Water-free shutdown control method for drainage pump and washing equipment

Abstract

The invention discloses a drainage pump water-free shutdown control method and washing equipment, the terminal voltage of a single-phase permanent magnet synchronous motor is collected during the running period of a drainage pump, and the terminal voltage of the corresponding part is the back electromotive force of the motor when the current is zero; a phase difference exists between the counter electromotive force and the current, the phase difference between the counter electromotive force and the current is close to 90 degrees when the motor is no-load, and the phase difference between the counter electromotive force and the current is between 30 degrees and 60 degrees when the motor is loaded; by analyzing the back electromotive force data when the current is continuously zero, the phase difference between the back electromotive force and the current can be determined, so that the load condition of the motor can be determined, and the drainage pump can be controlled to stop when no load of the motor indicates that no water exists in the drainage pump. Compared with an existing mode of acquiring current through a current sensor to judge the load condition of the motor, the method can be realized based on a software algorithm and a simple voltage acquisition circuit, the method is simple, and the cost is not increased.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of washing equipment, in particular, relates to a drain pump waterless shutdown control method and washing equipment. BACKGROUND

[0002] The washing equipment such as washing machine, dishwasher, etc. can improve the drainage efficiency by using single-phase permanent magnet synchronous motor, and can be designed to automatically judge waterless shutdown after the end of drainage. The existing waterless judgment method is to detect the motor current by setting current sensor, and when the average value or effective value of the current is greater than the specified value, it is judged that the drain pump is running without water, but this judgment method needs to increase the current sensor, resulting in increased cost. SUMMARY

[0003] The purpose of the present application is to provide a drain pump waterless shutdown control method and washing equipment, which does not need current sensor to collect current data, detects the back electromotive force during the period when the current of single-phase permanent magnet synchronous motor is continuously zero, judges the motor load condition by analyzing the back electromotive force, controls the drain pump to stop without water when the motor is in no-load state, and the method is simple and reliable after verification.

[0004] The present application is implemented by using the following technical solutions: A drain pump waterless shutdown control method is proposed, which is applied to washing equipment driven by single-phase permanent magnet synchronous motor, including: S1, during the operation of the drain pump, the terminal voltage of the single-phase permanent magnet synchronous motor is collected in real time; S2, find the voltage data during the period when the current is continuously zero, and store it as a back electromotive force array; S3, judge the load condition of the single-phase permanent magnet synchronous motor according to the change of data in the back electromotive force array, and control the drain pump to stop without water when the motor is in no-load state.

[0005] Compared with the prior art, the advantages and positive effects of the application are that: in the water pump no water shutdown control method, the terminal voltage of the single-phase permanent magnet synchronous motor is collected during the operation of the water pump, when the current is zero, the terminal voltage of the corresponding part only shows the back electromotive force in the motor stator coil; the back electromotive force and the current have a phase difference, when the motor is in no-load, the current is used to overcome the no-load loss, the phase difference between the back electromotive force and the current is close to 90°, when the motor is in load, the motor current needs to provide the torque required by the load in addition to overcoming the no-load loss, the phase difference between the back electromotive force and the current is between 30° and 60°; by analyzing the back electromotive force data during the period when the current is continuously zero, the phase difference between the back electromotive force and the current can be determined, so that the motor load condition can be determined, when the motor is in no-load, it indicates that the water pump has no water, and the water pump can be controlled to stop. Compared with the current acquisition mode by the current sensor to determine the motor load, the application can be realized based on the software algorithm and the simple voltage acquisition circuit, the method is simple and does not increase the cost.

[0006] In some embodiments of the application, the voltage data during the period when the current is continuously zero is found by the following way: Taking the voltage zero-crossing as a node, the terminal voltage data is segmented; In each segment of the stored data, recording starts from the first falling data and stops after the rising.

[0007] The stator winding of the single-phase permanent magnet synchronous motor is inductive load in nature, according to the characteristics of alternating current circuit, the inductive element will make the current phase lag behind the voltage phase, the lag angle depends on the inductance and the power frequency, which shows that when the voltage is zero, the current has not yet zero; and the current of the single-phase permanent magnet synchronous motor is affected by the complexity of the motor structure and the magnetic field distribution, the back electromotive force, the duty cycle of the pulse in the chopping control, the load characteristics and the mechanical inertia, etc., at the zero-crossing point, the current zero state will last for a period of time, the current of the single-phase permanent magnet synchronous motor crosses zero after the voltage zero-crossing point and lasts for a period of time. When the current is zero, the power switch tube of the chopping control is cut off, the terminal voltage of the motor is only the back electromotive force voltage, the back electromotive force voltage amplitude is significantly lower than the supply voltage during the chopping control, so the voltage data found by the above way is the back electromotive force data corresponding to the period when the current is continuously zero.

[0008] In some embodiments of the application, S4 judges the load condition of the single-phase permanent magnet synchronous motor according to the change of the data in the back electromotive force array, including: Calculate the cumulative sum S1 of the first half of the data in the back electromotive force array; Calculate the cumulative sum S2 of the second half of the data in the back electromotive force array; Compare the cumulative sum S1 of the first half and the cumulative sum S2 of the second half, when the difference between the two is less than the set limit, it is judged that the motor is in no-load, otherwise, it is judged that the motor is in load.

[0009] In some embodiments of the present application, S4 determines the load condition of the single-phase permanent magnet synchronous motor according to the change of the data in the back EMF array, including: calculating the continuous change rate of the data in the back EMF array; determining that the motor is no-load when the change rates are all less than a set value, and determining that the motor is loaded when the change rates are all greater than the set value.

[0010] The back EMF phase and the current phase are related. When the motor is no-load (corresponding to the water pump being empty), the back EMF phase and the current phase are nearly 90° apart, which is shown in the curve graph as the top of the steamed bun wave of the back EMF curve corresponding to the zero phase position of the current curve. When the motor is loaded (corresponding to the water pump having water), the back EMF phase and the current phase are between 30° and 60° apart, which is shown in the curve graph as the left half of a steamed bun wave of the back EMF curve corresponding to the zero phase position of the current curve. Therefore, if the motor is no-load, the top of the back EMF curve corresponds to the zero part of the current phase, and this part of the back EMF curve is relatively flat and the data changes are not obvious. If the motor is loaded, the left half of the back EMF curve corresponds to the zero part of the current phase, and this part of the back EMF curve has a large slope and the data changes are obvious. Based on the above, the embodiments of the present application can obtain the change trend of the back EMF data during the current being zero by analyzing the back EMF data, and can determine whether the motor is no-load or loaded, and then can determine whether the water pump has water or is empty.

[0011] In some embodiments of the present application, S4 further includes: continuously judging the continuously collected back EMF array, adding 1 when the motor is no-load, subtracting 1 when the motor is loaded, and determining that the motor is no-load when the cumulative count reaches a threshold value. The threshold value is used to limit the occasional no-load condition before the water is drained, so as to ensure that the equipment is completely drained before stopping.

[0012] A washing equipment is provided, which is configured with a water pump using a single-phase permanent magnet synchronous motor, including: an end voltage acquisition circuit, configured to acquire the end voltage of the single-phase permanent magnet synchronous motor in real time during the operation of the water pump; a back EMF detection unit, configured to find the voltage data during the current being zero from the end voltage data, and store the voltage data as a back EMF array; a motor load determination unit, configured to determine the load condition of the single-phase permanent magnet synchronous motor according to the change of the data in the back EMF array, and send the determination result to a water pump control unit; the water pump control unit controls the water pump to stop without water when the determination result is that the motor is no-load.

[0013] Compared with the prior art, the advantages and positive effects of the present application are that: the washing equipment provided by the present application is configured with a drainage pump applying a single-phase permanent magnet synchronous motor, an end voltage acquisition circuit acquires the end voltage of the single-phase permanent magnet synchronous motor during the operation of the drainage pump, when the current is zero, the end voltage of the corresponding part only shows the back electromotive force in the motor stator coil; the back electromotive force and the current have a phase difference, when the motor is in no-load, the current is used to overcome the no-load loss, the phase difference between the back electromotive force and the current is close to 90°, when the motor is in load, the motor current needs to provide the torque required by the load in addition to overcoming the no-load loss, the phase difference between the back electromotive force and the current is between 30° and 60°; therefore, the motor load judgment unit can determine the phase difference between the back electromotive force and the current by analyzing the back electromotive force data in the period when the current is continuously zero, so as to determine the motor load condition, when the motor is in no-load, it indicates that the drainage pump has no water, and the drainage pump control unit can control the drainage pump to stop. Compared with the current method of judging the motor load by collecting the current through the current sensor, the present application can be realized based on the software algorithm and the simple voltage acquisition circuit, the method is simple and does not increase the cost.

[0014] In some embodiments of the present application, the back electromotive force detection unit finds the voltage data during the period when the current is continuously zero from the end voltage data in the following steps: Taking the voltage zero-crossing as a node, the end voltage data is segmented; In each segment of the stored data, recording starts from the first falling data and stops after the rising appears.

[0015] In some embodiments of the present application, the motor load judgment unit is specifically used for: calculating the cumulative sum S1 of the first half of the back electromotive force array data; calculating the cumulative sum S2 of the second half of the back electromotive force array data; comparing the cumulative sum S1 of the first half and the cumulative sum S2 of the second half, and judging that the motor is in no-load when the difference between the two is less than the set limit, otherwise, judging that the motor is in load.

[0016] In some embodiments of the present application, the motor load judgment unit is specifically used for: calculating the continuous change rate of the data in the back electromotive force array; judging that the motor is in no-load when the change rate is less than the set value, and judging that the motor is in load when the change rate exceeds the set value.

[0017] In some embodiments of the present application, the motor load judgment unit is further used for: continuously judging the continuously collected back electromotive force array, adding 1 when the motor is in no-load, subtracting 1 when the motor is in load, and judging that the motor is in no-load when the cumulative count reaches the threshold.

[0018] Other features and advantages of the present application will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0020] Figure 1 The current, voltage and back electromotive force curve of the single-phase permanent magnet synchronous motor is shown in the figure; Figure 2 The execution steps of the water pump waterless shutdown control method are shown in the figure; Figure 3 The relationship between the back electromotive force phase and the current phase of the single-phase permanent magnet synchronous motor is shown in the figure; Figure 4 One embodiment of the voltage acquisition circuit in the washing equipment is shown in the figure. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort belong to the protection scope of the present application.

[0022] In the description of the present application, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation to the present application.

[0023] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances. In the description of the above embodiments, the specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0024] The terms "first", "second", "third", etc. are used only for descriptive purposes and should not be construed as implying or suggesting relative importance or an indicated number of the technical features indicated. Thus, features defined with "first", "second", etc. can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise stated.

[0025] The method of the present application proposes a method for judging under-water for a drainage pump using a single-phase permanent magnet synchronous motor. The single-phase permanent magnet synchronous motor is powered by single-phase alternating current, and the permanent magnet rotor and the stator rotate synchronously. It has the advantages of simple structure and high energy saving.

[0026] The judgment principle of the present application will be described first as follows: 1. In the structure of the single-phase permanent magnet synchronous motor, the coil is fixed on the stator, and the permanent magnet is fixed on the rotor. When the rotor rotates, the magnetic field generated by the permanent magnet on the rotor will rotate, and the coil on the stator will cut the rotating magnetic field. According to the law of electromagnetic induction, the conductor cutting the magnetic induction line will generate induced electromotive force, thereby generating a counter electromotive force in the stator coil.

[0027] 2. The single-phase permanent magnet synchronous motor usually converts single-phase alternating current into direct current through "AC-DC-AC" conversion (i.e. frequency converter), and then converts it into variable frequency and variable voltage alternating current through an inverter (such as a bridge circuit composed of IGBT or MOSFET) to supply power to the stator winding. In order to generate a smooth rotating magnetic field, the stator winding needs to pass through a sinusoidal current to drive the rotor permanent magnet synchronous coupling. The sinusoidal current has a zero point, and when the current is zero, there is only one coil on the motor, and the voltage on the motor is the counter electromotive voltage at this time.

[0028] 3. The stator winding of the single-phase permanent magnet synchronous motor is essentially an inductive load. According to the characteristics of alternating current circuit, the inductive element will make the current phase lag behind the voltage phase, and the lag angle depends on the inductance and the power frequency, which is shown as Figure 1 When the voltage is zero, the current has not yet passed zero.

[0029] 4. The alternating current voltage has a zero point, and the voltage commutates at the zero point. In the single-phase permanent magnet synchronous motor, after the voltage commutates, the power switch tube (IGBT, MOSFET) drive circuit in the inverter implements chopper control through high-frequency switching to adjust the supply voltage, thereby achieving the purpose of controlling the electromagnetic torque and speed of the motor.

[0030] 5. The power switch tube is cut off when the input current is zero.

[0031] 6. The current of the single-phase permanent magnet synchronous motor is affected by the complexity of the motor structure, the magnetic field distribution, the back electromotive force, the duty cycle of the pulse in the chopping control, the load characteristics and the mechanical inertia, and at the zero-crossing point, the current is zero for a period of time.

[0032] Summary: (1) Based on the analysis of 1 and 2 above, the voltage across the motor is exactly the back electromotive force voltage when the current of the single-phase permanent magnet synchronous motor is zero. (2) Based on the analysis of 3, 4, 5 and 6, there is a current zero interval after the voltage zero-crossing in the unidirectional permanent magnet synchronous motor, and the power switch tube for chopping control is turned off during the interval.

[0033] According to the above two summaries, it can be known that there is a period of time after the voltage zero-crossing in the single-phase permanent magnet synchronous motor during which the back electromotive force can be detected.

[0034] Based on the above idea, the method for judging the operation state of the drainage pump provided by the application judges the operation state of the drainage pump by the following means: collecting the voltage across the motor, finding the back electromotive force voltage part after the voltage zero-crossing, analyzing the phase of the back electromotive force to judge the position of the rotor, and judging the load size according to the position of the rotor. If the load is large, it means that there is water in the drainage pump, and if the load is small, it means that there is no water in the drainage pump.

[0035] Specifically, as shown in Figure 2 , the method comprises the following steps: S1: During the operation of the drainage pump, the terminal voltage of the single-phase permanent magnet synchronous motor is collected in real time.

[0036] Taking 50Hz AC power supply as an example, the terminal voltage of the motor is sampled at a sampling frequency of 100us during each 10ms doughnut wave, and 100 voltage signals can be sampled in one doughnut wave.

[0037] S2: Find the voltage data during the current zero interval and store it as a back electromotive force array.

[0038] The sampled voltage signals are segmented and stored as multiple arrays according to the zero-crossing points, that is, the voltage signals collected in each doughnut wave are divided into an array according to the zero-crossing points of the power supply voltage.

[0039] Since the current phase of the unidirectional permanent magnet synchronous motor lags behind the voltage phase, when the voltage crosses zero, the current has not yet crossed zero, and the power switch tube in the motor inverter continues to perform chopping control because the current has not yet crossed zero. Therefore, at the beginning of a doughnut wave, the sampled voltage data is the terminal voltage data of the motor, and when the current crosses zero, the sampled voltage data is the back electromotive force data. As shown in Figure 1 , the pink curve is the voltage zero-crossing signal, the green curve is the current curve, and the red curve is the voltage curve. When the voltage crosses zero, the current lags behind the voltage.

[0040] After the current of a single-phase permanent magnet synchronous motor crosses zero, it will remain for a period of time, such as... Figure 1 The green curve shown remains at zero for a period of time, corresponding to a gap in the red voltage curve (hereinafter referred to as the groove position, intervals A and B). The voltage detected during this gap is the back electromotive force (EMF). Therefore, the data after the voltage crosses zero includes a segment of back EMF data; taking a current duration of zero of 1 ms as an example, a sampling interval of 100 μs can sample 10 back EMF data points. Figure 1 As shown, the blue curve represents the back electromotive force, and the groove of the red voltage curve corresponds exactly to the back electromotive force curve.

[0041] Because the duty cycle of the power switch is adjusted and changed in real time during chopper control, the number of back EMF data samples in each round is not the same.

[0042] The back electromotive force data found within each steamed bun wave is stored as a judgment array ARRi, i=1, 2, 3, ...

[0043] S3: Determine the load status of the single-phase permanent magnet synchronous motor based on the changes in the data in the back electromotive force array, and control the drainage pump to stop when the motor is unloaded.

[0044] The phase of the back electromotive force (EMF) and the phase of the current are related as follows: Under no-load conditions, the motor current is mainly used to overcome no-load losses, and the phase difference between the back EMF and the current is close to 90°. Under load conditions, in addition to overcoming no-load losses, the motor current also needs to provide the torque required by the load. At this time, the phase difference between the back EMF and the current changes with the load. The larger the load, the larger the current, and the smaller the phase difference between the back EMF and the current. Conversely, the smaller the load, the smaller the current, and the larger the phase difference between the back EMF and the current. When the motor reaches the rated load, the phase difference between the back EMF and the current is usually between 30° and 60°.

[0045] like Figure 3 As shown, the phase difference between the back EMF curve 1 and the current curve is about 90°, which is reflected on the curves as follows: the top of the back EMF curve 1 corresponds to the part where the current phase is zero, corresponding to the motor's no-load state; the phase difference between the back EMF curve 2 and the current curve is within 60°, which is reflected on the curves as follows: the left half of the wave-like shape of the back EMF curve 2 corresponds to the part where the current phase is zero, corresponding to the motor's loaded state.

[0046] Combination Figure 1As shown, according to the change (obvious or not obvious) of the back electromotive force data collected during the current duration of zero, the phase difference between the back electromotive force curve and the current curve can be deduced: if the back electromotive force data changes slowly, it indicates that the phase difference between the back electromotive force curve and the current curve is about 90°, corresponding to the state of the motor being unloaded; if the back electromotive force data changes more obviously, it indicates that the phase difference between the back electromotive force curve and the current curve is between 30° and 60°, corresponding to the state of the motor having a load.

[0047] Therefore, in an embodiment of the present application, the change of the data in the back electromotive force array is determined by the following means: calculating the cumulative sum S1 of the first half of the data in the back electromotive force array, calculating the cumulative sum S2 of the second half of the data in the back electromotive force array, and calculating the difference between S1 and S2; setting a limit value, if the difference is within the limit value, it indicates that the data in the back electromotive force array does not change much, indicating that the top of the back electromotive force curve corresponds to the zero point of the current curve, and the phase difference between the back electromotive force curve and the current curve is about 90°, indicating that the motor is unloaded; if the difference exceeds the limit value, it indicates that the data in the back electromotive force array changes significantly, indicating that the left half of the back electromotive force curve corresponds to the zero point of the current curve, and the phase difference between the back electromotive force curve and the current curve is between 30° and 60°, indicating that the motor has a load. The limit value is obtained based on theoretical calculation or empirical value.

[0048] In an embodiment of the present application, the change of the data in the back electromotive force array can be determined by the following means: calculating the continuous change rate of the data in the back electromotive force array, if the change rate is less than a set value, it indicates that the data does not change much, indicating that the top of the back electromotive force curve corresponds to the zero point of the current curve, and the phase difference between the back electromotive force curve and the current curve is about 90°, corresponding to the state of the motor being unloaded; if the change rate is greater than the set value, it indicates that the data changes significantly, indicating that the left half of the back electromotive force curve corresponds to the zero point of the current curve, and the phase difference between the back electromotive force curve and the current curve is between 30° and 60°, corresponding to the state of the motor having a load. The set value is obtained based on theoretical calculation or empirical value.

[0049] The motor is unloaded, and there is no water in the drainage pump; the motor has a load, and there is water in the drainage pump.

[0050] In a specific embodiment of the present application, the continuously collected back electromotive force array is continuously determined, the count is increased by 1 when the motor is unloaded, and the count is decreased by 1 when the motor has a load, and when the cumulative count reaches a threshold value (for example, 50 times of continuous determination of the motor being unloaded), it is determined that the drainage pump has no water, and the drainage pump can be controlled to stop.

[0051] A washing apparatus is provided, which is configured with a drainage pump using a single-phase permanent magnet synchronous motor, comprising: An end voltage acquisition circuit is used to acquire the terminal voltage of the single-phase permanent magnet synchronous motor in real time during the operation of the drainage pump. For example,Figure 4 one embodiment.

[0052] a back electromotive force detection unit for finding voltage data during the period when the current is zero from the terminal voltage data and storing it as a back electromotive force array.

[0053] a motor load judging unit for judging the load condition of the single-phase permanent magnet synchronous motor according to the change of data in the back electromotive force array and sending the judging result to the drain pump control unit.

[0054] the drain pump control unit controls the drain pump to stop without water when the judging result is that the motor is idle.

[0055] In some embodiments of the present application, the back electromotive force detection unit finds the voltage data during the period when the current is zero from the terminal voltage data in the following steps: segment the terminal voltage data with voltage zero-crossing as the node; in the data stored in each segment, record from the first falling data until the rising data appears and stop recording.

[0056] In some embodiments of the present application, the motor load judging unit is specifically used for: calculating the cumulative sum S1 of the first half data in the back electromotive force array; calculating the cumulative sum S2 of the second half data in the back electromotive force array; comparing the cumulative sum S1 of the first half data and the cumulative sum S2 of the second half data, and judging that the motor is idle when the difference between the two is less than a set limit, otherwise, judging that the motor is loaded.

[0057] In some embodiments of the present application, the motor load judging unit is specifically used for: calculating the continuous change rate of the data in the back electromotive force array; judging that the motor is idle when the change rate is less than a set value, and judging that the motor is loaded when the change rate exceeds the set value.

[0058] In some embodiments of the present application, the motor load judging unit is further used for: continuously judging the back electromotive force array continuously collected, adding 1 when judging that the motor is idle, subtracting 1 when judging that the motor is loaded, and judging that the motor is idle when the cumulative count reaches a threshold.

[0059] The specific drain pump waterless control method in the washing equipment has been described in detail, which will not be repeated here.

[0060] It should be noted that in the specific implementation process, the control part can be realized by a processor in the form of hardware to execute computer execution instructions in the form of software stored in the memory, which is not described here, and the programs corresponding to the actions performed by the control circuit can be stored in the computer readable storage medium of the system in the form of software, so that the processor calls and executes the operations corresponding to each module.

[0061] The computer readable storage medium in the above can include a volatile memory, such as a random access memory; can also include a non-volatile memory, such as a read-only memory, a flash memory, a hard disk or a solid state disk; and can also include a combination of the above kinds of memories.

[0062] The processor mentioned above can also be a collective term for a plurality of processing elements. For example, the processor can be a central processing unit, or can be other general-purpose processors, digital signal processors, application-specific integrated circuits, field programmable gate arrays or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or can be any conventional processor, etc., and can also be a special-purpose processor.

[0063] It should be noted that the above description is not a limitation of the present application, and the present application is also not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present application should also be within the scope of the present application.

Claims

1. A waterless shutdown control method for a drain pump applied to a washing apparatus driven by a single-phase permanent magnet synchronous motor, characterized in that, The method comprises the following steps: S1, collecting the terminal voltage of the single-phase permanent magnet synchronous motor in real time during the operation of the drainage pump; S2, finding the voltage data during the current continuously being zero and storing the voltage data as an array of back electromotive force; S3, judging the load condition of the single-phase permanent magnet synchronous motor according to the change of the data in the array of back electromotive force, and controlling the drainage pump to stop without water when the motor is in no-load.

2. The dry run control method of a drainage pump according to claim 1, characterized by, S2, finding the voltage data during the current continuously being zero, comprising: segmenting the terminal voltage data with voltage zero-crossing as a node; in each segment of the stored data, recording from the first falling data until the rising data appears and then stopping the recording.

3. The dry run control method of a drainage pump according to claim 1, characterized by, S4, judging the load condition of the single-phase permanent magnet synchronous motor according to the change of the data in the array of back electromotive force, comprising: calculating the cumulative sum S1 of the first half of the data in the array of back electromotive force; calculating the cumulative sum S2 of the second half of the data in the array of back electromotive force; comparing the cumulative sum S1 of the first half and the cumulative sum S2 of the second half, and judging that the motor is in no-load when the difference between the two is less than a set limit, otherwise, judging that the motor is in load.

4. The dry run control method of a drainage pump according to claim 1, characterized by, S4, judging the load condition of the single-phase permanent magnet synchronous motor according to the change of the data in the array of back electromotive force, comprising: calculating the continuous change rate of the data in the array of back electromotive force; judging that the motor is in no-load when the change rate is less than a set value, and judging that the motor is in load when the change rate is more than the set value.

5. The dry run control method of a drainage pump according to claim 1, characterized by, S4 further comprises: continuously judging the continuously collected array of back electromotive force, adding 1 when the motor is in no-load, subtracting 1 when the motor is in load, and judging that the motor is in no-load when the cumulative count reaches a threshold value.

6. A washing apparatus configured with a drain pump using a single-phase permanent magnet synchronous motor, characterized by, The method comprises the following steps: an end voltage acquisition circuit, configured to collect the terminal voltage of the single-phase permanent magnet synchronous motor in real time during the operation of the drainage pump; a back electromotive force detection unit, configured to find the voltage data during the current continuously being zero from the terminal voltage data and store the voltage data as an array of back electromotive force; a motor load judgment unit, configured to judge the load condition of the single-phase permanent magnet synchronous motor according to the change of the data in the array of back electromotive force, and send the judgment result to a drainage pump control unit; the drainage pump control unit controls the drainage pump to stop without water when the judgment result is that the motor is in no-load.

7. The washing apparatus according to claim 6, characterized by The back electromotive force detection unit finds the voltage data during the current continuously being zero from the terminal voltage data by the following steps: segmenting the terminal voltage data with voltage zero-crossing as a node; in each segment of the stored data, recording from the first falling data until the rising data appears and then stopping the recording.

8. The washing apparatus according to claim 6, wherein The motor load judgment unit is specifically configured to: calculate the cumulative sum S1 of the first half of the data in the array of back electromotive force; calculate the cumulative sum S2 of the second half of the data in the array of back electromotive force; compare the cumulative sum S1 of the first half and the cumulative sum S2 of the second half, and judge that the motor is in no-load when the difference between the two is less than a set limit, otherwise, judge that the motor is in load.

9. The washing apparatus according to claim 6, wherein The motor load judgment unit is specifically configured to: calculate the continuous change rate of the data in the array of back electromotive force; judge that the motor is in no-load when the change rate is less than a set value, and judge that the motor is in load when the change rate is more than the set value.

10. The washing apparatus according to claim 6, wherein The motor load judgment unit is further configured to: continuously judge the continuously collected array of back electromotive force, add 1 when the motor is in no-load, subtract 1 when the motor is in load, and judge that the motor is in no-load when the cumulative count reaches a threshold value.

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