JP4622435B2 - Inverter control device and hermetic electric compressor - Google Patents

Description

  The present invention relates to an inverter control device that drives a motor by a PWM-controlled switching element, and is particularly suitable for driving a hermetic electric compressor for a refrigerator.

  Conventionally, in this type of inverter control device, a drop in current can be reduced by increasing the carrier frequency in a relatively low rotation region and shortening the energization OFF time in one cycle, and vibration and noise due to current ripple can be reduced. In other rotational speed regions, the carrier frequency is set small to reduce the leakage current (see, for example, Patent Document 1).

  The conventional inverter circuit will be described below with reference to the drawings.

  FIG. 4 is a block diagram of a conventional inverter control device described in Patent Document 1, and FIG. 5 is a diagram illustrating an example of a carrier frequency control pattern.

  In FIG. 4, 1 is a DC power supply unit, 2 is a main circuit unit, and 3 is a control circuit unit. The DC power supply unit 1 is configured by an electrolytic capacitor, a diode bridge circuit, and the like (not shown), converts AC power into DC power, and supplies DC power to the main circuit unit 2.

The main circuit unit 2 includes six switching elements Ua, Ub, Va, Vb, Wa, Wb and six free-wheeling diodes D1, D2,... D6, and each free-wheeling diode is connected in parallel with the switching elements. Has been. The switching elements Ua and Ub are connected in series to connect the arm part Uab, the switching elements Va and Vb are connected in series to connect the arm part Vab, and the switching elements Wa and Wb are connected in series, and the arm part Wab is connected to the arm part Uab. By forming and connecting these three arm portions Uab, Vab, and Wab in parallel, a three-phase bridge is formed. The common contacts U0, V0, and W0 of the switching elements of the three-phase arm portions Uab, Vab, and Wab are connected to the corresponding motor terminals U, V, and W, respectively.

  The control circuit unit 3 includes an induced voltage detection unit 4, a rotor position calculation unit 5, a commutation control circuit unit 6, a speed control circuit unit 7, a PWM carrier frequency generation circuit unit 8, a duty control unit 9, and a PWM carrier frequency switching. It is composed of a command circuit unit 10 and an energization waveform switching command unit 11 and is a 120 ° energization PWM control inverter. The time for detecting the rotor position is 60 ° in electrical angle.

  Hereinafter, the operation principle of the control circuit unit 3 will be described.

  First, the induced voltage of each phase generated by the rotational drive of the motor is detected by the induced voltage detection unit 4 connected to the output terminals U, V, W of the main circuit unit 2. Based on the induced voltage waveform detected by the induced voltage detector 4, the rotor position calculator 5 calculates the rotor position from the zero cross point of the induced voltage. Next, based on the rotor position information calculated by the rotor position calculation unit 5, the commutation control circuit unit 6 generates ON / OFF signals for the switching elements Ua, Ub, Va, Vb, Wa, Wb of the main circuit unit 2. The switching element provided in the main circuit unit 2 is driven.

  On the other hand, the speed control circuit unit 7 connected in parallel with the rotor position calculation unit 5 receives the signal from the induced voltage detection unit 4 and calculates the rotation speed of the motor so that the rotation speed of the motor becomes equal to the command value. In addition, the voltage value is controlled by PWM (pulse width modulation) control.

  Further, upon receiving the rotational speed information of the speed control circuit unit 7, the PWM carrier frequency switching command circuit unit 10 determines the current fluctuation due to the current increase at the ON time and the current decrease at the OFF time in the duty control of the PWM carrier, that is, the current Select an appropriate carrier frequency to reduce the ripple amplitude and suppress vibration and noise. The carrier frequency selection can be easily extracted by experimentally obtaining the optimum carrier frequency characteristic with respect to the rotational speed in advance and storing it in a database in the PWM carrier frequency switching circuit.

  In FIG. 5, the horizontal axis represents the number of rotations and the vertical axis represents the carrier frequency.

  As shown in FIG. 5, the carrier frequency is set large in the relatively low rotational speed region, and the carrier frequency is set small in the other rotational speed regions.

Therefore, since the carrier frequency is increased in a relatively low rotational speed region, the energization OFF time in one cycle is shortened, current drop can be reduced, and vibration and noise due to current ripple can be reduced.
JP 2001-186787 A

  However, in the above-described conventional configuration shown in Patent Document 1, when the carrier frequency is switched in the control pattern of FIG. 5, a shift in commutation timing occurs continuously (this phenomenon is called a synchronous mode), and as a result, An excessive motor current continues to flow, resulting in an increase in power consumption. Further, the protection circuit is activated and the DC brushless motor may be stopped.

  This time, the cause of this synchronous mode has been clarified.

  FIG. 6 is a time chart of position detection, and FIG. 7 is a principle diagram of the synchronous mode.

  In FIG. 6, VU, VV, and VW are terminal voltages of the stator of the DC brushless motor, and CVU, CVV, and CVW are virtual neutral point voltages that are ½ of the terminal voltages VU, VV, and VW as reference voltages. The terminal voltages VU, VV, VW and the reference voltage are compared by a comparator. In FIG. 6, the PWM control is omitted.

  In the conventional inverter control device, the commutation timing for switching the phase of the stator through which current flows is determined as follows.

  First, the induced voltage and the reference voltage in a non-energized section of VU, VV, and VW are compared, a point where they intersect (hereinafter referred to as a zero cross point) is detected, and the position of the rotor of the DC brushless motor is detected from this point. . And it commutates at a timing delayed by 30 ° in electrical angle from this zero cross point. In other words, the rotor position is detected during a non-energization time T corresponding to an electrical angle of 60 °, and the delay time until commutation corresponds to just T / 2.

  Next, the principle that the synchronization mode occurs will be described with reference to FIG.

  FIG. 7 is an enlarged view of the electrical angle of 240 ° in the position detection section in FIG. 6. The vertical axis represents voltage and the horizontal axis represents time. It is assumed that the motor has 6 poles. The terminal voltage is PWM controlled, the operating speed is 55.6 r / s, the carrier frequency is 3 kHz, and the duty is 48%. Accordingly, the non-energization time T corresponding to an electrical angle of 60 ° for detecting the position of the rotor is 1000 μSEC and the carrier cycle C is 333.3 μSEC, and the time T and 3 times the carrier cycle C coincide. Since the duty is 48%, the ON time is 160 μSEC and the OFF time is 173.3 μSEC.

  In the position detection section at the initial electrical angle of 60 ° in the VU phase in FIG. 7, the correct zero cross point to be detected is the point A, but at the point A, the switching element is OFF and the terminal voltage is 0V. Therefore, the zero cross point cannot be detected. As a result, the zero-cross point is detected at the next moment (point B) when the switching element is turned on. In this case, the commutation timing is delayed by time R. And the same thing is repeated also in the next non-energization section, and the delay of commutation timing occurs stably and continuously. The above is the mechanism for generating the synchronous mode, which has been clarified this time.

  Here, the synchronization mode occurs when the position detection time, that is, the time T corresponding to the electrical angle of 60 °, and the carrier cycle n times (n is an integer) roughly match, so the smaller the Duty, the higher the probability that it will occur. Become.

  When the synchronous mode occurs and the commutation timing is delayed, the torque generated by the motor is reduced and the brake torque is activated. Therefore, an extra current flows in order to supplement the torque necessary for driving the motor. This excess current increases as the time R for which the commutation timing is delayed increases.

  When the motor is continuously operated in this state, a state in which the commutation timing is delayed by the time R continues to occur continuously, and abnormal motor current continues to flow.

  As a result, excessive power is consumed. In an actual inverter device, when an abnormal current flows, a protection circuit generally operates and the motor may stop.

  The present invention solves the above-described conventional problems, and provides an energy saving and highly reliable inverter control device.

In order to solve the above-described conventional problem, the inverter control device of the present invention has a time for detecting the position of the rotor at the first carrier frequency when the duty controlled by the drive circuit is 60% or less. The first carrier frequency is switched to the second carrier frequency at an operation speed that matches n times the carrier period (n is an integer), and the position of the rotor is detected from the second carrier frequency. In this case, a frequency in which n times the second carrier frequency does not coincide with the second carrier frequency can prevent the generation of the synchronous mode.

  The inverter control device of the present invention provides an energy saving and highly reliable inverter control device by preventing the occurrence of a synchronous mode.

The content of claim 1 includes a power unit configured by a plurality of drive switching elements, a position detection circuit that detects a position of a rotor of a DC brushless motor, and an output from the position detection circuit. Drive circuit for operating the switching element, a rotational speed calculation circuit for calculating the rotational speed of the DC brushless motor from the position information of the rotor by the position detection circuit, and a carrier frequency for generating a switching frequency of the switching element constituting the power unit and a generation circuit, in the following cases Duty 60% to be modified controlled by the drive circuit, and (n is an integer) n times the time and carrier cycle for detecting the position of the rotor at the first carrier frequency in the working rotational speeds match, the first carrier frequency, to switch to the second carrier frequency And forming said second carrier frequency, in which n times the time and the second carrier frequency for detecting a position of the rotor has a frequency that does not match, it is possible to prevent the occurrence of synchronous mode, energy saving Thus, a highly reliable inverter control device can be provided. Further, by switching to the second carrier frequency only when the duty is 60% or less, the frequency of switching the carrier frequency is lowered, so that an effect that the load on the CPU can be reduced is obtained.

  The content of claim 2 is that in the invention of claim 1, n is set to 4 or less, and the switching to the second carrier frequency at the high-order n which is difficult to generate the synchronization mode is omitted. In addition to the effects of the first aspect of the invention, the specifications of the inverter circuit can be simplified.

  The content of claim 3 is that in the invention of claim 1, the number of poles of the DC brushless motor is 6 or more, and the greater the number of poles, the easier it is to generate a synchronous mode. A highly reliable inverter control device can be provided.

  The content of claim 4 is the invention according to claim 1, wherein the difference between the first carrier frequency and the second carrier frequency is 0.2 kHz or less. In addition to the effect, the change of the timbre when the carrier frequency is switched is hardly recognized, so that the generation of unpleasant noise can be prevented.

Contents of claim 5, drives the hermetic electric compressor with an inverter control device according to any one of claims 1 to 4, reliable energy saving can prevent an abnormal current due to resonance It is possible to provide a hermetic electric compressor having a high height.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a block diagram of an inverter control apparatus according to Embodiment 1 of the present invention, and FIG. 2 is a principle diagram of avoiding a synchronous mode.

  In FIG. 1, an inverter control device 102 is connected to a commercial power source 101 and drives an AC / DC conversion unit 103 that converts commercial AC voltage into DC voltage, a power unit 104 that drives a DC brushless motor 109, and a power unit 104. Drive circuit 105, a carrier frequency generation circuit 106 that generates a switching frequency of the power unit 104, a position detection circuit 108 that detects the rotor position of the DC brushless motor 109 from the output of the power unit 104, and a rotor of the position detection circuit 108 A rotation speed calculation circuit 107 that calculates the rotation speed from the position information is configured.

  The DC brushless motor 109 is a 6-pole salient pole concentrated winding IPM (Interior Permanent Magnet) motor.

  The power unit 104 includes switching elements 110, 111, 112, 113, 114, and 115 called six (three-phase bridge-connected IGBTs (insulated gate bipolar transistors)).

  The position detection circuit 108 includes comparators 116, 117, 118 and the like, and compares the terminal voltage of the DC brushless motor 109 with a reference voltage by the comparators 116, 117, 118, and outputs the result.

  The drive circuit 105 calculates the commutation timing from the output of the position detection circuit 108, performs duty adjustment control, and turns on / off the switching elements 110, 111, 112, 113, 114, 115 of the power unit 104.

  The rotation speed calculation circuit 107 detects the rotation speed of the DC brushless motor 109 by counting the output signal of the position detection circuit 108 for a certain period or measuring the pulse interval.

  The carrier frequency generation circuit 106 monitors the rotation speed of the DC brushless motor 109 obtained from the rotation speed calculation circuit 107, and when the rotation speed at which a preset synchronous mode is generated is detected, the first frequency until then is detected. The carrier frequency is changed, and a second carrier frequency that does not generate the synchronization mode is generated and output to the drive circuit 105.

  In the present embodiment, as in the prior art, it is a 120 ° energization PWM control inverter, and the time for detecting the position of the rotor is 60 ° in electrical angle. Then, switching is made to a second carrier frequency that does not match at an operating rotational speed at which the time T for detecting the position of the rotor and the first carrier period n times 4 or less (n is an integer) roughly match. .

  That is, the first carrier frequency is set to 3 kHz, and the second carrier frequency is set at a rotational speed of 55.6 ± 2 r / s (n = 3) and 41.7 ± 2 r / s (n = 4). The frequency is switched to 3.2 kHz.

  The carrier frequency is switched only when the duty controlled by the drive circuit 105 is 60% or less.

  About the inverter circuit comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  The AC voltage supplied from the commercial power supply 101 is converted into a direct current by the AC / DC conversion unit 103, and the six switching elements 110 to 115 constituting the power unit 104 are operated by the output signal of the drive circuit 105. The voltage converted into the voltage drives the DC brushless motor 109.

  Then, at the rotational speeds of 55.6 ± 2 r / s (n = 3) and 41.7 ± 2 r / s (n = 4), the operation frequency is switched to the second carrier frequency of 3.2 kHz.

  Next, the principle of avoiding the synchronous mode will be described with reference to FIG.

  FIG. 2 shows a state of exiting the synchronous mode at 55.6 r / s (n = 3) and Duty of 48%. Even if the commutation timing is delayed by the time BA of the VU, the recognition of the next zero cross point is reduced, and the time of BA is reduced, and the zero cross point can be recognized almost accurately. Further, since the next zero-cross point is recognized when the current is ON, an accurate value can be recognized.

  As described above, in the operation speed at which the synchronous mode occurs, the chance of recognizing an accurate zero cross point is increased by slightly changing the carrier frequency, and the synchronous mode in which the commutation timing is delayed stably is released. It can be done.

  Here, in the present embodiment, the normal carrier frequency is set to 3 kHz, and the operation speed at which the synchronous mode is generated at this carrier frequency is 55.6 r / s (n = 3), 41.7 r / s (n = 4), 33.3 r / s (n = 5), 27.8 r / s (n = 6),.

  In these operating rotational speeds where the synchronous mode occurs, the time T becomes longer as the operating rotational speed becomes lower, but the carrier period is constant, and the time T and n times the carrier period (n is an integer) are roughly coincident. Since n increases and the ratio of the OFF time of the switching element decreases, the probability of occurrence of the synchronous mode decreases. Or even if it happens, the delay of commutation is small and the influence will not come out. It was experimentally confirmed that when n is 5 or more, the synchronous mode hardly occurs. In this embodiment, the carrier frequency is switched when n is 4 or less. As a result, the number of rotations for storing n can be reduced, and the specifications of the inverter circuit can be simplified.

  In addition, for example, when passing the operation speed where the synchronous mode is transiently generated when switching the operation speed, etc., there is a slight control delay, and the operation speed where the synchronous mode is generated may be slightly shifted. However, in this embodiment, by setting the range of the operating rotational speed of the DC brushless motor 109 that switches the carrier frequency to ± 2 r / s, it is possible to avoid the occurrence of the synchronous mode.

  Note that the range of the operating rotational speed of the DC brushless motor 109 that operates at the second carrier frequency can be arbitrarily determined within a range in which the synchronous mode does not occur at the second carrier frequency.

  Further, when the number of poles of the DC brushless motor is increased, more commutations are required to rotate the rotor once. Therefore, the time T corresponding to an electrical angle of 60 ° is halved.

  When the time T is reduced, the number of carrier pulses input during the time T is reduced, so that the synchronous mode is likely to occur as in the case where the operating rotational speed is increased. The synchronous mode is noticeably generated when the number of poles of the DC brushless motor 109 is 6 or more. In this case, the effect of avoiding the synchronous mode by switching the carrier frequency can be obtained more remarkably.

  In general, when the carrier frequency is greatly changed, the timbre of the magnetic noise due to the harmonic changes greatly due to the change of the ON / OFF time by the PWM control. Humans perceive changing noise as unpleasant noise, which is undesirable.

  In the present embodiment, the difference from the carrier frequency after switching is set to 0.2 kHz or less, and a change in timbre in the audible range is hardly recognized, so that unpleasant noise can be prevented from being generated.

  The carrier frequency is switched only when the duty controlled by the drive circuit 105 is 60% or less. This is because the synchronization mode is more likely to occur as the duty is smaller, and it has been confirmed from experiments that it does not occur when the duty exceeds 60%. As a result, the frequency of switching the carrier frequency to avoid the synchronization mode is low. As a result, it is possible to reduce the load on the CPU.

  As described above, according to the present embodiment, since the generation of the synchronous mode can be prevented, the power consumption does not increase and the DC brushless motor does not stop because the protection circuit is activated. A highly reliable inverter control device can be provided.

  In the present embodiment, the second carrier frequency is limited to one type, but an arbitrary plurality of carrier frequencies may be set.

(Embodiment 2)
FIG. 3 is a block diagram of a hermetic electric compressor driving method according to Embodiment 2 of the present invention.

  Hereinafter, the present embodiment will be described with reference to FIG. 3 (note that the same components as those of the first embodiment are denoted by the same reference numerals and detailed description thereof will be omitted).

  In FIG. 3, the inverter circuit is the inverter control device 102 used in the first embodiment, is connected to the commercial power source 101, and drives the hermetic electric compressor 219.

  The hermetic type electric compressor 219 includes a hermetic container 220, an electric element 221 including a stator and a rotor in the hermetic container 220, and a compression element 222.

  Since the generation of the synchronous mode can be avoided by operating the hermetic electric compressor 219 with the inverter control apparatus 102 in the first embodiment in the configuration as described above, an energy saving and highly reliable hermetic electric compressor is provided. Can do.

  As described above, since the inverter control device and the hermetic electric compressor according to the present invention can avoid the generation of the synchronous mode, the power consumption increases, the protection circuit works, and the DC brushless motor stops. Therefore, it is also useful as an inverter drive device for a sealed electric compressor for vending machines and air conditioners.

Block diagram of the inverter control apparatus in Embodiment 1 of the present invention Principle diagram of synchronous mode avoidance in the same embodiment Block diagram of a hermetic electric compressor driving method in Embodiment 2 of the present invention Block diagram of a conventional inverter control device The figure showing an example of the control pattern of the conventional carrier frequency Conventional position detection time chart Principle diagram of conventional synchronous mode

Explanation of symbols

DESCRIPTION OF SYMBOLS 102 Inverter control apparatus 104 Power part 105 Drive circuit 106 Carrier frequency generation circuit 107 Rotational speed calculation circuit 108 Position detection circuit 109 DC brushless motor 110, 111, 112, 113, 114, 115 Switching element 219 Sealed electric compressor

Claims (5)

A power unit composed of a plurality of drive switching elements, a position detection circuit for detecting the position of the rotor of the DC brushless motor, and a drive circuit for operating the switching elements of the power unit based on an output from the position detection circuit; A drive speed circuit comprising: a rotation speed calculation circuit for calculating a rotation speed of a DC brushless motor based on rotor position information by the position detection circuit; and a carrier frequency generation circuit for generating a switching frequency of a switching element constituting a power unit. at If Duty is 60% or less to be modified controlled, and (n is an integer) n times the time and carrier cycle for detecting the position of the rotor at the first carrier frequency in the operating rotational speed is matched, the first the first carrier frequency, a configuration to switch to a second carrier frequency, said second calibration The A frequency inverter control apparatus with a frequency n times the time and the second carrier frequency for detecting a position of the rotor do not match.   The inverter control device according to claim 1, wherein n is 4 or less.   The inverter control device according to claim 1, wherein the number of poles of the DC brushless motor is 6 or more.   The inverter control device according to claim 1, wherein a difference between the first carrier frequency and the second carrier frequency is 0.2 kHz or less. A hermetic electric compressor using the inverter control device according to any one of claims 1 to 4.

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