JP4506020B2 - Power converter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a power conversion device provided with an inverter circuit that converts a DC voltage into an AC voltage, and is an AC voltage that can be connected to a commercial power source by using a DC power source having a large output fluctuation such as a solar cell. The present invention relates to a power conversion device that generates
[0002]
[Prior art]
In recent years, it has become possible to interconnect a commercial power source and an AC voltage generated by a small-scale power generation facility. As a small-scale power generation facility, a DC power is generated by a solar cell that can be attached to a roof of a general house, etc., and this DC power is converted into an AC voltage by a power converter including an inverter circuit, and a commercial power source and system The structure to connect is beginning to spread.
[0003]
An example of this type of power converter is shown in FIG. The illustrated power conversion device 2 converts a DC-DC conversion circuit 5 that generates a DC voltage generated by the solar cell 1 and an output voltage of the DC-DC conversion circuit 5 into an AC voltage having a frequency equal to the frequency of the commercial power supply. And a filter circuit 7 that extracts a sine wave component, which is a fundamental wave component, from a rectangular wave AC voltage output from the inverter circuit 6. The DC-DC conversion circuit 5 and the inverter circuit 6 are each provided with switching elements Q1 to Q5, and the switching circuit Q1 to Q5 is turned on / off by a control circuit 8 mainly composed of a microcomputer. A sinusoidal AC voltage output from the filter circuit 7 is connected to the commercial power supply AC (system interconnection) via a disconnect switch (relay) 10. That is, the power converter 2 outputs an AC voltage through the disconnect switch 10 and supplies the output AC voltage to the load 4 in a grid connection with the commercial power supply AC.
[0004]
As described above, in order to link the output of the power conversion device 2 with the commercial power supply AC, it is necessary to manage the output quality of the power conversion device 2 so as not to affect the quality of the commercial power supply AC. In particular, it is essential to manage the output frequency and waveform symmetry of the power converter 2 (that is, the presence or absence of a DC component). Therefore, a current detection resistor Rd is inserted between the filter circuit 7 and the disconnect switch 10, and the control circuit 8 monitors the voltage across the resistor Rd to control the output quality of the power converter 2. In the control circuit 8, the DC-DC conversion circuit 5 and the inverter circuit 6 are feedback-controlled so that the output of the power converter 2 does not affect the quality of the commercial power supply AC. Here, the output voltage of the resistor Rd is passed through the low-pass filter 12 that removes the AC component through the insulation amplifier 11, and the DC component is extracted.
[0005]
The configuration of each part will be described more specifically. In this type of application, the output voltage of the solar cell 1 that is the power source of the DC-DC conversion circuit 5 generally varies in the range of 0 to 300 V depending on the amount of solar radiation. On the other hand, a voltage corresponding to the peak voltage of the commercial power supply is necessary for grid connection with the commercial power supply AC, which is about 280 V in the illustrated example. Therefore, when the output voltage of the solar cell 1 is 150 V or more, it is designed to be interconnected with the commercial power supply AC, and the switching element Q1 of the DC-DC conversion circuit 5 is set according to the output voltage of the solar cell 1. The voltage is boosted so as to obtain a voltage about the peak voltage of the commercial power supply AC. The DC-DC conversion circuit 5 includes a series circuit of a reactor L1 and a switching element Q1 connected between both ends of the solar cell 1, and a series circuit of a diode D1 and a smoothing capacitor C1 is connected to the switching element Q1. It has the structure connected in parallel. The DC-DC conversion circuit 5 having this configuration is known as a step-up chopper circuit, and the on / off of the switching element Q1 is controlled by the control circuit 8 at a high frequency. The output voltage of the DC-DC conversion circuit 5 is monitored by the control circuit 8, and the on-duty of the switching element Q1 is controlled by the control circuit 8 so that the output voltage is maintained at a constant voltage (the peak voltage of the commercial power supply AC). .
[0006]
On the other hand, the inverter circuit 6 is a so-called full-bridge type inverter circuit including a bridge circuit in which arms each having two switching elements Q2 to Q5 connected in series are connected in parallel. It is taken out from the connection point of the switching elements Q2, Q4, Q3, and Q5 that constitute it. In addition, the switching elements Q2 to Q5 constituting the inverter circuit 6 are alternately turned on / off by the switching elements Q2, Q4, Q3, Q5 constituting each arm, and the switching elements Q2, Q5 are simultaneously turned on, The switching elements Q3 and Q4 are controlled to be turned on simultaneously. Specifically, as shown in FIG. 9 (a), the control circuit 8 generates a triangular wave Vs as a reference signal, and compares the command value Ve changing in a sine wave shape with the triangular wave Vs to obtain a triangular wave Vs. ) As shown in (c), pulse trains SQ2 to SQ5 whose pulse widths change with time are generated, and on / off of the switching elements Q2 to Q5 is controlled by the pulse trains SQ2 to SQ5. As shown in the figure, the pulse trains SQ2 and SQ5 and the pulse trains SQ3 and SQ4 are turned on and off. That is, an output in which the pulse width is modulated in a sine wave shape by the PWM control of the switching elements Q2 to Q5 of the inverter circuit 6 is obtained. If the output of the inverter circuit 6 obtained in this way is passed through the filter circuit 7, the fundamental wave component is extracted and a sine wave voltage waveform is obtained. The filter circuit 7 includes two reactors L2 and L3 each having one end connected to each output terminal of the inverter circuit 6, and a capacitor C2 connected between the other ends of the reactors L2 and L3.
[0007]
The resistor Rd is provided for monitoring the output current of the inverter circuit 6 as described above. The voltage across the resistor Rd is input to the low-pass filter 12 via the insulation amplifier 11, and the low-pass filter 12 removes the AC component. That is, the output of the low-pass filter 12 becomes a DC component of the output of the inverter circuit 6. The output of the low-pass filter 12 is input to the control circuit 8, and the control circuit 8 determines the switching elements Q2 to Q5 according to the output from the low-pass filter 12 (that is, according to the amount of the DC component of the output of the inverter circuit 6). The signal for controlling on / off is adjusted to adjust the output so as to reduce the direct current component in the output of the inverter circuit 6 or to stop the output of the inverter circuit 6. If this configuration is adopted, the DC component of the output of the inverter circuit 6 can be detected as an analog quantity, so that the inverter circuit 6 can be controlled with high accuracy.
[0008]
Further, as a technique for detecting the DC component in the output of the inverter circuit 6, in addition to the configuration in which the insulation amplifier 11 and the low-pass filter 12 are combined as shown in FIG. 7, the voltage across the resistor Rd as shown in FIG. Is input to the low-pass filter 12 to remove the AC component, and the comparator 13 compares it with a threshold value defined in advance, thereby binarizing the presence or absence of the DC component, and then via the photocoupler 14 to the control circuit A configuration in which binary information is input to 8 is also known.
[0009]
[Problems to be solved by the invention]
By the way, in the configuration described above, the output side of the inverter circuit 6 is a voltage that is significantly higher than the power supply voltage of the control circuit 8, and the resistor Rd is used to detect the DC component contained in the output current of the inverter circuit 6. Therefore, it is necessary to insulate the resistor Rd provided on the output side of the inverter circuit 6 from the control circuit 8 that controls the inverter circuit 6. Therefore, in the configuration described above, the insulation amplifier 11 or the photocoupler 14 is provided to insulate the output of the inverter circuit 6 from the control circuit 8.
[0010]
In the configuration shown in FIG. 7, since the DC component of the output of the inverter circuit 6 can be input as an analog quantity to the control circuit 8, feedback control can be accurately performed so that the DC component does not increase in the output of the inverter circuit 6. However, a relatively expensive insulation amplifier 11 is required, and the insulation amplifier 11 has a problem that the response is generally slow.
[0011]
On the other hand, in the configuration shown in FIG. 8, since the photocoupler 14 is used for insulation, the price is low and the response is excellent. However, only binary information is given to the control circuit 8, and the DC component is Since it only determines whether it is less than or equal to the threshold value or exceeds the threshold value, there is a problem in that it is impossible to perform accurate control such as suppressing an increase in the DC component by appropriately controlling the inverter circuit 6 according to the amount of the DC component. There is. Although it is possible to transmit the analog quantity using the photocoupler 14, since the variation is large and an adjustment means for adjusting the input / output relationship of the photocoupler 14 is separately required, the configuration shown in FIG. It is not appropriate to use the photocoupler 14 in place of the insulation amplifier 11.
[0012]
The present invention has been made in view of the above reasons, and its purpose is to detect the DC component of the output of the inverter circuit and perform feedback control of the inverter circuit, so that the output between the inverter circuit and the control circuit is connected. Power conversion that enables highly accurate feedback control to reduce the DC component of the output of the inverter circuit by detecting the amount of DC component while adopting a configuration that uses a relatively inexpensive photocoupler for insulation To provide an apparatus.
[0013]
[Means for Solving the Problems]
The invention according to claim 1 includes at least one set of a series circuit of two switching elements, an inverter circuit that outputs a DC voltage to the series circuit of the switching elements and outputs an AC voltage, and controls an on period of each switching element. A control circuit for controlling the power in the positive polarity period and the negative polarity period of the AC voltage output from the inverter circuit, a current detection resistor inserted in a path through which the output current of the inverter circuit flows, and A zero-cross detection circuit that outputs a binary signal whose signal value is inverted at each zero-cross point of the output current of the inverter circuit detected as a voltage across the resistor, and an output of the inverter circuit interposed between the zero-cross detection circuit and the control circuit a photocoupler for insulating the side and a control circuit, and a current transformer for detecting an output current of the separate inverter circuit and the resistor, The control circuit, in the percentage of the DC component obtained from the time difference of two signal values of zero Rokurosu detection circuit, which corresponds to the absolute value of the DC component at the output of the inverter circuit by multiplying the output current detected by current transformer The value is obtained, and the on period of the switching element of the inverter circuit is feedback-controlled so that the value becomes zero . According to this configuration, since the time difference between the two signal values in the binary signal in which the polarity of the output current is binarized is obtained, the insulation between the output side of the inverter circuit and the control circuit can be performed by the photocoupler. It is possible to provide a small and inexpensive. In addition, since the direct current component is detected in about one cycle of the alternating current output from the inverter circuit, a relatively good response can be obtained.
[0014]
Further, a value corresponding to the absolute value of the DC component in the output current of the inverter circuit is obtained by using the value of the output current of the inverter circuit detected by the current transformer and the time difference reflecting the DC component in the output current of the inverter circuit. from the output control of the inverter circuit it can be performed more accurately, resulting in leading to improved responsiveness in the feedback control.
[0015]
According to a second aspect of the present invention, in the first aspect of the invention, the output current of the inverter circuit detected by the current measuring unit and the time difference obtained by the control circuit are associated with the ON period of the switching element of the inverter circuit. A data table is provided in the control circuit. According to this configuration, since the ON period of the switching element is determined using the data table, the responsiveness is as much as the processing by the program becomes unnecessary as compared with the case of calculating the ON period from the output current and the time difference. Will be improved.
[0016]
According to a third aspect of the present invention, in the first or second aspect of the present invention, the cutoff frequency is set sufficiently lower than the frequency of the alternating current output from the inverter circuit, and the ratio of the direct current component to the alternating current component is the resistance. A low-pass filter is inserted between the resistor and the zero-cross detection circuit so as to be larger than the ratio at the both-end voltage. According to this configuration, since the ratio of the direct current component to the peak value is increased by extracting the low frequency component of the output current of the inverter circuit, the time difference of the binary signal is emphasized, resulting in the direct current. The component detection accuracy is increased, and the accuracy of feedback control is further improved.
[0017]
The invention of claim 4 is the invention of claim 3 , wherein the low-pass filter is a secondary low-pass filter. According to this configuration, it is possible to configure a low-pass filter with a low cut-off frequency while having electronic components with relatively small constants, and it is possible to use general-purpose and inexpensive electronic components, as well as low-pass filters. The DC component can be extracted with a relatively small circuit without using multiple stages.
[0018]
According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, when the DC component of the output current of the inverter circuit detected as the voltage across the resistor exceeds a specified threshold, the output from the inverter circuit is stopped. An abnormality determination unit for instructing the control circuit is attached. According to this configuration, the output of the inverter circuit can be stopped when a sudden change occurs so that the response of the feedback control is not in time, and it can be used more safely.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
( Basic configuration )
As shown in FIG. 1, the basic configuration of the power conversion device 2 described in this example is the same as the conventional configuration shown in FIG. Therefore, hereinafter, differences from the conventional configuration shown in FIG. 7 will be mainly described, and components having the same functions as those of the conventional configuration shown in FIG.
[0020]
In this example , the voltage across the resistor Rd that detects the output current of the inverter circuit 6 is input to the zero-cross detection circuit 15, and the zero-cross detection circuit 15 outputs a binary signal corresponding to the polarity of the input voltage. For example, a binary signal is output such that it is H level when the input voltage is positive and L level when the input voltage is negative. Therefore, the zero cross detection circuit 15 can be easily realized by a comparator whose reference voltage is 0V. The output of the zero cross detection circuit 15 is input to the control circuit 8 after being insulated by the photocoupler 16.
[0021]
In the control circuit 8 of this example , the time difference between the H level period and the L level period is obtained for the binary signal output from the zero cross detection circuit 15, and it is determined that the DC component is larger as the time difference is larger. That is, when the output current of the inverter circuit 6 is a sine wave, the time interval at which the zero cross point appears is constant (positive and negative polarities are 50% each), and thus obtained as described above. In the output of the zero cross detection circuit 15, the H level period and the L level period are equal. On the other hand, if the zero-cross detection circuit 15 outputs H level when the input voltage is positive as described above, the H level period is longer than the L level period when a positive DC component is included. Conversely, when a negative DC component is included, the L level period becomes longer than the H level period. Therefore, it is possible to detect not only the amount of the DC component but also the polarity of the DC component. In the zero cross detection circuit 15, whether the output is set to H level or L level when the DC component of the input voltage is positive is appropriately set.
[0022]
In any case, the control circuit 8 controls on / off of the switching elements Q2 to Q5 of the inverter circuit 6 so that the time difference between the H level period and the L level period output from the zero cross detection circuit 15 is reduced. Adjust the pulse width (for example, when a positive DC component is included, the ON period of the switching elements Q2 to Q5 controlled during the positive output period is shortened, and a negative output is generated. The ON period of the switching elements Q2 to Q5 controlled in the period to be increased is increased). The time difference between the H level period and the L level period detected by the zero cross detection circuit 15 and the ratio for adjusting the on / off period of the switching elements Q2 to Q5 of the inverter circuit 6 are incorporated in the control circuit 8. It is desirable to associate with the specified data table.
[0023]
In the configuration of this example , the operation of the control circuit 8 is slightly different from the conventional configuration shown in FIG. 7, but since the control circuit 8 is configured by a microcomputer, the program of the control circuit 8 is required to realize the operation of this example. May be slightly changed from the conventional configuration. Other configurations and operations are the same as those of the conventional configuration shown in FIG.
[0024]
( First embodiment)
In the present embodiment, as shown in FIG. 2, a current transformer CT as a current measuring means is added to the basic configuration shown in FIG. 1, and the output current of the inverter circuit 6 detected by the current transformer CT is detected as zero crossing. This signal is given to the control circuit 8 together with the binary signal obtained by the circuit 15. That is, the time difference between the H level period and the L level period in the binary signal obtained by the zero cross detection circuit 15 is a measure of the DC component of the output of the inverter circuit 6, but the magnitude of the output current of the inverter circuit 6 is large. Does not reflect. Therefore, in this embodiment, the effective value of the output current of the inverter circuit 6 is detected by the current transformer CT, and the absolute value of the DC component is obtained by multiplying the ratio of the DC component obtained from the time difference by the output current obtained by the current transformer CT. The value corresponding to the value is obtained. The reason why the current transformer CT is provided in addition to the resistor Rd to detect the output current of the inverter circuit 6 is suitable for detecting a minute change in the DC component because the resistor Rd has a small error due to a temperature change. On the other hand, the current transformer CT is suitable for detecting a current that varies over a wide range, such as the output current of the inverter circuit 6. Here, the pulse width for controlling the switching elements Q2 to Q5 is obtained from the time difference between the H level period and the L level period obtained by the zero cross detection circuit 15 and the output current of the inverter circuit 6 detected by the current transformer CT. If the calculation is performed in the form of collation with a data table built in the control circuit 8, high-speed processing is possible.
[0025]
Although seeking effective value of the output current of the inverter circuit 6 in the present embodiment, Ru possible der be used as the peak value. Other configurations and operations are the same as the basic configuration .
[0026]
( Second Embodiment)
As shown in FIG. 3, this embodiment has a configuration similar to that of the first embodiment shown in FIG. 2, except that the voltage across the current detection resistor Rd is a cut-off frequency of 3 Hz. 17 is input to a zero cross detection circuit 15 configured to generate a pulse at a zero cross point. That is, because in the first embodiment using the time interval of the zero-crossing point in the output current of the inverter circuit 6, that seeking time difference times T1, T2 shown in FIG. 4 (a) to (T1-T2) Become. On the other hand, in this embodiment, since the zero cross point is extracted from the current after passing through the low pass filter 17, the zero cross point is increased in a state where the ratio of the DC component is increased by reducing the AC component through the low pass filter 17. Therefore, the time difference (T1′−T2 ′) is emphasized more like the times T1 ′ and T2 ′ shown in FIG. 4B, and the DC component can be detected with high resolution. It becomes possible.
[0027]
Specifically, the low-pass filter 17 used in the present embodiment employs the configuration shown in FIG. That is, one end of a series circuit of two resistors R1 and R2 is connected to the non-inverting input terminal of the operational amplifier OP, and a capacitor C3 is inserted between the connection point of the resistors R1 and R2 and the output terminal of the operational amplifier OP. The inverting input terminal and the output terminal of the operational amplifier OP are short-circuited, and the other end of the capacitor C4 whose one end is grounded is connected to the non-inverting input terminal of the operational amplifier OP. The resistors R1 and R2 have the same resistance value, and the capacitors C3 and C4 have the same capacitance. It is desirable to use film capacitors having excellent frequency characteristics and temperature characteristics for the capacitors C3 and C4.
[0028]
The low-pass filter having such a configuration is known as a second-order low-pass filter. Since the cutoff frequency decreases as the product of the resistors R1, R2 and the capacitors C3, C4 increases, the resistors R1, R2 and the capacitors C3, C4 It is possible to set the cut-off frequency low while using a relatively small constant. In other words, if capacitors C3 and C4 having a capacity of up to several μF are selected, general-purpose parts that are small and inexpensive can be used, and the resistors R1, R1 and C1 are set so that the cutoff frequency of the low-pass filter 17 is about 3 Hz. If the value of C2 is determined, any component can be used as a general-purpose component and can be configured with a small number of components. Other configurations and operations are the same as those of the first embodiment.
[0029]
( Third embodiment)
In this embodiment, as shown in FIG. 6, an abnormality determination unit 18 is added to the second embodiment. The abnormality determination unit 18 extracts only a direct current component from the voltage across the resistor Rd by a low-pass filter and compares it with an appropriately set threshold value, and outputs an abnormal signal when the direct current component exceeds the threshold value. In the illustrated example, the abnormality determination unit 18 is connected to the subsequent stage of the low-pass filter 17, and the DC component is easily extracted by extracting the DC component from the low-frequency component output from the low-pass filter 17. The abnormal signal is input to the control circuit 8 through the photocoupler 19. When the control circuit 8 receives the abnormal signal, the disconnection switch 10 is opened and the operation of the inverter circuit 6 is stopped. That is, when the DC component becomes abnormally large due to a failure of the switching elements Q2 to Q5 of the inverter circuit 6, an abnormal signal is generated in response to feedback control using the zero cross detection circuit 15 more quickly. Is stopped, and the outflow of the direct current component to the commercial power source AC is prevented. Other configurations and operations are the same as those in the second embodiment.
[0030]
In addition, it replaces with the abnormality determination part 18 in this embodiment, and the output of the zero cross detection circuit 15 is input into the control circuit 8, and the inverter circuit 6 is stopped when the time difference calculated | required from the output of the zero cross detection circuit 15 is abnormal. The same object can be achieved with the configuration. Also, when a data table is used when determining the pulse width for controlling the switching elements Q2 to Q5 from the time difference, an abnormality occurs when the value deviates from the range of the data table (when there is no value on the input side). It may be determined that the error has occurred.
[0031]
【The invention's effect】
According to the configuration of the first aspect of the invention , since the polarity of the output current is obtained as a time difference between the two signal values in the binary signal, the insulation between the output side of the inverter circuit and the control circuit is a photocoupler. And can be provided in a small and inexpensive manner. In addition, since the direct current component is detected in about one cycle of the alternating current output from the inverter circuit, a relatively good response can be obtained.
[0032]
Further, a value corresponding to the absolute value of the DC component in the output current of the inverter circuit is obtained by using the value of the output current of the inverter circuit detected by the current transformer and the time difference reflecting the DC component in the output current of the inverter circuit. from the output control of the inverter circuit it can be performed more accurately, resulting in leading to improved responsiveness in the feedback control.
[0033]
According to the configuration of the invention of claim 2, since determining the ON period of the switching element using the de Tateburu, program by processing unnecessary when compared to the case of performing the operation for obtaining the ON period from the output current time difference and As a result, the responsiveness is improved.
[0034]
According to the configuration of the invention of claim 3, since the percentage of the DC component to the peak value is increased by the low-frequency component of the output current of the inverter circuit is extracted, that the time difference between the binary signal is emphasized As a result, the detection accuracy of the DC component is increased and the accuracy of the feedback control is further improved.
[0035]
According to the configuration of the invention according to claim 4, while having a small electronic component having relatively constant it is possible to configure the low cut-off frequency low-pass filter, it can be used an inexpensive electronic components of the generic In addition, the DC component can be extracted with a relatively small circuit without using a multistage low-pass filter.
[0036]
According to the configuration of the invention of claim 5, it is possible to stop the output of the inverter circuit when the rapid change, such as the response of feedback control is not in time has occurred, it is possible to more safely use.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a basic configuration .
FIG. 2 is a circuit diagram showing a first embodiment of the present invention.
FIG. 3 is a circuit diagram showing a second embodiment of the present invention.
FIG. 4 is an operation explanatory view of the above.
FIG. 5 is a circuit diagram showing a low-pass filter used in the above .
FIG. 6 is a circuit diagram showing a third embodiment of the present invention.
FIG. 7 is a circuit diagram showing a conventional example.
FIG. 8 is a circuit diagram showing another conventional example.
FIG. 9 is an operation explanatory diagram showing a conventional example.
[Explanation of symbols]
6 Inverter circuit 8 Control circuit 15 Zero cross detection circuit 16 Photocoupler 17 Low pass filter 18 Abnormality judgment part Q2 to Q5 Switching element Rd resistance CT Current transformer

Claims (5)

An inverter circuit that has at least one set of a series circuit of two switching elements, a DC voltage is applied to the series circuit of the switching elements and outputs an AC voltage, and an output from the inverter circuit by controlling the ON period of each switching element A control circuit for controlling the power during the positive polarity period and the negative polarity period of the AC voltage to be detected, a current detection resistor inserted in a path through which the output current of the inverter circuit flows, and a voltage across the resistor. A zero-cross detection circuit that outputs a binary signal whose signal value is inverted at each zero-cross point of the output current of the inverter circuit, and an output side of the inverter circuit and the control circuit are isolated between the zero-cross detection circuit and the control circuit. a photocoupler that includes a current transformer for detecting an output current of the separate inverter circuit and the resistor, the control circuit is zero To the percentage of the DC component obtained from the time difference of two signal values of loss detection circuit obtains a value corresponding to the absolute value of the DC component at the output of the inverter circuit by multiplying the output current detected by current transformer, the value An on-period of the switching element of the inverter circuit is feedback-controlled so as to make zero . The control circuit is provided with a data table in which an output current of the inverter circuit detected by the current measuring unit and the time difference obtained by the control circuit are associated with an ON period of a switching element of the inverter circuit. The power conversion device according to claim 1. A low-pass filter that is set to a cut-off frequency sufficiently lower than the AC frequency output from the inverter circuit and that makes the ratio of the DC component to the AC component larger than the ratio at the voltage across the resistor, the resistor and the zero cross 3. The power conversion device according to claim 1 , wherein the power conversion device is inserted between the detection circuit and the detection circuit. The power converter according to claim 3, wherein the low-pass filter is a secondary low-pass filter . An abnormality determination unit is provided for instructing the control circuit to stop output when the direct current component of the output current of the inverter circuit detected as a voltage across the resistor exceeds a predetermined threshold value. power conversion equipment according to any one of claims 1 to 4.

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