JP2005110394A - Inverter control method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem wherein a complicated and high-speed operation is required for generating a switching pattern by a control part 8, an expensive high-speed operation element such as DVD is necessary for use, and the use of the other circuit must be taken into account for high-speed operation, in a conventional manner. <P>SOLUTION: An inverter that converts DC power to three-phase or multi-phase AC power comprises: a switching part that is arranged so as to correspond to the AC power at each phase, and converts the DC power to the AC power by chopping; and the control part that controls the switching operation of the switching part by creating a control indication value of each phase on the basis of a result obtained by measuring a phase current of each phase of the AC power, and drive-controls the switching part of the inverter on the basis of the control indication value. The control part operates the difference of the control indication value of each phase that is created on the basis of the phase current, and when the control indication value reaches a prescribed value or below, the control part changes the control indication values of two phases reaching the prescribed value or below to fixed values, thus drive-controlling the switching part on the basis of the control indication value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inverter device that supplies driving power to a permanent magnet synchronous motor or the like and an inverter control method.

  Generally, in order to efficiently control a three-phase motor, it is necessary to use a control algorithm that uses a three-phase current. Most inverter devices need information about the phase current. The first way to obtain these currents is to detect them directly. For this purpose, at least two sensors are required, and the phase must be detected directly according to the connection of the windings of the motor. This type of sensor is usually expensive because of the need to improve its sophistication and insulation performance.

  In the second method, only a line current is detected, and three phase currents are measured based on the line current. This method only requires a simple and inexpensive resistance as a sensor and does not need to be separated.

  Since the switching state of the inverter is directly controlled using a digital signal processor (hereinafter referred to as DSP), it is possible to grasp the exact electrical path through which the input current passes through the inverter and reaches each phase. . In this way, the phase current can be directly coupled to the line current. The resulting phase current is due to actual current detection and is not the result of a simulation that requires a model of the output circuit. Thus, the means of prediction is completely independent of the inverter input and output circuits.

  The phase current is predicted based on the DC line current as a function of the inverter state. In some states, the time difference between the two states of the inverter is very small. In this case, the phase signal becomes invisible on the line current to be processed due to the switching time of the transistors related to the structure of the inverter, the presence of the dead band, and the response delay of the electronic processing circuit. As a result, current measurement is not possible during this period.

  A method for solving this situation is already known.

  In this product, a resistance is inserted in the line between the DC power supply and the inverter to detect the line current, and it is judged whether the current cannot be measured from the switching time interval between the transistors of the inverter. In such a case, a switching pattern of a new transistor is generated and controlled by the DSP (see, for example, Patent Document 1).

  More specifically, in FIG. 1, 1 is a DC power source, 2 is an inverter that converts DC power of the DC power source 1 into three-phase power and outputs it, and 3 is driven by receiving the three-phase power supplied from the inverter 2. An electric motor 4 such as a synchronous motor is a shunt resistor for detecting a line current inserted in a line between the DC power source 1 and the inverter 2.

  The inverter 2 has an arm 5 that generates a U-phase, an arm 6 that generates a V-phase, and an arm 7 that generates a W-phase, and each arm is connected in parallel to the DC power supply 1. The arms 5, 6, and 7 are configured by connecting transistors S1 and S2, S3 and S4, and S5 and S6 in series, respectively. Further, the connection point between the transistors S1 and S2 of the arm 5 is connected to the U phase of the electric motor 3, the connection point between the transistors S3 and S4 of the arm 6 is connected to the V phase of the electric motor 3, and the transistor of the arm 7 The connection point between S5 and S6 is connected to the W phase of the electric motor 3. Each of these pairs of transistors is driven in a complementary manner.

  The inverter 2 also has a control unit 8 that detects a voltage drop of the shunt resistor 4 and outputs a drive signal to the transistors S1 to S6 according to the detected value. The control unit 8 is configured around a DSP.

  Such an operation will be described with reference to FIGS.

  There are eight on / off patterns that can be taken by the transistors S1 to S6 as follows.

  First, in the first pattern P1, when the transistor S1 is turned on and the transistors S3 and S5 are turned off (the paired transistors are driven complementarily, the transistor S2 is turned off and the transistors S4 and S6 are turned on). It is. At this time, the current Idc flowing through the shunt resistor 4 is only the line current Iu flowing through the U phase. This is because only the transistor S1 is turned on and flows only into the U phase via this transistor.

  Next, in the second pattern P2, when the transistor S1 is turned off, the transistor S3 is turned on, and the transistor S5 is turned off (the paired transistors are driven complementarily, the transistor S2 is turned on, the transistor S4 is turned off, the transistor S6 Is on.) At this time, the current Idc flowing through the shunt resistor 4 is only the line current Iv flowing through the V phase.

  In the third pattern P3, the transistors S1 and S3 are off, and the transistor S5 is on (the paired transistors are driven complementarily, so that the transistors S2 and S4 are on and the transistor S6 is off). At this time, the current Idc flowing through the shunt resistor 4 is only the line current Iw flowing through the W phase.

  In the fourth pattern P4, the transistor S1 is off, and the transistors S3 and S5 are on (each paired transistor is driven complementarily, so that the transistor S2 is on and the transistors S4 and S6 are off). At this time, the current Idc flowing through the shunt resistor 4 is the sum Iv + Iw of the line currents flowing through the V phase and the W phase. In normal motor connection, since the sum of the phase currents is zero, that is, a relationship of Iu + Iv + Iw = 0 holds, it can be said that the current Idc flowing through the shunt resistor 4 is equal to the line current −Iu flowing in the opposite direction to the U phase.

  In the fifth pattern P5, the transistor S1 is on, the transistor S3 is off, and the transistor S5 is on (each paired transistor is driven in a complementary manner, so that the transistor S2 is off, the transistor S4 is on, and the transistor S6 is Off.) At this time, the current Idc flowing through the shunt resistor 4 becomes the sum Iu + Iw of the line currents flowing in the U phase and the W phase, that is, the line current −Iv flowing in the direction opposite to the V phase.

  In the sixth pattern P6, the transistors S1 and S3 are on, and the transistor S5 is off (the paired transistors are driven complementarily, so that the transistors S2 and S4 are off and the transistor S6 is on). At this time, the current Idc flowing through the shunt resistor 4 becomes the sum Iu + Iv of the line currents flowing in the U phase and the V phase, that is, the line current −Iw flowing in the opposite direction to the W phase.

  The seventh pattern P7 is that all of the transistors S1, S3, and S5 are off (the transistors S2, S4, and S6 are all on because the paired transistors are complementarily driven). At this time, the current Idc flowing through the shunt resistor 4 does not flow and becomes zero.

  Finally, in the eighth pattern P8, the transistors S1, S3 and S5 are all on (the transistors S2, S4 and S6 are all off because the paired transistors are driven complementarily). At this time, the current Idc flowing through the shunt resistor 4 becomes zero due to the relationship of Iu + Iv + Iw = 0.

  Combining the above 8 patterns, each transistor is chopped to form a three-phase power source, and a three-phase motor is driven. A drive signal is transmitted from the control unit 8 to each of the transistors S1 to S6. In the control unit 8, a carrier signal, a U-phase control instruction signal, a V-phase control instruction signal, and a W-phase control instruction signal are generated. Here, the U-phase control instruction signal is a signal obtained by multiplying a predetermined amplitude value E by sin θ, and the V-phase control instruction signal is a signal obtained by multiplying the predetermined amplitude value E by sin (θ−120 °), Further, the W-phase control instruction signal is a signal obtained by multiplying a predetermined amplitude value E by sin (θ + 120 °). The amplitude value E and the angle θ are determined by calculation in the control unit.

  Then, the carrier signal, the U control instruction signal, the V phase control instruction signal, and the W phase control instruction signal are compared at each time point, and based on the result, the drive signals of the transistors S1 to S6 are generated to generate the drive signals from the transistors S1. Supply to S6.

  Here, when the switching pattern at the time when the magnitude of each control instruction signal satisfies U> V> W is seen in detail with reference to FIG. 3, the period during which the carrier signal goes from the peak value to the bottom value (hereinafter referred to as PWM first half cycle). The switching pattern changes in the order of P7-P1-P6-P8. When the period of the first pattern P1 in the first half cycle of PWM is t1, and the period of the sixth pattern P6 is t2, the currents Idc flowing through the shunt resistor 4 are Idc = Iu and Idc = −Iw, respectively. Similarly, other line currents can be detected independently in other periods.

  For example, if the phase angle Θ is 0 = <Θ <30 °, the switching pattern transition is P7-P3-P5-P8, and if the phase angle Θ is 30 ° = <Θ <90 °, the phase angle is P7-P1-P5-P8. P7-P1-P6-P8 if Θ is 90 ° = <Θ <150 °, P7-P2-P6-P8 if phase angle Θ is 150 ° = <Θ <210 °, and phase angle Θ is 210 ° = <Θ <. P7-P2-P4-P8 if 270 °, P7-P3-P4-P8 if phase angle Θ = 270 ° = <Θ <330 °, P7-P3-P5 if phase angle Θ = 330 ° = <Θ <360 ° −P8.

Therefore, by detecting the current flowing through the shunt resistor 4, each line current can be detected. (For example, see Patent Document 1.)
In the configuration described above, when the phase angle Θ is in the vicinity of 30 °, 90 °, 150 °, 210 °, 270 °, and 330 °, two indication values of the U, V, and W phase control indication values are obtained. The current detection period becomes very short, and current detection becomes impossible. Therefore, the control unit 8 determines whether or not measurement is possible from the control instruction value, and when it is determined that the measurement is impossible, generates a new switching pattern that can be measured, and detects current based on the generated pattern. It is controlled to do.
JP-A-10-155278

  However, in order to generate the switching pattern in the control unit 8 described above, complicated and high-speed calculation is required, and an expensive high-speed calculation element such as a DSP is used, or on other circuits for high-speed operation. It had to be taken into consideration, which was a factor in increasing costs.

  The present invention is intended to solve such problems.

  The inverter control method of the present invention is a control method of an inverter that converts a DC power source into a three-phase or multi-phase AC power source, and the inverter is provided corresponding to each phase of the AC power source and chopped. A switching unit that converts the DC power source into an AC power source, and a switching operation of the switching unit, a control instruction value for each phase is created based on a result of measuring a phase current of each phase of the AC power source, and the control instruction A control unit that drives and controls the switching unit of the inverter based on the value, and the control unit becomes equal to or less than the predetermined value when a difference between the control instruction values of the respective phases is equal to or less than the predetermined value. The control instruction value of the phase is set to a predetermined fixed value to drive-control the switching unit of the inverter.

  Moreover, the inverter control device of the present invention includes a DC power supply, an inverter that converts the DC power supply output to a three-phase or multiphase AC power supply, a phase current detection unit that detects a phase current of each phase of the AC power supply, The inverter is provided corresponding to each phase of the AC power supply, and a switching unit that performs chopping to convert the DC power supply to an AC power supply; and a switching operation of the switching unit, the phase current detection unit And a control unit that controls based on the phase current of each phase measured in step (b), and the control unit calculates a control instruction value for each phase based on the phase current of each phase measured by the phase current detection unit. When the difference between the calculation unit and the control instruction value of each phase at the calculation unit becomes a predetermined value or less, the two-phase control instruction value that becomes the predetermined value or less changes to a predetermined fixed value. Unit, the calculation unit, and the drive auxiliary unit Create a drive signal of the switching unit based on al signal, and having a drive signal output unit for outputting.

  According to the present invention, since a high speed can be realized with a simple configuration, an increase in cost can be suppressed while reducing torque pulsation of the electric motor.

  Since the configuration of the present invention is the same as the conventional technical configuration except for the configuration of the control unit 8, the description thereof will be omitted. The control unit 8 that is a feature of the present invention will be described below.

  In FIG. 4, 81 is a drive signal output unit that outputs a drive signal to each switching element based on the control instruction value changed by the drive auxiliary unit 83 and 81 is a shunt resistor 4. A calculation unit 83 calculates a control instruction value of each phase from the detected current of each phase. When the difference between the control instruction values of each phase calculated by the calculation unit 82 becomes a predetermined value or less, the calculation unit 83 becomes a predetermined value or less. The two-phase control instruction value is a drive assist unit that changes to a predetermined fixed value.

  The operation of this configuration will be described with reference to FIG.

  First, in step S1, it is determined whether or not the square value of the difference between the control instruction values of the U phase and the V phase calculated by the calculation unit 82 is smaller than the predetermined square value of the threshold value g. If it is determined in step S1 that the value is small, the process proceeds to step S2, where the drive assisting unit 83 determines that the U-phase control command value = (U-phase control command value + V-phase control command value + threshold g) / 2 and the V-phase control command value. = (U-phase control instruction value + V-phase control instruction value-threshold value g) / 2.

  If it is determined in step S1 that it is not small, the process proceeds to step S3, and the square value of the difference between the control instruction values of the V phase and the W phase is calculated by the calculation unit 82 as the square value of the predetermined threshold value g. Determine if it is less. If it is determined in step S3 that the value is smaller, the process proceeds to step S4, where the drive assisting unit 83 determines that the V-phase control command value = (V-phase control command value + W-phase control command value + threshold g) / 2 and the W-phase control command value. = (V-phase control instruction value + W-phase control instruction value-threshold value g) / 2.

  Further, if it is determined in step S3 that it is not small, the process proceeds to step S5 and the square value of the difference between the control instruction values of the W phase and the U phase calculated by the calculation unit 82 is a square value of a predetermined threshold value g. Determine if it is less. If it is determined in step S5 that the value is smaller, the process proceeds to step S6, where the driving assist unit 83 determines that the W-phase control command value = (W-phase control command value + U-phase control command value + threshold g) / 2 and the U-phase control command value. = (W-phase control instruction value + U-phase control instruction value-threshold g) / 2 is calculated.

  And it judges that it is not small at step S5, and after execution of each step S2, S4, S6, it transfers to step S7. In step S7, the drive signal output unit 81 generates a drive signal for the switching element by comparing each U-phase, V-phase, and W-phase control instruction value with the carrier signal, and gives the drive signal to each switching element of the inverter 2. The inverter 2 is driven.

  As described above, the driving of the electric motor 3 is controlled by repeating the operations from step S1 to step S7.

  Next, another driving method for the control unit 8 will be described with reference to FIG.

  In such control, in consideration of the magnitude relationship between the phase control instruction values, smoother control than that described above is realized.

  First, in step S10, it is determined whether or not the U-phase control instruction value−V-phase control instruction value calculated by the calculation unit 82 is greater than zero. If it is determined that it is large, the process proceeds to step S11. If it is determined that it is not large, the process proceeds to step S12. In step S11, it is determined whether or not the calculation result of the U-phase control instruction value−V-phase control instruction value is smaller than the threshold value g. In step S13, the drive assisting unit 83 determines that the U-phase control instruction value = (U-phase control instruction value + V-phase control instruction value + threshold g) / 2 and V-phase control instruction value = (U-phase control instruction value + V-phase control instruction value). Calculate the threshold g) ÷ 2.

  In step S12, it is determined whether the calculation result of the U-phase control instruction value−V-phase control instruction value calculated by the calculation unit 82 is larger than the threshold value g. If it is determined that the calculation result is larger, the process proceeds to step S14. In step S14, the driving assist unit 83 determines that the U-phase control instruction value = (U-phase control instruction value + V-phase control instruction value−threshold g) / 2 and V-phase control instruction value = (U-phase control instruction value + V-phase control instruction value). + Threshold g) ÷ 2.

  If it is determined in step S11 that it is not small or it is determined that it is not large in step S12, the process proceeds to step S15.

  In step S15, it is determined whether or not the V-phase control instruction value-W-phase control instruction value calculated by the calculation unit 82 is greater than zero. If it is determined that it is large, the process proceeds to step S16, and if it is not large, the process proceeds to step S17. In step S16, it is determined whether the calculation result of the V-phase control instruction value-W-phase control instruction value calculated by the calculation unit 82 is smaller than the threshold value g. If it is determined that the calculation result is smaller, the process proceeds to step S18. In step S18, the drive assisting unit 83 determines that the V-phase control command value = (V-phase control command value + W-phase control command value + threshold g) / 2 and the W-phase control command value = (V-phase control command value + W-phase control command value). Calculate the threshold g) ÷ 2.

  In step S17, it is determined whether the calculation result of the V-phase control instruction value-W-phase control instruction value calculated by the calculation unit 82 is larger than the threshold value g. If it is determined that the calculation result is larger, the process proceeds to step S19. In step S19, the driving assist unit 83 determines that the V-phase control command value = (V-phase control command value + W-phase control command value−threshold g) / 2 and the W-phase control command value = (V-phase control command value + W-phase control command value). + Threshold g) ÷ 2.

  If it is determined in step S16 that it is not small or it is determined that it is not large in step S17, the process proceeds to step S20.

  In step S20, it is determined whether or not the W-phase control instruction value-U-phase control instruction value calculated by the calculation unit 82 is greater than zero. If it is determined that it is large, the process proceeds to step S21. If it is determined that it is not large, the process proceeds to step S22. In step S21, it is determined whether the calculation result of the W-phase control instruction value-U-phase control instruction value calculated by the calculation unit 82 is smaller than the threshold value g. If it is determined that the calculation result is smaller, the process proceeds to step S23. In step S23, the drive assisting unit 83 determines that the W-phase control command value = (W-phase control command value + U-phase control command value + threshold g) / 2 and the U-phase control command value = (W-phase control command value + U-phase control command value). Calculate the threshold g) ÷ 2.

  In step S22, it is determined whether the calculation result of the W-phase control instruction value-U-phase control instruction value calculated by the calculation unit 82 is larger than the threshold value g. If it is determined that the calculation result is larger, the process proceeds to step S24. In step S24, the drive assisting unit 83 determines that the W-phase control command value = (W-phase control command value + U-phase control command value−threshold g) / 2 and the U-phase control command value = (W-phase control command value + U-phase control command value). + Threshold g) ÷ 2.

  After determining that it is not small in step S21 or not large in step S22, or after executing steps S13, S14, S18, S19, S23, and S24, the process proceeds to step S25. In step S25, the drive signal output unit generates a drive signal for the switching element by comparing each U-phase, V-phase, and W-phase control instruction value with the carrier signal, and gives the drive signal to each switching element of the inverter 2 to generate the inverter 2 Drive.

  As described above, the driving of the electric motor 3 is controlled by repeating the operations from step S10 to step S25.

An inverter circuit for driving a general three-phase motor is shown. It is a table | surface which shows the switching pattern of each switching element in FIG. It is a figure which shows the relationship of the control instruction value of each phase, a carrier signal, and a switching pattern. It is a figure which shows the control block of the control part in FIG. It is a figure which shows the operation | movement flowchart of one Example of a control part. It is a figure which shows the control flowchart of the other Example of a control part.

Explanation of symbols

3 Three-phase motor 4 Shunt resistor 5, 6, 7 Arm 8 Control unit 81 Drive signal output unit 82 Calculation unit 83 Drive auxiliary unit

Claims (2)

An inverter control method for converting a DC power source into a three-phase or multi-phase AC power source, wherein the inverter is provided for each phase of the AC power source, and chops to convert the DC power source into an AC power source. And switching operation of the switching unit, and a control instruction value for each phase is created based on a result of measuring a phase current of each phase of the AC power supply, and switching of the inverter is performed based on the control instruction value A control unit that drives and controls the control unit, and the control unit determines in advance a control instruction value for two phases that is less than or equal to a predetermined value when a difference between the control instruction values for each phase is less than or equal to a predetermined value. An inverter control method characterized in that the switching unit of the inverter is driven and controlled by changing to a fixed value. A DC power supply, an inverter that converts the DC power supply output into a three-phase or multiphase AC power supply, and a phase current detection unit that detects a phase current of each phase of the AC power supply, the inverter including the AC power supply A switching unit that is provided corresponding to each phase of the chopping to convert the DC power source into an AC power source, and the switching operation of the switching unit is based on the phase current of each phase measured by the phase current detection unit A control unit for controlling each phase based on the phase current of each phase measured by the phase current detection unit, and each control unit in the calculation unit. When the difference between the control instruction values of the phase is less than or equal to a predetermined value, the drive assist unit that changes the control instruction value of the two phases that is less than or equal to the predetermined value to a predetermined fixed value, the arithmetic unit, and the drive assist Switching based on the signal from the unit The inverter device of creating a drive signal, and having a drive signal output unit for outputting.