Abstract: Systems and methods for controlling potentially damaging inrushes of current to the capacitor bank of an electric drive system when the voltage on the capacitor bank is low. In one embodiment, a variable speed drive has a converter that converts AC power to DC power, a capacitor bank that receives the DC power, and an inverter that converts the DC power stored by the capacitor bank to AC output power. The converter has three sections that rectify the phases of three-phase input power. Each section has at least one controlled rectifier component, and the rectifier components have switches connected to them in parallel. When the voltage on the capacitor bank is low, the controlled rectifiers and switches are controlled to prevent dangerously high inrushes of current to the capacitor bank.

Abstract: Systems and methods in which DC power is provided to a common DC bus to which multiple ESP systems are connected. Each ESP system coupled through an interface unit to the common DC bus. The interface unit selectively allows power from the common DC bus to be provided to a drive which then produces AC power without first having to rectify the power received from the common bus. The AC power produced by the drive is provided to the ESP motor, which drives the pump to lift fluid from the well. Each interface unit may include an input contactor that is closed to couple the ESP to the common DC bus, a charging contactor that is closed to provide power to the ESP, and a charging resistor that allows a capacitor or local bus at the input of the drive to be charged before the charging contactor is closed.

Abstract: Systems and methods for driving downhole equipment using a variable speed drive that has a switching mechanism between a first, constant-voltage capacitor bank and a second capacitor bank to control the voltage on the second capacitor bank, thereby enabling generation of a six-step output waveform while maintaining low input harmonics. In one embodiment, a variable speed drive has a converter section, an inverter section, two capacitor banks and a chopper. The converter section is controlled by a controller to convert AC power to DC power and charges the first capacitor bank to a substantially constant voltage. A chopper selectively couples the first capacitor bank to the second capacitor bank and thereby controls the voltage on the second capacitor bank. The inverter section can then produce a six-step output waveform at the voltage of the second capacitor bank. The variable speed drive can operate alternately in a pulse width modulation mode.

Abstract: Systems and methods for controlling potentially damaging inrushes of current to the capacitor bank of an electric drive system when the voltage on the capacitor bank is low. In one embodiment, a variable speed drive has a converter that converts AC power to DC power, a capacitor bank that receives the DC power, and an inverter that converts the DC power stored by the capacitor bank to AC output power. The converter has three sections that rectify the phases of three-phase input power. Each section has at least one controlled rectifier component, and the rectifier components have switches connected to them in parallel. When the voltage on the capacitor bank is low, the controlled rectifiers and switches are controlled to prevent dangerously high inrushes of current to the capacitor bank.

Abstract: A system for detecting a backspin condition of a motor in an electrical submersible pump is described herein. The system comprises a variable speed drive for powering the motor via a power cable; and a controller, the controller having a memory, a computer processor, and a computer program product stored on the memory and executable by the processor. The computer program product comprises the instructions of: monitoring an input current or impedance on the power cable to determine changes in motor current impedance, comparing changes in the motor current impedance to a historical threshold value for backspin events to determine whether the motor is backspinning; impeding operable power to the motor when it is determined the motor is backspinning; supplying a low AC voltage to the motor after it is determined the motor is backspinning; and determining whether or not the motor has stopped backspinning by monitoring the low AC voltage.

Abstract: An electrical submersible pumping (ESP) system can include a pump located in a wellbore, a motor attached to the pump, a power source located at the surface, a cable electrically coupling the power source and the motor, and a current sensor. The ESP system can also include a controller communicating with the current sensor to calculate a voltage drop associated with the cable responsive to an impedance of the cable. The controller can also control a power source output voltage responsive to the calculated voltage drop. For example, the controller can adjust the power source output voltage to minimize a cable current while maintaining a minimum motor voltage. The controller can also control a motor shaft speed by changing a power source output voltage frequency to compensate for changing slip and adjust the power source output voltage to minimize the cable current while maintaining a minimum motor voltage.

Abstract: Systems and methods for providing electrical power and to downhole oil production equipment such as electrical submersible pumps, wherein the outputs of multiple power modules are individually filtered before being added together to obtain a high voltage output that is provided to the downhole equipment. In one embodiment, an electrical drive system includes multiple power modules and corresponding filters. Each of the power modules is configured to receive an input power signal and to provide a corresponding pulse width modulated or stepped intermediate signal. The signal output by each power module is individually filtered to remove at least a portion of high-frequency components in the signal. The power modules and filters are coupled together in a configuration in which the filtered signals of the power modules are added to produce an output drive signal that is used to drive equipment such as an electrical submersible pump.

Abstract: Systems and methods for using variable speed drives to restart downhole submersible pump motors. In one embodiment, a downhole pump is controlled using a variable speed drive that includes a control system configured to detect interruptions in the operation of the pump system. After an interruption that requires the restart of the pump motor, the control system determines the reverse rotational speed of the pump motor and restarts the motor when this speed is sufficiently low. The control system may be configured to reduce the output voltage of the variable speed drive and sweep through a range of output frequencies to determine the frequency at which the current drawn by the motor is lowest. This is the frequency at which the drive's output matches the speed of the motor and the apparent impedance of the motor is highest. When the speed is low enough, the motor is restarted.

Abstract: A system for detecting a backspin condition of a motor in an electrical submersible pump is described herein. The system comprises a variable speed drive for powering the motor via a power cable; and a controller, the controller having a memory, a computer processor, and a computer program product stored on the memory and executable by the processor. The computer program product comprises the instructions of: monitoring an input current or impedance on the power cable to determine changes in motor current impedance, comparing changes in the motor current impedance to a historical threshold value for backspin events to determine whether the motor is backspinning; impeding operable power to the motor when it is determined the motor is backspinning; supplying a low AC voltage to the motor after it is determined the motor is backspinning; and determining whether or not the motor has stopped backspinning by monitoring the low AC voltage.

Abstract: Systems and methods for reducing harmonic distortion in a power system resulting from non-linear loading on the power system. The power at an interface with a power source is measured, and then distortion in the waveforms of the supplied power is identified. Cancellation signals which cancel all or part of the distortion are then generated and injected at the interface. In one embodiment, the power is sampled to determine the waveform, and then a Fast Fourier Transform is performed on the waveform to convert it to the frequency domain. Harmonics of the fundamental frequency can then be identified, and conjugates of the harmonics generated. An inverse Fast Fourier Transform is performed on the conjugates to generate a signal which is amplified to produce the cancellation signal.

Abstract: Systems and methods for providing electrical power and to downhole oil production equipment such as electrical submersible pumps, wherein the outputs of multiple power modules are individually filtered before being added together to obtain a high voltage output that is provided to the downhole equipment. In one embodiment, an electrical drive system includes multiple power modules and corresponding filters. Each of the power modules is configured to receive an input power signal and to provide a corresponding pulse width modulated or stepped intermediate signal. The signal output by each power module is individually filtered to remove at least a portion of high-frequency components in the signal. The power modules and filters are coupled together in a configuration in which the filtered signals of the power modules are added to produce an output drive signal that is used to drive equipment such as an electrical submersible pump.

Abstract: 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.

Abstract: An electrical submersible pumping (ESP) system can include a pump located in a wellbore, a motor attached to the pump, a power source located at the surface, a cable electrically coupling the power source and the motor, and a current sensor. The ESP system can also include a controller communicating with the current sensor to calculate a voltage drop associated with the cable responsive to an impedance of the cable. The controller can also control a power source output voltage responsive to the calculated voltage drop. For example, the controller can adjust the power source output voltage to minimize a cable current while maintaining a minimum motor voltage. The controller can also control a motor shaft speed by changing a power source output voltage frequency to compensate for changing slip and adjust the power source output voltage to minimize the cable current while maintaining a minimum motor voltage.

Abstract: Systems and methods for reducing harmonic distortion in a power system resulting from non-linear loading on the power system. The power at an interface with a power source is measured, and then distortion in the waveforms of the supplied power is identified. Cancellation signals which cancel all or part of the distortion are then generated and injected at the interface. In one embodiment, the power is sampled to determine the waveform, and then a Fast Fourier Transform is performed on the waveform to convert it to the frequency domain. Harmonics of the fundamental frequency can then be identified, and conjugates of the harmonics generated. An inverse Fast Fourier Transform is performed on the conjugates to generate a signal which is amplified to produce the cancellation signal.

Abstract: Systems and methods for using variable speed drives to restart downhole submersible pump motors. In one embodiment, a downhole pump is controlled using a variable speed drive that includes a control system configured to detect interruptions in the operation of the pump system. After an interruption that requires the restart of the pump motor, the control system determines the reverse rotational speed of the pump motor and restarts the motor when this speed is sufficiently low. The control system may be configured to reduce the output voltage of the variable speed drive and sweep through a range of output frequencies to determine the frequency at which the current drawn by the motor is lowest. This is the frequency at which the drive's output matches the speed of the motor and the apparent impedance of the motor is highest. When the speed is low enough, the motor is restarted.

Abstract: 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.

Abstract: A sine wave filter including an inductor for each phase (three inductors) and three delta- or Y-connected capacitors is employed within a borehole power system, coupled within a three phase power system at the surface between the output of a variable frequency drive and a three phase power cable transmitting power to a borehole location, and boosts the output voltage of the drive. The sine wave filter is designed to have a resonant frequency higher than the maximum operational frequency of the drive, and a Q such that, at the maximum operational frequency of the drive, the filter provides a voltage gain equal to the ratio of the desired voltage to the drive's maximum output power at the maximum operational frequency. The sine wave filter also smooths the voltage waveform of a pulse width modulated variable frequency drive.

Abstract: A sine wave filter including an inductor for each phase (three inductors) and three delta- or Y-connected capacitors is employed within a borehole power system, coupled within a three phase power system at the surface between the output of a variable frequency drive and a three phase power cable transmitting power to a borehole location, and boosts the output voltage of the drive. The sine wave filter is designed to have a resonant frequency higher than the maximum operational frequency of the drive, and a Q such that, at the maximum operational frequency of the drive, the filter provides a voltage gain equal to the ratio of the desired voltage to the drive's maximum output power at the maximum operational frequency. The sine wave filter also smooths the voltage waveform of a pulse width modulated variable frequency drive.

Abstract: A method and circuit for detecting rapid increase in line voltages applied to variable speed drives utilizing a phase controlled converter. A three phase alternating current line voltage is applied to a full wave bridge rectifier to generate a direct current signal. A buffer amplifier having a high input impedance is coupled to the output of the rectifier and a diode is utilized to ensure that only positive voltage transients are detected. Positive voltage transients output through the buffer amplifier rapidly charge a capacitor through the low output impedance of the buffer amplifier and that charge is permitted to bleed off slowly through an associated resistor. The rate of change of the capacitor charge level is compared to a preset voltage level and increases beyond that preset level are utilized to trigger an inhibit signal which momentarily resets the delay angle of the switching devices within the phase controlled converter.

Abstract: A protection circuit for a power transistor cuts off the transistor if an overcurrent condition occurs. The protection circuit includes control transistors that are switched on and off to alternately supply positive voltage to the base of the power transistor to turn it on and negative voltage to turn it off. A control circuit provides signals to the control transistors to turn them on and off. A latch has an input connected across the collector and emitter of the power transistor for monitoring the voltage. If the voltage exceeds a threshold level at the latch, the latch will provide a disabling output to the control circuit to turn off the power transistor.