Control circuit of permanent magnet synchronous motor

Abstract

The present invention relates to a control circuit of a permanent magnet synchronous motor. The control circuit may include: a first controller for current-frequency control of a permanent magnet synchronous motor; a second controller for voltage / frequency control of the permanent magnet synchronous motor; and a selection unit for selecting a voltage output of the second controller by performing transition during the voltage output of the first controller, and determining an initial state in voltage / frequency control by detecting a position of an applied voltage at a transition time point.

Description

Control circuit of a permanent magnet synchronous motor

[0001] The present invention relates to a control circuit for a permanent magnet synchronous motor, and more specifically, to a control circuit for a permanent magnet synchronous motor to which different scalar control methods are applied.

[0002] In general, permanent magnet synchronous motors have higher energy density and efficiency than induction motors, and their scope of application is expanding into various technological fields.

[0003] The control methods for Permanent Magnet Synchronous Motors (PMSMs) can be divided into scalar control, which controls average torque, and vector control, which controls instantaneous torque.

[0004] Vector control methods have the advantage of being precise and maximizing efficiency, but they have the disadvantages of being difficult to implement within a product and lacking user convenience.

[0005] In contrast, scalar control has the advantage of high ease of use due to its simple control capabilities, although precision is relatively lower.

[0006] Scalar control methods can be further divided into two types: current-frequency (If) control and voltage-frequency (V / f) control.

[0007] In the case of If control, it has the advantage of being able to output rated torque from startup, but it has the disadvantage of low efficiency due to the possibility of unnecessary current being used during operation.

[0008] On the other hand, V / f control has the advantage of relatively high efficiency, but carries the risk of losing synchronization at low speeds.

[0009] Figure 1 is an example diagram of a control circuit of a conventional permanent magnet synchronous motor, and is a control circuit diagram of a current-frequency control method.

[0010] Referring to FIG. 1, a conventional control circuit of a current-frequency control method includes a current controller (110) that controls and supplies current according to a current command, a first coordinate converter (120) that converts the coordinates of the output current of the current controller (110), a PWM generator (130) that performs pulse width modulation (PWM) control with the output of the first coordinate converter (120), and a second coordinate converter (140) that detects the output current of the PWM generator (130), converts the three-phase coordinates into dq-axis coordinates, and inputs them to the current controller (110).

[0011] In the drawing, Qe represents the synchronous coordinate system.

[0012] The current controller (110) has d-axis and q-axis current commands (i d * , i q * The current is controlled based on independent standards for each of the d-axis and q-axis using the coordinate transformation results of the ) and the second coordinate converter (140).

[0013] The current controller (110) performs proportional-integral (PI) control and controls the output current based on the q-axis current, which is the torque component current. The gain value of the current controller (110) can be set using the motor resistance, inductance, and bandwidth.

[0014] The output current of the above current controller (110) is converted into three-phase coordinates of abc for driving a three-phase permanent magnet synchronous motor (PMSM) in the first coordinate converter (120).

[0015] The PWM generation unit (130) is intended to actually apply the voltage calculated from the current controller (110) to the PMSM, and the average voltage is implemented to be the same as the command voltage, thereby driving the PMSM.

[0016] At this time, the three-phase coordinates of the output current of the PWM generator (130) are converted to dq in the second coordinate converter (140).

[0017] As is known, the α-β coordinates are converted to a 90-degree phase difference, and the dq transformation is performed again to make it easier to calculate each current independently in the current controller (110).

[0018] In particular, the time delay of control can be reduced, making control easier.

[0019] In such a configuration example, current-frequency control has the advantage of being able to apply the rated current from a constant, thereby securing high starting torque.

[0020] However, if a constant rated current is continuously applied throughout the entire operating range, current is applied unnecessarily even in situations where a large load is not required, and thus there is a problem of reduced operating efficiency.

[0021] Figure 2 is an example of a V / f control method as another example of the prior art.

[0022] Referring to FIG. 2, the apparatus includes a third coordinate converter (220) that converts the output voltage of a voltage generator (210) into three-phase coordinates, a first PWM generator (230) that performs pulse width modulation control according to the output of the third coordinate converter (220), a fourth coordinate converter (240) that detects the output voltage of the first PWM generator (230) and converts it into a dq axis, and a stabilization controller (250) that stabilizes the voltage control.

[0023] The above voltage generating unit (210) is a frequency command (ω command It outputs a voltage proportional to ), which controls the three-phase PMSM through the third coordinate converter (220) and the first PWM generator (230).

[0024] At this time, the control voltage is coordinate-transformed through the fourth coordinate converter (240) and stabilized by the stabilization controller (250). As an example of using a stabilization controller in V / f control of a PMSM, Korean Registered Patent No. 10-2199277 (registered on December 30, 2020, MPA control device and method for V / f operation of a permanent magnet synchronous machine) is known.

[0025] The stabilization controller (250) is used for coordinate transformation by multiplying the variation in input power by a gain value to compensate for the variation in the frequency command.

[0026] The V / f control method is characterized by its ability to operate with relatively higher efficiency compared to the If control method explained earlier.

[0027] However, there was a disadvantage in that if an inappropriate voltage is applied due to the voltage drop component during low-speed starting, loss of synchronization may occur, which could lead to a relatively high possibility of operation failure.

[0028] The problem that the present invention aims to solve, taking into account the problems of the conventional technology described above, is to provide a permanent magnet synchronous motor control circuit capable of mutually compensating for the disadvantages of the current-frequency control method and the voltage / frequency method for PMSM drive control.

[0029] More specifically, the present invention aims to provide a permanent magnet synchronous motor control circuit capable of stable and efficient operation throughout the entire operating range of the PMSM by combining a current-frequency control method and a voltage / frequency control method, utilizing the advantages of the current-frequency control method during initial startup and the advantages of the voltage / frequency control method during operation after initial startup.

[0030] In particular, another objective of the present invention is to provide a permanent magnet synchronous motor control circuit capable of stably managing changes in voltage and current at the point of switching from a current-frequency control method to a voltage / frequency control method, thereby resolving operational instability that may occur during the switching.

[0031] A permanent magnet synchronous motor control circuit according to a preferred embodiment of the present invention may include a first controller for current-frequency control of a permanent magnet synchronous motor, a second controller for voltage / frequency control of a permanent magnet synchronous motor, and a selection unit that switches among the voltage outputs of the first controller to select the voltage output of the second controller, and detects the position of the applied voltage at the time of switching to determine an initial state in voltage / frequency control.

[0032] In an embodiment of the present invention, the selection unit can output the voltage of the first controller at the beginning of the switching point and gradually attenuate it to output the voltage of the second controller.

[0033] In an embodiment of the present invention, the selection unit may include a voltage detection unit that provides position information of the applied voltage to the first coordinate transformation unit in a state of switching to the voltage of the second controller, a voltage adjustment unit that attenuates the voltage from the voltage of the first controller to the voltage of the second controller for a time set to the voltage of the second controller in a state of switching to the voltage of the second controller, and a voltage selection unit that selects the voltage of the voltage adjustment unit or the voltage of the first controller and applies it to the first coordinate transformation unit.

[0034] In an embodiment of the present invention, the voltage detection unit may include a calculation unit that calculates the position by performing an arctangent 2 operation on the voltage of the first controller, and a first switch that provides the position information of the voltage calculated by the calculation unit to the first coordinate transformation unit when switching to the voltage of the second controller.

[0035] In an embodiment of the present invention, the voltage adjustment unit may include a voltage attenuation unit that attenuates the voltage and a second switch that selects the voltage of the voltage attenuation unit when switching to the voltage of the second controller.

[0036] In an embodiment of the present invention, the voltage attenuation unit outputs the difference between the voltage of the first controller and the voltage of the second controller in the initial state to an adder when switching to the second controller, attenuates the difference for a set time so that the output voltage becomes zero voltage, and the adder can add the voltage of the voltage attenuation unit and the voltage of the second controller.

[0037] The permanent magnet synchronous motor control circuit of the present invention applies a current-frequency control method that facilitates torque control at low speeds, and performs high-efficiency voltage / frequency control at medium speeds or higher, thereby enabling stable and highly efficient control of the permanent magnet synchronous motor.

[0038] In particular, the present invention identifies the problem of sudden voltage and current changes that occur when switching between a current-frequency control method and a voltage / frequency control method, and enables stable operation in response to sudden voltage and current changes, thereby having the effect of enabling stable control and operation of a permanent magnet synchronous motor while applying different control methods.

[0039] Figure 1 is an example diagram of an If control circuit of a conventional permanent magnet synchronous motor.

[0040] Figure 2 is an example diagram of a V / f control circuit of a conventional permanent magnet synchronous motor.

[0041] FIG. 3 is a control circuit diagram of a permanent magnet synchronous motor according to a preferred embodiment of the present invention.

[0042] FIG. 4 is a circuit diagram of one embodiment of the selection unit applied to the present invention.

[0043] To fully understand the structure and effects of the present invention, preferred embodiments of the present invention are described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various modifications can be made. The description of the embodiments is provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention. In the attached drawings, components are depicted enlarged from their actual size for convenience of explanation, and the proportions of each component may be exaggerated or reduced.

[0044] Terms such as 'first' and 'second' may be used to describe various components, but said components should not be limited by said terms. These terms may be used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, 'first component' may be named 'second component,' and similarly, 'second component' may be named 'first component.' Furthermore, singular expressions include plural expressions unless the context clearly indicates otherwise. Unless otherwise defined, terms used in the embodiments of the present invention may be interpreted in the sense commonly known to those skilled in the art.

[0045] Hereinafter, a permanent magnet synchronous motor control circuit according to one embodiment of the present invention will be described in detail with reference to the drawings.

[0046] FIG. 3 is a block diagram of the permanent magnet synchronous motor control circuit of the present invention.

[0047] Referring to FIG. 3, the permanent magnet synchronous motor control circuit of the present invention comprises: a first controller (10) that performs current-frequency control; a second controller (20) that performs voltage / frequency control; a selection unit (30) that selects and outputs the voltage of the first controller (10) or the second controller (20), and adjusts and outputs the voltage at the point of switching from the control state of the first controller (10) to the control state of the second controller (20); a first coordinate conversion unit (40) that converts the coordinates of the output of the selection unit (30) into three-phase coordinates; a PWM generation unit (50) that generates a pulse width modulation signal for driving a PMSM (60) according to the voltage of the first coordinate conversion unit (40); and a circuit that detects the output of the PWM generation unit (50), converts it into a vertical coordinate system, and feeds it back to the first controller (10) and the second controller (20). It is configured to include a second coordinate transformation unit (70).

[0048] Hereinafter, the configuration and operation of the permanent magnet synchronous motor control circuit of the present invention, configured as described above, will be explained in more detail.

[0049] First, the first controller (10) is for current-frequency control and takes a current command as input and controls the d-axis and q-axis current (or voltage). The first controller (10) can use the current controller (110) used in FIG. 1 above.

[0050] Additionally, the second controller (20) is for voltage / frequency control and includes a stabilization loop to perform stable voltage / frequency control. The second controller (20) may include the stabilization controller (250) and the voltage generation unit (210) shown in FIG. 2.

[0051] The present invention controls the PMSM (60) using the current-frequency control method of the first controller (10) when the speed is below a set reference speed (which may be expressed as 'low speed' in the following description), and controls the PMSM (60) using the voltage / frequency control method of the second controller (20) when the speed exceeds the reference speed (which may be expressed as 'medium speed', 'medium speed or higher', or 'high speed' in the following description).

[0052] For example, medium speed can be greater than 10% and less than or equal to 70% of the rated value of PMSM (60), and high speed can be greater than 70% and less than or equal to 100%.

[0053] For such control, the present invention may further include a higher controller (70) for controlling the operation of the first controller (10) and the second controller (20) and the switching operation of the selection unit (30).

[0054] The above reference speed can be 5 to 10% of the rating of the PMSM (60).

[0055] For example, current-frequency control using the first controller (10) is performed in the range of 0% to 5% or 0% to 10% relative to the rated speed, and voltage / frequency control using the second controller (20) is performed in the control range exceeding the reference speed.

[0056] The control of the first controller (10) and the second controller (20) is selected by the selection unit (30).

[0057] The selection unit (30) may be composed of a combination of simple switches, but in this case, an unstable element may occur due to the difference between the magnitude of the voltage and current of the current-frequency control and the magnitude of the voltage and current of the voltage / frequency control, and thus an unstable PMSM (60) control state may occur due to the difference between the magnitudes of the voltage and current.

[0058] To solve this, the selection unit (30) of the present invention calculates the position of the applied voltage at the switching point and includes a configuration that gradually attenuates it according to the slope set by the voltage of the current-frequency control method and the voltage of the voltage / frequency control method.

[0059] This can be understood as linear damping according to the set slope.

[0060] FIG. 4 is a circuit diagram according to one embodiment of the selection unit (30).

[0061] Referring to FIG. 4, the selection unit (30) is configured to include a voltage detection unit (31) that detects the applied voltage at the time of switching, a voltage adjustment unit (32) that gradually reduces the voltage at the time of switching, and a voltage selection unit (33) that selects the voltage of the first controller (10) or the voltage adjusted by the voltage adjustment unit (32).

[0062] Below, the specific configuration and operation of the selection unit (30) will be explained.

[0063] First, in FIG. 4, the first switch (SW1) of the voltage detection unit (31), the second switch (SW2) of the voltage adjustment unit (32), and the third switch (SW3) of the voltage selection unit (33) all switch their states simultaneously, and the first contact (1), indicated as a contact in the drawing, is for current-frequency control, and the second contact (2) is for voltage / frequency control.

[0064] In this configuration, the voltage detection unit (31) includes a calculation unit (34).

[0065] The operation unit (34) performs an arctangent 2 (atan2) operation and calculates the angle between two points as the inverse function of the tangent function, thereby allowing the angle between two points to be calculated in a rectangular coordinate system.

[0066] That is, the calculation unit (34) can obtain position information of the applied voltage of the first controller (10).

[0067] Additionally, the voltage adjustment unit (32) includes a voltage attenuation unit (35) that gradually reduces the voltage of the first controller (10) to the voltage of the second controller (20) according to a predetermined slope at the second contact (2).

[0068] The voltage selection unit (33) selects the voltage of the first controller (10) or the voltage of the second controller (20) and outputs it to the first coordinate transformation unit (40), and outputs the voltage of the second controller (20) which is summed with the output of the voltage attenuation unit (35) which attenuates to the voltage of the second controller (20) for a set time at the point of switching from the voltage of the first controller (10) to the voltage of the second controller (20).

[0069] The time set above is based on the setting of the slope above, and an arbitrary time can be set.

[0070] The unexplained symbols ADD1 and ADD2 each represent an adder.

[0071] As explained above, during the initial operation (low speed) of the PMSM (60), the first switch (SW1), the second switch (SW2), and the third switch (SW3) are all positioned to be connected to the first contact (1) for current-frequency control and the output terminal.

[0072] Accordingly, the output voltage of the first controller (10) is applied to the first coordinate transformation unit (40) through the voltage selection unit (33), and after being converted into a three-phase coordinate system in the first coordinate transformation unit (40), is provided to the PWM generation unit (50).

[0073] The operation unit (34) that detects the position of the applied voltage is connected to the second contact (2) so as not to affect the operation, and the output of the voltage attenuation unit (35) is also connected to the second contact (2) so as not to be selected by the second switch (SW2) so as not to affect the operation.

[0074] The PWM generation unit (50) drives the PMSM (60) through PWM control, and the output of the PWM generation unit (50) is converted to the dq axis through the second coordinate transformation unit (70) and then fed back to the first controller (10) and the second controller (20), respectively.

[0075] The detected value at this time is generally used to verify whether control conforming to the initial command (current command or frequency command) is being performed, and to make corrections.

[0076] Therefore, the present invention can secure sufficient starting torque by using a current-frequency control method in the initial driving state of the PMSM (60).

[0077] The control method at this time uses voltage on both the d and q axes in the synchronous coordinate system.

[0078] In this state, the PMSM (60) is gradually accelerated, and when it reaches a medium speed exceeding the reference speed, the output of the second controller (20) that performs voltage / frequency control is selected through the selection unit (30).

[0079] That is, the first switch (SW1), the second switch (SW2), and the third switch (SW3) are switched to a state where the second contact (2) and the output terminal are connected.

[0080] According to the switching of the first switch (SW1), second switch (SW2), and third switch (SW3) as described above, the position information of the applied voltage, which is the result of the arctangent 2 calculation of the calculation unit (34), is selected by the first switch (SW1) and output to the adder (ADD1), and this information serves as a reference in the coordinate transformation of the first coordinate transformation unit (40). That is, it is used as the initial position in voltage / frequency control.

[0081] This involves verifying the voltage position in the current-frequency state and setting it as the initial position for voltage / frequency control; by performing average torque control rather than the concept of vector control for instantaneous torque control, it becomes scalar control.

[0082] In other words, the present invention can improve convenience by providing a scalar control method rather than complex vector control from the user's perspective.

[0083] Along with the initial state of voltage control, the voltage attenuation unit (35) checks the voltage magnitude of the current-frequency control method of the first controller (10) and the voltage magnitude of the voltage / frequency control method of the second controller (20), and can improve stability by gradually reducing the voltage value according to the slope set in the voltage state of the current-frequency control method.

[0084] The above voltage attenuation unit (35) applies a voltage corresponding to the difference between the voltage of the first controller (10) and the voltage of the second controller (20) to the second adder (ADD2) in the initial state of switching, and gradually reduces the voltage value according to the slope set from the initial state voltage, and applies a zero voltage when the set time has elapsed.

[0085] The second adder (ADD2) adds the voltage of the second controller (20) and the voltage of the voltage attenuation unit (35), and applies it to the first coordinate transformation unit (40) through the third switch (SW3).

[0086] Accordingly, in the initial state of switching from the current-frequency control method to the voltage / frequency control method, the voltage selected by the third switch (SW3) is the voltage of the first controller (10), and thereafter, as time elapses, it is attenuated to the voltage of the second controller (20).

[0087] Through such control, the voltage of the first controller (10) is rapidly switched to the voltage of the second controller (20), thereby preventing the stability from being controlled.

[0088] In addition, stable operation is possible because voltage / frequency control is performed by accurately verifying the initial voltage position.

[0089] As such, the present invention can provide stable torque by using a current-frequency control method in an initial low-speed driving state, and can increase efficiency by using a voltage / frequency control method in a medium-speed or higher driving state.

[0090] In particular, stability can be improved by verifying the initial position of the voltage / frequency control method at the point of switching from the current-frequency control method to the voltage / frequency control method, and by inducing a linear change from the voltage of the current-frequency control method to the voltage of the voltage / frequency control method.

[0091] Although embodiments according to the present invention have been described above, they are merely illustrative and those skilled in the art will understand that various modifications and equivalent embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the following claims.

Claims

1. A first controller for current-frequency control of a permanent magnet synchronous motor; A second controller for voltage / frequency control of a permanent magnet synchronous motor; and A permanent magnet synchronous motor control circuit comprising a selection unit that switches among the voltage outputs of the first controller to select the voltage output of the second controller, and detects the position of the applied voltage at the time of switching to determine the initial state in voltage / frequency control.

2. In Paragraph 1, The above selection unit is, A permanent magnet synchronous motor control circuit characterized by outputting the voltage of a first controller at the beginning of the switching point and gradually attenuating it to output the voltage of a second controller.

3. In Paragraph 1, The above selection unit is, A voltage detection unit that provides position information of the applied voltage to the first coordinate transformation unit in a state switched to the voltage of the second controller; A voltage adjustment unit that attenuates the voltage for a time set from the voltage of the first controller to the voltage of the second controller while in a state switched to the voltage of the second controller; and A permanent magnet synchronous motor control circuit comprising a voltage selection unit that selects the voltage of the voltage adjustment unit or the voltage of the first controller and applies it to the first coordinate transformation unit.

4. In Paragraph 3, The above voltage detection unit is, A calculation unit that calculates the position by performing an arctangent 2 operation on the voltage of the first controller; and A permanent magnet synchronous motor control circuit comprising a first switch that provides position information of the voltage obtained from the calculation unit to the first coordinate transformation unit when switching to the voltage of the second controller.

5. In Paragraph 3, The above voltage adjustment unit is, A voltage attenuation unit that attenuates the voltage; and A permanent magnet synchronous motor control circuit comprising a second switch that selects the voltage of the voltage attenuation unit when switching to the voltage of the second controller.

6. In Paragraph 5, The above voltage attenuation unit is, When switching to the above second controller, In the initial state, the difference between the voltage of the first controller and the voltage of the second controller is output to an adder, and attenuated for a set time so that the output voltage becomes zero voltage, and A permanent magnet synchronous motor control circuit characterized in that the above-mentioned adder adds the voltage of the above-mentioned voltage attenuation unit and the voltage of the above-mentioned second controller.

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