JP2006340410A - Ac direct converter unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AC direct converter unit in which a short circuit of power can be prevented inexpensively while preventing increase in switching loss or deterioration in voltage utilization rate and output voltage control performance. <P>SOLUTION: The AC direct converter unit comprises an AC direct converter 3 such as a matrix converter for converting an AC power supply voltage directly into an AC voltage of arbitrary magnitude and frequency, an input filter connected to the power supply side of the AC direct converter 3 and having a reactor and a capacitor wherein the input filter 2A has a resistor 23 connected in series with a capacitor 22. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for preventing a power supply short circuit due to a resonance frequency component caused by an input filter in an AC direct conversion device including an AC direct converter and an input filter.

FIG. 4 shows a conventional technique of this type of AC direct conversion device, in which the input / output of the AC direct converter 3 is an example of three phases (input phase is R, S, T phase, output phase is U, V and W phases).
In FIG. 4, 1 is a three-phase AC power source, 2 is an input filter comprising a reactor 21 and a capacitor 22, 3 is an AC direct converter such as a matrix converter, and 11 is an input voltage from each phase v _r , v _s , v _t. An input voltage magnitude discrimination means for detecting the maximum voltage phase, the intermediate voltage phase, and the minimum voltage phase and discriminating the magnitude relation of the input voltage, 12 is inputted with a magnitude discrimination result, an input current command and an output voltage command, and an AC direct converter 3 is a PWM signal creation means for creating and outputting a PWM signal of the semiconductor switch constituting the circuit 3. As will be described later, since the AC direct converter 3 switches the semiconductor switch to be switched according to the magnitude relationship between the input voltages of the respective phases, the PWM signal generating means 12 requires the determination result by the input voltage magnitude determining means 11.
In FIG. 4, v _rs is the primary side R-phase to S-phase line voltage, v _rsc is the secondary side line voltage, and v _rc , v _sc , and v _tc are the capacitors 22 respectively. Each phase voltage on the secondary side of the input filter 2 with respect to the common connection point 22c is shown.

  As is well known, the AC direct converter 3 cuts out the input voltage into a strip shape to obtain the output voltage, so that the current flowing through the semiconductor switch of the AC direct converter 3 also becomes a strip shape. For this reason, the input filter 2 is provided on the power source side of the AC direct converter 3 as a harmonic suppression device so that a strip-shaped current does not flow in the system.

FIG. 5 shows an equivalent circuit of one phase output (U phase in the example of FIG. 5) of the matrix converter which is an example of the AC direct converter 3. Of the three-phase input voltages, the maximum voltage phase voltage is represented by v _max , the intermediate voltage phase voltage is represented by v _mid , and the minimum voltage phase voltage is represented by v _min , and S ₁ is connected to the maximum voltage phase. that bidirectional switch, S ₂ is bidirectional switch, S ₃ being connected to the intermediate voltage phase is bidirectional switch connected to a minimum voltage phase. These bidirectional switches S ₁ , S ₂ , and S ₃ include, for example, _two semiconductor switching elements S _1A , S _1B , S _2A , S _2B , S _3A , and S _3B such as IGBTs having reverse breakdown voltage performance. Connected to and configured.
Since the maximum voltage phase, the intermediate voltage phase, and the minimum voltage phase change from moment to moment, the relationship between each voltage phase and each phase (U, V, W phase) on the input side is not fixed.

In general, a matrix converter is a power converter that directly obtains an AC output from an AC power supply voltage without going through a large energy buffer such as an electrolytic capacitor, has a long life, saves space, and is capable of regenerating power. Therefore, it is possible to control the input current harmonics. As is apparent from FIG. 5, this matrix converter directly connects the input / output terminals via the semiconductor switching element so as to generate any one of the voltages v _max , v _mid , and v _{min at} the output terminal. It has become. Therefore, a desired output voltage can be obtained by controlling the pulse width for turning on / off each switching element. That is, in the matrix converter, a desired voltage is output by switching the input terminal voltage (maximum voltage, intermediate voltage, minimum voltage) appearing at the output terminal.

FIG. 6 shows an example of the output voltage of the matrix converter, which corresponds to, for example, the U-phase output voltage v _u of FIG.
The switching operation from v _max to v _mid or v _mid to v _min in FIG. 6 is generally called commutation. For _{example, v if max} performing commutation to _{v mid} from the two switching elements _{S 2A} of the two switching elements _{S 1A, S 1B} and the bidirectional switch _{S 2} of the bidirectional switch _{S 1} in FIG. 5, There is a method of switching S _2B at the same time, that is, a method of turning on the bidirectional switch S ₂ at the same time as turning off the bidirectional switch S ₁ .

However, in this case, when the bidirectional switch S ₁ and S ₂ are turned on at the same time when the bidirectional switch S ₁ is turned off, the power supply is short-circuited via the switching elements S _1A and S _2B . Overcurrent flows through the switching element.
On the other hand, if the timing of turning on the bidirectional switch S ₂ is delayed, that is, if the bidirectional switches S ₁ and S ₂ are turned off at the same time, the continuity of the output current cannot be maintained. Is released and an overvoltage is applied to the switching element. Therefore, in either case, the switching element may be damaged in the worst case.
In an AC direct converter such as a matrix converter, it is required to prevent the short circuit of the power source and the opening of the load end as described above.

In order to avoid a short circuit of the power supply or an opening of the load end, several commutation methods for controlling the timing for turning on / off each switching element have been known.
Below, 4 step commutation generally used among these commutation methods is explained. However, voltage commutation that performs commutation according to the state of the power supply voltage will be described here, and current commutation that performs commutation according to the state of the load current will be omitted.

FIG. 7 is a timing chart of the switching element showing the voltage commutation operation, in which “High” level is on and “Low” level is off. For example, when commutation is performed from v _max to v _mid , the two switching elements S _1A and S _1B in the bidirectional switch S ₁ are both on before the commutation starts, and ₂ in the bidirectional switch S ₂ . Each of the switching elements S _2A and S _2B is off.

In the voltage commutation, since the commutation is performed without depending on the polarity of the load current, the switching element _S2A is first turned on as shown in FIG. 7 in order to maintain the continuity of the load current.
Next, in order to prevent a short circuit of the power source, the switching element _S1A is turned off, and then the _S2B is turned on. And finally, the commutation operation from v _max to v _mid is completed by turning off the switching element S _1B .

That is, the order in which the switching elements are turned on and off is
(1) S _2A on (2) S _1A off (3) S _2B on (4) S _1B off. Note that the period (a) shown in FIG. 7 will be described later.

Here, FIG. 8 is a waveform diagram of the three-phase power supply voltages v _r , v _s , and v _t , and a portion surrounded by a circle in the figure is a point where each phase power supply voltage intersects, that is, between two intersecting phases. This shows the vicinity where the line voltage becomes zero.

In the circuit configuration as shown in FIG. 4, the input filter 2 is oscillated with a resonance frequency component determined from the values of the reactor 21 and the capacitor 22.
FIG. 9 is a waveform diagram showing an example of the line voltage, and v _rs shows the waveform of the R phase-S phase line voltage (line voltage on the primary side of the input filter 2) when there is no resonance, and v _rsc Shows a waveform of a voltage (a line voltage on the secondary side of the input filter 2) in which a resonance frequency component is superimposed on a line voltage between the R phase and the S phase. In addition, the vertical axis | shaft of FIG. 9 is the voltage value displayed by the unit method.
Here, consideration is given to a case where the S-phase voltage is maximum, the R-phase voltage is intermediate, and the T-phase voltage is minimum, and the R-phase voltage is maximum, the S-phase voltage is intermediate, and the T-phase voltage is minimum. To do.

Originally, the polarity of the line voltage v _rs is switched at the time point b in FIG. 9, that is, the magnitude relationship between the S-phase voltage and the R-phase voltage is switched. However, when the resonance frequency component is superimposed, the input filter Although the magnitude relationship between the S-phase voltage and the R-phase voltage is not switched on the primary side of 2, the magnitude relationship is switched on the secondary side of the input filter 2 (that is, the input side of the AC direct converter 3). There may be. A section I in FIG. 9 is a section where this phenomenon occurs.

In this case, when the input voltage magnitude determining means 11 in FIG. 4 performs commutation to the section I in a state where the S-phase voltage is determined to be maximum and the R-phase voltage is determined to be intermediate (v _r <v _s ), the section I Since v _rc > v _sc on the secondary side of the input filter 2, a short-circuit path is formed via the switching elements S _2A and S _1B when four-step commutation is performed in the order described with reference to FIG. (Section (a) in FIG. 7).
That is, in the section I in FIG. 9, the maximum voltage phase v _max and the intermediate voltage phase v _mid in FIG. 5 are switched, and in this state, the switching elements S _2A and S _1B are both turned on as shown in FIG. As a result, a power supply short-circuit path from the power supply 1 via the switching elements S _2A and S _1B is formed.
As a result, overcurrent flows through these switching elements S _2A and S _1B , and in the worst case, they are damaged.

A means for solving the above problem is disclosed in Non-Patent Document 1, for example.
FIG. 10 shows an output voltage waveform proposed by Non-Patent Document 1, and corresponds to FIG. 6 described above.
That is, in Non-Patent Document 1, a voltage is always generated by performing commutation through the minimum voltage phase without performing commutation directly between the maximum voltage phase and the intermediate voltage phase. In the case of commutation from the maximum voltage phase to the minimum voltage phase, the order in which the switching elements are turned on and off only needs to replace S _2A in FIG. 7 with S _3A and S _2B with S _3B .

In other words, the order in which the switching elements are turned on and off is
(1) S _3A on (2) S _1A off (3) S _3B on (4) S _1B off.
In this case, even if commutation from the maximum voltage phase to the minimum voltage phase is performed in the section I in FIG. 9, since v _rc and v _sc are higher than v _{tc of the} minimum voltage phase, a short circuit path is not formed, and the power supply There is no short circuit.

By the way, when the voltage is generated as shown in FIG. 6, the switching element of the intermediate phase performs switching in a state where a voltage of v _max −v _mid is applied at the time of commutation from the maximum phase to the intermediate phase. On the other hand, when the voltage generation pattern as shown in FIG. 10 is made by the method of Non-Patent Document 1, the voltage of v _max −v _min is applied to the switching element of the minimum phase when commutation from the maximum phase to the minimum phase occurs. Switching is performed in the applied state. That is, when the method of Non-Patent Document 1 is used, there is a problem that the switching loss increases because the voltage difference when the switching element is turned on and off is large.

Further, in order to increase the voltage utilization factor, an output voltage that does not use the minimum voltage phase may be required. In the method of Non-Patent Document 1, the minimum voltage phase is essential, and thus the voltage utilization factor decreases. There is also.
Further, when the switching element is turned on with the vibration component as shown in FIG. 9 superimposed on the input voltage of the AC direct converter 3, the input / output terminals of the AC direct converter are directly connected as described above. Therefore, the vibration component on the input side is superimposed on the output voltage, resulting in a decrease in output voltage control performance.

Patent Document 1 below discloses a method for preventing the influence of vibration components from appearing on the output side in a PWM converter. In this method, the vibration component is extracted by a high-pass filter, and the influence of the vibration component is canceled by subtracting the vibration component from the command value of the PWM converter output.
However, when the technique described in Patent Document 1 is applied to an AC direct converter, it is necessary to add input current detection means for detecting an input current, which causes an increase in cost. Further, since the vibration component has a relatively high frequency, a high-speed arithmetic device is required.

Jochen Mahlein, Jens Igney, Jorg Weigold, Michael Braun, and Olaf Simon, "Matrix Converter Commutation Strategies With and Without Explicit Input Voltage Sign Measurement", IEEE Transactions on Industrial Electronics, Vol.49, No.2, April, 2002, pp .407-414 JP-A-10-336896 ([0010] to [0017], FIG. 2 etc.)

As described above, in the output voltage generation method described in Non-Patent Document 1, it is possible to prevent a power supply short circuit even if a harmonic component such as a resonance frequency component is superimposed on the input voltage of the AC direct converter. However, this is a method to deal with by changing the generation pattern of the output voltage without attenuating the harmonic component, which causes an increase in switching loss, a decrease in voltage utilization rate, and a decrease in output voltage control performance. There is.
Further, when the prior art of Patent Document 1 is applied to an AC direct converter, there is a problem that input current detecting means and a high-speed arithmetic device are required, resulting in high costs.
Therefore, the present invention is intended to solve the above problems and provide an AC direct conversion device that is low in cost and excellent in harmonic suppression performance.

In order to solve the above-mentioned problems, the invention described in claim 1 is connected to an AC direct converter that directly converts an AC power supply voltage into an AC voltage having an arbitrary magnitude and frequency, and a power supply side of the AC direct converter. And an AC direct conversion device comprising an input filter having a reactor and a capacitor,
The input filter has a resistor connected in series to the capacitor.
In this case, the series circuit of the capacitor and the resistor is star-connected or delta-connected between the respective phase input terminals of the AC direct converter.

  According to a second aspect of the present invention, in the first aspect, another resistor is connected in parallel to the reactor.

  According to a third aspect of the present invention, in the first or second aspect, the present invention further comprises a magnitude discrimination means for discriminating the magnitude of the input voltage of the AC direct converter in order to create a drive pulse for the AC direct converter. The means determines the magnitude of the input voltage based on the voltage on the power supply side of the input filter.

  According to a fourth aspect of the present invention, in the first or second aspect, the size determination unit includes the size determination unit, and the size determination unit determines the magnitude of the input voltage based on the voltage on the AC direct converter side of the input filter. To do.

According to the present invention, the resonance frequency component is suppressed by using the resistance in the input filter, so that it is possible to prevent a power supply short circuit due to switching without significantly increasing the cost, and switching as in the prior art. It is possible to prevent an increase in loss, a decrease in voltage utilization rate, and a decrease in output voltage control performance.
Also, if the input voltage is taken in from the AC direct converter side of the input filter and the magnitude of the input voltage is discriminated, the magnitude discrimination based on the voltage including the vibration component is possible even when the resonance frequency component cannot be sufficiently suppressed. By performing this, it is possible to prevent a power supply short circuit.
Furthermore, the resonance phenomenon due to the inductance component and the capacitance component of the capacitor itself can be suppressed by the resistor, and in the event that a short circuit occurs via the bidirectional switch in the matrix converter, the short circuit current is limited by the resistor. It is possible.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, FIG. 1 is a configuration diagram of an AC direct conversion device according to the first embodiment of the present invention, and the same components as those in FIG. 4 are denoted by the same reference numerals.
Below, it demonstrates centering on a different part from FIG.

In FIG. 1, an input filter 2 </ b> A includes a reactor 10 connected between each phase terminal of the three-phase AC power source 1 and each phase input terminal of the AC direct converter 3, and an AC direct converter of these reactors 10. It is comprised from three series circuits which consist of the resistor 23 and the capacitor | condenser 22 connected to each one end (each phase input terminal of AC direct converter 3) of 3 side.
In this embodiment, the series circuit of the resistor 23 and the capacitor 22 is star-connected, but may be a delta connection.

  The resistors 23 connected in series between the reactor 21 and the capacitor 22 suppress the flow of the resonance frequency component current, so that the resonance frequency component does not appear at the input terminal of the AC direct converter 3. Therefore, since the resonance frequency component of the line voltage as shown in FIG. 9 is attenuated, the output voltage generation pattern is equivalent to the section I in FIG. 9 even if the intermediate voltage phase is interposed as shown in FIG. There is no possibility that the power source 1 is short-circuited during the 4-step commutation operation of FIG.

  That is, since the resonance frequency component can be suppressed, the magnitude relationship of the power supply voltage determined on the primary side of the input filter 2A can be directly applied to the magnitude relationship of the input voltage of the AC direct converter 3 on the secondary side of the input filter 2A. It will be. Therefore, it is possible to prevent a short circuit of the power supply due to switching in a state where the magnitude relationship is switched between the primary side and the secondary side of the input filter as in the conventional case.

Further, in this embodiment, since it is not necessary to commutate from the maximum voltage phase via the minimum voltage phase as shown in FIG. 10, it is possible to reduce switching loss and avoid a decrease in voltage utilization rate.
Furthermore, there is no fear that the resonance frequency component is superimposed on the output voltage via the AC direct converter 3, and it is necessary to use an input current detection means or a high-speed arithmetic unit to reduce the vibration component as in Patent Document 1. Therefore, the cost can be reduced.

Next, FIG. 2 is a block diagram showing a second embodiment of the present invention.
In this embodiment, an input filter 2B is configured by connecting resistors 24 in parallel to the reactor 21 in the first embodiment. Also in this embodiment, a series circuit of the resistor 23 and the capacitor 22 may be delta-connected.

In the present embodiment, since the resistor 24 is coupled with the resistor 23 to suppress the resonance frequency component, it is possible to prevent the resonance frequency component from appearing at the input terminal of the AC direct converter 3.
Therefore, the same effect as that of the first embodiment can be obtained, and the generated loss can be shared by the resistors 23 and 24.

Although not shown, by connecting the input terminal of the input voltage magnitude discrimination means 100 in FIGS. 1 and 2 to the secondary side of the input filter 2A or 2B, that is, the input terminal of the AC direct converter 3, the AC The magnitude relationship may be determined from the input voltage of the direct converter 3.
In this case, even if the vibration component cannot be sufficiently suppressed by the input filter 2A or 2B and the waveform as shown in FIG. 9 is obtained, the magnitude is discriminated from the voltage including the vibration component, and the same voltage is exchanged based on the result. Since the direct converter 3 cuts out, a power supply short circuit can be prevented and an output voltage can be generated as shown in FIG.

  In each of the above embodiments, there is an effect that the resonance phenomenon of the capacitor 22 itself due to the inductance component and the capacitance component of the capacitor can also be suppressed. In addition, in the unlikely event that a short circuit occurs via the bidirectional switch in the matrix converter, the short circuit current can be limited by the resistors 23 and 24.

In each of the above embodiments, for example, an AC direct converter 3 such as a matrix converter is assumed. However, the present invention shows a PWM rectifier _{31 including} a semiconductor switch S31 as shown in FIG. 3 as a third embodiment. and is composed of an inverter 32 of semiconductor switches S _32, it is also applicable to AC direct converters 3A without the energy buffer to the DC link section.

It is a block diagram which shows 1st Embodiment of this invention. It is a block diagram which shows 2nd Embodiment of this invention. It is a block diagram which shows the principal part of 3rd Embodiment of this invention. It is a block diagram which shows a prior art. It is an equivalent circuit diagram for one output of the matrix converter. It is an output voltage waveform diagram of a matrix converter. It is a timing chart which shows the operation | movement of the voltage commutation (4 step commutation) in FIG. It is a wave form diagram of a three-phase power supply voltage. It is a wave form diagram which shows an example of a line voltage. 6 is an output voltage waveform diagram of a matrix converter disclosed in Non-Patent Document 1. FIG.

Explanation of symbols

1: Three-phase AC power supply 2A, 2B: Input filter 3: AC direct converter 11: Input voltage magnitude discrimination means 12: PWM signal creation means 21: Reactor 22: Capacitor 22c: Common connection point 23, 24: Resistance

Claims (4)

AC direct converter comprising an AC direct converter for directly converting an AC power supply voltage into an AC voltage of an arbitrary magnitude and frequency, and an input filter connected to the power supply side of the AC direct converter and having a reactor and a capacitor. In the conversion device,
The input filter is
An AC direct conversion device comprising a resistor connected in series to the capacitor. In the AC direct conversion device according to claim 1,
An AC direct conversion device characterized in that another resistor is connected in parallel to the reactor. In the AC direct conversion device according to claim 1 or 2,
A magnitude discrimination means for discriminating the magnitude of the input voltage of the AC direct converter in order to create a drive pulse of the AC direct converter,
The AC direct conversion device characterized in that the size discrimination means discriminates the size based on the voltage on the power source side of the input filter. In the AC direct conversion device according to claim 1 or 2,
A magnitude discrimination means for discriminating the magnitude of the input voltage of the AC direct converter to create a drive pulse of the AC direct converter,
The AC direct conversion device characterized in that the size determination means determines the size based on a voltage on the AC direct converter side of the input filter.

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