Motor drive system and corresponding method

Abstract

The invention provides a motor driving system and a corresponding method. The motor drive system may be configured to output a first drive signal, a second drive signal, and a third drive signal for driving the motor. The motor drive system may include a first power converter configured to generate a first drive signal, and a second power converter configured to generate a second drive signal. The motor drive system may include a third power converter configured to generate a third drive signal. Some or all of these power converters may be implemented as synchronous buck power converters.

Description

Technical Field

[0001] The present disclosure relates to a motor drive system for an electric motor. In particular, the present disclosure relates to a motor drive system for a brushless direct current (BLDC) motor such as a permanent magnet synchronous motor (PMSM). Background Art

[0002] In contrast to the 6-step commutation method used in BLDC drives, field-oriented motor control is a popular choice in applications where low torque ripple is desired. In addition, in inverter-based motor drives, the phase current ripple is inversely proportional to the pulse width modulation (PWM) switching frequency. Phase current ripple causes motor losses, which reduces the efficiency of the motor and increases the temperature of the motor. For precision servo drives that require high position accuracy, torque ripple has a negative impact on static position accuracy. The motor phase current ripple must be reduced to reduce the torque ripple of a given motor, which can be achieved by increasing the inverter PWM switching frequency. However, higher switching frequencies lead to higher switching losses in MOSFET-based inverter drives. In order to minimize switching losses at higher frequencies, GaN-based motor drives are used. Higher switching frequencies provide significantly reduced current ripple, resulting in lower RMS currents, resulting in less winding heating and higher motor efficiency. However, GaN-based motor drives can cause high dv / dt, and therefore, it introduces a lot of design work. Furthermore, higher dv / dt is not good for the motor, so additional filtering circuits are required before feeding it to the motor terminals. In conventional motor drive systems, an inverter is used to drive the motor, and the power transfer from the source to the motor is controlled by controlling the duty cycle of the MOSFET / IGBT / switch via switches. In brushless DC (BLDC) motors, a 16kHz to 20kHz switching frequency is typically used to drive the switches in the inverter. In this conventional approach, higher switching losses reduce the overall system efficiency, and even the motor terminals observe switching voltages that cause higher DC bus current ripple and acoustic noise in the motor. In order to control power and speed, the duty cycle is controlled within the MOSFET of the inverter, so switches are required in the conventional approach, but these switches cause the above consequences and higher torque ripple. One way to reduce torque ripple is to increase the switching frequency, in which case GaN is a popular choice.

[0003] In the following description, the limitations of current GaN-based motor drives are discussed. First, faster switching using GaN in the inverter requires a fast control loop, which requires a mid / high range MCU with a specific set of peripherals, such as high-resolution PWM and fast ADC, which increases the cost. Second, faster switching using GaN brings more challenges to inverter design because it may bring many problems related to EMI, ringing, high dv / dt, etc. Third, GaN switching at high switching frequency produces higher voltage gradient dv / dt, which - if directly connected to the motor terminals - may cause winding damage and cause noise problems. In addition, fourth, higher voltage gradient dv / dt may degrade the winding insulation, so they need to be avoided. High-frequency switching using GaN can produce higher dv / dt and can easily cross the allowed range, so additional LCR EMI output filters may usually be required, which increases the cost of the solution.

[0004] The object of the present disclosure is to overcome the above problems by providing a novel motor drive system. For example, the object is to eliminate the high dv / dt switching pulse voltage entering the motor terminals. It is expected that no switching harmonics will be observed at the motor terminals. Summary of the invention

[0005] According to one aspect, a motor drive system is provided. The motor drive system may be configured to output a first drive signal, a second drive signal, and a third drive signal for driving a motor. The motor drive system may include: a first power converter configured to generate the first drive signal, and a second power converter configured to generate the second drive signal. The motor drive system may include a third power converter configured to generate a third drive signal.

[0006] The first power converter, the second power converter and the third power converter may be connected in parallel between the first supply terminal and the second supply terminal of the power supply. In other words, if three power converters are implemented, the motor drive system may emulate a B6 inverter system.

[0007] As an alternative, the motor drive system may include only a first power converter and a second power converter. Instead of the third power converter, the motor drive system may include a third branch that may be connected between the first supply terminal and the second supply terminal of the power supply. The third branch may include a capacitor, and the third drive signal may be provided at the midpoint of the third branch. Therefore, using only two real power converters, the motor drive system can simulate the B4 inverter system as a cost-optimized system solution with a reduced number of circuit components (e.g., switches and inductors).

[0008] The power converter may be a DC / DC power converter. The power converters may have the same topology. In general, the power converter may be based on any kind of isolated or non-isolated topology. For example, the power converter may be based on a non-isolated topology such as buck, boost, buck-boost, SEPIC or switched capacitor topology. Alternatively, the power converter may be based on an isolated topology, such as a flyback topology or any kind of resonant topology (eg an LLC topology).

[0009] The motor may be, for example, a brushless direct current (BLDC) motor. Specifically, the motor may be a permanent magnet synchronous motor (PMSM). Some functions of the motor drive system may be implemented in hardware, and some functions may be implemented in software.

[0010] The power converter may be a switch mode power supply SMPS, and the switches of the SMPS may be implemented using gallium nitride GaN technology. Some or all switches of the SMPS may be implemented using GaN technology. Switches implemented using GaN technology may switch at a switching frequency of 1 MHz or higher.

[0011] In particular, the power converter can be a synchronous buck power converter. Each synchronous buck power converter can include a high-side switch element, which is coupled between a first input terminal and a switch node of the synchronous buck power converter. Each synchronous buck power converter can include a low-side switch element, which is coupled between a switch node and a second input terminal of the synchronous buck power converter. Each synchronous buck power converter can include an inductor, which is coupled between a switch node and an output terminal of the synchronous buck power converter.

[0012] As already mentioned in the foregoing description, the first power converter, the second power converter and the third power converter may be connected in parallel between the first supply terminal and the second supply terminal of the power supply. To this end, the first input terminal of each synchronous buck power converter may be coupled to the first supply terminal, and the second input terminal of each synchronous buck power converter may be coupled to the second supply terminal.

[0013] The switching element can be implemented using any suitable device, such as a metal oxide semiconductor field effect transistor MOSFET, an insulated gate bipolar transistor IGBT, a MOS gate thyristor or any other suitable power device. Some or all of the switching elements can be implemented using GaN technology. Specifically, the switching element can be implemented using III-V compound semiconductor materials for implementing, for example, GaN high electron mobility transistors HEMT. Each switching element can have a gate to which a corresponding drive voltage / current or control signal can be applied to turn on the switching element (i.e., close the switching element) or turn off the switching element (i.e., open the switching element). Without loss of generality, it is preferred that the switching elements of the synchronous buck power converter can be implemented using GaN technology, and they can be switched at a relatively high frequency, such as 1MHz.

[0014] Each synchronous buck power converter may include an output capacitor coupled between an output terminal of the synchronous buck power converter and a second input terminal of the corresponding synchronous buck power converter.

[0015] At the output of the first synchronous buck power converter, a first drive signal may be provided.At the output of the second synchronous buck power converter, a second drive signal may be provided.At the output of the third synchronous buck power converter, a third drive signal may be provided.

[0016] Each power converter can also be implemented using a multi-level topology. For example, the power converter can be a synchronous multi-level buck power converter, which includes an additional high-side switch element (which can be coupled between the first input terminal and the high-side switch element), an additional low-side switch element (which can be coupled between the low-side switch element and the second input terminal) and a flying capacitor. The flying capacitor can be coupled between a first node (located between the additional high-side switch element and the high-side switch element) and a second node (located between the additional low-side switch element and the low-side switch element).

[0017] The first drive signal, the second drive signal, and the third drive signal may have a continuous periodic shape and be phase-shifted by 120 degrees relative to each other. More specifically, each drive signal may have a sinusoidal waveform shape superimposed with a third harmonic.

[0018] The motor drive system can be configured to output a first drive signal at a first output node and output a second drive signal at a second output node, and the voltage between the first output node and the second output node can have a sinusoidal shape. Here, a sinusoidal shape means a shape similar to a sinusoidal waveform (possibly with a slight deviation). The motor drive system can be configured to output a third drive signal at a third output node. The voltage between the first output node and the third output node can have a sinusoidal shape, and the voltage between the second output node and the third output node can have a sinusoidal shape.

[0019] The first drive voltage, the second drive voltage and the third drive voltage can be directly connected to the three-phase terminals of the motor. In this way, high-frequency switching at the phase terminals is avoided. Alternatively, the smooth and continuous drive signals generated by the three power converters can be directly applied to the phase terminals of the motor. Unlike the prior art solutions, there may be no inverter circuit directly connected to the phase terminals.

[0020] The first drive signal, the second drive signal and the third drive signal may be periodic oscillation signals whose instantaneous frequency corresponds to the instantaneous rotation frequency of the motor. In other words, the oscillation of the drive signal may be synchronized with the rotation of the motor (or more specifically, the rotation of the rotor) (if applicable, with a leading angle or a lagging angle as will be described later).

[0021] The motor drive system may be configured to generate a first drive signal, a second drive signal, and a third drive signal for controlling a desired speed or a desired torque of the motor.

[0022] The first power converter may be configured to generate a first drive signal based on a first voltage reference and an output voltage sensed at the output terminal of the first power converter. Similarly, the second power converter may be configured to generate a second drive signal based on a second voltage reference and an output voltage sensed at the output terminal of the second power converter. The third power converter may be configured to generate a third drive signal based on a third voltage reference and an output voltage sensed at the output terminal of the third power converter. Typically, the functions of the second power converter and the third power converter may be similar or identical to those of the first power converter, and repeated descriptions will be omitted in the following description.

[0023] The first power converter may be configured to compare the first voltage reference with the sensed output voltage, for example using a comparator circuit. Alternatively or additionally, the first power converter may be configured to determine the difference between the first voltage reference and the sensed output voltage. The first power converter may include a proportional integral PI controller. The first power converter may also include a pulse width modulation PWM generator for generating a switching signal for controlling a switch of the first power converter.

[0024] The motor drive system may include a voltage sensing unit configured to determine the sensed output voltage based on the voltage at the output terminal of the first power converter. Similarly, the voltage sensing unit may be configured to sense the output voltage at the output terminal of the second power converter and the output terminal of the third power converter, respectively.

[0025] The motor drive system may be configured to determine a first voltage reference based on the rotor position information of the motor. Similarly, the motor drive system may be configured to determine a second voltage reference and a third voltage reference based on the rotor position information of the motor. The motor drive system may include a rotor position determination unit configured to determine the rotor position information of the motor. For example, the rotor position information of the motor may be determined by means of a Hall sensor, wherein the Hall sensor may or may not be part of the claimed rotor position determination unit. Alternatively, the rotor position determination unit may be configured to determine the rotor position information of the motor in a sensorless manner based on back electromotive force (BEMF) information or other observer models. For example, the rotor position information may include rotor angle or sector information, i.e., information identifying the current sector of the total number of sectors in which the rotor may be located.

[0026] The motor drive system can be configured to determine the first angle reference, the second angle reference and the third angle reference based on the rotor position information, and the first angle reference, the second angle reference and the third angle reference can be periodic signals with a phase shift of 120 degrees. The motor drive system can be configured to determine the first angle reference, the second angle reference and the third angle reference based on the space vector modulation SVM theory.

[0027] The motor drive system may be configured to determine a first voltage reference by multiplying an initial voltage reference by a first angle reference. The motor drive system may be configured to determine a second voltage reference by multiplying an initial voltage reference by a second angle reference. The motor drive system may be configured to determine a third voltage reference by multiplying an initial voltage reference by a third angle reference.

[0028] In voltage mode control, the initial voltage reference may be a user-defined value fed to the three power converters. Alternatively, in torque mode control, the initial voltage reference may be determined based on the torque reference and the sensed motor current. For example, the motor drive system may include a current sensor for determining the sensed motor current. The motor drive system may also include a torque PI controller for determining the initial voltage reference in torque mode control.

[0029] In summary, the proposed solution can eliminate the high dv / dt switching pulse voltages into the motor terminals. As a result, the motor terminals can observe no switching harmonics and the system efficiency is improved, thus delivering higher output power. By using three synchronous buck converters composed of GaN switches, scalar control can be achieved in the abc (each individual phase) domain, thus reducing the computational load on the MCU compared to conventional high switching frequency drives. But at the same time, similar / better performance of conventional GaN-based inverters can be achieved.

[0030] According to another aspect, a method for driving a motor is proposed. The method may include steps corresponding to the functional features of the motor drive system described throughout the present disclosure. The method may include: generating a first drive signal by a first power converter, and generating a second drive signal by a second power converter. The method may include generating a third drive signal by a third power converter. The first power converter, the second power converter, and the third power converter may be a switch mode power supply device SMPS, and the switch of the SMPS may be implemented using gallium nitride GaN technology. The power converter may be a synchronous buck power converter. Each synchronous buck power converter may include: a high-side switching element coupled between a first input terminal and a switch node of the synchronous buck power converter; a low-side switching element coupled between the switch node and the second input terminal of the synchronous buck power converter; and an inductor coupled between the switch node and the output terminal of the synchronous buck power converter. The first drive signal, the second drive signal, and the third drive signal may have a continuous periodic shape and may be phase-shifted by 120 degrees relative to each other.

[0031] The method may include outputting, by the motor drive system, a first drive signal at a first output node and a second drive signal at a second output node, and a voltage between the first output node and the second output node may have a sinusoidal shape.

[0032] The first drive signal, the second drive signal and the third drive signal may be periodic oscillation signals whose instantaneous frequency corresponds to the instantaneous rotation frequency of the motor.

[0033] The method may include generating, by the motor drive system, a first drive signal, a second drive signal, and a third drive signal for controlling a desired speed or desired torque of the motor. The method may include generating, by the first power converter, a first drive signal based on a first voltage reference and an output voltage sensed at an output terminal of the first power converter. The method may include determining a first voltage reference based on rotor position information of the motor. The method may include determining a first angle reference, a second angle reference, and a third angle reference based on the rotor position information, wherein the first angle reference, the second angle reference, and the third angle reference may be periodic signals with a phase shift of 120 degrees. The method may include determining a first voltage reference by multiplying an initial voltage reference by a first angle reference.

[0034] It should be noted that the methods and systems as outlined in the present disclosure (including preferred embodiments thereof) can be used alone or in combination with other methods and systems described in the present disclosure. In addition, the features outlined in the context of the system also apply to the corresponding method. Furthermore, all aspects of the methods and systems outlined in the present disclosure can be combined arbitrarily. In particular, the features in the claims can be combined with each other in any manner.

[0035] In the present disclosure, the term "coupled" or "coupled" refers to elements that are in electrical communication with each other, whether directly connected, for example, via a wire, or indirectly connected via other circuit elements between them. For example, even if there is a circuit element such as a switch (which can be turned on and off) between the two elements, they can be said to be coupled. On the other hand, the term "connected" or "connected" refers to elements being directly electrically connected to each other, for example, via a wire, and no circuit element is positioned between them. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention is illustrated by way of example, and not by way of limitation, in the accompanying drawings in which like references indicate similar or identical elements, and in which:

[0037] Figure 1 Two example motor drives according to the present invention are shown,

[0038] Figure 2 shows a more detailed view of an example motor drive,

[0039] Figure 3 shows yet another more detailed view of an example motor drive,

[0040] Figure 4 An exemplary implementation of a PI controller using a comparator operational amplifier is shown,

[0041] Figure 5An alternative implementation of a voltage reference for a voltage regulator using a conversion is shown,

[0042] Figure 6 shows the simulation results of voltage mode control,

[0043] Figure 7 Additional simulation results for voltage mode control are shown,

[0044] Figure 8 Still other simulation results of voltage mode control are shown,

[0045] Fig. 9 shows the simulation results of a ramp load change in voltage mode control, and

[0046] Fig.10 Additional simulation results for ramped load changes in voltage mode control are shown. DETAILED DESCRIPTION

[0047] Figure 1 Two example motor drives according to the present invention are shown. Figure 1 In the upper part of , a first exemplary motor drive system 1 is shown. The motor drive system 1 outputs a first drive signal, a second drive signal and a third drive signal for driving a motor 14. The phase terminals of the motor 14 are respectively represented as A, B and C. The motor drive system 1 includes: a first power converter 11, which is configured to generate a first drive signal; and a second power converter 12, which is configured to generate a second drive signal. In addition, the motor drive system 1 includes a third power converter 13 configured to generate a third drive signal.

[0048] exist Figure 1 In the lower part of FIG. 1 , a second exemplary motor drive system 1 is shown with only two power converters 11 and 12. A third branch of the motor drive system may include capacitors 15 and 16, and a third drive signal may be provided at a midpoint of the third branch.

[0049] Figure 2 A more detailed view of an example motor drive 1 is shown. In fact, Figure 2 All components shown in the figure except the motor 14 may form part of the motor drive system 1 of the present invention.

[0050] The motor drive system 1 includes voltage regulators 110, 120, 130 for implementing respective power converters. At the output of each voltage regulator, a sensing circuit 112, 122, 132 is used to sense the output voltage across the capacitors 111, 121, 131. At nodes 113, 123, 133, the sensed output voltage is subtracted from the respective voltage reference. Subsequently, a voltage PI controller and a PWM generator generate switching signals for controlling the switches of the voltage regulators 110, 120, 130.

[0051] The motor drive system determines the voltage reference by multiplying (at nodes 114, 124, 134) the initial voltage reference with the angle references ref1, ref2, and ref3 generated at the angle reference generation module 17. The rotor position determination unit 18 determines the rotor angle (rotor position information) and provides this information to the angle reference generation module 17.

[0052] In voltage mode control, the initial voltage reference can be a user-defined value fed to the three power converters (in Figure 2 denoted as user voltage reference in ). Alternatively, in torque mode control, the initial voltage reference can be determined based on the torque reference and the sensed motor current. For example, the motor drive system may include a current sensor 19 for determining the sensed motor current. The motor drive system may also include a torque PI controller 20 for determining the initial voltage reference in torque mode control.

[0053] Figure 3 A further more detailed view of an example motor drive is shown. Figure 2 compared to, Figure 3 A single switch 31 to 36 is shown for an exemplary implementation as a synchronous buck converter.

[0054] The proposed solution eliminates the high frequency switching at the motor terminals by using three GaN based synchronous buck converters connected in parallel at the source port, and each output DC voltage from each synchronous buck converter is connected to the corresponding three-phase terminal of the motor, as shown in FIG. Figure 3As shown. Each of the three synchronous buck converters generates a sinusoidal output voltage signal based on SVM theory with a 120-degree phase shift of the third harmonic component, so that when these output terminals are connected to the three-phase motor terminals, each phase-to-phase terminal voltage is a pure sinusoidal voltage waveform. Therefore, the desired voltage waveform is applied at the motor phase terminals without any switching. The buck converter is composed of GaN devices and switches at a very high switching frequency, so the required inductance and output capacitance are low. Therefore, a smooth and ripple-free output waveform can be constructed from these GaN-based synchronous buck converters, and high-frequency switching at the motor terminals is eliminated. The speed of the motor can be controlled by controlling the output voltage of the buck converter, and the torque output to the motor can be controlled by controlling the duty cycle of the buck converter to provide the required current. The rotor angle information may be required to generate a voltage reference based on SVM theory for the buck converter, which can be extracted from the Hall signal. Alternatively, in sensorless control, the rotor angle information can be determined based on a BEMF estimator / PLL estimator. Here, the voltage to the PMSM motor is controlled directly instead of the duty cycle to the inverter switches, which is how PWM switching at the motor terminals is avoided. However, the power transfer is controlled by the buck converter. The idea of ​​controlling the duty cycle to transfer power or adjust the speed is replaced here by changing the voltage output of the buck converter to adjust to the required speed.

[0055] Each synchronous buck converter consists of two GaN devices (such as Figure 3 The invention is composed of a GaN device switching at a high switching frequency (e.g., 1 MHz) and operating in voltage mode control. The voltage reference for the buck converter can be a user voltage reference (voltage mode control) or a voltage reference from a torque PI controller (torque mode control). The speed loop generates a torque reference for the torque PI controller. Current limiting can be applied by sensing the online DC input current, which can also be used as a torque reference. The rotor angle information is fed into the SVM block to calculate three 120 degree phase offset references, which are fed to each of the three buck converters as a voltage reference for their control when multiplied by the generated voltage reference from the torque mode control or voltage mode control, and thus three 120 degree phase offset gates are generated for the GaN switch. The SVM block can also use phase angle lead / lag for flux weakening or enhancement operation.

[0056] The output voltage nodes of these synchronous buck converters are directly connected to the three-phase terminals of the PMSM motor. This architecture is different compared to conventional VSIs because here the GaN switches are switched at a high switching frequency (similar to conventional VSIs), however the motor terminals are not connected to these device terminals, the motor terminals are connected at each output node of the buck converter. Each buck converter follows a 120 degree phase shifted reference (from the SVM block multiplied with the voltage PI or torque PI output), and therefore the motor terminals observe a smooth sinusoidal voltage at the fundamental frequency (speed of the motor).

[0057] Since the buck converter is driven at a very high switching frequency using GaN devices, the required buck inductor is very small, which makes the solution very compact and can be used in drones / cordless power tools or can be placed directly on the motor. In addition, by using GaN devices at 1MHz or higher, the size of the required bus capacitor is also significantly reduced. Due to its basic buck converter control, it can be easily implemented and can be implemented at very high switching frequencies even with low-end controllers. For applications that require higher inrush current, a large-capacitance capacitor can be used at the input to reduce the voltage ripple on the source / battery. This ripple has no effect on the torque ripple, which depends on the size of the output capacitor at the buck converter, which is small due to the high-frequency switching operation. If the application has such a requirement, a diode can be connected at the source to prevent current from returning to the source. Otherwise, bidirectional power flow can be used to support regenerative braking of the motor and reverse (boost direction) replenishment of the battery.

[0058] In summary, the proposed solution eliminates high frequency switching at the motor terminals and instead smoothly controls the voltage of the inverter, which results in smaller ripple in the DC bus current and thus improved system level efficiency. In addition, for motor control, high control loop bandwidth is not required, so the CPU load can be significantly reduced.

[0059] The advantages of the motor drive type proposed according to the present disclosure can be summarized as follows:

[0060] No high switching frequency is injected into the motor terminals.

[0061] Very low dv / dt at the motor terminals, so ringing, EMI or torque ripple problems can be easily eliminated.

[0062] No additional filtering circuits are required to limit high dv / dt, thus reducing the overall cost.

[0063] No mid / high-end MCU is required, as the control loop frequency can be kept low. The MCU does not require any specialized peripheral set (e.g., high-resolution PWM or fast ADC) to drive the motor, so the solution cost is optimized.

[0064] Compared with CSI, the dynamic response is fast because the voltage is directly controlled.

[0065] The use of scalar control eliminates multiple transformations, so the computational load on the MCU is significantly reduced compared to conventional implementations of FOC.

[0066] The DC bulk capacitance can be lower in this architecture compared to conventional VSIs, since the torque ripple does not depend on this capacitance but on the buck capacitance which is low due to the high switching frequency operation.

[0067] In sensor control, only rotor angle information is required from the motor end. Voltage sensing is required only at the buck regulator side and only line current sensing is required at the DC input side. Stator current sensing is not required in this architecture. The buck inductor current is directly connected to the stator winding, so all three stator currents are available without the need for any shunt resistors.

[0068] Typically, a buck converter has a limitation in generating 100% output voltage and is limited by the duty cycle in generating the minimum voltage. Therefore, by using angle lead / lag in the SVM block, the speed range on both the high and low ends can be further extended, which also has a positive effect on deceleration (fast deceleration with lag angle).

[0069] The proposed concept can be implemented using three GaN-based synchronous buck converters (connected in parallel to the source) plus an MCU to control the converters and the motor, as shown in Figure 3 An alternative to the buck converter topology could be any other voltage regulator topology.

[0070] It is also possible to implement the PI voltage and current control of the buck converter by using only the comparator OP AMP to reduce the computational load on the MCU and is much easier and hence also reduces the cost of the MCU. Figure 4 An exemplary implementation of a PI controller using a comparator operational amplifier is shown.

[0071] In conventional field oriented control (vector control) methods, high-end MCUs need to perform multiple transformations (Clarke transform, park transform, inverse Clarke transform, and park transform), which limits its application use. With the proposed idea, scalar control is used to avoid multiple transformations, thereby reducing the computational burden on the MCU. However, an alternative method for generating a reference (i.e., a first angle reference, a second angle reference, and a third angle reference) for a 120 degree phase shift of a buck converter is to use a scalar control method such as Figure 5 The transformation shown. Figure 5 An alternative implementation of a voltage reference for a voltage regulator using switching (ie, vector control) is shown.

[0072] Currently, with the buck regulator, the speed range can be a maximum at 95% to 97% of the input voltage to a minimum at 1.5% to 2% of the input voltage. To achieve higher speeds, the maximum speed using the buck converter is less than 100% due to losses in the buck converter and practical limitations of the buck converter. To achieve the rated motor speed, the angle lead feature (lead angle - flux weakening) can be used. To overcome the buck minimum voltage output that limits the minimum achievable speed, an angle lead feature (lag angle) can be introduced to make a decrement (flux enhancement) in the control signal. The same feature can also be used to make faster decelerations.

[0073] The basic idea behind the proposed method is to eliminate fast switching, thereby eliminating high dv / dt fed directly into the motor terminals, and to achieve field-oriented control, i.e., scalar control, in a simplified manner that avoids multiple transformations. The proposed solution removes the switching source at the motor terminals. A voltage reference based on SVM theory is fed to three 120-degree phase-shifted synchronous buck converters consisting of GaN devices to produce a sinusoidal voltage output between the motor phase terminals, so that the torque ripple is negligible due to field-oriented control. Only rotor angle sensing is required to provide a voltage reference to the buck regulator and for angle propulsion so that field weakening / field enhancement (for fast deceleration / low-speed operation) is achieved. The rotor angle can be extracted from the Hall signal or extracted using a PLL estimator / back EMF estimator in sensorless control. FOC is achieved by controlling each phase voltage using a buck regulator, and can also be achieved by using scalar control to eliminate the need for multiple transformations, which simplifies the calculations for the MCU. The motor terminals observe a clean voltage at their terminals and only the fundamental frequency from the motor speed is observed. The buck converter can be adjusted from full maximum duty cycle to minimum duty cycle, which can be used to control the speed / torque range of the motor. However, the high speed range and low speed range can also be extended by using the angle lead / lag feature which is independent of the buck converter limitations.

[0074] Figure 6Shown according to Figure 3 Simulation results of voltage-mode control of the topology. Figure 6 The rotor speed 61, the electromagnetic torque 62, the buck converter output voltage 63 of phase A (ie, the voltage across capacitor 111), and the DC bus current (which corresponds to the voltage generated by Figure 2 and Figure 3 More specifically, Figure 6 The response of the motor speed 61, torque 62 and buck converter output voltage 63 and DC bus current 64 to a load step change of 0.1Nm to 0.8Nm at 0.1s is shown.After the load step, the pulse width of the M-shaped sinusoidal pulse increases while the pulse frequency decreases.

[0075] Figure 7 The simulation results of voltage mode control are shown. In particular, Figure 7 Shown with Figure 6 The same rotor speed 71, electromagnetic torque 72, buck converter output voltage 73 and DC bus current 74 are shown in FIG. 1 , but are amplified during the time interval between 0.12 s and 0.17 s. Therefore, it is apparent that the DC bus current 74 is Figure 7 There is an oscillation / fluctuation between the upper and lower boundaries shown (and reference numeral 74 actually indicates the area between the two boundaries). Figure 8 The stator current (into the phase terminals A, B and C of the motor 14) is shown at Figure 8 81, 82 and 83. Also shown is the voltage difference between terminal A and terminal B of the motor 14, which is Figure 8 It is represented as the line voltage Vab 84. Fig. 9 and Fig.10 The behavior of a ramp load change from 0 Nm to 0.8 Nm within 0.1 s is shown.

[0076] It should be noted that the description and the accompanying drawings illustrate only the principles of the proposed method and system. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or illustrated herein, embody the principles of the present invention and are included within the spirit and scope of the present invention. In addition, all examples and embodiments outlined in this document are primarily and explicitly intended to be for illustrative purposes only, to help the reader understand the principles of the proposed method and system. In addition, all statements of the principles, aspects and embodiments of the present invention and their specific examples provided herein are intended to cover their equivalents.

Claims

1. A motor drive system, the motor drive system being configured to output a first drive signal, a second drive signal and a third drive signal for driving a motor, the motor drive system comprising: - a first power converter configured to generate the first drive signal, and - a second power converter configured to generate the second drive signal. 2 . The motor drive system of claim 1 , comprising a third power converter configured to generate the third drive signal.

3. The motor drive system according to claim 1 or 2, wherein: The power converter is a switch mode power supply (SMPS), and wherein switches of the SMPS are implemented using gallium nitride (GaN) technology.

4. A motor drive system according to any one of the preceding claims, wherein: The power converter is a synchronous buck power converter.

5. The motor drive system according to claim 4, wherein: Each synchronous buck power converter includes: - a high-side switching element coupled between the first input terminal of the synchronous buck power converter and a switching node, a low-side switching element coupled between the switching node and a second input terminal of the synchronous buck power converter, and - an inductor coupled between the switch node and an output of the synchronous buck power converter.

6. A motor drive system according to any one of the preceding claims, wherein: The first drive signal, the second drive signal, and the third drive signal have a continuous periodic shape and are phase-shifted by 120 degrees relative to each other.

7. A motor drive system according to any one of the preceding claims, wherein: The motor drive system is configured to output the first drive signal at a first output node and to output the second drive signal at a second output node, and wherein a voltage between the first output node and the second output node has a sinusoidal shape.

8. A motor drive system according to any one of the preceding claims, wherein: The first drive signal, the second drive signal and the third drive signal are periodic oscillation signals whose instantaneous frequencies correspond to the instantaneous rotational frequency of the motor.

9. A motor drive system according to any one of the preceding claims, wherein: The motor drive system is configured to generate the first drive signal, the second drive signal, and the third drive signal for controlling a desired speed or a desired torque of the motor.

10. A motor drive system according to any one of the preceding claims, wherein: The first power converter is configured to generate the first drive signal based on a first voltage reference and an output voltage sensed at an output terminal of the first power converter. 11 . The motor drive system of claim 10 , further comprising a voltage sensing unit configured to determine the sensed output voltage based on a voltage at an output terminal of the first power converter.

12. The motor drive system according to claim 10 or 11, wherein: The motor drive system is configured to determine the first voltage reference based on rotor position information of the motor. 13 . The motor drive system according to claim 12 , further comprising a rotor position determination unit configured to determine the rotor position information of the motor.

14. The motor drive system according to claim 13, wherein: The motor drive system is configured to determine a first angle reference, a second angle reference, and a third angle reference based on the rotor position information, and wherein the first angle reference, the second angle reference, and the third angle reference are periodic signals that are phase-shifted by 120 degrees relative to each other.

15. The motor drive system according to claim 14, wherein: The motor drive system is configured to determine the first voltage reference by multiplying an initial voltage reference by the first angle reference.

16. A method for driving a motor, the method comprising: - generating a first drive signal by a first power converter, and - A second drive signal is generated by a second power converter.

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