JP4157737B2 - Brushless DC motor driving device and refrigerator using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a brushless DC motor driving device and a refrigerator using the same.
[0002]
[Prior art]
A reciprocating compressor is used as a compressor for compressing a refrigerant in a refrigeration cycle of a refrigerator. The drive source of this reciprocating compressor is a brushless DC motor.
[0003]
The brushless DC motor is driven by a so-called bipolar drive method. That is, the control circuit outputs an energization signal based on PWM (Pulse Width Modulation) to the gate drive circuit based on the position of the rotor, and outputs the gate signal from the gate drive circuit to the switching circuit. Based on the above, a drive signal is output to the three-phase stator winding of the brushless DC motor and rotated.
[0004]
The rotor position can be detected by using a position detection element such as a Hall IC. However, a brushless DC motor used in a compressor generally uses a sensorless system.
[0005]
In the sensorless method, when the stator winding is Y-connected, the induced voltage of the non-conducting phase of the three phases is compared with the DC intermediate voltage, and the timing at which both coincide is detected by the comparator. The timing of the next commutation (switching of the energized phase) is taken based on the previous time interval with reference to the time when the signal comes in each time (time every 60 ° in electrical angle).
[0006]
The induced voltage of the non-energized phase is generated during the ON period of the PWM signal. In addition to the true induced voltage immediately after the ON, a noise component accompanied by ringing is superimposed on the induced voltage during the ON period. This noise component can be removed to some extent by a capacitor or the like. However, if the capacitance of the capacitor is increased to completely remove it, the waveform becomes dull and the detection delay of position detection increases. Further, there is a problem that the capacitor capacity cannot be increased even when the carrier frequency has to be increased (when the ON period is short).
[0007]
Therefore, when the ringing noise cannot be reduced by the capacitor, a sampling delay time is set for prohibiting detection for a certain time from the ON period in order to prevent erroneous detection. The sampling delay time is conventionally set so as not to cause uneven rotation due to erroneous detection of noise during steady rotation.
[0008]
[Problems to be solved by the invention]
However, at the time of start-up, since no induced voltage is generated in the case of the sensorless system, it is unknown where the rotor is located, so forced commutation is performed in a certain time period from a certain energization pattern. . Then, when the rotor rotates even a little and an induced voltage is detected, the next commutation timing is created based on the position signal from that point and bipolar driving is performed. On the other hand, since the rotor is in a stopped state immediately after starting, the drive current flowing through the stator winding increases rapidly. A current limit detection circuit that cuts the ON period when a threshold value is exceeded is provided so that the value of the drive current does not exceed the rating of the switching element.
[0009]
For this reason, the current limit by the current limit detection circuit operates at the time of start-up, and the ON period becomes short as shown in FIG. 7, and there is a problem that the induced voltage cannot be detected at all.
[0010]
If this position cannot be detected, commutation is delayed and smooth acceleration cannot be achieved, resulting in increased compressor vibration.
[0011]
In particular, the direct current winding of the brushless DC motor is less than the distributed winding, so that there is a problem that the direct current resistance component is reduced, current limitation is likely to be applied immediately after startup, and the above problems are more likely to appear.
[0012]
Therefore, in view of the above-described problems, the present invention uses a brushless DC motor drive device that can be smoothly accelerated even if the current limit operates immediately after startup and the ON period of the PWM signal is shortened. The refrigerator was provided.
[0013]
[Means for Solving the Problems]
The invention of claim 1 includes a three-phase brushless DC motor and a DC circuit of two switching elements upstream and downstream of each other in accordance with the direction of current for three phases, and at the switching element connection point of each series circuit A switching circuit for connecting two-phase stator windings of the brushless DC motor, and performing two-phase energization by turning on an upstream switching element of one series circuit and a downstream switching element of another series circuit; Position detection for detecting the induced voltage generated in the stator winding of the remaining non-energized one phase other than the two-phase energized, and detecting the position of the rotor of the brushless DC motor from this induced voltage Circuit, a DC voltage application circuit for applying a DC voltage to each series circuit, and a PWM signal generated based on the rotational position of the rotor detected by the position detection circuit to generate the two-phase energization A brushless DC motor driving device having sequential control means, wherein when the current flowing from the DC voltage application circuit to each series circuit exceeds a threshold value, the control means limits the ON period of the PWM signal. , Detecting the induced voltage from the position detection circuit during the ON period of the PWM signal, and the induced voltage during a predetermined sampling delay time from the time when the PWM signal is ON, which is the rise time of the induced voltage. The brushless DC motor driving device is characterized in that the sampling delay time at the time of starting is shorter than the sampling delay time at the time of steady rotation.
[0014]
According to a second aspect of the invention, the control means detects the induced voltage after a lapse of the sampling delay time at the start-up until the position detection is performed a predetermined number of times by the induced voltage from the position detection circuit. 2. The brushless DC motor driving apparatus according to claim 1, wherein the induced voltage is detected after a sampling delay time during the steady rotation has elapsed.
[0015]
A third aspect of the present invention is the brushless DC motor driving apparatus according to the first or second aspect, wherein the brushless DC motor is a direct winding type.
[0016]
The invention of claim 4 is a refrigerator having a refrigeration cycle to which a compressor, a condenser, and an evaporator are connected. The drive source of the compressor is a brushless DC motor, and the drive device of the brushless DC motor is claim 1. It is a drive device given in 2 or 3, It is a refrigerator characterized by things.
[0017]
A fifth aspect of the present invention is the refrigerator according to the fourth aspect, wherein the compressor is a reciprocating compressor.
[0018]
According to the brushless DC motor driving apparatus of claim 1, the current flowing from the DC voltage application circuit to each series circuit at the time of start-up is made shorter by setting the sampling delay time at start-up shorter than the sampling delay time at the time of steady rotation. Even if the ON time of the PWM signal is limited beyond this, the induced voltage can be detected, so that the brushless DC motor can be accelerated smoothly.
[0019]
According to the brushless DC motor drive device of claim 2, since the induced voltage is detected after the sampling delay time at the start-up until the position detection is performed a predetermined number of times by the induced voltage, the position detection is surely performed at the start-up. After that, since the induced voltage is detected after the sampling delay time at the time of steady rotation, the rotation unevenness due to erroneous detection of noise does not occur.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
[0021]
The present embodiment will be described with reference to FIGS.
[0022]
(1) Structure of refrigerator 1 FIG. 1 is a cross-sectional view of a cold-cooled refrigerator 1 showing the present embodiment.
[0023]
In the refrigerator 1, a refrigerator room 2, a vegetable room 3, a switching room 4, and a freezer room 5 are provided from the top. An ice making chamber (not shown) is provided as a part of the freezing chamber 5 next to the switching chamber 4.
[0024]
A compressor room 12 and a condenser blower fan 29 are provided in the machine room 6 at the back of the freezer room 5.
[0025]
On the back surface of the switching chamber 4, a freezer compartment evaporator (hereinafter referred to as “F EVA”) 26 for cooling the switching chamber 4 and the freezer compartment 5 is provided. In addition, on the back surface of the switching chamber 4, a switching chamber damper 8 that adjusts the flow rate of the cold air from the F-evaporator 26 and adjusts the internal temperature of the switching chamber 4 to the set temperature is disposed.
[0026]
On the back side of the vegetable compartment 3, a refrigerator compartment 2 (hereinafter referred to as “R EVA”) 18 for cooling the refrigerator compartment 2 and the vegetable compartment 3 is provided.
[0027]
A blower fan (hereinafter referred to as “F fan”) 28 for blowing the cold air cooled by the F EVA 26 to the switching chamber 4 and the freezing chamber 5 is provided above the F EVA 26.
[0028]
A blower fan (hereinafter referred to as “R fan”) 20 for blowing cold air cooled by the R evaporator 18 to the refrigerator compartment 2 and the vegetable compartment 3 is provided above the R evaporator 18.
[0029]
A deodorizing device 32 is provided on the partition plate 30 of the refrigerator compartment 2 and the vegetable compartment 3.
[0030]
A main controller 7 made of a microcomputer is provided on the back of the refrigerator 1. The main control unit 7 controls the compressor 12, the R fan 20, the F fan 28, and a three-way valve 22 described later. The operation unit 9 of the main control unit 7 is provided on the front surface of the door of the refrigerator compartment 2.
[0031]
(2) Configuration of Refrigeration Cycle 10 FIG. 2 shows the refrigeration cycle 10 of the refrigerator 1.
[0032]
The incombustible refrigerant discharged from the compressor 12 passes through the condenser 14, and then the refrigerant flow path is switched by the refrigerant switching mechanism of the three-way valve 22.
[0033]
The refrigeration side capillary tube 16 and the R EVA 18 are sequentially connected to one outlet of the three-way valve 22, and the refrigeration side capillary tube 24 is connected to the other outlet of the three-way valve 22. It joins and is connected to the inlet side of the F EVA 26. The outlet side piping of the F EVA 26 is connected to the suction side of the compressor 12.
[0034]
(3) Alternate cooling operation First, the alternate cooling operation in the refrigerator 1 will be described.
[0035]
In the alternate cooling operation, the high-temperature refrigerant compressed and pressurized by the compressor 12 is radiated by the condenser 14, and the refrigerant discharged from the refrigerant enters the three-way valve 22 to cool the R EVA 18 or F EVA 26 and Means an operation in which the refrigeration cooling mode (hereinafter referred to as R mode) and the refrigeration cooling mode (hereinafter referred to as F mode) described alternately are performed.
[0036]
(3-1) R mode In the R mode, the three-way valve 22 is switched, the refrigerant flows through the refrigeration side capillary tube 16, evaporates by the R evaporator 18, and this cold air is transferred to the refrigeration room 2 and the vegetable room 3 by the R fan 20. Sent to cool.
[0037]
(3-2) F Mode In the F mode, the three-way valve 22 is switched, the refrigerant flow path is switched so that the refrigerant flows through the refrigeration-side capillary tube 24, the F evaporation 26 is evaporated, and the compressor 12 is returned. The cold air in the F-eva 26 is sent to the freezer compartment 5 and the like by the F fan 28.
[0038]
(3-3) Timing of switching between the R mode and the F mode When the R mode and the F mode are alternately performed as described above, the switching of the mode is performed every predetermined time or inside the refrigerator compartment 2 Each mode is started when the temperature is higher than the upper limit temperature in the refrigerator or when the internal temperature of the freezer compartment 5 is higher than the upper limit temperature in the refrigerator.
[0039]
Further, when the internal temperature of the refrigerator compartment 2 becomes lower than the internal lower limit temperature, and the internal temperature of the freezer compartment 5 becomes lower than the internal lower limit temperature, the compressor 12 stops.
[0040]
(4) Driving Configuration of Compressor 12 The compressor 12 is a reciprocating compressor and is driven by a three-phase brushless DC motor 101 of a direct winding type. Hereinafter, the driving device 100 of the brushless DC motor (hereinafter simply referred to as a motor) 101 will be described with reference to FIGS.
[0041]
(4-1) Structure of Drive Device 100 The structure of the drive device 100 will be described based on the circuit diagram of FIG.
[0042]
The driving device 100 is roughly composed of a switching circuit 102, a voltage doubler rectifier circuit 103, an AC power supply 104, a gate drive circuit 105, a position detection circuit 106, a motor control unit 107, and a current limit detection circuit 108.
[0043]
The driving apparatus 100 is configured to generate a DC power supply 280V from an AC 100V AC power supply 104 by a voltage doubler rectifier circuit 103 and drive a motor 101 by a switching circuit 102.
[0044]
(4-1-1) Switching circuit 102
The switching circuit 102 composed of a three-phase bridge driver has the following configuration.
[0045]
Two NPN-type switching transistors Tr1 and Tr4 are connected in series, and diodes 118 and 121 are connected between the collector terminals and the emitter terminals of the switching transistors Tr1 and Tr4 to form one series circuit. Yes. Similarly, the switching transistors Tr2 and Tr5 and the diodes 119 and 122 constitute one series circuit, and the switching transistors Tr3 and Tr6 and the diodes 120 and 123 constitute one series circuit, and these three series circuits are connected in parallel. ing.
[0046]
The Y-connected stator windings 101u, v, w of the motor 101 are connected to the connection points 125u, 125v, 125w of the two switching transistors Tr1, Tr4 and Tr2, Tr5, Tr3, Tr6 of each series circuit, respectively. ing.
[0047]
(4-1-2) Voltage doubler rectifier circuit 103
As described above, the voltage doubler rectifier circuit 103 converts AC100V to DC280V, and after full-wave rectification by the bridge circuit 109 formed of a diode, the voltage is doubled by the smoothing capacitors 110 and 111.
[0048]
(4-1-3) Gate drive circuit 105
The gate drive circuit 105 generates and outputs gate signals to the gate terminals of the six switching transistors Tr1 to Tr6 of the switching circuit 102 by energization signals based on the PWM signals from the motor control unit 107, respectively.
[0049]
(4-1-4) Position detection circuit 106
The position detection circuit 106 detects a drive current flowing through the stator windings of each phase, and branches detection lines from the stator windings 101u, 101v, 101w of each phase. Of these, detection resistors 130 and 131 are connected in series to the detection line branched from the u phase and then grounded. In the v phase, the detection resistors 132 and 133 are connected in series and then grounded. The detection resistors 134 and 135 are connected in series and grounded.
[0050]
Two resistors 128 and 130 are connected between the emitter-side terminals of the three switching transistors Tr1, Tr2 and Tr3 and between the collector-side terminals of the switching transistors Tr4, Tr5 and Tr6. An intermediate detection line for taking a DC intermediate voltage is drawn from the connection point.
[0051]
In the u-phase comparator 136, the above-described intermediate voltage detection line is connected to the negative terminal side, and a line for taking a voltage between the detection resistors 130 and 131 in the u-phase detection line is connected to the positive terminal. Yes. Similarly, in the v-phase comparator 137 and the w-phase comparator 138, the DC intermediate voltage line and the detection line for each phase are connected to the negative terminal side and the positive terminal side.
[0052]
The outputs of the three comparators 136, 137, and 138 are connected to the input terminal of the motor control unit 107. Hereinafter, the output from this comparator is referred to as position signal Pu1. Let Pv1 and Pw1.
[0053]
(4-1-5) Current limit detection circuit 108
The current limit detection circuit 108 detects a current flowing through a shunt resistor 140 provided between the voltage doubler rectifier circuit 103 and the switching circuit 102, and limits the output when the current exceeds a threshold value. A restriction instruction signal for instructing to output to the motor control unit 107
[0054]
(4-1-6) Motor control unit 107
The motor control unit 107 formed of a microcomputer generates an energization signal by PWM control from the position signal from the position detection circuit 106, the limit instruction signal from the current limit detection circuit 108, and the speed command signal from the main control unit 7 of the refrigerator 1. It is generated and output to the gate drive circuit 105.
[0055]
The motor control unit 107 is provided with a ROM 127b and a RAM 127a for storing data.
[0056]
(4-2) Operating State of Driving Device 100 The operating state of the driving device 100 will be described with reference to FIGS.
[0057]
The position detection of the rotor of the motor 101 is a method of detecting the induced voltage generated in the non-energized phase in the 120 ° energization rectangular wave driving method, and is based on the drive currents of the stator windings 101u, 101v, 101w of the motor 101. Voltage and an intermediate voltage of DC 280V are respectively divided and compared by the comparators 136 to 138, and the position signals Pu1. Pv1 and Pw1 are input to the motor control unit 107.
[0058]
This position signal Pu1. Pv1 and Pw1 become reference signals for rotating the motor 101, and inside the motor control unit 107, as shown in the waveform diagram of FIG. 4, these signals are based on the position signals Pu1, Pv1 and Pw1 of the comparators 136 to 138. Position signals Pu2, Pv2, and Pw2 corrected by shifting the phase by 30 ° are generated. These phase corrected position signals are logically converted to generate energization signals. Although the PWM signal is omitted in FIG. 4, for example, the voltage is adjusted by combining with the PWM signal of the switching transistor on the high side, that is, the upstream side, and an energization signal based on the PWM signal is output so as to adjust the rotation speed To do.
[0059]
When performing position detection, as shown in FIGS. 4A to 4D, the signal changes from high to low or from low to high every 60 ° in electrical angle, so this time is measured every time. Then, half the time is set to 30 ° of electrical angle, and phase shift, that is, commutation is performed.
[0060]
Furthermore, the current limit in the current limit detection circuit 108 is converted into a voltage by the shunt resistor 140 and compared with a reference voltage in a comparator in the current limit detection circuit 108. When the current increases above the threshold, the motor control unit 107 outputs the PWM signal. Cut the ON period.
[0061]
(4-3) Sampling delay time When the position signals Pu1, Pv1, Pw1 from the position detection circuit 106 are detected, a sampling delay time is provided.
[0062]
The sampling delay time will be described with reference to FIG.
[0063]
As shown in FIG. 6, the induced voltage of the stator winding that is the source of generation of the position signals Pu1, Pv1, and Pw1 is generated during the ON period of the PWM signal, and a noise component (ringing) is generated for a predetermined time from the ON time. Are superimposed. In order to prevent erroneous detection of the position due to the ringing, the motor control unit 107 prohibits sampling of the position signals Pu1, Pv1, and Pw1 until the first ringing wave is settled. This is the sampling delay time.
[0064]
Now, in the case of sensorless driving at the time of start-up, since the rotor is stopped, no induced voltage is generated, and it is unknown where the rotor is located. Therefore, forced commutation is performed in a certain time period from an arbitrary energization pattern. Then, when the rotor rotates even a little and the induced voltage is detected, the next commutation timing is created based on the position signal from that point, and driving is performed. However, at startup, the current flowing through the shunt resistor 140 is very large, and the current limit detection circuit 108 operates to limit the ON period of the PWM signal.
[0065]
Position detection when the current is limited will be described.
[0066]
FIG. 5 is a waveform diagram of Pu1 in the u phase of the induced voltage Vu and the position signal when the current is limited.
[0067]
As shown in FIG. 5A, the induced voltage Vu gradually increases at the time of start-up. When this threshold is exceeded with reference to the intermediate voltage Vdc / 2 of the induced voltage, the position signal Pu1 is output from the comparator 136. Is output. In the motor control unit 107, the position signal Pu1 ′ excluding ringing is detected based on the sampling delay time.
[0068]
If the period during which Pu1 becomes high is finished during the sampling delay time after the PWM signal is turned on, detection is not performed as shown in the position signal Pu1 ′ of the conventional example in FIG. It becomes. That is, as shown in FIG. 7, when the sampling delay time is 20 μsec, this position cannot be detected if the induced voltage Vu falls below the intermediate voltage (threshold value) in about 18 μsec. Then, forced commutation is continued, the vibration of the compressor increases, and the target rotational speed may not be reached.
[0069]
For this reason, in this embodiment, the sampling delay time is shortened from 20 μs to 10 μs until the position detection is performed three times after the start signal of the motor 101 is received from the main control unit 7, and forced. Position detection is performed. That is, as shown in FIG. 6, when the sampling delay time is 10 μsec, this position can be detected even when the induced voltage Vu falls below the intermediate voltage (threshold) in about 18 μsec.
[0070]
Then, after the position detection is performed three times, it is assumed that the rotation is steady, and the normal sampling delay time is changed to 20 μsec. After the position detection is performed in this way, if the energized phases are sequentially switched and accelerated, the current detected by the shunt resistor 140 is reduced, so even if the position detection is performed with a normal sampling delay time, it is sufficient. The position of the rotor can be detected.
[0071]
Since the sampling delay time is only shortened, position detection can be performed while preventing ringing at the time of startup.
[0072]
(Modification 1)
In the above embodiment, the direct-winding motor 101 is used. However, the present invention is not limited to this, and a distributed-winding brushless DC motor may be used.
[0073]
(Modification 2)
In the above-described embodiment, up to three times as the steady rotation, it may be four times or twice instead.
[0074]
【The invention's effect】
As described above, according to the present invention, even if the current limit operates immediately after the brushless DC motor is started and the ON period of the PWM signal is shortened, the position of the rotor can be detected and the brushless DC motor can be smoothly accelerated. can do.
[0075]
Further, in the case of the compressor using the brushless DC motor driving device, vibration or the like does not occur at the time of activation, and the target rotational speed can be reached smoothly.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a refrigerator showing an embodiment of the present invention.
FIG. 2 is a configuration diagram of a refrigeration cycle.
FIG. 3 is a circuit diagram of a driving device.
FIG. 4 is a waveform diagram of the driving device.
FIG. 5 is a waveform diagram in the position detection circuit.
FIG. 6 is an enlarged waveform diagram of the present example showing the relationship between the induced voltage and the delay time.
FIG. 7 is an enlarged waveform diagram of a conventional example showing an induced voltage and a sampling delay time.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 Driver 101 Motor 102 Switching circuit 103 Voltage doubler rectifier circuit 104 AC power supply 105 Gate drive circuit 106 Position detection circuit 107 Motor control part 108 Current limit detection circuit 140 Shunt resistance

Claims (5)

A three-phase brushless DC motor;
There are three phases of DC circuits of two switching elements that are upstream and downstream according to the current direction, and the stator windings of each phase of the brushless DC motor are connected to the switching element connection points of the series circuits. A switching circuit for conducting two-phase energization by turning on an upstream switching element of one series circuit and a downstream switching element of another series circuit;
Position for detecting the induced voltage generated in the stator winding of the remaining non-energized one phase other than the two-phase energized, and detecting the position of the rotor of the brushless DC motor from this induced voltage A detection circuit;
A DC voltage application circuit for applying a DC voltage to each of the series circuits;
Control means for generating a PWM signal based on the rotational position of the rotor detected by the position detection circuit and sequentially conducting the two-phase energization;
In the drive device of the brushless DC motor having
The control means includes
When the current flowing from the DC voltage application circuit to each series circuit exceeds a threshold value, the ON period of the PWM signal is limited,
Detection of the induced voltage from the position detection circuit is performed during an ON period of the PWM signal, and the induced voltage is detected during a predetermined sampling delay time from the time when the PWM signal is turned on when the induced voltage rises. Without detection,
A brushless DC motor driving apparatus characterized in that a sampling delay time at startup is shorter than a sampling delay time at steady rotation. The control means includes
The induced voltage is detected after elapse of the sampling delay time at the start-up until the position detection is performed a predetermined number of times by the induced voltage from the position detection circuit, and thereafter, the induced voltage is detected after the sampling delay time at the steady rotation is elapsed. 2. The brushless DC motor driving apparatus according to claim 1, wherein voltage is detected. 3. The brushless DC motor driving apparatus according to claim 1, wherein the brushless DC motor is a direct winding system. In a refrigerator having a refrigeration cycle to which a compressor, a condenser, and an evaporator are connected,
A driving source of the compressor is a brushless DC motor;
4. A refrigerator, wherein the brushless DC motor driving device is the driving device according to claim 1, 2, or 3. The refrigerator according to claim 4, wherein the compressor is a reciprocating compressor.

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