JP2004336865A - Initial position detector of synchronous motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an initial position detector of a synchronous motor which is obtained using a low-cost current polarity detecting means, with no current sensor of high cost and precision required. <P>SOLUTION: An inverter circuit 3 applies a pulse voltage to a coil of a plurality of phases, and a current polarity detecting part 4 (sense MOSFET31ul, 31vl, and 31wl) detects the polarity of a current flowing to the coil of a specific phase where the pulse voltage is applied. A micro computer 5 discriminates the position of a rotor of a motor 2 based on the current polarity detected by the current polarity detecting part 4. Thus, the initial position of the rotor of the motor 2 is surely detected using a low-cost current polarity detecting means, with no use of a position sensor such as an encoder nor a current sensor of high precision. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for detecting a rotor initial position without using a position sensor for a synchronous motor having saliency and having coils of a plurality of phases.
[0002]
[Prior art]
When starting the synchronous motor without a position sensor, there is a problem that the synchronous operation cannot be performed unless the position and speed of the rotor are known. In view of such problems, conventionally, as a technique for detecting a rotor position without a position sensor, a pulse-like voltage is applied to a motor coil, and the rotor position is determined from the rate of change of the current value of the current flowing through the motor coil. A detection method has been proposed (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-11-55988
[Problems to be solved by the invention]
However, in the prior art described in Patent Document 1 described above, an accurate current value is required when measuring the rate of change of the current value, so that a high-precision and expensive current sensor is indispensable, resulting in high cost. There is such a problem.
[0005]
The present invention has been made in view of the above-described problems, and provides an initial position detecting device for a synchronous motor that can be realized using an inexpensive current polarity detecting unit without requiring an accurate and expensive current sensor. Is an issue to be solved.
[0006]
[Means for Solving the Problems]
To achieve this object, an apparatus for detecting an initial position of a synchronous motor according to claim 1 is an apparatus for detecting an initial position of a rotor of a synchronous motor having a salient polarity having coils of a plurality of phases. Voltage applying means for applying a predetermined voltage to the coils of the plurality of phases, current polarity detecting means for detecting the polarity of the current flowing through the coil of a specific phase by applying a voltage by the voltage applying means, and the current polarity detecting means And a rotor position determining means for detecting a rotor position of the synchronous motor based on the detected current polarity.
[0007]
Therefore, the voltage application unit applies a predetermined voltage (preferably, a pulse voltage) to the coils of the plurality of phases, and the current polarity detection unit detects the polarity of the current flowing through the coil of the specific phase by applying the voltage by the voltage application unit. The rotor position determining means determines the rotor position of the synchronous motor based on the current polarity detected by the current polarity detecting means. Therefore, the rotor initial position of the synchronous motor can be reliably detected by using inexpensive current polarity detection means without using a position sensor such as an encoder or a high-precision current sensor.
[0008]
Further, in the synchronous motor initial position detecting device according to claim 2, the voltage applying unit applies a predetermined voltage in a direction orthogonal to a specific phase, and the current polarity detecting unit performs the identification by the voltage applying unit. The polarity of the current flowing through the coil of the specific phase is detected by applying a voltage in a direction orthogonal to the phase.
[0009]
Accordingly, the current polarity detecting means detects the polarity of the current flowing through the coil of the specific phase by applying a voltage in a direction orthogonal to the specific phase by the voltage applying means, and the rotor position determining means determines the polarity of the current polarity in the specific phase. Thus, it can be determined whether the rotor is at a position of 0 to 90 degrees or a position of 90 to 180 degrees with respect to a specific phase. Also, by applying a predetermined voltage in a direction orthogonal to the specific phase, the current amplitude of the specific phase for detecting the current polarity can be maximized, so that erroneous detection of the current polarity due to noise can be reduced. .
[0010]
Also, in the synchronous motor initial position detecting device according to claim 3, the voltage applying unit sequentially applies a pulse voltage in a predetermined direction to each of the plurality of phases, and the current polarity detecting unit includes: The polarity of the current flowing in each phase is sequentially detected by applying a pulse voltage in a predetermined direction to each phase by the voltage application unit, and the rotor position determination unit detects the polarity of each phase detected by the current polarity detection unit. The rotor position of the synchronous motor is determined based on a combination of current polarities.
[0011]
Therefore, the voltage applying means sequentially applies a pulse voltage to each of the plurality of phases in a predetermined direction, and the current polarity detecting means applies a pulse voltage to each of the phases by the voltage applying means in the predetermined direction. Since the polarity of the flowing current is sequentially detected, and the rotor position determining means determines the rotor position of the synchronous motor based on the combination of the current polarities of the respective phases detected by the current polarity detecting means, so that the rotor position can be more accurately determined. Can be detected. For example, when the synchronous motor has three phases, there are six positive / negative combinations of current polarities of each phase, so that the rotor position can be detected every 30 degrees.
[0012]
Further, the synchronous motor initial position detecting device according to claim 4, further comprising: storage means for storing a rotor position of the synchronous motor and a combination of the current polarities of the respective phases in advance in association with each other; The determining unit reads the rotor position corresponding to the combination of the current polarities stored in the storage unit based on the combination of the current polarities of the respective phases detected by the current polarity detecting unit. The rotor position of the synchronous motor is determined.
[0013]
Therefore, a storage means is provided for storing a combination of the rotor position of the synchronous motor and the combination of the current polarities of the respective phases in advance, and the rotor position determining means stores the set of the current polarities of the respective phases detected by the current polarity detecting means. Since the rotor position corresponding to the combination of the current polarities stored in the storage means can be read out based on the matching, the calculation processing of the rotor position becomes unnecessary, and the detection processing of the rotor position can be performed at high speed.
[0014]
Further, in the synchronous motor initial position detecting device according to claim 5, the voltage applying means applies a voltage to a specific phase in a predetermined direction for a first predetermined time, and the current polarity detecting means includes After the voltage application in the direction for the first predetermined time is completed, the current polarity in the specific phase is detected, and the voltage application unit detects the current polarity in the direction opposite to the predetermined direction after the current polarity detection by the current polarity detection unit. 2 is characterized in that a voltage is applied for a predetermined time.
[0015]
Therefore, the voltage applying means applies a voltage to the specific phase in a predetermined direction for a first predetermined time, and the current polarity detecting means sets the current polarity in the specific phase after the application of the voltage for the first predetermined time in the predetermined direction. Is detected, the polarity of the current flowing through the coil of the specific phase in response to the voltage application can be reliably detected. Further, the voltage application means applies a voltage in a direction opposite to the predetermined direction for a second predetermined time after the current polarity detection means detects the current polarity, so that the current flowing through the coil quickly becomes 0, and Thus, the influence of the current flowing through the coil does not remain, and erroneous detection of the current polarity in another specific phase can be prevented.
[0016]
Further, in the synchronous motor initial position detecting device according to claim 6, the voltage applying means applies a pulse voltage to a specific phase in a predetermined direction, and the current polarity detecting means detects a current polarity in the specific phase. After a predetermined period of time during which no voltage is applied after the detection of a specific phase, a pulse voltage is applied in a predetermined direction to another specific phase different from the specific phase.
[0017]
Therefore, after providing a predetermined time during which no voltage is applied after the detection of the current polarity in the specific phase by the current polarity detection means, a pulse voltage is applied in a predetermined direction to another specific phase different from the specific phase. The influence of the current flowing through the coil due to the previous voltage application does not remain, and erroneous detection of the current polarity in another specific phase can be prevented.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a motor control device embodying a synchronous motor initial position detection device of the present invention will be described with reference to the drawings.
[0019]
As shown in FIG. 1, a motor control device 1 of the present embodiment includes a synchronous reluctance motor (SynRM) as a salient-polarity synchronous motor having a stator composed of coils of a plurality of phases (three phases) and an iron core rotor. (Hereinafter simply referred to as a motor) 2 includes an inverter circuit 3, a current polarity detector 4, and a microcomputer (hereinafter referred to as a microcomputer) 5.
[0020]
As shown in the circuit diagram of FIG. 2, the inverter circuit 3 is connected to a DC power supply 30 and supplies a power MOSFET 31 uh (upper arm), a sense MOSFET 31 ul (lower arm), and a V-phase A power MOSFET 31vh (upper arm), a sense MOSFET 31vl (lower arm), a power MOSFET 31wh (upper arm), and a sense MOSFET 31wl (lower arm) that supply power to the W-phase are connected to each other. Incidentally, the inverter circuit 3 constitutes the voltage applying means of the present invention.
[0021]
The current polarity detection unit 4 is specifically constituted by sense MOSFETs 31ul, 31vl, 31wl connected to the lower stage of each phase arm of the inverter circuit 3, and an arm current signal flowing when the gate signal of the lower stage arm of each phase is ON. Is detected. Here, the motor current and the arm current of each phase have the same polarity, and the polarity of the motor current of each phase is detected by dividing the arm current of each phase in the sense MOSFET 31ul (31vl, 31wl) and detecting the current polarity. Can be detected. Note that the current polarity detection unit 5 (that is, the sense MOSFETs 31ul, 31vl, 31wl) constitutes a current polarity detection unit of the present invention.
[0022]
The microcomputer 5 includes a CPU 5a, a ROM 5b, and a RAM 5c. The CPU 5a reads a program stored in the ROM 5b and executes the program to execute a rotor initial position detection process of the motor 2 and a drive control process of the motor 2. It is configured. Note that the microcomputer 5 constitutes the rotor position determining means of the present invention. The ROM 5b stores a rotor position reference table 5d, and the ROM 5b constitutes storage means of the present invention.
[0023]
Next, the principle of rotor position detection in the present embodiment will be described with reference to FIGS.
[0024]
The present embodiment detects the rotor position by using the fact that the inductance differs depending on the rotor position in a synchronous motor having saliency. FIG. 3 is a diagram schematically illustrating a relationship between a motor coil and a rotor in a three-phase synchronous motor, and illustrates a state where the rotor is at a rotational position of an angle θ with respect to the U phase. Here, it is known that the inductances of the U, V, and W phases (Lu, Lv, Lw) change as shown in FIG. 4 as the rotor position changes. For example, when a voltage is applied so as to be orthogonal to the U phase (for example, 12 V between V and W, 6 V between U and V), the inductance Lv> Lw (rotor position 0 to 90 degrees, 180 to 270 degrees) At times, the polarity of the U-phase current Iu becomes-(negative) (see FIG. 5). On the other hand, when Lv> Lw (rotor positions 90 to 180 degrees, 270 to 360 degrees), the polarity of the U-phase current Iu becomes + (positive) (see FIG. 6). This is because the easiness of current flow changes due to a change in inductance which is a magnetic resistance of the motor coil. In the present embodiment, the rotor position is detected by applying a pulse voltage to a specific phase of the synchronous motor in a predetermined direction to detect the polarity of the current flowing in the specific phase. Since the synchronous reluctance motor has no polarity in the rotor and has a motor torque cycle of 180 degrees, the angle θ = 0 to 180 degrees and 180 to 360 degrees are not distinguished.
[0025]
Next, the flow of the rotor position detection process in the present embodiment will be described. The outline of the rotor position detection is as follows. Pulse voltages orthogonal to the U, V, and W phases are sequentially applied, and immediately after the pulse voltage is applied, the current polarities of the phases orthogonal to the pulse voltage are measured, and the U, V, and W phases are measured. The rotor position is detected with an accuracy of 30 degrees based on the combination of the current polarities. Hereinafter, the flow of the rotor position detection process will be described in detail with reference to the flowchart of FIG.
[0026]
First, in step 101 (hereinafter, referred to as S101; other steps are the same), an initial value 1 is substituted for n. In S102, a pulse voltage orthogonal to the U phase is applied. When Vu6 [V], Vv0 [V], Vw12 [V] or PWM is performed, the duty of U, V, W is set to 50%, 0%, and 100% (see FIG. 5). After the pulse voltage is applied for a predetermined time (T1), the current polarity of the U phase is detected (detects negative) in S103, and the current polarity detection result is stored in the RAM 5c in S104. Next, in S105, a pulse voltage is applied in the reverse direction for a predetermined time (T1) in order to quickly reduce the current to zero. When Vu6 [V], Vv12 [V], Vw0 [V] or PWM is performed, the duty of U, V, W is set to 50%, 100%, and 0%. Similarly, orthogonal pulse voltages are sequentially applied to the V and W phases until n = 3, and the current polarities are detected. In S107, a predetermined time interval (T2) is provided before moving to the next phase detection process. FIG. 8 shows this state in chronological order. The current polarity is detected at the timing when the circle is added to the current waveform in FIG. The predetermined time for applying the pulse voltage in the forward direction corresponds to the first predetermined time of the present invention, and the predetermined time for applying the pulse voltage in the reverse direction corresponds to the second predetermined time.
[0027]
Then, in the U-phase orthogonal pulse voltage, it is possible to determine whether the rotor position is 0 to 90 degrees (180 to 270 degrees) or 90 to 180 degrees (270 to 360 degrees) depending on the polarity of the current polarity. By performing each of the V and W phases, it is possible to determine the rotor position based on the combination of the current polarities of each phase. In the present embodiment, a rotor position reference table 5d in which the combinations of the current polarities of the respective phases and the rotor positions shown in FIG. 9 are associated with each other is stored in the ROM 5b in advance, and in S109, the rotor position reference table 5d is referred to. By reading the rotor position corresponding to the combination of the current polarities of the respective phases, the rotor position is determined. For example, in the example of the rotor position of 15 degrees, since the current polarities of the U, V, and W phases are (-,-, +), it is determined that the rotor position exists in the range of 0 to 30 degrees (FIG. 9).
[0028]
Here, the reason for applying the pulse voltage in the reverse direction in S105 will be described. This is because, if the reverse pulse voltage is not applied immediately after the application of the pulse voltage, the current does not quickly become 0 and erroneous detection may occur. For example, FIG. 10 shows an example of erroneous detection of the current polarity. FIG. 10 shows the detection result when the rotor position is 15 degrees as in FIG. 8. However, since the current polarity is detected before the current becomes zero in the W phase, it is originally + (positive). Although it should be determined, it is erroneously detected as-(negative). In the present embodiment, as shown in FIG. 8, the current polarity can be accurately detected.
[0029]
The reason why the predetermined time interval T2 in which no voltage is applied in S107 is that the current is not completely zero immediately after the application of the pulse voltage (see FIG. 11), so that the current polarity of the next phase is immediately set. This is because there is a risk of erroneous detection if the detection is performed.
[0030]
As is clear from the above, according to the present embodiment, according to the present embodiment, the inverter circuit 3 applies a predetermined voltage (pulse voltage) to the multi-phase coil, and the current polarity detection unit 4 (the sense MOSFETs 31ul, 31vl, 31wl). ) Detects the polarity of the current flowing through the coil of the specific phase by applying the voltage, and the microcomputer 5 determines the rotor position of the motor 2 based on the current polarity detected by the current polarity detection unit 4. Therefore, the rotor initial position of the motor 2 can be reliably detected by using inexpensive current polarity detection means without using a position sensor such as an encoder or a high-precision current sensor.
[0031]
Further, according to the present embodiment, the polarity of the current flowing through the coil of the specific phase is detected by the current polarity detection unit 4 by applying a voltage in the direction orthogonal to the specific phase by the inverter circuit 2, and the microcomputer 5 Based on the polarity of the current polarity, it is possible to determine whether the rotor is at a position of 0 to 90 degrees or 90 to 180 degrees with respect to a specific phase. Also, by applying a predetermined voltage in a direction orthogonal to the specific phase, the current amplitude of the specific phase for detecting the current polarity can be maximized, so that erroneous detection of the current polarity due to noise can be reduced. .
[0032]
Further, according to the present embodiment, the inverter circuit 2 sequentially applies a pulse voltage to each of the plurality of phases in a predetermined direction, and the current polarity detection unit 4 outputs a pulse in a predetermined direction to each phase by the voltage application unit. The microcomputer 5 sequentially detects the polarity of the current flowing through each phase by applying the voltage, and the microcomputer 5 determines the rotor position of the motor 2 based on the combination of the current polarity of each phase detected by the current polarity detection unit 4. Thus, the rotor position can be detected with higher accuracy. In the above-described embodiment, since the motor 2 has three phases, and there are six combinations of positive and negative current polarities of each phase, the rotor position can be detected every 30 degrees.
[0033]
Further, according to the present embodiment, the rotor position reference table 5 d in which the rotor position of the motor 2 is associated with the combination of the current polarities of the respective phases is stored in the ROM 5 b in advance, and is detected by the current polarity detector 4. Since the rotor position corresponding to the combination of the current polarities can be read from the rotor position reference table 5d based on the combination of the current polarities of the respective phases, the calculation processing of the rotor position becomes unnecessary, and the detection processing of the rotor position can be performed. Can be done at high speed.
[0034]
Further, according to the present embodiment, the inverter circuit 2 applies a voltage to the specific phase in the predetermined direction for the first predetermined time, and the current polarity detection unit 4 detects the first predetermined time T1 in the predetermined direction. Since the polarity of the current in the specific phase is detected after the completion of the voltage application, the polarity of the current flowing through the coil of the specific phase in response to the voltage application can be reliably detected. Further, after the current polarity detection unit 4 detects the current polarity, the inverter circuit 2 applies a voltage in a direction opposite to the predetermined direction for a second predetermined time T1, so that the current flowing through the coil quickly becomes zero. In addition, the influence of the current flowing through the coil due to the previous voltage application does not remain, and erroneous detection of the current polarity in another specific phase can be prevented.
[0035]
Further, according to the present embodiment, after the predetermined period T2 during which no voltage is applied after the current polarity detection unit 4 detects the current polarity in the specific phase, the specific direction is determined with respect to another specific phase different from the specific phase. Since the pulse voltage is applied to the first phase, the influence of the current flowing through the coil due to the previous voltage application does not remain, and erroneous detection of the current polarity in another specific phase can be prevented.
[0036]
Then, by controlling the driving of the motor 2 based on the detection result of the rotor position described above, it is possible to generate a desired torque in the motor 2. Further, as described above, since only the polarity information of the motor current is used, there is no need to use a high-precision and expensive current sensor, and an inexpensive sense MOSFET can be used as the current polarity detection means. Manufacturing cost can be kept low.
[0037]
The present invention is not limited to the above-described embodiments, and various changes can be made without departing from the gist of the present invention.
[0038]
For example, in the above-described embodiment, an example has been described in which the present invention is a control device for a synchronous reluctance motor. However, the present invention can be configured as a control device for another type of synchronous motor having saliency. For example, the present invention may be applied to a control device of an internal magnet type permanent magnet synchronous motor (IPM motor) having a permanent magnet housed in a rotor core. FIG. 12A is a diagram illustrating a configuration of a rotor in a synchronous reluctance motor, and FIG. 12B is a diagram illustrating a configuration of a rotor in an IPM motor. In a synchronous reluctance motor that does not use a magnet for the rotor, the motor torque cycle is 180 degrees (see the graph of the reluctance torque in FIG. 13). Could be detected. On the other hand, in the IPM motor, as shown in FIG. 13, the reluctance torque having a period of 180 degrees and the magnet torque having a period of 360 degrees are combined to generate a motor torque (IPM torque). By applying the present invention, the magnetic pole position can be detected every 30 degrees from 0 to 180 degrees or from 180 to 360 degrees. Further, by combining with the technique of determining the polarity (N pole, S pole) of the magnetic pole described in JP-A-2002-10679 or the like, the rotor position is in the range of 0 to 180 degrees or 180 to 360 degrees. It is determined whether the area is the area, and the rotor position can be detected every 30 degrees from 0 to 360 degrees.
[0039]
【The invention's effect】
As described above, according to the synchronous motor initial position detecting device of the present invention, the polarity of the current flowing through the coil of a specific phase by applying a voltage to the coil is detected, and the rotor of the synchronous motor is detected based on the detection result of the current polarity. Since the position is determined, the initial rotor position of the synchronous motor can be reliably detected by using inexpensive current polarity detection means without using a position sensor such as an encoder or a high-precision current sensor.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of a motor control device according to an embodiment of the present invention.
FIG. 2 is a circuit diagram of an inverter circuit.
FIG. 3 is a schematic diagram showing a relationship between a motor coil and a rotor.
FIG. 4 is a graph showing a relationship between a rotor position and an inductance.
FIG. 5 is a diagram showing the relationship between the current in the motor coil and the rotor position when the polarity of the U-phase current is negative.
FIG. 6 is a diagram illustrating a relationship between a current in a motor coil and a rotor position when the polarity of a U-phase current is positive.
FIG. 7 is a flowchart illustrating a flow of a rotor position detection process.
FIG. 8 is a diagram showing an example of a pulse voltage and current response in a time series.
FIG. 9 is a table showing an example of a rotor position reference table.
FIG. 10 is a diagram illustrating an example of erroneous detection of a current polarity.
FIG. 11 is a diagram illustrating a change in current caused by application of a pulse voltage.
12A is a diagram illustrating a configuration of a rotor in a synchronous reluctance motor, and FIG. 12B is a diagram illustrating a configuration of a rotor in an IPM motor.
FIG. 13 is a diagram illustrating a cycle of a motor torque.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Motor control device (Synchronous motor position detecting device), 2 ... Synchronous reluctance motor (Synchronous motor having saliency), 3 ... Inverter circuit (Voltage applying means), 31ul, 31vl, 31wl ... Sense MOSFET (Current polarity) Detecting means), 4 ... current polarity detecting section (current polarity detecting means), 5 ... microcomputer (rotor position discriminating means), 5a ... CPU, 5b ... ROM (storage means), 5c ... RAM, 5d ... rotor position reference table (Storage means).

Claims (6)

An apparatus for detecting an initial position of a rotor of a synchronous motor having saliency with coils of a plurality of phases,
Voltage applying means for applying a predetermined voltage to the multi-phase coil,
Current polarity detection means for detecting the polarity of the current flowing through the coil of the specific phase by the voltage application by the voltage application means,
Rotor position determining means for determining the rotor position of the synchronous motor based on the current polarity detected by the current polarity detecting means,
An initial position detecting device for a synchronous motor, comprising: The voltage applying means applies a predetermined voltage in a direction orthogonal to the specific phase,
2. The synchronous motor according to claim 1, wherein the current polarity detection unit detects the polarity of a current flowing through the coil of the specific phase by applying a voltage in a direction orthogonal to the specific phase by the voltage application unit. 3. Position detection device. The voltage applying means sequentially applies a pulse voltage to each of the plurality of phases in a predetermined direction,
The current polarity detection means sequentially detects the polarity of the current flowing through each phase by applying a pulse voltage in a predetermined direction to each phase by the voltage application means,
3. The rotor position determination unit according to claim 1, wherein the rotor position determination unit determines the rotor position of the synchronous motor based on a combination of the current polarities of the respective phases detected by the current polarity detection unit. 4. Initial position detector for synchronous motor. Storage means for storing a combination of the rotor position of the synchronous motor and the combination of the current polarities of the respective phases in advance;
With
The rotor position determining means reads a rotor position corresponding to the combination of the current polarities stored in the storage means based on the combination of the current polarities of the respective phases detected by the current polarity detecting means. 4. The synchronous motor initial position detecting device according to claim 3, wherein the rotor position of the synchronous motor is determined by the following. The voltage applying means applies a voltage in a predetermined direction to a specific phase for a first predetermined time,
The current polarity detection means detects a current polarity in the specific phase after the end of the voltage application for the first predetermined time in the predetermined direction,
5. The synchronous motor according to claim 3, wherein the voltage application unit applies a voltage in a direction opposite to the predetermined direction for a second predetermined time after the current polarity detection unit detects the current polarity. 6. Initial position detector. The voltage application unit applies a pulse voltage in a predetermined direction to a specific phase, and after providing a predetermined time during which no voltage is applied after the current polarity detection unit detects the current polarity in the specific phase, 6. The synchronous motor initial position detecting device according to claim 3, wherein a pulse voltage is applied in a predetermined direction to another specific phase different from the specific phase.

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