Method for controlling a rectifier / inverter and a vehicle that has this

Abstract

Method (200) for controlling a rectifier / inverter (22) coupled to an electric motor (16, 17) in a vehicle powertrain (13) comprising a power machine (12), wherein the rectifier / inverter (22) comprises rectifier / inverter switches (28A, 28B, 28C, 30A, 30B, 30C), wherein the method (200) comprises that: a voltage waveform signal (27) and a switching frequency signal (27) are generated with the aid of a controller (24), which control a voltage waveform provided by the switches (28A, 28B, 28C, 30A, 30B, 30C) and a switching frequency of the switches (28A, 28B, 28C, 30A, 30B, 30C); wherein the voltage waveform signal (27) and / or the switching frequency signal (27) are at least partially based on at least one commanded power machine operating parameter (32); characterized in that the switching frequency signal (27) is for a predetermined first switching frequency when the commanded motor speed for the electric motor (16, 17) is less than a predetermined minimum motor speed threshold, and for a predetermined second switching frequency when the commanded motor speed for the electric motor (16, 17) is greater than a predetermined maximum motor speed threshold; wherein the second switching frequency and the predetermined maximum motor speed threshold are greater than the first switching frequency and the predetermined minimum motor speed threshold, respectively; and the at least one commanded power engine operating parameter (32) includes an on / off state of the power engine (12); wherein the predetermined minimum engine speed threshold and the predetermined maximum engine speed threshold are greater when the on / off state of the power engine (12) is switched on.

Description

TECHNICAL AREA

[0001] The teachings presented here generally comprise a method for controlling a rectifier / inverter of a hybrid vehicle. BACKGROUND

[0002] Motors / generators used in hybrid powertrains typically require a three-phase alternating current to be supplied to the stator windings. A rectifier / inverter contains switches that move between on and off positions to pulse the voltage so that it approximates a desired waveform separately for each of the three windings. The motor / generator acts, in effect, as a low-pass filter to filter the pulsating voltage waveform, resulting in an essentially sinusoidal current waveform with a small superimposed ripple component. The switching frequency can be modified, and the voltage can be kept on and / or off for varying durations to implement the desired modulation type (e.g.,discontinuous pulse width modulated (DPWM), continuous pulse width modulated (CPWM), etc.).

[0003] Switching losses from rectifiers / inverters constitute a significant percentage of the total energy losses in a hybrid electric vehicle. Reducing the switching frequency reduces energy losses due to switching operations. However, as the switching frequency decreases, switching noises are generally perceived to be more audible, whereas as the switching frequency increases, switching noises are generally perceived to be less audible. Control strategies for rectifiers / inverters have included masking switching noises, particularly at low frequencies, by ensuring that background noise remains at a relatively high level.This was achieved by limiting low-frequency switching to periods where the operating characteristics of the motor / generator, such as the torque level or speed level of the motor / generator, ensure sufficient masking of the switching noise.

[0004] DPWM can deliver essentially sinusoidal current waveforms while minimizing rectifier / inverter switching losses. This is achieved by adding a suitable zero-voltage sequence to each rectifier / inverter phase while maintaining an essentially sinusoidal line-to-line voltage excitation for the motor / generator. The zero-voltage sequence is chosen such that each rectifier / inverter phase will be saturated for one-third of the motor's fundamental electrical period at a duty cycle of either 0% or 100%. Switching losses for a specific phase are eliminated when operating at 0% or 100% duty cycles. The resulting DPWM waveforms use a single zero vector for each PWM period, unlike the two different zero vectors used in CPWM implementations.Consequently, a DPWM waveform, which switches less frequently, is generally noisier than a CPWM waveform with its more frequent switching. The DPWM waveform tends to minimize rectifier / inverter switching losses while increasing current ripple and audible noise compared to a CPWM waveform.

[0005] DE 10 2011 008 201 A1 discloses a method for controlling a rectifier / inverter according to the preamble of claim 1.

[0006] US patent 2012 / 0 112 674 A1 discloses a control system for a rectifier / inverter for an electric motor which uses either a DPWM waveform or a CPWM waveform depending on a threshold value for a commanded torque for the electric motor.

[0007] DE 10 2008 052 923 A1 discloses a method for controlling a rectifier / inverter for an electric motor, in which, depending on a commanded torque for the electric motor, the switching frequency of the rectifier / inverter is set to a first frequency below a first torque threshold and is determined between the first torque threshold and a second torque threshold as a function of the commanded torque. SUMMARY

[0008] A method for controlling a rectifier / inverter coupled to an electric motor in a vehicle powertrain comprising a drive unit is provided. The method includes generating a voltage waveform signal and a switching frequency signal for switches of the rectifier / inverter using a controller. The voltage waveform signal and / or the switching frequency signal are based, at least partially, on at least one commanded drive unit operating parameter.The switching frequency signal is present for a predetermined first switching frequency when the commanded motor speed for the electric motor is less than a predetermined minimum motor speed threshold, and for a predetermined second switching frequency when the commanded motor speed for the electric motor is greater than a predetermined maximum motor speed threshold; where the second switching frequency and the predetermined maximum motor speed threshold are greater than the first switching frequency and the predetermined minimum motor speed threshold, respectively. For example, the on / off state of the motor, the motor torque, and the motor speed can be factors on which the waveform signal or the voltage switching frequency signal is based.The predetermined minimum motor speed threshold and the predetermined maximum motor speed threshold are higher when the on / off state of the power unit is switched on. By considering one or more power unit operating parameters, the control of the switches can be optimized more effectively for both efficiency and noise reduction across different powertrain operating parameters than if only motor operation or vehicle speed were considered. A vehicle is also provided that features a controller with a stored algorithm for controlling the rectifier / inverter as described.

[0009] The foregoing features and advantages and other features and advantages of the present invention will be readily apparent from the following detailed description of the best ways of carrying out the invention when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of a vehicle that has a hybrid powertrain with an electric motor; Fig. Figure 2 is a schematic representation of a hybrid motor controller, a rectifier / inverter, and an electric motor of the vehicle from Fig. 1; Fig. Figure 3 is a flowchart of a first procedure for controlling the rectifier / inverter of Fig. 1-2; and Fig. Figure 4 is a flowchart of a second method for controlling the rectifier / inverter of Fig. 1-2. Fig. Figure 5 is a graphical representation of an exemplary voltage waveform of a typical CPWM duty cycle instruction, recorded over a fundamental electrical period of an electric motor. Fig. Figure 6 is a graphical representation of an exemplary voltage waveform of a typical DPWM duty cycle instruction recorded over one fundamental electrical period of an electric motor. DETAILED DESCRIPTION

[0010] With reference to the figures where the same reference symbols denote the same or similar components in the multiple views, Fig. Figure 1 schematically depicts a vehicle 10 comprising a hybrid powertrain 13 with a motor 12 and a hybrid transmission 14, which includes a first electric motor 16 and optionally an additional electric motor 17. The transmission 14 also includes a mechanical gearbox and optionally one or more torque transmission mechanisms such as clutches and brakes to enable different gear ratios and operating modes for the transmission 14.

[0011] The motors 16, 17 can each be selectively operated either as a motor or as a generator to contribute power to drive the gearbox 14 when operated as a motor, and to generate power that is used by the other motor or stored in an energy storage device, such as a battery 18, for later use when operating as a generator. Alternatively, each motor 16, 17 can be operated only as a generator or only as a motor. The motors 16, 17 are alternating current machines. The term "alternating current machine (AC machine)," as used here, generally refers to a device or apparatus that converts electrical energy into mechanical energy or vice versa. Alternating current motors can be generally classified as synchronous AC motors and asynchronous AC motors. Synchronous AC motors can include permanent magnet motors and reluctance motors.Permanent magnet motors include surface-mount permanent magnet motors (SMPMMs) and interior permanent magnet motors (IPMMs). Asynchronous AC motors include induction motors. Although an AC motor can function like a motor (e.g., a device used to convert alternating electrical energy or power at its input to produce mechanical energy or power), an AC motor, as used here, can also include generators, which are used to convert mechanical energy or power at their drive unit into alternating electrical energy or power at their output. Any of the motors 16, 17 can therefore be an AC motor, an AC generator, or both. An AC motor is an electric motor driven by an alternating current.In some implementations, an AC motor contains a stationary outer stator with coils that conduct an alternating current in response to a voltage applied to the motor to generate a rotating magnetic field, and an inner rotor attached to the output shaft, which is given torque by the rotating field. In other implementations, the rotor may surround the stator.

[0012] The transmission 14 can operate in standard modes, electric modes, or hybrid modes. In a standard operating mode, the transmission 14 is driven solely by the power unit 12. Under certain operating parameters of the vehicle 10, typically when the power demand for the vehicle 10 is low, the power unit 12 can be switched off, and the power required to drive the transmission 14 can be supplied by the motor 16 and / or the motor 17 in an electric operating mode. In a hybrid operating mode, the power unit 12 supplies power, and the motor 16 and / or the motor 17 are controlled to function as either a motor or a generator. In the hybrid operating mode, the transmission 14 can respond similarly to a continuously variable transmission to provide smooth operation of the vehicle 10 over a wide speed range.Once the vehicle 10 has reached a cruising speed at which little or no acceleration is required, the transmission 14 can operate in a fixed gear and be powered solely by the engine 12. The fixed gear is selected based on the cruising speed of the vehicle 10, the specific transmission 14, and the gear ratios. The vehicle 10 can be a plug-in hybrid vehicle, and the methods 100 and 200 described here for controlling the rectifier / inverter for the engine are particularly advantageous for the types of engines that can be installed in a plug-in hybrid vehicle. A plug-in hybrid vehicle can be equipped with a socket interface and an on-board charger for connection to an external power supply system, which is used to recharge the battery 18, as understood by those skilled in the art.

[0013] An electronic control unit (ECU) 20 is effectively connected to the power unit 12, the motors 16, 17, and the transmission 14 to control various vehicle functions, including the operating mode for the transmission 14. The ECU 20 can also be connected to various other components, such as, without limitation, sensors and control modules useful for controlling the vehicle 10. The electronic control unit 20 can also be referred to as a hybrid controller and it contains a Fig. 2 hybrid control processor 21 shown, which contains a stored algorithm for determining and executing the different operating modes of the powertrain 13 under different operating conditions.

[0014] A rectifier / inverter 22 and a motor controller 24 are also effectively connected to the ECU 20 to control the operation of the motor 16. The motor controller 24 receives acquired vehicle data and commanded vehicle operating parameters from the ECU 20. The motor controller 24 has a processor 25 with one or more stored algorithms that control the operation of the electric motors 16 and 17 and that control the switching frequency of the rectifier / inverter 22 and the pulsating voltage waveform produced by the rectifier / inverter 22 to generate the multiphase current in the motor 16, as described herein. The term "multiphase," as used herein, refers to two or more phases and can be used to describe electric motors that have two or more phases.A multi-phase electric motor is typically powered in response to a voltage applied via a multi-phase PWM rectifier / inverter. An example of such a multi-phase motor is a three-phase AC motor. In a three-phase system, the rectifier / inverter 22 will be a three-phase rectifier / inverter to drive one or more three-phase AC motors 16, 17. As a person skilled in the art understands, a star or delta connection scheme can be used.

[0015] The algorithms that control the switching frequency and the waveform are described here as being stored in the processor 25 of the motor controller 24; alternatively, the algorithms can be executed by both the ECU 20 and the motor controller 24, such that some of the procedural steps can be performed by the ECU 20, while others can be performed by the motor controller 24. For example, the ECU 20 can make determinations regarding power machine operating parameters and, based on these, supply control signals (i.e., bits with 0 or 1) to the motor controller 24, while the motor controller 24 can make determinations regarding motor operating parameters. Alternatively, the ECU 20 and the motor controller 24 can be combined in a single controller.

[0016] With reference to Fig. 2 The controller 24 inputs control signals, referred to here as duty cycle command signals 27, into the rectifier / inverter 22 based on commanded vehicle operating parameters provided by the ECU 20. The duty cycle command signals 27 can include a voltage waveform signal, a frequency signal, and a dithering signal. The rectifier / inverter 22 receives an input DC voltage (V dc ) from battery 18. The rectifier / inverter 22 contains a three-phase circuit 26 with several switches 28A, 28B, 28C, 30A, 30B and 30C which are switched in accordance with the duty cycle command signals 27 at a controlled frequency to generate a DC voltage from the input DC voltage (V dc ) to generate a desired voltage waveform from battery 18, resulting in a three-phase AC output i a , i b , i cinto the motor 16. Three of the switches 28A, 28B, 28C are connected to the positive output of the battery 18, and three of the switches 30A, 30B and 30C are connected to the negative output of the battery 18. In addition, in the embodiment shown, the multiple switches 28A, 28B, 28C, 30A, 30B and 30C are connected such that they form three pairs, which provide three current outputs i a , i b , i c from the rectifier / inverter 22. That is, the output of switch 28A is connected to the output of switch 30A to determine the current output i a to be formed from the rectifier / inverter 22. The output of switch 28B is connected to the output of switch 30B to form the current output i p to be formed from the rectifier / inverter 22. Finally, the output of switch 28C is connected to the output of switch 30C to form the current output i cto be generated from the rectifier / inverter 22. DC power from the battery 18 results in a three-phase output i a , i b , i c by repeatedly opening and closing the multiple switches 28A, 28B, 28C, 30A, 30B, and 30C at a controlled frequency based on the duty cycle command signals 27 from the controller 24 to produce a controlled waveform. Although the rectifier / inverter 22 is shown with three sets of switches and three current outputs because the motor 16 is a three-phase motor, the rectifier / inverter 22 and the motor 16 could be designed to operate with additional phases. If a delta connection scheme is used, the output currents i a , i e , i c not the phase currents in the motor windings, as the expert in the field understands.

[0017] To mask switching noises while reducing switching losses, a method 100 for controlling the rectifier / inverter 22 by the controller 24 is implemented, as shown in Fig. 3 is shown. Procedure 100 comprises a step 102, determining data inputs, and then a step 114, generating a waveform signal and a switching frequency signal for the rectifier / inverter 22 based on the inputs in step 102. The data inputs are generally commanded operating parameters, as discussed here, and can be received as signals 32 from the ECU 20. Step 102 includes a step 104, determining at least one commanded power machine operating parameter. That is to say, in procedure 100, at least one of the data inputs on which the generated voltage waveform signal and the switching frequency signal are based must be a power machine operating parameter.

[0018] The engine operating parameter can be an on / off state of engine 12, an engine speed, or an engine torque, which may be based on a commanded throttle position. Step 104, for example, may include a substep 104A, determining an on / off state of engine 12. As used herein, the on / off state is "on" when fuel is being supplied to engine 12, and it is "off" when no fuel is being supplied. The supply of fuel to engine 12 may be determined by a command sent as a control signal from the ECU 20 to actuate a fuel injection system.When power machine 12 is off, there is no power machine masking noise, so any switching noises will likely be more audible than if power machine 12 were on. Consequently, the waveform signal and the switching frequency signal generated at step 114 may be intended for quieter variants to the extent that commanded operating conditions can be achieved with these quieter waveforms. In general, a discontinuous pulse-width modulated waveform (DPWM waveform) results in lower losses than a continuous pulse-width modulated waveform (CPWM waveform). The DPWM waveform is more efficient than the CPWM waveform because it includes fewer switching operations, with the switches off for significant portions of each wave period. DPWM uses only a single zero vector per PWM period, which tends to increase current ripple and audible noise.Furthermore, switching at lower frequencies is generally associated with more audible switching noises.

[0019] The various embodiments can employ a variety of different types of DPWM and CPWM techniques. Generally, CPWM is defined as a PWM technique in which each phase leg of the rectifier / inverter 22 switches continuously over the complete 360-degree cycle of the modulated voltage waveform. Some examples, without limitation, of suitable CPWM techniques include sine wave PWM (SPWM), third harmonic injection PWM, and classical space vector PWM (SVPWM).

[0020] Similarly, DPWM is defined here as a PWM technique in which each phase leg of the rectifier / inverter 22 is not switched over the full 360-degree cycle of the modulated waveform. Some examples of suitable DPWM techniques include, without limitation, generalized DPWM (GDPWM), DPWM0, DPWM1, DPWM2, DPWMMIN, and DPWMMAX, as these terms are well understood in the technical field.

[0021] Fig. Figure 5 is a recording of the duty cycle versus the angular position (in radians) of an electric motor, showing an exemplary waveform of a typical CPWM duty cycle command recorded over one electrical fundamental period (six radians) of the electric motor. This example uses a classic space-vector PWM technique (SVPWM technique). Over the entire electrical fundamental period of the motor, the commanded duty cycle is greater than zero and less than one. Because the duty cycle is always greater than 0 and less than 1, the corresponding switches of the rectifier / inverter remain constantly switched during motor operation. Compared with SPWM, SVPWM adds some additional harmonics to the pole voltages, which can result in a higher fundamental voltage output before the maximum voltage limit is reached.

[0022] Fig. Figure 6 is a plot of the duty cycle versus angular position (in radians) of an exemplary waveform 50 of a typical DPWM duty cycle instruction recorded over one fundamental electrical period of an electric motor. This example uses a DPWM2 technique. In the DPWM duty cycle instruction technique shown, the duty cycle 52 is fixed to either zero or one for two 60-degree (approximately 1 radian) segments of the fundamental electrical period. During these fixed-rate periods, the respective rectifier / inverter switches are not engaged. Consequently, no switching losses occur in the corresponding phase leg during these fixed-rate periods. Therefore, using a DPWM technique can reduce switching losses to half the level that would occur when using CPWM.DPWM places the harmonic spectrum (motor current, bus DC) at a lower frequency and is more distorted, potentially generating more audible noise. CPWM places the harmonics at a higher frequency and is typically quieter. DPWM is usually more efficient (lower switching losses); consequently, a trade-off between efficiency and audible noise can be made when choosing the method.

[0023] Step 104 may include a further sub-step 104B, the determination of a commanded engine speed. The commanded engine speed may be indicated as a received signal 32 from the ECU 20. As the engine speed increases, the shifting frequency generated in step 114 may decrease, since the increased noise (and greater efficiency) of shifting at a lower frequency can be sufficiently masked by the engine 12.

[0024] Step 104 may include a sub-step 104C, determining a commanded engine torque. The commanded engine torque may be indicated as a received signal 32 from the ECU 20. The commanded engine torque may be achieved by a commanded throttle position. Consequently, signal 32 may represent a commanded throttle position. As the engine torque increases, the masking noise of the engine 12 may decrease; consequently, procedure 100 may cause the switching frequency generated in step 114 to increase as the engine torque increases.

[0025] Step 102 may also include data inputs of vehicle operating parameters other than those of the power unit 12. For example, the operating parameters of the electric motor 16, to which the rectifier / inverter 22 is effectively connected, may be considered. In step 106, the procedure 100 may determine the commanded torque of the electric motor 16. At relatively low motor torques, with the power unit 12 switched off, the waveform generated in step 114 may be a voltage waveform, which requires less switching or switching at a lower frequency, such as a DPWM waveform, since less switching noise is generated at low motor torques.At relatively high motor torques with the power machine 12 switched off, the waveform generated in step 114 can be a voltage waveform that produces relatively low acoustic noise, such as a CPWM waveform, since louder switching noises are generated at high motor torques.

[0026] In step 108, the procedure 100 can determine the commanded speed of the electric motor 16. At relatively low motor speeds, a lower frequency switching event can be generated in step 114, and at relatively high motor speeds, a higher frequency switching event can be generated. In a digital control system, the control bandwidth is limited by the sampling rate. Furthermore, in vector-controlled motor drives, the ratio of the switching frequency to the fundamental frequency of the motor should remain sufficiently high to control the phase currents stably and with high accuracy. A ratio of 10:1 is often considered a reasonable limit. Consequently, the higher the motor speed, the higher the fundamental frequency and thus the switching frequency required for good control.

[0027] Method 100 can also consider the operation of any other electric motors that can be operated as drive motors in the hybrid powertrain 13 and that are not effectively connected to the rectifier / inverter 22. For example, in step 110, the method can determine the torque and / or speed of motor 17. The waveform and switching frequency signals generated for motor 16 in step 114 can then be based in part on the effect that motor 17 has on the masking of noise and the overall efficiency losses in the powertrain 13.

[0028] Additionally, step 102 may include step 112, which determines the commanded vehicle speed. This input data for vehicle speed may be a combination of the throttle position and commanded power unit and engine operating conditions, from which the vehicle speed is determined. The waveform and shift frequency signals generated in step 114 may then be at least partially based on the vehicle speed, with the effect of increasing vehicle speed tending to indicate a lower frequency shift signal for the lower shift losses associated with shifting at a lower frequency, despite the typically increased noise level.

[0029] Step 114 may include a step 116 in which the switching frequency signal commands dithering or fluctuating of the switching frequency when one or more predetermined vehicle operating parameters are met. The vehicle operating parameters may include, but are not limited to, that a commanded motor torque of motor 16 is within a range of predetermined motor torques, that the vehicle speed is within a range of predetermined vehicle speeds, that the commanded waveform signal is for a predetermined waveform type (e.g., DPWM or CPWM), and that the commanded frequency signal is for a frequency within a predetermined range of switching frequencies.The relevance of some or all of these vehicle operating parameters considered in determining oscillation at step 116 may be specifically tailored to the acoustic nature of the particular vehicle model, which is determined by testing the vehicle.

[0030] Fig.Figure 4 shows a method 200 for controlling a rectifier / inverter 22. Method 200 is a specific implementation of the broader method 100. Specifically, method 200 begins at start 202. Then, at step 204, method 200 determines whether the on / off state of the power machine 12 is switched on. If the power machine 12 is switched on, method 200 proceeds to step 206 and generates an initial waveform signal for the rectifier / inverter 22, so that the rectifier / inverter 22 will control the switches to deliver the initial voltage waveform to the motor 16. In an unrestricted example, the initial waveform signal can be a discontinuous pulse-width modulated (DPWM) waveform signal due to its better efficiency, as the power machine 12 can mask its relatively high noise level.

[0031] Once it has been determined that the power machine 12 is switched on, the procedure 200 can also consider the operating parameters of the motor 16 to determine the switching frequency of the rectifier / inverter 24. Specifically, the procedure proceeds from step 206 to step 208, in which the controller 24 determines whether the commanded speed of the motor 16 is less than a predetermined minimum motor speed threshold (i.e., a first motor speed), such as, but not limited to, 200 revolutions per minute (RPM).If the commanded motor speed is less than the predetermined minimum motor speed threshold, then procedure 200 proceeds to step 210, in which the controller 24 generates a predetermined first switching frequency signal and sends it to the rectifier / inverter 22, so that the rectifier / inverter 22 switches the switches 28A-C and 30A-C at a predetermined first frequency, about 2 kilohertz (kHz), but without being limited to it.

[0032] If, at step 208, it is determined that the commanded motor speed is not less than the predetermined minimum motor speed threshold, the procedure 200 proceeds to step 212 and determines whether the commanded motor speed 16 is greater than a predetermined maximum motor speed threshold (i.e., a second motor speed), such as, but not limited to, 1000 RPM. If the commanded motor speed is greater than the predetermined maximum motor speed threshold, the procedure 200 proceeds to step 214, and the controller 24 generates a predetermined second switching frequency signal for a second predetermined frequency, such as, but not limited to, 10 kHz.

[0033] If, at step 212, it was determined that the commanded motor speed is not greater than the predetermined maximum motor speed threshold, then the procedure 200 proceeds to step 216 and the controller 24 generates a switching frequency signal for a switching frequency that lies between the first switching frequency and the second switching frequency and is proportional to the commanded motor speed (i.e., establishing a linear relationship between the switching frequency and the commanded motor speed between the minimum and maximum motor speed thresholds).

[0034] Returning to step 204, if it is determined that the power engine operating state is not engaged (i.e., no fuel is being supplied to power engine 12), procedure 200 proceeds to step 218 and determines whether the commanded engine torque of engine 16 is less than a predetermined minimum engine torque threshold, such as 200 newton meters (Nm) without restriction. If the commanded engine torque is less than the predetermined minimum engine torque threshold, procedure 200 proceeds to step 220 and generates the first waveform signal of step 206, such as the DPWM signal. Consequently, the controller 24 commands the rectifier / inverter 22 to control switches 28A-28C and 30A-30C to supply a DPWM voltage waveform to engine 16.However, if the commanded motor torque is not lower than the predetermined minimum motor torque threshold, then procedure 200 proceeds to step 222 and generates a second waveform signal, such as, without limitation, a continuous pulse-width modulated waveform (CPWM waveform signal), or a sine waveform (SPWM). Consequently, the controller 24 commands the rectifier / inverter 22 to control the switches so that a CPWM voltage waveform is supplied to the motor 16.

[0035] In addition to the motor torque, procedure 200 also considers the rotational speed of motor 16 when the power machine 12 is off. Consequently, after each of steps 220 and 222, procedure 200 proceeds to step 224 to determine whether the commanded rotational speed of motor 16 is less than a predetermined minimum motor speed threshold (i.e., a third motor speed), which may differ from the minimum motor speed threshold of step 208 in the case when the power machine 12 is on. For example, the predetermined minimum motor speed threshold of step 224 may be 100 RPM.If the commanded motor speed of motor 16 is less than the predetermined minimum motor speed threshold of step 224, the procedure 200 proceeds to step 226 and the controller 24 generates a predetermined first frequency signal (duty cycle command signal 27) and sends it to the rectifier / inverter 22, so that the rectifier / inverter 22 controls the switches 28A-28C, 30A-30C to switch at the first frequency, approximately without restriction at 2 kHz.

[0036] However, if the commanded speed of motor 16 is not less than the predetermined minimum motor speed threshold of step 224, then procedure 200 proceeds to step 228, and controller 24 determines whether the commanded speed of motor 16 is greater than a predetermined maximum motor speed threshold (i.e., a fourth motor speed), which may differ from the maximum motor speed threshold of step 212, applied when the power machine 12 is switched on. In an example without restrictions, the predetermined maximum motor speed threshold of step 228 may be 500 RPM.If the commanded speed of motor 16 is greater than the predetermined maximum motor speed threshold of step 228, then procedure 200 proceeds to step 230, in which the controller 24 generates a predetermined second switching frequency signal, so that the rectifier / inverter 22 will control switches 28A-28C, 30A-30C to switch at the second frequency, such as without restriction of a switching frequency of 10 kHz.

[0037] However, if the speed of motor 16 is not greater than the predetermined maximum motor speed threshold of step 228, then procedure 200 proceeds to step 232, in which the controller 24 generates a switching frequency signal for a frequency between the predetermined first frequency of step 226 and the predetermined second frequency of step 230, and proportional to the speed of motor 16. In procedure 200, the motor speed thresholds for implementing the first or second predetermined frequencies are lower when power machine 12 is off than when power machine 12 is on. This ensures that the generally more audible but more efficient switching at lower frequencies will be implemented less frequently when power machine 12 is off than when power machine 12 is on, because there is less masking noise for switches 28A-28C and 30A-30C.

[0038] Method 200 can also ensure that the rectifier / inverter 22 dithers the frequency of switches 28A-28C and 30A-30C under suitable conditions, as dithering has been shown to disrupt the tonality of a specific switching frequency. Dithering is a method for reducing the amplitude of specific harmonics in the current spectrum by rapidly changing the switching frequency at a set rate. For example, dithering can vary the pulsating current between 9 and 11 kHz with a desired mean of 10 kHz, thereby reducing harmonics that might otherwise be present if a constant frequency of 10 kHz is used. When dithering is used, the frequency is periodically adjusted within a specific band around the mean. Equation (1) shows the instantaneous rectifier / inverter switching frequency that incorporates dithering: fsw=fsw_avg+Krand⋅fspan where f sw the instantaneous switching frequency in kHz is, f sw_avg the time-averaged switching period in kHz is, f span The total peak-to-peak fluctuation in the switching frequency due to dithering is in kHz and K rand a pseudo-random number in the range of -0.5 to +0.5. A pseudo-random number generator is used to generate the number K. rand to calculate a value that can fluctuate from -0.5 to +0.5. This number is calculated using the dither rate (f). rate ) is updated. Consequently, the instantaneous switching frequency is updated every f rat\e jump to a new random value. The key parameters that determine the behavior of dithering with respect to spectrum spreading are the dither span and the dither rate (f). span or f rateIncreasing the dither span spreads each harmonic over a wider frequency range. Increasing the dither rate makes frequency adjustments faster, thus reducing the time the rectifier / inverter 22 will operate at any given instantaneous frequency. A typical dither rate can be 2–10 milliseconds, while the dither span can be in the range of 10% peak-to-peak around the mid-switching frequency. The exact values ​​will vary depending on the application.

[0039] After each of steps 214, 216, 230, and 232, the procedure 200 proceeds to step 234, in which the controller 24 determines whether one or more predetermined vehicle operating conditions are met under which the frequency to be generated according to step 214, 216, 230, or 232 is to be dithered. The predetermined vehicle operating conditions may include, but are not limited to, one or more of the following: that the speed of the vehicle 10 is within a predetermined range of vehicle speeds; that the commanded motor torque of the motor 16 is within a range of commanded motor torques; the type of waveform signal generated by the controller; and the switching frequency signal generated by the controller 24.For example, in step 234, the commanded switching frequency can be compared to a predetermined dither threshold frequency, which may differ from the frequencies considered in steps 210, 214, 216, and 230. If the predetermined dither threshold frequency for step 234 is 12 kHz, then controller 24 can command dithering in step 236 if the commanded switching frequency is less than 12 kHz. The relevance of some or all of the vehicle operating parameters considered in determining dithering in step 234 may be specifically tailored to the acoustic nature of the particular vehicle model, which is determined through vehicle testing.

[0040] If, at step 234, it is determined that the predetermined vehicle operating conditions for dithering are met, the procedure proceeds to step 236 and the commanded frequency is further refined to be a dithered frequency. Then, procedure 200 returns to the starting point at step 202 and continues to continuously adjust the commanded voltage waveform, voltage frequency, and frequency dithering to be supplied to the motor 16 by the rectifier / inverter 22.

[0041] If, at step 234, it is determined that the predetermined vehicle operating conditions for dithering are not met, then procedure 200 reverts to the start at step 202, without the switching frequency signal containing a command for dithering. Optionally, the torque and speed of the auxiliary motor 17 and the vehicle speed can also be considered in procedure 200 to determine the commanded waveform and frequency for the rectifier / inverter 22.

[0042] Although the best ways of carrying out the invention have been described in detail, the person skilled in the art in the field relating to this invention will recognize various alternative designs and embodiments for putting the invention into practice within the scope of the attached claims.

Claims

[1] Method (200) for controlling a rectifier / inverter (22) coupled to an electric motor (16, 17) in a vehicle powertrain (13) comprising a power machine (12), wherein the rectifier / inverter (22) comprises rectifier / inverter switches (28A, 28B, 28C, 30A, 30B, 30C), wherein the method (200) comprises that: a voltage waveform signal (27) and a switching frequency signal (27) are generated with the aid of a controller (24), which control a voltage waveform provided by the switches (28A, 28B, 28C, 30A, 30B, 30C) and a switching frequency of the switches (28A, 28B, 28C, 30A, 30B, 30C); wherein the voltage waveform signal (27) and / or the switching frequency signal (27) are based at least partially on at least one commanded power machine operating parameter (32); characterized by , that the switching frequency signal (27) is for a predetermined first switching frequency when the commanded motor speed for the electric motor (16, 17) is less than a predetermined minimum motor speed threshold, and for a predetermined second switching frequency when the commanded motor speed for the electric motor (16, 17) is greater than a predetermined maximum motor speed threshold; wherein the second switching frequency and the predetermined maximum motor speed threshold are greater than the first switching frequency and the predetermined minimum motor speed threshold, respectively; and the at least one commanded power engine operating parameter (32) includes an on / off state of the power engine (12); wherein the predetermined minimum engine speed threshold and the predetermined maximum engine speed threshold are greater when the on / off state of the power engine (12) is switched on. [2] Method (200) according to claim 1, wherein the switching frequency signal (27) is for a switching frequency which increases linearly between the predetermined first switching frequency and the predetermined second switching frequency in relation to the commanded motor speed of the electric motor (16, 17) when the commanded motor speed of the electric motor (16, 17) is between the predetermined minimum motor speed threshold and the predetermined maximum motor speed threshold. [3] Method (200) according to claim 1, wherein the switching frequency signal (27) commands dithering of the switching frequency based on at least one predetermined vehicle operating condition.

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