WO2014141345A1

WO2014141345A1 - Motor drive device and electric device using same

Info

Publication number: WO2014141345A1
Application number: PCT/JP2013/007535
Authority: WO
Inventors: 田中　秀尚; 義典竹岡
Original assignee: パナソニック株式会社
Priority date: 2013-03-15
Filing date: 2013-12-24
Publication date: 2014-09-18
Also published as: JP6134905B2; CN105027419A; JP2014180149A; CN105027419B

Abstract

A motor drive device (22) includes: a rectifying and smoothing circuit (2) for rectifying the inputted AC current to DC current; and an inverter (3) for converting DC current output from the smoothing circuit (2) to three-phase AC current and driving a brushless DC motor (4). The motor drive device (22) further includes: a position detector (5) for detecting the rotational position of the brushless DC motor (4); and a speed estimation unit (7) for estimating the driving speed of the brushless DC motor (4) from a signal detected by the position detector (5). The motor drive device (22) still further includes: a PWM setting unit (10) for setting the on-duty and carrier frequency using pulse width modulation on the basis of the driving speed such that the carrier frequency is reduced to lower than the carrier frequency having an on-duty greater than a prescribed value by maintaining a constant PMW minimum pulse width when the on-duty is lower than a prescribed value; and a waveform generation unit (11) for generating a driving waveform for the inverter (3) by superimposing the on-duty and the carrier frequency set by the PWM setting unit onto the rotational position and the driving speed.

Description

Motor drive device and electric device using the same

The present invention relates to a motor driving device for driving a brushless DC motor and an electric device using the motor driving device.

FIG. 7 is a block diagram including a first conventional motor driving device.

The first conventional motor driving device performs rectangular wave driving of speed feedback control by pulse width modulation (hereinafter referred to as PWM) control so that the driving speed matches the target speed.

The first conventional motor drive device will be described with reference to FIG.

AC power generated in the AC power supply 201 is converted into DC power by the rectifying and smoothing unit 202. The converted DC power is input to the inverter 203. The inverter 203 is configured by connecting six switching elements 203a to 203f in a three-phase bridge connection. The inverter 203 converts the input DC power into AC power having a predetermined frequency and outputs the AC power to the brushless DC motor 204.

The position detection unit 205 acquires the zero-cross position that appears at the output terminal of the non-conducting winding phase inverter 203 as information on the induced voltage generated by the rotation of the brushless DC motor 204. Based on this information, the position detection unit 205 detects the relative position of the rotor 204a of the brushless DC motor 204. The speed estimation unit 206 calculates the rotation speed of the brushless DC motor 204 based on the signal detected by the position detection unit 205. The waveform generation unit 207 calculates a PWM duty on width according to the rotation speed calculated by the speed estimation unit 206, and determines a phase to be supplied to the inverter 203 based on the signal detected by the position detection unit 205. The drive unit 208 drives the switching elements 203a to 203f of the inverter 203 based on the signal from the waveform generation unit 207.

The first conventional motor driving device can realize a motor driving device that drives while arbitrarily changing the speed of the brushless DC motor.

Also, the second conventional motor drive device is driven while reducing the capacity of the smoothing capacitor and including a large ripple component in the bus voltage as disclosed in, for example, Patent Document 1. FIG. 8 is a block diagram including a second conventional motor driving device.

A second conventional motor driving device will be described with reference to FIG. The second conventional motor driving device uses a small-capacity smoothing capacitor.

In FIG. 8, the AC power generated in the AC power supply 301 is rectified to DC power by the rectifier diodes 302a to 302d of the rectifying and smoothing unit 302. The DC power rectified by the rectifying diodes 302a to 302d of the rectifying / smoothing unit 302 is smoothed by the smoothing capacitor 302e. However, since the capacitance of the smoothing capacitor 302e is small, the smoothed DC power is input to the inverter 303 in a state including a large ripple component. The inverter 303 is configured by connecting six switching elements 303a to 303f in a three-phase bridge. The inverter 303 converts the input DC voltage including the ripple into AC having a predetermined frequency and outputs the AC voltage to the brushless DC motor 304.

The position detection unit 305 acquires information on the induced voltage generated by the rotation of the brushless DC motor 304 based on the voltage of the output terminal of the inverter 303. Based on this information, the position detection unit 305 detects the relative position of the rotor 304a of the brushless DC motor 304. Further, in the voltage including a large ripple output from the rectifying / smoothing unit 302, it is difficult for the position detecting unit 305 to accurately detect the relative position when the voltage is low. Therefore, based on the position information of the position detecting unit 305. The position estimation unit 306 estimates the relative position. When the output voltage of the rectifying / smoothing unit 302 detected by the voltage detecting unit 307 is equal to or lower than a predetermined value, the switching unit 308 uses the output voltage of the rectifying / smoothing unit 302 detected by the position estimating unit 306 as a position detection signal. The waveform generator 309 determines the energized phase and the PWM duty width. Based on the signal generated by the waveform generation unit 309, the drive unit 310 drives the switching elements 303a to 303f of the inverter 303.

The second conventional motor driving device can drive the brushless DC motor while arbitrarily changing the speed of the DC bus voltage including a large ripple than the first conventional motor driving device. In addition, an inexpensive and small motor drive device can be realized.

However, the first and second conventional motor driving devices have the following problems.

First, the problem of the first conventional motor drive device will be described.

FIG. 9 is a state diagram showing the output terminal voltage of the inverter of the conventional motor drive device. In FIG. 9, the solid line indicates the waveform of the output terminal voltage, and the alternate long and short dash line indicates the reference voltage that is ½ of the inverter input voltage. Each switching element is active high, and the upper element is turned on when the PWM signal is high. The waveform shown in FIG. 9 is a U-phase terminal voltage waveform. The V-phase and W-phase terminal voltage waveforms are ± 120 degrees out of phase from the U-phase terminal voltage waveforms.

7, the output terminal voltage waveform of the inverter 203 and the reference voltage are output to the position detection unit 205. A section a in FIG. 9 is a section in which the U-phase lower arm switching element 203b is turned on, and the terminal voltage is connected to the rectified and smoothed output GND through the switching element. A section c in FIG. 9 is a section in which the U-phase upper arm switching element 203a is on. The upper switching element is repeatedly turned on / off at a constant timing by PWM control. When the switching element 203a is turned on, the upper switching element is connected to the plus side of the rectified and smoothed output. Connected to the side. Therefore, the terminal voltage in the section c has a waveform in which high and low with the PWM output superimposed are changed.

In section b and section d of FIG. 9, the switching elements of the U-phase upper and lower arms are in the OFF state, and an induced voltage generated by the rotation of the brushless DC motor appears at this time. In addition, since the PWM output has a waveform superimposed by the PWM switching of the other phase, the induced voltage can be confirmed only when the PWM output is on.

Further, spike voltages X and Y generated in the section b and the section d in FIG. 9 appear when the winding current flows through the circulating

current diodes

203g and 203h by turning off the switching elements 203b and 203a, respectively. While these diodes are conducting, the terminal voltage is high and low, and the induced voltage cannot be detected.

The position detector 205 compares the induced voltage that appears when both the upper and lower switching elements are off with the reference voltage, and detects the timing at which the magnitude relationship changes as a position signal. That is, in the section b and the section d where the induced voltage appears, in the PWM on section after the spike voltages X and Y converge, the position detection unit 205 has a point A where the magnitude relationship between the inverter output terminal voltage and the reference voltage is reversed. And B are detected.

Note that the reference voltage that the position detection unit 205 compares with the terminal voltage includes ½ of the inverter input voltage, a virtual neutral point potential of the motor winding connected to each output terminal voltage of the inverter via a resistor, and the like. Generally used.

In such a position detection method as described above, the accuracy of position detection depends on the PWM carrier frequency and the PWM on period. In other words, when the PWM duty is low, such as at startup or when the load is low, or when the PWM carrier frequency is low, the number of PWM off intervals during which position detection cannot be sampled increases, so the delay in position detection timing increases. Based on the position detection timing, the driving speed of the brushless DC motor is calculated and the winding to be energized is switched. This delay in position detection causes an increase in current distortion and an increase in loss due to driving in the lag phase. Problems such as vibration and noise increase due to speed fluctuations occur. In particular, the ratio of the position error with respect to the rotation angle of the brushless DC motor becomes large and the influence increases when driving at high speed.

Therefore, stable driving of a brushless DC motor is required to suppress a position detection delay due to a PWM OFF section by using a somewhat high PWM carrier frequency.

Next, the problem of the second conventional motor driving device will be described.

In the second conventional motor drive device, a DC voltage including a large ripple is input to the inverter 303. For this reason, even if the brushless DC motor is in a stable driving state, a slight speed fluctuation occurs due to the influence of the input voltage. In a section where the DC input voltage of the inverter 303 is higher than the average voltage, the applied torque is higher than the load torque, and the brushless DC motor is in an accelerated state. At this time, the applied voltage of the brushless DC motor changes with a lag phase with respect to the induced voltage phase.

Furthermore, in the above-described PWM control at a low carrier frequency, when a delay in position detection due to the PWM off interval is added, a larger delayed phase state is generated than in the first conventional motor drive device.

Also, in a configuration in which a large ripple is included in the inverter input voltage, the electric power supplied to the motor in a section where the voltage is high is large, and the peak current increases.

Therefore, in the second conventional motor drive device, a larger peak current flows than when a smoothed DC voltage is input, and an increase in current due to a delay phase is added, resulting in occurrence of an overcurrent stop or overcurrent. Increased possibility of demagnetization. Furthermore, driving with a lag phase can cause an increase in loss and a decrease in driving torque.

Therefore, the second conventional motor driving device requires PWM control at a high carrier frequency.

However, even when PWM control with a high carrier frequency is performed, there are the following problems.

FIG. 10 is a state diagram showing an enlarged waveform near the position detection timing of the output terminal voltage of the conventional inverter.

FIG. 10 shows the terminal voltage state in the vicinity of the position detection timing B in FIG. 9 in detail.

In FIG. 10, the solid line indicates the U-phase terminal voltage, the broken line indicates the induced voltage due to the rotation of the brushless DC motor, and the alternate long and short dash line indicates the reference voltage. In FIG. 10, the lower rectangular waveform indicates a PWM output, and each switching element is active high, so that each switching element is turned on in the PWM high interval.

Although this subject is a common subject of the first and second conventional motor driving devices, for the sake of simplicity, the first conventional motor driving device that inputs a stable DC voltage that does not include ripples. The waveform will be described.

From the terminal voltage waveform shown in FIG. 10, it can be seen that an induced voltage appears in the terminal voltage when PWM is on, but a high-frequency noise component is superimposed immediately after PWM is on.

The position detection signal detects the timing at which the magnitude relationship between the inverter output terminal voltage and the reference voltage is changed as the zero cross of the induced voltage in the section b and the section d in FIG. Therefore, the ideal position detection point (that is, the zero cross point of the induced voltage) is the intersection of the induced voltage and the reference voltage, that is, point B in FIG. However, high-frequency noise is superimposed on the terminal voltage waveform, and the timing at which the magnitude relationship between the terminal voltage and the reference voltage first changes due to the influence of the noise is point B1. Accordingly, since the position detection unit 305 detects the position detection point as B1, an error from the normal position occurs.

Since the switching of the brushless DC motor winding to be energized is based on the position detection timing, this error in the position detection timing will cause a shift in the commutation timing, which will adversely affect the stable operation performance and efficiency of the brushless DC motor. .

In order to suppress this position detection error due to noise detection, a method is used in which position detection sampling is started when a certain period of time during which the amplitude of the noise component converges immediately after PWM is turned on (section D in FIG. 10 is position detection). Sampling prohibited section).

Since this noise component is generated by resonance due to the winding inductance, stray capacitance, etc. of the motor, the resonance frequency is lowered and the noise frequency is reduced especially in motors that have achieved higher efficiency by increasing the number of windings of the stator winding. Lower. Therefore, in a high-efficiency motor with an increased number of stator windings, the period of high-frequency noise becomes long, so that the position detection sampling prohibition section after PWM on needs to be lengthened in order to suppress erroneous position detection due to noise. .

However, since the above-described sampling prohibition section is the PWM minimum ON width in the sensorless drive, the PWM minimum duty increases as the PWM carrier frequency increases. Therefore, the minimum duty is limited, and the minimum speed and the minimum load are restricted. Further, when the brushless DC motor is started, the voltage is gradually increased (that is, the duty is gradually increased) from a low voltage (that is, a small duty width), and a smooth startup is performed. However, when a high duty that secures the minimum duty width is given from the time of start-up, there are problems such as start-up failure due to excessive voltage, demagnetization of the brushless DC motor rotor permanent magnet due to overcurrent, and overcurrent.

JP 2005-198376 A

The present invention solves the conventional problem and ensures stable driving performance regardless of the inverter input voltage by detecting the position of the brushless DC motor with certainty. Accordingly, an object of the present invention is to put into practical use a motor drive device having an extremely small smoothing capacitor capacity, and to reduce the size, weight, and cost of the motor drive device.

A motor driving device of the present invention includes a rectifying / smoothing circuit that rectifies input alternating current into direct current, and an inverter that converts direct current output from the rectifying / smoothing circuit into arbitrary three-phase alternating current and drives a brushless DC motor. . In addition, the motor drive device of the present invention includes a position detection unit that detects the rotational position of the brushless DC motor, and a speed estimation unit that estimates the drive speed of the brushless DC motor from the signal from the position detection unit. Furthermore, the motor drive device of the present invention turns on the carrier frequency by making the on-duty and the carrier frequency constant from the driving speed by pulse width modulation, and when the on-duty is a predetermined value or less, the PWM minimum pulse width is constant. The drive waveform of the inverter by superimposing the on-duty and the carrier frequency set by the PWM setting unit on the rotation position and the driving speed so that the duty is reduced below the carrier frequency exceeding the predetermined value. Has a waveform generation unit for generating.

Thereby, the motor driving device of the present invention can ensure the minimum necessary PWM ON width even in a state where the PWM duty is small immediately after startup or at a low speed / low load. Accordingly, it is possible to always reliably detect the position of the brushless DC motor.

In addition, by setting the resonance frequency of the capacitor and reactor of the rectifying and smoothing circuit to be higher than 40 times the frequency of the AC power supply, the smoothing capacitor capacitance can be made extremely small and a large ripple can be applied to the inverter input voltage. Even when it is included, the rotational position of the brushless DC motor can be reliably detected, and stable driving is possible.

The motor drive device of the present invention can perform stable drive by reliable position detection regardless of the state of the input voltage, and the capacitance of the smoothing capacitor can be made extremely small, resulting in small size, light weight and low cost. A motor drive device that achieves the above can be realized.

FIG. 1 is a block diagram including a motor drive device according to Embodiment 1 of the present invention. FIG. 2 is a flowchart of the drive sequence of the motor drive device according to Embodiment 1 of the present invention. FIG. 3 is a state diagram showing an enlarged waveform near the position detection timing of the output terminal voltage of the inverter according to the first embodiment of the present invention. FIG. 4A is a state diagram showing an input voltage waveform of the inverter according to Embodiment 1 of the present invention. FIG. 4B is a state diagram showing an input voltage waveform of the inverter according to Embodiment 1 of the present invention. FIG. 5 is a flowchart for setting the PWM carrier frequency in the sensorless control (step 6) of FIG. FIG. 6 is a block diagram of the refrigerator in the second embodiment of the present invention. FIG. 7 is a block diagram including a first conventional motor driving device. FIG. 8 is a block diagram including a second conventional motor driving device. FIG. 9 is a state diagram showing the output terminal voltage of the inverter of the conventional motor drive device. FIG. 10 is a state diagram showing an enlarged waveform near the position detection timing of the output terminal voltage of the conventional inverter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited by this embodiment.

(Embodiment 1)
FIG. 1 is a block diagram including a motor drive device 22 according to Embodiment 1 of the present invention.

In FIG. 1, an AC power source 1 is a general commercial power source, and is a 50 or 60 Hz power source with an effective value of 100 V in Japan. The motor driving device 22 is connected to the AC power source 1 and drives the brushless DC motor 4. Hereinafter, the motor drive device 22 will be described with reference to FIG.

The rectifying / smoothing circuit 2 is a circuit that rectifies and smoothes AC power generated in the AC power source 1 into DC power, and includes four bridge-connected rectifier diodes 2a to 2d, a smoothing capacitor 2e, and a reactor 2f. Is done. The output of the rectifying / smoothing circuit 2 is input to the inverter 3.

Further, the smoothing capacitor 2e and the reactor 2f constitute a smoothing unit 2g and are set so that the resonance frequency is higher than 40 times the AC power supply frequency. As a result, the current due to the resonance frequency falls outside the range of the power supply harmonic regulation, and the harmonic current can be reduced. Further, by setting the smoothing capacitor 2e to such a value, the bus voltage includes a large pulsation (ripple component) such that the maximum voltage becomes twice or more than the minimum voltage. And since the electric current which flows into the smoothing capacitor 2e from the alternating current power supply 1 also becomes a current close | similar to the frequency component of the alternating current power supply 1, a harmonic current can be reduced.

Note that the reactor 2f may be inserted either before or after the rectifier diodes 2a to 2d because it may be inserted between the AC power supply 1 and the smoothing capacitor 2e. Furthermore, when the common mode filter which comprises a high frequency removal part is provided in the circuit, the reactor 2f considers the synthetic | combination component with the reactance component of a high frequency removal part.

The inverter 3 converts the DC power from the rectifying / smoothing circuit 2 containing a large ripple component in a cycle twice the power cycle of the AC power source 1 into AC power. The inverter 3 is configured by connecting six switching elements 3a to 3f in a three-phase bridge. The six return current diodes 3g to 3l are connected to the switching elements 3a to 3f in the reverse direction.

The brushless DC motor 4 includes a rotor 4a having a permanent magnet and a stator 4b having a three-phase winding. The brushless DC motor 4 rotates the rotor 4a when the three-phase alternating current generated by the inverter 3 flows in the three-phase winding of the stator 4b.

The position detection unit 5 acquires the terminal voltage of the brushless DC motor 4. That is, the magnetic pole relative position of the rotor 4a of the brushless DC motor 4 is detected. Specifically, the position detector 5 detects the relative rotational position of the rotor 4a based on the induced voltage generated in the three-phase winding of the stator 4b. As another position detection method, there is a method of estimating the magnetic pole position by performing vector calculation on the detection result of the motor current (phase current or bus current).

The voltage detector 6 detects the voltage across the smoothing capacitor 2e, which is the voltage between the DC buses.

The speed estimation unit 7 estimates the driving speed of the brushless DC motor from the position information detected by the position detection unit 5. However, when the voltage detected by the voltage detection unit 6 is equal to or lower than the threshold, the speed estimation is stopped, and after the first position detection performed by the position detection unit 5 after the bus voltage becomes equal to or higher than the threshold again, the speed estimation is performed. To resume. The threshold value for stopping the speed estimation is a value of the bus voltage at which the position detection by the position detection unit 5 becomes unstable, and is determined in advance by the system.

The position information of the position detection unit 5 becomes unstable when the bus voltage is below a predetermined voltage. Therefore, the switching unit 8 selects and outputs the position information of the position estimation unit 9 instead of the position information of the position detection unit 5 when the detected value of the bus voltage detected by the voltage detection unit 6 is equal to or less than the threshold value. When the voltage value detected by the voltage detection unit 6 exceeds the threshold value, the switching unit 8 selects and outputs the position information of the position detection unit 5 again.

The position estimation unit 9 estimates and outputs the position of the rotor 4 a of the brushless DC motor 4 from the position information output from the switching unit 8 and the speed estimated by the speed estimation unit 7. For example, when the control cycle is 100 μs, when the position from the switching unit 8 is 60 degrees in electrical angle and the speed estimated by the speed estimation unit 7 is 50 r / s, the brushless DC motor 4 has four poles. Since the current frequency is 100 Hz which is twice the speed, the position information of 63.6 deg is output by adding 60 deg to the phase in which the current of 100 Hz advances during 100 μsec.

The PWM setting unit 10 sets the carrier frequency in PWM and the duty of high / low output.

Specifically, when the duty is equal to or less than the preset minimum duty, the PWM pulse frequency is adjusted so that the PWM pulse width is kept constant and the required duty is secured. When the duty is larger than the minimum duty, the duty cycle is adjusted by increasing or decreasing the PWM ON width at a preset frequency.

The waveform generation unit 11 determines the energization winding, energization period, and timing of the brushless DC motor based on the position information from the switching unit 8 and the speed information from the speed estimation unit 7, and the PWM carrier set by the PWM setting unit 10. And the drive waveform of the inverter 3 is generated by superimposing the duty.

Further, the waveform generation unit 11 uses the bus voltage detected by the voltage detection unit 6 to perform waveform control so that the advance angle becomes large when the voltage drops.

The drive unit 12 outputs a drive signal for turning on / off the switching elements 3a to 3f of the inverter 3 based on the waveform signal output from the waveform generation unit 11. As a result, the switching element is turned on and driven in the brushless DC motor so as to energize an appropriate winding according to the rotor position.

The rectifying / smoothing circuit 13 includes a rectifying unit 13a and a smoothing unit 13b. The rectifying / smoothing circuit 13 absorbs the voltage when the brushless DC motor is regenerated, or when the input voltage of the inverter 3, that is, the output voltage of the rectifying / smoothing circuit 2 rises due to LC resonance of the rectifying / smoothing circuit 2. Further, since the voltage of the smoothing unit 13b is stable in the vicinity of the peak voltage of the AC power supply 1 at normal times, the smoothing unit 13b is connected to the motor driving device and peripheral devices from both ends of the smoothing unit 13b. It is also possible to use as an input of a switching power supply (not shown) for generating.

The operation of the motor driving apparatus configured as described above will be described.

FIG. 2 is a flowchart of the drive sequence of the motor drive device 22 according to the first embodiment of the present invention. In FIG. 2, when the brushless DC motor 4 is in a stopped state and a target speed is set as a drive signal (ie, motor drive is instructed) (step 1), the PWM setting unit 10 sets the initial PWM carrier frequency and the initial value as initial values. PWM on-duty is set (step 2). For example, the initial carrier frequency is 1 kHz and the initial duty is 5%. The PWM carrier frequency as an initial value is set to a value that can ensure a predetermined PWM minimum ON width in the PWM ON section (that is, the section in which the switching element is turned ON) in the starting duty determined by the starting torque of the device. For example, when the PWM minimum ON width is 50 μs and the initial duty at startup is 5%, the carrier frequency is set to 1 kHz or less.

When the initial value is input, the waveform generation unit 11 can stably stop the stator position at a specified position on the winding of the specific phase as a positioning waveform, and energize the inverter 3 for a relatively long time (for example, 1 second). Then, a waveform for driving the switching element is generated (step 3). Then, the signal is output to the drive unit 12, and the switching element is energized (for example, if the W-phase winding is energized from the U-phase winding, the

switching elements

3e and 3b are turned on for 1 second).

After the rotor position is determined to be a predetermined position by the positioning control, the waveform generator 11 performs a forced synchronous operation for switching the energized phase at a predetermined frequency as the synchronous pull-in control to forcibly rotate the rotor ( step 4). This forced synchronous operation is continued until the zero cross point of the induced voltage generated in the stator winding is input to the position detector 5 as a position signal (step 5).

Here, the minimum width of the PWM ON section will be described with reference to FIG.

FIG. 3 is a state diagram showing an enlarged waveform near the position detection timing of the output terminal voltage of the inverter 3 according to the first embodiment of the present invention.

FIG. 3 shows the vicinity of the zero cross point (point B in FIG. 9) of the induced voltage generated by driving the brushless DC motor at the output terminal voltage of the arbitrary phase of the inverter 3. The switching elements above and below the phase of the waveform shown in FIG. 3 are off (specifically, when the U-phase terminal voltage is indicated, both switching

elements

3a and 3b are off). A section t in which the PWM output is high is a section in which the switching element of the other phase is turned on by PWM control.

As described above, the position detection unit 5 detects the point where the magnitude relationship between the output terminal voltage of the inverter and the reference voltage (1/2 of the inverter input voltage in the present embodiment) changes, so that the brushless DC motor. The zero cross point (point B in FIG. 3) of the induced voltage generated with the rotation of is recognized as a position signal. However, immediately after the PWM is turned on, a high-frequency noise component is superimposed on the induced voltage, and the position detection unit may erroneously detect the position signal as point B1.

Therefore, the start of sampling for position detection suppresses erroneous detection of noise as a position signal by delaying (interval C) until the superimposed noise component converges to some extent. Thus, the PWM minimum ON width of the PWM ON section sets the section C from the PWM rising edge to the start of position detection sampling.

As described above, the position detection unit 5 can acquire an accurate position detection signal by setting the sampling prohibition period for position detection.

Thereafter, based on the position signal, the speed estimation unit 7 detects the speed of the brushless DC motor 4, and the PWM setting unit 10 increases or decreases the PMW duty based on the deviation between the drive speed and the target speed. Then, the waveform generation unit 11 sets the energization period (that is, the commutation cycle) and the energization pattern (that is, which switching element is turned on) based on the driving speed, and superimposes the PWM waveform by the PWM setting unit 10. After that, the signal is output to the drive unit 12 and the brushless DC motor 4 is driven by the inverter 3. In this way, the brushless DC motor 4 is driven at the target speed by speed feedback control that performs PWM duty adjustment based on the deviation between the drive speed and the target speed.

When the input voltage of the inverter 3 includes a large ripple, and the voltage detection unit 6 detects a section where the input voltage of the inverter 3 is lower than the predetermined voltage, the switching unit 8 is not based on the position detection unit 5, Based on the driving speed of the brushless DC motor by the speed estimator 7, the magnetic pole position estimated by the position estimator 9 is selected as position information. As described above, after the position signal is acquired by the position detection unit 5, sensorless driving by speed feedback control is performed based on the position information by the position detection unit 5 or the position information by the estimated magnetic pole position by the position estimation unit 9. (Step 6).

Next, the setting of the carrier frequency will be described. As described above, the delay time of the position detection sampling (section C in FIG. 3) is the PWM minimum ON width. The PWM minimum ON width is set by the frequency of the noise component superimposed at the PWM rising timing of the inverter output terminal voltage, and does not depend on the PWM carrier frequency. Therefore, the higher the carrier frequency, the larger the PWM on-duty for ensuring the PWM minimum on-width. Specifically, when 50 μsec is secured for the PWM minimum ON width, the duty is equivalent to 5% at a carrier frequency of 1 kHz, but equivalent to 40% at 8 kHz. In other words, the minimum duty at a carrier frequency of 8 kHz is 40%. When a brushless DC motor is started at this minimum duty, an overcurrent stop due to an excessive voltage application or a demagnetization of the rotor permanent magnet due to a large current occurs. There is a concern.

Therefore, at startup, it is necessary to give a PWM carrier frequency according to the startup duty and the PWM minimum pulse width. In the present embodiment, 50 μsec is required for noise component removal (PWM minimum ON width), the starting duty is set to 5%, and the PWM carrier frequency is set to 1 kHz. As a result, the PWM minimum pulse width of 50 μs at startup is secured, and the brushless DC motor can be stably started without step-out stop or the like by reliable position detection by the position detection unit and an appropriate start-up duty.

Here, consider a case where the first carrier frequency (for example, 1 kHz) is used as the PWM carrier frequency at the time of low duty, and the second carrier frequency (for example, 8 kHz) is used as the normal PWM carrier frequency.

When the brushless DC motor is started at the first carrier frequency, the PWM duty increases with acceleration, and the PWM pulse width can be secured at the second carrier frequency (specifically, the PWM duty is 40% for the 1 kHz carrier). After the timing, consider the case of driving at the second carrier frequency.

The rectifying / smoothing circuit 2 includes a smoothing capacitor 2e and a reactor 2f, and has a frequency at which LC resonance occurs. When the switching frequency (that is, PWM carrier frequency) by the inverter 3 is close to the LC resonance frequency, the LC A large voltage amplitude is generated in the inverter input voltage due to resonance.

4A and 4B are state diagrams showing input voltage waveforms of the inverter 3 according to Embodiment 1 of the present invention.

4A and 4B show input voltage waveforms of the inverter 3 when 50 Hz and 220 V are input to the AC power supply 1.

FIG. 4A shows an input voltage waveform when a PWM carrier frequency close to the resonance frequency of the rectifying and smoothing circuit 2 is used. The input voltage waveform of the inverter 3 is originally a waveform close to the full-wave rectification waveform of the AC power supply having a large ripple when a capacitor having a very small capacitance is used. However, a high frequency component due to large LC resonance is superimposed on the waveform of FIG. 4A. Further, when the AC power supply is 220V, the input voltage of the inverter 3 (that is, the output voltage of the rectifying / smoothing circuit 2) has a maximum value of about 310V, but the peak value increases by 50V or more due to LC resonance. .

上昇 In the worst case, the rise in the voltage peak value due to LC resonance may cause circuit damage due to excessive component ratings. Therefore, it is necessary to set the PWM carrier frequency to a frequency away from the LC resonance frequency. However, the resonance of the input voltage of the inverter 3 is not determined only by the smoothing capacitor 2e and the reactor 2f but is influenced by the power source impedance of the AC power source 1. Particularly in emerging countries, a power supply environment with a long lead-in wiring and a very large inductance component of the power source impedance is considered, and considering the inductance component, the resonance frequency is lower than the resonance frequency of the smoothing capacitor 2e and the reactor 2f. It becomes. Therefore, the PWM carrier frequency is higher than the resonance frequency of the smoothing capacitor 2e and the reactor 2f.

FIG. 4B shows an input voltage waveform of the inverter 3 when a PWM carrier frequency of about twice the LC resonance frequency is used. In FIG. 4B, the superposition of the high frequency component by PWM switching can be confirmed a little. However, it shows a waveform close to the full-wave rectified waveform of the AC power supply without a significant increase in peak voltage.

On the other hand, as described above, since it is necessary to provide the PWM minimum ON width, it is necessary to use a relatively low carrier frequency at the start-up time when the PWM duty is low. Furthermore, since the value of the power supply impedance varies depending on the AC power supply used, it is impractical to set the carrier frequency while avoiding the resonance frequency including the power supply impedance.

Therefore, in the present embodiment, when the brushless DC motor is started and accelerated, the PWM carrier frequency is gradually increased while the PWM minimum pulse width is secured while increasing to a certain duty. The PWM duty is increased.

FIG. 5 is a flowchart for setting the PWM carrier frequency in the sensorless control (step 6) of FIG.

The operation will be described in detail with reference to FIG.

First, in step 11, it is determined whether or not the current driving speed of the brushless DC motor matches the target speed, that is, whether or not the PWM duty needs to be adjusted by speed feedback control. If the drive speed matches the target speed, the process exits this flowchart. If not coincident with the target speed, the process proceeds to step 12 to increase or decrease the PWM duty.

The PWM waveform at this time is a value set at that time. For example, immediately after startup, the PWM carrier frequency and the PWM on-duty that are initially set in FIG. 2 are set to 1 kHz and 5% in this embodiment.

Next, proceeding to step 13, it is determined whether the increased or decreased PWM duty has reached a prescribed duty width.

Here, a method for setting the specified duty will be described. The specified duty is set as a duty that can secure the PWM minimum pulse width at the carrier frequency in normal driving other than at the time of startup. In this embodiment, assuming that 8 kHz is used as the carrier frequency during normal driving, the delay time from the PWM rising edge to the start of position detection sampling, that is, the PWM minimum pulse width is set to 50 μsec. And At this time, the specified duty is
(Specified duty) = (PWM minimum pulse width) x (normal carrier frequency)
Is required. In this embodiment, 40% is set, and it is confirmed whether the PWM on-duty is 40% or more. When the specified duty is reached in step 13 (that is, 40% in the present embodiment), the process proceeds to step 14, and the carrier frequency to be used is set as the specified value in the normal driving (that is, in the present embodiment). 8 kHz).

In step 13, if the PWM on-duty has not reached the specified duty, the carrier frequency is calculated in step 15.

The carrier frequency is set such that the duty is changed by increasing or decreasing the carrier frequency while keeping the PWM pulse width constant at the PWM minimum pulse width. For example, in this embodiment, the initial PWM is started with a duty of 5% and a PWM carrier frequency of 1 kHz, and the duty by speed feedback is increased to accelerate to the target speed. In step 12, when the duty is increased by 2% to 7%, the pulse width is not changed, but the carrier frequency calculated based on the following equation is applied.
(Carrier frequency) = (Newly set duty) / (PWM minimum pulse width)
That is, when the duty is 7%, it is driven with a carrier frequency of 1.4 kHz and a pulse width of 50 μsec.

In another example, when the PWM on-duty is 40% or less, the carrier frequency is reduced to a carrier frequency of 8 kHz or less, which is lower than the carrier frequency exceeding 8 kHz when the PWM on-duty exceeds 40%.

Thus, until the PWM on-duty reaches the specified duty width, the duty adjustment is performed by adjusting the carrier frequency. As a result, it can be avoided that the resonance frequency is always equal to the PWM carrier frequency regardless of the value of the resonance frequency, and abnormal oscillation and voltage increase of the inverter input voltage due to LC resonance can be suppressed. In some cases, there is a timing that coincides with the power source impedance at the stage of changing the carrier frequency, but the inverter input voltage rises due to the short period of coincidence due to the variable PWM period and the absorption of the peak voltage by the smoothing unit 13b. There is nothing.

In step 16, a PWM waveform based on the PWM carrier frequency and the duty width set in step 14 or step 15 is generated by the PWM setting unit 10, and the process exits the flowchart of FIG. The energization period (that is, the commutation cycle) of each phase winding generated from the driving speed of the brushless DC motor detected by the speed estimation unit 7, the energization pattern (that is, which switching element is turned on), and the PWM setting unit 10 is superimposed and output to the drive unit 12. As a result, the inverter 3 energizes the switching element, and drives the brushless DC motor 4 by sensorless driving by speed feedback control.

As described above, the motor drive device 22 according to the present embodiment converts the input alternating current into direct current, the rectifying / smoothing circuit 2, converts the direct current output from the rectifying / smoothing circuit 2 into three-phase alternating current, and performs brushless DC And an inverter 3 for driving the motor 4. The motor drive device 22 includes a position detection unit 5 that detects the rotational position of the brushless DC motor 4, and a speed estimation unit 7 that estimates the drive speed of the brushless DC motor 4 from the signal from the position detection unit 5. In addition, the motor drive device 22 includes a PWM setting unit 10 that sets the on-duty and the carrier frequency from the driving speed by pulse width modulation. When the on-duty is less than or equal to a predetermined value, the PWM setting unit 10 sets the PWM minimum pulse width to be constant and sets the carrier frequency to be lower than the carrier frequency at which the on-duty exceeds the predetermined value. Furthermore, the motor drive device 22 includes a waveform generation unit 11 that generates a drive waveform of the inverter 3 by superimposing the on-duty and the carrier frequency set by the PWM setting unit on the rotation position and the drive speed. As a result, the rotational position of the brushless DC motor 4 can be reliably detected even when the PWM on-duty of pulse width modulation is very small, such as when the brushless DC motor 4 is started up or when the load state is very low. Therefore, a very stable driving performance can be exhibited even at the time of start-up and at low speed and low load.

In addition, when the on-duty is 40% or less, the PWM setting unit 10 of the motor drive device 22 of the present embodiment sets the PWM minimum pulse width to 50 μsec and the carrier frequency set by the PWM setting unit to 8 kHz or less. . Thereby, the position detection unit 5 performs reliable position detection, and the brushless DC motor 4 is driven stably.

The rectifying / smoothing circuit 2 of the present embodiment includes a smoothing capacitor 2e and a reactor 2f, and is set to a resonance frequency higher than 40 times the frequency of the AC power supply. Thereby, even when the electrostatic capacitance of the smoothing capacitor is extremely reduced and the inverter input voltage includes a large ripple, the rotational position of the brushless DC motor can be reliably detected, and stable driving is possible. Therefore, it is possible to reduce the size of the smoothing capacitor and the reactor, and it is possible to realize a small, light, and low-cost motor driving device.

The rectifying / smoothing circuit 2 of the present embodiment includes a smoothing capacitor 2e and a reactor 2f, and the carrier frequency set by the PWM setting unit is higher than the resonance frequency of the capacitor and the reactor. Thereby, the influence of the inductance component of the power source impedance can be reduced.

Further, in the motor drive device 22 of the present embodiment, the on-duty in the pulse width modulation in the predetermined period from the start of the brushless DC motor 4 is the carrier set by the PWM setting unit while keeping the PWM minimum pulse width constant. It is set by changing the frequency. As a result, even when the on-duty of the pulse width modulation is low, the PWM on-width can be secured wide and the magnetic pole position of the brushless DC motor rotor can be reliably detected, so that stable start-up performance can be ensured. it can.

Furthermore, since the carrier frequency of pulse width modulation is not fixed, it is possible to prevent the resonance frequency caused by the capacitor, the reactor, and the power source impedance component from always matching the carrier frequency of pulse width modulation. Accordingly, abnormal oscillation and overvoltage of the inverter input due to LC resonance can be prevented, so that the reliability of the motor driving device can be improved.

(Embodiment 2)
FIG. 6 is a block diagram of the refrigerator 21 according to Embodiment 2 of the present invention.

6, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

The refrigerator 21 of the present embodiment uses the motor driving device 22 of the first embodiment.

In this embodiment, a reciprocating compressor 17 is used.

In the compressor 17, the rotational motion by the rotor 4a of the brushless DC motor 4 is converted into reciprocating motion by a crankshaft (not shown). A piston (not shown) connected to the crankshaft reciprocates in a cylinder (not shown) to suck, compress, and circulate the refrigerant.

As a compression method (mechanism method) of the compressor, an arbitrary method such as a rotary type or a scroll type is used, but in this embodiment, a reciprocating type is used. The reciprocating compressor 17 has a large inertia and a small drive speed fluctuation even with an inverter input voltage in which the bus voltage fluctuates. Therefore, the reciprocating compressor 17 can be said to be one of the applications that are very suitable for a motor driving device in which the capacitance of the smoothing capacitor is extremely small and the bus voltage includes a large ripple.

Furthermore, the compressor 17 constitutes a refrigeration cycle in which the refrigerant passes through the condenser 18, the decompressor 19, and the evaporator 20 in this order and returns to the compressor 17 again. In this refrigeration cycle, the condenser 18 dissipates heat and the evaporator 20 absorbs heat, so that cooling and heating can be performed. Furthermore, in this Embodiment, this refrigeration cycle is used for the refrigerator 21, and the evaporator 20 cools the inside of the refrigerator 21.

In a motor drive device used in a conventional refrigerator, a smoothing capacitor and a reactor are large, and a large space is required to be incorporated into the system. However, in the present embodiment, the smoothing capacitor having a capacitance of about 400 μF can be reduced to several μF, and the volume of the motor driving device can be reduced to 1/3 or less. In addition, if the application is driven with a relatively low load, such as the refrigerator 21, a reactor of about several millimeters H can be covered with the inductance component of the filter, which enables a significant reduction in size and cost. Become.

In addition, to apply a motor drive device that can be driven at a variable speed to a compressor-controlled refrigerator that is driven at a constant speed using an induction motor or the like, the installation space for the motor drive device is small and easy. Could not be incorporated into. However, since the motor drive device 22 of the present embodiment can be made very small, restrictions on installation space are eased, and it becomes easy to replace the conventional motor drive device with a motor drive device capable of variable speed drive. . Thereby, since the inside of a store | warehouse | chamber can be cooled with the optimal drive speed according to the load state of the refrigerator 21, a cooling system efficiency can be improved and a refrigerator with low power consumption can be implement | achieved.

The motor drive device of the present invention reduces the capacity of the smoothing capacitor, reduces the size, and enables stable and smooth driving. Thereby, it can apply to the drive of the compressor not only in a refrigerator and an air blower but in a vending machine, a showcase, a heat pump water heater, and a heat pump washer / dryer. Furthermore, it is possible to provide electric equipment using a brushless DC motor, such as a washing machine, a vacuum cleaner, and a pump, which can contribute to downsizing of the equipment.

DESCRIPTION OF SYMBOLS 1 AC power supply 2

Rectification smoothing circuit

2a, 2b, 2c, 2d Rectifier diode 2e Smoothing capacitor 2f Reactor 2g Smoothing part 3

Inverter

3a, 3b, 3c, 3d, 3e,

3f Switching element

3g, 3h, 3i, 3j, 3k, 3l Reflux current diode 4 Brushless DC motor 4a Rotor 4b Stator 5 Position detection unit 6 Voltage detection unit 7 Speed estimation unit 8 Switching unit 9 Position estimation unit 10 PWM setting unit 11 Waveform generation unit 12 Drive unit 13 Rectification smoothing circuit

13a Rectification Section

13b Smoothing section 17 Compressor 18 Condenser 19 Decompressor 20 Evaporator 21 Refrigerator 22 Motor drive device

Claims

A rectifying / smoothing circuit that rectifies input alternating current into direct current;
An inverter for converting a direct current output from the rectifying and smoothing circuit into a three-phase alternating current and driving a brushless DC motor;
A position detector for detecting the rotational position of the brushless DC motor;
A speed estimation unit that estimates a driving speed of the brushless DC motor from a signal from the position detection unit;
Based on the driving speed, the on-duty and the carrier frequency are adjusted by pulse width modulation. When the on-duty is less than or equal to a predetermined value, the PWM minimum pulse width is made constant and the on-duty exceeds the predetermined value. A PWM setting unit to be set so as to reduce the carrier frequency,
A motor drive device comprising: a waveform generation unit that generates a drive waveform of the inverter by superimposing the on-duty and the carrier frequency set by the PWM setting unit on the rotation position and the drive speed.
2. The motor drive according to claim 1, wherein when the on-duty is 40% or less, the PWM setting unit sets the PWM minimum pulse width to 50 μs and sets the carrier frequency set by the PWM setting unit to 8 kHz or less. apparatus.
The motor driving apparatus according to claim 1, wherein the rectifying and smoothing circuit includes a capacitor and a reactor, and is set to a resonance frequency higher than 40 times the frequency of the AC power supply.
The motor driving apparatus according to claim 1, wherein the rectifying and smoothing circuit includes a capacitor and a reactor, and the carrier frequency set by the PWM setting unit is higher than a resonance frequency of the capacitor and the reactor.
The on-duty from the start of the brushless DC motor to a predetermined period is set by changing the carrier frequency set by the PWM setting unit while keeping the PWM minimum pulse width constant. Motor drive device.
An electric device using the motor drive device according to any one of claims 1 to 5.