JP2006320160A - Controller of power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To acquire a controller of a power converter for surely estimating and compensating an offset of a current detector without stopping the power converter during a transient operation of the power converter, and achieve an accurate current control. <P>SOLUTION: The controller of the power converter comprises a plurality of semiconductor switching elements, and is provided with the current detector 2 for detecting an output current from the power converter, and an offset estimator 21 for estimating the offset of the current detector. The offset estimator 21 estimates the offset using a feedback loop based on a voltage instruction in the controller of the power converter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for a power converter that outputs desired power by turning on and off an upper and lower arm composed of switching elements, and in particular, a power converter that drives a switching element using pulse width modulation (hereinafter referred to as a power converter). , Described as a PWM inverter).

A general operation of the control apparatus when supplying desired power to a load using a PWM inverter will be described with reference to FIG. For the explanation of the operation, a three-phase PWM inverter is set as a power converter, and a three-phase AC motor is set as a load.
In FIG. 1, 1 is a control device of a power converter, 2 is a current detector, 3 is a detected current signal, 4 is an offset compensator of the current detector 2, 5 is a coordinate converter, 6 is a phase, 7 is Detected current signal, 8 is a current command, 9 is a current controller, 10 is a voltage command, 11 is a coordinate converter, 12 is a voltage command, 13 is a dead time compensation signal calculator, 14 is a dead time compensation signal, 15 Is a PWM pattern calculator, 16 is a PWM pattern signal, 17 is a PWM inverter, 18 is a three-phase AC motor, 19 is an offset recorder, and 23 is an offset compensation signal for the current detector 2.
The current detector 2 detects the current flowing through the three-phase AC motor 18. The detected current signal 3 is taken into the control device 1. In the offset compensator 4, the offset component superimposed by the current detector 2 is removed. After that, the coordinate converter 5 performs coordinate conversion based on the phase 6 to obtain a current signal 7 on the dq axis rotation coordinates. The same phase component as phase 6 is defined as a d-axis component. A lead phase component of 90 degrees with respect to phase 6 is defined as a q-axis component. The acquisition method of the phase 6 differs depending on the type of the three-phase AC motor 18. In the case of an induction motor, the magnetic flux phase is obtained from a slip frequency calculator. If it is a synchronous motor, it is a magnetic pole position of a rotor, and is obtained by a detector such as an encoder. It is omitted in FIG. The current controller 9 performs current control according to the detected current signal 7 and the current command 8 and outputs a voltage command 10. The voltage command 10 is converted into a voltage command signal 12 on three-phase stationary coordinates by a coordinate converter 11, subjected to dead time compensation, and then converted to a PWM pattern signal 16 by a PWM pattern calculator 15.
The dead time compensation signal 14 is calculated from the detected current signal 3 by the dead time compensation signal calculator 13. Further, coordinate conversion may be performed on the current command 8 and a dead time compensation signal may be obtained based on the signal, but this is omitted in FIG.
The PWM pattern calculator 15 calculates a pattern by inserting a dead time in order to prevent a short circuit between the upper and lower switching elements of the PWM inverter 17. The PWM inverter 17 applies the predetermined voltage to the three-phase AC motor 18 by driving the upper and lower switching elements of each phase in accordance with the PWM pattern signal 16 described above.
The control device 1 for the PWM inverter repeatedly performs such processing to perform a control operation for supplying desired power to the load.
Now, the detected current signal 3 from the current detector 2 often includes an offset. In the control device for the power converter shown in FIG. 1, the output current of the PWM inverter 17 vibrates due to the offset. As a result, vibration is also generated in the output torque of the three-phase AC motor 18. The frequency of vibration is the same as the frequency of the fundamental frequency component of the PWM inverter output voltage or output current (hereinafter referred to as the primary frequency). Because of such a problem, processing for removing the offset superimposed by the current detector 2 has been performed. Most of them are methods of recording the detected current signal of the current detector as an offset before turning on the power converter and using it for offset compensation during operation of the power converter. In the example shown in FIG. 1, an offset recorder 19 is used for the offset recording.

However, after a long time operation, the ambient temperature of the current detector and the element temperature inside the detector change, and the offset included in the detection current signal of the current detector varies. For this reason, even if the offset acquired before power-on is used, optimal compensation is not performed, and there is a problem that vibration occurs in the load current. In order to re-acquire the offset included in the detected current signal, the power converter needs to be temporarily stopped, and there is a problem that re-acquisition cannot be performed when continuous operation is required.
As a technique for solving this problem, there are techniques disclosed in Patent Documents 1 and 2, for example. This is a technique in which a low-pass filter process is performed on a current signal detected by a current detector to detect and compensate for an offset (see Patent Document 1). Further, it is a technique for detecting an offset by performing integration processing for a predetermined period on a current signal detected by a current detector (see Patent Document 2).

JP-A-7-170799 JP 2001-169578 A

  However, the technique disclosed in Patent Document 1 has a problem that the offset can be detected only during steady operation. In order to detect the offset with high accuracy, it is necessary to appropriately set the cutoff frequency of the low-pass filter. Further, in the technique disclosed in Patent Document 2, it is possible to detect an offset by performing integration processing for a predetermined period on the current signal detected by the current detector. However, as in the technique of Patent Document 1, only during steady operation. Can only be detected.

  The present invention has been made to solve the above-described problems, and reliably estimates and compensates for the offset of the current detector without stopping the power converter and even when the power converter is in a transient operation state. The present invention provides a power converter control device capable of realizing highly accurate current control.

  In the power converter control device according to the present invention, in the power converter control device configured by a plurality of semiconductor switching elements, the current detector includes a current detector that detects an output current of the power converter, and the current detector includes The offset estimator includes an offset estimator that estimates an offset and a compensation arithmetic unit, and the offset estimator performs offset estimation using a feedback loop based on a voltage command in a control device of the power converter. .

  According to the present invention, it is possible to reliably detect and compensate for the offset of the current detector without stopping the power converter and even when the power converter is in a transient operation state. As a result, highly accurate current control can be realized.

Embodiment 1 FIG.
FIG. 2 is an explanatory diagram for explaining the control device for the power converter according to the first embodiment of the present invention. For the explanation of the operation, a three-phase PWM inverter was set as a power converter, and a three-phase AC motor was set as a load.
In FIG. 2, 1 is a control device of the power converter, 2 is a current detector, 3 is a detected current signal, 4 is an offset compensator of the current detector 2, 5 is a coordinate converter, 6 is a phase, 7 is Detected current signal, 8 is a current command, 9 is a current controller, 10 is a voltage command, 11 is a coordinate converter, 12 is a voltage command, 13 is a dead time compensation signal calculator, 14 is a dead time compensation signal, 15 Is a PWM pattern calculator, 16 is a PWM pattern signal, 17 is a PWM inverter, 18 is a three-phase AC motor, 20 is a current command phase calculator, 21 is an offset estimator, 22 is a current command phase, and 23 is a current detector 2. Offset compensation signal. In FIG. 2, the dead time compensation signal 14 is obtained from the detected current signal 3, but may be obtained from the current command 8 as described in the background art.
The current command phase calculator 20 calculates a current command phase 22 from the phase 6 and the current command 8. The offset compensator 4 includes an offset estimator 21 and a compensation calculator. The offset estimator 21 estimates the offset of the current detector 2 from the current command phase 22, the voltage command 10 and the phase 6. At this time, the offset estimator 21 operates by detecting distortion of the voltage command 10.
Next, the operation of the offset estimator 21 will be described with reference to FIG. FIG. 3A shows a phase current waveform for one phase of the three-phase AC motor 18 obtained by the current detector 2. FIG. 3B shows a voltage command (hereinafter referred to as Vdis) that is orthogonal to the current command vector on the dq-axis (two-axis orthogonal) rotational coordinates. In FIG. 3B, the voltage command is distorted near the polarity inversion (zero cross) of the phase current due to the influence of the voltage disturbance due to the dead time of the PWM inverter 17. Here, when a positive offset occurs in the current detector 2, the distortion in FIG. 3B changes as shown in FIG. 3C, and the waveform in which the magnitude of distortion differs between the upstream and downstream of the phase current waveform. It becomes. Even when a negative offset occurs in the current detector 2, the magnitude of the distortion changes as shown in FIG. 3E, but the magnitude of the distortion is reversed from the case where a positive offset occurs.
Here, the phase section is divided based on the current command phase 22. It is set so that the distortion caused by the current zero cross of Vdis enters the section divided here. Execute integration calculation within the set interval to obtain and record the average value. The difference shown in FIGS. 3D and 3F occurs in the average value due to the distortion of Vdis. Av1 is the average value of Vdis in section 1, and Av7 is the average value of Vdis in section 7. When the offset of the current detector 2 is compensated, the distortion of the voltage command is uniform as shown in FIG. That is, the average value also agrees. For this reason, the offset can be estimated by using the difference between the average values. For example, the difference between the average values is integrated to obtain an estimated offset value. If the offset of the current detector 2 is compensated, the difference between the above average values is also zero, and the integration calculation is stopped. In FIG. 3, for the sake of explanation, one phase is used. However, when two-phase detection or three-phase detection is performed in actual operation, a distortion component corresponding to each phase may be used. For this reason, offset compensation can be performed independently for the three phases.
In FIG. 3B, the distortion of the voltage command Vdis has an upward thorn shape. Depending on the type of load, the configuration of the dead time compensator, the operating conditions such as the primary frequency and the current, etc., the shape may be downward. This is shown in FIG. However, the magnitude relationship between the positive / negative of the offset generated in the current detector 2 and the average values Av1 and Av7 is the same. (Below)
○ When a positive offset occurs in the current detector ………… Av1 <Av7
○ When a negative offset occurs in the current detector ………… Av1> Av7
In order to realize the operation as described above, for example, the configuration of the offset estimator 21 may be configured as shown in FIG. In FIG. 5, a voltage command in a direction orthogonal to the current command vector is obtained by the coordinate converter 21d from the current command phase 22 and the phase 6, and this signal is assigned to Vdis 21b. A filter 21e has a function of removing a component unnecessary for offset amount estimation from the Vdis 21b.
The phase division / offset estimated value updater 21c shown in FIG. 5 executes the average value calculation and the offset estimation / update operation for each section shown in FIG. 3 or FIG. As a configuration for realizing the operation, for example, there is a configuration shown in FIG. 21c-1 is a reset signal generator, 21c-2 is a Vdis integrator, 21c-3 is an average value calculation gain, 21c-4 is a sample hold unit, 21c-5 is a sample hold timing generator, and 21c-6 is Vdis. An average value recorder 21c-7 is an offset updater and includes an integrator 21c-7a and a gain 21c-7b. 21c-8 is an operation timing generator. In FIG. 6, Vdis 21b is integrated by an integrator 21c-2. The gain 21c-3 is a gain for converting the integral value into an average value, and is variable depending on the primary frequency. As shown in FIG. 3 and FIG. 4, in order to obtain the average value of Vdis 21b for each predetermined section, it is sampled and held at a predetermined timing of the current command phase and stored in the recorder 21c-6. Sample hold timing and operation are performed by a sample hold timing generator 21c-5 and a sample hold device 21c-4. Immediately after the sample hold, the value of the integrator 21c-2 is reset to zero. The timing is generated by the reset signal generator 21c-1 based on the current command phase 22. The offset updater 21c-7 reads the average value for each section of the Vdis 21b stored in the recorder 21c-6 at the timing set by the operation timing generator 21c-8, and executes the integration operation by taking the difference. 3 and 4, the operation timing of the offset updater 21c-7 can be set immediately after section 2 or immediately after section 8.
As described above, in the control apparatus for the power converter shown in FIG. 2, the offset of the current detector 2 is estimated by operating the offset estimator 21 as shown in FIGS. Offset compensation can be realized. In addition, since low-pass filter processing is not used, highly accurate offset compensation can be realized even during transient operation. As a result, highly accurate current control can be realized.
That is, the control device for a power converter according to the present invention includes a current detector that detects an output current of the power converter, an offset estimator that estimates an offset of the current detector, and an offset calculator. A compensator is provided, and the offset estimator solves the problem by performing offset estimation using a feedback loop based on a voltage command in a control device of the power converter.
Moreover, the control device for the power converter described above solves the problem by using a voltage command used in the offset estimator as a voltage command expressed on two-axis orthogonal rotation coordinates.
In addition, the control device for the power converter uses one of the voltage commands expressed on the two-axis orthogonal rotation coordinates, and uses the output current of the power converter or the power converter as a reference for switching. The problem is solved by setting the output voltage frequency or the current command in the control device of the power converter or the type of load connected to the power converter.
Further, the control device for the power converter described above uses the voltage command used for the offset estimator as a voltage command expressed on the biaxial orthogonal rotational coordinates, and the power converter expressed on the two axial orthogonal rotational coordinates. The problem is solved by making the component orthogonal to the output current vector or the current command vector in the control device of the power converter.
In the power converter control device described above, the offset estimator performs processing by dividing one cycle of the current command phase in the power converter control device into a plurality of sections, and on the stationary coordinates in the section. The problem is solved by including the output current of the expressed power converter or the polarity reversal (zero crossing) of the current command on the control device of the power converter.

Embodiment 2. FIG.
In the first embodiment, the offset estimator 21 has the configuration shown in FIG. 5, but in the second embodiment, the configuration shown in FIG. 7 is used. In this case, the voltage command switching unit 21a in FIG. 7 receives the voltage command 10 output from the current controller 9, and assigns the d-axis voltage command or the q-axis voltage command to the signal Vdis21b that is the basis of the offset estimation. This is because the distortion as shown in FIGS. 3 and 4 can be detected even if the direction is not strictly orthogonal to the current vector or the current command vector as shown in FIG. For this reason, as a reference for switching, a setting is made to assign a voltage command that can detect the largest distortion of Vdis 21b. For example, the detection current signal 3 or the current command 8 of the three-phase AC motor 18 or the primary frequency may be used for switching. Moreover, you may switch according to the kind of connected three-phase alternating current motor. These switching criteria may be used in parallel. The configuration of FIG. 7 can be simplified because the coordinate converter 21d is not used.

It is explanatory drawing for demonstrating the control apparatus of a general power converter. It is explanatory drawing for demonstrating the control apparatus of the power converter in Embodiment 1 of this invention. It is explanatory drawing for demonstrating operation | movement of the current detector offset estimation of the control apparatus of the power converter in Embodiment 1 of this invention. It is explanatory drawing for demonstrating operation | movement of the current detector offset estimation of the control apparatus of the power converter in Embodiment 1 of this invention. It is a block diagram of the offset estimator of the current detector of the control apparatus for the power converter in the first embodiment of the present invention. It is a block diagram which shows the phase division | segmentation and offset estimated value updater of the control apparatus of the power converter in Embodiment 1 of this invention. It is a block diagram of the offset estimator of the current detector of the control apparatus of the power converter in Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control apparatus of power converter 2 Current detector 3 Detected current signal 4 Offset compensator of current detector 5 Coordinate converter (used for conversion from quantity on three-phase stationary coordinate to quantity on rotating coordinate)
6 Phase 7 Detected current signal (expressed on rotating coordinates)
8 Current command 9 Current controller 10 Voltage command (expressed on rotating coordinates)
11 Coordinate converter (used to convert the quantity on rotating coordinates to the quantity on three-phase stationary coordinates)
12 Voltage command (expressed on three-phase stationary coordinates)
13 Dead Time Compensation Signal Calculator 14 Dead Time Compensation Signal 15 PWM Pattern Calculator 16 PWM Pattern Signal 17 PWM Inverter 18 Three-Phase AC Motor 19 Current Detector Offset Recorder 20 Current Command Phase Calculator 21 Offset Estimator 21a Voltage Command Switcher 21b Vdis
21c Phase division / offset estimated value updater 21c-1 Reset signal generator 21c-2 Vdis integrator 21c-3 Average value calculation gain 21c-4 Sample hold device 21c-5 Sample hold timing generator 21c-6 Vdis average value Recorder 21c-7 Offset updater 21c-7a Integrator 21c-7b Gain 21c-8 Operation timing generator 21d of offset compensation amount updater Coordinate converter (conversion to current command vector or detected current vector orthogonal direction)
21e Filter 22 Current command phase 23 Current detector offset compensation signal

Claims (6)

  In a control device for a power converter composed of a plurality of semiconductor switching elements, a current detector that detects an output current of the power converter, an offset estimator that estimates an offset of the current detector, and a compensation calculator A control device for a power converter, wherein the offset estimator performs offset estimation using a feedback loop based on a voltage command in the control device for the power converter.   2. The control apparatus for a power converter according to claim 1, wherein the voltage command used in the offset estimator is a voltage command expressed on two-axis orthogonal rotation coordinates.   Either one of the voltage commands expressed on the two-axis orthogonal rotation coordinates used in the offset estimator is switched and used as the switching reference, the output current of the power converter, the output voltage frequency of the power converter, or the power conversion 3. The control device for a power converter according to claim 2, wherein a current command in the control device for the power generator or a type of a load connected to the power converter is used.   The voltage command used for the offset estimator is a component orthogonal to the output current vector of the power converter expressed on the biaxial orthogonal rotation coordinates or the current command vector in the control device of the power converter. The power converter control device according to claim 2.   The offset estimator performs processing by dividing one cycle of a current command phase in a control device of the power converter into a plurality of sections. Control device.   The offset estimator performs processing by dividing one period of the current command phase in the control device for the power converter into a plurality of sections, and the output current of the power converter or the control device for the power converter in the section in which the processing is executed 6. The control device for a power converter according to claim 5, comprising polarity inversion (zero crossing) of the current command.

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