METHOD AND SYSTEM FOR CALIBRATING A GENERATOR CONTROL UNIT

Abstract

A method for calibrating a control system of a generator (106) with a rotor (110) and a stator (112), comprising the following steps: Supplying a source current to the stator (112); Determining a relative rotor speed based on a sensor signal provided by a rotor speed sensor (130); Determining a relative rotor position associated with the relative rotor speed; Determining an absolute rotor position based on the sensor signal and phase currents, featuring: Applying a phase control loop to one or more of the phase currents of the stator (112), Transforming the phase currents into two DC signals, Control one of the two DC signals to zero, and Determining the absolute rotor position based at least partially on a phase of the DC signals; and Calibrating the sensor signal based on an offset between the relative rotor position and the absolute rotor position.

Description

Technical field

[0001] The present disclosure relates generally to electric drive units, and in particular to systems and methods for calibrating the control of electric machines. background

[0002] An electrical machine is generally used to convert one form of energy into another and can include a motor, a generator, or any other electrical machine that has a rotational output or source. For example, a motor can be used to convert electrical power into mechanical or rotational power, while a generator can be used to convert mechanical or rotational power into electrical power. More specifically, a generator in an electrical drive unit, such as an electric power generation system, a generator set, or the like, is typically used to convert mechanical power received from a primary power source, such as an internal combustion engine, into electrical power that can be delivered to one or more electrical loads.Such a generator can also function as a motor to convert electrical power stored within a common bus or storage device of the electric drive into mechanical power. Among the various types of generators available for use with an electric drive unit, switched reluctance generators have received considerable attention due to their robustness and cost-effectiveness. While currently existing systems and methods for controlling electrical machines, such as switched reluctance generators, provide adequate control, there is room for improvement.

[0003] One aspect of electric drive control that deserves attention relates to the initial detection of the generator's rotor position. Furthermore, it is crucial to accurately detect or monitor the current position of the generator's rotor, associated with the electric drive, in order to operate the machine's electric drive efficiently. Currently existing electric drives for switched reluctance generators, for example, may rely on a speed wheel or angle sensor to track the rotor position during operation. However, such control schemes are prone to errors, such as during the initial rotor position detection stage, and are also susceptible to a significant loss of efficiency.For example, an error of 2 degrees in the detected mechanical rotor position of a switched reluctance generator, caused by a warped sensor, mechanical misalignment of the angle encoder, or similar, can correspond to a 0.5% reduction in the efficiency of the electric drive unit at full load.

[0004] Accordingly, it is important to provide more precise and robust means for determining the rotor position of generators and thereby improve the overall efficiency of electric drive units. The disclosed system and method are aimed at addressing one or more of the aforementioned requirements.

[0005] JP 2000 - 069 779 A discloses an adaptation method for the rotation angle sensor of a switched reluctance motor, in which a relative angle between a stator and a rotor is adapted to a detection value on the angle sensor.

[0006] US 2006 / 0049809A1 discloses a method for controlling a generator, wherein, in the drive control of a generator, a PWM control of a circuit comprising a FET and a diode connected to the opposite ends of a winding is performed.

[0007] US 2010 / 0253258A1 discloses a method and a device for calibrating a position sensor mounted on the shaft of a permanent magnet synchronous motor.

[0008] KR 10 2003 0 072 727 A discloses a method for controlling the switching angle by self-synchronizing control of a switched reluctance motor. US 2006 / 0 232 069 A1 discloses a switched reluctance (SR) generator with a boost converter for controlling an excitation voltage of an excitation capacitor, which can supply a phase winding with an excitation current.

[0009] EP 1 622 255 A2 discloses a rotor position detection system for an electric machine with a rotor position sensor that provides output signals to a control system containing errors due to component defects and manufacturing flaws. These errors are determined by comparison with calibrated data, and corrections are made available to the machine's control system.

[0010] The present invention is aimed at overcoming one or more of the problems or disadvantages associated with the prior art. Summary of Revelation

[0011] The object of the present invention is achieved by a method according to claim 1 and by a system according to claim 6. The dependent claims relate to preferred embodiments of the invention. Brief description of the drawings Fig. Figure 1 is a schematic view of an exemplary embodiment of a rotor speed estimation system as applied to a typical electric drive; Fig. Figure 2 is a flowchart of a procedure for estimating the rotor speed of a generator for an electric drive; Fig. Figure 3 is a graphical view of the outputs of a speed sensor and a current sensor; Fig. Figure 4 is a graphical view of inductance as a function of rotor position; Fig. Figure 5 is a graphical representation of the inductance in a generator and the corresponding phase current; Fig. Figure 6 is a graphical view of the absolute rotor position of a generator and the corresponding phase current; Fig. Figure 7 is a graphical view of a single-phase current in a stator of a generator; Fig. Figure 8 is a graphical view of the three-phase currents in a stator of a generator; Fig. Figure 9 is a graphical view of the three-phase currents of the Fig. 8, which were transformed into two DC signals using a phase-locked loop; Fig. Figure 10 is a graphical view of the phase angle output of the phase-locked loop that was used to adjust the two DC signals of the Fig. 9 to transform; and Fig. Figure 11 is a flowchart of an exemplary procedure for estimating the rotor speed of an electric drive. Detailed description

[0012] Specific embodiments or features are now discussed in detail, examples of which are shown in the accompanying drawings. Generally, corresponding reference numerals are used across the drawings to refer to the same or corresponding parts.

[0013] Fig. Figure 1 schematically represents an exemplary electric drive 100 that can be used to transfer power between a primary power source 102 and one or more electrical loads 104. The primary power source 102 may, for example, comprise a diesel engine, a gasoline engine, a natural gas engine, or any other type of rotating source commonly used to generate power. The load 104 may comprise one or more devices or components that consume electrical power. For example, in the context of industrial machinery or mobile work vehicles, the load 104 may comprise one or more motors for operating the machine's tools and / or one or more traction motors to propel the vehicle.The primary power source 102 can also be configured to mechanically transmit power to an electric machine 106 of the electric drive 100 via a coupling 108, such as an axially rotating drive shaft or the like. The electric machine 106 can comprise any suitable machine configured to produce electrical power in response to an externally supplied rotational input.

[0014] In this particular embodiment of the Fig. 1. The electric machine 106 can take the form of a switched reluctance generator configured to produce electrical power in response to the rotational input from the primary power source or motor 102. As is well known in the art, the generator 106 can have a rotor 110 rotatably arranged within a fixed stator 112. The rotor 110 of the generator 106 can be rotatably coupled to an output of the motor 102 via the coupling 108 or, in other embodiments, via a direct crankshaft, a gear train, a hydraulic circuit, or the like. The stator 112 of the generator 106 can be electrically coupled to a common bus 114 of the electric drive 100 via a converter circuit 116.During a generation mode of operation, while the rotor 110 of the generator 106 is rotated within the stator 112 by the motor 102, an electric current can be induced within the stator 112 and supplied to the converter circuit 116. The converter circuit 116 can, in turn, convert the electrical signals into a suitable direct current voltage, hereinafter also referred to as DC voltage, for distribution to the electrical load 104 and / or any other device via the common bus 114. The common bus 114 can provide a positive line 118 and a negative line or ground line 120, via which the common bus 114 can transmit a common DC bus voltage between one or more electrically parallel devices of the electric drive unit 100.The load 104 can include a circuit for converting the DC voltage supplied by the converter circuit 116 into suitable electrical signals for operating one or more of the electrical devices associated with the electric drive 100. It can also be arranged that the generator 106 additionally causes the rotor 110 to rotate in response to electrical signals provided to the stator 112 by the common bus 114, for example, during a starting mode of operation, or when the electrical load 104 becomes the source of electrical power.

[0015] The converter circuit 116 can comprise an array of transistors or gate switches 122 and diodes 124 to selectively activate one or more phase windings of the generator 106. For example, a three-phase switched reluctance generator 106 can be driven using a converter circuit 116 with six switches 122 and six diodes 124 to selectively activate and deactivate each of the three phases of the generator 106. Each of the switches 122 can further be activated or deactivated via the gate signals, while an external or secondary power source 126 provides power via the positive and negative lines 118, 120 of the common bus 114 to conduct current through the appropriately activated switches 122 and diodes 124.The initial power to the converter circuit 116 and the generator 106 can be supplied by a secondary power source 126, which may take the form of, for example, a battery, or a residual voltage stored in a capacitor of the common bus 114, or any other suitable DC power source.

[0016] Still on Fig. With reference to Section 1, the electric drive 100 can also be provided with an exemplary rotor speed estimation system 128, which is configured to calibrate the electric drive 100 based on the rotational frequency of the electric machine 106. The rotor speed estimation system 128 can include one or more speed sensors 130 and an associated control device 132. Furthermore, the speed sensors 130 can include a Hall effect sensor, a variable reluctance sensor, an anisotropic magnetoresistance sensor, or any other suitable sensor that can be adapted to generate a speed sensor signal corresponding to the rotational frequency of the rotor 110 relative to the stator 112. In addition, the speed sensors 130 can be located in close proximity to the rotor 110 and configured to determine the rotational frequency of the rotor 110 with respect to the stator 112.The speed sensors 130 can optionally be arranged in close proximity to the coupling 108, or to any other rotational output of the motor 102, in order to indirectly provide feedback corresponding to the rotational frequency of the rotor 110 based on known mechanical relationships between the rotor 110 and the coupling 108, which is rigidly coupled to it. By assigning an initial readout from the speed sensor 130 as a reference and by tracing the speed sensor signals or the rotational frequency of the rotor 110 from this reference, it may be possible to derive the position of the rotor 110 relative to the stator 112. The speed sensor signals generated by the speed sensors 130 can be transmitted to an input of the control device 132 for further processing.

[0017] Responding to the speed sensor signals and based on the analyses of the phase currents of the generator 106, the control device 132 can Fig. 1. The appropriate gate signals are supplied to the converter circuit 116 to provide more efficient control of the associated generator 106. More specifically, the control device 132 can employ current sensors or any other suitable means to detect the phase currents of the generator 106. Based on the detected phase currents and the detected frequencies and / or phases thereof, and using a closed-loop control system or algorithm, the control device 132 can be configured to supply a minimum phase current to the generator 106. Accordingly, the inductance caused by the rotation of the rotor 110 within the generator 106 can vary the current and further generate a substantially sinusoidal back electromotive force (BEMF).Analysis of the BEMF waveform enables the control device 132 to additionally determine the rotational speed as well as the absolute position of the rotor 110 within the generator 106. The control device 132 can be implemented using one or more of the following elements: a processor, a microcontroller, a digital signal processor (DSP), a field-programmable gate array (FGPA), an electronic control module (ECM), an electronic control unit (ECU), or any other suitable means for electronically controlling the functionality of the rotor speed estimation system 128. The control device 132 can be configured to operate according to a predetermined algorithm or set of instructions to actuate the electric drive 100 based on the rotational speed or position of the rotor 110 and the overall operating conditions of the electric drive unit 100.Such an algorithm or set of instructions may be pre-programmed or contained in a memory of the control device 132, as is commonly used in the art.

[0018] Now on Fig. With reference to Figure 2, an exemplary method for estimating the rotor speed is provided, comprising a plurality of steps that can be selectively performed by the control device 132, either periodically or, for example, during the start-up of the associated electric drive 100. In an initial step, the control device 132 can supply a DC source current to the generator 106 while the rotor rotates from a primary power source 102, enabling the inductance of the rotating machine to generate a periodic waveform or phase current in each phase of the generator 106. As the rotor 110 rotates relative to the stator 112, the control device 132 can additionally monitor the speed sensor signals provided by the speed sensors 130 to determine a relative rotor speed or the relative position of the rotor 110 with respect to the stator 112.More precisely, the speed sensor signals can respond to the offset of the rotor 110 with respect to the stationary stator 112 and exhibit square waveforms, as in . Fig. Figure 3 shows that while the square waveforms can indicate the speed or frequency of the rotor 110, the corresponding phase of the speed sensor signal can provide an indication of the relative position of the rotor 110 relative to the stator 112. Accordingly, it may be possible to derive the relative rotor position based on the feedback provided by the speed sensors 130.

[0019] As previously discussed, the inductance, as well as the phase currents and consequently the BEMF of generator 106, can vary as the rotor 110 rotates relative to the stator 112. As at 0° and 360° in Fig. As shown in Figure 4, the inductance can be greatest, for example, when the winding carriers or pole shoes 134 of the stator 112 are in direct alignment with one of the poles 136 of the rotor 110. Conversely, the inductance generated by the generator 106 can be lowest when the winding carriers 134 of the stator 112 are completely misaligned with the poles 136 of the rotor 110. As shown in the diagram of Fig. As shown in Figure 5, when a small direct current is supplied to the stator 112, changes in the inductance can induce essentially sinusoidal phase currents or BEMFs. Based on further analysis of the inductance and the resulting phase currents, it may be possible to determine a waveform that provides an indication of the absolute rotor position, as shown in Figure 5. Fig. 6 is shown and discussed in more detail below.

[0020] Back to Fig. 2 Referring to this, the control device 132 can monitor the phase currents and / or inductance of the generator 106 and use the previously derived relative rotor position to determine an absolute rotor position or the absolute position of the rotor 110 relative to the stator 112. In particular, the control device 132 can determine the absolute rotor position by applying peak detection, maximum derivative detection, and / or similar methods to the substantially sinusoidal waveforms of the phase currents. For example, as in Fig. As shown in Figure 7, the control device 132 correlates the absolute rotational position and / or the timing of the rotor 110 with selected points of the phase current waveform that exhibit the peak detection of maximum magnitude and / or the greatest rate of change of the maximum derivative. The control device 132 can also determine the absolute rotor position based on a PLL or phase-locked loop analysis. As shown in Fig. As shown in Figure 8, for example the control device 132 can originally supply three alternating phase currents I A , I B , I C from the generator 106. Using suitable filters, the control device 132 can be able to convert the three essentially sinusoidal phase currents into two DC phase signals I. α I β to convert, as in Fig. 9 shown. Furthermore, using classical proportional-integral or PI control, for example the control device 132 can be able to control one of the two DC phase signals I α , I β to control to zero. The two DC phase signals I α , I β can be derived, for example, using [IαIβ]=23⋅[cosθcosθ−(2π3)cosθ+(2π3)cosθ−sinθ−(2π3)−sinθ+(2π3)][IAIBIC]

[0021] From the essentially normalized DC phase signals I α , I β The control device 132 can further be configured to determine the absolute rotor position from the applied offset θ, as in Fig. 10 shown.

[0022] Once both the relative and absolute rotor positions have been determined, the control device 132 can compare the two rotor positions for any error or offset. If there is an offset between the relative and absolute rotor positions introduced by the phase currents and the speed sensor signals, the control device 132 can adjust or calibrate the speed sensor signals so that they match the absolute rotor position, essentially eliminating the offset. Furthermore, the speed sensor signals can be adjusted by the control device 132, for example, by modifying their timing or phase, so that the relative rotor position directly matches the absolute rotor position.Once the rotor position has been calibrated to the absolute rotor position, the control device 132 can activate the dynamic operator control of the generator 106, so that it is based on the calibrated speed sensor signals and ensures its efficient performance. Furthermore, the control device 132 can optionally complete further phase current analyses until the next calibration request or until the next start-up of the electric drive 100.

[0023] Now Fig. Turning to Figure 11, another exemplary method for estimating the rotor speed of a generator 106, as applied to an electric drive 100, is provided. As shown, the control device 132 of the electric drive 100 can initially monitor whether a machine key, button, or similar device is activated, for example, by an operator. During start-up, the primary power source or machine 102, as well as a secondary power source 126, can be started and activated. Once the power has been activated, the relative rotor speed or position can be determined based on the analysis of a speed-time control wheel or angle encoder, or similar device. The control device 132 can remain ready and wait until the motor 102 reaches a steady idle speed and the electric drive 100 builds up a predefined minimum equilibrium DC voltage.In equilibrium, the control device 132 can proceed to supply the DC voltage or source current to the generator 106 ui to induce a phase current for each phase winding of the generator 106. In a manner similar to the process of... Fig.Similarly, the control device 132 can derive an absolute position of the rotor 110 based on the previously derived relative rotor position and the analysis of the induced phase current waveforms exhibited by the generator 106. The control device 132 can then calibrate or adjust the speed sensor signal waveforms provided by the speed sensor 130 so that they directly correspond to the previously derived absolute rotor position. Once the calibration is complete and there is no significant offset between the relative and absolute rotor positions, the control device 132 can activate full operator control of the electric drive unit 100. Industrial applicability

[0024] In general, the foregoing disclosure has benefits in various applications related to power generation. In particular, the disclosed systems and methods can be used to provide more efficient control of generators typically used in conjunction with the electric drive units of power generating machines, as well as with the electric drive units of industrial vehicles, mobile machinery, and the like. Furthermore, the disclosed rotor position estimation scheme can be applied to electric drive units that incorporate switched reluctance generators. Moreover, the systems and methods disclosed herein can be configured to be recalibrated as often as desired to optimize the efficiency and robustness of the associated electric drive unit.

Claims

[1] A method for calibrating a control of a generator (106) having a rotor (110) and a stator (112) comprising the following steps: Supplying a source current to the stator (112); Determining a relative rotor speed based on a sensor signal provided by a rotor speed sensor (130); Determining a relative rotor position associated with the relative rotor speed; Determining an absolute rotor position based on the sensor signal and phase currents, featuring: Applying a phase control loop to one or more of the phase currents of the stator (112), Transforming the phase currents into two DC signals, Control one of the two DC signals to zero, and Determining the absolute rotor position based at least partially on a phase of the DC signals; and Calibrating the sensor signal based on an offset between the relative rotor position and the absolute rotor position. [2] The method according to claim 1, wherein the source current is supplied at least partially by a residual voltage in a common bus (114) associated with the generator (106). [3] The method according to claim 1, wherein the source current is supplied at least partially by a DC power source (126). [4] The method according to claim 1, which further comprises a step of activating the dynamic control of the generator (106) based on the calibrated sensor signal. [5] The method according to claim 1, wherein the phase currents of the stator (112) respond to the source current and an induced electricity between the rotor (110) and the stator (112). [6] A system (128) for calibrating a control of a generator (128) with a rotor (110) and a stator (112), comprising the following: a speed sensor (130) configured to generate a sensor signal corresponding to a speed of the rotor (110) relative to the stator (112); and a control device (132) in electrical transmission connection with the speed sensor (130) and the stator (112), wherein the control device (132) is configured as follows: to determine a relative rotor position based on the sensor signal, To determine an absolute rotor position based on the sensor signal and phase currents using: Applying a phase control loop to one or more of the phase currents of the stator (112), Transforming the phase currents into two DC signals, Control one of the two DC signals to zero, and Determining the absolute rotor position based at least partially on a phase of the DC signals; and to calibrate the sensor signal based on an offset between the relative rotor position and the absolute rotor position. [7] The system (128) according to claim 6, wherein the control device (132) is configured to selectively transfer a source current to the stator (112), wherein one or more of the phase currents of the stator (112) respond to the source current and an induced electricity between the rotor (110) and the stator (112). [8] The system (128) according to claim 6, wherein the control device (132) is connected to the stator (112) by a converter circuit (116). [9] The system (128) according to claim 6, wherein the control device (132) transforms the phase currents into two DC signals.

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