Motor control device and washing machine using the same

Abstract

This ensures necessary and sufficient deceleration while preventing a voltage rise in the DC link. [Solution] This motor control device controls the rotation of motor 5a by converting the DC voltage Vdc input from DC link 20 into an AC voltage Vinv using inverter 6b and outputting it to motor 5a. When motor 5a is decelerated, the controller 10 changes the rotation speed ω by switching control of inverter 6b based on the rotation speed ω and DC voltage Vdc of motor 5a, so that the voltage Vemf generated by the back electromotive force of motor 5a does not exceed the maximum limit voltage Vdc set.

Description

Technical Field

[0001] The disclosed technology relates to a motor control device and a washing machine using the same.

Background Art

[0002] Currently, many household washing machines are electric, and it is common for each washing process to be automated. That is, the processes from washing to rinsing and dehydration are automated and can be performed by button operations. There are also models that can perform drying.

[0003] And the drum for accommodating laundry generally rotates by the drive of a motor (permanent magnet synchronous motor). The rotation speed of the motor is changed high and low by the switching control of an inverter.

[0004] Fig. 1 shows an example of a washing machine. The washing machine includes an AC / DC converter 201, an inverter 202, etc. as a power supply device for supplying power to a motor 200. The AC / DC converter 201 may be included in the inverter 202.

[0005] The voltage Vac of the AC power supply supplied to a general household is converted into a DC voltage Vdc of a predetermined magnitude by the AC / DC converter 201, and then the DC voltage Vdc is supplied to the inverter 202 via a DC link 203. Incidentally, the DC link 203 is the name of an electrical circuit part where the DC voltage Vdc is applied and the DC voltage Vdc is input to the inverter 202.

[0006] By performing switching control in the inverter 202, the DC voltage Vdc is converted into a predetermined three-phase AC voltage Vinv with different phases, and the AC voltage Vinv is applied to the motor 200. By doing so, a three-phase drive current flows through the motor 200 and the motor 200 rotates.

[0007] When motor 200 rotates, electromagnetic induction generates a back electromotive force (EMF) in motor 200. Therefore, the actual voltage acting on motor 200 during operation (actual voltage Vef) is the applied AC voltage Vinv minus the voltage of the back EMF (back EMF voltage Vemf).

[0008] As the rotational speed of motor 200 increases, the back electromotive force Vemf also increases. Therefore, when the rotational speed of motor 200 increases and the back electromotive force Vemf reaches the AC voltage Vinv, motor 200 can no longer be driven. In contrast, in the dewatering process, the drum is rotated at high speed (e.g., 1000 rpm or more). In other words, the rotational speed of motor 200 is high. For this reason, in such high rotational speed regions, flux weakening control is often performed to reduce the back electromotive force.

[0009] In this way, the high-speed rotating drum and motor 200 are decelerated. During deceleration, the AC voltage Vinv applied to the motor 200 decreases. As a result, when the back electromotive force Vemf exceeds the AC voltage Vinv, that voltage is applied to the DC link 203 via the inverter 202 (so-called power regeneration). The voltage of the DC link 203 increases. This effect is particularly significant when the motor 200 is rotating at high speed.

[0010] If the voltage of DC link 203 becomes excessive, it may exceed the rated voltage of DC link 203 and AC / DC converter 201. Therefore, in conventional washing machines, the inverter 202 is stopped during the deceleration of the spin cycle to prevent the voltage of DC link 203 from becoming excessive, but vibration and noise are generated when the inverter 202 is stopped.

[0011] In response to this, a technique has been proposed to prevent the DC link voltage from becoming excessive without stopping the inverter (Patent Document 1).

[0012] In other words, this technology detects the voltage of the DC link and compares it to a predetermined threshold lower than the upper limit that triggers an alarm stop. If the voltage exceeds that threshold, the rate of change for motor deceleration is changed to a smaller, pre-stored value, thereby reducing the regenerative power. Since the inverter's switching operation does not need to be stopped, the motor control device does not trigger an alarm stop.

[0013] Regarding the disclosed technology, the inventors have previously proposed a noise cancellation technology for washing machines (Patent Document 2). Specifically, in the spin-drying process of a washing machine, the motor's cogging torque is controlled to produce a torque current (cancellation current) that is in the opposite phase to the periodic fluctuations of the motor's cogging torque. This suppresses the noise generated during the spin-drying process. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2016-226253 [Patent Document 2] Japanese Patent Publication No. 2022-158077 [Overview of the Initiative] [Problems that the invention aims to solve]

[0015] The technology described in Patent Document 1 detects the voltage of the DC link and compares it to a predetermined threshold. In other words, it is necessary to set an appropriate threshold in advance, and it is necessary to constantly monitor the DC link voltage and compare it to that threshold.

[0016] When that threshold is exceeded, the rate of change for motor deceleration is changed to a smaller value. However, in the case of washing machines, the load on the motor varies, making it difficult to set an appropriate value. Therefore, it is not possible to ensure the necessary and sufficient deceleration. Moreover, this technology is intended for motor devices that can also regenerate power. Washing machines cannot regenerate power, so they are not eligible.

[0017] Therefore, this specification discloses a technology suitable for the spin-drying process of a washing machine that ensures necessary and sufficient deceleration while preventing a voltage rise in the DC link. [Means for solving the problem]

[0018] The disclosed technology relates to a motor control device that controls the rotation of a motor by converting a DC voltage input from a DC link into an AC voltage using an inverter and outputting it to the motor.

[0019] The motor control device comprises a controller for switching control of the inverter, a rotation speed detection means for detecting the rotation speed of the motor and outputting it to the controller, and a DC voltage detection means for detecting the DC voltage and outputting it to the controller.

[0020] Then, when the motor is decelerated, the controller performs non-regenerative braking control, which changes the rotational speed while decelerating the motor by switching control the inverter based on the input rotational speed of the motor and the DC voltage, so that the voltage generated by the back electromotive force of the motor does not exceed a predetermined limit voltage maximum value.

[0021] In other words, according to this motor control device, when the motor is decelerated, the controller changes the rotational speed while decelerating by switching control the inverter so that the voltage generated by the motor's back electromotive force does not exceed the maximum limit voltage that is set in advance, taking into account the overvoltage protection voltage.

[0022] Regardless of the load on the motor, the controller adjusts the rotational speed accordingly by performing non-regenerative braking control. Furthermore, it ensures that the voltage generated by the motor's back electromotive force does not exceed the maximum limit voltage, thereby preventing a voltage surge in the DC link while ensuring the necessary and sufficient deceleration.

[0023] For example, the controller may include a rotation control unit that generates an amplitude command value of the AC voltage based on a rotation speed command value of the motor and the input rotation speed of the motor, a voltage limiter that limits the amplitude command value, and a limiter control unit that controls the limitation of the voltage limiter. When the motor is decelerating, the limiter control unit may lower the upper limit of the amplitude command value based on the input DC voltage so that the voltage generated by the counter electromotive force of the motor does not exceed the maximum limit voltage.

[0024] If so, non-regenerative brake control can be executed with only a relatively simple control block configuration.

[0025] The inverter has an inverter circuit including a pair of main lines consisting of a positive electrode side and a negative electrode side, three arms connected in parallel between the pair of main lines, and two switching elements arranged in series in each of the arms. When the motor decelerates and reaches a preset predetermined rotation speed, the controller may execute short-circuit brake control by stopping the non-regenerative brake control and turning off all of the switching elements located on the upper side of the arm in the inverter circuit and turning on all of the switching elements located on the lower side of the arm.

[0026] If short-circuit brake control to stop the inverter is executed at high speed rotation, problematic noise will occur. However, if the rotation speed decreases, the noise also becomes small and does not pose a problem. Therefore, if non-regenerative brake control is executed at high speed rotation and switched to short-circuit brake control when such a rotation speed is reached, deceleration can be achieved in a short time without generating problematic noise.

[0027] During the execution of the non-regenerative brake control, the controller may also use noise cancellation control to perform switching control of the inverter so that a reverse-phase torque that cancels the cogging torque generated in the motor is generated in the motor.

[0028] Noise cancellation control requires current to flow to the motor, so it presupposes that switching control is performed by an inverter. In contrast, with non-regenerative braking control, switching control is performed by an inverter, so noise cancellation control can be used in conjunction with it. By using noise cancellation control in conjunction with non-regenerative braking control, noise during deceleration can be further reduced.

[0029] The motor control device described above is preferably applied to a washing machine.

[0030] In other words, a washing machine equipped with the motor control device described above further comprises a water-storable tub, a drum housed in the tub in a rotatable state and into which laundry is loaded, a drive device including the motor that rotates the drum, and a power supply device including the DC link and the inverter that supplies power to the motor, wherein the non-regenerative braking control is performed during the dewatering process.

[0031] Alternatively, the non-regenerative braking control and the short-circuit braking control may be performed during the dewatering process, or the non-regenerative braking control may be performed in combination with the noise cancellation control during the dewatering process.

[0032] This would allow for the creation of a high-performance washing machine with excellent quietness. [Effects of the Invention]

[0033] The disclosed technology ensures sufficient deceleration while preventing a voltage surge in the DC link. Therefore, when applied to a washing machine, it enables efficient spin-drying. [Brief explanation of the drawing]

[0034] [Figure 1] This is a diagram illustrating the motor drive of a typical washing machine. [Figure 2] This is a schematic cross-sectional view of a washing machine to which the disclosed technology is applied. [Figure 3]This is a circuit diagram of the controller and related devices involved in motor rotation control. [Figure 4] This diagram shows the profile of the dehydration process. [Figure 5] This is a circuit diagram showing the operation of short brake control. [Figure 6] This is a block diagram related to non-regenerative braking control. [Figure 7A] This is a spatial vector diagram related to the voltage conversion of an inverter. [Figure 7B] This is a diagram illustrating the function of the limiter control unit. [Figure 8] This graph shows the results of the verification test. [Modes for carrying out the invention]

[0035] The following describes the technologies being disclosed. However, the following description is essentially illustrative.

[0036] <Washing machine> Figure 2 shows an example of a washing machine to which the disclosed technology is applied. This washing machine 1 is a so-called drum-type washing machine. Furthermore, this washing machine 1 is a so-called fully automatic type, and is configured so that a series of processes consisting of washing, rinsing, and spinning can be performed automatically.

[0037] The washing machine 1 mainly consists of a casing 2, a tub 3, a drum 4, a drive unit 5, a power supply unit 6, a water supply unit 7, a drainage unit 8, and a controller 10.

[0038] The casing 2 is a box-shaped container made of panels and a frame, and constitutes the outer casing of the washing machine 1. A circular opening 2a is formed on the front of the casing 2 for loading and unloading laundry. A door 2b with a transparent window is attached to the opening 2a. The opening 2a is opened and closed by the door 2b. An operating section 2c, which has switches and other controls for user operation, is installed above the opening 2a on the casing 2.

[0039] Inside the housing 2 is a tab 3 that communicates with the input port 2a. The tab 3 is a bottomed cylindrical container capable of storing water, and its opening is connected to the input port 2a. The tab 3 is supported by a damper (not shown) provided inside the housing 2 so that it is stable in a position where its central axis J is slightly tilted upward toward the front.

[0040] A water supply system 7, consisting of a water supply pipe 7a, a water supply valve 7b, and a chemical dispenser 7c, is provided at the top of tab 3. The upstream end of the water supply pipe 7a protrudes outside the washing machine 1 and is connected to a water source not shown in the figure. The downstream end of the water supply pipe 7a is connected to a water inlet that opens at the top of tab 3. The chemical dispenser 7c contains chemicals such as detergent and fabric softener, and dispenses these chemicals into tab 3 by mixing them with the supplied water.

[0041] A drain is provided at the bottom of tab 3. The drain is connected to the suction port of the drain pump 8b via the upstream drain pipe 8a. The downstream drain pipe 8c is connected to the discharge port of the drain pump 8b. The downstream drain pipe 8c is drawn out from the bottom of the housing 2 to the outside.

[0042] The drum 4 is a cylindrical container slightly smaller in diameter than the tab 3, and is housed inside the tab 3 with its central axis J aligned with the tab 3. A circular opening is formed at the front of the drum 4, facing the input opening 2a. Laundry is put into the drum 4 through the input opening 2a and its opening.

[0043] The drum 4 has numerous dewatering holes 4a formed around its entire circumference (only a portion is shown in Figure 2). Additionally, several lifters 4b for agitation are attached to the inside of its sides. The front of the drum 4 is rotatably supported by the inlet 2a.

[0044] The drive unit 5 is installed at the rear of the tab 3. The drive unit 5 consists of a motor (permanent magnet synchronous motor) 5a, a shaft 5b, and the like. The shaft 5b is rotatably supported in the tab 3, passing through the rear of the tab 3. The tip of the shaft 5b protrudes into the interior of the tab 3 and is fixed to the center of the bottom of the drum 4.

[0045] The motor 5a is mounted on the rear of the tab 3 and is coaxially connected to the shaft 5b. In other words, the drive device 5 of this embodiment directly drives the drum 4 (a so-called direct drive system). As a result, the drum 4 rotates around the central axis J by the drive of the motor 5a.

[0046] The power supply device 6 is a device that supplies power to the motor 5a and is mounted on the rear of the tab 3 adjacent to the motor 5a. The power supply device 6 includes an AC / DC converter 6a and an inverter 6b, as will be described later. The power supply device 6 has a cable 6c that extends from the housing 2. A plug at the end of the cable 6c is connected to the commercial power supply. This inputs AC power (e.g., AC 100V) to the power supply device 6.

[0047] The motor 5a rotates using this AC power. The rotation of the motor 5a (and drum 4) is controlled by the controller 10. In this embodiment, the controller 10 constitutes a "motor control device".

[0048] The controller 10 is installed on top of the housing 2. The controller 10 comprehensively controls the operation of the washing machine 1, including the rotation of the motor 5a. The controller 10 consists of hardware such as a CPU and memory, and software such as control programs and various data.

[0049] The controller 10 controls the power supply unit 6, water supply valve 7b, drain pump 8b, etc., according to instructions input from the operation unit 2c. As a result, the washing machine 1 performs a series of processes including a washing process, a rinsing process, and a spin-drying process.

[0050] <Controller and related devices> Figure 3 shows the circuit diagram of the controller 10 and its related devices for controlling the rotation of the motor 5a.

[0051] As described above, AC power is input to the power supply device 6 via cable 6c. Cable 6c is connected to the AC / DC converter 6a, and the AC power input to the power supply device 6 is converted to DC power by the AC / DC converter 6a. In this embodiment, the output side of the AC / DC converter 6a is connected to the DC link 20.

[0052] The DC link 20 consists of a pair of relay wires 21a and 21b, which are the positive and negative sides, and a smoothing capacitor 22. The smoothing capacitor 22 is connected between the two relay wires 21a and 21b, which are the positive and negative sides. As a result, when the washing machine 1 is started and AC power is input to the power supply device 6, a predetermined DC voltage Vdc is applied to the DC link 20, and the smoothing capacitor 22 is charged. The DC link 20 is maintained at its predetermined DC voltage Vdc.

[0053] DC link 20 is connected to inverter 6b. Therefore, the DC voltage Vdc of DC link 20 is input to inverter 6b. Inverter 6b has a known inverter circuit 60. Inverter circuit 60 has a positive terminal main line 61a connected to the positive terminal relay line 21a and a negative terminal main line 61b connected to the negative terminal relay line 21b.

[0054] Three arms 62 are installed in parallel between the positive and negative main lines 61a and 61b. Two switching elements 63 are arranged in series on each of these three arms 62. The switching elements 63 are, for example, IGBTs and MOSFETs (so-called power transistors). A freewheeling diode 64 is connected in antiparallel to each switching element 63.

[0055] The ON (enable) and OFF (unenable) states of these switching elements 63 are controlled by the controller 10. The area between the two switching elements 63, 63 in each arm 62 is connected to the motor 5a via output wiring 65. Each arm 62 constitutes a half-bridge circuit corresponding to three phases consisting of U, V, and W.

[0056] A voltage sensor 11 (an example of a DC voltage detection means) is installed on the DC link 20. The voltage sensor 11 detects the DC voltage Vdc applied to the DC link 20 and outputs it to the controller 10. A rotation sensor 12 (an example of a rotation speed detection means) is installed on the motor 5a. The rotation sensor 12 detects the rotation speed of the motor 5a and outputs it to the controller 10.

[0057] A current sensor 13 is installed on the inverter 6b. The current sensor 13 detects the drive current input to the motor 5a and outputs it to the controller 10. The drive current includes a d-axis component that forms a magnetic flux corresponding to the direction of the magnetic flux of the motor 5a, and a q-axis component that forms a magnetic flux in a direction perpendicular to the d-axis component. The controller 10 obtains the values ​​of each of these components from the detected drive current value.

[0058] While the washing machine 1 is in operation, the controller 10 controls the inverter 6b (so-called PWM control) based on the input signals from the sensors 11, 12, and 13, and adjusts the AC voltage Vinv output to the motor 5a. For example, when driving the motor 5a to rotate the drum 4, the controller controls the on / off state of the switching elements 63 of each arm 62 (switching control) so that three AC voltages Vinv with different phases are output to the motor 5a.

[0059] In other words, the controller 10 switches the inverter 6b, converting the DC voltage Vdc of the DC link 20 into AC voltages Vinv for each phase, which are then output to the motor 5a. As a result, drive currents with different phases flow through the motor 5a, causing the motor 5a to rotate while changing its rotational speed to high or low as required.

[0060] Furthermore, when motor 5a rotates, a back electromotive force is generated in motor 5a due to electromagnetic induction. Therefore, the actual voltage acting on motor 5a during operation is the AC voltage Vinv minus the back electromotive force Vemf.

[0061] (Problems with the dehydration process and its deceleration) During operation of the washing machine 1, after the washing and rinsing processes are completed, a spin-drying process is performed. In the spin-drying process, centrifugal force is used to remove water from the laundry. Therefore, the drum 4 rotates at high speed. Figure 4 shows the profile of the spin-drying process in the washing machine 1 of this embodiment.

[0062] In this washing machine 1, the spin-drying process consists of two stages: a pre-spin-drying PD and a main spin-drying MD. The pre-spin-drying PD is a preliminary process performed before the main spin-drying MD. The pre-spin-drying PD corrects any imbalance in the laundry contained in the drum 4. This suppresses vibration and noise during the main spin-drying MD.

[0063] In the pre-spin cycle PD, the target rotation speed is set to r1 (for example, around 500 rpm), which is lower than the target rotation speed r2 (for example, 1000 rpm or more) of the drum 4 and motor 5a in the main spin cycle MD. As a result, in this washing machine 1, the drum 4 and motor 5a are decelerated twice from a high-speed rotation state (during the period from t1 to t2 and during the period from t3 onward).

[0064] During these decelerations, the AC voltage Vinv applied to the motor 5a decreases. As a result, when the back electromotive force Vemf exceeds this AC voltage Vinv, the excess voltage is applied to the DC link 20 via the inverter 6b (so-called power regeneration). Consequently, the voltage Vdc of the DC link 20 increases.

[0065] If the voltage Vdc of DC link 20 becomes excessive, it may exceed the rated voltage of DC link 20 and AC / DC converter 6a. The regenerative power generated during deceleration from high-speed rotation is large. Therefore, it is necessary to prevent the voltage Vdc of DC link 20 from becoming excessive during deceleration in the dewatering process.

[0066] (Short brake control) Short-circuit brake control is a means to prevent the voltage Vdc of the DC link 20 from rising during deceleration. Figure 5 shows a specific example of short-circuit brake control. In short-circuit brake control, as simplified in Figure 5, all of the switching elements 63 located above each arm 62 in the inverter circuit 60 are turned off, and all of the switching elements 63 located below each arm 62 are turned on.

[0067] In other words, in short-circuit brake control, the controller 10 does not perform switching control, but instead stops the inverter 6b in a predetermined circuit configuration. As a result, even if a back electromotive force is generated in the motor 5a, current (regenerative current) does not flow back into the DC link 20, and the DC voltage Vdc of the DC link 20 can be maintained.

[0068] As an example, Figure 5 shows that the W-phase current during short-circuit brake control flows as indicated by the dashed arrow. Similarly, the currents flowing through the U-phase and V-phase also return to the motor 5a through the arms 62 of the other phases. Therefore, no regenerative current flows into the DC link 20.

[0069] However, when the inverter 6b is stopped in order to perform short-circuit brake control during deceleration, noise is generated. Specifically, when switching from switching control to short-circuit brake control while the motor 5a is rotating at high speed, the driving state of the motor 5a changes abruptly, and this shock generates a relatively loud abnormal noise.

[0070] This abnormal noise may cause discomfort or unease to the user. Moreover, in the case of this washing machine 1, this abnormal noise occurs during the deceleration phases of both the pre-spin cycle (PD) and the main spin cycle (MD).

[0071] (Non-regenerative braking control) Therefore, in this washing machine 1, even if switching control is maintained during these deceleration phases in the spin-drying process, the voltage rise of the DC link 20 can be suppressed, and deceleration can be made smoothly.

[0072] In other words, when the motor 5a is decelerated during the dewatering process, the controller 10 controls the inverter 6b by switching it to change the rotation speed ω while decelerating (non-regenerative braking control) so that the back electromotive force Vemf generated by the back electromotive force of the motor 5a does not exceed a predetermined limit voltage maximum value Vdc set.

[0073] Figure 6 shows a block diagram relating to non-regenerative braking control. The controller 10 has a functional configuration that includes a rotation control unit 101, a voltage limiter 102, a limiter control unit 103, a flux weakening control unit 104, and so on.

[0074] The rotation control unit 101 generates an amplitude command value Vs* for the AC voltage Vinv based on the rotation speed command value ω* of the motor 5a and its rotation speed ω. Specifically, the rotation control unit 101 includes a speed controller 101a, a current controller 101b, and an amplitude command value generation unit 101c. The rotation speed command value ω* of the motor 5a and its rotation speed ω are input to the speed controller 101a.

[0075] The rotational speed command value ω* of motor 5a is a set value based on the profile of the dewatering process. The rotational speed ω of motor 5a is a feedback value input from the rotation sensor 12 and corresponds to the actual rotational speed of motor 5a. The speed controller 101a generates the d-axis current command value Id* and the q-axis current command value Iq* based on the rotational speed command value ω* of motor 5a and its rotational speed ω. The d-axis current command value Id* is the command value for the d-axis component of the drive current, and the q-axis current command value Iq* is the command value for the q-axis component of the drive current.

[0076] The d-axis current command value Id* and the q-axis current command value Iq* are input to the current controller 101b. The current controller 101b also receives the d-axis component value Id and the q-axis component value Iq of the drive current. The drive current is a feedback value input from the current sensor 13. The d-axis component value Id and the q-axis component value Iq are obtained from this feedback value.

[0077] The current controller 101b generates the d-axis voltage command value Vd* and the q-axis voltage command value Vq* based on the d-axis current command value Id* and the q-axis current command value Iq*, as well as the d-axis component value Id and the q-axis component value Iq. The d-axis voltage command value Vd* and the q-axis voltage command value Vq* are input to the amplitude command value generation unit 101c. The amplitude command value generation unit 101c generates the amplitude command value Vs* based on these values ​​Vd* and Vq* using the formula shown in Figure 6.

[0078] The amplitude command value Vs* is a command value corresponding to the amplitude of the AC voltage Vinv output to the motor 5a. The amplitude command value Vs* sets the magnitude of the AC voltage Vinv. The amplitude command value Vs* is limited by the voltage limiter 102.

[0079] In other words, the voltage limiter 102 has a predetermined upper limit value that caps out above a predetermined value, and a predetermined lower limit value that caps out below a predetermined value. As a result, the voltage limiter 102 limits the input amplitude command value Vs* to between these upper and lower limits and outputs it. The upper limit value of these limits is controlled by the limiter control unit 103 (details of the limiter control unit 103 will be described later).

[0080] The amplitude command value Vs*lim, whose upper limit is restricted by the voltage limiter 102, is input to the flux weakening control unit 104. The flux weakening control unit 104 then performs flux weakening control.

[0081] As the rotational speed ω of motor 5a increases, the back electromotive force also increases accordingly. Therefore, when the rotational speed ω of motor 5a increases and the back electromotive force Vemf reaches the voltage Vinv input to motor 5a, the drive current stops flowing. In other words, motor 5a can no longer be driven.

[0082] In contrast, during the dewatering process, the drum 4 is rotated at high speed (e.g., 1000 rpm or more). The rotational speed ω of the motor 5a is very high, and the motor 5a cannot be driven as is. Therefore, in the region of such high rotational speed ω, the flux weakening control unit 104 performs flux weakening control to weaken the back electromotive force by adjusting the d-axis current (specifically, the d-axis voltage command value Vd*).

[0083] The flux weakening control unit 104 outputs the d-axis voltage command value Vd* and the q-axis voltage command value Vq*, which have been adjusted by flux weakening control, to the inverter 6b.

[0084] (Limiter control unit) The limiter control unit 103 includes a PI controller 103a, an integrator 103b, and the like. When the motor 5a is decelerated, the limiter control unit 103 lowers the upper limit of the amplitude command value Vs* based on the DC voltage Vdc input from the voltage sensor 11 so that the back electromotive force Vemf of the motor 5a does not exceed the voltage Vdc of the DC link 20.

[0085] The limiter control unit 103 has presets for the maximum limit voltage Vdc set of the DC link 20 and the maximum voltage Vdc max that can be applied to the motor 5a with the voltage Vdc of the DC link 20. The maximum voltage Vdc max is the maximum amplitude of the AC voltage Vinv that can be input to the motor 5a by the PWM control of the inverter 6b.

[0086] In contrast, the maximum limiting voltage Vdc set is the maximum value of the voltage Vdc limited by the DC link 20. The maximum limiting voltage Vdc set is set to an appropriate value lower than the rated voltage of the DC link 20, for example.

[0087] The voltage Vdc (measured value) of the DC link 20 input to the limiter control unit 103 is subtracted from the maximum limit voltage Vdc set and then input to the PI controller 103a. When the deviation input to the PI controller 103a is negative, the output is limited to 0.

[0088] The output of the PI controller 103a is integrated by being input to the integrator 103b. When the regenerative mode is entered during deceleration, the output of the integrator 103b increases during the period when the maximum limit voltage Vdc set is greater than the voltage Vdc of the DC link 20 (Vdc set > Vdc). Therefore, the deviation between the maximum voltage Vdc max and the output of the integrator 103b becomes the voltage limit value of the voltage limiter 102.

[0089] During the period when the maximum limit voltage Vdc set is less than the voltage Vdc of the DC link 20 (Vdc set < Vdc), the voltage limit value of the voltage limiter 102 decreases, and when it reverses, the limit value of the voltage limiter 102 does not decrease and maintains the previous value. The output value from the integrator 103b is subtracted from the maximum voltage Vdc max and then input to the voltage limiter 102 and set as the upper limit of the voltage limiter 102.

[0090] The amplitude command value Vs* is limited by the upper limit of the voltage limiter 102. That is, if the amplitude command value Vs* reaches its upper limit, it is limited to that value. On the other hand, the upper limit of the voltage limiter 102 decreases in response to an increase in the voltage Vdc of the DC link 20. Thereby, the rotational speed is changed so that the back electromotive force Vemf of the motor 5a does not exceed the maximum limit voltage Vdc set.

[0091] Fig. 7A shows a space vector diagram regarding the voltage conversion of the inverter 6b. The hexagonal frame represents the output limit by the voltage Vdc of the DC link 20. (100), etc. shown at each vertex correspond to the on / off states (1 is on, 0 is off) of the switching element 63 located on the upper side of the arm 62 of each phase U, V, W. Note that the on / off states of the switching element 63 located on the lower side of the arm 62 of each phase are reversed.

[0092] The inscribed circle of the output limit frame represents the maximum voltage Vdc max described above. The amplitude command value Vs* is set within the range of this maximum voltage Vdc max according to the on / off state of each switching element 63. Therefore, in a normal driving state where power is not regenerated, as shown in Figure 7A, the maximum voltage Vdc max is the upper limit of the voltage limiter 102.

[0093] As power is regenerated during deceleration, the voltage Vdc of the DC link 20 increases. In response to this, in this washing machine 1, as shown by the white arrow in Figure 7B, the limiter control unit 103 gradually lowers the upper limit of the limiter control unit 103 in accordance with the increase in the voltage Vdc of the DC link 20, so that even if the voltage Vdc of the DC link 20 increases due to regeneration, it does not exceed the maximum limit voltage Vdc set.

[0094] By implementing this non-regenerative braking control, the washing machine 1 can suppress the voltage rise of the DC link 20 while maintaining switching control during deceleration in the spin-drying process, enabling smooth deceleration. Consequently, no abnormal noises are generated during the deceleration of either the pre-spin-drying PD or the main spin-drying MD. The inverter 6b can continue to operate, and the stability of the control can also be improved.

[0095] (In combination with noise cancellation control) Furthermore, with non-regenerative braking control, switching control is performed in inverter 6b even during deceleration (inverter 6b does not stop). This also enables noise cancellation control.

[0096] In other words, when non-regenerative braking control is performed, the controller 10 can also use a control method (noise cancellation control) that switches the inverter 6b so that a reverse-phase torque is generated in the motor 5a that cancels out the cogging torque generated in the motor 5a.

[0097] Noise cancellation control essentially works by controlling the motor 5a so that a torque current (cancellation current) with the opposite phase to the periodic fluctuation of the motor 5a's cogging torque flows through the motor 5a. This generates an opposite-phase torque in the motor 5a that cancels out the cogging torque, thereby suppressing noise caused by the cogging torque.

[0098] Noise cancellation control is a well-known technique (for example, as described in Patent Document 2 above). Therefore, a detailed explanation will be omitted.

[0099] By using this type of noise cancellation control in conjunction with non-regenerative braking control, it is possible to suppress not only the noise caused by short braking control but also the noise caused by cogging torque. Therefore, the quietness of the washing machine 1 can be improved.

[0100] (In combination with short-range brake control) As described above, when switching from switching control to short brake control while motor 5a is rotating at high speed, the driving state of motor 5a changes abruptly, and this shock generates a relatively loud abnormal noise.

[0101] However, if motor 5a is rotating at a low speed, even if an abnormal noise occurs when switching from switching control to short brake control, the noise will be small and acceptable. Therefore, non-regenerative brake control and short brake control may be used in combination.

[0102] Specifically, when the motor 5a decelerates and reaches a predetermined rotational speed, the controller 10 should stop non-regenerative braking control and perform short-circuit braking control. Typically, loud abnormal noises occur when the rotational speed of the drum 4 (and motor 5a) is higher than the frequency at which the washing machine 1 resonates.

[0103] Therefore, it is preferable to perform short-circuit brake control when the rotational speed reaches a level lower than the resonant frequency of the washing machine 1. Specifically, the rotational speed of the drum 4 and motor 5a is preferably 400 rpm or less, and more preferably 350 rpm or less.

[0104] By combining short-circuit braking control with non-regenerative braking control in this way, noise caused by short-circuit braking control can be suppressed, and deceleration can be achieved in a shorter time. Therefore, the quietness and efficiency of washing machine 1 can be improved.

[0105] <Verification of effectiveness> Tests were conducted to verify the effectiveness of the disclosed technology (noise suppression). Using a test washing machine (drum-type washing machine), the noise generated was measured in three patterns: when the drum (empty) and motor were rotating at 350 rpm, deceleration was performed using only short brake control (Comparative Example: C), when deceleration was performed using non-regenerative brake control (Example 1: E1), and when noise cancellation control was used in combination with non-regenerative brake control (Example 2: E2).

[0106] Figure 8 shows the results. Deceleration begins at timing ts. In the comparative example, temporary noise is generated due to fluctuations when switching to deceleration. In contrast, no such noise is observed in Example 1. Furthermore, in Example 2, noise is reduced over a wider range compared to the comparative example and Example 1 due to the reduction of noise caused by cogging torque.

[0107] Incidentally, the deceleration time for the comparative example was approximately 10 seconds, while the deceleration time for Example 1 was approximately 20 seconds. Although non-regenerative braking control results in a slightly longer deceleration time compared to short-braking control, the difference is negligible in practical terms.

[0108] Thus, applying the disclosed technology to a washing machine can reduce noise during the spin-drying process. Consequently, a high-performance washing machine can be realized.

[0109] The disclosed technology is not limited to the embodiments described above, but also encompasses various other configurations. For example, although a drum-type washing machine was used as an example in the embodiments, the disclosed technology is also suitable for top-loading washing machines. It can effectively suppress shock and noise during the spin-drying process.

[0110] A transmission mechanism consisting of a transmission, belt, pulley, gears, etc., may be interposed between the drum and the motor. Both noise cancellation control and short-circuit brake control may be used in combination for non-regenerative braking control. The disclosed technology is applicable to devices other than washing machines. [Explanation of symbols]

[0111] 1. Washing machine 2 cabinets 3 tabs 4 drums 5. Drive unit 5a motor 6 Power supply device 6a AC / DC converter 6b Inverter 6c cable 7 Water supply device 8 Drainage system 10 Controllers 11 Voltage Sensor 12 Rotation Sensor 13 Current Sensor 20 DC Links 22 Smoothing Capacitors 60 Inverter Circuit 62 Arms 63 Switching elements 64 Freewheeling diode 65 Output Wiring 101 Rotation Control Unit 101a Speed ​​controller 101b Current Controller 101c Amplitude command value generation unit 102 Voltage Limiter 103 Limiter Control Unit 103a PI controller 103b Integrator 104 Magnetic flux weakening control unit

Claims

1. A motor control device that controls the rotation of a motor by converting a DC voltage input from a DC link into an AC voltage using an inverter and outputting it to the motor, A controller that controls the switching of the inverter, A rotation speed detection means that detects the rotation speed of the motor and outputs it to the controller, A DC voltage detection means that detects the DC voltage and outputs it to the controller, Equipped with, A motor control device that performs non-regenerative braking control, wherein, when the motor is decelerated, the controller changes the rotational speed of the inverter by switching control based on the input rotational speed of the motor and the DC voltage, so that the voltage generated by the back electromotive force of the motor does not exceed a predetermined limit voltage maximum value.

2. In the motor control device according to claim 1, The aforementioned controller, A rotation control unit that generates the amplitude command value of the AC voltage based on the rotation speed command value of the motor and the input rotation speed of the motor, A voltage limiter that limits the amplitude command value, A limiter control unit that controls the limit of the voltage limiter, It has, A motor control device in which, when the motor is decelerating, the limiter control unit lowers the upper limit of the amplitude command value based on the input DC voltage so that the voltage generated by the back electromotive force of the motor does not exceed the maximum limit voltage.

3. In the motor control device according to claim 1, The inverter has an inverter circuit that includes a pair of main lines consisting of a positive terminal side and a negative terminal side, three arms connected in parallel between the pair of main lines, and two switching elements arranged in series with each of the arms. A motor control device that, when the motor decelerates and reaches a predetermined rotational speed, stops the non-regenerative braking control and performs short-circuit braking control, turning off all of the switching elements located on the upper side of the arm in the inverter circuit and turning on all of the switching elements located on the lower side of the arm.

4. In the motor control device according to claim 1, A motor control device that combines noise cancellation control, wherein, when the non-regenerative braking control is executed, the controller switches the inverter so that the motor generates an inverse-phase torque that cancels out the cogging torque generated by the motor.

5. A washing machine equipped with a motor control device according to claim 1 or 2, A water-storable tub, The aforementioned tab houses a drum into which laundry is placed, which is rotatable, A drive device that includes the motor and rotates the drum, A power supply device that supplies power to the motor, including the DC link and the inverter, Furthermore, A washing machine that performs the non-regenerative braking control during the dewatering process.

6. A washing machine comprising the motor control device described in claim 3, A water-storable tub, The aforementioned tab houses a drum into which laundry is placed, which is rotatable, A drive device that includes the motor and rotates the drum, A power supply device that supplies power to the motor, including the DC link and the inverter, Furthermore, A washing machine that performs the non-regenerative braking control and the short-circuit braking control during the dewatering process.

7. A washing machine equipped with the motor control device described in claim 4, A water-storable tub, The aforementioned tab houses a drum into which laundry is placed, which is rotatable, A drive device that includes the motor and rotates the drum, A power supply device that supplies power to the motor, including the DC link and the inverter, Furthermore, A washing machine that performs the non-regenerative braking control in combination with the noise cancellation control during the dewatering process.

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