JPH11150986A - Control equipment of parallel multiplex power inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize cost reduction by making it unnecessary to develop or design a special control system when the number of multiplex is changed. SOLUTION: When a three-phase induction motor 5 is driven and controlled by using a plurality (two in figure) of inverters 41, 42 which are connected in parallel, output currents of each of the inverters 41, 42 are divided into a first current component parallel with the motor magnetic flux, a second current component perpendicular to the first current component, and a third current component as the zero-phase component, and each of the current components is independently fed back and controlled by adjusting devices 11, 12, 13. As a result, controls to the inverters 41, 42 are made identical, and a circulation current flowing between them is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for driving a polyphase AC load such as a three-phase AC motor using a plurality of power converters (for example, inverters).

[0002]

2. Description of the Related Art As a method of forming a multiplex inverter,
It is known that a plurality of voltage type inverters are connected in parallel, and an interphase reactor is connected between the in-phase outputs of these inverters. FIG. 4 shows a two-phase inverter with three-phase output.
FIG. 5 shows a configuration example of a three-phase output three-multiplex inverter (for example, see Japanese Patent Application Laid-Open No. 60-98875).
Here, the interphase reactor 9 in FIG. 4, interphase reactor 91 to 93 in FIG. 5 has an action to suppress a harmonic component of the circulating current flowing between a plurality of inverters (i _k).

[0003] The interphase reactor can suppress the harmonic component of the circulating current, but cannot suppress the circulating current of the DC component and the low frequency component generated due to a control error or the like. Therefore, the low-frequency circulating current may become excessive, and this phenomenon may cause the inverter to fail due to the overcurrent. In order to solve this, for example, in the method described in JP-A-3-253293, one inverter controls the output current of the inverter, and the other inverter controls the average value of the output currents of the two inverters. As a result, the circulating current is set to zero.

[0004]

In the case of configuring a multiplex inverter, if a plurality of inverters and control devices can be simply combined and multiplexed, not only can development and design costs be reduced, but also product cost can be reduced. preferable. However, in the method described in JP-A-3-253293, a function of calculating an average value of two sets of currents is added, so that it is not possible to simply combine two sets of inverters and perform multiplexing. Also, in the case of triple multiplexing, a function different from the case of double multiplexing may be required. As described above, it is necessary to develop and design a control device according to the number of multiplexes, such as a control device for two multiplexes and a control device for three multiplexes, which causes an increase in cost. Therefore, an object of the present invention is to provide a low-cost control device that can configure a multiplex inverter by combining a plurality of inverters without requiring special development or design corresponding to the number of multiplexes.

[0005]

For example, in the control of a polyphase AC machine, a vector for controlling the polyphase AC current by decomposing it into a magnetizing current component parallel to the direction of the magnetic flux of the motor and a torque current component orthogonal thereto. Control is well known. In this control, a magnetizing current control system that feeds back a magnetizing current and a torque current control system that feeds back a torque current are used. On the other hand, in the control of a conventional parallel multiplex inverter, a control system is generally configured based on the idea of averaging output currents of a plurality of inverters.

According to the present invention, in addition to the above-described control of the magnetizing current and the torque current, if a zero-phase current included in the output current of the inverter is detected and controlled so that the zero-phase current becomes zero, a plurality of naturally occur. Focusing on the fact that the output current of the inverter is averaged, the zero-phase current is controlled stably using a proportional amplifier. In other words, by performing feedback control by the proportional amplifier so that the zero-phase current becomes zero, the circulating current flowing between the inverters can be controlled to zero and stably. In addition, even if the number of multiplexes is arbitrary, the control of each inverter is the same, and even if the number of multiplexes is increased, development and design for the inverter are not required.

[0007]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and shows a control block diagram of a two-multiplex inverter for driving a three-phase induction motor by vector control. In the figure, 11 is a magnetizing current regulator, 12 is a torque current regulator, 13 is a zero-phase current regulator, 21 to 23 are coordinate converters, 3 is a PWM (pulse width modulation) controller, 41 and 42.
Is an inverter, 5 is an induction motor (induction machine, IM), 6 is an integrator, and 7 is a slip calculator. That is, the magnetizing current controller 11, the torque current controller 12, the zero-phase current controller 13, the coordinate converters 21 to 23, P
A control means including the WM control device 3, the integrator 6, the slip calculator 7 and the like is provided, and the inverter 42 has the same function.

In FIG. 1, i _M ^* is a command value of magnetizing current, i _T ^*
Is the command value of the torque current, and the detected value of the three-phase current is calculated by the coordinate converter 21 using
It is converted into a phase alternating current iα, iβ and a zero-phase current i0. In addition,
As the definition of the zero-phase current, the proportional coefficient of equation 1 (1/3) ^1/2
May be used instead of, but any one may be used as long as a current proportional to the sum of the currents of the respective phases can be detected.

[0009] [Equation 1] ^{iα = (2/3) 1/2 (ia} -ib / 2-ic / 2) iβ = (2/3) 1/2 (3 1/2 ib / 2-3 1 / ² ic /
2) i0 = (1/3) ^1/2 (ia + ib + ic)

[0010] i.alpha, i.beta further be coordinate transformed by the coordinate converter 22 into a current on rotating flux in the next few 2, i _M and i _T is obtained. Here, θ indicates the intersection angle between the stator axis (α axis) of the induction machine and the magnetic flux axis (M) axis obtained from the slip calculator and the integrator. [Equation 2] i _M = iαcosθ + iβsinθ i _T = −iαsinθ + iβcosθ

FIG. 2 shows the relationship between the coordinate transformed i _M , i _T and i α, i β. The intersection angle θ between the α-β axis and the MT axis is obtained as follows. That is, the slip calculator 7 first calculates the slip angular velocity of the induction motor 5 from i _M and i _T , and adds the speed obtained from the speed detector to the angular velocity of the secondary magnetic flux of the induction motor 5. Is integrated by the integrator 6 to obtain a secondary magnetic flux axis with respect to the α-β axis, that is, M
-The angle of the T axis will be determined.

The magnetizing current regulator 11 is set so that both the detected values i _M and i _T coincide with the respective command values i _M ^* and i _T ^*.
Is feedback-controlled by the torque current controller 12.
The outputs of both regulators are M-axis voltage command values v _M ^* and T, respectively.
Axis is a voltage command value v _T ^*. Further, the command value of the zero-phase current is zero, and feedback control is performed so that the zero-phase current becomes zero. The output of the zero-phase current controller 13 is a zero-phase voltage v0 ^* .

From v _M ^* , v _T ^* and v 0 ^* , the three-phase voltage command va is calculated by the coordinate converter 23 using the following equations (3) and (4).
^* , Vb ^* and vc ^* are determined. Formula 3 ^{_{vα * = v M * cosθ-}} v T * sinθ vβ * = v M * sinθ + v T * cosθ [Equation 4] ^{va * = (2/3) 1/2 (} vα * -v0 * / 2 1 ^{/ 2) vb * = (2/3} ) 1/2 (-vα * / 2 + 3 1/2 vβ *
^{/ 2 + v0 * / 2 1/2} ) vc * = (2/3) 1/2 (-vα * / 2-3 1/2 vβ *
/ 2 + v0 ^* / ^21/2 )

Further, the three-phase voltage command is subjected to pulse width modulation (PWM) to control the inverter. Since the control is exactly the same for the other inverter,
Description is omitted. According to the configuration described above, i _M, so i _T and zero-phase current i0 is controlled equivalently be controlled 3-phase current, circulating current never flows between the inverter. Furthermore, in the above configuration, since the control of each inverter is the same, there is no need to change the control of the inverter even if the number of multiplexes increases to three or more. In addition, although the description has been given of the drive of the induction motor, the same applies to the control of the synchronous motor.

FIG. 2 is a block diagram showing a second embodiment of the present invention, in which the load 5A is a resistor or an inductance. That is, the two-phase oscillator 8 outputs a phase θ given by θ = ω ^* t (t: time) from the frequency command ω ^* . Since the magnitude I of the current is given by the following equation 5 with respect to the first current command i ₁ ^* and the second current command i ₂ ^* , for example, i ₁ ^* is made equal to the magnitude of the current I, and i ₂ ^* may be set to zero. The other parts are the same as those in FIG. [Equation 5] I = (i ₁ ^{* 2} + i ₂ ^{* 2} ) ^1/2

By the way, the current regulators 11 and
Numeral 12 is generally a proportional-integral adjuster (PI adjuster) composed of a proportional element and an integral element in order to reduce the steady-state deviation to zero. On the other hand, it is desirable that the zero-phase current regulator 13 is a proportional regulator (P regulator). The reason is as follows. In the examples of FIGS. 1 and 3, the number of independent variables of the current is five. This may be achieved, for example i _M of the first inverter 41 in FIG. 1, a i _T, i0, i _M of the second inverter 42, if i _T is controlled, i0 is uniquely of the second inverter 42 Is determined. Therefore, i _M , i _T , i0 of the first inverter 41
When feedback control of i _M , i _T , and i 0 of the second inverter 42 is performed independently of each other by the PI controller, there is a possibility that control may be disabled due to a control error. Therefore, if the zero-phase current adjuster is a P adjuster, a steady-state deviation occurs and the above problem can be avoided. Note that this steady-state deviation can be made very small by increasing the gain of the P adjuster, so that there is no practical problem.

[0017]

According to the present invention, since the zero-phase current feedback control is performed, the control of each of the inverters constituting the multiplex inverter can be made the same.
Even if the number of multiplexes is increased, there is no need to change the control of the inverter. In other words, since there is no need to perform new development or design depending on the number of multiplexed inverters, there is an advantage that the cost of the product can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a relationship between each current and coordinate axes in FIG.

FIG. 3 is a configuration diagram showing a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing a conventional example of a parallel two-multiplex inverter.

FIG. 5 is a configuration diagram showing a conventional example of a parallel three-multiplex inverter.

[Explanation of symbols]

11: magnetizing current regulator, 12: torque current regulator, 13
... Zero-phase current controller, 21-23 ... Coordinate converter, 3 ... PW
M control device, 41, 42 inverter, 5 induction motor (induction machine, IM), 5A load, 6 integrator, 7 slip calculator, 8 oscillator.

Claims (3)

[Claims] 1. A control device for a parallel multiplex power converter for driving a three-phase AC motor using a plurality of power converters connected in parallel, comprising: an output for each of the plurality of power converters; The current is decomposed into a first current parallel to a magnetic flux or a magnetic pole of the motor, a second current orthogonal to the first current, and a third current that is a zero-phase component, and each current component is independently controlled by feedback. And control means for controlling the zero-phase current to zero. 2. A control device for a parallel multiplex power converter in which a plurality of power converters connected in parallel are used to supply power to a three-phase AC load. Is decomposed into two sets of first and second currents of a rotating coordinate system that are DC currents in a steady state and a third current that is a zero-phase component, and each current component is independently feedback-controlled, A control device for a parallel multiple power converter, further comprising control means for controlling the zero-phase current to zero. 3. The control device for a parallel multiplex power converter according to claim 1, wherein a proportional regulator is used as said zero-phase current control means.