Semiconductor devices, motor drive systems, and motor control programs

Abstract

The present disclosure relates to a semiconductor device, a motor drive system and a motor control program. In order to stably detect the back electromotive force generated in the non-conducting phase at an extremely low duty cycle, the motor drive system includes a three-phase motor, an inverter circuit and a semiconductor device. The controller included in the semiconductor device compares the voltage at the output node corresponding to the non-conducting phase of the inverter circuit with a reference voltage, thereby estimating the position of the rotor of the three-phase motor and generating a pulse width modulation signal based on the estimated position of the rotor. When the duty cycle of the pulse width modulation signal is less than a threshold value, the controller detects the voltage at the output node of the non-conducting phase in the regeneration period of the pulse width modulation signal, and the regeneration period is a period in which the current flows to the three-phase motor on the regeneration path.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The disclosure of Japanese Patent Application No. 2017-235713 filed on December 8, 2017 including the specification, drawings and abstract is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to a semiconductor device, a motor drive system, and a motor control program, and can be suitably used to control a sensorless brushless DC motor (also referred to as a permanent magnet synchronous motor), for example. Background Art

[0004] In sensorless control of a brushless DC motor, back electromotive force (BEMF) generated in a stator winding of a non-conducting phase due to rotation of a rotor of the motor is detected to estimate the relative position of a magnetic pole pair of the rotor with respect to the stator winding.

[0005] The speed control of such a sensorless brushless DC motor generally uses PWM (pulse width modulation) control. When the motor rotates at a high speed under PWM control, the duty cycle (also known as the conduction ratio) becomes larger. When the motor rotates at a low speed, the duty cycle becomes lower.

[0006] However, when the duty cycle is made extremely low to achieve low-speed rotation, the duration of the back electromotive force generated in the stator winding during the non-conduction period also becomes extremely short, thereby making it difficult to detect the back electromotive force. This is because when the on time becomes shorter than the delay time of the control signal of the motor control circuit, it becomes difficult to set the timing for reading the back electromotive force.

[0007] Japanese Unexamined Patent Application Publication No. 2012-165603 relates to the above problem. Specifically, the motor drive device described in the document makes the PWM frequency smaller in a stepwise manner as the rotation speed of the motor decreases. This drive makes the on time longer in the case of low-speed rotation, thereby enabling the back electromotive force to be read. Summary of the invention

[0008] In recent years, the performance of brushless DC motors is being improved, and brushless DC motors with sensors can be controlled even at a duty ratio close to 0%. Therefore, it is required that the sensorless brushless DC motor also has the same or similar performance as the brushless DC motor with sensors. In this case, it is desirable that there is no restriction on PWM frequency such as described in Japanese Unexamined Patent Application Publication No. 2012-165603.

[0009] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0010] A semiconductor device according to an embodiment is configured to detect a back electromotive force generated in a non-conducting phase in a regeneration period of a pulse width modulation signal when a duty ratio of a pulse width modulation signal output to an inverter circuit for driving a three-phase motor is less than a threshold value. The regeneration period is a period in which a current is caused to flow to the three-phase motor on a regeneration path.

[0011] According to the above-described embodiment, even at an extremely low duty ratio, the back electromotive force generated in the non-conducting phase can be stably detected. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a block diagram illustrating a configuration example of a motor drive system.

[0013] FIG. 2A to FIG. 2C It is an explanatory diagram of six conduction modes in the 120-degree conduction method (part 1).

[0014] FIG. 3A to FIG. 3C It is an explanatory diagram of six conduction modes in the 120-degree conduction method (part 2).

[0015] FIG. 4A to FIG. 4C The figure shows that when the brushless DC motor 130 is PWM driven, the motor current is Figure 3B Flow in conduction mode as shown in the figure.

[0016] Figure 5A and Figure 5B When the brushless DC motor 130 is PWM driven, Figure 3B The diagram in the figure is an explanatory diagram of the back electromotive force generated in the brushless DC motor in the conduction mode.

[0017] Figure 6 is a timing diagram schematically illustrating a motor current waveform.

[0018] Figure 7 is a flowchart illustrating a control process of the motor drive system according to the first embodiment.

[0019] Figure 8 The waveform of the motor output voltage and the waveform of the gate signal when the duty ratio of the PWM signal is equal to or greater than the threshold are schematically illustrated.

[0020] Fig. 9 The waveform of the motor output voltage and the waveform of the gate signal when the duty ratio of the PWM signal is lower than the threshold are schematically illustrated.

[0021] Fig.10 A more detailed illustration Fig. 9 The voltage waveform of the non-conducting phase in .

[0022] Fig.11An example of a method of determining the detection timing of the back electromotive force is illustrated.

[0023] Fig.12 is a flowchart illustrating a control process of the motor drive system according to the second embodiment.

[0024] Fig.13 The waveform of the motor output voltage and the waveform of the gate signal in the motor drive system according to the second embodiment when the duty ratio of the PWM signal is equal to or greater than the threshold value are schematically illustrated.

[0025] Fig.14 The waveform of the motor output voltage and the waveform of the gate signal in the motor drive system according to the second embodiment when the duty ratio of the PWM signal is lower than the threshold value are schematically illustrated.

[0026] Fig.15 A more detailed illustration Fig.14 The voltage waveform of the non-conducting phase in . DETAILED DESCRIPTION

[0027] The embodiments are described in detail below with reference to the accompanying drawings. The same or corresponding parts are marked with the same reference numerals, and their description is not repeated.

[0028] First embodiment

[0029] [Overall configuration of the motor drive system]

[0030] Figure 1 is a block diagram illustrating a configuration example of a motor drive system. Figure 1 The motor drive system 90 includes a three-phase brushless DC motor 130 , an inverter circuit 120 , and a semiconductor device 100 that controls the inverter circuit 120 .

[0031] (1. Brushless DC motor)

[0032] The brushless DC motor 130 includes stator windings 131U, 131V, and 131W in a Y-shaped connection and a rotor (not shown) having one or more magnetic pole pairs. The rotor is driven to rotate synchronously with the three-phase AC current supplied to the stator windings 131U, 131V, and 131W from the inverter circuit 120. The node of the stator windings 131U, 131V, and 131W is called a midpoint 132.

[0033] (2. Inverter circuit)

[0034] The inverter circuit 120 includes a MOS (metal oxide semiconductor) transistor UH for the U-phase upper arm, a MOS transistor UL for the U-phase lower arm, a MOS transistor VH for the V-phase upper arm, a MOS transistor VL for the V-phase lower arm, a MOS transistor WH for the W-phase upper arm, and a MOS transistor WL for the W-phase lower arm. The upper arm and the lower arm may be referred to as the high side and the low side, respectively. The coupling of these transistors is now briefly described.

[0035] MOS transistor UH and MOS transistor UL are coupled in this order between first power supply node 121 providing power supply voltage VM and second power supply node 122 providing ground voltage GND. Output node NU as a coupling point between MOS transistor UH and MOS transistor UL is coupled to one end of U-phase stator winding 131U.

[0036] Similarly, the MOS transistor VH and the MOS transistor VL are coupled in series in this order between the first power supply node 121 and the second power supply node 122. The output node NV as a coupling point between the MOS transistor VH and the MOS transistor VL is coupled to one end of the V-phase stator winding 131V. The MOS transistor WH and the MOS transistor WL are coupled in series in this order between the first power supply node 121 and the second power supply node 122. The output node NW as a coupling point between the MOS transistor WH and the MOS transistor WL is coupled to one end of the W-phase stator winding 131W.

[0037] Each of the MOS transistors UH, UL, VH, VL, WH, and WL includes a body diode (not shown) coupled in parallel in a reverse bias direction. Therefore, when both the upper arm transistor and the lower arm transistor of the same phase are turned off, current can flow through these body diodes on the regeneration path.

[0038] exist Figure 1 In the embodiment, all MOS transistors UH, UL, VH, VL, WH and WL are configured by N-channel MOS transistors. Alternatively, the upper arm MOS transistors UH, VH and WH or the lower arm MOS transistors UL, VL and WL can be configured by N-channel MOS transistors, while the other can be configured by P-channel MOS transistors. Further, all MOS transistors UH, UL, VH, VL, WH and WL can be configured by P-channel MOS transistors.

[0039] In addition, as a semiconductor switching element forming the inverter circuit 120, for example, the MOS transistor may be replaced by another type of field effect transistor, a bipolar transistor, or an IGBT (insulated gate bipolar transistor). However, in the case of using another type of transistor, it is necessary to couple an anti-parallel flywheel diode to each transistor so that the current flows on the regeneration path when both the upper arm transistor and the lower arm transistor of the same phase are turned off.

[0040] (3. Semiconductor equipment)

[0041] Semiconductor device 100 includes switch circuit 150, virtual midpoint generating circuit 160, differential amplifier circuit 140, and microcontroller unit (MCU) 110. Switch circuit 150 and differential amplifier circuit 140 configure detector 115 for detecting a voltage at an output node of a non-conducting phase of inverter circuit 120.

[0042] The switch circuit 150 is coupled to the output nodes NU, NV, and NW. According to the phase selection signals SLU, SLV, and SLW output from the MCU 110, the switch circuit 150 couples an output node of a selected phase among the output nodes NU, NV, and NW and a detection node 151 to each other.

[0043] The virtual midpoint generating circuit 160 provides a virtual midpoint 162 having the same voltage as the voltage at the midpoint 132 of the brushless DC motor 130. Specifically, the virtual midpoint generating circuit 160 includes a resistance element 161U coupled between the virtual midpoint 162 and the output node NU, a resistance element 161V coupled between the virtual midpoint 162 and the output node NV, and a resistance element 161W coupled between the virtual midpoint 162 and the output node NW. The resistance elements 161U, 161V, and 161W have mutually equal resistance values.

[0044] The differential amplifier circuit 140 amplifies the difference between the voltage Vd at the detection node 151 and the reference voltage Vref. The voltage at the middle point 132 or the virtual middle point 162 is used as the reference voltage Vref.

[0045] As an example of a specific circuit configuration, such as in Figure 1, the differential amplifier circuit 140 includes an operational amplifier 141 and resistor elements 142, 143, 144, and 145. The resistor element 143 is coupled between the virtual midpoint 162 and the positive terminal of the operational amplifier 141. One end of the resistor element 142 is coupled to the positive terminal of the operational amplifier 141, and an offset voltage Vofst is provided to the other end. The resistor element 145 is coupled between the detection node 151 and the negative terminal of the operational amplifier 141. The resistor element 144 is coupled between the negative terminal of the operational amplifier 141 and the output terminal.

[0046] In the circuit configuration described above, it is assumed that the voltage at the detection node 151 is Vd, the voltage at the virtual midpoint 162 is Vref, the resistance value of the resistance elements 143 and 145 is R1, and the resistance value of the resistance elements 142 and 144 is R2. Then, the output voltage Vout of the operational amplifier 141 is expressed by the following expression.

[0047] Vout=(Vref-Vd)×R2 / R1+Vofst (1)

[0048] Therefore, by setting the power supply voltage of the operational amplifier 141 to VDD [V] and setting the offset voltage Vofst to VDD / 2, the output voltage of the operational amplifier 141 varies within the range of 0 to VDD [V], and when the voltage Vd at the detection node 151 is equal to the voltage Vref at the virtual midpoint 162, the output voltage of the operational amplifier 141 is equal to VDD / 2.

[0049] MCU 110 is a computer including a CPU (central processing unit) and a memory, for example, the CPU and the memory are incorporated into one integrated circuit. MCU 110 implements various functions described in this specification by executing a program stored in the memory. MCU 110 also includes an AD (analog-to-digital) converter 111, and converts the output of the differential amplifier circuit 140 into a digital value.

[0050] Based on the detected value of the motor current obtained by the shunt resistor (not shown), the estimated position of the rotor based on the output of the differential amplifier circuit 140, and the control command value (e.g., the rotation speed command value 112), the MCU 110 generates PWM signals GUH, GUL, GVH, GVL, GWH, and GWL. The MCU 110 outputs the generated PWM signals GUH, GUL, GVH, GVL, GWH, and GWL to the gates of the MOS transistors UH, UL, VH, VL, WH, and WL configuring the inverter circuit 120, respectively. The MCU 110 also generates phase selection signals SLU, SLV, and SLW for switching the switch circuit 150 based on the generated GUH, GUL, GVH, GVL, GWH, and GWL.

[0051] [Conduction mode in 120 degree conduction method]

[0052] In the present embodiment, the MCU 110 controls the brushless DC motor 130 by a 120-degree conduction method. The 120-degree conduction method is a method in which a 120-degree period in a half cycle of an electrical angle is used as a conduction period, and the remaining 60-degree period is used as a non-conduction period. In the non-conduction period, a back electromotive force occurs. For a three-phase brushless DC motor, the conduction phase is switched every 60 degrees of electrical angle, and therefore, there are six conduction modes.

[0053] Moreover, when a period in a half cycle of an electrical angle (where the electrical angle is 120 degrees or more and less than 180 degrees) is set as a conduction period, the technology of the present disclosure can be applied as long as the back electromotive force generated in the non-conduction period can be measured.

[0054] Note that the conduction period and the non-conduction period of the 120-degree conduction method described above refer to periods different from the conduction period and the regeneration period in the PWM control described later. In this specification, in the case where it is necessary to clearly distinguish the conduction period and the non-conduction period in the 120-degree method from the conduction period and the regeneration period in the PWM control from each other, the conduction period and the non-conduction period in the 120-degree conduction method are referred to as the on period and the off period, respectively.

[0055] FIG. 2A to FIG. 2C as well as FIG. 3A to FIG. 3C This is a diagram for explaining the six conduction modes in the 120-degree conduction method.

[0056] Reference Figure 2A, when the W-phase upper arm MOS transistor WH and the U-phase lower arm MOS transistor UL in the inverter circuit 120 are controlled to be turned on and the other transistors are controlled to be turned off, the motor current A flows from the W-phase stator winding 131W to the U-phase stator winding 131U. The V-phase stator winding 131V is in a non-conductive state, and a back electromotive force occurs. In the following description, this conduction mode is referred to as conduction mode A.

[0057] Further, in conduction mode A, the V phase is called a "non-conduction phase", the W phase is called an "upstream conduction phase", and the U phase is called a "downstream conduction phase". The motor current flows from the stator winding of the upstream conduction phase to the stator winding of the downstream conduction phase. Similar definitions are also applied to other conduction modes.

[0058] Reference Figure 2B , when the W-phase upper arm MOS transistor WH and the V-phase lower arm MOS transistor VL are controlled to be turned on and the other transistors are controlled to be turned off, the motor current B flows from the W-phase stator winding 131W to the V-phase stator winding 131V. The U-phase stator winding 131U is in a non-conductive state, and a back electromotive force occurs. In the following description, this conduction mode is referred to as conduction mode B.

[0059] Reference Figure 2C , when the U-phase upper arm MOS transistor UH and the V-phase lower arm MOS transistor VL are controlled to be turned on and the other transistors are controlled to be turned off, the motor current C flows from the U-phase stator winding 131U to the V-phase stator winding 131V. The W-phase stator winding 131W is in a non-conductive state, and a back electromotive force occurs. In the following description, this conduction mode is referred to as conduction mode C.

[0060] Reference Figure 3A , when the U-phase upper arm MOS transistor UH and the W-phase lower arm MOS transistor WL are controlled to be turned on and the other transistors are controlled to be turned off, the motor current D flows from the U-phase stator winding 131U to the W-phase stator winding 131W. The V-phase stator winding 131V is in a non-conductive state, and a back electromotive force occurs. In the following description, this conduction mode is referred to as conduction mode D.

[0061] Reference Figure 3B , when the V-phase upper arm MOS transistor VH and the W-phase lower arm MOS transistor WL are controlled to be turned on and the other transistors are controlled to be turned off, the motor current E flows from the V-phase stator winding 131V to the W-phase stator winding 131W. The U-phase stator winding 131U is in a non-conductive state, and a back electromotive force occurs. In the following description, this conduction mode is referred to as conduction mode E.

[0062] Reference Figure 3C, when the V-phase upper arm MOS transistor VH and the U-phase lower arm MOS transistor UL are controlled to be turned on and the other transistors are controlled to be turned off, the motor current F flows from the V-phase stator winding 131V to the U-phase stator winding 131U. The W-phase stator winding 131W is in a non-conductive state, and a back electromotive force occurs. In the following description, this conduction mode is referred to as conduction mode F.

[0063] When the inverter circuit 120 is controlled in such a manner that current flows in the brushless DC motor 130 in the above-described conduction modes A, B, C, D, E, and F in this order, the conduction phases are sequentially switched in the order of U phase, V phase, W phase, and U phase, ... Therefore, the rotor of the brushless DC motor 130 also rotates synchronously with the rotating electromagnetic field. In this specification, for convenience, the rotation direction is referred to as the positive direction.

[0064] Meanwhile, when the inverter circuit 120 is controlled in such a manner that the current flows in the brushless DC motor 130 in the reverse order to that described above (i.e., in the conduction modes F, E, D, C, B, and A in this order), the conduction phases are sequentially switched in the order of W phase, V phase, U phase, and W phase, ... Therefore, the rotor of the brushless DC motor 130 also rotates synchronously with the rotating electromagnetic field. In this specification, for convenience, the rotation direction is referred to as the reverse direction.

[0065] [Current and Voltage in Stator Winding in PWM Control] Next, the current flowing in the stator winding 131 of the conduction phase and the back electromotive force generated in the stator winding 131 of the non-conduction phase when the brushless DC motor 130 of the 120-degree conduction method is PWM controlled are described.

[0066] FIG. 4A to FIG. 4C The figure shows that when the brushless DC motor 130 is PWM driven, Figure 3B The flow of motor current in the conduction mode is shown in the figure. FIG. 4A to FIG. 4C In the conduction mode E shown in FIG. 1 , the U phase is a non-conducting phase, the V phase is an upstream conducting phase, and the W phase is a downstream conducting phase. The motor current flows from the V phase stator winding 131V of the upstream conducting phase to the W phase stator winding 131W of the downstream conducting phase.

[0067] In PWM control, two periods are repeated. In one period, such as Figure 4A As shown in FIG. 1 , the power supply voltage VM is supplied to the brushless DC motor 130 so that the current flows in the conduction path. In another period, as in Figure 4B or Figure 4C As shown in FIG. 1 , the current flows on the regeneration path. In this specification, the former period is referred to as a "conduction period", and the latter period is referred to as a "regeneration period".

[0068] Figure 4A The flow of motor current is illustrated in the case where both the V-phase upper arm MOS transistor VH and the W-phase lower arm MOS transistor WL (the V-phase and the W-phase are the conducting phases) are turned on (conducting period) (i.e., the power supply voltage is supplied to the brushless DC motor 130). Specifically, as in Figure 4A As shown in the figure, the motor current flows in the following order through the first power node 121 provided with the power voltage VM, the MOS transistor VH, the V-phase stator winding 131V, the midpoint 132, the W-phase stator winding 131W, the MOS transistor WL and the second power node 122 provided with the ground voltage GND.

[0069] Figure 4B The following is illustrated: the MOS transistor VH which is the V-phase upper arm MOS transistor VH and the W-phase lower arm MOS transistor WL (V-phase and W-phase are the conducting phases) are turned off, and the V-phase lower arm MOS transistor VL is turned on (regeneration period). In this case, as in Figure 4B As shown in FIG. 1 , current flows on a regenerative path that circulates through V-phase stator winding 131V, midpoint 132 , W-phase stator winding 131W, MOS transistor WL, and MOS transistor VL in this order.

[0070] In this way, in Figure 4B In the embodiment of the present invention, the current flows on the regeneration path to the lower arm switching element of the inverter circuit 120. In this specification, this control mode is referred to as the "lower arm regeneration mode". In this lower arm regeneration mode, the inverter circuit 120 can be controlled by turning on / off the V-phase MOS transistors VH and VL of the upstream conduction phase so that the conduction period and the lower arm regeneration period appear alternately.

[0071] Figure 4C The following is illustrated: the MOS transistor WL which is the V-phase upper arm MOS transistor VH and the W-phase lower arm MOS transistor WL (V-phase and W-phase are the conducting phases) are turned off, and the W-phase upper arm MOS transistor WH is turned on (regeneration period). In this case, as in Figure 4C As shown in FIG. 1 , current flows on a regenerative path that circulates through V-phase stator winding 131V, midpoint 132 , W-phase stator winding 131W, MOS transistor WH, and MOS transistor VH in this order.

[0072] In this way, in Figure 4C In the above embodiment, the current flows on the regeneration path to the upper arm switching element of the inverter circuit 120. In this specification, this control mode is referred to as the "upper arm regeneration mode". In this upper arm regeneration mode, the inverter circuit 120 can be controlled by turning on / off the W-phase MOS transistors WH and WL of the upstream conduction phase so that the conduction period and the upper arm regeneration period appear alternately.

[0073] In the following description, the case of using the "lower arm regeneration mode" will be described in the first embodiment, and the case of using both the "upper arm regeneration mode" and the "lower arm regeneration mode" will be described in the second embodiment. Note that it is also possible to perform PWM control using only the "upper arm regeneration mode".

[0074] Figure 5A and Figure 5B When the brushless DC motor 130 is PWM driven, Figure 3B The diagram in the figure is an explanatory diagram of the back electromotive force generated in the brushless DC motor in the conduction mode.

[0075] Figure 5A The diagram shows Figure 4A In the corresponding conduction period, a voltage is generated at the midpoint 132 and a back electromotive force is generated in the stator winding 131U of the U phase which is the non-conduction phase.

[0076] As in Figure 5A , the midpoint 132 is coupled to the first power supply node 121 (power supply voltage VM) via the V-phase stator winding 131V and the turned-on MOS transistor VH, and is coupled to the second power supply node 122 (ground voltage GND) via the W-phase stator winding 131W and the turned-on MOS transistor WL. Therefore, a voltage of about VM / 2 is applied to the midpoint 132. Note that the voltage at the midpoint 132 will not be completely equal to VM / 2 because a back electromotive force is also generated in the stator windings 131V and 131W of the conducting phase according to the position of the rotor.

[0077] At the same time, the stator winding 131U of the U phase, which is a non-conducting phase, is not coupled to any of the power supply nodes 121 and 122, and has a high impedance (Hi-Z). In this case, a voltage of approximately VM / 2±α[V] is generated in the stator winding 131. The voltage α is the back electromotive force generated according to the position of the rotor. Therefore, the position of the rotor can be estimated based on the voltage difference (±α) between the output node NU of the U phase of the inverter circuit 120 and the midpoint 132 of the brushless DC motor 130. Note that in the motor drive system 90 of the present embodiment, instead of the voltage at the midpoint 132, the voltage at Figure 1 The voltage at the virtual midpoint 162 in .

[0078] Figure 5B The diagram shows Figure 4B In the corresponding lower arm regeneration period, a voltage is generated at the midpoint 132 and a counter electromotive force is generated in the stator winding 131U of the U phase which is a non-conducting phase.

[0079] As in Figure 5B, the midpoint 132 is coupled to the second power supply node 122 (ground voltage GND) via the V-phase stator winding 131V and the turned-on MOS transistor VL, and is coupled to the second power supply node 122 (ground voltage GND) via the W-phase stator winding 131W and the turned-on MOS transistor WL. Therefore, a voltage of approximately the ground voltage GND is applied to the midpoint 132. Note that the voltage at the midpoint 132 will not be completely equal to the ground voltage GND because a back electromotive force is also generated in the stator windings 131V and 131W of the conducting phase according to the position of the rotor.

[0080] At the same time, a voltage of about GND±α[V] is generated in the stator winding 131U of the U phase which is a non-conducting phase. The voltage α is a back electromotive force generated according to the position of the rotor. Therefore, the position of the rotor can be estimated based on the voltage difference (±α) between the output node NU of the U phase of the inverter circuit 120 and the midpoint 132 of the brushless DC motor 130. Note that in the motor drive system 90 of the present embodiment, instead of the voltage at the midpoint 132, the voltage at the midpoint 132 is used. Figure 1 The voltage at the virtual midpoint 162 in .

[0081] [Overview of Motor Drive Control]

[0082] Next, referring to the schematic motor current waveform, the drive and control Figure 1 An overview of the process of the motor drive system 90 is illustrated in FIG.

[0083] Figure 6 is a timing diagram schematically illustrating the motor current waveform. Figure 6 , current waveforms are schematically illustrated from detection of the position of the rotor of the brushless DC motor during stop until the brushless DC motor is continuously driven.

[0084] Reference Figure 6 , from time t1 to time t2, detection of the position of the rotor during the stop period is performed (inductive sensing). FIG. 2A to FIG. 2C as well as FIG. 3A to FIG. 3C In each of the six conduction modes described in Figure 1 The MCU 110 in the embodiment applies a driving voltage to the brushless DC motor for a short duration. Figure 6 In the case of the conduction mode B, A, F, E, D and C, the driving voltage is applied to the brushless DC motor 130 through the inverter circuit 120. Then, the MCU 110 detects the voltage difference between the voltage generated in the stator winding 131 of the non-conduction phase and the voltage generated at the virtual midpoint 162 through the differential amplifier circuit 140. The MCU 110 estimates the current position of the rotor based on the detected voltage difference.

[0085] In the next time period from time t2 to time t3, based on the estimated current position of the rotor, the MCU 110 applies voltage to the brushless DC motor 130 through the inverter circuit 120 so that torque is generated on the rotor in the desired rotation direction (driving operation). Figure 6 In the case of Figure 3C 1 is applied to the brushless DC motor 130 through the inverter circuit 120 in the conduction mode F described in . Assuming that the inductive sensing (from time t1 to time t2) and driving operation (from time t2 to time t3) described above form a position detection operation, the MCU 110 repeats the position detection operation (from time t3 to time t10) until the brushless DC motor 130 rotates continuously.

[0086] After time t10, the brushless DC motor 130 continues to rotate. According to the conduction pattern during this continuous rotation, the MCU 110 detects the back electromotive force generated in the stator winding 131 of the non-conducting phase, thereby estimating the position of the rotor. Figure 7 As described in the subsequent drawings, the motor control semiconductor device of the present embodiment has a feature in the timing of detecting the back electromotive force.

[0087] Note that in the 120-degree conduction method, as has been described, the conduction phase is switched every 60 degrees in electrical angle. Figure 6 The FG signal in is a signal generated at the current switching timing. The conduction mode is switched in the order of D, C, B, A, F, E, D, C, B, A, and F, and the rotor rotates in the reverse direction.

[0088] [Details of motor drive control]

[0089] Figure 7 is a flowchart illustrating a control process of the motor drive system according to the first embodiment. Figure 1 The MCU 110 in the embodiment operates according to the control program to implement the steps described below.

[0090] Reference Figure 1 and Figure 7 Based on the estimated current position of the rotor, the detected value of the motor current, and a control command (such as a rotation speed command value 112), the MCU 110 generates a PWM signal to be output to the gate of each semiconductor switching element configuring the inverter circuit 120. Thus, the duty ratio PWM_Duty of the PWM signal is updated (step S100).

[0091] When the conducting phase has been switched (“YES” in step S101 ), the MCU 110 switches the switch circuit 150 to couple the output node of the non-conducting phase of the inverter circuit 120 to the detection node 151 (step S102 ).

[0092] In the next step S103, the MCU 110 determines whether the duty cycle PWM_Duty is lower than a predetermined threshold. Figure 7 The example of illustrates the case where the threshold is at a standard level (ie, 50%), but the threshold is not limited thereto. Note that the duty ratio PWM_Duty means the ratio of the on period in one cycle of the PWM signal, ie, on period / (on period+regeneration period).

[0093] When the duty ratio PWM_Duty is less than the threshold value ("Yes" in step S103), the MCU 110 changes the detection timing of the back electromotive force (BEMF) to be in the "regeneration period" (step S104). Then, the MCU 110 detects the back electromotive force (BEMF) in the regeneration period ( Fig. 9 The back electromotive force generated in the stator winding of the non-conduction phase is detected in the regeneration period III in the conduction period (step S105). In this way, when the threshold value is 50%, the BEMF is detected in the regeneration period longer than the conduction period. Therefore, it is easy to set the timing of BEMF detection. Thereafter, the process returns to step 100 and is repeated.

[0094] Back to Figure 7 103 in FIG. 10 describes a case where the duty ratio PWM_Duty is equal to or greater than the threshold value (“No” in step S103 ). In this case, the MCU 110 changes the timing of BEMF detection to be in the “on period” (step S106 ).

[0095] In the next step S107, the MCU 110 performs the on-time period ( Figure 8 In the conduction period I in the non-conduction phase, the back electromotive force generated in the stator winding of the non-conduction phase is detected. In this way, when the threshold value is 50%, the BEMF is detected in the conduction period longer than the regeneration period. Therefore, it is easy to set the timing of BEMF detection. Thereafter, the process returns to step 100 and is repeated.

[0096] Here, for Figure 7The logic levels of the PWM signals in step S104 and step S106 are supplementarily described. In the first embodiment, the "lower arm regeneration mode" is used. Specifically, the following situation is described: the upper arm semiconductor switching element of the first phase and the lower arm semiconductor switching element of the second phase are controlled to be turned on during the conduction period of the PWM control. In this case, in the lower arm regeneration period, the MCU 110 controls the upper arm semiconductor switching element of the first phase as the upstream conduction phase to be turned off, and controls the lower arm semiconductor switching element of the first phase to be turned on. The MCU 110 also keeps the lower arm semiconductor switching element of the second phase as the downstream conduction phase turned on during the lower arm regeneration period.

[0097] Therefore, in the case described above, based on the logic level of the PWM signal supplied to the gate of the upper arm semiconductor switching element of the first phase as the upstream conduction phase, it can be determined whether the current time falls into the conduction period or the regeneration period. The PWM signal supplied to the gate of the lower arm semiconductor switching element of the first phase is a signal obtained by inverting the PWM signal supplied to the gate of the upper arm semiconductor switching element of the first phase. Therefore, it is also possible to determine whether the current time falls into the conduction period or the regeneration period based on the logic level of the PWM signal supplied to the gate of the lower arm semiconductor switching element of the first phase.

[0098] Specifically, in the example described above, it is assumed that the semiconductor switching element is turned on when the logic level of the PWM signal is at the H level, and is turned off when the logic level of the PWM signal is at the L level. Then, the PWM signal supplied to the gate of the upper arm semiconductor switching element of the first phase as the upstream conduction phase is at the H level in the conduction period (in step S106), and is at the L level in the regeneration period (in step S104).

[0099] Figure 8 The waveform of the motor output voltage and the waveform of the gate signal when the duty ratio of the PWM signal is equal to or greater than the threshold are schematically illustrated.

[0100] Figure 8 The waveforms of the output voltages output from the output nodes NU, NV, and NW of the U-phase, V-phase, and W-phase of the inverter circuit 120 to the brushless DC motor 130 are illustrated. Also, the waveforms of the PWM signals GUH, GUL, GVH, GVL, GWH, and GWL output to the gates of the corresponding MOS transistors configuring the inverter circuit 120 are illustrated. Figure 8 The horizontal axis in represents the electrical angle [degrees].

[0101] exist Figure 8 In the range of electrical angle from 300 degrees to 360 degrees, the MCU 110 controls the inverter circuit 120 to Figure 3BThe brushless DC motor 130 is driven in the conduction mode E described in the above. Further, PWM control is implemented in the lower arm regeneration mode.

[0102] In this case, according to the PWM signals GVH and GVL, the on / off of the upper arm MOS transistor VH and the lower arm MOS transistor VL of the V phase as the upstream conduction phase are switched. Therefore, the voltage at the output node NV of the V phase is also sequentially switched between the H level and the L level. The upper arm MOS transistor WH of the W phase as the downstream conduction phase is controlled to be always off by the PWM signal GWH at the L level, and the lower arm MOS transistor WL of the W phase is controlled to be always on by the PWM signal GWL at the H level. Therefore, the voltage at the output node NW of the W phase is equal to the ground voltage GND.

[0103] At the same time, the MOS transistors UH and UL of the U phase as the non-conducting phase are controlled to be always disconnected by the PWM signals GUH and GUL at the L level (Hi-Z). In this case, the back electromotive force causes an induced voltage to be generated at the output node Nu of the U phase. According to the change of the V phase voltage, the U phase induced voltage is alternately switched between the H level and the L level. Each of the H level and L level voltage values ​​gradually decreases.

[0104] In the conduction period I of the V phase, the MCU 110 detects the induced voltage generated in the U phase which is a non-conducting phase. Figure 8 In this case, the conduction period I is longer than the regeneration period III, and therefore, it is easy to set the timing for detecting the back electromotive force.

[0105] exist Figure 8 In the range of electrical angle from 360 degrees to 420 degrees, the MCU 110 controls the inverter circuit 120 to Figure 3C The brushless DC motor 130 is driven in the conduction mode F described in . Further, PWM control is implemented in the lower arm regeneration mode.

[0106] In this case, according to the PWM signals GVH and GVL, the on / off of the upper arm MOS transistor VH and the lower arm MOS transistor VL of the V phase as the upstream conduction phase are switched. Therefore, the voltage at the output node NV of the V phase is also alternately switched between the H level and the L level. The upper arm MOS transistor UH of the U phase as the downstream conduction phase is controlled to be always off by the PWM signal GUH at the L level, and the lower arm MOS transistor UL of the U phase is controlled to be always on by the PWM signal GUL at the H level. Therefore, the voltage at the output node NU of the U phase is equal to the ground voltage GND.

[0107] At the same time, the MOS transistors WH and WL of the W phase as the non-conducting phase are controlled to be always disconnected by the PWM signals GWH and GWL at the L level (Hi-Z). In this case, the back electromotive force causes an induced voltage to be generated at the output node NW of the W phase. According to the change of the V phase voltage, the W phase induced voltage is alternately switched between the H level and the L level. Each of the H level and L level voltage values ​​gradually increases.

[0108] In the conduction period I of the V phase, the MCU 110 detects the induced voltage generated in the W phase which is a non-conducting phase. Figure 8 In this case, the conduction period I is longer than the regeneration period III, and therefore, it is easy to set the timing for detecting the back electromotive force.

[0109] Fig. 9 The waveform of the motor output voltage and the waveform of the gate signal when the duty ratio of the PWM signal is less than the threshold are schematically illustrated.

[0110] Fig. 9 The timing diagram and Figure 8 However, since the duty cycle PWM_Duty of the PWM signal is Figure 8 Therefore, the motor output voltage is different from the period when the PWM signal is at the H level and the period when the motor output voltage is at the L level in Figure 8 The situation is different. Fig. 9 The other points in Figure 8 The same situation.

[0111] exist Fig. 9 In the range of electrical angle from 300 degrees to 360 degrees, the MCU 110 detects the induced voltage generated in the U phase which is a non-conductive phase in the regeneration period III of the V phase. Fig. 9 In the case of , the regeneration period III is longer than the conduction period I, and therefore, it is easy to set the timing for detecting the back electromotive force. Fig. 9 In the range of electrical angles of 360 to 420 degrees, the MCU 110 detects the induced voltage generated in the W phase, which is a non-conductive phase, in the regeneration period III of the V phase. Figure 8 In this case, the regeneration period III is longer than the conduction period I, and therefore, it is easy to set the timing for detecting the back electromotive force.

[0112] Fig.10 A more detailed illustration Fig. 9 The voltage waveform of the non-conducting phase in the circuit. For an electrical angle from 300 degrees to 360 degrees, the voltage waveform at the U-phase output node NU is shown by a solid line ( Fig. 9 202 in the figure). For an electrical angle from 360 degrees to 420 degrees, a voltage waveform at the W-phase output node NW is illustrated by a solid line ( Fig. 9 203 in FIG. 1 ). Further, the voltage waveform at the virtual midpoint 162 is illustrated by a dotted line.

[0113] As in Fig.10 As shown in the figure, the U-phase voltage, the W-phase voltage and the midpoint voltage vary in the range from voltage (-Vf) to voltage (VM+Vf), the voltage (-Vf) being lower than the ground voltage GND at the forward voltage Vf of the body diode, and the voltage (VM+Vf) being higher than the power supply voltage VM at the forward voltage Vf.

[0114] In the range of electrical angles of 300 to 360 degrees, the voltage of the U phase as the non-conducting phase and the midpoint voltage are each switched alternately between the H level and the L level according to the change in the voltage of the V phase as the upstream conducting phase. In this case, each of the H level and L level voltage values ​​gradually decreases. However, the rate of decrease of the U phase voltage is greater than the rate of decrease of the midpoint voltage. Therefore, an intersection of the two reduction rates is generated, and the position of the rotor can be estimated based on the position of the intersection.

[0115] Similarly, within the range of 360 to 420 degrees of electrical angle, according to the change of the voltage of the V phase as the upstream conductive phase, the voltage of the W phase as the non-conductive phase and the midpoint voltage are each switched alternately between the H level and the L level. In this case, each of the H level and L level voltage values ​​gradually increases. However, the rate of increase of the W phase voltage is greater than the rate of increase of the midpoint voltage. Therefore, an intersection of the two increase rates is generated, and the position of the rotor can be estimated based on the position of the intersection.

[0116] When the detection waiting time Tw has elapsed after switching the PWM signal, the MCU 110 detects the U-phase voltage or the V-phase voltage and the midpoint voltage. Specifically, when the duty ratio of the PWM signal is less than Fig.10 In the case of the threshold value in , the MCU 110 detects the U-phase voltage or the W-phase voltage and the midpoint voltage at the electrical angles of θ10, θ11, θ14, and θ15 in the regeneration period. Fig.10 In the embodiment, the regeneration period of the PWM signal is longer than the conduction period, and therefore, it is easy to set the timing for detecting the back electromotive force.

[0117] When the duty ratio of the PWM signal is equal to or greater than the threshold value, the MCU 110 detects the U-phase voltage or the W-phase voltage and the midpoint voltage at the electrical angles of θ12, θ13, θ16, and θ17 in the conduction period. In this case, the conduction period becomes longer, and therefore, the timing for detecting the back electromotive force can be set more easily in the conduction period than in the regeneration period.

[0118] exist Figure 1In the circuit example illustrated in , the MCU 110 receives a voltage value obtained by adding an offset voltage Vofst to the voltage difference between the U-phase voltage or the W-phase voltage and the midpoint voltage. The timing of receiving the voltage value is the time when the detection waiting time Tw has passed after the PWM signal is switched. When the offset voltage Vofst is set to VDD / 2, the detection threshold for detecting whether the U-phase voltage or the W-phase voltage and the midpoint voltage are equal to each other is VDD / 2. In the case where the range from 0 [V] to the power supply voltage VDD is converted into a digital value by a 10-bit AD converter, the detection threshold described above is 512. Fig.10 In FIG. 1 , values ​​obtained by AD conversion are shown in brackets.

[0119] [Modification of the timing for detecting back electromotive force]

[0120] exist Fig.10 In the example of , the timing of detecting the back electromotive force is set to the time when the detection waiting time Tw has elapsed after the PWM signal is switched. Using a carrier signal when generating a PWM signal makes it easier to set an appropriate timing.

[0121] Fig.11 An example of a method of determining the timing of detecting the back electromotive force is shown in the figure. Fig.11 , the MCU 110 compares the voltage command value VC and the carrier signal CS when generating the PWM signal, and determines the level of the PWM signal, ie, the H level or the L level, based on the comparison result.

[0122] For example, in Fig.11 In the example of , a triangular wave is used as the carrier signal CS. In the section from time t30 to time t32 and the section from time t34 to time t36, because the carrier signal CS is larger than the voltage command value VC, the PWM signal is set at the H level. In the other sections, because the carrier signal CS is smaller than the voltage command value VC, the PWM signal is set at the L level.

[0123] exist Fig.11 , each of time t31 and time t35 when the carrier signal CS takes the maximum value MAX is the center of the portion where the PWM signal is at the H level. Time t33 when the carrier signal CS takes the minimum value MIN is the center of the portion where the PWM signal is at the L level (i.e., the portion from t32 to t34). Therefore, by setting the time when the carrier signal CS takes the maximum value or the minimum value as the timing for detecting the back electromotive force, the back electromotive force can be detected at an appropriate timing.

[0124] [Beneficial Effects]

[0125] As described above, according to the first embodiment, when the duty ratio of the PWM signal output to the inverter circuit for driving the three-phase motor is less than the threshold value, the back electromotive force generated in the non-conduction phase is detected in the regeneration period of the PWM signal in which the current is caused to flow to the three-phase motor on the regeneration path. Therefore, even at an extremely low duty ratio, the back electromotive force generated in the non-conduction phase can be stably detected.

[0126] Second embodiment

[0127] In a motor used for, for example, an electric tool, both the upper arm regeneration mode and the lower arm regeneration mode are used to distribute the heat generated in the MOS transistor configuring the inverter circuit to make the life of the MOS transistor uniform. For example, in the 120 degree conduction method, when the conduction mode is switched every 60 degrees of electrical angle, the upper arm regeneration mode and the lower arm regeneration mode are switched.

[0128] In the second embodiment, the case where both the upper arm regeneration and the lower arm regeneration are used in the case where the current is caused to flow on the regeneration path in the PWM control as described above is described. Figure 1 The general configuration of the motor drive system 90 described is also common to the second embodiment, and therefore, the description is not repeated.

[0129] [Control process of motor drive system]

[0130] Fig.12 is a flowchart illustrating a control process of the motor drive system according to the second embodiment. Figure 1 The MCU 110 in the embodiment operates according to the control program to implement the steps described below.

[0131] Reference Figure 1 and Fig.12 Based on the estimated current position of the rotor, the detected value of the motor current, and a control command (such as a rotation speed command value 112), the MCU 110 generates a PWM signal to be output to the gate of each semiconductor switching element configuring the inverter circuit 120. Thus, the duty ratio PWM_Duty of the PWM signal is updated (step S200).

[0132] When the conducting phase has been switched (“YES” in step S201 ), the MCU 110 switches the switch circuit 150 to couple the output node of the non-conducting phase of the inverter circuit 120 to the detection node 151 (step S202 ).

[0133] The following control process is switched based on whether the duty ratio PWM_Duty is smaller than a threshold value (step S203 ) and whether the current mode is the lower arm regeneration mode (steps S203 and S208 ).

[0134] exist Fig.12 In the example, the case where the threshold is 50% is illustrated. However, the threshold is not limited thereto. Further, Fig.12 An example is illustrated in which PWM control is performed by lower arm regeneration in any of conduction modes A, C, and E, and PWM control is performed by upper arm regeneration in any of conduction modes B, D, and F. However, how to apply lower arm regeneration and upper arm regeneration is not limited to this example.

[0135] (1.PWM_Duty<50% and lower arm regeneration)

[0136] When the duty ratio PWM_Duty is less than the threshold value and PWM control is performed by lower arm regeneration ("Yes" in step S203 and "Yes" in step S204), the MCU 110 changes the detection timing of the back electromotive force (BEMF) to be in the "lower arm regeneration period" (step S205). Then, the MCU 110 detects the BEMF in the lower arm regeneration period ( Fig.14 In the regeneration period III in the non-conduction phase, the back electromotive force generated in the stator winding is detected (step S206). Thereafter, the process returns to step 200 and is repeated.

[0137] (2.PWM_Duty<50% and upper arm regeneration)

[0138] When the duty ratio PWM_Duty is less than the threshold value and PWM control is performed by upper arm regeneration ("Yes" in step S203 and "No" in step S204), the MCU 110 changes the detection timing of the back electromotive force (BEMF) to be in the "upper arm regeneration period" (step S207). Then, the MCU 110 detects the BEMF in the upper arm regeneration period ( Fig.14 In the regeneration period II in the non-conduction phase, the back electromotive force generated in the stator winding is detected (step S206). Thereafter, the process returns to step 200 and is repeated.

[0139] The difference between the "upper arm regeneration mode" and the "lower arm regeneration mode" is now further described. For example, the following situation is described: in which the upper arm semiconductor switching element of the first phase and the lower arm semiconductor switching element of the second phase are controlled to be turned on during the conduction period of PWM control. In this case, in the lower arm regeneration period, the MCU 110 controls the upper arm semiconductor switching element of the first phase as the upstream conduction phase to be turned off, and controls the lower arm semiconductor switching element of the first phase to be turned on. The MCU 110 also controls the lower arm semiconductor switching element of the second phase as the downstream conduction phase to be turned on in the lower arm regeneration period. At the same time, in the upper arm regeneration period, the MCU 110 controls the lower arm semiconductor switching element of the second phase as the downstream conduction phase to be turned off, and controls the upper arm semiconductor switching element of the second phase to be turned on. The MCU 110 also controls the upper arm semiconductor switching element of the first phase as the upstream conduction phase to be turned on in the upper arm regeneration period.

[0140] Therefore, in the case of lower arm regeneration in the example described above, the conduction period and the regeneration period are alternately switched by the PWM signal supplied to the gate of the upper arm or lower arm semiconductor switching element of the first phase as the upstream conduction phase. Therefore, the timing of detecting the back electromotive force can be determined based on the PWM signal for the upstream conduction phase. In the case of upper arm regeneration, the conduction period and the regeneration period are switched by the PWM signal supplied to the gate of the upper arm or lower arm semiconductor switching element of the second phase as the downstream conduction phase. Therefore, the timing of detecting the back electromotive force can be determined based on the PWM signal for the downstream conduction phase.

[0141] Specifically, in the example described above, it is assumed that the semiconductor switching element is turned on when the voltage level of the PWM signal is at the H level, and is turned off when the voltage level of the PWM signal is at the L level. Then, in the case where PWM control is performed in the lower arm regeneration mode, the PWM signal supplied to the gate of the upper arm switching element of the first phase as the upstream conduction phase is at the H level in the conduction period (in step S210), and is at the L level in the lower arm regeneration period (in step S205). On the other hand, in the case where PWM control is performed in the upper arm regeneration mode, the PWM signal supplied to the gate of the upper arm switching element of the second phase as the downstream conduction phase is at the L level in the conduction period (in step S212), and is at the H level in the regeneration period (in step S207).

[0142] (3.PWM_Duty≥50% and lower arm regeneration)

[0143] When the duty ratio PWM_Duty is equal to or greater than the threshold and PWM control is performed in the lower arm regeneration mode ("No" in step S203 and "Yes" in step S209), the MCU 110 changes the detection timing of the back electromotive force (BEMF) to be in the "on period" (step S210). This "on period" corresponds to the case where the PWM signal supplied to the gate of the upper arm semiconductor switching element of the first phase as the upstream conduction phase in the aforementioned example is at the H level. Then, the MCU 110 changes the detection timing of the back electromotive force (BEMF) to be in the "on period" (step S210). Fig.13 In the conduction period I in the non-conduction phase, the back electromotive force generated in the stator winding is detected (step S211). Thereafter, the process returns to step 200 and is repeated.

[0144] (4.PWM_Duty≥50% and upper arm regeneration)

[0145] When the duty ratio PWM_Duty is equal to or greater than the threshold and PWM control is performed by upper arm regeneration ("No" in step S203 and "No" in step S209), the MCU 110 changes the detection timing of the back electromotive force (BEMF) to be in the "on period" (step S212). The "on period" corresponds to the case where the PWM signal supplied to the gate of the upper arm semiconductor switching element of the second phase as the downstream conduction phase in the aforementioned example is at the L level. Then, the MCU 110 changes the detection timing of the back electromotive force (BEMF) to be in the "on period" (step S212). Fig.13 The back electromotive force generated in the stator winding of the non-conducting phase is detected in the conduction period IV in the non-conducting phase (step S213). Thereafter, the process returns to step 200 and is repeated.

[0146] [Specific examples of motor output voltage waveform and gate signal waveform]

[0147] Fig.13 The waveform of the motor output voltage and the waveform of the gate signal in the motor drive system according to the second embodiment when the duty ratio of the PWM signal is equal to or greater than the threshold value are schematically illustrated.

[0148] Fig.13 The waveforms of the output voltages output from the output nodes NU, NV, and NW of the U-phase, V-phase, and W-phase of the inverter circuit 120 to the brushless DC motor 130 are illustrated. Also, the waveforms of the PWM signals GUH, GUL, GVH, GVL, GWH, and GWL output to the gates of the corresponding MOS transistors configuring the inverter circuit 120 are illustrated. Fig.13 The horizontal axis in represents the electrical angle [degrees].

[0149] Further, Fig.13 The diagram shows the reference FIG. 2A to FIG. 2C as well as FIG. 3A to FIG. 3CIn the motor drive system of the second embodiment, the 120-degree conduction method is adopted, and the upper arm regeneration and the lower arm regeneration are switched when the conduction phase is switched. Specifically, Fig.13 In the case of , the inverter circuit 120 is PWM controlled by using the lower arm regeneration mode in conduction modes A, C and E, and the inverter circuit 120 is PWM controlled by using the upper arm regeneration mode in conduction modes B, D and F.

[0150] exist Fig.13 In the range of electrical angle from 300 degrees to 360 degrees, the MCU 110 controls the inverter circuit 120 to Figure 3B The brushless DC motor 130 is driven in the conduction mode E described in the above. Further, PWM control is implemented in the lower arm regeneration mode. Therefore, the waveform in this case is different from that in Figure 8 The waveform within the range of electrical angles from 300 degrees to 360 degrees is the same, and therefore, the detailed description is not repeated.

[0151] exist Fig.13 In the range of electrical angle from 360 degrees to 420 degrees, the MCU 110 controls the inverter circuit 120 to Figure 3C The brushless DC motor 130 is driven in the conduction mode F described in . Further, PWM control is implemented in the upper arm regeneration mode. In this case, according to the PWM signals GUH and GUL, the on / off of the upper arm MOS transistor UH and the lower arm MOS transistor UL of the U phase as the downstream conduction phase are switched. Therefore, the voltage at the output node NU of the U phase is also alternately switched between the H level and the L level. The upper arm MOS transistor VH of the V phase as the upstream conduction phase is controlled to be always on by the PWM signal GVH at the H level, and the lower arm MOS transistor VL of the V phase is controlled to be always off by the PWM signal GVL at the L level. Therefore, the voltage at the output node NV of the V phase is equal to the power supply voltage VM.

[0152] At the same time, the MOS transistors WH and WL of the W phase as the non-conducting phase are controlled to be always disconnected by the PWM signals GWH and GWL at the L level (Hi-Z). In this case, the back electromotive force causes an induced voltage to be generated at the output node NW of the W phase. According to the change of the U phase voltage, the induced voltage of the W phase is alternately switched between the H level and the L level. Each of the H level and L level voltage values ​​gradually increases.

[0153] The MCU 110 detects the induced voltage generated in the W phase which is a non-conductive phase during the conduction period IV of the U phase. Fig.13 In this case, the conduction period IV is longer than the regeneration period II, and therefore, it is easy to set the timing for detecting the back electromotive force.

[0154] Fig.14 The waveform of the motor output voltage and the waveform of the gate signal in the motor drive system according to the second embodiment when the duty ratio of the PWM signal is less than a threshold value are schematically illustrated.

[0155] Fig.14 The timing diagram and Fig.13 However, since the duty cycle PWM_Duty of the PWM signal is Fig.13 Therefore, the motor output voltage is different from the period when the PWM signal is at the H level and the period when the motor output voltage is at the L level in Fig.13 The situation is different. Fig.14 The other points in Fig.13 The same situation.

[0156] exist Fig.14 In the range of electrical angle from 300 degrees to 360 degrees, the MCU 110 detects the induced voltage generated in the U phase which is a non-conductive phase in the regeneration period III of the V phase. Fig.14 In the case of , the regeneration period III is longer than the conduction period I, and therefore, it is easy to set the timing for detecting the back electromotive force. Fig.14 In the range of electrical angles from 360 degrees to 420 degrees, the MCU 110 detects the induced voltage generated in the W phase, which is a non-conductive phase, in the regeneration period II of the U phase. Fig.14 In this case, the regeneration period II is longer than the conduction period IV, and therefore, it is easy to set the timing for detecting the back electromotive force. Fig.15 A more detailed diagram shows Fig.14 The voltage waveform in the non-conducting phase in the U phase is shown by a solid line for the electrical angle from 300 degrees to 360 degrees. Fig.14 206 in the figure). For an electrical angle from 360 degrees to 420 degrees, a voltage waveform at the W-phase output node NW is illustrated by a solid line ( Fig.14 207 in FIG. 1 ). Further, the voltage waveform at the virtual midpoint 162 is illustrated by a dotted line.

[0157] As in Fig.15 As shown in the figure, the U-phase voltage, the W-phase voltage and the midpoint voltage vary in the range from voltage (-Vf) to voltage (VM+Vf), the voltage (-Vf) being lower than the ground voltage GND at the forward voltage Vf of the body diode, and the voltage (VM+Vf) being higher than the power supply voltage VM at the forward voltage Vf.

[0158] In the range of electrical angles from 300 degrees to 360 degrees, the U-phase voltage and the midpoint voltage are each switched alternately between the H level and the L level according to the change in the voltage of the V-phase as the upstream conducting phase. In this case, each of the H-level and L-level voltage values ​​gradually decreases. However, the rate of decrease of the U-phase voltage is greater than the rate of decrease of the midpoint voltage. Therefore, an intersection of the two reduction rates is generated, and the position of the rotor can be estimated based on the position of the intersection.

[0159] Similarly, within the range of electrical angles from 360 degrees to 420 degrees, the W-phase voltage and the midpoint voltage are alternately switched between the H level and the L level according to the change in the voltage of the U-phase as the downstream conducting phase. In this case, each of the H-level and L-level voltage values ​​gradually increases. However, the rate of increase of the W-phase voltage is greater than the rate of increase of the midpoint voltage. Therefore, an intersection of two increase rates is generated, and the position of the rotor can be estimated based on the position of the intersection.

[0160] When the detection waiting time Tw has elapsed after the PWM signal is switched, the MCU 110 detects the U-phase voltage or the W-phase voltage and the midpoint voltage. Specifically, when the duty ratio of the PWM signal is lower than Fig.15 In the case of the threshold value in , the MCU 110 detects the U-phase voltage or the W-phase voltage and the midpoint voltage at the electrical angles of θ20, θ21, θ26, and θ27 in the regeneration period. Fig.15 In the embodiment, the regeneration period of the PWM signal is longer than the conduction period, and therefore, it is easy to set the timing for detecting the back electromotive force.

[0161] When the duty ratio of the PWM signal is equal to or greater than the threshold value, the MCU 110 detects the U-phase voltage or the W-phase voltage and the midpoint voltage at the electrical angles of θ22, θ23, θ24, and θ25 in the conduction period. In this case, the conduction period becomes longer, and therefore, the timing for detecting the back electromotive force can be set more easily in the conduction period than in the regeneration period.

[0162] exist Figure 1 In the circuit example illustrated in , the MCU 110 receives a voltage value obtained by adding an offset voltage Vofst to the voltage difference between the U-phase voltage or the W-phase voltage and the midpoint voltage. The timing of receiving the voltage value is the time when the detection waiting time Tw has passed after the PWM signal is switched. When the offset voltage Vofst is set to VDD / 2, the detection threshold for detecting whether the U-phase voltage or the W-phase voltage and the midpoint voltage are equal to each other is VDD / 2. In the case where the range from 0 [V] to the power supply voltage VDD is converted into a digital value by a 10-bit AD converter, the detection threshold described above is 512. Fig.15 In FIG. 1 , values ​​obtained by AD conversion are shown in brackets.

[0163] [Beneficial Effects]

[0164] According to the second embodiment, the timing of detecting the back electromotive force generated in the non-conduction phase is determined based on the PWM signal of the downstream conduction phase in the upper arm regeneration mode, and the timing is determined based on the PWM signal of the upstream conduction phase in the lower arm regeneration mode. Therefore, even in the case where the upper arm regeneration mode and the lower arm regeneration mode are alternately executed, control similar to that in the first embodiment can be performed, so that the three-phase motor can be stably controlled in a non-sensing manner even at an extremely low duty cycle.

[0165] In the above, the invention made by the inventor of the present application has been specifically described by way of embodiment. However, it is naturally understood that the present invention is not limited to the aforementioned embodiment, and the present invention can be changed in various ways within the scope not departing from the gist of the present invention.

Claims

1. A semiconductor device for controlling an inverter circuit, wherein the inverter circuit is used to drive a three-phase motor, the semiconductor device comprising: a detector coupled to output nodes of corresponding phases of the inverter circuit for outputting a motor voltage to detect a voltage at one of the output nodes of the corresponding phase, the one output node corresponding to a non-conducting phase; as well as a controller for comparing the voltage at the output node of the non-conducting phase and a reference voltage with each other to estimate a position of a rotor of the three-phase motor, and for generating a pulse width modulation signal for controlling the inverter circuit based on the estimated position of the rotor, wherein when the duty cycle of the pulse width modulation signal is less than a threshold value, the controller detects the voltage at the output node of the non-conducting phase in a regeneration period of the pulse width modulation signal, the regeneration period being a period in which current is caused to flow to the three-phase motor on a regeneration path, wherein when the duty cycle of the pulse width modulation signal is equal to or greater than the threshold value, the controller detects the voltage at the output node of the non-conducting phase in a conduction period of the pulse width modulation signal, the conduction period being a period in which the current is caused to flow to the three-phase motor on a conduction path, The detector comprises: a switching circuit that selects one of the output nodes of the corresponding phase according to a command from the controller, and a differential amplifier that amplifies a difference between a voltage at an output node selected by the switch circuit and the reference voltage and adds an offset voltage to the difference, The controller uses the offset voltage as a threshold value and compares an output value of the differential amplifier with the threshold value, thereby comparing the voltage at the output node of the non-conducting phase with the reference voltage.

2. The semiconductor device according to claim 1, wherein the three-phase motor comprises stator windings in a Y-connection, and The reference voltage is a voltage at a midpoint which is a node of the stator winding.

3. The semiconductor device according to claim 1 , further comprising a virtual midpoint coupled to the output node of the corresponding phase via a resistor element, The reference voltage is a voltage at the virtual midpoint.

4. The semiconductor device according to claim 1, wherein the controller has: a first control mode in which the current is caused to flow to the upper arm semiconductor switching element of the inverter circuit on the regeneration path during the regeneration period, and a second control mode in which the current is caused to flow to the lower arm semiconductor switching element of the inverter circuit on the regeneration path during the regeneration period.

5. The semiconductor device according to claim 4, The controller controls the inverter circuit in the regeneration period by using any one of the first control mode and the second control mode.

6. The semiconductor device according to claim 4, The controller switches between the first control mode and the second control mode whenever a conducting phase among three phases is switched.

7. The semiconductor device according to claim 4, Wherein, when the controller controls the upper arm semiconductor switching element of the first phase to be turned on and the lower arm semiconductor switching element of the second phase to be turned on during the conduction period, and the current control mode is the first control mode, based on the pulse width modulation signal that controls the on / off of the semiconductor switching element of the second phase, the controller determines the timing of detecting the voltage at the output node of the non-conducting phase.

8. The semiconductor device according to claim 4, Wherein, when the controller controls the upper arm semiconductor switching element of the first phase to be turned on and the lower arm semiconductor switching element of the second phase to be turned on during the conduction period, and the current control mode is the second control mode, based on the pulse width modulation signal that controls the on / off of the semiconductor switching element of the first phase, the controller determines the timing of detecting the voltage at the output node of the non-conducting phase.

9. A motor drive system, comprising: Three-phase motor; An inverter circuit, used for driving the three-phase motor; as well as A semiconductor device for controlling the inverter circuit, The semiconductor device comprises: a detector coupled to an output node of a corresponding phase of the inverter circuit for outputting a motor voltage to detect a voltage at one of the output nodes of the corresponding phase, the one output node corresponding to a non-conducting phase, and a controller for comparing the voltage at the output node of the non-conducting phase and a reference voltage with each other to estimate a position of a rotor of the three-phase motor, and for generating a pulse width modulation signal for controlling the inverter circuit based on the estimated position of the rotor, and wherein when the duty cycle of the pulse width modulation signal is less than a threshold value, the controller detects the voltage at the output node of the non-conducting phase in a regeneration period of the pulse width modulation signal, the regeneration period being a period in which current is caused to flow to the three-phase motor on a regeneration path, wherein when the duty cycle of the pulse width modulation signal is equal to or greater than the threshold value, the controller detects the voltage at the output node of the non-conducting phase in a conduction period of the pulse width modulation signal, the conduction period being a period in which the current is caused to flow to the three-phase motor on a conduction path, The detector comprises: a switching circuit that selects one of the output nodes of the corresponding phase according to a command from the controller, and a differential amplifier that amplifies a difference between a voltage at an output node selected by the switch circuit and the reference voltage and adds an offset voltage to the difference, The controller uses the offset voltage as a threshold value and compares an output value of the differential amplifier with the threshold value, thereby comparing the voltage at the output node of the non-conducting phase with the reference voltage.

10. A motor control program product, comprising program instructions, which when executed cause a computer to perform the following operations: determining whether a duty cycle of a pulse width modulation signal for controlling an inverter circuit for driving a three-phase motor is less than a threshold value; when the duty ratio of the pulse width modulation signal is less than the threshold value, detecting, by a detector, a back electromotive force generated in a stator winding of a non-conducting phase of the three-phase motor in a regeneration period of the pulse width modulation signal, the regeneration period being a period in which a current is caused to flow to the three-phase motor on a regeneration path, and comparing the detected back electromotive force and a reference voltage with each other to estimate a position of a rotor of the three-phase motor, and generating the pulse width modulation signal based on the estimated position of the rotor, wherein when the duty cycle of the pulse width modulation signal is equal to or greater than the threshold value, the detection detects the back electromotive force in the conduction period of the pulse width modulation signal, the conduction period being a period during which the current flows to the three-phase motor on the conduction path, The detector comprises: a switching circuit that selects one of the output nodes of the corresponding phase according to a command from the controller, and a differential amplifier that amplifies a difference between a voltage at an output node selected by the switch circuit and the reference voltage and adds an offset voltage to the difference, The comparison uses the offset voltage as a threshold value, and compares the output value of the differential amplifier with the threshold value, thereby comparing the detected back electromotive force with the reference voltage.

11. The motor control program product according to claim 10, wherein when the program instructions are executed, the computer further performs the following operations: When the conducting phase of the three-phase motor is switched, the first control mode and the second control mode are switched, wherein in the first control mode, the pulse width modulation signal is generated to cause the current to flow to the upper arm semiconductor switching element of the inverter circuit on the regeneration path during the regeneration period, and wherein in the second control mode, the pulse width modulation signal is generated to cause the current to flow to the lower arm semiconductor switching element of the inverter circuit on the regeneration path during the regeneration period.

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