Variable Speed Drive Ride-Through via Capacitor Bank Control
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Solution Overview
Problem
Downhole submersible pumps experience disruptive interruptions and variations in power supply, leading to costly production delays due to lack of inertia and increased torque requirements, which existing ride-through mechanisms fail to adequately address without causing damage from current inrushes.
Innovation Solution
A variable speed drive system incorporating a converter, inverter, and capacitor bank, which shuts down the converter section during power disruptions, uses stored energy from the capacitor bank to maintain operation, and resumes converter operation in a controlled manner to prevent sudden current inrushes, with detection mechanisms for ride-through events based on AC input voltage thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ride-through mechanisms increase DC bus capacitance to maintain operation during power interruptions, then the pump can continue running during short interruptions, but current inrush occurs when power returns that can blow fuses or damage components
Solution Approach 1:
The control system detects the restoration of input voltage before full power return and preemptively adjusts converter operation to limit current inrush. The system transitions the converter from shutdown state to a controlled partial-power state, gradually charging the DC bus capacitance rather than allowing uncontrolled current surge, thus preventing fuse blowing or component damage while maintaining pump operation continuity
Solution Approach 2:
The control system continuously monitors input voltage levels and DC bus voltage to detect power interruption and restoration events. Based on this feedback, the system dynamically adjusts converter switching signals to limit current inrush when power returns, creating a closed-loop control that prevents damage while maintaining reliability
2Object-affected harmful factors
If impedance is added between AC line and drive input to mitigate current inrush, then some protection is provided for shallow line transients, but the solution is ineffective for deeper or longer interruptions
Solution Approach 1:
The converter operation mode is dynamically adjusted based on the detected power interruption characteristics. During shallow transients, the converter can operate with partial power; during deeper interruptions, the converter shuts down completely and relies on DC bus capacitance; upon restoration, the converter gradually resumes operation. This dynamic adaptation makes the system effective across all interruption depths without requiring fixed impedance protection
3Reliability
If the converter section remains operational during power interruptions to maintain continuous power to the pump, then pump operation can be maintained, but the converter components are exposed to damaging voltage conditions and current inrush
Solution Approach 1:
Before the full power interruption damage can occur to the converter, the control system detects the power loss and shuts down the converter switches. This preliminary protective action isolates the converter components from damaging voltage conditions during the interruption. When power restores, the converter is brought back online in a controlled manner, preventing both interruption damage and inrush damage
Solution Approach 2:
The DC bus capacitance acts as an intermediary energy storage element between the AC input and the pump motor. During power interruptions, the converter shuts down but the capacitance maintains voltage to keep the pump running. This intermediary allows the converter to be protected from interruption damage while the pump continues operating, decoupling the converter's vulnerability from the pump's operational continuity requirement
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 system effectively rides through power interruptions, minimizing pump stoppages and preventing damage from current surges, thereby reducing operational costs and maintaining continuous oil production.
Implementation Method 1
The variable speed drive includes converter and inverter sections, as well as a capacitor bank and control systems. The drive shuts down the converter section upon detecting a disruption in the AC input power (a ride-through event) and continues to generate output power for the pump by drawing on the energy stored in the capacitor bank.
Data Source
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AI summary
Systems and methods for providing ride-through for interruptions in the power supplied to drives that are used to control equipment such as downhole submersible pumps. In one embodiment, a variable speed drive includes converter and inverter sections, a capacitor bank and a control system. The drive shuts down the converter section upon detecting a disruption in the AC input power and continues to generate output power by drawing on the energy stored in the capacitor bank. When the AC input power returns (or begins to return) to normal, the drive resumes operation of the converter section in a controlled manner (e.g., by presetting the firing angle of the SCR's in the converter to match the voltage across the capacitor bank.) The drive thereby limits the current that recharges the capacitor bank and prevents sudden inrushes of current that could damage the drive.