Active Rectifier Ripple Current Minimization
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Solution Overview
Problem
Existing power converter systems face challenges in reducing ripple current and harmonic currents, leading to increased capacitor sizes and costs, as well as exposure to high instantaneous currents, which affect system performance and efficiency.
Innovation Solution
An active rectifier controller minimizes ripple current by relating DC link voltage to the speed of the AC motor, employing harmonic compensators, and synchronizing switching frequencies, while also providing pre-charge capabilities for the DC link capacitor and acting as an active filter to reduce harmonics generated by non-linear loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a capacitor or filter is used to reduce ripple current on the DC link, then ripple reduction is achieved, but the capacitor size and cost become increasingly large
Solution Approach 1:
The patent extracts the ripple current reduction function from the capacitor and relocates it to the active rectifier. The active rectifier is controlled to generate a DC link voltage that inherently minimizes ripple current, eliminating the need for large capacitors while achieving the same ripple reduction effect
Solution Approach 2:
The active rectifier is designed to perform multiple functions: it rectifies AC to DC, controls DC link voltage, minimizes ripple current, and provides harmonic compensation. This multi-functionality eliminates the need for separate ripple reduction components, reducing overall system complexity and component size
2Object-generated harmful factors
If a capacitor is used to reduce ripple current, then ripple reduction is achieved, but the capacitor is exposed to high instantaneous currents at initialization
Solution Approach 1:
The patent implements a pre-charge function that activates before the main power conversion begins. The active rectifier pre-charges the DC link capacitor at a controlled rate, preventing high instantaneous currents from damaging the capacitor while ensuring it is ready for normal operation
Solution Approach 2:
The system uses feedback control to monitor DC link voltage and adjust the active rectifier output accordingly. This feedback mechanism ensures the capacitor is charged at a safe rate during initialization and maintains optimal voltage during operation, protecting the capacitor from excessive currents
3Object-generated harmful factors
If capacitive and inductive elements are added to reduce harmonic currents from non-linear loads, then harmonic reduction is achieved, but the size and cost of these elements increase
Solution Approach 1:
The active rectifier serves itself by generating sinusoidal input currents that inherently cancel harmonics. The controlled switching of the active rectifier creates input currents that are automatically sinusoidal, eliminating the need for external harmonic filtering components
Solution Approach 2:
The patent changes the operating parameters of the active rectifier to operate in a mode that generates sinusoidal input currents. By adjusting the switching patterns and control signals, the system transforms the input current waveform to be sinusoidal, naturally eliminating harmonics without additional filtering elements
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 the size and cost of capacitors, minimizes ripple and harmonic currents, and enhances the overall performance of the power converter system by optimizing DC link voltage and current control, thereby improving power quality and efficiency.
Implementation Method 1
a pulse width modulated (PWM) rectifier converting the AC power provided by the AC power supply to DC power
Implementation Method 2
a DC link capacitor located between the PWM rectifier and the PWM inverter
Implementation Method 3
a pulse width modulated (PWM) inverter converting the DC power provided by the PWM rectifier to AC power
Implementation Method 4
an AC motor being supplied with power by the converter
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A power converter includes a PWM active rectifier (14) and controller (16) that minimize harmonic ripple currents on the DC link during an engine start mode (first stage) in which power is provided to an AC starter motor (24). The PWM active rectifier (14) and controller also minimize harmonic currents on AC input lines during a second stage (active filter mode). The power converter also includes a PWM inverter (20) and corresponding inverter controller (22) that controls the performance of the AC starter motor (24) during the first stage based on mode selection input received. The power converter system further includes pre-charge circuitry that charges a DC link capacitor (18) located within the power converter system to a desired level prior to providing the power converter system with AC power.