Inverter operating at high switching frequency and method for operating an inverter

Abstract

The present disclosure relates to an inverter operating at a high switching frequency and a method for operating an inverter. A motor controller performing a current regulator and a modulation routine in separate update intervals provides an improved fundamental voltage waveform to a motor controlled by the motor controller. The current regulator is performed at a first periodic update rate and the modulation routine is performed at a second periodic update rate, where the frequency at which the modulation routine is performed is at least twice the frequency at which the current regulator is performed. Performing the current regulator and the modulation routine at different frequencies results in the current regulator generating a single voltage reference signal over multiple cycles of the modulation routine. To reduce voltage ripple caused by decoupling the performance of the current regulator and the modulation routine, the motor controller extrapolates the voltage reference generated by the current regulator as multiple voltage reference signals, where a unique voltage reference signal is provided for each cycle of the modulation routine.

Description

Technical Field

[0001] The subject matter disclosed herein relates to a motor controller configured to operate at a high switching frequency. More specifically, the motor controller is configured to execute a current regulator to generate a voltage reference for the motor at a first update rate and to execute a modulation routine to output a desired voltage to the motor at a second update rate. Background Technology

[0002] As known to those skilled in the art, a motor driver is used to control the operation of a motor. According to a common configuration, the motor driver includes a DC bus with a DC voltage of suitable amplitude, from which an AC voltage can be generated and supplied to an AC motor. The DC voltage can be provided as an input to the motor driver, or alternatively, the motor driver can include a converter section that converts the AC voltage input into a DC voltage present on the DC bus. The converter section can be passive, including conventional diode rectification; or it can be active, including controlled power electronic switching devices, either of which can convert the AC voltage input into a DC voltage for the DC bus. The power electronic switching devices in the active rectifier can be selected from transistors, such as insulated-gate bipolar transistors (IGBTs) or metal-oxide-semiconductor field-effect transistors (MOSFETs), thyristors, or silicon controlled rectifiers (SCRs). The power electronic switching devices can also include a reverse-conducting power electronic device, such as a freewheeling diode, connected in parallel across the power electronic switching devices. The reverse-conducting power electronic device is configured to conduct during time intervals when the power electronic switching devices are not conducting. The controller in the motor driver generates switching signals to selectively turn each switching device on or off, thereby generating the desired DC voltage on the DC bus.

[0003] The motor driver receives command signals instructing the desired operation of the motor. These command signals can be the desired torque, speed, or position for which the motor is to operate. The motor's torque, speed, or position is controlled by changing the amplitude and frequency of the AC voltage applied to the motor's stator. An inverter section is positioned between the DC bus and the motor driver's output to generate a controlled AC voltage. The inverter section includes power electronic switching devices such as IGBTs, MOSFETs, thyristors, or SCRs; and reverse-conducting power electronic devices connected in parallel across the power electronic switching devices. The motor is connected to the output of the motor driver, and the controller generates switching signals to rapidly turn the switching devices in the inverter on and off at a predetermined switching frequency, thereby alternately connecting or disconnecting the DC bus from the output, and consequently, from the motor. Depending on the nature of the switches, the output waveform is rectangular, connecting or disconnecting the motor driver's output from the DC bus such that the output is at the DC voltage present on the DC bus or zero volts. The amplitude of the output voltage is changed by varying the duration of each switching cycle during which the motor driver's output is connected to the DC voltage. Motor controllers use modulation techniques such as pulse width modulation (PWM) to change the amplitude of the output voltage at each cycle of the desired base frequency in order to synthesize a waveform with the desired amplitude and frequency.

[0004] Previously, the current regulation and modulation routines were executed within a single periodic update interval. The current regulator received a current feedback signal corresponding to the current output to the motor and generated a voltage reference signal corresponding to the desired operation of the motor. The modulation routine received the voltage reference signal from the current regulator and generated a switching signal for the switching device to output an appropriate voltage as a result of the voltage reference signal generated by the current regulator. Executing these two routines within a single periodic update interval was ideal because the modulation routine updated the voltage output to the motor at the same rate as the current regulator generated the voltage reference signal.

[0005] The trend in motor controllers is towards executing current regulator and modulation routines at increasingly higher frequencies. Increasing the frequency allows the motor controller to update the average voltage at finer time intervals, generating an output voltage at the base operating frequency that more closely approximates a sinusoidal output voltage compared to executing the same modulation routine at a lower switching frequency. However, the control routines used to execute current regulator and modulation routines are typically computationally intensive. Increasing the frequency of current regulator and modulation routine updates places greater demands on the computational capabilities of the motor controller. Therefore, there is a practical limitation on the maximum achievable current regulator update frequency due to the computational capabilities of the motor controller. Improving computational speed through additional processing cores or by increasing the clock frequency increases the cost and complexity of the motor controller.

[0006] Therefore, it is ideal to provide a motor controller with an increased maximum switching frequency without requiring a corresponding increase in the motor controller's computing power.

[0007] Another trend in motor controllers is to provide increased operating speeds to the motors connected to them. In the past, motor controllers supplied motors with an output voltage having a fundamental frequency that varied between zero speed and a conventional line frequency of 50 or 60 Hz. More recently, motor controllers have been configured to provide output voltages with upper limits to the fundamental frequency of hundreds or thousands of Hz to achieve higher motor speeds. However, increasing the fundamental frequency reduces the number of periodic update intervals of the current regulator and modulation routines that execute during each cycle of the output voltage. Reducing the number of update intervals per cycle of the fundamental voltage decreases the approximation of the output voltage to a sinusoidal waveform.

[0008] Therefore, it is ideal to provide a motor controller with an increased maximum switching frequency to deliver an improved voltage waveform at an increased base frequency. Summary of the Invention

[0009] According to one embodiment of the invention, an inverter configured to operate at a high switching frequency includes: a direct current (DC) bus, an output terminal, a plurality of switching devices, and a processing unit. The DC bus is configured to have a DC voltage present on the DC bus, and the output terminal is configured to provide an alternating current (AC) voltage to a motor operatively connected to the inverter. Each switching device is operatively connected between the DC bus and the output terminal and is selectively controlled to convert the DC voltage to an AC voltage. The processing unit is configured to execute a series of instructions to: determine a first reference voltage at a first update rate, and determine a plurality of second reference voltages at a second update rate. The first reference voltage corresponds to a desired AC voltage supplied to the motor. The second update rate is a multiple of the first update rate, and each second reference voltage is a function of the first reference voltage and a desired rotational speed of the motor.

[0010] According to another embodiment of the present invention, a method for operating an inverter at a high switching frequency is disclosed. A first reference voltage for an AC motor operatively connected to the output of the inverter is determined during a first periodic interval. A plurality of second reference voltages for the AC motor are determined at second periodic intervals. The second periodic interval is shorter than the first periodic interval, and each of the second reference voltages is determined based on the first reference voltage and the desired rotational speed of the motor.

[0011] According to another embodiment of the invention, an inverter configured to operate at a high switching frequency includes a direct current (DC) bus, an output terminal, a plurality of switching devices, and a processing unit. The DC bus is configured to have a DC voltage present on the DC bus, and the output terminal is configured to provide an alternating current (AC) voltage to a motor operatively connected to the inverter. Each of the switching devices is operatively connected between the DC bus and the output terminal and is selectively controlled to convert the DC voltage to an AC voltage. The processing unit is configured to execute a series of instructions to: execute a current regulator at a first update rate and execute a modulation routine at a second update rate. The second update rate is at least twice the first update rate. The current regulator generates a first reference voltage, and the modulation routine generates a plurality of second reference voltages based on the first reference voltage and the desired rotational speed of the motor.

[0012] These and other advantages and features of the invention will become apparent to those skilled in the art from the detailed description and accompanying drawings. However, it should be understood that while the detailed description and drawings indicate preferred embodiments of the invention, they are given by way of illustration and are not restrictive. Many changes and modifications can be made within the scope of the invention without departing from its spirit, and the invention includes all such modifications. Attached Figure Description

[0013] Various exemplary embodiments of the subject matter disclosed herein are illustrated in the accompanying drawings, in which the same reference numerals denote the same parts throughout the drawings, and in the drawings:

[0014] Figure 1 This is a block diagram of a motor driver that includes one embodiment of the present invention;

[0015] Figure 2 It comes from Figure 1 A block diagram of the rectifier section of the motor driver;

[0016] Figure 3 It comes from Figure 1 A block diagram showing the inverter section and gate driver module of the motor driver;

[0017] Figure 4 It comes from Figure 1 A block diagram illustrating one implementation of a controller for a motor driver;

[0018] Figure 5 This is a graphical representation of the periodic execution interval of a current regulator and modulation routine according to an embodiment of the present invention;

[0019] Figure 6 This is a block diagram representation of voltage reference extrapolation according to an embodiment of the present invention;

[0020] Figure 7 This is a block diagram representation of voltage reference extrapolation according to another embodiment of the present invention;

[0021] Figure 8 This is a block diagram representation of voltage reference extrapolation according to another embodiment of the present invention;

[0022] Figure 9 This is a block diagram representation of voltage reference extrapolation according to another embodiment of the present invention;

[0023] Figure 10 This is a graphical representation of the voltage output from the motor driver as a result of decoupling the execution of the current regulator and modulation routine in the absence of an extrapolated voltage reference; and

[0024] Figure 11 It is a graphical representation of the voltage output from the motor driver under the condition of decoupling execution of the current regulator and modulation routine and extrapolation of the voltage reference.

[0025] In describing the various embodiments of the invention illustrated in the accompanying drawings, specific terminology will be used for clarity. However, it is not intended to limit the invention to the specific terminology chosen, and it should be understood that each specific term includes all technical equivalents that operate in a similar manner to achieve a similar purpose. For example, the words "connection," "attachment," or similar terms are frequently used. They are not limited to direct connections but include connections made through other elements that are considered equivalent by those skilled in the art. Detailed Implementation

[0026] The various features and advantageous details of the subject matter disclosed herein will be more fully described with reference to the non-limiting embodiments described in detail below.

[0027] This paper discloses a motor controller with an increased maximum switching frequency without requiring a corresponding increase in the motor controller's computational power. The motor controller separates the current regulator and modulation routine into separate update intervals. The current regulator executes at a first periodic update rate, and the modulation routine executes at a second periodic update rate. In this way, the frequency of executing the modulation routine can be increased while keeping the frequency of executing the current regulator at a lower rate. Furthermore, the modulation routine can be implemented in dedicated hardware circuitry, thus not increasing the computational load on the processor. It is expected that the frequency of the modulation routine execution is at least twice the frequency of the current regulator execution.

[0028] Executing the current regulator and modulation routine at different frequencies causes the current regulator to generate a single voltage reference signal over multiple cycles of the modulation routine. Maintaining a constant voltage reference over multiple cycles of the modulation routine results in fundamental frequency distortion. This distortion may manifest as voltage ripple superimposed on the output voltage waveform.

[0029] According to another aspect of the invention, voltage ripple is reduced by extrapolating a voltage reference generated by a current regulator into a plurality of voltage reference signals, wherein a unique voltage reference signal is provided for each cycle of the modulation routine. Increasing the modulation frequency and extrapolating the voltage reference signals to provide a unique voltage reference signal for each cycle of the modulation routine results in a voltage waveform from the motor driver output that more closely approximates a sinusoidal waveform at an increased fundamental frequency.

[0030] First turn Figure 1 This illustration shows one embodiment of a motor driver 20 incorporating a high PWM switching frequency. An AC voltage 12 is supplied to the motor driver 20 at input 22. According to the illustrated embodiment, the AC voltage 12 is a three-phase AC input voltage. The motor driver supplies an AC output voltage from its output terminal 160 to a motor 10 operatively connected to the motor driver 20 via cable 14. The output voltage is a three-phase AC output voltage, wherein for each phase of the motor, a separate conductor is shown extending between the motor 10 and the driver 20. It should be understood that the conductors shown can be combined within cable 14, operated as separate conductors, or in combination thereof, depending on application requirements.

[0031] The AC input voltage 12 is supplied to the converter section 40 of the motor driver 20. One or more additional filters may be included between the input terminal 22 of the motor driver and the converter section 40, depending on application requirements. The converter section 40 may include any electronic device suitable for passive or active rectification as understood in the art. See also... Figure 2The converter section 40 shown is a passive converter and includes a set of diodes 44 forming a diode bridge. The converter section 40 receives an AC voltage 12 at input 42, rectifies the three-phase AC voltage into a DC voltage, and provides the DC voltage to the DC bus 50 at the output of the converter section. Optionally, the converter section can be an active converter, which includes gate-controlled switching devices, including but not limited to thyristors, silicon controlled rectifiers (SCRs), or silicon-based transistors such as IGBTs or MOSFETs. The converter section may alternatively include high-frequency switching devices, including but not limited to silicon carbide (SiC) or gallium nitride (GaN) wide-bandgap IGBTs or MOSFETs, which can switch in the range of 20 kHz to megahertz to convert the voltage at input 42 from AC voltage to DC voltage for the DC bus 50. The DC bus 50 is connected to the output of the converter section 40, and the DC voltage output by the converter exists between the positive rail 52 and the negative rail 54 of the DC bus 50.

[0032] Refer again Figure 1 A DC bus capacitor 55 is connected between the positive rail 52 and the negative rail 54 to reduce the amplitude of the ripple voltage generated by converting AC voltage to DC voltage. It should be understood that the DC bus capacitor 55 can be a single capacitor or multiple capacitors connected in parallel, series, or a combination thereof. The amplitude of the DC voltage between the negative rail 54 and the positive rail 52 is typically equal to the peak amplitude of the AC input voltage.

[0033] Other examples Figure 1 As shown, the DC bus charging circuit 57 can be connected to the DC bus 50. In the illustrated embodiment, the DC bus charging circuit 57 is connected between the output of the converter section 40 and the DC bus capacitor 55. Initially, the switch 56 is in the normally open state, thereby establishing a conduction path from the output of the converter section 40 to the positive rail 52 via the charging resistor 58. As understood in the art, the charging resistor 58, in conjunction with the DC bus capacitor 55, establishes a charging time constant to allow the DC voltage on the DC bus 50 to charge from zero volts DC at power supply to a voltage level approximately equal to the full DC bus voltage generated by rectifying the AC input voltage. When the DC voltage level reaches a preset charging level, the switch 56 closes, thereby bypassing the charging resistor 58 and allowing current to flow directly from the converter section 40 to the DC bus 50.

[0034] DC bus 50 is connected in series between converter section 40 and inverter section 100. One or more additional filters may be included between converter section 40 and inverter section 100 depending on the application requirements. Inverter section 100 includes gate-controlled switching elements as described for active converter 40, such as silicon-based and / or broadband materials for IGBTs or MOSFETs, or silicon gate-controlled thyristors (SCGTs) and gate-turn-off thyristors (GTOs) as known in the art for medium-voltage, high-power inter-cell transistors. See also... Figure 3 The inverter section 100 shown includes power metal-oxide-semiconductor field-effect transistors (MOSFETs) 106 and a reverse connection device 108. The reverse connection device 108 can be a freewheeling diode or an inherent diode of the MOSFET connected in pairs between the positive rail 52 and each phase of the output voltage (110U, 110V, 110W) and between the negative rail 54 and each phase of the output voltage. Each of the transistors 106 receives a switching signal 116 to selectively activate the transistor 106 and convert the DC voltage from the DC bus into a controlled three-phase output voltage for the motor 10. When activated, each transistor 106 connects a corresponding rail 102, 104 of the DC bus to an output phase 110, which in turn connects the inverter section 100 to the output terminal 160. One or more additional filters can be included between the output terminal of the inverter section 100 and the output terminal 160 of the motor driver 20, depending on application requirements.

[0035] A current sensing module 150 is disposed at the output of the motor driver. The current sensing module 150 includes a current sensor 152 on each phase of the AC output voltage. Each current sensor 152 generates a current feedback signal 154 for each phase of the AC output corresponding to the current present at the output 160 of the motor driver.

[0036] In operation, the motor driver 20 is configured to control the operation of the motor 10 connected at the output terminal 160. According to... Figure 1In the embodiments shown, processor 112 and driver circuitry 114 may include modules for controlling the operation of motor driver 20 and managing the execution of these modules. The embodiments shown are not intended to be limiting, and it should be understood that various features of each module may be executed by another module and / or various combinations of other modules may be included in processor 112 without departing from the scope of the invention. Modules may be stored programs that execute on one or more processors, logic circuits, or combinations thereof. Processor 112 may be implemented, for example, in a microprocessor, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or other such custom devices. Motor driver 20 also includes a memory device 115 that communicates with processor 112. Memory device 115 may include transient memory, non-transitory memory, or a combination thereof. Memory device 115 may be configured to store data and programs, the programs comprising a series of instructions executable by processor 112. It is contemplated that memory device 115 may be a single device, multiple devices, or may be incorporated, for example, as part of another device such as an application-specific integrated circuit (ASIC). Processor 112 communicates with memory 115 to read instructions and data as needed to control the operation of motor driver 20.

[0037] According to one embodiment of the invention, processor 112 receives a reference signal identifying a desired operation of motor 10 connected to motor driver 20. The reference signal may be, for example, a torque reference (T*), a speed reference (ω*), or a position reference (θ*). Processor 112 also receives a feedback signal indicating the current operation of motor driver 20. Motor driver 20 may include voltage and / or current sensors operatively connected to DC bus 50 and generating feedback signals corresponding to the magnitudes of voltage and / or current present on DC bus. Motor driver 20 may further include one or more current sensors 152 on each phase of the AC output voltage and one or more voltage sensors generating feedback signals 154 corresponding to the magnitudes of output current and / or voltage present at output terminal 160 of motor driver 20.

[0038] The processor 112 uses feedback signals and reference signals to control the operation of the inverter section 100 to generate an output voltage with the desired amplitude and frequency for the motor 10. See also... Figure 4An exemplary controller 120 for a motor driver 20 is shown. The controller 120 can be implemented as a series of instructions stored in a memory 115 of the motor driver 20 and executed on a processor 112. The controller 120 receives a position reference signal (θ*) 47 as input to a series of cascaded control loops. The controller 120 includes a position control loop, a speed control loop, and a current control loop. The control loops are shown as cascaded control loops, where the output of one control loop is provided as an input to another control loop. Various other control topologies can be contemplated for use within the motor driver 20.

[0039] In the position control loop, the position reference signal (θ*) 47 is compared with the position feedback signal (θ) 121 at the first summing junction 122. The position error signal is output from the first summing junction 122 and input to the position loop controller 124. According to the illustrated embodiment, the position loop controller 124 is a proportional-integral (PI) controller. Optionally, the position loop controller 124 may be just a proportional (P) controller or may also include a derivative (D) component. Each of the proportional (P), integral (I), and / or derivative (D) components of the position loop controller 124 includes a controller gain. The position loop controller gain is generally referred to as the position loop proportional gain (Kpp), position loop integral gain (Kpi), and position loop derivative gain (Kpd). The output of the position loop controller 124 is the speed reference signal (ω*).

[0040] In the speed control loop, a speed reference signal (ω*) is compared with a speed feedback signal (ω) at the second summing junction 126. The speed feedback signal (ω) is generated by differentiating the position feedback signal (θ), as shown in the differentiator block 123. The speed feedback signal (ω) can also be filtered by a speed filter block 125. A speed error signal is output from the second summing junction 126 and input to the speed loop controller 128. According to the illustrated embodiment, the speed loop controller 128 is a proportional-integral (PI) controller. Alternatively, the speed loop controller 128 may be just a proportional (P) controller or may also include a derivative (D) component. Each of the proportional (P), integral (I), and / or derivative (D) components of the speed loop controller 128 includes a controller gain. The speed loop controller gain is commonly referred to as the speed loop proportional gain (Kvp), speed loop integral gain (Kvi), and speed loop derivative gain (Kvd). The output of the speed loop controller 128 is an acceleration reference signal.

[0041] The controller 120 may also include a feedforward branch. According to the illustrated embodiment, the controller 120 includes feedforward branches for both the velocity element and the acceleration element. A position reference signal (θ*) 47 is passed through a first differentiating element 132 to obtain a velocity feedforward signal. The velocity feedforward signal is multiplied by a velocity feedforward gain (Kvff) 134 and combined with the velocity reference signal (ω*) and the velocity feedback signal (ω) at a second summing junction 126. The velocity feedforward signal is passed through a second differentiating element 136 to obtain an acceleration feedforward signal. The acceleration feedforward signal is multiplied by an acceleration feedforward gain (Kaff) 138 and combined with the acceleration reference signal at a third summing junction 140 to generate a torque reference signal (T*).

[0042] The torque reference signal (T*) output from the third summing junction 140 is further processed before generating the gating signal 116 for the inverter section 100. The torque reference signal (T*) is provided as input to a filter section 142, which may include one or more filters to remove unwanted components from the control system, including, for example, a low-pass filter to attenuate unwanted high-frequency components, or a notch filter to attenuate specific frequency components that have an undesirable effect on the controlled mechanical load. The output of the filter section 142 passes through a torque gain block 144. The torque gain block 144 may include a torque constant (Kt) that defines the relationship between the current supplied to the motor 10 and the torque output by the motor. The torque gain block 144 may include one or more additional gain elements, such as inertia-related gains, which are combined with the torque constant (Kt) to generate a desired current reference (I*) for the current regulator 146. The current regulator 146 receives a current feedback signal (Ifdbk) from the current sensor 152 at the output of the motor driver 20 and utilizes a current controller, which may include proportional, integral and / or derivative components for regulating the current in the motor 10.

[0043] The controller 120 receives current feedback signals (Ifdbk) as corresponding signals to the respective motors. As shown, the current feedback signal (Ifdbk) comprises multiple feedback signals, each corresponding to a current amplitude measured on one phase of the multiphase motor 10. For a three-phase motor, it is intended to measure the current amplitude in all three phases of the motor. Optionally, the current amplitude is measured in two phases of the motor, and the amplitude of the third phase is determined based on the amplitudes of the two measured phases. The measured feedback signals are then provided to a reference frame converter 145 within the controller 120 for use by the current regulator 146.

[0044] The reference frame converter 145 is configured to transform the current feedback signal from a static, physical reference frame to a rotating reference frame. The reference frame converter 145 receives the phase current measured in the static reference frame (Ifdbk) and the position feedback signal (θ) as input. The position feedback signal (θ) corresponds to the angular position of the motor 10. The position feedback signal (θ) can be the mechanical angular position of the motor or an electrical angular position corresponding to the electrical angle of the current supplied to the motor 10. However, the transformation between reference frames utilizes the electrical angle position of the current to convert the current feedback signal from the static reference frame to the rotating reference frame. Therefore, if the position feedback signal (θ) is the mechanical angular position of the motor, the reference frame converter 145 first converts the mechanical angular position of the motor to the electrical angle of the current according to the number of poles in the motor. In the static reference frame, the current applied to the motor 10 varies sinusoidally at the command frequency output by the motor controller 20. If the current feedback signal is converted to a reference frame rotating at the same frequency as the command frequency, the rotating reference frame is synchronized with the output current, and the current feedback signal becomes a "DC" value or a constant value.

[0045] The reference frame converter 145 is used to convert the measured current feedback signal into a synchronous reference frame that rotates at the fundamental frequency of the current output to the motor 10. As shown in Equations 1 and 2 below, the frame conversion uses the electrical angle of the motor and the measured current amplitude in the motor to generate a synchronous current feedback signal that rotates at the fundamental frequency of the motor. Equation 1 defines the current in the "d" axis, and Equation 2 defines the current in the "q" axis. Both currents are present when referring to the feedback current in the dq axis. The synchronous current feedback signal output from the reference frame converter 145 in the synchronous reference frame is also called the dq reference frame, which includes both the d-axis component and the q-axis component of the current. The synchronous current feedback signal is provided as an input to the current regulator 146 to generate a voltage reference signal, wherein the voltage reference signal generates the desired current reference I* when applied to the motor 10, and the current reference I* is input to the current regulator 146.

[0046]

[0047]

[0048] in,

[0049] θ = electrical angle;

[0050] i a = Current amplitude in phase "a" of the motor;

[0051] i b = The current amplitude in phase "b" of the motor; and

[0052] i c = The current amplitude in phase "c" of the motor.

[0053] The output of the current regulator 146 is provided to the gate driver 114, which in turn generates a switching signal 116 to the inverter section 100. The output of the gate driver 114 is shown as being provided to the control system's feed 130. In a motion control system, the feed 130 typically includes the inverter section 100 of the motor driver 20, the motor 10, a mechanical load, a position feedback device, and mechanical coupling between the motor and the mechanical load or between the motor and the position feedback device. The position feedback device generates a position feedback signal (θ) used by the controller 120.

[0054] Gate driver module 114 converts a voltage reference output from the current regulator into a desired output voltage with variable amplitude and frequency, wherein the amplitude and frequency are selected to produce the desired operation of motor 10. Gate driver module 114 then generates a strobe signal 116, using pulse width modulation (PWM) or other modulation techniques, to control the switching elements in inverter section 100 to produce the desired output voltage. Strobe signal 116 then enables / disables transistor 106 to provide the desired output voltage to motor 10, which in turn causes the desired operation of the mechanical load coupled to motor 10.

[0055] As previously mentioned, the current regulator and modulation routine execute at periodic intervals. In the past, both the current regulator and modulation routine executed at the same periodic interval. Increasing the frequency or decreasing the duration of the periodic intervals in which the current regulator and modulation routine execute allows the motor driver 20 to generate an output voltage waveform with a fundamental frequency component that more closely approximates a sine wave. Recent advances in power switching devices for the inverter 100 allow these devices to operate at higher modulation frequencies. However, simply increasing the frequency of the current regulator and modulation routine execution increases the computational burden on the processor 112. This invention decouples the execution of the current regulator from the modulation routine, allowing each to execute at its own periodic interval, allowing for an increase in the switching frequency without significantly increasing the computational burden on the processor 112.

[0056] Next turn Figure 5 An exemplary timing diagram 170 is shown for the periodic intervals used to execute the current regulator 146 and the modulation routine. A first interrupt 172 occurs at a first periodic interval 174T. I Execution, second interrupt 182 at second periodic interval 184T PWMExecution. According to the illustrated embodiment, the second interrupt 182 occurs at a frequency four times that of the first interrupt 172. The illustrated embodiment is intended to be exemplary and not limiting. It is contemplated that the second interrupt 182 may occur fewer or more than four times in each instance of the first interrupt 172. It is also contemplated that the motor driver 20 includes parameters storing the desired frequency of both the first and second frequencies, wherein the parameters are stored in memory 115 and can be configured according to application requirements. According to one embodiment of the invention, the first periodic frequency may be set between one and twenty kHz (1-20 kHz), and the second periodic frequency may be set greater than fifty kHz (>50 kHz). According to another embodiment of the invention, the first frequency may be set up to thirty-two kHz (1-32 kHz), and the second frequency may be in the range of fifty to two hundred kHz (50-200 kHz).

[0057] like Figure 5 To further illustrate, both the current regulator 146 and the modulation routine are executed for a portion of their respective periodic intervals, as indicated by the hash region within each interval. Therefore, the practical limitation on the upper limit frequency at which each periodic interval can be executed is the duration required to execute the current regulator or the modulation routine. If a dedicated processing core is allocated to each module, the current regulator or modulation routine can be used for up to the entire duration of the periodic interval in which it executes. According to one aspect of the invention, the gate driver 114 may be a dedicated processor, processing core, or other dedicated processing circuitry configured to alleviate the computational burden associated with the modulation routine by the processor 112. Although the current regulator 146 may be implemented as a dedicated processor or processing core, the current regulator is typically executed by a processor configured to also perform other tasks. Therefore, the frequency at which the current regulator 146 is executed will be set to be less than the frequency at which the modulation routine is executed.

[0058] Executing modulation routines with periodic intervals larger than the current regulator's periodic interval can have some adverse effects on the output voltage. (Refer to...) Figure 10 The diagram illustrates the three-phase output voltage generated by the motor driver 20 when the current regulator and modulation routine are decoupled. Each phase 190, 192, 194 of the output voltage has a ripple voltage superimposed on the fundamental frequency. The ripple voltage is a result of maintaining the voltage generated from the current regulator at the same reference level over multiple cycles of the modulation routine execution. (See below for further details.) Figure 11 The inventors have determined that extrapolating the voltage reference to provide a unique voltage reference for each cycle of the modulation routine eliminates voltage ripple. Figure 11 Each phase 191, 193, 195 corresponds to Figure 10 The same phases 190, 192, and 194, except in Figure 11During the operation of the motor driver 20, a unique voltage reference is provided to each cycle of the modulation routine. The processing for extrapolating the voltage reference is discussed below.

[0059] As described above, the current regulator 146 is typically configured to regulate the current in the dq reference frame. As shown in Equations 1 and 2, the frame transformation utilizes the measured electrical angle θ from the position feedback device to convert the measured three-phase current to the dq reference frame. The voltage reference signals generated by the current regulator are initially located in the dq reference frame. These voltage reference signals are located in the synchronous reference frame and correspond to the desired magnetic flux (d-axis) and torque (q-axis) generated in the motor. However, in order to supply voltage to the motor 10, this voltage must be a voltage output in the static reference frame.

[0060] A static reference frame can be represented as a three-phase voltage reference or a two-phase voltage reference. In a three-phase voltage reference, each phase of the voltage reference corresponds to one phase of the motor 10. A two-phase static reference frame is also called an α-β reference frame. Unlike a synchronous reference frame, where the reference frame rotates at the desired angular velocity of the motor and the voltage references on the d-axis and q-axis become constant or DC values, a static reference frame is static, and the voltage references on the α-axis and β-axis can be represented as vectors rotating about the origin of the α-axis and β-axis. The angle of the vector corresponds to the desired electrical angle of the motor 10, and the vector rotates about the α-axis and β-axis at the desired angular velocity of the motor 10. The conversion between the synchronous dq reference frame and the static α-β reference frame can be performed using knowledge of the electrical angle θ.

[0061] It is anticipated that the present invention can be implemented in multiple different reference frames. Furthermore, the conversion between reference frames is a function of the desired angular velocity of the motor 10 and the current electrical angle of the motor. Figures 6 to 9 Four exemplary embodiments of the present invention are illustrated. Each exemplary embodiment will be discussed in more detail below. However, it should be understood that these embodiments are illustrative of the inventive concept and not limiting of the implementation.

[0062] First turn Figure 6 The current regulator 146 may include a conversion block, or a separate system conversion block may exist after the current regulator 146 provides the first set of voltage reference signals 200 in a three-phase static reference frame. The three-phase voltage reference signals 200 can be converted to a two-phase static reference frame using a Clark transformation, which can be implemented in block 202. The Clark transformation converts the three-phase voltages in the abc reference frame to two-phase voltages in the α-β reference frame. Figure 6As shown below, the desired electrical angle θ and desired angular velocity ω of the motor 10 can be determined using the arctangent block 204 and the differential block 206. The differential block 206 is implemented by storing the desired electrical angle from the previous periodic interval θ(k-1) and finding the difference in electrical angle between consecutive periods to determine the angular velocity based on the duration of the periodic interval in which the differential block 206 is executed. Figure 6 In the embodiment shown, the three-phase to two-phase conversion 202, the arctangent block 204, and the differential block 206 are all located at the first periodic interval T. I The current regulator is used for execution. Two-phase static reference frame (v) α and v β The first voltage reference, the desired electrical angle θ, and the desired angular velocity ω are all provided to the modulation routine and kept constant until the first periodic interval T. I The next execution in the process.

[0063] Therefore, the modulation routine receives the first reference voltage, desired electrical angle, and desired angular velocity of the motor 10 as inputs. The modulation routine assumes that in the first periodic interval T I A constant angular velocity is required throughout the duration. For the first periodic interval T I The second periodic interval T is executed during one of the periods. PWM For each of these, the modulation routine extrapolates a second set of reference voltages. Voltage extrapolation block 210 uses a first voltage reference 220, which can be represented as a vector in the α-β reference system, and defines a series of second voltage references 230. According to the illustrated embodiment, the second periodic interval T... PWM With the first periodic interval T I It executes at four times the frequency.

[0064] The modulation routine utilizes a first voltage reference 220 and determines the desired electrical angle of the motor at each of the additional second periodic intervals during which the current regulator output remains constant, based on the desired angular velocity ω of the motor 10. See also... Figure 5 The current regulator executes during the first periodic interval 174 starting at time t0. During a portion of the interval indicated by the hash region, all instructions configured to be executed during that interval, including those of the current regulator 146, are executed. The current regulator generates a first voltage reference value 220, which is then used during subsequent first periodic intervals 174 starting at time t4. At time t4, the instructions configured to be executed during the first periodic interval 174, including those of the current regulator 146, are executed again, and a new first voltage reference 220 is generated by the current regulator for use during the next first periodic interval 174. This process is repeated continuously at each first periodic interval 174.

[0065] The modulation routine is then executed during each second periodic interval 184. In the case of a second periodic interval 184 starting from time t4, the modulation routine determines the expected electrical angle of motor 10 at each second periodic interval 184 from time t4 to t7. The change in electrical angle during one of the second periodic intervals can be achieved by multiplying the expected angular velocity ω by the second periodic interval T. PWM The duration is determined. The electrical angle θ received as input to the modulation routine is used as the electrical angle for the second periodic interval starting at time t4. The electrical angle for each subsequent second periodic interval is then increased by the expected change in each periodic interval. The first voltage reference value 220, shown as a vector in block 210, can be used as the first value in this set of second voltage reference values. The vector is then rotated by an electrical angle equal to the expected change in electrical angle for each second periodic interval 184 to generate three additional values ​​in the second set of voltage reference values ​​230A, 230B, and 230C. At the second periodic interval starting at time t5, the modulation routine uses the second vector 230A from this set of second voltage references. At the second periodic interval starting at time t6, the modulation routine uses the third vector 230B from this set of second voltage references. At the second periodic interval starting at time t7, the modulation routine uses the fourth vector 230C from this set of second voltage references. The voltage vectors in the α-β reference frame are then converted back to the three-phase reference voltages using the Clarke transform at block 212. The desired output voltage of each phase of the three-phase motor is used to generate a switching signal 116 for each switching device in the inverter section 100 of the motor driver 20.

[0066] Next turn Figure 7 The current regulator 146 may include a conversion block, or a separate system conversion block may exist after the current regulator 146 that provides the first set of voltage reference signals 201 in the two-phase static reference frame. Since the first set of voltage reference signals 201 is already in the α-β reference frame, it can be skipped. Figure 6 The initial steps of the Clarke transform 202 are shown. Both the inverse dicing block 204 and the differential block 206 are related to... Figure 6 The same approach discussed in the first periodic interval T I Execution in the middle. Two-phase static reference frame (v α and v β The first voltage reference, the desired electrical angle θ, and the desired angular velocity ω are all provided to the modulation routine and kept constant until the next first periodic interval T. I Execution. The modulation routine is performed at each second periodic interval T. PWM Execute here, in accordance with the above regarding Figure 6 The second set of voltage reference signals is extrapolated in the same manner as discussed.

[0067] Next turn Figure 8 It is anticipated that the output of the current regulator 146 in the dq synchronous reference frame can be provided as a first reference voltage 215. Similarly, the electrical angle θ obtained as a feedback signal from the encoder coupled to the motor 10 and used in the system converter 145 can be provided as the desired electrical angle of the output voltage. Provided as described above regarding... Figure 6 The differential block 206 under discussion is used to determine the desired angular velocity of the motor. The first voltage reference (v) in the two-phase synchronous reference frame... d and v q The desired electrical angle θ and desired angular velocity ω are both provided to the modulation routine and kept constant until the next first periodic interval T. I Execution. Optionally, to make the first periodic interval T I By minimizing additional calculations during this period, only the first voltage reference (v) in the two-phase synchronous reference frame needs to be provided to the modulation routine. d and v q The values ​​are the current regulator 146 output and the desired electrical angle θ. These values ​​are known either as the output of the current regulator 146 or as a feedback signal for the measurement, and no additional calculations are required to occur within the first periodic interval. The second periodic interval T can be... PWM The differential block 206 is executed to determine the desired angular velocity ω.

[0068] Therefore, as Figure 8 As shown, the modulation routine receives at least a first reference voltage and the desired electrical angle of motor 10 as inputs. The modulation may also receive a desired angular velocity as input, or optionally, the desired angular velocity may be determined. Because the first reference voltage is in a two-phase synchronous reference frame, the desired value of the first reference voltage does not rotate, and therefore remains constant in each of the four second periodic intervals 184 executed during each first periodic interval 174. Therefore, extrapolation block 211 only needs to determine the electrical angle difference Δθ(m) between consecutive second periodic intervals 184. At each consecutive period, the electrical angle increases by the desired electrical angle difference Δθ(m) between consecutive second periodic intervals 184. The reference voltage and the different electrical angles are provided to conversion block 213, which is configured to perform a Park conversion. The Park conversion switches the voltage reference between a two-phase synchronous frame and a three-phase static frame. The output of conversion block 213 is the three-phase reference voltage corresponding to the desired operation of motor 10.

[0069] Turn now Figure 9 It provides information related to the above. Figure 6 The first voltage reference signal 200 discussed is the same in a three-phase static reference frame. The three-phase voltage reference signal 200 can be converted to a two-phase static reference frame using the Clarke transform, which can be implemented in block 202. Figure 9In the embodiment shown, the desired electrical angle and angular velocity are at the first periodic interval T. I The previously determined values ​​during this period. As a result, the arctangent block 204 and differential block 206 discussed above are not required. The three-phase to two-phase transformation 202 occurs during the first periodic interval T. I The current regulator is used to execute the process again. Two-phase static reference frame (v) α and v β The first voltage reference, desired electrical angle θ, and desired angular velocity ω are provided again to the modulation routine and kept constant until the next first periodic interval T. I Execution. The modulation routine is performed at each second periodic interval T. PWM Execute here, in accordance with the above regarding Figure 6 The second set of voltage reference signals is extrapolated in the same manner as discussed.

[0070] like Figures 6 to 9 As shown, several different embodiments of the invention allow for the extrapolation of a second set of voltage references for use by the modulation routine at a second periodic interval, wherein the second set of voltage references is decoupled from the execution of the current regulator during the first periodic interval. An additional voltage reference signal is extrapolated using the expected electrical angle of the motor in each instance of the second periodic interval, based on a first voltage reference signal output from the current regulator.

[0071] It should be understood that the invention is not limited in its application to the construction details and arrangement of components set forth herein. The invention can have other embodiments and can be practiced or performed in various ways. Variations and modifications to the foregoing are within the scope of the invention. It should also be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more individual features mentioned or apparent from the text and / or drawings. All these different combinations constitute various alternative aspects of the invention. The embodiments described herein explain the known best mode for practicing the invention and will enable those skilled in the art to utilize the invention.

[0072] Various embodiments have been described in the preceding description with reference to the accompanying drawings. However, it will be apparent that various modifications and alterations can be made thereto, and additional embodiments can be implemented, without departing from the broader scope of the invention as set forth in the appended claims. Therefore, the description and drawings are to be considered illustrative rather than restrictive.

Claims

1. An inverter configured to operate at a high switching frequency, the inverter comprising: A DC bus, configured to have a DC voltage present on the DC bus; The output terminal is configured to provide AC voltage to a motor that can be operatively connected to the inverter; A plurality of switching devices operatively connected between the DC bus and the output terminal, wherein the plurality of switching devices are selectively controlled to convert the DC voltage to the AC voltage; and The processing unit is configured to execute a series of instructions to: A first reference voltage is determined at a first update rate, the first reference voltage corresponding to the desired AC voltage supplied to the motor. A plurality of second reference voltages are determined at a second update rate, wherein the second update rate is at least twice the first update rate, and each of the plurality of second reference voltages is a function of the first reference voltage and the desired rotational speed of the motor.

2. The inverter according to claim 1, wherein, The processing unit further includes: A first processing core, configured to determine the first reference voltage at the first update rate; and A second processing core is configured to determine the plurality of second reference voltages at the second update rate.

3. The inverter according to claim 1, wherein, The desired rotational speed of the motor is defined by an angular velocity reference or an angular position reference.

4. The inverter according to claim 1, wherein: The first reference voltage is the three-phase voltage in a static reference frame. During each periodic interval executed at the first update rate, the angular position of the first reference voltage is stored in the inverter's memory, and The desired rotational speed of the motor is determined based on the value of the angular position of the first reference voltage stored in the memory at a previous periodic interval and the value of the angular position of the first reference voltage determined at the first update rate during the current periodic interval.

5. The inverter according to claim 1, wherein: The first reference voltage is a two-phase voltage in a static reference frame. During each periodic interval executed at the first update rate, the angular position of the first reference voltage is stored in the inverter's memory, and The desired rotational speed of the motor is determined based on the value of the angular position of the first reference voltage stored in the memory at a previous periodic interval and the value of the angular position of the first reference voltage determined at the first update rate during the current periodic interval.

6. The inverter of claim 1, further comprising an input terminal configured to receive a position feedback signal from a position feedback device operatively connected to the motor, wherein, The position feedback signal corresponds to the angular position of the motor.

7. The inverter according to claim 6, wherein: The first reference voltage is a two-phase voltage in a synchronous reference frame, and The desired rotational speed of the motor is determined based on the position feedback signal.

8. The inverter according to claim 6, wherein: The first reference voltage is a three-phase voltage in a static reference frame, and The desired rotational speed of the motor is determined based on the position feedback signal.

9. A method for operating an inverter at a high switching frequency, the method comprising the steps of: A first reference voltage is determined for an AC motor that can be operatively connected to the output of the inverter, wherein the first reference voltage is determined during a first periodic interval; and A plurality of second reference voltages are determined for the AC motor, wherein: Each of the plurality of second reference voltages is determined at a second periodic interval. The second periodic interval is shorter than the first periodic interval, and Each of the plurality of second reference voltages is determined based on the first reference voltage and the desired rotational speed of the motor.

10. The method according to claim 9, wherein, The desired rotational speed of the motor is defined by an angular velocity reference or an angular position reference.

11. The method according to claim 9, wherein, The first reference voltage is a three-phase voltage in a static reference frame, and the method further includes the following steps: During each periodic interval executed at the first update rate, the value of the angular position of the first reference voltage is stored in the inverter's memory; and The desired rotational speed of the motor is determined based on the angular position of the first reference voltage stored in the memory at a previous periodic interval and the angular position of the first reference voltage determined at the first update rate during the current periodic interval.

12. The method according to claim 9, wherein, The first reference voltage is a two-phase voltage in a static reference frame, and the method further includes the following steps: During each periodic interval executed at the first update rate, the value of the angular position of the first reference voltage is stored in the inverter's memory; and The desired rotational speed of the motor is determined based on the angular position of the first reference voltage stored in the memory at a previous periodic interval and the angular position of the first reference voltage determined at the first update rate during the current periodic interval.

13. The method of claim 9, further comprising the step of: The inverter receives a position feedback signal from a position feedback device operatively connected to the motor at its input, wherein the position feedback signal corresponds to the angular position of the motor.

14. The method according to claim 13, wherein, The first reference voltage is a two-phase voltage in a synchronous reference system, and the method further includes the following step: determining the desired rotational speed of the motor based on the position feedback signal.

15. The method according to claim 13, wherein, The first reference voltage is a three-phase voltage in a static reference frame, and the method further includes the following step: determining the desired rotational speed of the motor based on the position feedback signal.

16. An inverter configured to operate at a high switching frequency, the inverter comprising: A DC bus, configured to have a DC voltage present on the DC bus; The output terminal is configured to provide AC voltage to a motor that can be operatively connected to the inverter; A plurality of switching devices operatively connected between the DC bus and the output terminal, wherein the plurality of switching devices are selectively controlled to convert the DC voltage to the AC voltage; and The processing unit is configured to execute a series of instructions to: The current regulator is executed at a first update rate, wherein the current regulator generates a first reference voltage, and The modulation routine is executed at the second update rate, wherein: The second update rate is at least twice the first update rate, and The modulation routine generates each of a plurality of second reference voltages based on the first reference voltage and the desired rotational speed of the motor.

17. The inverter according to claim 16, wherein: The current regulator output serves as the first reference voltage for the three-phase voltages in the static reference frame. The processing unit is also configured to perform system transformation. The system transformation provides the first reference voltage to the modulation routine in the two-phase static reference system. The system transformation provides the modulation routine with the angular position and angular velocity of the first reference voltage, and The modulation routine generates the plurality of second reference voltages based on the first reference voltage in the two-phase static reference frame and the angular position and angular velocity of the first reference voltage.

18. The inverter according to claim 16, wherein: The current regulator outputs the first reference voltage, which serves as the two-phase voltage in the static reference frame. The angular position and angular velocity corresponding to the two-phase voltages are provided to the modulation routine, and The modulation routine generates the plurality of second reference voltages based on the first reference voltage in the two-phase static reference frame and the angular position and angular velocity of the first reference voltage.

19. The inverter according to claim 16, wherein: The current regulator output serves as the first reference voltage for the two-phase voltages in the synchronous reference system. The angular position and angular velocity corresponding to the two-phase voltages are provided to the modulation routine, and The modulation routine generates the plurality of second reference voltages based on the first reference voltage in the two-phase synchronous reference frame and the angular position and angular velocity of the first reference voltage.

20. The inverter according to claim 16, wherein: The current regulator output serves as the first reference voltage for the three-phase voltages in the static reference frame. The processing unit is also configured to perform system transformation. The system transformation provides the first reference voltage to the modulation routine in the two-phase reference system. The system transformation provides the modulation routine with the angular position and angular velocity of the first reference voltage, and The modulation routine generates the plurality of second reference voltages based on the first reference voltage in the two-phase reference frame and the angular position and angular velocity of the first reference voltage.

Images