Brake Controller for Wellhead Direct Drive Motor
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Solution Overview
Problem
Existing braking systems for permanent magnet motor-driven progressive cavity pumps in fluid wells face challenges in safely managing rotational energy release and fluid settling, with bi-directional braking causing inefficiencies and potential safety issues due to constant resistance and varying braking torque.
Innovation Solution
A braking controller that utilizes back electromotive force (EMF) to power an electrical control circuit, which connects or disconnects a brake resistor based on motor speed and direction, using an electrically controlled switch to manage braking torque effectively and efficiently, while monitoring electrical properties to prevent faults and overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a brake resistor is constantly connected to the PM motor back EMF, then the system provides continuous braking resistance, but the braking torque becomes excessive at low speeds and causes inefficiency and potential damage
Solution Approach 1:
The brake resistor connection is made dynamic through an electrically controlled switch (IGBT) that adjusts the braking resistance based on motor speed and operational state. The controller dynamically connects the brake resistor only when backspin is detected above a threshold speed, and disconnects it when speed drops below the threshold or during forward operation, optimizing braking efficiency across different operating conditions
Solution Approach 2:
The braking system changes the electrical parameter (resistance connection state) based on the motor's operational parameters (speed and direction). The controller monitors back EMF frequency to determine motor speed and uses this information to adjust whether the brake resistor is connected, effectively changing the electrical circuit configuration to match operational requirements
2Reliability
If the brake resistor is connected during forward motor operation, then continuous braking resistance is applied, but this creates inefficiency and potential safety hazards
Solution Approach 1:
The system dynamically adjusts brake resistor connection based on motor rotation direction detected through back EMF polarity analysis. The electrically controlled switch remains open during forward operation and closes only during reverse backspin conditions, ensuring braking resistance is applied only when needed for safety
Solution Approach 2:
The controller continuously monitors the back EMF signal from the PM motor to detect rotation direction and speed. This feedback mechanism enables the controller to make real-time decisions about brake resistor connection, ensuring efficient forward operation while providing safety braking when backspin occurs
3Reliability
If the brake controller uses external power supply, then the control circuit can operate continuously, but this increases system complexity and power requirements
Solution Approach 1:
The brake controller is designed to be self-powered by utilizing the back EMF generated by the PM motor during rotation. The control circuit draws power directly from the motor's back EMF signal through a rectifier and capacitor, eliminating the need for a separate external power supply and reducing overall system complexity
Solution Approach 2:
The back EMF signal from the PM motor serves multiple functions: it provides the control power for the brake controller circuitry, carries the rotational speed information for control decisions, and enables the braking function itself when the resistor is connected. This multi-functionality reduces the need for additional system 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 solution provides improved braking control by selectively engaging and disengaging the brake resistor based on motor speed and direction, ensuring safe energy dissipation and preventing faults, thereby enhancing the efficiency and safety of the braking process in fluid well operations.
Implementation Method 1
the brake resistor dissipating the back EMF as heat
Implementation Method 2
the PM electromagnetic circuit produces a back EMF. In this way, the PM motor acts as a generator
Implementation Method 3
a rectifier may convert the alternating current (AC) back electromotive force (EMF) into a direct current (DC) back EMF
Data Source
AI summary
The invention relates to fluid drive systems used in fluid wells and brake systems for permanent magnet wellhead direct drives. The braking controller connects or disconnects a brake resistor from a back EMF. A variable frequency drive (VFD) drives the motor and communicates with the control circuitry of the brake controller. The control circuitry monitors the brake resistor and depending on the rotational speed and direction of the motor and operating state of the VFD, disconnects or connects the brake resistor. If the direction of the motor is in reverse and above a threshold speed, it connects the brake resistor. If the direction of the motor is in reverse and below the threshold speed, the control circuitry dissipates stored back EMF through the brake controller. The amount of stored back EMF corresponds to the time to empty a pump.