JP7571631B2 - Power conversion device, control device, and control method - Google Patents

Description

The present invention relates to a power conversion device, a control device, and a control method.

Conventionally, in a power conversion device having an AC/DC converter section, the lower limit when adjusting the target value of the DC voltage of the AC/DC converter section is determined by the AC voltage on the input side. In this case, the conventional power conversion device sets the DC voltage target value so that the converted DC voltage is equal to or greater than the amplitude of the AC voltage, and so that an overcurrent of the input current does not occur.

Patent No. 6656341

However, when a power conversion device is used, the input AC voltage varies. Therefore, if the target value of the converted DC voltage is too high compared to the input AC voltage, power loss increases and power conversion efficiency decreases.

Therefore, in one aspect, the object of the present invention is to provide a power conversion device, a control device, and a control method that can perform power conversion at a desired target value of DC voltage according to the input voltage.

An embodiment according to the present invention is exemplified by the following power conversion device. In a first aspect, the power conversion device includes:
A power conversion device that adjusts power supplied to a load after converting an AC source to DC, comprising:
A reactance element connected in series to a path between the AC source and the load;
A capacitor provided in parallel with the load;
a switching element capable of short-circuiting and opening an AC voltage from the AC source via the reactance element;
A control unit that controls the switching element;
Equipped with
The control unit is
a zero-cross detection unit that detects the phase of the AC voltage from the AC source;
a means for inducing a substantially sinusoidal AC current in phase with the AC voltage by executing PWM control on the switching element in a half cycle in which the phase is positive or negative in the AC voltage, and charging the capacitor so that the terminal voltage of the capacitor approaches a charging target voltage;
a means for acquiring a duty ratio in the PWM control in a phase in which the AC voltage is in the vicinity of a positive or negative peak;
and means for decreasing a charging target voltage of the capacitor from a current value when the duty ratio is greater than a first reference value, and for increasing a charging target voltage of the capacitor from a current value when the duty ratio is smaller than a second reference value that is smaller than the first reference value.

Here, the zero-crossing detection unit detects the timing when the AC voltage input to the power conversion device becomes zero. Moreover, PWM stands for pulse width modulation. The duty ratio means the ratio of the on period to the total period of the on and off periods in PWM. Moreover, the on period means the period of high potential in PWM, and the off period means the period of low potential in PWM.

This power conversion device reduces the charging target voltage of the capacitor from the current value when the duty ratio is greater than a first reference value, and increases the charging target voltage of the capacitor from the current value when the duty ratio is smaller than a second reference value that is smaller than the first reference value. Therefore, this power conversion device can dynamically and automatically set or adjust the charging target voltage of the capacitor based on the PWM duty ratio during power conversion. Also, if the terminal voltage of the capacitor (and the charging target voltage) is too high compared to the amplitude (peak value) of the AC voltage input to this power conversion device, the duty ratio becomes large near the positive or negative peak of the AC voltage. In this case, power loss increases and the efficiency of power conversion decreases. Therefore, in this case, the control unit can simply lower the charging target voltage of the capacitor.

On the other hand, if the terminal voltage of the capacitor (and the charging target voltage) is low and close to the amplitude (peak value) of the AC voltage input to this power conversion device, the duty ratio becomes small when the AC voltage is near the positive or negative peak. In this case, there is a risk that the peak value of the AC voltage will approach the terminal voltage of the capacitor. Therefore, in this case, the control unit can simply increase the charging target voltage of the capacitor. Through the above processing, this power conversion device can set the charging target voltage of the capacitor to an appropriate value and perform power conversion efficiently.

In a second aspect, the power converter includes:
a circuit including a full-wave rectifier circuit powered by the AC source or powered from the AC source via a full-wave rectifier circuit, and supplying power to the load;
the switching element is connected in parallel with the capacitor via an element having a rectifying function at a load-side contact of the reactance element,
The element having a rectifying function has a cathode connected to a first terminal on the high potential side of the capacitor, and an anode connected to a junction between the switching element and the load side of the reactance element.

That is, the control unit of this power conversion device can be applied to a power conversion device that includes a full-wave rectifier circuit, or a power conversion device that is powered from an AC source via a full-wave rectifier circuit. Also, a configuration in which a switching element is connected in parallel to a capacitor that is provided in parallel with a load via an element having a rectification function at the load-side contact of a reactance element is a type of chopper circuit. That is, the control unit of this power conversion device can perform full-wave rectification and can be applied to a configuration that includes a chopper circuit.

In a third aspect, the power conversion device includes a first circuit portion and a second circuit portion,
The first circuit portion comprises:
a first reactance element connected to a first terminal of the AC source;
a first rectifying element having an anode side connected to the first reactance element and a cathode side connected to the first terminal of the capacitor;
a first switching element connected in parallel to the capacitor via the first rectifying element;
The second circuit portion is
a second reactance element connected to a second terminal of the AC power supply; and a second rectifying element having an anode side connected to the second reactance element and a cathode side connected to the first terminal of the capacitor;
and a second switching element connected in parallel to the capacitor via the second rectifying element.

Here, the combination of the first circuit part and the second circuit part can be said to be a full-wave rectifier circuit. In addition, the first circuit part and the second circuit part can each be said to be a chopper circuit. Therefore, the control unit of this power conversion device can perform full-wave rectification and can be applied to a configuration that includes a chopper circuit.

In a fourth aspect, the power converter includes:
a reactance element connected to a first terminal of the AC source;
a full-wave rectifier circuit connected to the AC source via the reactance element,
The full-wave rectifier circuit includes:
a first switching element having a rectifying function, the anode side of which is connected to the reactance element and the cathode side of which is connected to a first terminal of the capacitor;
a second switching element having a rectifying function, the cathode side of which is connected to the first reactance element and the anode side of which is connected to a second terminal of the capacitor;
a first rectifying element having a cathode connected to the first terminal of the capacitor;
a second rectifying element having a cathode connected to the anode side of the first rectifying element and the second terminal of the AC source, and an anode side connected to the second terminal of the capacitor. The control unit of the power conversion device of the present invention can be applied to a power conversion device having the above configuration.

In a fifth aspect, this embodiment is specified by a control unit of the power conversion device. In a sixth aspect, this embodiment is specified by a control method of the control unit of the power conversion device.

At least one aspect of this embodiment provides a power conversion device, a control device, and a control method that can perform power conversion at a desired DC voltage target value according to the input voltage.

FIG. 1 is a diagram illustrating a three-phase AC power conversion device including a control device to which a control method according to an embodiment is applied. FIG. 2 is a diagram illustrating a process of the power conversion device according to the first embodiment. FIG. 3 is a diagram illustrating a specific configuration of the power conversion device according to the first embodiment. FIG. 4 is a circuit diagram of a power conversion device focusing on two of the three phases. FIG. 5 is a diagram illustrating the process of the control unit. FIG. 6 is a diagram illustrating a configuration of a power conversion device according to the second embodiment. FIG. 7 is a diagram illustrating a configuration of a power conversion device according to the third embodiment. FIG. 8 is a diagram illustrating a configuration of a power conversion device according to the fourth embodiment. FIG. 9 is a diagram illustrating a configuration of a power conversion device according to the fifth embodiment.

Hereinafter, embodiments (first to fifth embodiments) according to one aspect of the present invention will be described with reference to the drawings. However, the present embodiments described below are merely examples of the present invention in every respect. It goes without saying that various improvements and modifications can be made without departing from the scope of the present invention. In other words, when implementing the present invention, specific configurations according to the present embodiments may be appropriately adopted.

<Application Examples>
First, an example of a situation in which the present invention is applied will be described with reference to Fig. 1. Fig. 1 is a diagram illustrating a three-phase AC power conversion device 1 including a control circuit 100 to which a control method of the present embodiment is applied. The power conversion device 1 includes a filter circuit F inserted in a path from a three-phase AC power source,
The power conversion device 1 includes a boost reactor element L, switching elements TD1 to TD6, and a smoothing capacitor C1 connected in parallel to the load. The power conversion device 1 further includes an AC voltage sensor V1, an AC current sensor A1, a DC voltage sensor V2, and a control circuit 100.

In the example of FIG. 1, the AC voltage sensor V1 is connected to the power path closer to the three-phase AC power source. The AC voltage sensor V1 measures the input voltage of each phase from the three-phase AC power source and transmits the measured voltage to the control circuit 100.

The filter circuit F has, for example, a configuration in which a reactance element is connected in series to the power path of each phase, and a capacitor is connected in parallel to the power path. The boost reactor element L has, for example, a configuration in which a reactance element is connected in series to the power path of each phase.

The switching elements TD1 to TD6 are illustrated as being configured by combining a bipolar transistor and a diode. In FIG. 1, a diode is combined in the opposite direction to the direction from the collector to the emitter of the bipolar transistor. That is, the cathode of the diode is connected to the collector of the bipolar transistor, and the anode is connected to the emitter. However, the switching elements TD1 to TD6 may be unipolar transistors such as MOSFETs. When the switching elements TD1 to TD6 are MOSFETs or the like, a configuration similar to that of the switching element TD1 in FIG. 1 can be realized by utilizing a parasitic diode in the element. A Pulse Width Modulation (PWM) control signal (also called a PWM switching signal) is input from a control circuit to the control terminals (bases) of the switching elements TD1 to TD6.

The switching elements TD1 to TD6 full-wave rectify AC power that is shifted in phase by 120 degrees each to charge the capacitor C1. The capacitor C1 stores power from the current rectified by the switching elements TD1 to TD6, smooths it, and supplies DC power to the load. The switching elements TD1 to TD6 are an example of a three-phase full-wave rectifier circuit. The boost reactor element L and the switching elements TD1 to TD6 can be considered to be a circuit that integrates a full-wave rectifier circuit (bridge) and a power factor correction circuit, so they can also be considered to be a bridgeless power factor correction circuit.

The DC voltage sensor V2 measures the voltage across the capacitor C1 and notifies the control circuit 100. The load includes, for example, an AC load such as a motor. When the load includes an AC load, AC power is typically generated by a DC-AC conversion circuit such as an inverter and supplied to the AC load. The control circuit 100 (and the control circuits 100B to 100E described below) is an example of a control unit.

First Embodiment
Hereinafter, a power conversion device 1 according to one embodiment of the present invention (first embodiment) will be described with reference to Figs. 2 to 9 .

(Processing example)
FIG. 2 is a diagram illustrating the processing of the power conversion device 1 of the first embodiment. A part of a three-phase AC power conversion circuit is illustrated on the left side of FIG. 2. However, the circuit of FIG. 2 can also be said to be a bridgeless power factor correction circuit for single-phase AC. When the R-phase terminal is at a higher potential than the S-phase terminal, if the switch Q3 is turned on, a current flows from the R-phase terminal through the diode of the switch Q1 and the switch Q3 (on state), and energy is stored in each reactance element. In this state, if the switch Q3 is turned off, an electromotive force is generated in each reactance element in a direction that maintains the current, and a current flows to charge the capacitor C1. At this time, the energy of each reactance element is released. As in the above description, even if the switch Q2 is turned on and off, the capacitor C1 can be charged in the same way, although the path of the current that charges the capacitor C1 is different.
1 turns on and off the switch Q3 (or Q2) so that the AC current flowing through each phase of the three-phase AC changes as similarly as the AC voltage as possible. That is, the control circuit 100 turns on and off the switch Q3 (or Q2) so that an average current having the same phase as the AC voltage flows. To this end, the control circuit 100 keeps the switch Q3 (or Q2) on until a predetermined target current flows, and then repeats pulse width modulation to turn off the switch Q3 (or Q2).

This pulse width modulation causes a sawtooth reactor current to flow through the reactance element (also called a reactor), as shown in the waveform on the right side of Figure 2. Note that in the waveform in Figure 2, the section where the drain (collector) of switch Q3 is at high potential indicates that switch Q3 is off, and the section where the drain (collector) of switch Q3 is at low potential indicates that switch Q3 is on.

The above has been explained using an example where the R-phase terminal is at a higher potential than the S-phase terminal, but when the R-phase terminal is at a lower potential than the S-phase terminal, turning Q1 (or Q4) on and off allows charging of the capacitor C1. A detailed explanation will be omitted.
The control circuit 100 sets the duty ratio to a value closer to 1 as the difference between the charging target voltage of the capacitor (hereinafter referred to as the target DC voltage) and the input side AC voltage (amplitude, peak value) increases. This is because the higher the target DC voltage, the longer the period of time that current needs to flow. Therefore, the control circuit 100 can grasp to some extent the difference between the target DC voltage and the amplitude of the input side AC voltage by acquiring the duty ratio of the pulse width modulation. Therefore, in this embodiment, the control circuit 100 acquires the duty ratio of the pulse width modulation of the power factor correction circuit and adjusts the target DC voltage based on this.

In other words, if the duty ratio of the pulse width modulation is greater than a certain first reference value, the control circuit 100 determines that the difference between the target DC voltage and the amplitude (peak value) of the AC voltage on the input side is too large. In such a case, it is easy for power conversion efficiency to be wasted. Therefore, the control circuit 100 lowers the target DC voltage.

On the other hand, if the duty ratio of the pulse width modulation is smaller than a second reference value that is smaller than the first reference value, the control circuit 100 determines that the difference between the target DC voltage and the amplitude (peak value) of the AC voltage on the input side is too small. In such a case, it is predicted that the peak value of the AC voltage on the input side will exceed the voltage across the capacitor C1 on the output side, causing an overcurrent in the AC circuit and each element. Therefore, the control circuit 100 increases the target DC voltage.

That is, the control circuit 100 observes the On-Duty near the peak phase (desired section). A high On-Duty ratio means that the difference between the peak value of the AC voltage and the DC voltage is large. Therefore, if the switching On-Duty ratio is higher than the desired value (first reference value), the target DC voltage is lowered.

On the other hand, a low On-Duty ratio in the desired section means that the difference between the peak value of the AC voltage and the target DC voltage is small. Therefore, if the On-Duty ratio of the switching is lower than the desired value (second reference value), the target DC voltage is increased. Here, the second reference value is a value smaller than the first reference value.

By such control, the power conversion device 1 of the present embodiment can perform power factor correction at an appropriate target DC voltage. That is, the control circuit 100 can boost the DC voltage to the required limit while suppressing power supply harmonics regardless of the amplitude of the three-phase input voltage. As a result, the control circuit 100 suppresses harmonics in a circuit including AC/DC conversion while simultaneously achieving energy saving. That is, the control circuit 100 can reduce power loss in the power factor correction circuit and improve the efficiency of power conversion.

As shown in the waveform of Figure 2, in the pulse width modulation of the power factor correction circuit, the closer to the zero crossing and the beginning of the period, the larger the duty ratio. This is because the amplitude of the AC voltage is small at the beginning of the period, close to the zero crossing, and it takes time for the actual current value to reach the target current value. On the other hand, near the peak of the input AC voltage, the amplitude of the AC voltage is large and the duty ratio is small. In any case, it can be said that the control circuit 100 attempts to determine the relationship between the amplitude of the input AC voltage and the appropriate target DC voltage by the duty ratio of the PWM control near the peak of the input AC voltage.

(Control Circuit Configuration)
Fig. 3 is a diagram illustrating a specific configuration of the power conversion device 1 of the present embodiment. In Fig. 3, the configuration of the three-phase AC circuit is simplified, and the configuration of the control circuit 100 is illustrated in detail. The configuration of the three-phase AC circuit in Fig. 3 is the same as that in Fig. 1. In Fig. 3, an AC voltage sensor V1, an AC current sensor A1, and a DC voltage sensor V2 are also illustrated together with the control circuit 100.

As shown in FIG. 3, the control circuit 100 has a target DC voltage register 101, an adder 102, a comparator 103, a voltage regulator 104, a subtractor 105, a current regulator 106, a pulse width modulator 107, a duty ratio detection unit 108, a threshold register 109, an adjustment unit 110, a target DC voltage adjustment amount register 111, and a zero cross detection unit 112.

The target DC voltage register 101 stores an initial value of the target DC voltage. The initial value of the target DC voltage is set, for example, according to the specifications of the power conversion device 1. The initial value of the target DC voltage is also set, for example, when the power conversion device 1 is installed. The target DC voltage register 101 inputs the initial value of the target DC voltage to the adder 102.

The adder 102 adds (or subtracts) the adjustment amount input from the target DC voltage adjustment amount register 111 to the initial value of the target DC voltage to adjust the target DC voltage. If the adjustment amount is negative, the process of the adder 102 is subtraction. The adder 102 inputs the adjusted target DC voltage to the comparator 103. The comparator 103 subtracts the output DC voltage measured by the DC voltage sensor V2 from the adjusted target DC voltage, and inputs the difference value to the voltage regulator 104. Here, the output DC voltage is the voltage across the capacitor C1 illustrated in FIG. 1.

The voltage regulator 104 operates when the zero-crossing detector 112 outputs an enable signal. Here, the enable signal is enabled (asserted) in the positive half cycle (or negative half cycle) for each phase of the three-phase circuit. The enable signal of the voltage regulator 104 may be used to control whether or not to enable the operation of the pulse width modulator 107, instead of the voltage regulator 104.

For example, when the enable signal is asserted, the voltage regulator 104 calculates the target current value based on the difference between the target DC voltage and the output DC voltage, which is the calculation result of the comparator 103, and inputs it to the subtractor 105. The target current is a current that charges the capacitor C1 to reduce the difference between the target DC voltage and the output DC voltage, and is a current that is in phase with the AC voltage detected by the zero-cross detection unit 112. The subtractor 105 calculates the difference between the target current value and the AC current measurement value from the AC current sensor A1, and inputs it to the current regulator 106.

The current regulator 106 instructs the pulse width modulator 107 to turn on or off based on the difference between the target current value and the measured current value. That is, the current regulator 106 instructs the pulse width modulator 107 to output an on signal until the measured current value reaches the target current value. On the other hand, when the measured current value reaches the target current value, the current regulator 106 instructs the pulse width modulator 107 to output an off signal.

The pulse width modulator 107 generates a control signal (PWM switching signal) for pulse width modulation. The pulse width modulator 107 controls the control terminals (for example, the base terminals of each element in FIG. 1) of the switching elements TD1 to TD6 of the three-phase AC circuit by the generated PWM switching signal. Therefore, for example, the pulse width modulator 107 keeps the control terminals of the corresponding elements on until the current measurement value from the AC current sensor A1 reaches the target current value output from the voltage regulator 104. Then, when the current value from the AC current sensor A1 reaches the target current value output from the voltage regulator 104, the control terminals of the corresponding elements are turned off. By repeating such processing, the circuit from the voltage regulator 104 to the pulse width modulator 107 induces an approximately sinusoidal AC current so that the AC voltage of each input phase overlaps (is in phase with) the positive (or negative) half cycle as much as possible. As described above, the target DC voltage register 101, the adder 102, the comparator 103, the voltage regulator 104, the subtractor 105, the current regulator 106, and the pulse width modulator 107 execute PWM control of the switching elements in a half cycle in which the phase of the AC voltage is positive or negative. As a result, these circuits induce an approximately sinusoidal AC current that is in phase with the AC voltage, and can be said to be an example of a means for charging the terminal voltage of the capacitor C1 so that it approaches the charging target voltage (also called the target DC voltage).

Furthermore, the zero-cross detection unit 112 determines whether the current time is in a period near the voltage peak in the phase in which the zero-cross of the AC voltage measured by the AC voltage sensor V1 is detected. If the current time is in a period near the voltage peak, the zero-cross detection unit 112 outputs an enable signal to the duty ratio detection unit 108.

When the duty ratio detection unit 108 receives an enable signal from the zero-cross detection unit 112, it acquires the duty ratio from the pulse width modulator 107. The duty ratio detection unit 108 outputs the acquired duty ratio to the adjustment unit 110. The duty ratio detection unit 108 can be considered an example of a means for acquiring a duty ratio.

The adjustment unit 110 compares the input duty ratio with the duty ratio threshold value set in the threshold register 109, and calculates the adjustment amount of the target DC voltage according to the comparison result. The adjustment unit 110 sets the calculated adjustment amount of the target DC voltage in the target DC voltage adjustment amount register 111.

Here, a first threshold and a second threshold smaller than the first threshold are set in the threshold register 109. When the duty ratio input from the duty ratio detection unit 108 is higher than the first threshold, the adjustment unit 110 determines that the difference between the target DC voltage and the output DC voltage is sufficiently large. As a result, the adjustment unit 110 sets a negative adjustment amount in the target DC voltage adjustment amount register 111 so as to lower the target DC voltage.

On the other hand, when the duty ratio input from the duty ratio detection unit 108 is lower than the second threshold value which is smaller than the first threshold value, the adjustment unit 110 judges that the difference value between the target DC voltage and the output DC voltage is too small. As a result, the adjustment unit 110 sets a positive adjustment amount in the target DC voltage adjustment amount register 111 so as to increase the target DC voltage. The adjustment amount of the target DC voltage adjusted in this way is added to the initial value of the target DC voltage in the adder 102, and the target DC voltage is adjusted. The adjustment unit 110, the target DC voltage adjustment amount register 111, and the adder 102 can be said to be an example of a means for decreasing the charging target voltage of the capacitor C1 from the current value when the duty ratio is larger than the first reference value. Also, these can be said to be an example of a means for increasing the charging target voltage of the capacitor C1 from the current value when the duty ratio is smaller than a second reference value which is smaller than the first reference value.

In this embodiment and other embodiments described later, the value of the first threshold and the adjustment amount of the target DC voltage relative to the first threshold are determined experimentally or empirically. Also, the value of the second threshold and the adjustment amount of the target DC voltage relative to the second threshold are determined experimentally or empirically.

In the example of FIG. 2, the initial value of the target DC voltage is fixed in the target DC voltage register 101. However, the adjusted target DC voltage may be held in the target DC voltage register 101. In other words, the target DC voltage held in the target DC voltage register 101 may be changed for each process by the processing of the adjustment unit 110.

Incidentally, at least a part of any of the components of the control circuit 100 in FIG. 2 may be provided by a central processing unit (CPU) and a main storage device such as a memory.
That is, one or more CPUs may execute the processing of each unit or any part of the units in FIG. 2 by a computer program that is executable and deployed on memory.

The CPU is also called a processor. The CPU is not limited to a single processor, and may have a multi-processor configuration. A single CPU may have a multi-core configuration. The main memory stores computer programs executed by the CPU, data processed by the CPU, etc. The control circuit 100 may also include a digital signal processor (DSP), a graphics processing unit (GPU), etc., and the CPU may cooperate with these processors. The main memory may be a dynamic random access memory (DRAM), a static random access memory (SRAM), a read only memory (ROM), etc.

At least a part of each unit of the control circuit 100 is an Analog-to-Digital (ADI)
D) Converters, Digital-to-Analog (DA) converters, and other digital and analog circuits may be included.

(Configuration of power conversion circuit)
Fig. 4 is a circuit diagram of the power conversion device 1 focusing on two of the three phases in Fig. 1. For example, Fig. 4 illustrates the first and second phases. The power conversion device 1 converts AC power from an AC source into DC power, and then supplies the power to a load. As already mentioned, the load is an electric motor or the like. When the load is an AC machine, the power converted into DC power is converted back into AC power. Therefore, when the load is an AC machine, the load further includes a power conversion circuit such as an inverter.

As shown in FIG. 4, the power conversion device 1 has reactance elements L1 and L2 connected in series to a path between an AC power source and a load. The power conversion device 1 also has a capacitor C1 that is provided in parallel with the load. The power conversion device also includes switching elements TD11 to TD14 that can short-circuit and open the AC voltage from the AC source via the reactance elements, and a control circuit 100 that controls the switching elements TD11 to TD14.

In addition, each of the switching elements TD11 to TD14 has a structure in which a bipolar transistor and a diode are combined, as in FIG. 1. However, each of the switching elements TD11 to TD14 may be a combination of a MOSFET and a parasitic diode. In that case, the orientation of the parasitic diode is the same as that of the diode in FIG. 1, with the cathode of the parasitic diode connected to the drain of the MOSFET and the anode of the parasitic diode connected to the source of the MOSFET. The switching elements TD11 to TD14 also act as a full-wave rectifier circuit. Therefore, it can be said that the power conversion device 1 includes a full-wave rectifier circuit. The switching elements TD11 and TD13 have diodes, and therefore can be said to be elements having a rectification function. Therefore, it can be said that the switching elements TD12 and TD14 are connected in parallel to the capacitor C1 via the switching elements TD11 and TD13 having a rectification function. The cathodes of the switching elements TD11 and TD13 having a rectifying function are connected to the high potential terminal (first terminal) of the capacitor C1, and the anodes of the switching elements TD11 and TD13 having a rectifying function are connected to the contacts between the switching elements TD12 and TD14 and the load sides of the reactance elements L1 and L2.

Furthermore, reactance element L1 and switching elements TD11 and TD12 are an example of a first circuit part. Reactance element L2 and switching elements TD13 and TD14 are an example of a second circuit part.

(PWM operation of power conversion circuits)
Assuming that the AC voltage of each of the three phases is positive or negative, the basic operating principle of turning on and off multiple switching elements to pass a charging current through the capacitor C1 is the same as that of the single-phase circuit. However, in the case of three phases, the input voltage is generally converted to α-β-γ coordinates using a d-q coordinate conversion method, and then PWM modulation is performed to generate drive signals for three phases of switching elements (TD1 to TD6 in Figure 1). Note that this is widely disclosed as a control technology for three-phase PWM converters, so a detailed explanation will be omitted (for example, see "Software Control of Three-Phase PWM Inverters and Converters" by Takeshita Takaharu, Doctoral Dissertation of Engineering, Nagoya University, Report No. Otsu 3809, 1990 (July 6, 1990), pp. 145-174).

(Processing sequence of the control circuit 100)
FIG. 5 illustrates the process of the control circuit 100. The zero-cross detection unit 112 of the control circuit 100 monitors the zero-cross of the AC voltage of each phase, and when the zero-cross is detected, the control circuit 100 starts the process of FIG. 4. In this process, the zero-cross detection unit 112 of the control circuit 100 determines whether the AC voltage has entered a predetermined range near the peak after the zero-cross (S1). The predetermined range near the peak is determined experimentally or empirically. When the AC voltage enters the predetermined range near the peak, the zero-cross detection unit 112 sends an enable signal to the duty ratio detection unit 108. Then, the duty ratio detection unit 108 obtains the duty ratio Rd from the pulse width modulator 107 (S2).

Then, the adjustment unit 110 of the control circuit 100 judges whether the acquired duty ratio Rd is greater than the first reference value (S3). If the acquired duty ratio Rd is greater than the first reference value (YES in S3), the control circuit 100 uses the adder 102 to reduce the target DC voltage by a predetermined amount. The reason why the duty ratio Rd is large is because the amplitude (peak value) of the input AC voltage is far from the target DC voltage, that is, to increase the current to be charged to the capacitor C1. Conversely, this can also be said to mean that the target DC voltage is too high. In this case, the conversion efficiency of the power conversion device 1 decreases, so the control circuit 100 reduces the target DC voltage. Then, the control circuit 100 advances the control to S7.

On the other hand, if the determination in S3 indicates that the acquired duty ratio Rd is smaller than the first reference value (DS: YES), the adjustment unit 110 of the control circuit 100 determines whether the acquired duty ratio Rd is smaller than a second reference value (S5). Here, the second reference value is a value even smaller than the first reference value.

If the acquired duty ratio Rd is smaller than the second reference value (YES in S5), the control circuit 100 increases the target DC voltage by a predetermined amount using the adder 102. The reason why the duty ratio Rd is small is because the amplitude (peak value) of the input AC voltage is close to the target DC voltage. Conversely, this can also be said to mean that the target DC voltage is too low. In this case, in the power conversion device 1, the possibility that the amplitude (peak value) of the AC voltage will exceed the voltage across the capacitor C1 increases, so the control circuit 100 increases the target DC voltage. Then, the control circuit 100:
The control proceeds to S7.

Then, the control circuit 100 judges whether the processing has ended (S7). Whether the processing has ended is determined by whether the phase of the AC voltage has moved away from the peak vicinity, and is judged by the zero-cross detection unit 112. If the processing has not ended, the control circuit 100 returns control to S1. On the other hand, if the processing has ended, the control circuit 100 ends the processing. Then, when a zero-cross is detected in any other phase, the control circuit 100 executes the processing of FIG. 5.

(Effects of the embodiment)
As described above, according to this embodiment, the control circuit 100 can dynamically set an appropriate target DC voltage based on the duty ratio of the pulse width modulator 107 during power conversion of the power conversion device 1. Therefore, the target DC voltage does not need to be fixed to a set value at the time of shipment of the power conversion device 1 from the factory, at the time of installation at the shipping destination, or at the time of maintenance. Therefore, the power conversion device 1 having the control circuit 100 can flexibly and automatically set the target DC voltage according to the environment of the shipping destination, such as the AC voltage. As a result, it is possible to perform power conversion with high power conversion efficiency, i.e., low loss and power factor correction, according to the environment of the shipping destination, such as the AC voltage.

<Modification>
The control circuit 100 adjusts the target DC voltage by adding or subtracting the adjustment amount to the target DC voltage using the adder 102 in FIG. 3. However, the processing of the control circuit 100 is not limited to such processing. For example, the control circuit 100 may adjust the target DC voltage using a multiplier. In that case, a ratio is set in the adjustment amount register 111 of the target DC voltage. For example, when the duty ratio Rd is greater than the first reference value, a value smaller than 1 is set in the target DC voltage adjustment amount register 111, and the target DC voltage may be reduced at the ratio of this value. Also, when the duty ratio Rd is smaller than the second reference value, a value larger than 1 is set in the target DC voltage adjustment amount register 111, and the target DC voltage may be increased at the ratio of this value. In this case, the first reference value and the second reference value may be set experimentally and empirically.

<Other embodiments>
In the above embodiment, the control circuit 100 of the power conversion device 1 sets a target DC voltage for the power factor correction circuit exemplified in Fig. 1, Fig. 2, or Fig. 4. However, the configuration of the power conversion device 1 is not limited to the power factor correction circuit exemplified in Fig. 1 or Fig. 4.

FIG. 6 is a diagram illustrating the configuration of a power conversion device 1B according to a second embodiment. The power conversion device 1B includes a full-wave rectifier circuit that is fed from an AC power source. The full-wave rectifier circuit includes diodes D1 to D4. Diodes D1 and D2 are connected in series, and diodes D3 and D4 are connected in series. One terminal of the AC power source is connected to the connection point between the anode of diode D1 and the cathode of diode D2. One terminal of the AC power source is connected to the connection point between the anode of diode D3 and the cathode of diode D4. The cathode of diode D1 and the cathode of diode D3 are connected to a reactance element L3 that constitutes a chopper circuit. The chopper circuit has a reactance element L3 that is connected in series to a path from the power source, a switching element QD1 that is connected in parallel to a path from the power source, and a diode D5 that is connected in series to a path from the power source. The chopper circuit also has a smoothing capacitor C1 that is connected in parallel to a path from the power source. Capacitor C1 smoothes the DC voltage and supplies the DC voltage to the load.

The diode D5 is an example of an element having a rectifying function. Therefore, the switching element QD1 is connected in parallel to the capacitor C1 via the diode D5 at the load side contact of the reactance element L3. The diode D5, which is an element having a rectifying function, has a cathode connected to the high potential side terminal (first terminal) of the capacitor C1 and an anode connected to the contact between the switching element QD2 and the load side of the reactance element L3.

In the power conversion device 1B, the control circuit 100B performs PWM by switching the switching element QD1. That is, the control circuit 100B induces an approximately sinusoidal AC current that is as in phase as possible with the AC voltage to the positive and negative half-frequency transformers from the AC power source that pass through the diodes D1 to D4, which are a full-wave rectifier circuit, thereby improving the power factor of the power input to the power conversion device 1B.

The control circuit 100B has the same configuration as the control circuit 100 in FIG. 3, except that the PWM switching signal PWM controls only one control terminal of the switching element QD1 (there is only one PWM control signal). Therefore, as in the case of FIG. 3, the control circuit 100B can set and adjust a target DC voltage, which is a target value of the DC voltage supplied to the load, by obtaining the duty ratio of the PWM control near the peak of the AC voltage. Note that the power conversion device 1D in FIG. 6 can be applied to both single-phase AC power sources and three-phase AC power sources.

Figure 7 is a diagram illustrating the configuration of a power conversion device 1C according to a third embodiment. The power conversion device 1C differs from the power conversion device 1B in Figure 6 in that a chopper circuit is provided in parallel with the path from the AC power source. That is, the first chopper circuit has a reactance element L3 connected in series with the path from the power source, a switching element QD1 connected in parallel with the path from the power source, and a diode D5 connected in series with the path from the power source. The second chopper circuit has a reactance element L4 connected in series with the path from the power source, a switching element QD2 connected in parallel with the path from the power source, and a diode D6 connected in series with the path from the power source. A smoothing capacitor C1 is connected in parallel with the path from the power source.

The processing of the power conversion device 1C is the same as that of the power conversion device 1B in FIG. 6, except that the two chopper circuits operate in parallel. That is, the control circuit 100C has the same configuration as the control circuit 100 in FIG. 3, except that the PWM switching signal PWM controls the two control terminals of the switching elements QD1 and QD2.

Therefore, the control circuit 100C in FIG. 7 PWM controls the switching elements QD1 and QD2 of the two chopper circuits in parallel. In this case, the input AC voltage is common, and the output DC voltage is also common, so the duty ratio of the PWM control is also common for the switching elements QD1 and QD2 of the two chopper circuits.

Diodes D5 and D6 are examples of elements having a rectifying function. Therefore, switching elements QD1 and QD2 are connected in parallel with capacitor C1 via diodes D5 and D6, which are elements having a rectifying function, at the load side contact of reactance elements L3 and L4. In addition, the cathode side of diodes D5 and D6, which are elements having a rectifying function, is connected to the high potential side terminal (first terminal) of capacitor C1. In addition, the anode side of diode D5 is connected to the contact between switching element QD1 and the load side of reactance element L3. The anode side of diode D6 is connected to the contact between switching element QD2 and the load side of reactance element L4.

Therefore, in the power conversion device 1C in Fig. 7, the control circuit 100C can set and adjust a target DC voltage, which is a target value of a DC voltage supplied to a load, by acquiring a duty ratio of PWM control near the peak of an AC voltage, similarly to the power conversion device 1B in Fig. 6. Note that the control circuit 100C of the power conversion device 1C controls the switching elements Q
The duty ratios of D1 and QD2 may be averaged and used to set the target DC voltage. The power conversion device 1D in Fig. 7 is applicable to both a single-phase AC power supply and a three-phase AC power supply.

Figure 8 is a diagram illustrating the configuration of a power conversion device 1D according to a fourth embodiment. The power conversion device 1D has a first circuit portion and a second circuit portion. The first circuit portion has a first reactance element L11 connected to a first terminal, which is one of the AC power sources. The first circuit portion also has a diode D11 having a first rectification function, the anode side of which is connected to the first reactance element L11 and the cathode side of which is connected to a first terminal on the positive side of the capacitor C1. The first circuit portion also has a first switching element QD11 connected in parallel to the capacitor C1 via the diode D11.

The second circuit portion also has a second reactance element L12 connected to the other second terminal of the AC power supply. The second circuit portion also has a diode D12 having a second rectification function, the anode side of which is connected to the second reactance element L12 and the cathode side of which is connected to the first terminal on the positive side of the capacitor C1. The second circuit portion also has a second switching element QD12 connected in parallel to the capacitor C1 via the diode D12.

The diodes D11 and D12 are examples of elements having a rectifying function. Therefore, the first switching element QD11 and the second switching element QD12 are connected in parallel to the capacitor C1 via the diodes D11 and D12 at the load side contacts of the first reactance element L11 and the second reactance element L12. The diodes D11 and D12, which are elements having a rectifying function, have their cathodes connected to the high potential side terminal (first terminal) of the capacitor C1. The anode side of the diode D11 is connected to the contact between the first switching element QD11 and the load side of the first reactance element L11. The anode side of the diode D12 is connected to the contact between the second switching element QD12 and the load side of the second reactance element L12.

The configuration of the power conversion device 1D is the same as that of the power conversion device 1 in FIG. 4, except that the switching elements TD11 and TD13 are replaced with diodes D11 and D12. Therefore, the control circuit 100D of the power conversion device 1D, like the control circuit 100 of the power conversion device 1, controls the first switching element QD11 to be turned on and off in the positive half-frequency converter of the AC voltage, and keeps the second switching element QD12 off. Also, the control circuit 100D keeps the first switching element QD11 off and controls the second switching element QD12 to be turned on and off in the negative half-frequency converter of the AC voltage. In this way, the control circuit 100D, with the same configuration as the control circuit 100, can set and adjust the target DC voltage, which is the target value of the DC voltage supplied to the load, by acquiring the duty ratio of the PWM control near the peak of the AC voltage.

The power conversion device 1 in FIG. 4 can be said to have a first circuit portion and a second circuit portion, similar to the power conversion device 1D in FIG. 8. Therefore, the power conversion device 1D in FIG. 8 can be applied to both a single-phase AC power source and a three-phase AC power source.

Figure 9 is a diagram illustrating the configuration of a power conversion device 1E according to a fifth embodiment. The power conversion device 1D includes a reactance element L20 connected to a first terminal of an AC source, and a full-wave rectifier circuit. This full-wave rectifier circuit has a first switching element QD21 with a rectifying function, the anode side of which is connected to the reactance element L20, and the cathode side of which is connected to a first terminal on the positive side of the capacitor C1. Here, the first switching element QD21 has a structure that combines, for example, a MOSFET and a parasitic diode.

The full-wave rectifier circuit also has a second switching element QD22 with a rectifying function, the cathode of which is connected to the reactance element L20 and the anode of which is connected to the second terminal of the capacitor. Here, the second switching element QD22 has a structure that combines, for example, a MOSFET and a parasitic diode.

This full-wave rectifier circuit also has a diode D21, which is a first rectifier element, whose cathode is connected to the first terminal on the positive side of the capacitor C1. This full-wave rectifier circuit also has a diode D22, which is a second rectifier element, whose cathode is connected to the anode side of the diode D21 and the second terminal of the AC power source, and whose anode is connected to the second terminal on the negative side of the capacitor C1.

The configuration of the power conversion device 1E in FIG. 9 is the same as that of the power conversion device 1 in FIG. 4, except that one of the reactance elements L1 and L2, L2, is removed, and the switching elements TD13 and TD14 are replaced with diodes 21 and 22.

Therefore, the control circuit 100E of the power conversion device 1E, like the control circuit 100 of the power conversion device 1, may keep the first switching element QD11 off and control the second switching element QD12 on and off in the positive half-frequency converter of the AC voltage. Also, the control circuit 100D may control the first switching element QD11 on and off and keep the second switching element QD12 off in the negative half-frequency converter of the AC voltage. In this way, the control circuit 100D, with the same configuration as the control circuit 100, can set and adjust the target DC voltage, which is the target value of the DC voltage supplied to the load, by acquiring the duty ratio of the PWM control near the peak of the AC voltage. Note that the power conversion device 1D of FIG. 9 can be applied to both single-phase AC power sources and three-phase AC power sources.

(Additional Note)
1. A power conversion device (1, 1B to 1E) that adjusts the power supplied to a load after converting an AC source to DC,
reactance elements (L1, L2, L3, L4, L11, L12, L20) connected in series to a path between the AC source and the load;
A capacitor (C1) provided in parallel with the load;
switching elements (TD1 to TD6, TD11 to TD14, QD1, QD2, QD11, QD12, QD21, QD22) capable of short-circuiting and opening an AC voltage from the AC source via the reactance element;
A control unit (100, 100B to 100E) for controlling the switching element;
Equipped with
The control unit (100, 100B to 100E)
A zero-cross detection unit (112) that detects the phase of the AC voltage from the AC source;
a means (101 to 106) for inducing a substantially sinusoidal AC current in phase with the AC voltage by executing PWM control on the switching element in a half cycle in which the AC voltage has a positive or negative phase, and for charging the capacitor so that the terminal voltage of the capacitor approaches a charging target voltage;
A means (108) for acquiring a duty ratio in the PWM control in a phase in which the AC voltage is near a positive or negative peak;
and means (110, 111, 102) for lowering a charging target voltage of the capacitor from a current value when the duty ratio is greater than a first reference value, and for increasing the charging target voltage of the capacitor from a current value when the duty ratio is smaller than a second reference value that is smaller than the first reference value.
2. The power conversion device is
a circuit including a full-wave rectifier circuit (TD11 to TD14, or QD21, QD22, D21, D22, or D11, QD11, D12, QD12) that is powered from the AC source, or a circuit that is powered from the AC source via a full-wave rectifier circuit (D1 to D4, or D11, D12, QD11, QD12) and supplies power to the load,
The switching elements (TD12, TD14, QD1, QD2, QD11, QD12) are connected in parallel with the capacitor (C1) via elements (TD11, TD13, D5, D6, D11, D12) having a rectifying function at the load side contacts of the reactance elements (L1, L2, L3, L4),
The power conversion device described in paragraph 1 above, wherein the elements (TD11, TD13, D5, D6, D11, D12) having the rectification function have their cathodes connected to the first terminal on the high potential side of the capacitor (C1) and their anodes connected to the contact points between the switching elements (TD12, TD14, QD1, QD2, QD11, QD12) and the load sides of the reactance elements (L1, L2, L3, L4, L11, L12).
3. The power conversion device has a first circuit portion and a second circuit portion,
The first circuit portion comprises:
a first reactance element (L1, L3, L11) connected to a first terminal of the AC source;
a first rectifying element (TD11, D5, D11) having an anode side connected to the first reactance element and a cathode side connected to the first terminal of the capacitor;
a first switching element (TD12, QD1, QD11) connected in parallel to the capacitor (C1) via the first rectifying element;
The second circuit portion is
a second reactance element (L2, L4, L12) connected to a second terminal of the AC power supply; and a second rectifying element (TD13, D6, D12) having an anode side connected to the second reactance element and a cathode side connected to the first terminal of the capacitor (C1);
The power conversion device described in claim 1 or 2, further comprising: a second switching element (TD14, QD2, QD12) connected in parallel to the capacitor via an element (TD13, D6, D12) having the second rectification function.
4. A reactance element (L20) connected to the first terminal of the AC source;
a full-wave rectifier circuit connected to the AC source via the reactance element (L20);
The full-wave rectifier circuit includes:
a first switching element (QD21) having a rectifying function, the anode side of which is connected to the reactance element (L20) and the cathode side of which is connected to a first terminal of the capacitor;
a second switching element (QD22) having a rectifying function, the cathode side of which is connected to the first reactance element and the anode side of which is connected to a second terminal of the capacitor;
a first rectifying element (D21) having a cathode connected to the first terminal of the capacitor;
The power conversion device described in claim 1, further comprising: a second rectifying element (D22) having a cathode side connected to the anode side of the first rectifying element (D21) and the second terminal of the AC source, and an anode side connected to the second terminal of the capacitor.
and a means for increasing a charging target voltage of the capacitor from a current value.
5. (Missing number)
6. A method for controlling a power conversion device (1, 1B to 1E) that adjusts power supplied to a load after converting an AC source into DC, comprising:
The power conversion device is
A reactance element (L1, L2) connected in series to a path between the AC source and the load
2, L3, L4, L11, L12, L20) and
A capacitor (C1) provided in parallel with the load;
switching elements (TD1 to TD6, TD11 to TD14, QD1, QD2, QD11, QD12, QD21, QD22) capable of short-circuiting and opening an AC voltage from the AC source via the reactance element;
Detecting the phase of an AC voltage from the AC source (S1);
Inducing a substantially sinusoidal AC current in phase with the AC voltage by executing PWM control on the switching element in a half cycle in which the phase is positive or negative in the AC voltage, and charging the capacitor so that the terminal voltage approaches a charging target voltage (101 to 106);
Obtaining a duty ratio in the PWM control in a phase in which the AC voltage is near a positive or negative peak (S2);
A control method for a power conversion device, comprising: reducing a charging target voltage of the capacitor from a current value when the duty ratio is greater than a first reference value (S4); and increasing the charging target voltage of the capacitor from the current value when the duty ratio is smaller than a second reference value that is smaller than the first reference value (S6).

1 Power conversion device 100, 100B, 100C, 100D, 100E Control device 101 Target DC voltage register 102 Adder/subtractor 103 Comparator 104 Voltage regulator 105 Subtractor 106 Voltage regulator 107 Pulse width modulator 108 Duty ratio detection unit 109 Duty ratio threshold register 110 Comparator 111 Target DC voltage adjustment amount register A1 AC current sensor C1 Capacitor D1, D2, D3, D4, D5, D6 Diode L1, L2, L3, L4, L11, L12, L20 Reactance element QD1, QD2, QD11, QD12, QD21, QD22 Switching element TD1, TD2, TD3, TD4, TD5, TD6 Switching element V1 AC voltage sensor V2 DC voltage sensor

Claims (6)

A power conversion device that adjusts power supplied to a load after converting an AC source to DC, comprising:
A reactance element connected in series to a path between the AC source and the load;
A capacitor provided in parallel with the load;
a switching element capable of short-circuiting and opening an AC voltage from the AC source via the reactance element;
A control unit that controls the switching element;
Equipped with
The control unit is
a zero-cross detection unit that detects the phase of the AC voltage from the AC source;
a means for inducing a substantially sinusoidal AC current in phase with the AC voltage by executing PWM control on the switching element in a half cycle in which the phase is positive or negative in the AC voltage, and charging the capacitor so that the terminal voltage of the capacitor approaches a charging target voltage;
a means for acquiring a duty ratio in the PWM control in a phase in which the AC voltage is in the vicinity of a positive or negative peak;
means for reducing a charging target voltage of the capacitor from a current value when the duty ratio is greater than a first reference value, and for increasing the charging target voltage of the capacitor from a current value when the duty ratio is smaller than a second reference value that is smaller than the first reference value. The power conversion device includes a full-wave rectifier circuit that is powered from the AC source, or is a circuit that is powered from the AC source via a full-wave rectifier circuit and supplies power to the load,
the switching element is connected in parallel with the capacitor via an element having a rectifying function at a load-side contact of the reactance element,
2. The power conversion device according to claim 1, wherein the element having the rectification function has a cathode side connected to a first terminal on the high potential side of the capacitor and an anode side connected to a contact between the switching element and the load side of the reactance element. The power conversion device has a first circuit portion and a second circuit portion,
The first circuit portion comprises:
a first reactance element connected to a first terminal of the AC source;
a first rectifying element having an anode side connected to the first reactance element and a cathode side connected to the first terminal of the capacitor;
a first switching element connected in parallel to the capacitor via the first rectifying element;
The second circuit portion is
a second reactance element connected to the second terminal of the AC source; and a second rectifying element having an anode connected to the second reactance element and a cathode connected to the first terminal of the capacitor;
3. The power conversion device according to claim 1, further comprising: a second switching element connected in parallel to the capacitor via the second rectifying element. a reactance element connected to a first terminal of the AC source;
a full-wave rectifier circuit connected to the AC source via the reactance element,
The full-wave rectifier circuit includes:
a first switching element having a rectifying function, the anode side of which is connected to the reactance element and the cathode side of which is connected to a first terminal of the capacitor;
a second switching element having a rectifying function, the cathode of which is connected to the reactance element and the anode of which is connected to a second terminal of the capacitor;
a first rectifying element having a cathode connected to the first terminal of the capacitor;
2. The power conversion device according to claim 1, further comprising: a second rectifying element having a cathode side connected to an anode side of the first rectifying element and a second terminal of the AC source, and an anode side connected to the second terminal of the capacitor. A control unit of a power conversion device that adjusts power supplied to a load after converting the power from an AC source to DC,
The power conversion device is
A reactance element connected in series to a path between the AC source and the load;
A capacitor provided in parallel with the load;
a switching element capable of short-circuiting and opening an AC voltage from the AC source via the reactance element;
A control unit that controls the switching element;
Equipped with
The control unit is
a zero-cross detection unit that detects the phase of the AC voltage from the AC source;
a means for inducing a substantially sinusoidal AC current in phase with the AC voltage by executing PWM control on the switching element in a half cycle in which the phase is positive or negative in the AC voltage, and charging the capacitor so that the terminal voltage of the capacitor approaches a charging target voltage;
a means for acquiring a duty ratio in the PWM control in a phase in which the AC voltage is in the vicinity of a positive or negative peak;
a means for reducing a charging target voltage of the capacitor from a current value when the duty ratio is greater than a first reference value, and for increasing the charging target voltage of the capacitor from a current value when the duty ratio is smaller than a second reference value that is smaller than the first reference value. A method for controlling a power conversion device that adjusts power supplied to a load after converting an AC source into a DC source, comprising the steps of:
The power conversion device is
A reactance element connected in series to a path between the AC source and the load;
A capacitor provided in parallel with the load;
a switching element capable of short-circuiting and opening an AC voltage from the AC source via the reactance element;
detecting a phase of an AC voltage from the AC source;
Inducing a substantially sinusoidal AC current having the same phase as the AC voltage by executing PWM control on the switching element in a half cycle in which the phase of the AC voltage is positive or negative, and charging the capacitor so that the terminal voltage of the capacitor approaches a charging target voltage;
Obtaining a duty ratio in the PWM control in a phase in which the AC voltage is near a positive or negative peak;
A control method for a power conversion device, comprising: reducing a charging target voltage of the capacitor from a current value when the duty ratio is greater than a first reference value; and increasing the charging target voltage of the capacitor from the current value when the duty ratio is smaller than a second reference value that is smaller than the first reference value.

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