Semiconductor device and motor control system

Abstract

Embodiments of the present disclosure relate to a semiconductor device and a motor control system. A semiconductor device for vector control of an AC motor via an inverter, comprising: a dq-axis reference current value generator generating dq-axis reference current values, a three-phase / two-phase converter generating dq-axis detected current values from three-phase current values of the inverter and a rotor position of the AC motor, a current controller generating dq-axis reference voltage values based on the dq-axis reference current values, the dq-axis detected current values, an angular speed of rotation of the AC motor, and motor parameter setting values through proportional control and proportional integral control, wherein an integral controller provides an initial voltage value to an integrator before switching to proportional integral control, and wherein the initial voltage value is based on one of a proportional gain and the dq-axis reference voltage values, the dq-axis reference current values, the dq-axis detected current values, the angular speed of rotation, and the motor parameter setting values.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a semiconductor device, and more particularly to a semiconductor device for controlling a motor and a motor control system. BACKGROUND

[0002] PWM (pulse width modulation) control using an inverter is known as a basic control method of an AC motor (for example, a permanent magnet synchronous motor (PM motor)) mounted on an electric vehicle (EV), a hybrid vehicle (HV), a railway vehicle, or the like. As a torque control method of an AC motor, a vector control method capable of independently controlling a current of a magnetic flux axis (d-axis) and a current of a torque axis (q-axis) is generally used.

[0003] In the vector control, a current flowing in a rotating coordinate (the d-axis is defined in a direction of a magnetic flux of a permanent magnet incorporated in the AC motor, and the q-axis is defined in a direction of the d-axis advanced by 90 degrees) is controlled to have a desired value. Feedback control by proportional control (also referred to as P control), integral control (also referred to as I control), and proportional integral control (also referred to as PI control) is used for this current control.

[0004] Patent Literature 1 describes a technique of sine wave PWM control, vector control, and PI control for an AC motor.

[0005] [Related Art Documents]

[0006] [Patent Literature]

[0007] [Patent Literature 1] International Patent Application Publication No. WO 2014 / 064836 SUMMARY

[0008] In AC motor control using an inverter, sine wave PWM control or overmodulation PWM control is generally used. In the sine wave PWM control and the overmodulation PWM control, both the magnitude and the phase of a voltage vector can be controlled. This fact that the magnitude and the phase of the voltage vector can be controlled indicates that PI control can be applied to independently control a d-axis (magnetic flux axis) current and a q-axis (torque axis) current in a rotating coordinate. However, while the sine wave PWM control and the overmodulation PWM control are effective when the AC motor rotates at a low speed or a medium speed, they are not suitable when the AC motor rotates at a high speed and the output voltage of the inverter is saturated. This is because, when the AC motor rotates at a high speed, the output voltage of the inverter is saturated by the maximum voltage that the inverter can output. Therefore, when the AC motor rotates at a high speed, rectangular wave control is used. In the case of the rectangular wave control, since only the phase of the voltage vector can be controlled, it is difficult to apply PI control, and the control system must be switched to a voltage phase control method or a P control method.

[0009] As described above, by switching the control method according to the rotational speed of the AC motor, it is possible to stabilize the output torque of the AC motor. PI control is executed when the AC motor rotates at a low speed or a medium speed, and P control is executed when the AC motor rotates at a high speed. However, if the current control method is suddenly switched, an impact such as a sudden jump in current or a rotational speed vibration can occur. In particular, when the control method is switched from P control to PI control, the response of the integral calculation of the PI control is delayed, and thus an impact is easily generated.

[0010] Other objects and novel features will become apparent from the description and drawings.

[0011] A semiconductor device for vector control of an AC motor via an inverter includes a dq-axis reference current value generator that generates dq-axis reference current values, a three-phase / two-phase converter that generates dq-axis detected current values from three-phase current values of the inverter and a rotor position of the AC motor, a current controller that generates dq-axis reference voltage values based on the dq-axis reference current values, the dq-axis detected current values, a rotational angular speed of the AC motor, and motor parameter setting values by proportional control and proportional integral control, wherein an integral controller provides an initial voltage value to an integrator before switching to the proportional integral control, and wherein the initial voltage value is based on one of a proportional gain and the dq-axis reference voltage values, the dq-axis reference current values, the dq-axis detected current values, the rotational angular speed, and the motor parameter setting values.

[0012] In one embodiment, a semiconductor device for motor control can reduce an impact when a motor is switched from proportional control to proportional integral control. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a schematic diagram of a motor control system of a first embodiment;

[0014] Figure 2 is a schematic diagram of a current controller of the first embodiment;

[0015] Figure 3 is a diagram of an integrator of the first embodiment;

[0016] Figure 4 is a schematic diagram of an integrator of the first embodiment;

[0017] Figure 5 is a diagram of an integrator of the first embodiment;

[0018] Figure 6 is a flowchart for explaining an operation of the motor control system of the first embodiment;

[0019] Figure 7 is a diagram of an integrated controller of the first embodiment;

[0020] Figure 8 is a diagram of an integrated controller of the first embodiment;

[0021] Figure 9 is a diagram for explaining an effect of the motor control system of the first embodiment;

[0022] Figure 10 is a diagram for explaining an effect of the motor control system of the first embodiment;

[0023] Figure 11 is a diagram of an integrated controller of the second embodiment;

[0024] Figure 12 is a diagram of an integrated controller of the second embodiment; and

[0025] Figure 13 is a diagram of a motor control system of the third embodiment. DETAILED DESCRIPTION

[0026] Hereinafter, a semiconductor device according to an embodiment will be described in detail with reference to the accompanying drawings. In the specification and the drawings, the same or corresponding elements are denoted by the same reference numerals, and repetitive description thereof will be omitted. In the drawings, the configuration can be omitted or simplified for convenience of description. In addition, at least some of the embodiments can be arbitrarily combined with each other.

[0027] First Embodiment

[0028] Figure 1 is a block diagram showing a configuration of a motor control system of the first embodiment.

[0029] As shown in Figure 1 , a semiconductor device 10 controls a PM (permanent magnet) motor 12 via an inverter 11. The semiconductor device 10 includes an angular velocity detector 14, a three-phase / two-phase converter 15, a dq-axis reference current generator 16, a current controller 17, a sequencer 18, a two-phase / three-phase converter 19, and a PWM generator 20.

[0030] The PWM generator 20 is connected to the inverter 11. The inverter 11 is connected to the PM motor 12. A PS (position sensor) 13 is connected to the PM motor 12. The angular velocity detector 14 is connected to the PS 13. A current detector 21 is connected to the inverter 11.

[0031] The PM motor 12 is a motor using a permanent magnet. The PS 13 is a position sensor capable of detecting a rotational position θ of a rotor of the PM motor 12, which is also referred to as a rotational magnetic pole position or a rotor position. The angular velocity detector 14 calculates a rotational angular velocity ω from the rotational position θ.

[0032] The inverter 11 is formed of power MOS transistors or the like. The inverter 11 receives PWM signals from the PWM generator 20 and generates three-phase PWM voltages for driving the PM motor 12.

[0033] The three-phase / two-phase converter 15 converts three-phase alternating current values iu, iv, iw acquired from a current detector 21 connected to the inverter 11 into two-phase detected direct current values id_ad, iq_ad on dq axes based on a rotational position θ acquired from the PS 13.

[0034] The dq-axis reference current generator 16 generates dq-axis reference current values id_ref, iq_ref required for torque generation by the PM motor 12 based on a reference torque T_ref transmitted from an application that controls the PM motor 12, a direct current bus voltage Vdc of the inverter 11, and a rotational angular velocity ω of the PM motor 12.

[0035] The current controller 17 generates dq-axis reference voltage values vd_ref, vq_ref (described later) based on the dq-axis reference current values id_ref, iq_ref, the dq-axis two-phase detected direct current values id_ad, iq_ad, the rotational angular velocity ω, and a control signal seq from the sequencer 18. The current controller 17 is constituted of a current regulator for suppressing a deviation between the dq-axis reference current values and the dq-axis two-phase detected direct current values and a disturbance-free controller for canceling an intermediate voltage between the dq axes of the PM motor 12. Details will be described later.

[0036] The sequencer 18 determines whether or not the output voltage of the inverter 11 is saturated based on the dq-axis reference voltage values vd_ref, vq_ref and the direct current bus voltage Vdc (or a modulation factor) of the inverter 11. The determination result is output as the control signal seq. Details will be described later.

[0037] The two-phase / three-phase converter 19 converts the dq-axis reference voltage values vd_ref and vq_ref into three-phase AC reference voltage values vu_ref, vv_ref, and vw_ref based on the rotational position θ.

[0038] The PWM generator 20 generates PWM signals for driving the inverter 11 based on the three-phase AC reference voltage values vu_ref, vv_ref, and vw_ref. Specifically, the PWM generator 20 generates carrier signals using an in-built PWM timer and compares the carrier signals with the three-phase AC reference voltage values to generate the PWM signals. The generated PWM signals are supplied to gates of power MOS transistors included in the inverter 11.

[0039] Next, details of the current controller 17 will be described. Figure 2is a block diagram showing the configuration of the current controller 17. The current controller 17 includes subtractors 1701, 1702, 1719, proportional operators 1703, 1704, integrators 1705, 1706, integral controllers 1707, 1708, limiters 1709, 1710, 1723, 1724, adders 1711, 1712, 1715, 1716, 1720, 1722, and operators 1713, 1714, 1717, 1718, 1721. In this case, the operator multiplies an input signal by a predetermined parameter when there is the input signal. When there is no input signal, the operator outputs the parameter as it is.

[0040] The operators 1717, 1718, and 1721, the subtractor 1719, and the adders 1720 and 1722 constitute a disturbance-free controller. The subtractors 1701 and 1702, the proportional operators 1703 and 1704, the integrators 1705 and 1706, the integral controllers 1707 and 1708, the limiters 1709 and 1710, and the adders 1711 and 1712 constitute a current regulator. The proportional operators 1703 and 1704 perform proportional control. Kpd and Kpq are proportional gains. The integrators 1705 and 1706 perform integral control. The proportional-integral control simultaneously operates the proportional operators 1703 and 1704 and the integrators 1705 and 1706.

[0041] When Figure 2 The current controller 17 shown in FIG. 17 is expressed by voltage equations. For simplicity of description, it is assumed that the output voltage from the subtractor 1701, the proportional operator 1703, and the integrator 1705 is vd_pi_ref. The output voltage from the subtractor 1702, the proportional operator 1704, and the integrator 1706 is denoted by vq_pi_ref. The operations of the limiters 1709, 1710, 1723, and 1724 are omitted.

[0042]

[0043] In Equation 1, Rs is a winding resistance set value, Φfs is an armature flux linkage set value, Lds, Lqs are dq-axis inductance set values. The values of Rs, Φfs, Lds, and Lqs are set in advance in the semiconductor device 10 in accordance with the winding resistance R, the armature flux Φf, and the dq-axis inductances Ld, Lq of the PM motor 12, and do not necessarily coincide with the actual values of Rs, Φfs, Lds, and Lqs. Rs, Lds, and Lqs are also referred to as motor parameter set values.

[0044] It is assumed that the output voltages of the proportional operators 1703 and 1704 are vd_p and vq_p, and the output voltages of the integrators 1705 and 1706 are vd_i and vq_i, to obtain the following equations.

[0045]

[0046] On the other hand, the voltage equation in the dq-axis rotating coordinate system of the PM motor 12 is as follows.

[0047]

[0048] In Equation 3, vd and vq are dq-axis voltages, and p is a differential operator. Equation 3 is generally called vector control of the PM motor, and thus a detailed description thereof is omitted.

[0049] The semiconductor device 10 (i.e., the current controller 17) performs control so that id_ref = id_ad and iq_ref = iq_ad.

[0050] Figures 3-5 is a block diagram showing the configuration of the integrators 1705 and 1706. The integrators 1705 and 1706 have any configuration shown in Figures 3 to 5 Fig. 6. Gτ represents a low-pass filter gain, Z -1 represents a delay element, and Gi represents an integral gain. Details will be described later.

[0051] Next, the basic operation of the semiconductor device 10 will be described. Figure 6 is a flowchart for explaining the operation of the semiconductor device 10.

[0052] When the PM motor 12 is controlled by sinusoidal wave PWM or overmodulation PWM (first rotational speed: medium-speed rotation), the semiconductor device 10 performs PI control. When the PM motor is controlled by square wave control (second rotational speed: high-speed rotation), the semiconductor device 10 performs P control. In this first embodiment, whether the PM motor 12 is controlled by sinusoidal wave PWM (or overmodulation PWM) or by square wave control is determined by the modulation factor M.

[0053] The modulation factor M will be described. First, when the direct-current bus voltage of the inverter 11 is Vdc, the maximum possible effective value Vuv_rms_max between the output lines of the inverter 11 is represented by the following equation.

[0054]

[0055] The relationship between the line voltage Vuv_rms of the inverter 11 and the dq-axis reference voltage values vd_ref and vq_ref is represented by the following equation.

[0056]

[0057] The modulation factor M is obtained by the following equation.

[0058] M = Vuv_rms / Vdc (Equation 6)

[0059] When the PM motor 12 is in high-speed rotation (P control), the modulation factor is Mp. When the PM motor 12 is in low-speed rotation (PI control), the modulation factor is Mpi. In this case, Mp > Mpi. Therefore, whether the PM motor 12 is P control or PI control can be determined based on the modulation rate.

[0060] Referring again to Figure 3 The operation of the semiconductor device 10 will be described. Here, it is assumed that the semiconductor device 10 shifts from a P control mode in which the PM motor 12 is controlled by P control to a PI control mode in which the PM motor 12 is controlled by PI control. In the P control mode, the integrators 1705 and 1706 do not operate. In the P control mode, the integrators 1705 and 1706 are configured as shown in Figure 3 That is, the input voltage of the integrator 1705 and 1706 is set to 0.

[0061] First, the sequencer 18 determines whether the semiconductor device 10 is in the P control mode (step S1: Yes). Next, in step S2, the sequencer 18 determines whether the modulation factor M is equal to or less than a predetermined value Mth-1. The Mth-1 value can be determined in advance by the modulation factor in which the PM motor 12 can be controlled by PI control.

[0062] If the modulation factor M is equal to or less than the predetermined value Mth-1, the sequencer 18 waits for a predetermined period of time to elapse (step S3). After the predetermined period of time elapses, the sequencer 18 outputs a signal seq for setting the semiconductor device 10 to the transition mode (step S4). The semiconductor device 10 returns to step S1.

[0063] When the semiconductor device 10 enters the transition mode (No in step S1, Yes in step S5), the integral controller 1707 generates an initial voltage value vid-pre of the integrator 1705 (step S9). The integral controller 1706 also generates an initial voltage value viq_pre of the integrator 1706. The method of generating the initial voltage values vid-pre and viq_pre will be described later.

[0064] In the transition mode, the integrators 1705 and 1706 are configured as shown in Figure 4 That is, the input voltage of the integrator 1705 is set to the initial voltage value vid-pre processed by a low-pass filter (Gτ). Similarly, the input voltage of the integrator 1706 is set to the initial voltage value viq_pre processed by a low-pass filter. The low-pass filter consists of a first-order filter, but can consist of a second-order or higher-order filter.

[0065] Thereafter, when a predetermined time elapses (step S10), the sequencer 18 outputs a signal seq for setting the PI mode (step Sll). In the PI mode, the integrators 1705 and 1706 are configured as shown in Figure 5 The input voltage of the integrator 1705 is switched from an initial voltage value vid pre to the output of the subtractor 1701, i.e., the deviation between the reference current value id ref and the detection current value id ad. That is, the integrator 1705 is a normal integrator. The same applies to the integrator 1706. Thereafter, the semiconductor device 10 enters the PI control mode.

[0066] As described above, when shifting from the P control mode to the PI control mode, the semiconductor device 10 is characterized in that, before shifting to the PI control, the initial voltage values vid pre and viq pre are set to the input voltages of the integrators 1705 and 1706.

[0067] Next, the shift of the semiconductor device 10 from the PI control mode to the P control mode will be described. The sequencer 18 determines whether the semiconductor device 10 is in the PI control mode (step S1: No, step S5: No). In operation S6, the sequencer 18 determines whether the modulation factor M is equal to or greater than a predetermined modulation factor Mth-2. The Mth-2 value can be predetermined by the modulation factor with which the PM motor 12 can be controlled by the P control mode.

[0068] If the modulation factor M is equal to or greater than the predetermined modulation factor Mth-2, the sequencer 18 waits for a predetermined period of time to elapse in operation S7. In operation S8, the sequencer 18 outputs a signal seq for setting the semiconductor device 10 to the P control mode. The semiconductor device 10 returns to S1.

[0069] When the semiconductor device 10 is in the P control mode, the integrators 1705 and 1706 are not operated. In the P control mode, the integrators 1705 and 1706 are configured as shown in Figure 3 The input voltages of the integrators 1705 and 1706 are set to 0.

[0070] Here, the initial voltage values vid_pre and viq_pre will be described. As described above, the semiconductor device 10 performs control such that id_ref = id_ad and iq_ref = iq_ad. It is assumed that the rotational speed of the PM motor 12 is constant and the dq-axis two-phase detected direct current values id_ad and iq_ad are in a balanced state following the reference current values id_ref and iq_ref. In the balanced state, the output voltages of the proportional calculators 1703 and 1704 are 0. The element of the differential calculator p to which Equation 3 is applied can be approximated to 0. Also, Rs = R can be approximated to hold. This is because the winding resistance R of the PM motor 12 varies depending on temperature, but the winding resistance set value Rs can be adjusted based on the temperature detected by a temperature sensor (not shown). At this time, the following equation is derived from Equations 1, 2, and 3.

[0071]

[0072] Referring to Equation 7, it can be seen that the output voltages of the integrators 1705 and 1706 are induced voltages due to the difference between the dq-axis inductances Ld and Lq of the PM motor 12 and the dq-axis inductance set values Lds and Lqs of the semiconductor device 10 and the difference between the armature flux Φf of the PM motor 12 and the armature flux set value Φfs of the semiconductor device 10.

[0073] Next, it is assumed that the semiconductor device 10 operates in the P control mode. Assuming that the output voltages of the integrators 1705 and 1706 in Equations 1 and 2 are 0, the following equation is derived.

[0074]

[0075] The output voltages of the proportional calculators 1703 and 1704 are represented by the following equation using a proportional gain.

[0076]

[0077] When Equations 3, 8, and 9 are transformed in consideration of the balanced state, the following equation is derived.

[0078]

[0079]

[0080] Since the d-axis inductance Ld has a smaller range of variation than the q-axis inductance Lq due to magnetic saturation, the difference between Ld and the d-axis inductance set value Lds can be approximated to 0. Therefore, the third term on the right side of Equation 10 can be approximated to 0.

[0081] When the equation 7 after the approximation and the equation 10 are compared here, it can be understood that the right side of the equation 7 and the right side of the equation 10 are the same. That is, when the PM motor 12 is in the equilibrium state by the P control, the voltage value obtained on the left side of the equation 10 can be approximated to the output voltage of the integrators 1705 and 1706. In other words, when switching from the P control to the PI control, the voltage value obtained on the left side of the equation 10 can be used as the initial voltage value of the integrators 1705 and 1706. Since there is no factor (Ld, Lq, Φf) attributable to the PM motor 12, the left side of the equation 10 is calculated by the set values (Rs, Kpd, Kpq, Lds, Lqs) of the semiconductor device 10, the dq-axis reference current values id_ref, iq_ref, and the measured values (id_ad, iq_ad, ω).

[0082] Therefore, in the present first embodiment, the initial voltages vid_pre and viq_pre of the integrators 1705 and 1706 at the time of shifting from the P control mode to the PI control mode are set as follows.

[0083]

[0084] Figure 7 The initial voltage vid_pre generator 17071 included in the integral controller 1707 is shown. Figure 8 The initial voltage viq_pre generator 17081 included in the integral controller 1708 is shown. Figure 7 And 8 Based on the equation 11.

[0085] Note that the dq-axis two-phase detected current values id_ad and iq_ad include low-order high-frequency components such as 5 times or 7 times of the fundamental component, and thus it is desirable to calculate the initial voltages vid_pre and viq_pre using the current values obtained by performing a filtering process on id_ad and iq_ad.

[0086] The semiconductor device 10 can be composed of a dedicated circuit, or can be composed of software. The semiconductor device 10 includes a CPU and a memory, and the CPU executes a program on the memory. The program realizes the functions of the angular velocity detector 14, the three-phase / two-phase converter 15, the dq-axis reference current value generator 16, the current controller 17, the sequencer 18, the two-phase / three-phase converter 19, and the PWM generator 20.

[0087] As described above, when shifting from the P control to the PI control, the semiconductor device 10 sets the initial voltage values vid_pre and viq_pre as the input voltages of the integrators 1705 and 1706 before shifting to the PI control. In this way, it is less likely that a shock occurs after switching to the PI control. Figure 9Changes in the dq-axis reference current values id_ref, iq_ref and the dq-axis two-phase detected current values id_ad, iq_ad in the first embodiment are shown. Figure 10 Changes in the dq-axis reference current values id_ref, iq_ref and the dq-axis two-phase detected current values id_ad and iq_ad in the first embodiment are shown. Comparing Figure 9 and Figure 10 It can be seen that the current change is small in the first embodiment when the PI control mode (PI mode) is shifted from the P control mode (P mode). In the related art, when switching to PI control, for example, the initial voltage values of the integrators 1705 and 1706 are set to 0. However, when the initial voltage values are set to 0, the response of the integrators 1705 and 1706 is delayed, and thus an impact such as a current change is easily caused.

[0088] Second Embodiment

[0089] The second embodiment has the same configuration as the semiconductor device 10. The difference from the first embodiment is the configuration of the initial voltage vid_pre generator and the initial voltage viq_pre generator included in the integrated controllers 1707 and 1708.

[0090] When the right side of Equation 11 is transformed using Equations 8 and 9, the following equation is obtained.

[0091]

[0092] Figure 11 An initial voltage vid_pre generator 17072 included in the integral controller 1707 is shown. Figure 12 An initial voltage viq_pre generator 17082 included in the integral controller 1708 is shown. Figure 11 and 12 Based on Equation 12.

[0093] In the present second embodiment, the same effects as the first embodiment can be obtained.

[0094] Third Embodiment

[0095] Figure 13 is a block diagram showing the structure of a motor control system of the third embodiment. In the first embodiment, the rotational position θ of the PM motor 12 is detected by the PS 13. The third embodiment uses a sensorless control scheme that does not use the PS 13.

[0096] As Figure 13As shown, the semiconductor device 100 includes a position and speed estimator 111 instead of the angular velocity detector 14. The position and speed estimator 111 estimates the rotational position θ and the rotational angular velocity ω of the PM motor 12 from the dq-axis reference voltage values vd_ref, vq_ref and the dq-axis two-phase detected current values id_ad and iq_ad. The components other than the position and speed estimator 111 are the same as those of the first embodiment. Since the operation of the semiconductor device 100 is the same as that of the first embodiment, the description thereof is omitted.

[0097] In the sensorless control method, a method of estimating the rotational position θ and the rotational angular velocity ω of the PM motor 12 by estimating an induced voltage generated on the dq-axis of the PM motor 12 is known. The position and speed estimator 111 also employs this estimation method. The details of the estimation method are omitted.

[0098] In the third embodiment, the same effect as that of the first embodiment can be obtained even if the sensorless motor control system is used.

[0099] It should be noted that the present application is not limited to the above-described embodiments, and various modifications can be made without departing from the gist thereof.

Claims

1. A semiconductor device for vector control of an AC motor via an inverter, the semiconductor device comprising: a dq-axis reference current value generator that generates reference current values for a flux axis (d-axis) and a torque axis (q-axis) based on a reference torque value; a three-phase / two-phase converter that generates dq-axis detected current values from three-phase current values detected by a current detector coupled to the inverter and a rotor position of the AC motor; a current controller that includes a proportional operator, an integrator, and an integral controller that controls the integrator, and generates dq-axis reference voltage values by proportional control and proportional-integral control based on the dq-axis reference current values, the dq-axis detected current values, an angular velocity of rotation of the AC motor, and motor parameter setting values; and a sequencer that switches between the proportional control and the proportional-integral control, wherein when the sequencer switches from the proportional control to the proportional-integral control, the integral controller provides an initial voltage value to the integrator before switching to the proportional-integral control, and wherein the initial voltage value is determined based on one of the dq-axis reference voltage values and a proportional gain set in the proportional operator, the dq-axis reference current values, the dq-axis detected current values, the angular velocity of rotation of the AC motor, and the motor parameter setting values.

2. The semiconductor device according to claim 1, wherein the sequencer calculates a modulation factor based on the dq-axis reference voltage values and a direct current bus voltage of the inverter, and switches the proportional control and the proportional-integral control based on the modulation factor.

3. The semiconductor device according to claim 1, wherein when the AC motor is at a first rotational speed, the AC motor is controlled by the proportional-integral control, and wherein when the AC motor is at a second rotational speed higher than the first rotational speed, the AC motor is controlled by the proportional control.

4. The semiconductor device according to claim 1, wherein the initial voltage value has a d-axis initial voltage value and a q-axis initial voltage value, wherein the motor parameter setting values have a winding resistance setting value and dq-axis inductance setting values, wherein the proportional gain has dq-axis proportional gains, wherein the d-axis initial voltage value is obtained by the following equation: {(Rs + Kpd) * (id_ref - id_ad) - ω * Lqs * (iq_ref - iq_ad)} * iq_ref / iq_ad wherein the q-axis initial voltage value is obtained by the following equation: ω * Lds * (id_ref - id_ad) + (Rs + Kpq) * (iq_ref - iq_ad) where Rs is the winding resistance setting value, Kpd, Kpq are the dq-axis proportional gains, id_ref, iq_ref are the dq-axis reference current values, id_ad, iq_ad are the dq-axis detected current values, Lds, Lqs are the dq-axis inductance setting values, and ω is the angular velocity of rotation of the AC motor.

5. The semiconductor device according to claim 1, wherein the initial voltage value has a d-axis initial voltage value and a q-axis initial voltage value, wherein the motor parameter setting value has a winding resistance setting value, a dq-axis inductance setting value, and an armature flux linkage, wherein the d-axis initial voltage value is obtained by the following equation: (vd_ref-Rs*id_ad+ω*Lqs*iq_ad)*iq_ref wherein the q-axis initial voltage value is obtained by the following equation: vq_ref-ω*Lds*id_ad-Rs*iq_ad-ω*Φfs wherein vd_ref, vq_ref are the dq-axis reference voltage values, Rs is the winding resistance setting value, id_ad, iq_ad are the dq-axis detected current values, iq_ref is the dq-axis reference current value, Lds, Lqs are the dq-axis inductance setting values, Φfs is the armature flux linkage setting value, and ω is the rotational angular velocity of the AC motor.

6. The semiconductor device according to claim 1, further comprising: a position and velocity estimator that estimates a rotor position and a rotational angular velocity of the AC motor based on the dq-axis reference voltage values and the dq-axis detected current values.

7. A motor control system comprising: an AC motor; an inverter; a current detector that detects an output current of the inverter; and a semiconductor device that controls the AC motor via the inverter by vector control, wherein the semiconductor device includes: a dq-axis reference current value generator that generates reference current values of a flux axis (d-axis) and a torque axis (q-axis) based on a reference torque value; a three-phase / two-phase converter that generates dq-axis detected current values from three-phase current values detected by a current detector coupled to the inverter and a rotor position of the AC motor; a current controller that includes a proportional operator, an integrator, and an integral controller that controls the integrator, and generates dq-axis reference voltage values by proportional control and proportional integral control based on the dq-axis reference current values, the dq-axis detected current values, a rotational angular velocity of the AC motor, and a motor parameter setting value; a sequencer that switches between the proportional control and the proportional integral control, wherein the integral controller provides an initial voltage value to the integrator before switching to the proportional integral control when the sequencer switches from the proportional control to the proportional integral control, and wherein the initial voltage value is determined based on one of the dq-axis reference voltage values and a proportional gain set in the proportional operator, the dq-axis reference current values, the dq-axis detected current values, the rotational angular velocity of the AC motor, and the motor parameter setting value.

8. The motor control system according to claim 7, wherein wherein the sequencer calculates a modulation factor based on the dq-axis reference voltage values and a direct current bus voltage of the inverter, and switches the proportional control and the proportional integral control based on the modulation factor.

9. The motor control system according to claim 7, ​ wherein when the AC motor is at a first rotational speed, the AC motor is controlled by the proportional-integral control, and wherein when the AC motor is at a second rotational speed higher than the first rotational speed, the AC motor is controlled by the proportional control.

10. The motor control system of claim 7, wherein the initial voltage values have a d-axis initial voltage value and a q-axis initial voltage value, wherein the motor parameter setting values have a winding resistance setting value and a dq-axis inductance setting value, wherein the proportional gain has a dq-axis proportional gain, wherein the d-axis initial voltage value is obtained by the following equation: {(Rs+Kpd)*(id_ref-id_ad)-ω*Lqs*(iq_ref-iq_ad)}*iq_ref / iq_ad wherein the q-axis initial voltage value is obtained by the following equation: ω*Lds*(id_ref-id_ad)+(Rs+Kpq)*(iq_ref-iq_ad) where Rs is the winding resistance setting value, Kpd, Kpq are the dq-axis proportional gain, id_ref, iq_ref are the dq-axis reference current values, id_ad, iq_ad are the dq-axis detected current values, Lds, Lqs are the dq-axis inductance setting values, and ω is the rotational angular speed of the AC motor.

11. The motor control system of claim 7, wherein the initial voltage values have a d-axis initial voltage value and a q-axis initial voltage value, wherein the motor parameter setting values have a winding resistance setting value, a dq-axis inductance setting value, and an armature flux linkage, wherein the d-axis initial voltage value is obtained by the following equation: (vd_ref-Rs*id_ad+ω*Lqs*iq_ad)*iq_ref / iq_ad wherein the q-axis initial voltage value is obtained by the following equation: vq_ref-ω*Lds*id_ad-Rs*iq_ad-ω*Φfs where vd_ref, vq_ref are the dq-axis reference voltage values, Rs is the winding resistance setting value, id_ad, iq_ad are the dq-axis detected current values, iq_ref is the dq-axis reference current value, Lds, Lqs are the dq-axis inductance setting values, Φfs is the armature flux linkage setting value, and ω is the rotational angular speed of the AC motor.

12. The motor control system of claim 7, further comprising: a position and speed estimator to estimate a rotor position and a rotational angular speed of the AC motor based on the dq-axis reference voltage values and the dq-axis detected current values.

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