Control device for electric power steering system and electric power steering system

Abstract

Control device (3) for controlling an electric power steering device (4) which uses a three-phase synchronous motor (2) as a power assistance during a steering operation, comprising the following a rotation position estimation unit (16) that estimates a position of a rotor of the three-phase synchronous motor (2) on the basis of a neutral point potential or a potential of a virtual neutral point of the three-phase synchronous motor (2), and a command signal calculation unit (17) which calculates a command signal to the three-phase synchronous motor (2) on the basis of the position of the rotor which is estimated by the rotation position estimation unit (16), wherein a position signal, detected by a rotary position detector (21) which detects the position of the rotor of the three-phase synchronous motor (2), is input to the control device (3), the command signal calculation unit (17) calculates a command signal to the three-phase synchronous motor (2) either on the basis of the position of the rotor detected by the rotation position detector (21) or the position of the rotor estimated by the rotation position estimation unit (16) and The command signal calculation unit (17) then, when the position signal is abnormal, calculates the command signal to the three-phase synchronous motor (2) on the basis of the position of the rotor, which is estimated by the rotation position estimation unit (16), and wherein Then, when the position of the rotor detected by the rotary position detector (21) generally matches the position of the rotor estimated by the rotary position estimation unit (16), a calculation of the command signal to the three-phase synchronous motor (2) based on the position of the rotor detected by the rotary position detector (21) and a calculation of the command signal to the three-phase synchronous motor (2) based on the position of the rotor estimated by the rotary position estimation unit (16) are exchanged.

Description

Technical field

[0001] The present invention relates to a control device for an electric power steering system and to an electric power steering system. background

[0002] An electric power steering system uses a small, high-efficiency three-phase synchronous motor. In this motor, a magnetic detection element, such as a Hall-effect IC, typically detects the rotational position of a rotor equipped with a magnet. Based on this detection, the stator-side armature coils are energized, causing the rotor to rotate. Additionally, it is possible to drive the three-phase synchronous motor with a sinusoidal current and reduce vibrations and noise caused by torque ripple or similar factors by using a rotary encoder, absolute encoder, GMR sensor, or similar precise position detectors.

[0003] The three-phase synchronous motor can no longer rotate once this rotary position detector fails. The same applies if the rotary encoder, absolute encoder, or GMR sensor is used instead of the Hall-effect IC as the rotary position detector. Since such a failure in the rotary position detector causes a malfunction or anomalous operation of the electric power steering system, an improvement has been requested.

[0004] According to patent document 1, if such a rotary position detector fails, other rotary position estimators besides the rotary position detector, which estimates a position from an induced voltage and an induced current induced by a magnet of a three-phase synchronous motor, are used as an alternative to an output from the rotary position detector. This makes it possible to drive the three-phase synchronous motor stably even if the rotary position detector fails. However, if the rotational speed of the three-phase synchronous motor is less than 10% of its rated speed, the induced voltage is masked by noise, and this rotary position estimator therefore cannot detect the position of a rotor at the low speed.In particular, in the case of an electric power steering system, the three-phase synchronous motor is used for assisting a steering operation at a speed that is zero or near zero, so that the rotational position estimators of patent document 1 unfortunately cannot estimate the position.

[0005] As an alternative to rotational position estimators based on induced voltage, which are incapable of estimating rotational position at zero or low speeds, the number of rotational position detectors is increased to two or more, while one is used normally. This makes it possible to ensure detection with a rotational position accuracy at zero or low speeds equivalent to that achieved before failure. However, in electric power steering systems, increasing the number of rotational position detectors, which are hardware components, is difficult due to space and cost constraints.

[0006] To address these problems, proposed rotational position estimators are software for a low-speed range based on 120-degree line control of a synchronous motor via a virtual neutral potential, as disclosed, for example, in JP 2009-189176 A (Patent Document 2). This makes it possible to control the three-phase synchronous motor even in the low-speed range where the induced voltage is low. Furthermore, proposed rotational position estimators estimate a rotational position from a neutral potential of three-phase windings, as disclosed in JP 2013-55744 A (Patent Document 3). This makes it possible to control the synchronous motor with a sinusoidal waveform even in the low-speed range where the induced voltage is low. State-of-the-art documents, patent documents Patent Document 1: JP 2010-022196 A Patent Document 2: JP 2009-189176 A Patent Document 3: JP 2013-55744 A Patent document 4: WO 2014 / 162 579 A1 Patent document 5: DE 10 2009 030 954 A1 Patent document 6: DE 103 14 696 A1 Summary of the invention Problems to be solved by the invention

[0007] The problem with the technique described in patent document 1 is that it is impossible to estimate the position in an operating range of the three-phase synchronous motor in which the three-phase synchronous motor is frequently used in electric power steering, while continuous control, which is required for electric power steering, can be achieved by using rotary position estimators, which are software as an alternative to the rotary position detector, which is hardware when the rotary position detector fails.

[0008] Each of the techniques described in patent documents 2 and 3 can estimate the rotor position in the operating range of the three-phase synchronous motor, where the three-phase synchronous motor is commonly used in electric power steering, by estimating the position using the neutral point potential. However, patent documents 2 and 3 do not specify how the position estimation is performed using the position detector originally employed in electric power steering, nor how to handle a failure of the position detector. Patent document 4 discloses a drive device equipped with a circuit for detecting a hypothetical neutral point potential of the AC electric motor and a circuit for generating a reference voltage that differs from this potential.Patent document 5 discloses a motor control device comprising a power supply function for supplying electrical power from a power source to a motor, a rotation position detection function for determining the rotation position of a rotor of the motor for the respective phases of the motor and for outputting initial rotation position data according to the result of the determination, furthermore a control function for controlling the power supply operation of the power supply function in accordance with the initial rotation position data, and an induced voltage detection function for determining induced voltages of the respective phases of the motor.Patent document 6 discloses a device for rotor position detection of an electric machine, to which an electronic commutation device is assigned, with a rotor position detection device for supplying at least one winding of the machine with measuring pulses serving for rotor position detection.

[0009] One object of the present invention is to provide an electric power steering device that can improve the reliability of a control device for a three-phase synchronous motor without increasing the cost of the control device. Means of solving the problems

[0010] The invention is described in the attached set of claims. Advantageous embodiments are defined in the dependent claims. Impact of the invention

[0011] An electric power steering device according to a preferred embodiment of the present invention estimates a position of a rotor based on a signal of either a neutral point potential or a potential of a virtual neutral point in an operating range with a speed of zero or a low speed, in which a three-phase synchronous motor is commonly used in an electric power steering system, and controls the three-phase synchronous motor, thereby making it possible to continue assisting during a steering operation.

[0012] The other tasks and characteristics of the present invention will become apparent from the embodiments described below. Brief description of the drawings Fig. Figure 1 is a configuration diagram of a control device according to a first embodiment. Fig. Figure 2 is a block diagram representing a rotation position estimation unit 16A based on a potential of a virtual neutral point. Fig. Figure 3 is a configuration diagram of the control unit to which a rotary position estimation unit 16B is applied based on a neutral point potential. Fig. Figure 4 is a configuration diagram of a control device according to a second embodiment. Fig. 5 represents processes that are carried out by a determination unit 18 for detected position. Fig. Figure 6 is a configuration diagram of a control device according to a third embodiment. Fig. 7 is a flowchart that describes a process configuration of rotary position comparators 18 of Fig. 6 represents. Fig. Figure 8 is a configuration diagram of a control device according to a fourth embodiment. Fig. Figure 9 represents a configuration of a printed circuit board 1 according to the fourth embodiment. Fig. Figure 10 is a configuration diagram of a control device according to a fifth embodiment. Fig. Figure 11 is a configuration diagram of a control device according to a sixth embodiment. Fig. Figure 12 is a block diagram representing a configuration of a rotation position estimation / comparison unit 18. Fig. Section 13 outlines interruption detection in the event of an open failure in a derivative line of a neutral point potential. Fig. Figure 14 is a configuration diagram of a control device according to a seventh embodiment. Fig. Figure 15 is a block diagram representing a configuration of a rotary position comparison unit 19. Fig. 16 is a flowchart that describes a process configuration of rotary position comparators 19A of Fig. 15 represents. Fig. Figure 17 represents an example of an electric power steering system configuration. Methods for carrying out the invention

[0013] The following describes embodiments of an electrical power converter according to the present invention with reference to the drawings. It should be noted that identical elements in the drawings are designated by the same reference numerals and repeated descriptions are omitted.

[0014] Fig. Figure 17 represents a configuration of an electric power steering system 4. When a driver operates a steering wheel 41, a torque sensor 42 detects a torque from the rotation of the steering wheel 41. The torque detected by the torque sensor 42 is input to a control device 3. The control device 3 comprises a three-phase synchronous motor 2 and a printed circuit board 1 that controls the three-phase synchronous motor 2. The printed circuit board 1 controls the three-phase synchronous motor 2 in response to the torque detected by the torque sensor 42. Based on a command, the three-phase synchronous motor 2 outputs torque to assist with steering. The torque output from the three-phase synchronous motor 2 assists with steering force via a steering assist mechanism 32 and is output to a steering mechanism 44. The steering mechanism 44 then steers the wheels 45.

[0015] As embodiments of a control device that controls the electric power steering system, the control of the actuator 3, which outputs the torque based on the torque detected by the torque sensor 42 to assist in the steering process, and the printed circuit board 1 and the three-phase synchronous motor 2, which form the actuator 3, are described below. The present invention, which is described in several of the following embodiments, is characterized in that position estimation means, which are based either on a potential of a virtual neutral point or a neutral point potential, are applied to an electric power steering system that frequently uses a speed of zero or a low speed equal to or less than 10% of a rated speed.This makes it possible to continue supporting the steering process by controlling the three-phase synchronous motor even in an operating range with a speed of zero or a low speed. (First embodiment)

[0016] Fig. Figure 1 represents a configuration of a control device 3 according to a first embodiment. A configuration of the printed circuit board 1 that is characteristic of a control device according to the present embodiment is described with reference to Fig. 1. will be described.

[0017] The printed circuit board 1 of the present embodiment includes an inverter 12, pulse width modulation signal output means 13, a virtual neutral point circuit 14, a current / voltage detection unit 15, a rotation position estimation unit 16A, and a command signal calculation unit 17. The inverter 12 converts a DC current input from a DC power supply 11 into a three-phase AC current and outputs the three-phase AC current to the three-phase synchronous motor 2. Switching elements Sup to Swn, which form the inverter 12, are controlled on the basis of a pulse width modulation signal calculated by the pulse width modulation signal output means 13.

[0018] The rotary position estimation unit 16A estimates rotary position information about the three-phase synchronous motor 2 based on a potential Vn0 of the virtual neutral point, which is input by the virtual neutral point circuit 14. The operation of the rotary position estimation unit 16A will be described later with reference to Fig. 2. An output signal from the rotation position estimation unit 16A is designated by the symbol θ1. The command signal calculation unit 17 calculates the pulse width modulation signal based on the rotation position information estimate θ1 and outputs the pulse width modulation signal. The output pulse width modulation signal is sent to the inverter 12 via the pulse width modulation signal output device 13.

[0019] Fig. Figure 2 is a block diagram representing a configuration of a rotation position estimation unit 16A. The rotation position estimation unit 16A estimates the rotation position θ1 based on the potential Vn0 of the virtual neutral point. While the position in the present embodiment is estimated based on the potential of the virtual neutral point, the position can also be estimated based on the neutral point potential.

[0020] The rotary position estimating unit 16A is configured with a non-line phase potential selector switch 161, a reference level switch 162, a comparator device 163 and line mode decision device 164.

[0021] The non-conducting phase potential selector 161 samples and maintains the virtual neutral potential in response to a mode command output from the line-mode decision device 164. The reference level switch 162 sets a positive-side reference voltage and a negative-side reference voltage in response to the mode command, compares the non-conducting phase potential selector 161 and the reference level switch 162, and outputs a comparison result to the line-mode decision device 164. This configuration maintains the necessary potential in a non-conducting phase. The configuration described above can achieve sensorless position detection at low rotational speeds.The control device for the electric power steering system in the present embodiment allows the three-phase synchronous motor to be controlled in a state in which a position detector is not present, at a speed of zero or at a low speed equal to or less than 10% of the rated speed at which the three-phase synchronous motor is frequently used in the electric power steering system, and allows the torque to be output.

[0022] Although a method for calculating the mode command from the virtual neutral point potential and estimating the position using the rotary position estimator 16A has been introduced, this method is based on 120-degree conduction and therefore causes current waveform distortion. For this reason, the rotary position estimator 16A can be replaced by a rotary position estimator 16B, which provides position estimation based on the neutral point potential derived from three-phase windings, as described in Fig. 3 is shown. (Second embodiment)

[0023] Fig. Figure 4 is a block diagram illustrating a configuration of a control device 3 according to a second embodiment. The control device 3 of the present embodiment is characterized in that it comprises a position detector 21, which is hardware, and a position detection and determination device 18.

[0024] The electric power steering system is equipped with a position detector that detects the position of the rotor of the three-phase synchronous motor 2 with regard to the reliability of the position detection. In the present embodiment, an output θ3 from the position detector 21 is used when the detected position determination unit 18 determines that the position detected by the position detector 21 is a normal signal, and the output θ1 from the rotation position estimation unit 18 is used when the position detected by the position detector 21 is an abnormal signal.

[0025] If the output suddenly switches from output θ3 from the position detector 21 to output θ1 from the rotary position estimator 18, when the position signal detected by the position detector 21 changes from the normal signal to the abnormal signal, vibrations and / or noise will occur in the motor. To address this problem, the detected position estimator 18, when it is determined that a deviation is being generated between output θ3 from the position detector 21 and output θ1 from the rotary position estimator 18, and that the position detector is failing, switches the position signal with a time delay at which position θ2 from the position detector 21 generally coincides with position θ1 from the rotary position estimator 18, as described in Fig. 5 is shown.

[0026] With such a configuration, it is possible to use not only position information from the position detector but also position information from the position estimation unit, and to configure a redundant electric power steering system at low cost. Furthermore, it is possible to obtain an electric power steering system that ensures low switching shock to prevent the driver from experiencing discomfort even if the position detector 21 fails.

[0027] If the signal from position detector 21 is the normal signal, the detected position determination unit 18 compares the output θ1 from the rotational position estimation unit 16 with the output θ3 from position detector 21 and synchronizes the signal with that of position detector 21. This makes it possible to adjust for individual differences between three-phase synchronous motors with respect to the magnetic saturation characteristics used in the rotational position estimation unit 16. Consequently, it is possible to achieve cost-effective adjustment of individual differences between multiple three-phase synchronous motors.

[0028] While the rotation position estimation unit 16 in Fig. 4 as described in the present embodiment, while the position estimation unit 16A is based on the potential of the virtual neutral point, the position estimation unit 16B can be used based on the neutral point potential. (Third embodiment)

[0029] Fig. Figure 6 is a block diagram illustrating a configuration of the control device 3 according to a third embodiment. The control device 3 of the present embodiment is characterized, in comparison to the second embodiment, in that it comprises not only the position detector 21 but also a position detector 22, in order to form a position detection system in a redundant configuration.

[0030] In many cases, the electric power steering system is equipped with two or more position detectors that detect the position of the rotor of the three-phase synchronous motor 2 with a view to improving the reliability of position detection. In the present embodiment, a case in which the number of position detectors is two will be described as a typical example.

[0031] With a configuration of two position detectors, if one of the position detectors fails, it is difficult to distinguish which one has failed. To address this problem, the rotary position estimation unit 16A is used in addition to the two position detectors according to the present embodiment, so that it is possible to determine which one has failed, position detector 21 or 22. It is therefore possible to control the electric power steering system using the normal position detector.

[0032] Fig. Figure 7 is a flowchart that represents a process configuration of the detected position determination unit 18. First, the detected position determination unit 18 compares the output signals from position detectors 21 and 22. If the output signals match, the signal from position detector 21 is used. If the output signal θ3 from position detector 21 does not match an output signal θ4 from position detector 22, the detected position determination unit 18 compares the output signal θ1 from the rotary position estimation unit 16A with the output signal θ3 and / or θ4. If the output signal θ3 from the position detector 21 matches the output signal θ1 from the rotation position estimation unit 16A, then the detected position determination unit 18 determines that the position detector 21 is normal and the output signal θ2 from the position detector 21 is used.If the output signal θ4 from the position detector 22 matches the output signal θ1 from the rotation position estimation unit 16A, then the detected position determination unit 18 determines that the position detector 22 is normal and the output signal θ4 from the position detector 22 is used. If neither the output signal θ3 from the position detector 21 nor the output signal θ4 from the position detector 22 matches the output signal θ1 from the rotation position estimation unit 16A, the output signal θ1 from the rotation position estimation unit 16A is used.

[0033] With such a configuration, the rotation position estimation unit can identify which of the position detectors has failed, even if one of the two position detectors has failed. Furthermore, it is possible to achieve continuous support at low cost using the position information from the other position detector. (Fourth embodiment)

[0034] Fig. Figure 8 is a block diagram illustrating a configuration of the control device 3 according to a fourth embodiment. In the present embodiment, a method is described using the rotation position estimation unit, which is based in particular on the potential 14 of the virtual neutral point.

[0035] The rotation position estimation unit 16A is controlled based on the potential 14 of the virtual neutral point. As in Fig. As shown in Figure 9, the virtual neutral point circuit 14 is installed on the printed circuit board 1, on which microcomputers are mounted. This configuration eliminates the need for a separate neutral point potential trace for the three-phase windings and simplifies the connection of the printed circuit board 1 to the three-phase synchronous motor 2. Furthermore, installing the virtual neutral point circuit 14 on the printed circuit board 1 can prevent operational errors due to connection noise or increased ripple in detected voltages. Additionally, installing the virtual neutral point circuit 14 on the printed circuit board 1 can reduce connection lengths and thus achieve cost savings.

[0036] The resistance value of this virtual neutral point circuit 14 is configured to have a resistance value 100 times or more than that of a winding resistance value of the three-phase synchronous motor 2. By making the resistance value different from that of the virtual neutral point circuit, as described above, the resistance value of the virtual neutral point circuit can be isolated from the impedance of the three-phase windings. Therefore, it is possible to detect fluctuations in the potential of the virtual neutral point due to saturation with high accuracy and to improve the positional accuracy of the estimation unit 16 for the detected position.

[0037] The rotary position estimation unit 16A is controlled based on the potential 14 of the virtual neutral point under 120-degree power control. Due to this, the accuracy of an electrical angle is only ±30 degrees, so that a position error within a control cycle is large at high rotational speed, leading to the occurrence of a back torque or a fall-out. To address these problems, when the speed of the three-phase synchronous motor 2 exceeds a predetermined speed, for example 3000 min⁻¹, the unit is automatically deactivated. -1 If the current exceeds a certain threshold, it is set to zero to stop the assistance. This makes it possible to achieve stable control of the power steering system. (Fifth embodiment)

[0038] Fig. Figure 10 is a block diagram illustrating a configuration of the control device 3 according to a fifth embodiment. In the present embodiment, the rotation position estimation unit 16 is configured to use, in particular, the neutral point potential of the three-phase windings of the three-phase synchronous motor 2.

[0039] With such a configuration, it is possible to achieve control using a sinusoidal wave and to reduce vibrations and noise due to torque ripples, unlike position estimation based on the potential of the virtual neutral point. (Sixth embodiment)

[0040] Fig. Figure 11 is a block diagram illustrating a configuration of the control device 3 according to a sixth embodiment. The present embodiment is characterized by the use of two signals: the neutral point potential of the three-phase windings and the potential of the virtual neutral point of the three-phase synchronous motor 2.

[0041] Fig. Figure 12 represents a configuration of the rotary position estimation / comparison unit 18. The rotary position estimation / comparison unit 18 is configured with the rotary position estimation unit 16A, which estimates the position based on the virtual neutral point potential, the rotary position estimation unit 16B, which estimates the position based on the neutral point potential, and the rotary position estimation / comparison unit 18, which detects a failure in the virtual neutral point potential circuit or an interruption in the neutral point potential lead.

[0042] The rotation position estimation / comparison unit 18 compares the virtual neutral point potential with the neutral point potential, thereby detecting an open failure in a resistor installed on the virtual neutral point potential circuit or an open failure in the derivative of the neutral point potential.

[0043] An overview of the detection of the open failure in the neutral point potential derivative line is given with reference to Fig. 13 will be described. Fig. Figure 13 represents the waveforms of a voltage applied to an upper arm in each phase of inverter 2, the neutral point potential Vn, and the virtual neutral point potential Vn0. Fig. In Figure 13, the neutral point potential Vn is indicated by a dashed line and the potential Vn0 of the virtual neutral point is indicated by a solid line.

[0044] As in an upper section of Fig. As shown in Figure 13, the potential Vn0 of the virtual neutral point coincides with the neutral point potential Vn during one period in which all upper arms of inverter 2 are switched on, provided the neutral point potential's supply line is not interrupted. However, if, as shown in a lower section of Fig. As shown in Figure 13, if the neutral point potential's derivative line is interrupted in the open failure, the virtual neutral point potential does not match the neutral point potential. Therefore, comparing the neutral point potential with the virtual neutral point potential allows for the detection of the interruption.

[0045] If one of the position estimation units fails—rotational position estimation unit 16A, which estimates the position based on the virtual neutral point potential, and rotational position estimation unit 16B, which estimates the position based on the neutral point potential—it is possible to continue steering assistance by switching to the other, non-failing rotational position estimation unit. The virtual neutral point potential and the actual neutral point potential are provided and compared, making it possible to detect the neutral point potential and any interruption in the virtual neutral point potential's signal path without requiring any additional circuitry from another system. (Seventh embodiment)

[0046] Fig. Figure 14 is a block diagram illustrating a configuration of the control device 3 according to a seventh embodiment. The control device of the present embodiment is characterized in that it uses not only the two signals, i.e., the neutral point potential and the potential of the virtual neutral point, but also the signal from the rotation position detection unit 21.

[0047] Fig. Figure 15 represents a configuration of a rotation position comparison unit 19. The rotation position comparison unit 19 is configured with the rotation position estimation unit 16A, which estimates the position based on the potential of the virtual neutral point, the rotation position estimation unit 16B, which estimates the position based on the neutral point potential, and the rotation position comparison means 19, which compare the outputs 16A and 16B from the rotation position estimation units with the output θ3 from the rotation position detector.

[0048] Fig.Figure 16 is a flowchart representing a process configuration of the rotary position comparators 19. The rotary position comparators 19 compare the output from the position detector 21 with the output from the rotary position estimator 16B and determine which of the two outputs failed due to the output from the rotary position estimator 16A. The rotary position comparators 19A compare the output signal θ3 from the position detector 21 with the output signal θ2 from the rotary position estimator 16B, and the signal from the position detector 21 is used if the signals match. If the output signal θ3 from the position detector 21 does not match the output signal θ2 from the rotary position estimator 16B, the rotary position comparators 19A compare the output signal θ3 from the position detector 21 with the output signal θ1 from the rotary position estimator 16A.If the output signal θ3 from the position detector 21 matches the output signal θ1 from the rotary position estimator 16A, then the rotary position comparators 19A determine that the position detector 21 is normal and the output signal θ3 from the position detector 21 is used. If the output signal θ2 from the rotary position estimator 16B matches the output signal θ1 from the rotary position estimator 16A, the output signal θ2 from the rotary position estimator 16B is used. If neither the output signal θ3 from the position detector 21 nor the output signal θ2 from the rotary position estimator 16B matches the output signal θ1 from the rotary position estimator 16A, the output signal θ1 from the rotary position estimator 16A is used.

[0049] With such a configuration, it is possible to ensure a triple-redundant system at low cost, even though the configuration uses a single position detector, which is hardware-based. Although an example where the number of rotary position detectors is one has been introduced in the present embodiment, it is possible to achieve further redundancy by using two or more rotary position detectors. Description of reference symbols 1 printed circuit board 11 DC power supply 12 inverters 13 Pulse Width Modulation Signal Output Devices 14. Circuit of the virtual neutral point 15 Current detection unit, voltage detection unit 16 Rotation position estimation unit 161 Non-line phase potential selector switch 162 Reference level switches 163 Comparison device 164 Line mode decision device 17 Command signal calculation unit 18 Rotation position estimation / comparison unit 2 three-phase synchronous motors 3 Control device 4 electric power steering system 41 Steering wheel 42 Torque sensor 43 Steering support mechanism 44 Steering mechanism 45 tires

Claims

[1] Control device (3) for controlling an electric power steering system (4) which uses a three-phase synchronous motor (2) as a power assistance during a steering operation, comprising the following a rotation position estimation unit (16) that estimates a position of a rotor of the three-phase synchronous motor (2) on the basis of a neutral point potential or a potential of a virtual neutral point of the three-phase synchronous motor (2), and a command signal calculation unit (17) which calculates a command signal to the three-phase synchronous motor (2) on the basis of the position of the rotor which is estimated by the rotation position estimation unit (16), wherein a position signal, detected by a rotary position detector (21) which detects the position of the rotor of the three-phase synchronous motor (2), is input to the control device (3), the command signal calculation unit (17) calculates a command signal to the three-phase synchronous motor (2) either on the basis of the position of the rotor detected by the rotation position detector (21) or the position of the rotor estimated by the rotation position estimation unit (16) and The command signal calculation unit (17) then, when the position signal is abnormal, calculates the command signal to the three-phase synchronous motor (2) on the basis of the position of the rotor, which is estimated by the rotation position estimation unit (16), and wherein Then, when the position of the rotor detected by the rotary position detector (21) generally matches the position of the rotor estimated by the rotary position estimation unit (16), a calculation of the command signal to the three-phase synchronous motor (2) based on the position of the rotor detected by the rotary position detector (21) and a calculation of the command signal to the three-phase synchronous motor (2) based on the position of the rotor estimated by the rotary position estimation unit (16) are exchanged. [2] Control device (3) for the electric power steering device (4) according to claim 1, wherein a first position signal, detected by a first rotary position detector which detects the position of the rotary position detector (21), and a second position signal, detected by a second rotary position detector which detects the position of the rotor of the rotary position detector (21), are input to the control device (3) as the position signal. [3] Control device (3) for the electric power steering device (4) according to claim 1, wherein the control device (3) corrects the position of the rotor, which is estimated by the rotation position estimation unit (16), on the basis of the position of the rotor, which is detected by the rotation position detector (21). [4] Control device (3) for the electric power steering device (4) according to claim 1, wherein, when it is determined that the position signal is abnormal, the control device (3) switches from a calculation to a calculation of the command signal to the three-phase synchronous motor (2) based on the position of the rotor estimated by the rotation position estimation unit (16), while maintaining the position of the rotor detected by the rotation position detector (21) before the anomaly has been detected. [5] Control device (3) for the electric power steering device (4) according to claim 1, wherein, when the position signal is normal, the command signal calculation unit (17) calculates the command signal to the three-phase synchronous motor (2) on the basis of the position of the rotor detected by the rotary position detector (21). [6] Control device (3) for the electric power steering device (4) according to claim 1, comprising the following a circuit (14) of a virtual neutral point which outputs the potential of a virtual neutral point of the three-phase synchronous motor (2), wherein The rotation position estimation unit (16) estimates the position of the rotor of the three-phase synchronous motor (2) on the basis of a potential output of the virtual neutral point from the virtual neutral point circuit (14). [7] Control device (3) for the electric power steering device (4) according to claim 6, wherein the circuit (14) of the virtual neutral point is mounted on a printed circuit board (1) on which a microcomputer controlling the control device (3) is mounted. [8] Control device (3) for the electric power steering device (4) according to claim 6, wherein when the speed of the three-phase synchronous motor (2) exceeds a predetermined speed, assistance of the steering process by the three-phase synchronous motor (2) is stopped. [9] Control device (3) for the electric power steering device (4) according to claim 6, wherein each resistance value of the circuit (14) of the virtual neutral point is set to be 100 times or more as high as a resistance value of a winding resistance value of the three-phase synchronous motor (2). [10] Control device (3) for the electric power steering device (4) according to claim 1, comprising the following a neutral point potential derivative line that outputs the neutral point potential of the three-phase synchronous motor (2) to the command signal calculation unit (17), wherein the rotation position estimation unit (16) estimates the position of the rotor of the three-phase synchronous motor (2) on the basis of the neutral point potential of the three-phase synchronous motor (2). [11] Control device (3) for the electric power steering device (4) according to claim 1, comprising the following a circuit (14) of a virtual neutral point which outputs the potential of a virtual neutral point of the three-phase synchronous motor (2), and a neutral point potential derivative line that outputs the neutral point potential of the three-phase synchronous motor (2) to the command signal calculation unit (17), wherein The interruption of the neutral point potential's feedforward line is detected by comparing the neutral point potential of the three-phase synchronous motor (2) with the potential of the virtual neutral point of the three-phase synchronous motor (2). [12] Control device (3) for the electric power steering device (4) according to claim 1, wherein the rotation position estimation unit (16) comprises a first rotation position estimation unit (16A) and a second rotation position estimation unit (16B) and The command signal calculation unit (17) calculates the command signal to the three-phase synchronous motor (2) on the basis of the position of the rotor, which is estimated either by the first rotation position estimation unit (16A) or the second rotation position estimation unit (16B). [13] Control device (3) for the electric power steering system (4) according to claim 12, wherein a position signal, detected by a rotary position detector (21) which detects the position of the rotor of the three-phase synchronous motor (2), is input to the control device (3), and the command signal calculation unit (17) calculates the command signal to the three-phase synchronous motor (2) on the basis of the position of the rotor detected by the rotation position detector (21) or the position of the rotor estimated either by the first rotation position estimation unit (16A) or the second rotation position estimation unit (16B). [14] Control device (3) for the electric power steering device (4) according to claim 1, wherein the rotation position estimation unit (16) estimates the position of the rotor of the three-phase synchronous motor (2) either only on the basis of the neutral point potential or the potential of the virtual neutral point of the three-phase synchronous motor (2). [15] Electric power steering system (4) comprising the following a steering operating mechanism that steers steered wheels (45) in response to a steering action; a three-phase synchronous motor (2) which exerts a steering force on the steering operating mechanism; a control device (3) according to one of claims 1 to 14, which controls the three-phase synchronous motor (2) to be controlled. [16] Electric power steering device (4) according to claim 15, comprising the following a circuit (14) of a virtual neutral point which outputs the potential of a virtual neutral point of the three-phase synchronous motor (2), wherein The rotation position estimation unit (16) estimates the position of the rotor of the three-phase synchronous motor (2) on the basis of a potential output of the virtual neutral point from the virtual neutral point circuit (14). [17] Electric power steering device (4) according to claim 16, wherein the circuit (14) of the virtual neutral point is mounted on a printed circuit board (1) on which a microcomputer controlling the control device (3) is mounted.

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