, generating a switching signal to control the switching element, thereby reducing errors and noise by accumulating current deviations at specific phase angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the carrier frequency is increased to control reactor current constant, then current control performance is improved, but loss and noise of the power converter are increased
Solution Approach 1:
The patent implements a feedback control mechanism where the reactor current is detected and compared with a command value, and the current deviation is integrated over one power supply period. This feedback loop enables accurate current control by continuously adjusting the switching element's on-duty based on the integrated deviation, achieving constant reactor current while allowing the carrier frequency to be lowered, thus reducing loss and noise.
2Loss of energy
If the carrier frequency is decreased to reduce loss and noise, then loss and noise are reduced, but reactor voltage fluctuations increase due to insufficient current control response
Solution Approach 1:
The patent applies preliminary action by integrating the current deviation over one complete power supply period before using it to adjust the switching element's on-duty. This integration accumulates the deviation information in advance, enabling the control system to compensate for reactor voltage fluctuations even at lower carrier frequencies, thus maintaining reactor voltage stability while reducing loss and noise.
3Measurement precision
If a high carrier frequency is used to maintain constant reactor current, then current control accuracy is improved, but the complexity and cost of the control system increase
Solution Approach 1:
The patent employs periodic action by integrating the current deviation over one power supply period and using this integrated value to control the switching element's on-duty in a periodic manner synchronized with the power supply frequency. This approach simplifies the control system architecture compared to high-frequency PWM control, reducing computational complexity and microcomputer requirements while maintaining accurate current control.
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 approach reduces switching loss and noise while suppressing reactor voltage fluctuations, even at lower carrier frequencies, improving current control performance and allowing for less expensive microcomputer usage, thus lowering costs.
Implementation Method 1
a rectifier, which is configured to rectify three-phase AC power
Implementation Method 2
a capacitor, which is configured to smooth an output voltage of the transformation circuit
Implementation Method 3
a transformation circuit, which includes a reactor, a switching element, and a backflow prevention element, and is configured to transform a voltage rectified in the rectifier
Data Source
AI summary
A power converter includes a transformation circuit configured to transform a rectified voltage, and a converter control unit configured to control a switching element of the transformation circuit. The converter control unit calculates a current command value based on a line voltage or the phase voltage, calculates a current deviation between the current command value and the reactor current, and calculates a switching command value from the current deviation. The converter control unit includes a plurality of integrators for the respective different phase angles of a power supply voltage. The integrator corresponding to a power supply phase angle is caused to accumulate the current deviation, and the integrator corresponding to a phase angle that is advanced by a set delay phase from the power supply phase angle is caused to output the control amount. A switching signal is generated with use of the control amount and the switching command value.