JP5188734B2 - DC brushless motor controller - Google Patents

Description

  The present invention relates to a DC brushless motor control device, and more particularly, to a DC brushless motor control device capable of controlling a pulse width modulation frequency.

As a method of variably controlling the pulse width modulation frequency of a DC brushless motor driving device during operation, a technique described in Patent Document 1 is known. In this document, when the pulse width of a signal output by pulse width modulation becomes short, the pulse width is widened even at the same duty ratio by lowering the pulse width modulation frequency, and thereby the DC brushless motor. It is shown that position detection is ensured and stable operation control is possible.
JP 2000-316294 A

  According to the prior art, the pulse width modulation frequency of the DC brushless motor driving device can be stably and variably controlled during operation. However, there is no description about a measure for operating the DC brushless motor driving device with high efficiency.

  The present invention has been made in view of such problems, and it is an object of the present invention to provide a highly efficient DC brushless motor driving device by controlling the frequency of pulse width modulation to an optimum frequency.

  In order to solve the above problems, the present invention employs the following means.

A DC brushless motor comprising: a converter that converts an AC input voltage into a DC voltage; and an inverter that outputs an AC voltage by pulse width modulation of the DC voltage output from the converter, and the DC brushless motor is driven to rotate by the output voltage of the inverter In the control device, the inverter has a characteristic that loss increases as the pulse width modulation frequency increases, and the DC brushless motor has a characteristic that loss decreases as the pulse width modulation frequency increases, and the pulse width modulation frequency of the inverter is increased. A controller that variably controls the DC voltage, the AC input current, the DC input current, and the number of revolutions, and when the input power increases and the DC voltage decreases, the pulse width modulation frequency is increased. reduce the pulse width modulation frequency when decreasing the motor speed, the input power decreases, the When flowing force current decreases by decreasing the pulse width modulation frequency, to improve the converter, inverter, and DC consists brushless motor device overall efficiency.

  Since the present invention has the above-described configuration, it is possible to provide a highly efficient direct current brushless motor driving device by controlling the frequency of pulse width modulation to an optimum frequency.

  Hereinafter, the best embodiment will be described with reference to the accompanying drawings. In the following example, a permanent magnet type synchronous motor (hereinafter referred to as a PM motor) will be described as a DC brushless motor. Applicable.

  FIG. 1 is a diagram for explaining a DC brushless motor driving apparatus according to the first embodiment. In FIG. 1, reference numeral 1 denotes a rotation speed command generator which gives a rotation speed command N * to the electric motor. Reference numeral 2 denotes a controller that calculates an AC applied voltage to be applied to the PM motor, converts it into a pulse width modulated wave signal (PWM signal), and outputs it. An inverter 3 is driven by the PWM signal. 4 is a converter that supplies power to the inverter 3, 5 is a PM motor to be controlled, and 6 is a load of the PM motor (for example, a compressor constituting a heat pump such as an air conditioner). 7 is a current detector for detecting a current Id supplied from the converter to the inverter, and 8 is a DC voltage detector for detecting the DC voltage V0 of the converter.

  The controller 2 detects the current Id and generates three-phase AC command voltages Vu *, Vv *, Vw * (* indicates that the preceding code is a “command value”) to be applied to the PM motor 5. A motor applied voltage calculator 10 for calculating, a PWM frequency command generator 11 for determining a PWM frequency command f * based on the DC voltage Vd of the converter 4, and the three-phase AC command voltages Vu *, Vv *, Vw * and A PWM signal generator 12 that generates a pulse width modulation signal (PWM signal) u +, u−, v +, v−, w +, w− based on the PWM frequency f is provided.

  The converter 4 that supplies power to the inverter 3 includes an AC power supply 41, a diode bridge 42 that rectifies the AC, and a smoothing capacitor 43 that suppresses pulsation components included in the DC power supply.

  Next, a DC brushless motor driving apparatus according to the present embodiment will be described with reference to FIG. First, the motor applied voltage calculator 10 is based on the rotational speed command N * transmitted by the rotational speed command generator 1, the current Id detected by the current detector 7, and the voltage Vd detected by the DC voltage detector 8. Motor application voltage commands Vu *, Vv *, Vw * are determined.

  The PWM frequency command generator 11 determines the PWM frequency command f * based on the voltage Vd detected by the DC voltage detector 8. The PWM signal generator 12 generates pulse width modulation signals (PWM signals) u +, u−, v +, v−, w +, w based on the motor applied voltage commands Vu *, Vv *, Vw * and the PWM frequency command f *. -Is generated.

FIG. 2 is a diagram illustrating the relationship between each loss and the inverter PWM frequency in the DC brushless motor driving apparatus. In order to increase the efficiency of the DC brushless motor drive device, it is necessary to reduce the losses of the converter, inverter, and motor that constitute the device. If the total loss of the brushless motor drive device is Pt, the converter loss is Pc, the inverter loss is Pi, and the motor loss is Pm, the total loss Pt is
Pt = Pc + Pi + Pm (1)
Can be expressed as

  As shown in FIG. 2, the inverter loss Pi increases as the inverter PWM frequency increases, and the motor loss Pm decreases as the inverter PWM frequency increases.

  Here, since the inverter loss Pi increases in proportion to the inverter PWM frequency, the inverter loss and the inverter PWM frequency have a relationship similar to a linear function that rises to the right.

  As the motor loss Pm increases as the inverter PWM frequency increases, the motor current waveform approaches a sine wave, the motor power factor increases, the inverter frequency component of the ripple current decreases, and the effective value of the motor current decreases. Motor loss is reduced.

  Thus, as the inverter PWM frequency increases, the inverter loss increases and the motor loss decreases. For this reason, the DC brushless motor can be operated with high efficiency by making the inverter PWM frequency variable and selecting the inverter PWM frequency that reduces the total loss.

  FIG. 3 is a diagram showing the relationship between motor output and device (converter input to motor output) efficiency. In this figure, motor output is plotted on the horizontal axis, device efficiency is plotted on the vertical axis, and efficiency data when the converter output voltage Vd is changed to 250, 260, and 270V.

  As shown in FIG. 3, the lower the converter output voltage Vd, the better the efficiency until the input power (≈motor output) is about 700 W. This is because when the output voltage Vd is reduced for the same load, the inverter loss and the motor loss are reduced. That is, because the output voltage Vd is reduced, the switching loss is reduced and the motor power factor is further increased.

  However, the output voltage Vd does not decrease when the input power is low. This is particularly noticeable when the input voltage is 200V. The same applies when voltage doubler rectification is performed at an input voltage of 100V. When the input power is low, the output voltage Vd increases. Therefore, it is preferable to reduce the inverter loss by reducing the inverter PWM frequency. When the input power increases and the output voltage Vd decreases, the inverter PWM frequency may be increased. In this case, the inverter loss increases slightly, but the motor loss decreases, so that the efficiency can be increased.

  Next, the effect of changing the inverter PWM frequency will be described. When the inverter frequency is 3.63 kHz between the output voltages Vd = 270 to 260 V and 4 kHz when Vd = 250 V or less, the total efficiency is 0.2 as compared with the case where the inverter PWM frequency is constant 3.63 kHz. % Effect. Here, an example in which the inverter PWM frequency is set in two stages according to the DC voltage has been described, but the inverter PWM frequency may be set more finely according to the DC voltage. Further, the relationship between the DC voltage and the inverter PWM frequency may be set linearly, or may be set by a quadratic function or a multi-order function higher than that.

  FIG. 4 is a diagram for explaining the second embodiment. In the figure, reference numeral 13 denotes a motor rotation speed calculator, which calculates a motor rotation speed N based on the current I0 detected by the current detector 7. 4 that are the same as those shown in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted.

  The difference from the first embodiment is a method of determining the PWM frequency f. The motor rotation number calculator 13 calculates the motor rotation number N based on the current Id detected from the current detector 7. The PWM frequency command generator 11 determines the PWM frequency command f * based on the calculated rotation speed N.

  Next, a method for determining the frequency command f * will be described. When driving a motor, an induced voltage represented by the following equation is generated in the motor according to the number of rotations.

Vr = Ke × N (Formula 2)
Here, Vr is an induced voltage, Ke is an induced voltage constant, and N is a rotation speed.

  The increase in motor power factor, which is a factor for reducing motor loss, is largely due to the difference between this induced voltage and DC voltage. Therefore, the efficiency can be improved by determining the inverter PWM frequency based on the motor rotation speed N. For example, it is 3.63 kHz for 2000 revolutions or less, and 4 kHz for more than 2000 revolutions. In this case, the same effect as in the first embodiment can be expected.

  Here, an example in which the inverter PWM frequency is set in two stages according to the DC voltage has been described, but the inverter PWM frequency may be set more finely according to the motor speed. At this time, the relationship between the motor rotation speed and the inverter PWM frequency may be set linearly, or may be set by a quadratic function or a multi-order function higher than that.

  Further, here, the example in which the rotational speed N is calculated from the motor current Id has been described, but the rotational speed command N * may be used, or the motor rotational speed measured using an encoder or a hall sensor may be used. Good.

  FIG. 5 is a diagram for explaining the third embodiment. In the figure, reference numeral 44 denotes an AC current detector that detects an AC input current. 5 that are the same as those shown in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted.

  The difference from the first embodiment is the method of determining the PWM frequency command f *. In this example, the PWM frequency command generator 11 determines the PWM frequency command f * based on the AC input current Is detected by the AC current detector 44.

  Next, a method for determining the frequency command f * will be described. When the motor load torque is T, the motor output (N × T) and the AC input current Is are expressed by the following relational expression.

N × T = Vs × Is × cos θ × ηc × ηi × ηm (Expression 3)
Here, Vs is an AC input voltage, cos θ is a power factor, ηc is a converter efficiency, ηi is an inverter efficiency, and ηm is a motor efficiency. Since the AC input voltage Vs is approximately constant at 100V or 200V, the magnitude of the motor load can be determined from the AC input current. Therefore, even if the inverter PWM frequency is determined based on the AC input current Is, the same effect as in the first embodiment can be obtained. For example, the AC input current of 8 A or less is 3.63 kHz, and if it exceeds 8 A, it is set to 4 kHz. Here, the example in which the inverter PWM frequency is set in two stages according to the AC input current has been described. However, the inverter PWM frequency may be set more finely according to the AC input current, or the AC input current and the inverter PWM frequency may be set. The relationship may be set linearly, or may be set by a quadratic function or a multi-order function higher than that.

  FIG. 6 is a diagram for explaining the fourth embodiment. In the figure, reference numeral 14 denotes a DC current calculator for calculating a DC current ID based on the current I0 detected by the current detector 7. In the figure, the same parts as those shown in FIG.

  The difference from the first embodiment is the method of determining the PWM frequency command f *. In this example, the direct current calculator 14 calculates a direct current (average value) ID based on the current Id detected by the current detector 7, and the PWM frequency command generator 11 based on the direct current ID. The PWM frequency command f * is determined.

  Next, a method for determining the frequency command f * will be described. If the load torque of the motor is T, the motor output (N × T) and the direct current ID are expressed by the following relational expression.

N × T = Vd × ID × ηi × ηm (Formula 4)
Since the magnitude of the motor load is known from the direct current Id, the same effect as in the first embodiment can be obtained even if the inverter PWM frequency is determined based on the direct current Id. For example, when the direct current is 5 A or less, 3.63 kHz, and when exceeding 5 A, the frequency is 4 kHz. Here, the example in which the inverter PWM frequency is set in two stages according to the direct current has been described. However, the inverter PWM frequency command may be set more finely according to the direct current, or the relationship between the direct current and the inverter PWM frequency may be set. It may be set linearly or may be set by a quadratic function or a multi-order function higher than that.

  FIG. 7 is a diagram collectively showing the determination method of the PWM frequency in each of the above embodiments. FIG. 7A shows the state quantities of the DC voltage Vd, the rotational speed N, the AC current Is, and the DC current Id. FIG. 7B is a diagram showing the relationship between the operation time (elapsed time after the start of operation) and the PWM frequency.

  The lower part of each embodiment in FIG. 7A shows a high load state after the start of operation, and the upper part shows a light load state immediately after the start of operation and after the operation is stabilized.

  As shown in FIG. 7B, for example, a first predetermined period (for example, 3 minutes) set in advance from the start of operation of a compressor constituting a heat pump such as an air conditioner is set to a first PWM frequency (for example, 3.. 63 kHz), and after the elapse of the predetermined period, it is driven at a second PWM frequency (for example, 4 kHz) higher than the first PWM frequency, and the temperature change of the room in which the air conditioner is installed is set in a predetermined range. When it falls within (for example, after 60 minutes have elapsed from the start of operation and the load has become lighter), the motor is driven at a third frequency (eg, 3.63 kHz) lower than the second PWM frequency.

  In the above description, various numerical values are used. However, these numerical values are examples, and other numerical values may be used.

  Further, as a method of controlling the inverter, a method of detecting the current Id of the DC power supply 4 and reproducing the motor current is used. However, each phase current can also be detected directly using a Hall CT or a shunt resistor.

  As described above, according to the present embodiment, the pulse width modulation frequency is controlled to an optimum frequency. For this reason, inverter loss and motor loss can be reduced, and highly efficient operation can be realized.

It is a figure explaining the direct-current brushless motor drive device concerning a 1st embodiment. It is a figure explaining the relationship between each loss and the PWM frequency of an inverter in a direct-current brushless motor drive device. It is a figure which shows the relationship between motor output electric power and apparatus efficiency. It is a figure explaining 2nd Embodiment. It is a figure explaining 3rd Embodiment. It is a figure explaining 4th Embodiment. It is a figure which shows collectively the determination method of PWM frequency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotational speed command generator 2 Controller 3 Inverter 4 DC power supply 5 PM motor 6 Compressor 7 Current detector 10 Motor applied voltage calculator 11 PWM frequency command generator 12 PWM signal generator 13 Motor rotational speed calculator

  14 DC current calculator

Claims (2)

A converter that converts an AC input voltage into a DC voltage;
An inverter that outputs an AC voltage by pulse-width modulating the DC voltage output by the converter;
In the DC brushless motor control device that rotationally drives the DC brushless motor by the output voltage of the inverter,
The inverter has a characteristic that the loss increases as the pulse width modulation frequency increases, and the DC brushless motor has a characteristic that the loss decreases as the pulse width modulation frequency increases,
A controller for variably controlling the pulse width modulation frequency of the inverter according to changes in the DC voltage, AC input current, DC input current, and rotation speed;
When the input power is increased and the DC voltage is decreased, the pulse width modulation frequency is increased,
Lowering the pulse width modulation frequency when lowering the motor speed,
When the input power is reduced and the AC input current is reduced, the pulse width modulation frequency is lowered,
A direct current brushless motor control device for improving the efficiency of the entire device comprising the converter, the inverter, and the direct current brushless motor. A converter that converts an AC input voltage into a DC voltage;
An inverter that outputs an AC voltage by pulse-width modulating the DC voltage output by the converter;
In the DC brushless motor control device that rotationally drives the DC brushless motor by the output voltage of the inverter,
The inverter has a characteristic that the loss increases as the pulse width modulation frequency increases, and the DC brushless motor has a characteristic that the loss decreases as the pulse width modulation frequency increases,
A controller for variably controlling the pulse width modulation frequency of the inverter according to changes in the DC voltage, AC input current, DC input current, and rotation speed;
When the input power is increased and the DC voltage is decreased, the pulse width modulation frequency is increased.When the motor rotational speed is decreased, the pulse width modulation frequency is decreased.
When the input power decreases and the DC input current decreases, the pulse width modulation frequency is decreased,
A direct current brushless motor control device for improving the efficiency of the entire device comprising the converter, the inverter, and the direct current brushless motor.

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