Active Rectifier HVDC Regulation for CT Power Distribution
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Solution Overview
Problem
Medical imaging systems, particularly CT imaging systems, face inefficiencies due to unregulated high voltage direct current (HVDC) voltage drops during X-ray scans, leading to increased heat and power dissipation, distorted current, and low power factor, which affects the performance and reliability of components like the X-ray generator and gantry.
Innovation Solution
A high efficiency power distribution unit (HEPDU) with an active rectifier, such as a three-phase Vienna rectifier topology, regulates HVDC voltage and includes a digital control board for monitoring and diagnostics, ensuring a constant and stable voltage output, reducing harmonic currents, and improving power factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If unregulated HVDC voltage is used during heavy X-ray shots, then utility power sag occurs and components experience voltage instability, but adding voltage regulation increases device complexity
Solution Approach 1:
The active rectifier performs preliminary regulation of the HVDC voltage before it reaches the X-ray generator and other components. By pre-regulating the voltage and maintaining it within specified limits (e.g., 400V to 800V DC), the system prevents voltage sag and instability issues before they affect downstream components, eliminating the need for additional regulation stages at each component level.
Solution Approach 2:
The active rectifier serves multiple functions simultaneously: it rectifies AC to DC, regulates HVDC voltage, reduces harmonic currents, and improves power factor. This multi-functionality consolidates what would otherwise require separate devices into a single unit, maintaining reliability while avoiding excessive complexity multiplication.
2Power
If switching parts (IGBT, MOSFET, SiC MOSFET) pass more current to deliver enough power to the X-ray tube, then sufficient power is delivered, but heat and power dissipation increase
Solution Approach 1:
The active rectifier changes the electrical parameters (voltage and current) at the input stage of the power distribution system. By regulating HVDC voltage to precise levels and reducing harmonic content, it optimizes the current waveform and voltage levels before they reach the switching parts, reducing unnecessary current peaks and harmonic losses that would generate heat in IGBTs, MOSFETs, and SiC MOSFETs.
Solution Approach 2:
The system converts the potentially harmful effect of unregulated voltage fluctuations and harmonics into beneficial stable voltage conditions. The active rectifier uses control algorithms to detect and correct voltage deviations, transforming what would be harmful voltage sags and harmonics into stable, clean DC voltage, thereby reducing stress and heat generation in power switching components.
3Power
If three-phase input currents are distorted with harmonic current during heavy X-ray shots, then power delivery capability is maintained, but power factor decreases to around 0.85
Solution Approach 1:
The active rectifier incorporates feedback control mechanisms that continuously monitor the three-phase input currents and HVDC output voltage. When harmonic distortion or power factor degradation is detected, the control system adjusts the switching patterns of the rectifier to correct the current waveform, reducing harmonics and improving power factor while maintaining the required power delivery capability to the X-ray tube and other components.
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
The HEPDU enhances efficiency by stabilizing voltage, reducing component sizes, and increasing power factor to near 1.0, resulting in cost savings and improved performance of medical imaging systems, enabling smaller and cheaper X-ray generators.
Implementation Method 1
an active rectifier configured to regulate a high voltage direct current outputted to components of the medical imaging system
Data Source
AI summary
A medical imaging system includes an X-ray source configured to emit X-rays. The medical imaging system also includes a high voltage generator configured to provide power to the X-ray source. The medical imaging system further includes a high efficiency power distribution unit configured to receive electrical power from an electrical grid and to store the electrical power, wherein the high efficiency power distribution unit includes an active rectifier configured to regulate a high voltage direct current outputted to components of the medical imaging system including the high voltage generator.