AC motor control device

Abstract

The invention provides an AC motor control device capable of suppressing harmonic components of current flowing through an AC motor and reducing loss generated in the AC motor. This AC motor control device is provided with: an inverter (3) that performs power conversion from DC power to AC power; and an AC motor control unit (2) which has pulse generation units (22, 23) for generating pulses on the basis of the voltage phase, and which drives the AC motor (1) using the AC power. In a dq orthogonal coordinate system, the pulse generation units (22, 23) generate the pulses such that the pulse interval in voltage phases in a first specific range including an inductance smaller than the average value of the varied inductances of the AC motor is shorter than the pulse interval in voltage phases in a second specific range including an inductance smaller than the average value of the varied inductances of the AC motor. The second specific range of voltage phases includes an inductance greater than the average value.

Description

Technical Field

[0001] This invention relates to a control device for driving an AC motor. Background Technology

[0002] In recent years, due to the increasing demand for energy conservation, AC motor control devices that drive AC motors have been widely used in home appliances, infrastructure, vehicle equipment, and other applications.

[0003] PWM control is typically used as the control device for driving such AC motors. In PWM control, a modulation signal is generated based on the voltage command signal applied to the AC motor. By comparing the modulation signal with the carrier wave, a PWM pulse signal is generated to turn the switching elements of the power conversion device on and off. This allows DC power to be converted into AC power to drive the AC motor.

[0004] In this way, DC power can be converted to AC power through PWM control. However, because the switching elements of the power conversion device are repeatedly turned on and off at high speed, the output voltage is applied to the AC motor in a pulsed manner. Therefore, the current flowing through the AC motor contains high-order harmonic components, which become the cause of noise and losses.

[0005] For example, Patent Document 1 discloses a technique for reducing noise and losses caused by the switching elements of such power conversion devices during conduction and cutoff.

[0006] The technology described in Patent Document 1 involves shortening the period of the carrier wave near the current zero-crossing point. In this way, by dispersing the high-order harmonic components of the voltage applied to the AC motor in a pulsed manner, the high-order harmonic components of the current flowing through the AC motor can be dispersed. Therefore, a solution is proposed to reduce noise generated by the AC motor and suppress DC voltage fluctuations.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2019-47688 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] As mentioned above, in PWM control, there is a problem that the current flowing in the AC motor contains high-order harmonic components, which increases noise and losses.

[0012] However, while the technology described in Patent Document 1 can disperse the high-order harmonic components of the voltage applied to the AC motor in a pulsed manner, it does not disclose a configuration for actively suppressing the high-order harmonic components of the current flowing through the AC motor. Furthermore, it does not disclose a configuration that allows the output pulse waveform to vary according to the characteristics of the motor.

[0013] Therefore, the technology described in Patent Document 1 cannot sufficiently reduce the noise and losses associated with PWM control.

[0014] The purpose of this invention is to provide an AC motor control device that can suppress the high-order harmonic components of the current flowing through the AC motor and reduce the losses generated in the AC motor.

[0015] Problem-solving methods

[0016] To achieve the above objectives, the present invention is configured as follows.

[0017] An AC motor control device includes: an inverter that performs power conversion from direct current to alternating current; and an AC motor control unit having a pulse generation unit that generates pulses based on voltage phases and drives an AC motor using the alternating current. In a dq orthogonal coordinate system, the pulse generation unit generates pulses such that the pulse interval in a first specific range of voltage phases is shorter than the pulse interval in a second specific range of voltage phases, the first specific range of voltage phases including an inductance smaller than the average value of the varying inductance of the AC motor, and the second specific range of voltage phases including an inductance larger than the average value.

[0018] The effects of the invention

[0019] According to the present invention, an AC motor control device can be provided that, by shortening the pulse interval of the phase in which the inductance decreases based on the voltage phase without using a carrier wave, thereby suppressing the high-order harmonic components of the current flowing through the AC motor and reducing the losses generated in the AC motor. Attached Figure Description

[0020] Figure 1 This is a block diagram showing the overall configuration of the AC motor control device according to Embodiment 1 of the present invention.

[0021] Figure 2 This is a diagram showing an example of the waveforms of the carrier wave, modulation signal, and pulse during typical PWM control.

[0022] Figure 3 This is a diagram showing an example of the pulse waveform during typical PWM control.

[0023] Figure 4This is a diagram illustrating the pulse waveform and inductance changes during typical PWM control when driving a reverse salient pole motor.

[0024] Figure 5 This is a waveform example showing the changes in current and inductance during typical PWM control when driving a reverse salient pole motor.

[0025] Figure 6 This is a diagram showing the pulse waveform and inductance change during the driving of the reverse salient pole motor in Embodiment 1.

[0026] Figure 7 This is a waveform example showing the change in current and inductance during the reverse salient pole motor drive in Embodiment 1 according to the present application.

[0027] Figure 8 This is a diagram illustrating the pulse waveform and inductance changes during typical PWM control of a salient-pole motor drive.

[0028] Figure 9 This is a diagram showing an example of the pulse waveform and inductance change of Embodiment 1 of the present invention when driven by a salient pole motor.

[0029] Figure 10 This is a waveform example showing the changes in current and inductance during typical PWM control when driving a salient pole motor.

[0030] Figure 11 This is a waveform example showing the changes in current and inductance during the driving of a parasitic motor according to Embodiment 1 of the present invention.

[0031] Figure 12 This is a diagram showing waveform examples of sinusoidal voltage at the fundamental frequency and sinusoidal voltage at three times the frequency.

[0032] Figure 13 This is a block diagram of the pulse generation unit in Embodiment 3 of the present invention.

[0033] Figure 14 This is a schematic diagram of Embodiment 4 of the present invention.

[0034] Figure 15 This is a schematic diagram of the pulse generation unit in Embodiment 5 of the present invention. Detailed Implementation

[0035] Hereinafter, embodiments of the present invention will be described using the accompanying drawings.

[0036] Example

[0037] (Example 1)

[0038] An example of the AC motor 1 being driven by the AC motor control unit 2 will be used to illustrate Embodiment 1 of the present invention.

[0039] (Overall outline)

[0040] First, use Figure 1 The overall general structure of the AC motor control device in this embodiment will be described.

[0041] exist Figure 1 In this AC motor control device, there are an inverter 3 and an AC motor control unit 2. The inverter 3 performs power conversion from DC to AC, and the AC motor control unit 2 has a vector control unit 21 and a pulse generation unit 22 that generates pulses based on voltage phase, and drives the AC motor 1 using AC power.

[0042] In Embodiment 1 of the present invention, the AC motor control unit 2 calculates the modulation rate command value 21A based on the current detection circuit 4 that detects the current flowing through the AC motor 1 and the position sensing information 5A from the position sensor 5 that detects the rotational position of the AC motor 1.

[0043] Based on the calculated modulation rate command value 21A, the pulse generation unit 22 generates pulse 22A based on voltage phase pulse generation. Based on the generated pulse 22A, the inverter 3, which performs power conversion from DC to AC, supplies AC power to the AC motor 1.

[0044] (Explanation of PWM carrier in a typical reverse salient pole motor)

[0045] Next, the general PWM carrier wave in the case of a reverse salient pole motor will be explained.

[0046] One common way to control an AC motor 1 is through PWM control. Figure 2 This is a diagram showing an example of the waveforms of the carrier wave, modulation signal, and pulse during typical PWM control.

[0047] like Figure 2 As shown, in PWM control mode, the modulation signal is compared with the carrier wave. When the modulation signal is large, a turn-on pulse is output, and when the modulation signal is small, a turn-off pulse is output.

[0048] By comparing the sinusoidal modulation signal with the carrier wave using such PWM control, it is possible to output... Figure 3 The pulse waveform shown.

[0049] In PWM control, since the pulse waveform is generated based on the carrier wave, it becomes the basis for outputting turn-on and turn-off pulses in each carrier cycle.

[0050] Therefore, in PWM control, a voltage higher harmonic component is generated that is proportional to the carrier period.

[0051] (The relationship between the dq axis inductance and the voltage phase angle in a typical reverse salient pole motor)

[0052] Next, the relationship between the dq-axis inductance and the voltage phase angle will be explained.

[0053] In automotive applications, AC motors used for driving sometimes employ embedded permanent magnet synchronous motors (IPMSMs) that offer high output density. In IPMS motors, the inductance is not constant, resulting in salient poles.

[0054] In an orthogonal coordinate system, the state in which the inductance of a motor is greater in the direction of the torque axis (q-axis) that is orthogonal to the direction of the magnet axis (d-axis) is called reverse salient pole.

[0055] Compared to a reverse salient pole motor, when the voltage and current phases are very close in the q-axis direction during vector control, the change in inductance relative to the U-phase pulse waveform of the three-phase AC voltage pulse is as follows: Figure 4 As shown.

[0056] like Figure 4 As shown, the inductance increases or decreases with the voltage phase, exhibiting the characteristic of decreasing near 0 degrees, 180 degrees, and 360 degrees, and increasing near 90 degrees and 270 degrees.

[0057] (Explanation of high-order harmonics of current in a typical reverse salient pole motor (phase current and inductance))

[0058] Figure 5 Indicates based on Figure 4 The pulse shown illustrates the U-phase current waveform and inductance changes when the inverter drives the reverse salient pole motor.

[0059] The higher harmonic components of the current are proportional to the product of the higher harmonic components of the voltage and the inductance and the frequency of the higher harmonic components.

[0060] In other words, when the inductance is small, the higher harmonic components of the current become larger relative to the same voltage higher harmonic components.

[0061] Therefore, as Figure 5 As shown, the current ripple increases in the region of low inductance and decreases in the region of high inductance.

[0062] (A summary of typical reverse salient pole motors)

[0063] As mentioned above, in a typical PWM control method, the turn-on and turn-off pulses are generated based on the carrier wave. Therefore, the higher harmonic components of the voltage are concentrated on the frequency components that are proportional to the carrier wave period.

[0064] Therefore, the higher harmonic components of the current are concentrated on the frequency components that are proportional to the carrier period.

[0065] In addition, such as Figure 5 As shown, when driving an IPMS motor, current ripple increases in the region where the inductance is small.

[0066] Due to the high-order harmonic components of such current, the torque pulsation of the motor increases, and the high-order harmonic losses increase.

[0067] In Embodiment 1 of the present invention, a method is proposed that pulses are generated at unequal intervals based on voltage phase without using a carrier wave, and by shortening... Figure 4 The pulse interval in the region where the inductance decreases is used to suppress the higher harmonic components of the current.

[0068] The function and effects of Embodiment 1 of the present invention will be explained.

[0069] (Explanation of higher harmonic voltage in Example 1 (pulse and inductance): reverse salient pole)

[0070] Figure 6 This is a diagram showing the U-phase pulse waveform and inductance change during reverse salient pole motor driving in Embodiment 1.

[0071] like Figure 6 As shown, in Embodiment 1 of the present invention, pulses are generated at unequal intervals by the pulse generation unit 22. In the dq orthogonal coordinate system, pulses are generated in the voltage phase where the inductance decreases (the region where the inductance decreases) with shorter pulse intervals. More specifically, the pulse generation unit 22 generates the pulses in the dq orthogonal coordinate system with pulse intervals shorter than those in the voltage phase where the inductance is smaller than the average value of the varying inductance in a specific range, compared to pulse intervals in the voltage phase where the inductance is larger than the average value.

[0072] In other words, in the region where the inductance decreases, it becomes a structure that disperses and increases the frequency of higher harmonic components of the voltage.

[0073] As a result, the region of inductance variation is divided into two regions: a region with small inductance (in the dq orthogonal coordinate system, the voltage phase of a first specific range of inductance smaller than the average value of the varying inductance) and a region with large inductance (the voltage phase of a second specific range of inductance larger than the average value). The number of pulses in the region with larger inductance than the average value is smaller than the number of pulses in the region with smaller inductance than the average value.

[0074] (Explanation of higher harmonic currents obtained by setting a shorter pulse interval in the region where the inductance is reduced (phase current and inductance): reverse salient pole)

[0075] Figure 7 Indicates based on Figure 6 The pulse shown illustrates the U-phase current waveform and inductance changes when inverter 3 drives the reverse salient pole motor.

[0076] like Figure 7 As shown, the effect of suppressing current ripples can be achieved in the region where the inductance is smaller.

[0077] This is because by dispersing the higher harmonic components of the voltage by increasing their frequency, the product of the inductance of the higher harmonic components of the voltage and the frequency of the high-frequency components increases, while the higher harmonic components of the current decrease.

[0078] (Summary of the reverse salient pole motor in Example 1)

[0079] As described above, in the pulse waveform of Embodiment 1 of this application, pulses are generated at unequal intervals based on the voltage phase, and the pulse interval is shortened in the region where the inductance is small, thereby making the higher harmonic components of the voltage more frequent and dispersed.

[0080] Therefore, as Figure 7 As shown, this suppresses current pulsation in the region where the inductance decreases.

[0081] Thus, according to Embodiment 1 of the present invention, in the case of reverse salient poles, by suppressing the higher harmonic components of the current, it is possible to suppress the torque pulsation and higher harmonic losses of the motor.

[0082] (Regarding the salient pole motor of Example 1)

[0083] Here, in an orthogonal coordinate system, the state in which the inductance of the motor is greater than the inductance in the direction of the magnet axis (d-axis) relative to the torque axis (q-axis) is called salient pole.

[0084] To clarify the difference between the PWM control method and the method in Embodiment 1 of this application, the inductance change, pulse waveform, and current waveform in the case of the forward salient pole are shown in the same way as in the case of the reverse salient pole.

[0085] (Explanation of higher harmonics of voltage, pulses and inductance: parasaliency)

[0086] Figure 8 This example illustrates the U-phase pulse waveform and inductance variation in a typical PWM control method when using a salient-pole motor. Figure 9 This illustrates an example of Embodiment 1 of the present invention. In the case of a parasaliency electrode, the inductance increases with voltage phase changes around 0 degrees, 180 degrees, and 360 degrees, and decreases around 90 degrees and 270 degrees. For example... Figure 9 As shown, in this application, similar to the case of reverse salient pole, the pulse interval becomes shorter in the region of low inductance.

[0087] (Explanation of higher harmonics of current, U-phase current and inductance: parasaliency)

[0088] Figure 8 This is a diagram illustrating the pulse waveform and inductance changes during typical PWM control of a salient-pole motor drive. Figure 9 This is a diagram showing an example of the pulse waveform and inductance change of Embodiment 1 of the present invention when driven by a salient pole motor. Figure 10 This is a waveform example showing the changes in current and inductance during typical PWM control when driving a salient pole motor. Figure 11 This is a waveform example showing the changes in current and inductance during the driving of a parasitic motor according to Embodiment 1 of the present invention.

[0089] like Figure 10 As shown, in PWM control mode, it can be confirmed that the current ripple increases in the region where the inductance decreases.

[0090] like Figure 11 As shown, in the current waveform of Embodiment 1 of the present invention, the effect of suppressing current pulsation can be achieved by shortening the pulse interval in the region of low inductance.

[0091] (Summary of the salient pole motor in Example 1)

[0092] As described above, even when the motor is salient, the pulse waveform of Embodiment 1 of the present invention can suppress the high-order harmonic components of the current.

[0093] In addition, by suppressing the higher harmonic components of the current in this way, it is possible to suppress the torque pulsation and higher harmonic losses of the motor.

[0094] According to a first embodiment of the present invention, an AC motor control device can be provided that can suppress the high-order harmonic components of the current flowing in the AC motor and reduce the losses generated in the AC motor.

[0095] (Example 2)

[0096] Next, a second embodiment of the present invention will be described.

[0097] (Explanation of the disappearance of the tertiary components in three-phase alternation)

[0098] Typically, in order to drive an AC motor, a three-phase AC voltage needs to be output from an inverter.

[0099] In such a three-phase AC voltage, high-order harmonic components with frequencies three times the fundamental rotational frequency of the motor cannot be represented in an orthogonal coordinate system.

[0100] Specifically, in the sinusoidal voltage phase from 0 degrees to 180 degrees from the fundamental rotation frequency, the three-fold frequency component is as follows: Figure 12 As shown.

[0101] like Figure 12 As shown, in the three-fold frequency component, the voltage increases near 30 degrees and 150 degrees, and is smaller at 0 degrees, 90 degrees, and 180 degrees.

[0102] In other words, in the three-fold frequency component, there are more conduction pulses near 30 degrees and 150 degrees, and more cutoff pulses near 0 degrees, 90 degrees, and 180 degrees, which makes it easier to generate the three-fold frequency component.

[0103] Therefore, in the pulse waveform of Embodiment 2 of the present invention, in the U-phase pulse waveform, pulse waveforms of 0 degrees, 90 degrees, 180 degrees and pulse intervals shortened every 90 degrees starting from 0 degrees are generated.

[0104] Therefore, the pulse interval can be shortened on orthogonal coordinates without increasing higher harmonic components.

[0105] As a specific waveform, such as Figure 6 , Figure 9 As shown in the waveform, a pulse waveform is generated by shortening the pulse interval every 90 degrees starting from 0 degrees.

[0106] According to a second embodiment of the present invention, an AC motor control device can be provided that can suppress the high-order harmonic components of the current flowing in the AC motor and reduce the losses generated in the AC motor, even for three-phase AC voltage.

[0107] (Variation Example 1)

[0108] Next, a variation of the above-described Embodiment 1 and Embodiment 2 will be described.

[0109] The first variation is an example of changing the pulse shape based on voltage amplitude and phase.

[0110] When the vector control unit 21 controls the AC motor 1, it controls the voltage amplitude and phase in the orthogonal coordinate system supplied to the AC motor 1.

[0111] Therefore, since the waveform of the pulse that suppresses voltage amplitude and higher harmonics of current changes, the same pulse waveform as in Example 1 or Example 2 is generated in accordance with this change.

[0112] According to the modified example, the same effect as in the first or second embodiment can also be obtained.

[0113] (Variation Example 2)

[0114] Next, a variation of the above-described Embodiment 1 and Embodiment 2 will be described.

[0115] The second variation is an example of changing the pulse shape by altering the current amplitude and phase.

[0116] Depending on the operating state of the AC motor 1, the amplitude and phase of the current in the orthogonal coordinate system change. When the vector control unit 21 controls the AC motor 1, it controls the amplitude and phase of the current in the orthogonal coordinate system supplied to the AC motor 1.

[0117] As a result, the characteristics of the inductor change due to the effect of magnetic saturation.

[0118] Therefore, the pulse generation unit 22 generates the same pulse waveform as in Embodiment 1 or Embodiment 2 based on the change in inductance.

[0119] According to the second variation, the same effect as in the first or second embodiment can also be obtained.

[0120] (Example 3)

[0121] Next, Embodiment 3 of the present invention will be described.

[0122] Embodiment 3 of the present invention is an example of switching between the mode of the present invention and the PWM control mode according to the operating conditions.

[0123] In the above embodiments one and two, pulses are generated at unequal intervals without using a carrier wave, and the high-order harmonic components of the current are suppressed by shortening the pulse interval in the region where the inductance is reduced.

[0124] However, in regions where the number of on / off pulses during one revolution of the sinusoidal voltage is sufficiently large, such as in the case of low speed or the application of components that can switch at high speed, the suppression effect of high-order harmonics of current in PWM control becomes smaller.

[0125] Therefore, as Figure 13 As shown, according to the operating conditions 1A of the AC motor 1 (representing the operating conditions of a region with a large number of pulses or a region with a small number of pulses), as shown in Embodiment 3 of the present invention, a pulse control mode switching unit 223 is provided to switch between the first pulse generation unit A221 that generates pulses based on the voltage phase and the second pulse generation unit B222 that generates pulses based on the carrier wave.

[0126] Therefore, in regions with a large number of pulses, a PWM control method that generates pulses based on a carrier wave is used, while in regions with a small number of pulses, as in this invention, the AC motor 1 can be driven in a way that shortens the pulse interval in regions where the inductance is smaller.

[0127] Therefore, PWM control can be used in regions with a large number of pulses, thus reducing the memory required to store the pulse waveform settings for shortening the pulse interval in regions where the inductance is small.

[0128] The operating conditions 1A of the AC motor 1 can be generated by the vector control unit 21 based on the position sensing information 5A from the position sensor 5, or it can be supplied by a separately provided operating condition setting unit (not shown).

[0129] According to Embodiment 3 of the present invention, in addition to achieving the same effects as Embodiment 1, it is also possible to achieve the effect of reducing the memory that stores the pulse waveform settings for shortening the pulse interval in the region where the inductance decreases.

[0130] (Example 4)

[0131] Next, Embodiment 4 of the present invention will be described.

[0132] Figure 14 This is a schematic diagram of Embodiment 4 of the present invention, which is an example of applying the AC motor control device 2 of Embodiments 1 to 3 to an electric vehicle 100.

[0133] exist Figure 14 In this process, the on-board motor host 101, which serves as the AC motor of the electric vehicle 100, is controlled by the aforementioned AC motor control device 2.

[0134] According to Embodiment 4 of the present invention, an electric vehicle with an AC motor control device can be provided, which can suppress the high-order harmonic components of the current flowing in the AC motor and reduce the losses generated in the AC motor.

[0135] (Example 5)

[0136] Next, Embodiment 5 of the present invention will be described.

[0137] In the on-board motor host 101 of the electric vehicle 100, if it is started at extremely low temperatures, the rotating part of the on-board motor host 101 may freeze, so a warm-up operation is sometimes performed. During such a warm-up operation, it is preferable that the losses generated from the on-board motor host 101 are large.

[0138] Therefore, in Figure 13 In the pulse control mode switching unit 223 shown, the configuration replaces the motor operating condition 1A with a temperature sensor 24 that supplies AC motor temperature information to the pulse control mode switching unit 223. Furthermore, the pulse control mode switching unit 223 switches between the first pulse generation unit 221 and the second pulse generation unit 222 based on the temperature detected by the temperature sensor 24.

[0139] By configuring the pulse control mode switching unit 223 to be set on the side of the first pulse generation unit A221 (the pulse generation unit of Embodiment 1, 2, or 3 of the present invention) when the temperature of the AC motor 1 is above a certain value, and to be set on the second pulse generation unit B222 (the pulse generation unit of the present invention not applied) when the temperature of the AC motor 1 is below a certain value, it is possible to increase the losses generated from the AC motor 1 to perform warm-up operation.

[0140] According to Embodiment 5, an electric vehicle with an AC motor control device can be provided. In addition to achieving the same effect as in Embodiment 1, the AC motor control device can also increase the losses generated from the AC motor 1 to perform warm-up operation when the temperature of the AC motor 1 is below a certain value.

[0141] Explanation of symbols

[0142] 1…AC motor, 1A…operating conditions, 2…AC motor control unit, 3…inverter, 4…current detection circuit, 5…position sensor, 5A…position sensing information, 21…vector control unit, 21A…modulation rate command value, 22, 23…pulse generation unit, 24…temperature sensor, 100…electric vehicle, 101…onboard motor host, 221…first pulse generation unit A, 222…second pulse generation unit B, 223…pulse control mode switching unit.

Claims

1. An AC motor control device, characterized in that, have: An inverter, which performs power conversion from direct current (DC) to alternating current (AC); and An AC motor control unit includes a pulse generation unit that generates pulses based on voltage phase, and drives an AC motor using the AC power. In the dq orthogonal coordinate system, the pulse generating unit generates the pulse in such a way that the pulse interval in the voltage phase of a first specific range is shorter than the pulse interval in the voltage phase of a second specific range. The first specific range of voltage phases includes an inductance smaller than the average value of the varying inductance of the AC motor, and the second specific range of voltage phases includes an inductance larger than the average value.

2. The AC motor control device according to claim 1, characterized in that, The pulse generation unit generates the pulse in such a way that the pulse interval shortens every 90 degrees, starting from 0 degrees of the voltage phase.

3. The AC motor control device according to claim 1 or 2, characterized in that, The AC motor control unit has a vector control unit that changes the waveform of the pulse according to the voltage amplitude and phase supplied to the AC motor.

4. The AC motor control device according to claim 1 or 2, characterized in that, The AC motor control unit has a vector control unit that changes the pulse waveform according to the amplitude and phase of the current supplied to the AC motor.

5. The AC motor control device according to claim 1 or 2, characterized in that, The pulse generation unit includes a pulse control mode switching unit. The pulse control mode switching unit switches between a first pulse generation unit based on voltage phase and a second pulse generation unit based on carrier wave, according to the operating state of the AC motor.

6. The AC motor control device according to claim 1 or 2, characterized in that, The main unit that controls the onboard electric motor of an electric vehicle.

7. The AC motor control device according to claim 6, characterized in that, have: Temperature sensor; as well as Pulse control mode switching unit, The pulse generating unit has: A first pulse generation unit based on voltage phase generation pulses and a second pulse generation unit based on carrier pulse generation pulses. The pulse control mode switching unit switches between the first pulse generation unit and the second pulse generation unit according to the temperature detected by the temperature sensor.

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