JP2016116315A - Control method for power conversion device, and control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method by which, when performing two-phase modulation on a power conversion device in which a switching element is driven by using a bootstrap circuit, the device can be small-sized and cost can be reduced by reducing the capacity of a capacitor that supplies a drive power supply voltage to the switching element, and a control apparatus.SOLUTION: The present invention relates to the control method for controlling a three-phase AC voltage at an output side or an input side of the power conversion device in accordance with a two-phase modulation PWM system. In the control method for the power conversion device where a drive power source of a semiconductor switching element forming the power conversion device is generated by the bootstrap circuit, during a predetermined period within a period in which a switching element 18 at an upper arm side of a non-modulation phase is conducted substantially at an electric angle of 60 degrees by a two-phase modulation operation, an operation for compulsory commutation from the switching element 18 at the upper arm side to a switching element 19 at a lower arm side is performed at least once.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control method and a control device for controlling an AC output voltage and an AC input voltage by performing two-phase modulation on a three-phase power converter.

FIG. 5 shows a main circuit of a three-phase inverter system that converts DC power into AC power using a power semiconductor switching element such as an IGBT.
In FIG. 5, a three-phase inverter 2 is connected between the positive and negative terminals of a DC voltage source 1 (including a single DC power supply alone, as well as an AC power supply and a power supply combining a rectifier and a large-capacity capacitor). A load 8 such as a three-phase motor is connected to the side. The three-phase inverter 2 is configured by bridge-connecting semiconductor switching elements 4 such as IGBTs to which free-wheeling diodes 5 are connected in antiparallel, and each switching element 4 is connected to a drive circuit 3 having a DC power source 7. Has been. In FIG. 5, only the driving circuit 3 for the upper and lower arms for one phase is shown.

Reference numeral 6 denotes a control circuit for generating a gate signal for the switching element 4. The control signal output from the control circuit 6 is sent to the drive circuit 3 for each phase.
In the above configuration, the control circuit 6, the drive circuit 3, and its DC power supply 7 are referred to as a control device.

When an AC motor is operated at a variable speed by a three-phase inverter, the torque of the motor can be controlled to be constant if the ratio between the output voltage and the output frequency of the inverter is controlled to be constant (V / F constant control).
Also, as a method for controlling the AC output voltage of the three-phase inverter, a sine wave-triangular wave comparison PWM (pulse width modulation) control method is generally applied. As a representative example of this method, three-phase modulation is used. There are a system and a 60 degree conduction type two-phase modulation system.

FIG. 9 is a waveform diagram for explaining the three-phase modulation method, and the peak value of the sinusoidal modulation signal (voltage command) is always controlled to be lower than the peak value of the carrier wave (triangular wave).
10 and 11 are waveform diagrams showing the 60-degree conduction type two-phase modulation method, and the period of electrical angle 60 degrees (period T _{0 in the} figure) within the half cycle (180 degrees) of the output frequency is as follows. In this method, one arm of the non-modulation phase is kept on. In this 60-degree conduction type two-phase modulation method, the control is complicated, but since the on / off state of the switching element of the non-modulation phase is fixed in the period T ₀ , the switching loss of the switching element and the freewheeling diode is reduced. Compared to the three-phase modulation method, it has an advantage that a higher voltage (theoretically, a voltage increased by 15 [%]) can be output.

On the other hand, as shown in FIG. 5, the power supply system of the drive circuit 3 is a 6-power system in which 6-arm power supplies are isolated and independent, and a 3-phase upper arm power supply is isolated and independent, respectively. There is a four power supply method in which the power supply of the lower arm is shared, and another method is a bootstrap method.
FIG. 6 shows a drive power supply circuit (hereinafter referred to as a bootstrap circuit) for one phase by this bootstrap system. The bootstrap circuit includes a DC power supply 11, capacitors 12, 15, diodes 13, resistors 14, and drive circuits 16, 17, which are switching elements 18, 19 (in FIG. 5) of the upper and lower arms. A gate signal for the switching elements 4 and 4 is output.

In the circuit of FIG. 6, the on-operation of the lower arm switching element 19 is used to discharge the capacitor 12 as the lower arm power supply, and the capacitor 15 as the upper arm power supply is charged to Establish power supply voltage.
FIG. 7 shows a current path when the power supply voltage of the upper arm is established by the above operation. The positive electrode of the capacitor 15 of the upper arm and the positive electrode of the capacitor 12 of the lower arm are connected between the diode 13 and the resistor 14. By connecting through a series circuit, a current path for charging the capacitor 15 when the switching element 19 is turned on is formed.
This bootstrap circuit does not require an insulating means such as a transformer for establishing the power supply voltage of the upper arm, and can be reduced in size and cost as compared with other power supply systems.

Here, the two-phase modulation method and the bootstrap circuit are also described in Patent Document 1 and Patent Document 2.
In Patent Document 1, when the motor rotation speed is high and the upper arm continuous on time does not reach the drive switching period, the motor is driven by the two-phase modulation method, and the motor rotation speed is slow and the upper arm continuous on time is driven. When the switching period is exceeded, the motor is driven by temporarily switching from the two-phase modulation method to the three-phase modulation method. Thereby, when the rotational speed of the motor is low, the switching loss is reduced by minimizing the operation period by the three-phase modulation method.

  Patent Document 2 discloses that when the amplitude of the phase voltage is less than a predetermined threshold value, the two-phase modulation method is interrupted and a three-phase AC voltage is output, and the amplitude of the phase voltage is equal to or greater than the predetermined threshold value. In this case, there is disclosed a π / 3-fixed two-phase modulation method in which each phase voltage is fixed in order every π / 3 period. According to this prior art, when the amplitude of the three-phase AC voltage is large, the two-phase modulation of the π / 3 fixed method is performed, and in particular, the switching loss of the three-phase inverter is reduced in the high torque power running high speed rotation region of the motor. Is possible.

JP 2013-208209 A (paragraphs [0014] to [0016], [0021], [0022], FIG. 2, FIGS. 5 to 7 etc.) JP-A-2005-229676 (paragraphs [0032] to [0044], FIGS. 4 to 7 etc.)

When the three-phase inverter using the bootstrap circuit as shown in FIG. 6 performs two-phase modulation, the switching element 18 of the upper arm of the non-modulation phase is fixed in the ON state during the 60-degree period of the output frequency. A phenomenon occurs in which the switching element 19 of the lower arm is fixed in the off state.
FIG. 8 shows an operation when the switching element 18 of the upper arm is turned on. During the period when the switching element 18 is on, the power supply voltage must be supplied from the capacitor 15 functioning as the power supply for the upper arm to the IC in the drive circuit 16 and the gate of the switching element 18.

However, if the switching element 19 of the lower arm is turned off during this period, there is no way to charge the capacitor 15 which is the power supply for the upper arm. The gate voltage of the switching element 18 is decreased, and the conduction loss is increased by the increase of the conduction voltage of the switching element 18.
In order to avoid the above problem, the capacity of the capacitor 15 may be increased. However, as the capacity is increased, new problems such as an increase in the size of the capacitor 15 and the device, an increase in cost, and an increase in charging time occur.

Equation 1 below shows the relationship between the capacitor capacity, the voltage fluctuation range, the average current consumption of the gate drive circuit, and the maximum conduction time during two-phase modulation. As is clear from Equation 1, when the voltage fluctuation width ΔV is constant, the average current consumption I or the maximum conduction time _tmax increases as the capacitor capacitance C increases. Therefore, it is desirable that the capacitor capacitance C is small.
[Formula 1]
C · ΔV = I · t _max
C: Capacitor capacity,
ΔV: voltage fluctuation range,
I: Average current consumption of the gate drive circuit,
t _max : Maximum conduction time during two-phase modulation

  Therefore, the problem to be solved by the present invention is that when a power conversion device that drives a semiconductor switching element using a bootstrap circuit is subjected to two-phase modulation PWM control, a capacitor having a small capacity can be used as a power source for the switching element. Thus, it is an object of the present invention to provide a control method and a control device for a power conversion device that can reduce the size and cost of the device.

In order to solve the above-described problem, a control method according to claim 1 is a control method for controlling a three-phase AC voltage on an output side or an input side of a power conversion device by a two-phase modulation PWM method, wherein the power conversion In a control method of a power conversion device that generates a drive power source of a semiconductor switching element constituting a device by a bootstrap circuit,
The upper arm side semiconductor switching element is forced from the upper arm side semiconductor switching element to the lower arm side semiconductor switching element for a predetermined period within a period in which the upper arm side semiconductor switching element of the non-modulation phase is conducted by approximately 60 degrees in electrical angle by the two-phase modulation operation. The commutation operation is performed at least once.

  A control method according to a second aspect is the method for controlling a power conversion device according to the first aspect, wherein the commutation timing is controlled by a time during which the upper arm side semiconductor switching element is conductive.

  According to a third aspect of the present invention, there is provided a method for controlling the power converter according to the first aspect, wherein the commutation timing is controlled by a phase angle at which the upper arm side semiconductor switching element is conducted. .

  The control method according to claim 4 is the control method of the power conversion device according to claim 1, wherein the commutation timing is approximately 30 degrees in electrical angle after the semiconductor switching element on the upper arm side starts to conduct. It is the time.

  According to a fifth aspect of the present invention, there is provided a control method for a power conversion device according to the first aspect, wherein the commutation timing is controlled in accordance with the magnitude of the power supply voltage for driving the semiconductor switching element on the upper arm side. is there.

  According to a sixth aspect of the present invention, the control method according to any one of the first to fifth aspects is performed when the output frequency of the power converter is lower than the set frequency.

The control device according to claim 7 is a control device for controlling the three-phase AC voltage on the output side or the input side of the power conversion device by a two-phase modulation PWM method, and is a semiconductor switching element constituting the power conversion device. In the control device of the power conversion device in which the drive power supply is generated by the bootstrap circuit,
The semiconductor switching element on the upper arm side is switched from the semiconductor switching element on the lower arm side to the semiconductor switching element on the lower arm side during a predetermined period within a period in which the semiconductor switching element on the upper arm side of the non-modulation phase is conducted by approximately 60 degrees in electrical angle by the two-phase modulation operation. A first means for generating a forced commutation pulse for flowing at least once.

  According to an eighth aspect of the present invention, there is provided the control device for the power conversion device according to the seventh aspect, further comprising: second means for detecting that the drive power supply voltage of the semiconductor switching element on the upper arm side is lower than the reference voltage. The forced commutation pulse is generated by the first means when it is detected by the second means that the drive power supply voltage has dropped below a set voltage.

  According to the present invention, in the bootstrap circuit, a capacitor having a small capacity can be used as a capacitor functioning as a power source for the semiconductor switching element, thereby enabling downsizing and cost reduction of the device.

It is a flowchart which shows 1st Embodiment of this invention. It is a flowchart which shows 2nd Embodiment of this invention. It is a flowchart which shows 3rd Embodiment of this invention. It is a block diagram of the control apparatus with which 3rd Embodiment of this invention is applied. It is a main circuit block diagram of a three-phase inverter system. It is a block diagram of a bootstrap circuit. It is a figure which shows the electric current path | route at the time of establishing the upper arm power supply voltage in FIG. In FIG. 6, it is a figure which shows the electric current path when the switching element of an upper arm is ON. It is a wave form diagram for demonstrating a three-phase modulation system. It is a wave form diagram for demonstrating a 60 degree | times conduction type two phase modulation system. It is a wave form diagram for demonstrating a 60 degree | times conduction type two phase modulation system. It is a wave form diagram which shows operation | movement of 1st Embodiment of this invention. It is a wave form diagram which shows operation | movement of 2nd Embodiment of this invention. It is a wave form diagram which shows operation | movement of 3rd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the following embodiment, a semiconductor switching element of a three-phase inverter that is two-phase modulated is driven by, for example, a bootstrap circuit configured similarly to FIG.
That is, the control device to which each embodiment is applied includes a bootstrap circuit having the DC power supply 11, capacitors 12 and 15, diode 13, resistor 14, and drive circuits 16 and 17 shown in FIG. , 17 and a control circuit (corresponding to the control circuit 6 in FIG. 5) that generates control signals, and the semiconductor switching elements 18, 19 are controlled to be turned on and off by the drive circuits 16, 17, respectively.

First, FIG. 1 is a flowchart showing the operation of the first embodiment of the present invention, and corresponds to the invention according to claims 1, 2, 6, and 7.
The control circuit of the three-phase inverter has an operation command (step S1 YES), and when the inverter output frequency f _out falls below the set frequency f _ref and two-phase modulation is performed (step S2 YES, S3). YES), the time of the electrical angle of 60 degrees in which the switching element of the upper arm of the non-modulation phase, for example, the switching element 18 in FIG. 6 is continuously conducted is calculated by T ₀ = 1 / (6 · f _out ). (Step S4).

When the calculated time T ₀ is equal to or longer than a certain set time T _ref (step S5 YES), as shown in the waveform diagram of FIG. 12, the upper arm side switching element 18 starts the two-phase modulation operation. After a set time T _{1 has} elapsed, a forced commutation pulse is output to the lower arm side drive circuit 17 for a predetermined period τ to turn on the switching element 19 to form a charging path for the upper arm capacitor 15 (step S6). ). Here, the predetermined time period tau, is set to a time sufficient to charge the capacitor 15 so as to compensate for the decreased amount of the gate voltage V _g of the upper arm side switching element 18.

  By turning on the switching device 19 on the lower arm side as described above, the capacitor 15 is charged and its voltage rises, and a predetermined power supply voltage for the driving circuit 16 and the switching device 18 on the upper arm side is established. Become. For this reason, it is not necessary to use a capacitor with a large capacity in anticipation of a decrease in voltage, and problems such as an increase in size, an increase in cost, and an increase in charging time due to the increase in capacity are avoided. Can do.

Next, FIG. 2 is a flowchart showing the operation of the second embodiment of the present invention, which corresponds to the invention according to claims 1, 3, 4, 6, and 7.
Steps S1 to S5 of the second embodiment are the same as those of the first embodiment. In step S5, in case it is time _{T 0} the set time _{T ref} above (step S5 YES), as shown in the waveform diagram of FIG. 13, the switching element 18 of the upper arm side starts to two-phase modulation operation From θ = 30 degrees, a forced commutation pulse is output to the lower arm side drive circuit 17 over a predetermined period τ to turn on the switching element 19 (step S6A). As a result, switching of the switching element 19 is performed approximately in the middle of the two-phase modulation operation period (60-degree period).

  Also in the second embodiment, since the charging path of the capacitor 15 on the upper arm side is formed by turning on the switching element 19 on the lower arm side, even if a small capacity component is used as the capacitor 15, the drive circuit 16 or A predetermined power supply voltage for the switching element 18 can be established.

  Next, FIG. 3 is a flowchart showing the operation of the third embodiment of the present invention, and corresponds to the invention according to claims 1, 5, 6 and 8. The third embodiment is applied to the control device of FIG. 4 corresponding to claim 8. First, the configuration of the control device will be described with reference to FIG.

  In FIG. 4, 1 is a DC voltage source, and 3a and 3b are drive circuits corresponding to the drive circuits 16 and 17 of FIG. Reference numerals 4a and 4b denote semiconductor switching elements such as IGBTs in which the free-wheeling diodes 5a and 5b are connected in antiparallel, and correspond to the switching elements 18 and 19 in FIG. These switching elements 4a and 4b are connected in a three-phase bridge, and a load 8 such as a three-phase motor is connected to the output side of the bridge circuit.

A capacitor 21 corresponding to the capacitor 15 in FIG. 6 is connected to the input side of the drive circuit 3a on the upper arm side. One end of the capacitor 21 is connected to the positive input terminal of the comparator 23, and the other end of the capacitor 21 is connected to the negative input terminal of the comparator 23 via a reference power supply 22 (its voltage is V _gref ). Here, the one end of the capacitor 21, the gate voltage V _g of the switching element 4a is turned to appear is detected.
The output terminal of the comparator 23 is connected to the control circuit 6 via an insulating means 24 such as a transformer. Here, the control circuit 6 constitutes a first means in claim 7, and the comparator 23 constitutes a second means in claim 8.

On the other hand, a DC power supply 7b corresponding to the DC power supply 11 of FIG. 6 is connected to the input side of the lower arm side drive circuit 3b.
The drive circuits 3a and 3b are also provided in the switching elements of the other two-phase upper and lower arms, but these are not shown for convenience.
Further, the switching elements 4a and 4b in FIG. 4 are also driven by the bootstrap circuit in FIG. 6, but in FIG. 4, the capacitors 12, diodes 13, resistors 14 and the like in FIG. Illustration is omitted for convenience.

In the third embodiment, the comparators 23 compare the voltages V _g and V _gref and input the comparison result to the control circuit 6 via the insulating means 24. The control circuit 6 receives the output signal of the comparator 23 via the insulating means 24, and turns on the lower arm switching element 4b for a predetermined period τ within the 60-degree conduction period of the upper arm switching element 4a to forcibly rotate. Let the flow do.

In the flowchart shown in FIG. 3, steps S1 to S3 are the same as those in the first embodiment and the second embodiment. Incidentally, since the circuit of Figure 4 detects the gate voltage V _g of the switching element 4a directly, may be omitted the step S2, S3.
In FIG. 3, (YES step S3) When performing two-phase modulation, detects the gate voltage _{V g} of the upper-arm switching elements 4a at the capacitor 21 of FIG. 4 (step S4). When the comparator 23 detects that the voltage V _g is lower than the reference voltage V _gref (YES in step S5A), a forced commutation pulse is output to the lower arm side drive circuit 3b over a predetermined period τ to switch the switching element 4b. Is turned on (step S6B).

FIG. 14 is a waveform diagram showing the operation of the third embodiment.
14, when starting the two-phase modulation operation at time t _a, the gate voltage V _g of the switching element 4a decreases accordingly. Thereafter, when reaching the reference voltage V _gref at time t _b, to turn on the switching element 4b of the lower arm side for a predetermined period of time tau, raising the gate voltage V _g of the switching element 4a. In FIG. 14, the period from time t _{a to} t _c is a 60-degree conduction period of the switching element 4 a on the upper arm side.

  Also in the third embodiment, since the charging path for the capacitor 21 on the upper arm side is formed by turning on the switching element 4b on the lower arm side, the drive circuit 3a or A predetermined power supply voltage for the switching element 4a can be established.

In addition, as a semiconductor switching element of the power converter device to which each embodiment is applied, not only IGBT but MOSFET may be used.
In each embodiment, the case where the forced commutation operation is performed once within the 60-degree conduction period has been described. However, this commutation operation may be performed a plurality of times within the 60-degree conduction period. However, if the number of commutations increases, the voltage value that can be output by the power converter such as an inverter decreases and the switching loss increases. Therefore, it is necessary to determine the number of commutations in consideration of these.

  The present invention can be used not only for controlling the AC output voltage of the three-phase PWM inverter but also for controlling the AC input voltage in the three-phase PWM rectifier.

1: DC voltage sources 3a, 3b, 16, 17: drive circuits 4a, 4b, 18, 19: semiconductor switching elements 5a, 5b: freewheeling diode 6: control circuit 7b, 11: DC power supply 8: loads 12, 15, 21 : Capacitor 13: Diode 14: Resistor 22: Reference power supply 23: Comparator 24: Insulating means

Claims (8)

A control method for controlling a three-phase AC voltage on an output side or an input side of a power conversion device by a two-phase modulation PWM method, and generating a drive power source of a semiconductor switching element constituting the power conversion device by a bootstrap circuit In the method for controlling the power conversion apparatus,
The upper arm side semiconductor switching element is forced from the upper arm side semiconductor switching element to the lower arm side semiconductor switching element for a predetermined period within a period in which the upper arm side semiconductor switching element of the non-modulation phase is conducted by approximately 60 degrees in electrical angle by the two-phase modulation operation. The control method of the power converter device characterized by performing the operation | movement which carries out a commutation at least once. In the control method of the power converter device according to claim 1,
A method for controlling a power converter, wherein the commutation timing is controlled by a time during which an upper arm semiconductor switching element is conductive. In the control method of the power converter device according to claim 1,
A control method for a power converter, wherein the commutation timing is controlled by a phase angle at which an upper arm semiconductor switching element is conducted. In the control method of the power converter device according to claim 1,
The method of controlling a power converter, wherein the commutation timing is set to a point in time when approximately 30 degrees in electrical angle has elapsed since the semiconductor switching element on the upper arm side began to conduct. In the control method of the power converter device according to claim 1,
A control method for a power converter, wherein the commutation timing is controlled in accordance with the magnitude of a power supply voltage for driving the semiconductor switching element on the upper arm side.   A method for controlling a power converter according to any one of claims 1 to 5, wherein the method for controlling a power converter is performed when an output frequency of the power converter is smaller than a set frequency. A control device for controlling a three-phase AC voltage on an output side or an input side of a power conversion device by a two-phase modulation PWM method, and generating a drive power source of a semiconductor switching element constituting the power conversion device by a bootstrap circuit In the control device for the power converter as described above,
The semiconductor switching element on the upper arm side is switched from the semiconductor switching element on the lower arm side to the semiconductor switching element on the lower arm side during a predetermined period within a period in which the semiconductor switching element on the upper arm side of the non-modulation phase is conducted by approximately 60 degrees in electrical angle by the two-phase modulation operation. A control device for a power converter, comprising: first means for generating a forced commutation pulse for flowing at least once. In the control apparatus of the power converter device according to claim 7,
A second means for detecting that the drive power supply voltage of the semiconductor switching element on the upper arm side is lower than the set voltage;
A control device for a power converter, wherein the forced commutation pulse is generated by the first means when the second means detects that the drive power supply voltage has dropped below a reference voltage.

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