OPERATION OF A DRIVE SYSTEM WITH A SINGLE-PHASE SYNCHRONOUS MOTOR

Description

[0001] The invention relates to a method for operating a drive system with a single-phase synchronous motor according to claim 1, a drive system for carrying out such a method according to claim 13, a household appliance component with such a drive system according to claim 14, and a household appliance with such a household appliance component according to claim 15.

[0002] Among the well-known electric motors are synchronous motors, which can be operated single-phase with alternating current or multi-phase with three-phase current. In each case, a constantly magnetized rotor is used. This rotor can be powered by permanent magnets or external electromagnetic excitation. The term "synchronous motor" derives from the fact that the rotor is driven synchronously by a rotating magnetic field in the stator. Thus, during operation, the synchronous motor exhibits synchronous motion with the alternating current, and its rotational speed is linked to the frequency of the alternating current via the number of pole pairs in the stator.

[0003] Multi-strand permanent magnet synchronous motors are typically operated via a frequency converter, enabling controlled operation by allowing the direction of rotation, speed, and torque of the synchronous motor to be specified via the frequency and amplitude of the frequency converter's output AC voltage. This allows for targeted control of the synchronous motor's rotational behavior, for example, during startup and depending on the load being driven.

[0004] When controlling a regulated single-phase synchronous motor, a sensor is usually required to determine the rotor position, which can then be used to determine the desired commutation times.

[0005] However, a disadvantage of this is that such a rotor position sensor involves additional costs. Furthermore, extra installation space must be provided for the rotor position sensor. The wiring and interconnection of the rotor position sensor are also highly complex, which can increase manufacturing costs and / or be a source of malfunctions.

[0006] In order to determine the rotor position of a controlled single-phase synchronous motor without the use of a rotor position sensor and thereby avoid the disadvantages of the rotor position sensor described above, it is known to determine the rotor position without a corresponding rotor position sensor.

[0007] DE 10 2019 110 045 A1 describes a method for operating a drive system with a single-phase synchronous motor with at least the following steps: Operating the single-phase synchronous motor with a first electrical frequency of a reference voltage, interrupting the operation of the single-phase synchronous motor for a measurement period, wherein the measurement period includes a zero crossing of a motor current, within the measurement period at the time of the zero crossing of the motor current, detecting an induced voltage, comparing the detected induced voltage with a target value of the induced voltage and re-operating the single-phase synchronous motor with a second electrical frequency of the reference voltage depending on the result of the comparison.

[0008] A disadvantage of the method described in DE 10 2019 110 045 A1 is that this method can only be used from a minimum frequency.

[0009] Another disadvantage is that the single-phase synchronous motor must be started in open-loop operation and then switched to closed-loop operation; that is, starting in a closed-loop operation is not possible. This makes the single-phase synchronous motor sensitive to external influences and can disrupt its start-up. This can lead to an aborted start-up. Therefore, this drive system has limited robustness.

[0010] DE 10 2013 218 041 A1 describes a method for operating a single-phase electric motor having a stator and a rotor rotatable relative to it, according to which the relative position of the rotor relative to the stator is determined by determining the electromotive restoring force (BEMF) generated in the stator coil of the stator, comprising the following steps: Switching off the electric stator current for the duration of an adjustable first dead time. After the first dead time has elapsed and with the current still switched off: Determining the time of a zero crossing of the electromotive restoring force (BEMF) and thus of the electric current induced in the stator coil. After determining such a zero crossing of the electromotive restoring force (BEMF): Commutating the current to the stator coil after an adjustable second dead time has elapsed.

[0011] A disadvantage of the method described in DE 10 2013 218 041 A1 is that the current is applied for a certain period (a time specified in the software), and the point at which the BEMF crosses zero is monitored. Commutation of the single-phase electric motor occurs at this point. However, it must be ensured that the rotor is moved more than 90° but not more than 180°. If the rotor is stiff or too loose, or if the load torque changes, the commutation point may be missed, the rotor may lock, and the control system may malfunction. In such cases, the method described in DE 10 2013 218 041 A1 is not applicable.

[0012] From US 2012019180 A1, a method for starting a single-phase permanent magnet synchronous motor is known which is simple and cost-effective to implement, wherein the method includes a step to apply a control logic of the switch which provides a first and a second condition for switching on, wherein the first condition is checked if a detected back-EMF signal has the same sign as an electrical mains voltage signal, wherein the second condition is checked if the back-EMF signal has the same sign as its first derivative value.

[0013] From DE 102019110045 A1, a method for operating a drive system with a single-phase synchronous motor is known, comprising at least the following steps: operating the single-phase synchronous motor with a first electrical frequency of a reference voltage, interrupting the operation of the single-phase synchronous motor for a measurement period, wherein the measurement period includes a zero crossing of a motor current, within the measurement period at the time of the zero crossing of the motor current, detecting an induced voltage, comparing the detected induced voltage with a target value of the induced voltage, and re-operating the single-phase synchronous motor with a second electrical frequency of the reference voltage depending on the result of the comparison.

[0014] The invention thus addresses the problem of providing a method for operating a drive system with a single-phase synchronous motor of the type described above, thereby expanding the possibilities for operating the drive system. In particular, it aims to build upon and improve the methods of DE 10 2019 110 045 A1 and DE 10 2013 218 041 A1, especially by overcoming their aforementioned disadvantages. This should be achieved as simply, cost-effectively, and / or reliably as possible. At the very least, it should provide an alternative to known methods for operating a drive system with a single-phase synchronous motor.

[0015] According to the invention, this problem is solved by a method with the features of claim 1, by a drive system with the features of claim 13, by a household appliance component with the features of claim 14, and by a household appliance with the features of claim 15. Advantageous embodiments and further developments of the invention are set forth in the following dependent claims.

[0016] Thus, the present invention relates to a method for operating a drive system with a single-phase synchronous motor comprising at least the following steps: Energizing the stator of a single-phase synchronous motor with a motor voltage of a predetermined sign until a predetermined current threshold of the stator current or a predetermined on-time is reached, terminating the energizing, continuously sensing the motor current of the stator in the region of the zero crossing of the motor current, sensing an induced voltage of the stator, determining the sign of the induced voltage, and if the sign of the induced voltage is the opposite sign of the predetermined sign of the motor voltage, changing the predetermined sign of the motor voltage to the sign of the induced voltage.

[0017] In other words, according to the invention, the stator can be energized to a certain predetermined degree, so that a corresponding voltage can be induced in the rotor by the stator. When the energization of the stator is stopped, both the motor current and the voltage in the rotor decay. However, the voltage in the rotor continues to induce a voltage in the stator, which, when the motor current has completely decayed and is zero, can be detected as the induced voltage of the stator. It should be noted that the motor voltage and motor current always have the same sign.

[0018] According to the invention, the zero-crossing region of the motor current can essentially correspond to the exact zero crossing, but can also deviate from the exact zero crossing to a certain extent. Preferably, the maximum deviation from the exact zero crossing is ±50%, based on the amplitude of the electromotive force (EMF), or ±30 degrees, based on the electrical angle; particularly preferably, ±25% or ±15 degrees, respectively.

[0019] The fundamental principle here is the electrical rotational frequency, which is the mechanical rotational frequency of the drive multiplied by the number of pole pairs, p, of the motor. In an example case, let p=1, meaning the mechanical and electrical frequencies are identical. At a speed of, for example, 3000 rpm, f_el = 50 Hz (T_el = 20 ms). A deviation of ±50% of the amplitude results in an electrical deviation of ±30° over time (with a reference value of 50% of the amplitude of the induced voltage, a phase of 30° arises between the current and the electromotive force, sin(30°) = 0.5). The period in this example is T_el = 20 ms. ±30° electrical * 20 ms gives approximately ±1.7 ms. This is an example for 50 Hz (i.e., here at p=1 and 3000 rpm).

[0020] The sign of the measured induced voltage of the stator can now be compared to the predetermined sign of the motor voltage to determine whether they are the same or not. If the signs of the induced voltage of the stator and the predetermined motor voltage are the same, the single-phase synchronous motor will operate, or the rotor will rotate, in the desired direction of rotation, as determined by the predetermined sign. Operation can then continue in this manner. Otherwise, the predetermined sign of the motor voltage must be reversed.

[0021] In contrast to the method of DE 10 2019 110 045 A1, the method according to the invention is applicable from the point at which the rotor is stationary, i.e., from zero rotational speed. Preferably, the rotor is aligned beforehand, as will be described in more detail below.

[0022] In contrast to the method of DE 10 2013 218 041 A1, the method according to the invention continuously samples the induced voltage of the stator, i.e., the electromotive force (EMF) or the electromotive force (BEMF), within one electrical period of the motor. This allows the single-phase synchronous motor to be started in a controlled manner using the method according to the invention. Accordingly, a sensorless controlled start of the rotor with higher inertia, e.g., in a fan, can be performed just as well as in applications with lower inertia.

[0023] According to one aspect of the invention, the predetermined sign of the motor voltage corresponds to a desired direction of rotation of the rotor of the single-phase synchronous motor. Accordingly, the direction of rotation of the rotor can be predetermined by specifying the sign of the motor voltage.

[0024] According to another aspect of the invention, the drive system does not include a sensor for detecting the position of a rotor of the single-phase synchronous motor. By omitting a rotor position sensor, the disadvantages described above can be avoided. The rotor position can still be taken into account as previously described.

[0025] According to a further aspect of the invention, the aforementioned steps of the inventive method are continuously repeated. This can enable continuous application or implementation of the inventive method during the operation of the drive system.

[0026] According to a further aspect of the invention, the motor voltage of the stator is supplied by means of a continuous voltage or by means of voltage pulses, preferably by means of PWM voltage pulses. This can enable the corresponding implementation.

[0027] According to another aspect of the invention, the predetermined current threshold of the motor current depends on the predetermined sign of the motor voltage. For example, the predetermined current threshold of the motor current can be 0.3 A or 0.4 A. In any case, this expands the possibilities for operating the drive system.

[0028] According to another aspect of the invention, the drive system is operated with a closed phase controller loop. This can enable corresponding controlled operation.

[0029] According to another aspect of the invention, the motor current is continuously detected by measuring the motor phase current. This can represent a way to continuously detect the motor current.

[0030] According to a further aspect of the invention, the motor current is continuously measured by means of two current-sensing resistors in both phases of an inverter. This can represent an alternative way to continuously measure the motor current.

[0031] According to a further aspect of the invention, the motor current is continuously measured by means of a current-sensing resistor in a DC link. This can represent an alternative way to continuously measure the motor current.

[0032] According to another aspect of the invention, the previously described method comprises the following preceding steps: Aligning a rotor of the single-phase synchronous motor into a predetermined starting position by imprinting a constant motor voltage on the stator, and, once alignment is complete, terminating the constant motor voltage on the stator during alignment.

[0033] In other words, at the start of operation of the single-phase synchronous motor, as described previously, i.e., when the motor starts, the rotor can be aligned to a defined initial position by applying a constant voltage for a short duration, for example, approximately 0.5 seconds. Then, the current, which can be supplied, for example, by a bridge rectifier, can be switched off so that the rotor returns to its (currentless) rest position. It should be noted that the rest position with and without current differs due to geometric asymmetries in the stator. The rest position is that of least magnetic resistance.

[0034] According to a further aspect of the invention, the constant motor voltage of the stator is applied by means of a continuous DC voltage or by means of DC voltage pulses. This can enable the corresponding implementation.

[0035] The present invention also relates to a drive system comprising a single-phase synchronous motor with a stator and a rotor, and a switching unit configured to operate the single-phase synchronous motor. The switching unit is further configured to energize the stator with a motor voltage of a predetermined polarity and to terminate the energizing process. The single-phase synchronous motor is configured to detect a motor current of the stator and an induced voltage of the stator. The drive system, preferably a control unit of the drive system, is configured to execute a method as described above. In this way, a drive system can be provided to implement the previously described method according to the invention, so that its properties and advantages can be utilized.

[0036] The present invention also relates to a household appliance component, preferably a drain pump, a condensate pump, or a fan, with a drive system as described above. In this way, the properties and advantages of a drive system according to the invention can be utilized in a household appliance component.

[0037] The present invention also relates to a household appliance, preferably a washing machine or a dishwasher, comprising a household appliance component as described above. In this way, the properties and advantages of a household appliance component according to the invention can be utilized.

[0038] An embodiment of the invention is shown schematically in the drawings and is described in more detail below. It shows Figure 1 is a schematic representation of a drive system according to the invention; and Figure 2 is a schematic flowchart of a method according to the invention.

[0039] A drive system 1-4 according to the invention comprises a single-phase synchronous motor 1, which has a stator 10, also called a stator 10, and a rotor 11, also called a stator 11, which is rotatably movable relative to the stator 10. The stator 10 has electrically conductive windings (not shown) across which a motor voltage U_motor can be applied to generate a motor current I_motor. The motor voltage U_motor can be tapped via a voltage divider (not shown). The rotor 11 has a permanent magnet 12 with a north pole 12a and a south pole 12b, see figure. Fig. 1 .

[0040] A control unit 2 has an input via which a variable setpoint value of a current threshold I_ref can be specified. The current threshold I_ref can be changed between two values, for example, 0.3 A and 0.4 A. Alternatively, these values ​​can also be specified as two current thresholds I_ref and used alternatively to each other. Furthermore, a measured value of a detected induced voltage Bemf_Sample is supplied to the control unit 2, which can be detected at the stator 10 of the single-phase synchronous motor 1, see [reference]. Fig. 1 .

[0041] Control unit 2 includes a phase controller (not shown) which can generate a reference voltage for the controlled operation of the single-phase synchronous motor 1. A processing unit 3 receives the reference voltage from control unit 2 as its input and generates four pulse-width modulated signals (not shown), which are fed to a switching unit 4.

[0042] Switching unit 4 is configured as an H-bridge (not shown) and accordingly has four switches, which can be implemented as power switches in the form of four MOSFETs or four IGBTs. The four switches connect a DC voltage to a ground potential and also generate the motor voltage U_motor. A shunt is provided at the ground potential to convert the motor current I_motor into a voltage signal, so that the motor current I_motor can be used as a measurement signal. Optionally, the measurement signal of the motor current I_motor can be amplified by means of an amplifier.

[0043] Figure 2 shows a schematic flowchart of a method according to the invention, which is used with the drive system 1-4 according to the invention. Figure 1 can be carried out.

[0044] When the single-phase synchronous motor 1 is started up, the rotor 11 of the single-phase synchronous motor 1 is aligned once 100 to a predetermined starting position by applying a constant motor voltage to the stator 10. Once the alignment is complete, the constant motor voltage of the stator 10 is discontinued 200.

[0045] The stator 10 of the single-phase synchronous motor 1 is now continuously or repeatedly energized with a motor voltage U_motor with a predetermined sign until the predetermined current threshold I_ref of the motor current I_motor of the stator 10 is reached. The predetermined sign of the motor voltage U_motor corresponds to a desired direction of rotation of the rotor 11 of the single-phase synchronous motor 1.

[0046] The current energizing process is then terminated. Next, the motor current I_motor of stator 10 is continuously measured. At the zero crossing of the motor current I_motor, the induced voltage Bemf_Sample of stator 10 is measured. The sign of the induced voltage Bemf_Sample is then determined, and if the sign of the induced voltage Bemf_Sample is the opposite of the predetermined sign of the motor voltage U_motor, the predetermined sign of the motor voltage U_motor is changed to the sign of the induced voltage Bemf_Sample; otherwise, it is not. Reference numeral list (part of the description)

[0047] Sample-induced voltage (back electromotive force) I_ref current threshold I_motor motor current U_motor motor voltage 1 Single-phase synchronous motor 10 Stator; stator 11 Rotor; runner 12 Permanent magnet 12a North pole 12b South pole 2 Control unit 3 Calculation unit 4 switching unit; H-bridge

Claims

1. Method for operating a drive system (1-4) having a single-phase synchronous motor (1), comprising at least the steps of: energising (300) a stator (10) of the single-phase synchronous motor (1) by applying a motor voltage (U_motor) having a predetermined polarity sign until a predetermined current threshold (I_ref) of a motor current (I_motor) of the stator (10) or a predetermined switch-on time is reached, ending (400) the energising (300), continuously detecting (500) the motor current (I_motor) of the stator (10), in the region of the zero crossing of the motor current (I_motor), detecting (600) an induced voltage (Bemf_Sample) of the stator (10), determining (700) the polarity sign of the induced voltage (Bemf_Sample), and characterised by, if the polarity sign of the induced voltage (Bemf_Sample) is the opposite polarity sign of the predetermined polarity sign of the motor voltage (U_motor), changing (800) the predetermined polarity sign of the motor voltage (U_motor) to the polarity sign of the induced voltage (Bemf_Sample).

2. Method according to claim 1, characterised in that the predetermined polarity sign of the motor voltage (U_motor) corresponds to a desired direction of rotation of a rotor (11) of the single-phase synchronous motor (1).

3. Method according to either claim 1 or claim 2, characterised in that the drive system (1-4) does not have a sensor for detecting the position of a rotor (11) of the single-phase synchronous motor (1).

4. Method according to any of the preceding claims, characterised in that the steps (300-800) are repeated continuously.

5. Method according to any of the preceding claims, characterised in that the motor voltage (U_motor) of the stator (10) is energised (300) by means of a continuous voltage or by means of voltage pulses, preferably by means of PWM voltage pulses.

6. Method according to any of the preceding claims, characterised in that the predetermined current threshold (I_ref) of the motor current (I_motor) depends on the predetermined polarity sign of the motor voltage (U_motor).

7. Method according to any of the preceding claims, characterised in that the drive system (1-4) is operated using a closed phase controller loop.

8. Method according to any of the preceding claims, characterised in that the motor current (I_motor) is continuously detected (500) by measuring the motor phase current.

9. Method according to any of the preceding claims, characterised in that the motor current (I_motor) is continuously detected (500) by means of measurement using two current-measuring resistors in both phases of an inverter.

10. Method according to any of the preceding claims, characterised in that the motor current (I_motor) is continuously detected (500) by means of measurement using a current-measuring resistor of a DC voltage intermediate circuit.

11. Method according to any of the preceding claims, characterised by the preceding steps: aligning (100) a rotor (11) of the single-phase synchronous motor (1) into a predetermined starting position by impressing a constant motor voltage on the stator (10), and once aligned, ending (200) the constant motor voltage of the stator (10) of the alignment (100).

12. Method according to claim 11, characterised in that the constant motor voltage of the stator (10) is impressed by means of a continuous DC voltage or by means of DC voltage pulses.

13. Drive system (1-4) comprising a single-phase synchronous motor (1) having a stator (10) and a rotor (11), and comprising a switching unit (4) which is designed to operate the single-phase synchronous motor (1), the switching unit (4) being further designed to energise (300) the stator (10) by applying a motor voltage (U_motor) having a predetermined polarity sign and end (400) the energising (300), the single-phase synchronous motor (1) being designed to detect a motor current (I_motor) of the stator (10) and an induced voltage (Bemf_Sample) of the stator (10), characterised in that the drive system (1-4), preferably a control unit (2) of the drive system (1-4), is designed to carry out a method according to any of the preceding claims.

14. Household appliance component, preferably a drain pump, a condensate pump or a fan, comprising a drive system (1-4) according to claim 13.

15. Household appliance, preferably a washing machine or a dishwasher, comprising a household appliance component according to claim 14.