JP2008193780A - Method of controlling inverter for driving motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform switching control while avoiding detection error of inverter current idc by grasping the amount of offset even when a motor 200 is rotating while avoiding the impact of the rotation. <P>SOLUTION: When a motor 200 is rotated by an external factor, e.g. wind received by a fan provided in the motor 200, a voltage is induced in the motor 200. When an unintended inverter current idc is flowing due to this phenomenon, offset cannot be grasped correctly even if offset of the inverter current idc is obtained. The induced voltage is thereby short-circuited using output lines 81-83 and then offset of the inverter current idc is obtained. Transistors 21-23 and 31-33 are switched based on the offset and the motor 200 is driven. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for controlling an inverter that drives a motor.

  Conventionally, there is a technique for driving a motor using electric power that is orthogonally changed by an inverter. The inverter receives a direct current voltage between the high potential side input line and the low potential side input line, and outputs an alternating current for each phase from the output line to the motor. In general, the inverter is connected in series with a pair of switching elements between the high-potential side input line and the low-potential side input line via a point where the output line is connected. A freewheeling diode is connected to each of these switching elements in parallel. The DC voltage is supported by a smoothing capacitor.

  When the motor is driven by this inverter, the direct current flowing between the motor and the inverter is monitored. Based on the current (hereinafter referred to as “inverter current”), and of course, based on the rotational speed of the motor, the switching control of the switching element is performed.

Japanese Patent No. 3757745

  When switching control is performed using an inverter current, it is necessary to correctly detect the inverter current. Therefore, even if the inverter current should not flow, if there is a value detected as the inverter current, it should be grasped as an offset amount.

  However, when the motor rotates due to a factor other than the inverter, an inverter current may flow due to the rotation. For example, when a fan is provided in the motor, the smoothing capacitor is charged from the motor through the freewheeling diode by an induced voltage generated by the motor when the fan is rotated by receiving wind. At this time, an inverter current flows.

  Thus, when the inverter current flows due to the induced voltage, it is not appropriate to grasp the offset amount. This is because the inverter current actually flows. However, if waiting for the wind to settle in order to grasp the offset amount, the inverter control cannot be performed in a timely manner. In addition, it is desirable to grasp the offset amount only every time the inverter control is started, not just once. Further, when grasping the offset amount, forcibly stopping the rotation of the motor requires a separate mechanical mechanism.

  From the above viewpoint, even when the motor is rotating, the present invention grasps the offset amount while avoiding the influence of the rotation, avoids an inverter current detection error, and performs switching control. Objective.

  The inverter control method according to the present invention is a method of controlling the inverter (1) that drives the motor (200). Each of the inverters is connected in series between a first potential point (VC) and a second potential point (G) having a lower potential than the first potential point, both of which are the first potential point. A pair of switching elements (21, 31; 22, 32; 23, 33) for passing a current from the first potential point to the second potential point, and a direction in which the switching element flows a current connected to each of the switching elements in parallel. On the other hand, a plurality of legs having free-wheeling diodes (D1, D4; D2, D5; D3, D6) for passing a current, and an output for connecting the connection point between the pair of switching elements in each leg and the motor Line (81; 82; 83).

  The first aspect of the inverter control method according to the present invention is: (a) all of the switching elements (21, 22, 23) on the first potential point side and the switching elements on the second potential point side ( 31, 32, 33) are alternatively selected to be conducted (S 1; S 4), and (b) in the conduction / non-conduction state of the switching element set in step (a), (S2) adopting a detected value (J) of a direct current (idc) flowing into and out of the first potential point or the second potential point as an offset amount, and (c) the switching element based on the offset amount Step (S3) for performing the switching control is executed.

  A second aspect of the inverter control method according to the present invention is the first aspect, and in the step (a), all of the switching elements (21, 22, 23) on the first potential point side are set. All the switching elements (31, 32, 33) on the second potential point side are made non-conductive (S1).

A third aspect of the inverter control method according to the present invention is the first aspect, wherein the inverter is provided corresponding to each of the legs, and has a potential higher than that of the second potential point (G). A bootstrap capacitor (71, 72, 73) provided between the high third potential point (VD) and the output line (81, 82, 83) corresponding to the leg is further provided. In step (a), (a1) a step (S41) in which all of the switching elements (21, 22, 23) on the first potential point side are turned off, and (a2) on the second potential point side. A step (S42) of conducting all the switching elements (33) is performed. Then, after the time (t ₅ -t ₃ ) required for charging the bootstrap capacitor has elapsed (S5) from the time when the switching element on the second potential point side starts to conduct, the step (b) Is executed.

A fourth aspect of the inverter control method according to the present invention is the third aspect, and in the step (a), all of the switching elements (21, 22, 23) on the first potential point side are set. All conduction of the switching elements (31, 32, 33) on the second potential point side is sequentially started (t ₁ , t ₂ , t ₃ ) while being kept non-conductive.

  A fifth aspect of the inverter control method according to the present invention is any one of the first to fourth aspects, wherein the inverter is between the first potential point (VC) and the leg, and the second A resistor (r) interposed between any one of the potential point (G) and the leg is provided. In step (b), the detected value (J) of the direct current (idc) is obtained based on the voltage drop (Vr) of the resistor.

  When the motor is rotating due to factors other than the inverter, for example, a fan is provided in the motor, and when the fan is rotated by receiving wind, an induced voltage is generated in the motor. If any switching element is non-conductive, current flows between the first potential point or the second potential point and the motor via the output line and the freewheeling diode. According to the first aspect of the motor drive inverter control method of the present invention, all of the switching elements on the first potential point side and all of the switching elements on the second potential point side are made conductive alternatively. By doing so, the induced voltage is short-circuited in the output line. Thus, the offset amount can be grasped in a state where the influence of the induced voltage is eliminated, and the switching control can be performed while avoiding the detection error of the direct current while avoiding the influence of the rotation.

  According to the second aspect of the inverter control method for driving a motor according to the present invention, the offset amount is grasped regardless of whether or not a bootstrap capacitor for driving the switching element on the first potential point side is provided. can do.

  When a bootstrap capacitor for driving the switching element on the first potential point side is provided, the charging current of the bootstrap capacitor flows when the switching element on the second potential point side is made conductive. According to the third aspect of the inverter control method for driving a motor according to the present invention, in order to avoid the influence of the charging current on the grasp of the offset amount, the time necessary for charging the bootstrap capacitor has elapsed. To know the offset amount.

  According to the fourth aspect of the motor drive inverter control method of the present invention, it is avoided that the charging current of the bootstrap capacitor flows abruptly.

  According to the fifth aspect of the motor drive inverter control method of the present invention, the direct current can be easily measured.

  FIG. 1 is a circuit diagram illustrating a configuration capable of executing the motor drive inverter control method according to the present invention. The inverter includes a plurality of legs connected in series between the first potential point VC and the second potential point G and corresponding to the number of AC phases to be output. The second potential point G is lower in potential than the first potential point VC. For example, the second potential point G is ground, and a positive potential is applied to the first potential point VC. The potential difference between the second potential point G and the first potential point VC is supplied from a converter (not shown) or supported by a smoothing capacitor (not shown). Since such AC / DC conversion is a well-known technique, illustration is omitted here.

  Each leg has a pair of switching elements that allow current to flow from the first potential point VC to the second potential point G. For example, in the U-phase leg, the transistor 21 and the transistor 31 are connected in series.

  The transistor 21 is provided on the first potential point VC side and functions as a high arm side switching element. The transistor 31 is provided on the second potential point G side and functions as a low arm side switching element. Both of the transistors 21 and 31 cause a current to flow from the first potential point VC to the second potential point G. Specifically, the collector of the transistor 21 is connected to the first potential point VC, and the emitter of the transistor 31 is connected to the second potential point G. However, a resistor r described later is interposed between the emitter of the transistor 31 and the second potential point G.

  An output line 81 is connected to a connection point between the transistors 21 and 31, specifically, a point where the collector of the transistor 31 and the emitter of the transistor 21 are connected. Therefore, a current flows from the first potential point VC to the output line 81 through the transistor 21 that has become conductive. Similarly, a current flows from the output line 81 to the second potential point G through the transistor 31 that is turned on.

  In addition, each leg is provided with a free-wheeling diode that is connected in parallel to each of the switching elements and flows current in the direction opposite to the direction in which the switching element flows current. For example, in the U-phase leg, diodes D1 and D4 are connected to the transistors 21 and 31, respectively. Specifically, the cathode and anode of the diode D1 are connected to the collector and emitter of the transistor 21, respectively. The cathode and anode of the diode D4 are connected to the collector and emitter of the transistor 31, respectively.

  Due to the function of these diodes, the output line 81 is changed from the first potential point VC to the first potential point VC, or the second potential point G is changed to the output line 81 according to the potential of the output line 81, regardless of whether the transistors 21 and 31 are conductive. Each current flows.

  Transistors 21, 31 and diodes D1. D4 and the output line 81, the transistors 22 and 32 and the diodes D2. D5 and output line 82 are transistors 23 and 33 and diodes D3. D6 and an output line 83 are provided respectively. Output lines 81 to 83 are connected to motor 200.

  The resistor r has one end connected to any emitter of the transistors 31, 32, and 33 and the other end connected to the second potential point G, and the voltage drop Vr is measured here. The voltage drop Vr is a basis for obtaining the inverter current idc. The resistor r may be interposed between the collectors of the transistors 21, 22, and 23 and the first potential point VC. In this case, the second potential point G may be connected to any emitter of the transistors 31, 32, and 33.

  In addition to the transistors 21, 22, 23, 31, 32, and 33, the switching element may be a field effect transistor or an insulated gate bipolar transistor. These switching operations are performed by the switching control circuit 6.

FIG. 2 is a block diagram illustrating the internal configuration of the switching control circuit 6. The switching control circuit 6 includes an operational amplifier 61, an interface 62, a CPU 63, and a signal generation unit 64. The operational amplifier 61 receives the voltage drop Vr and outputs a detection value J. The detection value J is input to the CPU 63 via the interface 62. The speed command value v ^* is also input to the CPU 63 via the interface 62. The CPU 63 estimates the inverter current idc from the detected value J, and causes the signal generator 64 to generate the switching signals S ₄₁ , S ₄₂ , S ₄₃ , S ₅₁ , S ₅₂ , S ₅₃ based on this and the speed command value v ^* .

Switching signals S ₄₁ , S ₄₂ , S ₄₃ , S ₅₁ , S ₅₂ , S ₅₃ are input to drivers ₄₁ , ₄₂ , ₄₃ , ₅₁ , ₅₂ , ₅₃ , respectively. By controlling the gate potential by the drivers 41, 42, 43, 51, 52, 53, the transistors 21, 22, 23, 31, 32, 33 are turned on / off, respectively.

  The high-arm drivers 41, 42, and 43 are supplied with voltages from bootstrap capacitors 71, 72, and 73, respectively, so that the gate potential can be appropriately applied to the high-arm transistors 21, 22, and 23. The bootstrap capacitors 71, 72, 73 are, for example, a third potential point VD having a higher potential than the second potential point G via resistors 11, 12, 13 provided corresponding to the U phase, V phase, and W phase. And the output lines 81, 82 and 83 are charged. That is, the resistors 11, 12 and 13 are connected in series to the charging path of the bootstrap capacitors 71, 72 and 73.

  Even when the potentials of the output lines 81, 82, 83 are high, the bootstrap capacitors 71, 72, 73 are not discharged between the resistor 11 and the bootstrap capacitor 71 and between the resistor 12 and the bootstrap capacitor 72. In the meantime, a diode is inserted between the resistor 13 and the bootstrap capacitor 73.

  In the inverter circuit configured as described above, particularly in the operation of outputting the sine wave to the output lines 81, 82, 83, it is desirable to appropriately operate the high-arm transistors 21 to 23 from the beginning of the operation. Therefore, it is desirable that the bootstrap capacitors 71, 72, 73 are not charged by a normal rotation operation but are initially charged before this rotation operation. In order to perform such initial charging, the low arm transistors 31 to 33 may be turned on.

First embodiment.
FIG. 3 is a timing chart showing the binary logic of the switching signals S ₄₁ , S ₄₂ , S ₄₃ , S ₅₁ , S ₅₂ , S _{53 in} the first embodiment. When these signals take “H” and “L”, the corresponding switching elements (transistors) are turned on and off, respectively. At times t _{1 to} t ₃ , the switching signals S ₅₁ , S ₅₂ , and S ₅₃ transition from “L” to “H”, and the transistors 31, 32, and 33 are turned on. At time t ₅ , the switching signals S ₅₁ , S ₅₂ , and S ₅₃ transition from “H” to “L”, and the transistors 31 to 33 are turned off. It is desirable to sequentially perform the conduction timing between the transistors 31 to 33 in this manner from the viewpoint of avoiding that the charging current of the bootstrap capacitors 71, 72, 73 suddenly flows as the inverter current idr.

After time t _5, the external factor when the transistor 2～23,31～33 is non-conductive, for example, a fan provided in the motor 200 and the like receiving the wind, when the motor 200 rotates, the motor 200 An induced voltage is generated. This then flows through the resistor r via the freewheeling diodes D1 to D6. At this time, it is necessary to avoid that the current flowing through the resistor r is misidentified as the offset amount of the detected value J of the inverter current idc.

Therefore, at time t ₄ (> t ₅ ), the switching signals S ₄₁ , S ₄₂ and S ₄₃ are set to “H”, and the switching signals S ₅₁ , S ₅₂ and S ₅₃ are set to “L”. Thereby, all of the transistors 21 to 23 on the high arm side are turned on, and the induced voltage of the motor 200 is short-circuited by the output lines 81 to 83 in combination with the diodes D1 to D3. As a result, the offset amount can be grasped without the influence of the induced voltage, and the switching control can be performed while avoiding the influence of the rotation of the motor while avoiding the detection error of the inverter current.

  FIG. 5 is a flowchart showing the operation of the motor drive inverter control method according to the present embodiment. In the present embodiment, the charging of the bootstrap capacitors 71, 72, 73 is not related to the detection of the inverter current, and therefore the charging process is not shown.

In step S1 after power-on (this corresponds to applying a positive potential to the first potential point VC), all the high-arm transistors 21 to 23 are turned on and all the low-arm transistors 31 to 33 are turned off. To do. Specifically, the states shown after time t ₄ in FIG. 3 may be taken by the switching signals S ₄₁ , S ₄₂ , S ₄₃ , S ₅₁ , S ₅₂ , S ₅₃ . Such control can be realized by the signal generator 64 generating the switching signals S ₄₁ , S ₄₂ , S ₄₃ , S ₅₁ , S ₅₂ , S _{53 in accordance} with a command from the CPU 63.

Of course, the timings at which the switching signals S ₄₁ , S ₄₂ , and S ₄₃ become “H” need not be aligned at time t ₄ as shown in FIG. However, since even if on all the high-arm side transistor 21-23 no charge the bootstrap capacitors 71, 72, 73, the switching signal S _41, S _42, S ₄₃ simultaneously at time t ₄ is "H" It may be.

  Thereafter, the detected value J of the inverter current idc output from the operational amplifier 61 while the state of step S1 is maintained is adopted as the offset amount (step S2). This is because the induced voltage from the motor 200 is short-circuited at this time, and no current should flow through the resistor r.

  When Step S2 is executed, in Step S3, switching control of the transistors 21 to 23 and 31 to 33 is performed based on the offset amount.

  As described above, by executing steps S1, S2, and S3, switching control can be performed while avoiding the detection error of the inverter current idc while avoiding the influence of the rotating motor 200 due to an external factor.

  Further, since the detected value J of the inverter current idc is obtained based on the voltage drop Vr of the resistor r, the inverter current idc can be easily measured. If the resistor r is interposed between the emitters of the transistors 31 and 33 and the second potential point G, the inverter current idc is measured as a current flowing into and out of the second potential point G. Further, if the resistor r is interposed between the collectors of the transistors 21 to 23 and the first potential point VC, the inverter current idc is measured as a current flowing into and out of the first potential point VC.

  Further, since the detected value J is output from the operational amplifier 61 that inputs the voltage drop Vr of the resistor r, the offset of the operational amplifier 61 can be corrected by the control based on the offset.

  In particular, in the first embodiment, since all of the high arm transistors 21 to 23 are made conductive and all of the low arm transistors 31 to 33 are made nonconductive, it is determined whether or not a bootstrap capacitor is provided. Regardless, the offset amount can be grasped.

Second embodiment.
FIG. 4 is a timing chart showing the binary logic of the switching signals S ₄₁ , S ₄₂ , S ₄₃ , S ₅₁ , S ₅₂ , S _{53 in} the second embodiment. At times t _{1 to} t ₃ , the switching signals S ₅₁ , S ₅₂ , and S ₅₃ transit from “L” to “H”, and at time t ₅ , the switching signals S ₅₁ , S ₅₂ , and S _{53 change} from “H”. The transition to “L” is the same as in the first embodiment.

In the present embodiment, at time t ₄ (> t ₅ ), the switching signals S ₄₁ , S ₄₂ and S ₄₃ are set to “L”, and the switching signals S ₅₁ , S ₅₂ and S ₅₃ are set to “H”. Thereby, all of the transistors 31 to 33 on the low arm side are turned on, and the induced voltage of the motor 200 is short-circuited by the output lines 81 to 83 in combination with the diodes D4 to D6. As a result, in the same manner as in the first embodiment, the offset amount is grasped without the influence of the induced voltage, and the switching control is performed while avoiding the influence of the rotation of the motor and avoiding the detection error of the inverter current. Can do.

  However, unlike the first embodiment, in this embodiment, it is desirable that the relationship with the charging of the bootstrap capacitors 71, 72, 73 is appropriate. The reason why all the transistors 31 to 33 on the low arm side are turned on is that the charging path of the bootstrap capacitors 71, 72, 73 is made conductive. Even if the induced voltage of the motor 200 is short-circuited by the output lines 81 to 83, the offset amount of the detected value J of the inverter current idc is appropriately grasped when the charging current of the bootstrap capacitors 71, 72, 73 is flowing. Can not. Therefore, in the present embodiment, it is desirable to first charge the bootstrap capacitors 71, 72, 73.

  FIG. 6 is a flowchart showing the operation of the motor drive inverter control method according to the present embodiment.

  First, after the power is turned on (this corresponds to applying a positive potential to the first potential point and the third potential point), the high arm transistors 21 to 23 are turned off in step S41, and then in step S42 the low arm transistors 31 to 31 are turned off. 33 is turned on. These steps S41 and S42 can also be grasped as steps S4 for charging the bootstrap capacitors 71, 72 and 73.

In step S5, a predetermined period is waited. The predetermined time is longer than the time necessary for charging the bootstrap capacitors 71 to 73 from the time when the conduction of the low arm transistors 31 to 33 starts. Here, since the switching signal S ₅₃ conducts at time t ₃ later than the other switching signals S ₅₁ and S ₅₂ , the difference (t ₅ −t ₃ ) between the time t ₅ and the time t ₃ becomes the above-mentioned fixed time. Equivalent to.

FIG. 4 shows control for turning off the low arm transistors 31 to 33 once at time t ₅ , but it may not be turned off once.

  By executing step S5 as described above, the charging current of the bootstrap capacitors 71 to 73 does not flow. Thereafter, steps S2 and S3 described in the first embodiment are executed. By performing such processing, the influence of the charging current on the grasp of the offset amount can be avoided.

Of course, as in the first embodiment, the timings at which the switching signals S ₄₁ , S ₄₂ , and S ₄₃ become “H” do not need to be aligned at time t ₄ as shown in FIG. It is not necessary to turn off the switching signals S ₄₁ , S ₄₂ , S ₄₃ once, and the timing when the switching signals S ₄₁ , S ₄₂ , S ₄₃ become “H” as in the first embodiment is shown in FIG. It is not necessary to align at time t ₄ as shown.

Understanding as a superordinate concept.
In the first embodiment, when step S2 is executed, all of the high arm transistors 21 to 23 are turned on, and all of the low arm transistors 31 to 33 are turned off. In the second embodiment, when step S2 is executed, all of the high arm transistors 21 to 23 are turned off and all of the low arm transistors 31 to 33 are turned on.

  Therefore, as a superordinate concept of the first embodiment and the second embodiment, when step S2 is executed, all of the high-arm side transistors 21 to 23 and all of the low-arm side transistors 31 to 33 are connected to each other. It can be grasped if it is made to conduct alternatively.

It is a circuit diagram which illustrates the composition which can perform the inverter control method for motor drive concerning this invention. It is a block diagram which illustrates the internal structure of a switching control circuit. It is a timing chart which shows the binary logic of the switching signal in 1st Embodiment. It is a timing chart which shows the binary logic of the switching signal in 2nd Embodiment. It is a flowchart which illustrates the inverter control method for motor drive concerning a 1st embodiment. It is a flowchart which illustrates the inverter control method for motor drive concerning 2nd Embodiment.

Explanation of symbols

200 motor VC first potential point G second potential point VD third potential point 21-23, 31-33 transistor D1-D6 freewheeling diode 71-73 bootstrap capacitor 81-83 output line

Claims (5)

A method for controlling an inverter (1) for driving a motor (200), comprising:
The inverter is
Each is connected in series between a first potential point (VC) and a second potential point (G) having a lower potential than the first potential point, and both are connected from the first potential point to the second potential. A pair of switching elements (21, 31; 22, 32; 23, 33) for passing a current to a point, and a current that is connected to each of the switching elements in parallel to the direction in which the switching element flows a current. A plurality of legs having flowing freewheeling diodes (D1, D4; D2, D5; D3, D6);
An output line (81; 82; 83) connecting a connection point between the pair of switching elements in each leg and the motor;
(A) Either all of the switching elements (21, 22, 23) on the first potential point side and all of the switching elements (31, 32, 33) on the second potential point side may be alternatively selected. And conducting (S1; S4),
(B) The detected value (J) of the direct current (idc) flowing into and out of the first potential point or the second potential point in the conduction / non-conduction state of the switching element set in the step (a). Step (S2) adopted as an offset amount;
(C) The inverter control method for motor drive which performs step (S3) which performs switching control of the said switching element based on the said offset amount.   In the step (a), all the switching elements (21, 22, 23) on the first potential point side are made conductive, and all the switching elements (31, 32, 33) on the second potential point side are turned on. The inverter control method for driving a motor according to claim 1, wherein non-conduction is performed (S 1). The inverter is
A third potential point (VD) provided corresponding to each of the legs and having a higher potential than the second potential point (G) and an output line (81, 82, 83) corresponding to the leg. A bootstrap capacitor (71, 72, 73) provided in
In step (a),
(A1) turning off all the switching elements (21, 22, 23) on the first potential point side (S41);
(A2) a step (S42) of conducting all the switching elements (33) on the second potential point side is performed,
After the time (t ₅ -t ₃ ) required for charging the bootstrap capacitor has elapsed (S5) from the time when the switching element on the second potential point side starts to conduct, the step (b) The motor drive inverter control method according to claim 1, wherein the motor drive inverter control method is executed. In the step (a), all of the switching elements (21, 22, 23) on the first potential point side are kept non-conductive, and the switching elements (31, 32, 33) on the second potential point side are maintained. The motor drive inverter control method according to claim ₃ , wherein all of the conductions are sequentially started (t ₁ , t ₂ , t ₃ ). The inverter includes a resistor (r) interposed between a first potential point (VC) and the leg and between the second potential point (G) and the leg.
5. The detection value (J) of the direct current (idc) is obtained based on the voltage drop (Vr) of the resistor in the step (b), according to claim 1. Inverter control method for motor drive.

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