Adjustable Speed Drive Regenerative Energy Control
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Solution Overview
Problem
Existing adjustable frequency drive (AFD) systems experience unstable DC link voltage and uncontrolled shutdown during deceleration, leading to stress on components, electromagnetic interference (EMI), and increased costs due to the need for braking resistors.
Innovation Solution
A dual loop control architecture is implemented, comprising an outer control loop that regulates capacitor energy and an inner control loop that manages active power consumption, calculating a compensation frequency to maintain a stable DC link voltage during deceleration without the use of braking resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the AFD applies a lower frequency to decelerate the motor during no load condition, then the deceleration rate is improved, but the DC link voltage becomes unstable and causes overvoltage trip
Solution Approach 1:
The patent implements a feedback control mechanism that monitors DC link voltage during deceleration and dynamically adjusts the switching control of the AFD. When regenerative energy causes voltage rise, the system detects this condition and modifies the switching strategy to maintain voltage within safe limits, preventing trips while preserving deceleration performance
Solution Approach 2:
The system changes operating parameters dynamically during deceleration by adjusting the switching frequency and pulse width modulation (PWM) duty cycle based on real-time DC link voltage conditions. This allows the AFD to adapt its energy handling capability to match the regenerative conditions, maintaining stable voltage while achieving fast deceleration
2Reliability
If the switching control is adjusted to prevent overvoltage trip, then the DC link voltage stability is improved, but the voltage begins to oscillate and disrupt normal deceleration
Solution Approach 1:
The patent employs dynamic control strategies that continuously adapt the switching parameters during deceleration. Rather than using fixed control settings, the system modulates the PWM duty cycle and switching frequency in real-time based on the instantaneous regenerative energy level, preventing both overvoltage trips and voltage oscillations by maintaining optimal control parameters throughout the deceleration process
Solution Approach 2:
The control system maintains continuous monitoring and adjustment of the DC link voltage throughout the entire deceleration process, ensuring that voltage stabilization actions are applied smoothly and continuously rather than in discrete steps. This continuous control prevents the on/off switching that causes voltage oscillations, maintaining stable deceleration performance
3Reliability
If a braking resistor is used to dissipate regenerative energy, then the DC link voltage stability is improved, but the device complexity and cost increase
Solution Approach 1:
The patent enables the AFD to handle regenerative energy internally through intelligent switching control and PWM modulation, allowing the system to dissipate or recycle regenerative energy without external braking resistors. The control system automatically manages the energy flow during deceleration, making the system self-sufficient and eliminating the need for additional energy dissipation components
Solution Approach 2:
The patent extracts the energy dissipation function from the physical braking resistor component and implements it through control algorithms and switching strategies. By removing the need for external energy dissipation hardware and handling regenerative energy through electronic control, the system reduces device complexity while maintaining voltage stability during deceleration
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 dual loop control system ensures a smooth and stable DC link voltage during deceleration, preventing uncontrolled shutdowns and EMI, while reducing system size and cost by eliminating the need for braking resistors.
Implementation Method 1
an adjustable frequency drive includes a capacitor coupled to a DC link
Implementation Method 2
the induction machine is in a generating mode of operation... causing power to flow from the induction machine back in to the AFD
Data Source
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AI summary
A system and method for controlling an adjustable speed drive (ASD) to decelerate an AC load during a generating mode of operation is disclosed. The ASD includes a capacitor and an inverter coupled to a DC link. A current sensor system is coupled to an output of the inverter. The ASD further includes a control system programmed to calculate an energy of the capacitor, generate a reference power using the calculated capacitor energy, and calculate a feedback power from realtime current signals received from the current sensor system. The control system compares the feedback power to the reference power, defines a frequency offset based on the comparison, generates a speed command using the frequency offset, and outputs the speed command to the inverter to maintain a smooth DC link voltage during deceleration.