JP3573028B2 - Power converter - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power converter and a control method thereof.
[0002]
[Prior art]
In driving a motor by a power conversion device, the supplied AC is partially converted to DC inside the power conversion device, and then converted to AC of a required variable voltage and variable frequency and output, and the AC motor is driven at a variable speed. ing. At this time, if the DC voltage inside the power converter fluctuates due to the fluctuation of the input AC voltage or the like, the output voltage of the power converter fluctuates, and the motor speed and the motor generated torque also fluctuate. Therefore, it is necessary to perform a correction to the fluctuation of the DC voltage so as to suppress the fluctuation of the output voltage. To solve such a problem, a method of controlling an output voltage using a detection value of the detection circuit by providing a DC voltage detection circuit as described in Japanese Patent Application Laid- Open No. 6-311787 is conventionally used. .
[0003]
[Problems to be solved by the invention]
In the above-described method, it is necessary to provide a DC voltage detection circuit. However, providing a DC voltage detection circuit causes an increase in the number of components, which leads to complication of the device and a decrease in reliability. An object of the present invention is to provide a power conversion device having a function of suppressing a change in output voltage with respect to a change in DC voltage without installing a DC voltage detection unit.
[0004]
[Means for Solving the Problems]
The above object is achieved by providing output voltage detection means, means for comparing the output voltage detection value with the output voltage command value, and correction means for correcting the output voltage command value using the result of the comparison means.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example 1)
FIG. 1 shows a first embodiment of the present invention. In FIG. 1, a component number 1 is an AC power supply that supplies power to the power converter, 2 is an AC / DC converter that converts AC to DC, 3 is a smoothing capacitor, and 4 is an orthogonal converter that converts DC to AC. 5 is an AC motor as a load of the power converter, 6 is output current detecting means for detecting the output current of the power converter, 7 is output voltage detecting means for detecting the output voltage of the power converter, 8 Is an output voltage command calculating means for giving an AC voltage command to the power converter, 9 is an output voltage command correcting means which is a feature of the present invention, and 10 is a limiter for limiting the voltage command.
[0006]
Next, the operation of the present invention will be described. The AC supplied from the AC power supply 1 is rectified by the AC / DC converter 2 and smoothed by the smoothing capacitor 3 to obtain a DC power supply. The orthogonal transformer 4 converts the DC power into an AC having an arbitrary frequency and phase based on the output of the output voltage command calculating means 8 and supplies the AC power to the AC motor 5 to drive the motor at a variable speed. The output voltage command calculation means 8 calculates and outputs an output voltage command value V * based on the speed command f0 * and the current detection value IoutFB by V / f control or sensorless vector control.
[0007]
Conventionally, a method of providing a DC voltage detection circuit inside the power conversion device and controlling the output voltage using the detected value is used.However, the provision of the DC voltage detection circuit increases the number of components and increases the number of components. This leads to complications and reduced reliability. On the other hand, the output voltage of the power converter is also detected for reasons such as restarting the motor at the moment of an instantaneous power failure, and if the fluctuation of the DC voltage is estimated using this output voltage detection, A DC voltage detection circuit can be omitted. In the configuration shown in FIG. 1, the output voltage command correction means 9 receives the output voltage detection value of the output voltage detection means 7 and the output voltage command value V * of the output voltage command calculation means 8 and receives the output voltage command value V *. It estimates and corrects the output voltage command value V *, and outputs the corrected output voltage command value V **. With the above configuration, it is possible to correct the output voltage command value when the DC voltage fluctuates, and to suppress the fluctuation of the output voltage of the power conversion device due to the fluctuation of the DC voltage.
[0008]
(Example 2)
FIG. 2 shows a second embodiment of the present invention. The second embodiment can be realized by replacing the output voltage command correction means 9 in FIG. 1 with a divider 9a and a multiplier 9b shown in FIG. In FIG. 2, reference numeral 9a denotes a DC voltage fluctuation detecting means, specifically, a divider for calculating the ratio between the corrected output voltage command value V ** and the output voltage detection value VoutFB, and 9b denotes an output voltage command correction. Specifically, it is a multiplier for multiplying the output of 9a by the output voltage command value V *.
[0009]
Next, the operation of the present invention will be described with reference to FIG. First, when the DC voltage fluctuates at the fluctuation rate α0 when the output voltage command value is V *, the actual output voltage Vout of the orthogonal transformer becomes Vout = α0 × V *. If α0 can be detected, the output voltage can be corrected by multiplying V * by 1 / α0. In the present invention, 1 / α0 is estimated using the output voltage detection value and the corrected output voltage command value .
[0010]
The divider 9a calculates the ratio between the corrected output voltage command value V ** and the output voltage detection value VoutFB to calculate the estimated DC voltage fluctuation rate 1 / α (where α = VoutFB / V *). * ). Then, the multiplier 9b, the original output voltage command value V * 1 / alpha multiplied, and outputs the output voltage command value V ** of the corrected. Therefore, if α0 = α, the corrected output voltage value Vout becomes equal to the output voltage command value V * .
[0011]
Therefore, according to the present invention, even when the DC voltage fluctuates, it is possible to obtain an output voltage according to the output voltage command value. In addition, if the series of calculations described above is performed using each instantaneous value, output voltage correction with no delay time can be performed in principle.
[0012]
(Example 3)
FIG. 4 shows a third embodiment of the present invention.
[0013]
In FIG. 4, part numbers 1 to 5 and 7, 10 are the same as those of the embodiment of FIGS. 1 and 2 having the same numbers. Reference numeral 10 denotes a detection voltage correction unit which is a characteristic part of the present invention, and reference numeral 11 denotes an output voltage command generation unit.
[0014]
The output voltage command generation means 11 operates in the same manner as the output voltage command calculation means 8 described above. However, the output voltage command generation means 11 uses the detected value of the output voltage in calculating the output voltage command value V *. The output voltage command generating means 11 corresponds to the second embodiment described above, or an observer for estimating the motor magnetic flux or the like based on the detected voltage value. When the output voltage detection value VFB is used as a part of the calculation of the output voltage command value V *, if the output voltage detection means 7 has a detection error, it becomes a disturbance, and the output voltage command value is output to the output voltage command calculation means. Affect. In particular, the voltage detector often includes a DC offset, which is a problem. Therefore, means for removing the DC error is required. In the embodiment shown in FIG. 4, the detection error is removed by using the detection voltage correction means 11 and used for the calculation of V *.
[0015]
FIG. 5 shows a configuration example of an output voltage detection error correction unit using an output voltage command value. In FIG. 5, 10av and 10avw are a voltage command and a first subtractor that calculates a deviation of the corrected voltage detection value. , A second subtractor for subtracting and correcting the integrated value of the deviation. FIG. 5 shows a case where the detection of the output voltage is performed by using the line voltage. Hereinafter, the description will be given using the output voltage detection value between the UV phases as an example, but the correction method is the same between the VW phases.
[0016]
The first subtracter 10a subtracts the output voltage command value Vuv * from the corrected output voltage detection value VuvFB ', and outputs a difference dVuv between the two. The integrator 10b calculates the time average of the output voltage detection error estimation value by integrating dVuv with time, and outputs it as the DC error estimation value DVuv of the output voltage detection value. The second subtracter 10c corrects the output voltage detection value by subtracting the DC error estimation value DVuv from the output voltage detection value VuvFB.
[0017]
Here, consider a case where a DC error dv occurs in VuvFB from a state where there is no DC error. Since Dvuv = 0 when there is no DC error, first, VuvFB = VuvFB '. When a DC error occurs, dv is gradually integrated, and DVuv keeps changing until Vuv * = VuvFB ′. Then, when DVuv = dv, Vuv * −VuvFB ′ = 0 for the first time.
And the correction is completed.
[0018]
Therefore, according to the present invention, by using the output voltage command value and the output voltage detection value, it is possible to correct a DC error caused by the output voltage detection value detecting means.
[0019]
Although FIG. 5 shows an embodiment in which the output voltage detection is performed by using the line voltage, the present invention can be implemented even when the output voltage detection is performed by using the phase voltage.
[0020]
(Example 4)
A fourth embodiment of the present invention will be described with reference to FIG.
[0021]
The present invention can be realized by replacing the detection voltage correction means 10 in FIG. 4 with that in FIG. In FIG. 6, 10d is an integrator for integrating the output current detection value IuvwFB for each phase, and 10e is a subtractor for correcting the output voltage detection value.
[0022]
In the invention of FIG. 6, the output voltage detection error is corrected using the output current detection value. The integrator 10d integrates the output current detection value IuvwFB with respect to time for each phase, and outputs an average value of the output phase currents IuFB, IvFB, and IwFB. Therefore, the output of the integrator corresponds to the direct current component of the output phase current, and the output of the integrator has a value only when direct current exists in the output current.
[0023]
When the output voltage detector has a DC offset, unless the offset is removed, a DC component is generated in the output current. In the third embodiment, the offset is canceled by using the voltage command. However, the offset of the voltage detector can be removed by using the detected current value.
[0024]
Next, the operation principle of the present invention will be described.
[0025]
First, when the output phase current has no DC current component, the output of the integrator is zero. Here, when a DC error (DC offset) of the output voltage detecting means 7 occurs, the output voltage command value V * is affected, and DC also exists in V *. As a result, a DC current is generated in the output current. If a DC component exists in the output current detection value, the output of the integrator 10d increases and corrects the output of the voltage detector. The output of the integrator 10d continues to fluctuate until the DC component becomes zero, and the correction is completed when the DC component becomes zero.
[0026]
Therefore, according to the present invention, it is possible to correct a DC error caused by the output voltage detection value detecting means by using the output current detection value. Generally, in order to drive the electric motor 5 with high performance by vector control or the like, it is necessary to detect a current value with high resolution. In that case, it is necessary to make the accuracy of the current detector higher than that of the voltage detector. Therefore, by using the current detection value, the voltage detection error can be removed with higher accuracy and higher sensitivity.
[0027]
(Example 5)
FIG. 7 shows a fifth embodiment in which a detection error correction unit 10 is added to the detection error caused by the output voltage detection unit 7 in the first embodiment.
As described above, when the output voltage detection means 7 has a detection error, the output voltage command correction means 9 does not function properly due to the influence of the detection error. Therefore, the detection error correction means of the third and fourth inventions are added so that the output voltage command correction means functions properly, and the influence of the DC error is removed.
[0028]
If the output voltage detection error correction means according to the third or fourth aspect is applied as the detection error correction means, it is not necessary to provide a special external circuit.
[0029]
(Example 6)
FIG. 7 shows a sixth embodiment, in which the present invention shown in the first embodiment is applied to a serial multiplex type power converter. In FIG. 7, a part number 100 is a serial multiplex power converter, 100 u to 100 v are U-phase to W-phase converters, 110 u to 140 u are inverter units that output low-voltage AC, and 112 u is a converter that converts AC to DC. The reference numeral 113u denotes a smoothing capacitor, and 114u denotes a single-phase inverter constituted by a full bridge.
[0030]
(Example 6)
FIG. 8 shows a sixth embodiment, in which the present invention shown in the first embodiment is applied to a serial multiplexing type power converter. In FIG. 8 , a part number 100 is a serial multiplex type power converter, 100u to 100v are U-phase to W-phase converters, 110u to 140u are inverter units that output low-voltage AC, and 112u is a converter that converts AC to DC. The reference numeral 113u denotes a smoothing capacitor, and 114u denotes a single-phase inverter constituted by a full bridge.
[0031]
In the power converter of the series multiplexing system by quadruple multiplexing as shown in FIG. 7, if a DC voltage detecting circuit is provided, four voltage detecting means are required for one phase, and the number of parts is increased. And lower reliability. However, by applying the present invention, it is possible to suppress the influence of the fluctuation of the DC voltage only by detecting the AC voltage without providing a DC voltage detector. Therefore, according to the present invention, it is not necessary to increase the number of voltage sensors, regardless of the number of stages, and the reliability of the device can be improved, regardless of the number of stages multiplexed.
[0032]
In the power conversion apparatus of the series multiplexing method using four multiplexes as shown in FIG. 8 , if a DC voltage detection circuit is to be provided, four voltage detection means are required for one phase, and the number of parts is increased, thereby complicating the apparatus. And lower reliability. However, by applying the present invention, it is possible to suppress the influence of the fluctuation of the DC voltage only by detecting the AC voltage without providing a DC voltage detector. Therefore, according to the present invention, it is not necessary to increase the number of voltage sensors, regardless of the number of stages, and the reliability of the device can be improved, regardless of the number of stages multiplexed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a power conversion device according to a first embodiment of the present invention.
FIG. 2 is a configuration diagram of a power converter according to a second embodiment of the present invention.
FIG. 3 is a configuration diagram illustrating an operation of a second exemplary embodiment of the present invention.
FIG. 4 is a configuration diagram of a power conversion device according to a third embodiment of the present invention.
FIG. 5 is a configuration diagram for explaining the operation of the third embodiment of the present invention.
FIG. 6 is a configuration diagram illustrating the operation of the fourth embodiment of the present invention.
FIG. 7 is a configuration diagram for explaining the operation of the fifth embodiment of the present invention.
FIG. 8 is a configuration diagram illustrating the operation of a sixth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... AC power supply, 2 ... AC / DC converter, 3 ... Smoothing capacitor, 4 ... Orthogonal converter, 5 ... AC motor, 6 ... Output current detecting means, 7 ... Output voltage detecting means, 8 ... Output voltage command calculating means, 9 ··· Output voltage command correction means, 9a ··· DC voltage fluctuation detection means, 9b ··· Output voltage command correction means, 10 ··· Detection voltage correction means, 10a ··· First subtractor, 10b ··· Integrator, 10c ··· Second subtractor 10d: Integrator, 10e: Subtractor, 11: Output voltage command calculating means, 100: Serial multiplex power converter, 100u to 100w: U-phase to W-phase converter, 110u to 140u: Inverter unit, 112u: AC / DC Converter, 113u: smoothing capacitor, 114u: single-phase inverter.

Claims (3)

In a power converter comprising a DC power supply, a power converter for converting the DC power supply to an AC, and an output voltage command calculating means for giving an output voltage command value to the power converter, an output voltage of the power converter Output voltage detection means for detecting the voltage fluctuation of the DC power supply using the detection result of the output voltage detection means and the output voltage command value, and from the estimation result, the output voltage command value A power conversion device comprising output voltage command correction means for correcting. 2. The power converter according to claim 1, wherein a DC voltage fluctuation detecting unit that calculates a ratio between the output voltage detection value and the output voltage command value, and the output voltage command based on an output of the DC voltage fluctuation detecting unit. A power conversion device comprising an output voltage command correction means for correcting the power voltage. A power converter, comprising a plurality of power converters connected in series to form one power converter, comprising the output voltage command correction means according to claim 1 or 2.

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