JP2022139264A - Power conversion device, control apparatus, and control method - Google Patents

Abstract

To execute a power conversion with a target value of a desired DC voltage according to an input voltage.SOLUTION: A power conversion device comprises: a zero-cross detection unit that detects a phase of an AC voltage; means for inducing an AC current of an approximately sine wave so that its phase is the same as the phase of AC voltage by executing PWM control on a switching element in a half period in which the phase is positive or negative, and charging a terminal voltage of a capacitor so as to approach a charging target voltage; means 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 for reducing the charging target voltage of the capacitor from the current value when the duty ratio is larger than a first reference value, and increasing the charging target voltage of the capacitor when the duty ratio is smaller than a second reference value smaller than the first reference value.SELECTED DRAWING: Figure 3

Description

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

Conventionally, in a power converter having an AC/DC converter section, the lower limit value for 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 converter sets the DC voltage target value so that the DC voltage after conversion is equal to or greater than the amplitude of the AC voltage and the overcurrent of the input current does not occur.

Japanese Patent No. 6656341

However, when a power converter is used, the AC voltage on the input side varies. Therefore, if the target value of the DC voltage after conversion is too high with respect to the AC voltage on the input side, the power loss increases and the power conversion efficiency decreases.

Accordingly, in one aspect, an object of the present invention is to provide a power conversion device, a control device, and a control method capable of executing power conversion at a desired DC voltage target value according to the input voltage.

Embodiments according to the invention are exemplified by the following power converters. In a first aspect, this power conversion device includes:
A power conversion device that adjusts the power supplied to a load after converting from an AC source to DC,
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 shorting and opening an alternating voltage from the alternating current source via the reactance element;
a control unit that controls the switching element;
with
The control unit
a zero-cross detection unit that detects the phase of the AC voltage from the AC source;
A substantially sinusoidal alternating current is induced so as to have the same phase as the alternating voltage by performing PWM control on the switching element in a half cycle in which the phase of the alternating voltage is positive or negative, and the terminal voltage of the capacitor is reduced. means for charging to approach a charging target voltage;
means for obtaining a duty ratio in the PWM control in a phase where the AC voltage is near a positive or negative peak;
When the duty ratio is greater than a first reference value, the charging target voltage of the capacitor is decreased from the current value, and when the duty ratio is less than a second reference value which is less than the first reference value, the capacitor is charged. and means for increasing the target voltage from the current value.

Here, the zero-cross detector detects the timing when the AC voltage input to this power conversion device becomes zero. PWM means pulse width modulation. The duty ratio refers to the ratio of the ON period to the total period of the ON and OFF periods in PWM. Also, the ON period means a high potential period in PWM, and the OFF period means a low potential period in PWM.

When the duty ratio is greater than a first reference value, the power conversion device reduces the charging target voltage of the capacitor from the current value, and when the duty ratio is less than a second reference value that is lower than the first reference value. increases the capacitor charging target voltage from the current value. Therefore, the present power converter 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 cycle will be reduced near the positive or negative peak of the AC voltage. ratio increases. In this case, power loss increases and efficiency of power conversion decreases. Therefore, in this case, the control unit should reduce the charging target voltage of the capacitor.

On the other hand, when 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 converter, the duty ratio is close to the positive or negative peak of the AC voltage. become smaller. In this case, the peak value of the AC voltage may approach the terminal voltage of the capacitor. Therefore, in this case, the controller should increase the charging target voltage of the capacitor. By the above processing, the present power converter can set the charging target voltage of the capacitor to an appropriate value, and can efficiently perform power conversion.

In a second aspect, this power conversion device
A circuit that supplies power to the load, including a full-wave rectifier circuit powered by the AC source, or powered by the AC source via the full-wave rectifier circuit,
The switching element is connected in parallel with the capacitor via an element having a rectifying function at a contact on the load side of the reactance element,
The element having a rectifying function has a cathode side connected to a first terminal on a high potential side of the capacitor, and an anode side connected to a contact point between the switching element and the load side of the reactance element.

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

In a third aspect, this 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;
an element having a first rectifying function, the anode side of which is connected to the first reactance element and the cathode side of which is connected to the first terminal of the capacitor;
a first switching element connected in parallel to the capacitor via the element having the first rectifying function;
The second circuit portion is
a second reactance element connected to the second terminal of the AC power supply; and a second rectifying function having an anode side connected to the second reactance element and a cathode side connected to the first terminal of the capacitor. an element having
and a second switching element connected in parallel to the capacitor via the element having the second rectifying function.

Here, the combination of the first circuit portion and the second circuit portion can also be said to be a full-wave rectifier circuit. Also, the first circuit portion and the second circuit portion can be said to be chopper circuits, respectively. Therefore, the control unit of this power converter can perform full-wave rectification and can be applied to a configuration including a chopper circuit.

In a fourth aspect, this power conversion device
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 is
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 the 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 the second terminal of the capacitor;
a first rectifying element having a cathode connected to the first terminal of the capacitor;
an anode side of the first rectifying element and a second rectifying element having a cathode side connected to the second terminal of the AC source and having an anode side connected to the second terminal of the capacitor. The control unit of this power conversion device can be applied to a power conversion device including the above configuration.

In a fifth aspect, the present embodiment is specified by the controller of this power converter. Moreover, in the sixth aspect, the present embodiment is specified by the control method of the control unit of the power converter.

According to at least one aspect of the present embodiment, it is possible to provide a power conversion device, a control device, and a control method capable of executing power conversion with 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 processing of the power conversion device of the first embodiment. FIG. 3 is a diagram illustrating a specific configuration of the power conversion device of the first embodiment. FIG. 4 is a circuit diagram of a power converter focusing on two phases out of three phases. FIG. 5 is a diagram illustrating the processing of the control unit; FIG. 6 is a diagram illustrating the configuration of the power conversion device according to the second embodiment. FIG. 7 is a diagram illustrating the configuration of a power conversion device according to the third embodiment. FIG. 8 is a diagram illustrating the configuration of a power converter according to the fourth embodiment. FIG. 9 is a diagram illustrating the configuration of a power converter according to the fifth embodiment.

Hereinafter, embodiments (first embodiment to fifth embodiment) according to one aspect of the present invention will be described with reference to the drawings. However, this embodiment described below is merely an example of the present invention in every respect. It goes without saying that various modifications and variations can be made without departing from the scope of the invention. That is, in carrying out the present invention, a specific configuration according to the present embodiment may be employed as appropriate.

<Application example>
First, an example of a scene to which the present invention is applied will be described with reference to FIG. FIG. 1 is a diagram illustrating a three-phase AC power converter 1 including a control circuit 100 to which the control method of this embodiment is applied. The power conversion device 1 includes a filter circuit F inserted in a path from a three-phase AC power supply,
It has a boosting reactor element L, switching elements TD1 to TD6, and a smoothing capacitor C1 connected in parallel to the load. Further, the power converter 1 has 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 supply. AC voltage sensor V<b>1 measures the input voltage of each phase from the three-phase AC power supply and transmits it to control circuit 100 .

The filter circuit F has, for example, a configuration in which a reactance element is connected in series with the power path of each phase and a capacitor is connected in parallel with the power path. The step-up reactor element L has, for example, a structure 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 a combination of bipolar transistors and diodes. In FIG. 1, diodes are combined in the direction opposite 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 or the like in FIG. 1 can be realized by utilizing the parasitic diodes in the elements. A pulse width modulation (PWM) control signal (also referred to as a PWM switching signal) is input from a control circuit to control terminals (bases) of the switching elements TD1 to TD6.

The switching elements TD1 to TD6 perform full-wave rectification of the alternating current power whose phase is shifted by 120 degrees to charge the capacitor C1. Capacitor C1 stores and smoothes power from the currents rectified by switching elements TD1-TD6 and supplies DC power to the load. The switching elements TD1 to TD6 are an example of a full-wave rectifier circuit of a three-phase circuit. Note that the reactor element L for boosting and the switching elements TD1 to TD6 can be said to be a circuit in which a full-wave rectifier circuit (bridge) and a power factor correction circuit are integrated, so they can be said to be a bridgeless power factor correction circuit.

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

<First embodiment>
A power converter 1 according to an embodiment (first embodiment) of the present invention will be described below with reference to FIGS. 2 to 9. FIG.

(Processing example)
FIG. 2 is a diagram illustrating processing of the power conversion device 1 of the first embodiment. A portion of a three-phase AC power conversion circuit is illustrated on the left side of FIG. However, the circuit in FIG. 2 can also be said to be a bridgeless power factor correction circuit for single-phase alternating current. When the R-phase terminal is at a higher potential than the S-phase terminal and the switch Q3 is turned on, current flows from the R-phase terminal through the diode of the switch Q1 and the switch Q3 (on state), and energy is transferred to each reactance element. is accumulated. In this state, when the switch Q3 is turned off, an electromotive force is generated in each reactance element in the direction of maintaining the current, and a current flows to charge the capacitor C1. At this time, the energy of each reactance element is released. Similarly to the above description, even if the switch Q2 is turned on and off, the capacitor C1 can be charged in the same manner, although the current path for charging the capacitor C1 is different.
The control circuit 100 illustrated in FIG. 1 turns on and off the switch Q3 (or Q2) so that the alternating current flowing through each phase of the three-phase alternating current changes as much as the alternating voltage. 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. Therefore, 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).

Due to this pulse width modulation, a sawtooth-shaped reactor current flows through the reactance element (also called a reactor), as shown by the waveform on the right side of FIG. In the waveforms of FIG. 2, the section in which the drain (collector) of the switch Q3 is at a high potential indicates that the switch Q3 is off, and the section in which the drain (collector) of the switch Q3 is at a low potential indicates that the switch Q3 is on.

In the above, the case where the R-phase terminal is at a higher potential than the S-phase terminal has been described as an example. , can charge the capacitor C1. Detailed description is omitted.
The control circuit 100 sets the duty ratio to a value closer to 1 as the difference between the capacitor charging target voltage (hereinafter referred to as target DC voltage) and the AC voltage (amplitude, peak value) on the input side increases. This is because the higher the target DC voltage, the longer the current needs to flow. Therefore, by acquiring the duty ratio of the pulse width modulation, the control circuit 100 can grasp the difference in amplitude between the target DC voltage and the AC voltage on the input side to some extent. 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.

That is, when 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, power conversion efficiency is likely to be wasted. Therefore, the control circuit 100 reduces the target DC voltage.

On the other hand, when the duty ratio of the pulse width modulation is smaller than the second reference value which is smaller than the first reference value, the control circuit 100 detects that the difference between the target DC voltage and the amplitude (peak value) of the AC voltage on the input side is judged to be too small. In such a case, it is foreseen 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 interval). 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 switching On-Duty ratio 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.

With such control, the power converter 1 of the present embodiment can improve the power factor with an appropriate target DC voltage. That is, the control circuit 100 can boost the DC voltage to the necessary limit while suppressing power source harmonics regardless of the amplitude of the three-phase input voltage. As a result, the control circuit 100 suppresses harmonics of the circuit including AC/DC conversion and achieves both energy saving. That is, the control circuit 100 can reduce the power loss in the power factor correction circuit and improve the efficiency of power conversion.

As shown in the waveforms of FIG. 2, in the pulse width modulation of the power factor correction circuit, the duty ratio increases at the beginning of the period, which is closer to the zero crossing. This is because the amplitude of the AC voltage is small at the beginning of the period, which is close to 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 identify the relationship between the amplitude of the input AC voltage and the proper target DC voltage by the duty ratio of the PWM control near the peak of the input AC voltage.

(Configuration of control circuit)
FIG. 3 is a diagram illustrating a specific configuration of the power conversion device 1 of this 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 in FIG. 3 also illustrates the AC voltage sensor V1, the AC current sensor A1, and the DC voltage sensor V2 together with the control circuit 100. As shown in FIG.

As shown in FIG. 3, the control circuit 100 includes 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, and a duty ratio detector 108. , a threshold value 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 the initial value of the target DC voltage. The initial value of the target DC voltage is set according to the specifications of the power converter 1, for example. Also, the initial value of the target DC voltage is set, for example, when the power converter 1 is installed. Target DC voltage register 101 inputs the initial value of the target DC voltage to adder 102 .

The adder 102 adds (or subtracts) the adjustment amount input from the target DC voltage adjustment amount register 111 to (or subtracts) the initial value of the target DC voltage to adjust the target DC voltage. If the adjustment amount is negative, the processing of adder 102 is subtraction. Adder 102 inputs the adjusted target DC voltage to comparator 103 . Comparator 103 subtracts the output DC voltage measured by DC voltage sensor V 2 from the adjusted target DC voltage, and inputs the difference value to voltage regulator 104 . Here, the output DC voltage is the voltage across the capacitor C1 illustrated in FIG.

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

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

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 pulse width modulation control signal (PWM switching signal). The pulse width modulator 107 controls the control terminal (for example, the base terminal of each element in FIG. 1) of the corresponding element among the switching elements TD1 to TD6 of the three-phase AC circuit by the generated PWM switching signal. Thus, for example, the pulse width modulator 107 keeps the control terminal of the relevant element on until the current measurement from the alternating current sensor A1 reaches the target current value output from the voltage regulator 104 . Then, when the current value from the alternating current sensor A1 reaches the target current value output from the voltage regulator 104, the control terminal of the corresponding element is turned off. By repeating such processing, the circuit from the voltage regulator 104 to the pulse width modulator 107 is arranged so that the AC voltage of each phase of the input overlaps the positive (or negative) half cycle as much as possible (in-phase ), inducing an approximately sinusoidal alternating current. 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 are used for the positive or negative half of the AC voltage. PWM control is performed on the switching element periodically. As a result, these circuits induce a substantially sinusoidal AC current that is in phase with the AC voltage, and charge the terminal voltage of the capacitor C1 so as to approach the charging target voltage (also referred to as the target DC voltage). can be said to be an example of

Furthermore, the zero-cross detection unit 112 determines whether or not the current time is in the vicinity of the voltage peak in the phase in which the zero-cross of the AC voltage measured by the AC voltage sensor V1 is detected. Then, when the current time corresponds to a period near the voltage peak, the zero-cross detection unit 112 outputs an enable signal to the duty ratio detection unit 108 .

Duty ratio detector 108 acquires the duty ratio from pulse width modulator 107 upon receiving the enable signal from zero cross detector 112 . Duty ratio detection section 108 outputs the acquired duty ratio to adjustment section 110 . The duty ratio detection unit 108 can be said to be an example of means for acquiring the duty ratio.

The adjustment unit 110 compares the input duty ratio with the threshold of the duty ratio set in the threshold value register 109, and calculates the adjustment amount of the target DC voltage according to the comparison result. The adjustment unit 110 sets the calculated target DC voltage adjustment amount 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 duty ratio detection section 108 is higher than the first threshold, adjustment section 110 determines that the difference value 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, if the duty ratio input from the duty ratio detection unit 108 is lower than the second threshold, which is smaller than the first threshold, the adjustment unit 110 determines that the difference between the target DC voltage and the output DC voltage is too small. to decide. 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 thus adjusted is added to the initial value of the target DC voltage in the adder 102 to adjust the target DC voltage. The adjustment unit 110, the target DC voltage adjustment amount register 111, and the adder 102 can be said to be an example of means for reducing the charging target voltage of the capacitor C1 from the current value when the duty ratio is greater than the first reference value. Also, these can be said to be an example of means for increasing the charging target voltage of the capacitor C1 from the current value when the duty ratio is smaller than the 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 amount of adjustment of the target DC voltage with respect to the first threshold are determined experimentally or empirically. Also, the value of the second threshold and the amount of adjustment of the target DC voltage with respect 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 target DC voltage register 101 . However, the adjusted target DC voltage may be held in the target DC voltage register 101 . That is, the target DC voltage held in the target DC voltage register 101 may be changed for each process by the process of the adjusting section 110 .

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

A CPU is also called a processor. The CPU is not limited to a single processor, and may have a multiprocessor configuration. Also, a single CPU may have a multi-core configuration. The main memory stores computer programs executed by the CPU, data processed by the CPU, and the like. Also, the control circuit 100 may 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 Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), Read Only Memory (ROM), or the like.

In addition, at least part of any of the units of the control circuit 100 is analog-to-digital (A
D) may include converters, Digital-to-Analog (DA) converters, other digital circuits, and analog circuits.

(Configuration of power conversion circuit)
FIG. 4 is a circuit diagram of the power converter 1 focusing on two phases out of the three phases in FIG. For example, FIG. 4 illustrates a first phase and a second phase. The power converter 1 supplies power to a load after converting AC power from an AC source into DC. As already mentioned, the load is an electric motor or the like. If the load is an AC machine, the power converted to DC is converted back to AC. 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 converter 1 has reactance elements L1 and L2 connected in series to a path between an AC power supply and a load. The power converter 1 also has a capacitor C1 provided in parallel with the load. The power conversion device also includes switching elements TD11 to TD14 capable of short-circuiting and opening AC voltage from an AC source via reactance elements, and a control circuit 100 for controlling the switching elements TD11 to TD14.

Each of the switching elements TD11 to TD14 has a structure in which a bipolar transistor and a diode are combined, as in FIG. 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 such that the cathode of the parasitic diode is connected to the drain of the MOSFET and the anode of the parasitic diode is connected to the source of the MOSFET, similar to the diode in FIG. 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. Since the switching elements TD11 and TD13 have diodes, they can be said to be elements having a rectifying function. Therefore, it can be said that the switching elements TD12 and TD14 are connected in parallel with the capacitor C1 via the switching elements TD11 and TD13 having a rectifying function. The switching elements TD11 and TD13 having a rectifying function have their cathode sides connected to the high potential side terminal (first terminal) of the capacitor C1. The anode sides 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.

Also, the reactance element L1 and the switching elements TD11 and TD12 are examples of the first circuit portion. Reactance element L2 and switching elements TD13 and TD14 are an example of a second circuit portion.

(PWM operation of power conversion circuit)
Assuming that the AC voltage of each of the three phases is positive or negative, the basic principle of operation is the same as that of the above single-phase circuit by turning on and off a plurality of switching elements to flow the charging current to the capacitor C1. . However, in the case of three-phase, in general, the input voltage is converted to α-β-γ coordinates using the d-q coordinate conversion method, and then PWM-modulated to generate switching elements (TD1 to TD6) Generate drive signals for three phases. In addition, since it will be widely disclosed as a control technology for three-phase PWM converters, detailed explanations are omitted (for example, "Software Control of Three-Phase PWM Inverter/Converter" Takaharu Takeshita, Doctoral Dissertation of Engineering, Nagoya University, Report No. Otsu 3809, 1990 Fiscal year (July 6, 1990), see pages 145-174).

(Processing Sequence of Control Circuit 100)
FIG. 5 illustrates the processing of the control circuit 100. As shown in FIG. The zero-cross detector 112 of the control circuit 100 monitors the zero-cross of the AC voltage of each phase, and upon detecting the zero-cross, the control circuit 100 activates the process of FIG. In this process, the zero cross detector 112 of the control circuit 100 determines whether or not the AC voltage has entered a predetermined range near the peak after the zero cross (S1). Note that the predetermined range near the peak is determined experimentally or empirically. When the AC voltage enters a predetermined range near the peak, zero-cross detector 112 sends an enable signal to duty ratio detector 108 . Then, the duty ratio detector 108 acquires the duty ratio Rd from the pulse width modulator 107 (S2).

Then, the adjustment unit 110 of the control circuit 100 determines whether or not 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), control circuit 100 causes adder 102 to decrease the target DC voltage by a predetermined amount. The reason why the duty ratio Rd is large is that the amplitude (peak value) of the input AC voltage is far from the target DC voltage, that is, the current for charging the capacitor C1 is increased. Conversely, it can also be said 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 decreases the target DC voltage. Then, the control circuit 100 advances the control to S7.

On the other hand, if it is determined in S3 that the acquired duty ratio Rd is smaller than the first reference value (YES in DS), the adjustment unit 110 of the control circuit 100 determines that the acquired duty ratio Rd is smaller than the second reference value. It is determined whether or not it is smaller (S5). Here, the second reference value is a value smaller than the first reference value.

If the obtained duty ratio Rd is smaller than the second reference value (YES in S5), control circuit 100 causes adder 102 to increase the target DC voltage by a predetermined amount. The duty ratio Rd is small because the amplitude (peak value) of the input AC voltage is close to the target DC voltage. Conversely, it can also be said that the target DC voltage is too low. In this case, in the power converter 1, the amplitude (peak value) of the AC voltage is more likely to exceed the voltage across the capacitor C1, so the control circuit 100 increases the target DC voltage. Then, the control circuit 100
Control advances to S7.

Then, the control circuit 100 determines whether or not the process has ended (S7). Whether or not the process has ended depends on whether or not the phase of the AC voltage has moved away from the vicinity of the peak. Then, if it is not finished, the control circuit 100 returns the control to S1. On the other hand, in the case of termination, the control circuit 100 terminates the processing. Then, when the zero crossing is detected in any other phase, the control circuit 100 executes the processing of FIG.

(Effect of Embodiment)
As described above, according to the present 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 converter 1. . Therefore, the target DC voltage does not need to be fixed to the set value when the power conversion device 1 is shipped from the factory, installed at the shipping destination, or maintained. Therefore, the power converter 1 having the control circuit 100 can flexibly and automatically set the target DC voltage according to the environment such as the AC voltage of the shipping destination. As a result, power conversion including power factor improvement can be performed with high power conversion efficiency, ie, low loss, according to the environment such as AC voltage at the shipping destination.

<Modification>
The control circuit 100 adjusts the target DC voltage by adding or subtracting the amount of adjustment to the target DC voltage using the adder 102 of FIG. However, the processing of the control circuit 100 is not limited to such processing. For example, control circuit 100 may adjust the target DC voltage with a multiplier. In that case, a ratio is set in the target DC voltage adjustment amount register 111 . 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 is preferably decreased at the ratio of this value. Also, when the duty ratio Rd is smaller than the second reference value, a value greater than 1 is set in the target DC voltage adjustment amount register 111, and the target DC voltage is preferably increased at the ratio of this value. Also 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 the target DC voltage for the power factor correction circuit illustrated in FIG. 1, FIG. 2, or FIG. However, the configuration of the power converter 1 is not limited to the power factor correction circuit illustrated in FIG. 1 or FIG.

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

Diode D5 is an example of an element having a rectifying function. Therefore, the switching element QD1 is connected in parallel with the capacitor C1 through 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 side connected to the high potential side terminal (first terminal) of the capacitor C1, and an anode side connected to a contact point between the switching element QD2 and the load side of the reactance element L3. It is

In the power conversion device 1B, PWM is performed by switching the switching element QD1 by the control circuit 100B. That is, the control circuit 100B generates a substantially sinusoidal AC current that is in phase with the AC voltage as much as possible for the positive half-cycle and negative half-cycle from the AC power supply that pass through the diodes D1 to D4, which are full-wave rectifier circuits. to improve the power factor of the power input to the power converter 1B.

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

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

The processing of the power converter 1C is the same as that of the power converter 1B of 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 of 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 of FIG. 7 PWM-controls the switching elements QD1 and QD2 of the two chopper circuits in parallel. In this case, since the input AC voltage is common and the output DC voltage is also common, the switching elements QD1 and QD2 of the two chopper circuits also have a common duty ratio for PWM control.

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

Therefore, in the power conversion device 1C of FIG. 7 as well, the control circuit 100C acquires the duty ratio of the PWM control near the peak of the AC voltage in the same way as in the power conversion device 1B of FIG. A target DC voltage can be set and adjusted. In addition, the control circuit 100C of the power conversion device 1C includes switching elements Q of the two chopper circuits.
The duty ratios of D1 and QD2 may be averaged and used to set the target DC voltage. Note that the power conversion device 1D of FIG. 7 can be applied to a single-phase AC power supply, and can also be applied to a three-phase AC power supply.

FIG. 8 is a diagram illustrating the configuration of a power conversion device 1D according to the 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 one first terminal of the AC power supply. The first circuit portion also has a diode D11 having a first rectifying function, the anode side of which is connected to the first reactance element L11 and the cathode side of which is connected to the positive first terminal of the capacitor C1. The first circuit portion also has a first switching element QD11 connected in parallel to the capacitor C1 via a 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 has a diode D12 having a second rectifying function, the anode side of which is connected to the second reactance element L12, and the cathode side of which is connected to the positive first terminal of the capacitor C1. The second circuit portion also has a second switching element QD12 connected in parallel to the capacitor C1 via a diode D12.

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 with 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. ing. In addition, the diodes D11 and D12, which are elements having a rectifying function, have their cathode sides 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 point between the first switching element QD11 and the load side of the first reactance element L11. The diode D12 has an anode side connected to a contact point between the second switching element QD12 and the load side of the second reactance element L12.

By the way, the power conversion device 1D has a configuration in which the switching elements TD11 and TD13 in the power conversion device 1 of FIG. 4 are changed to diodes D11 and D12. Therefore, like the control circuit 100 of the power conversion device 1, the control circuit 100D of the power conversion device 1D controls the on/off of the first switching element QD11 and the second switching element QD12 in the positive half-cycle of the AC voltage. should be kept off. Further, the control circuit 100D may keep the first switching element QD11 off and turn on/off the second switching element QD12 in the negative half-cycle of the AC voltage. In this manner, the control circuit 100D has a configuration similar to that of the control circuit 100, and acquires the duty ratio of the PWM control near the peak of the AC voltage. DC voltage can be set and adjusted.

It can be said that the power conversion device 1 of FIG. 4 also has a first circuit portion and a second circuit portion, like the power conversion device 1D of FIG. Therefore, the power converter 1D of FIG. 8 can be applied to a single-phase AC power supply, and can also be applied to a three-phase AC power supply.

FIG. 9 is a diagram illustrating the configuration of a power converter 1E according to the fifth embodiment. The power converter 1D includes a reactance element L20 connected to the first terminal of the AC source and a full-wave rectifier circuit. This full-wave rectifier circuit has 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 the first terminal on the positive side of the capacitor C1. Here, the first switching element QD21 has, for example, a structure in which a MOSFET and a parasitic diode are combined.

This full-wave rectifier circuit also has a second switching element QD22 having a rectifying function, the cathode side of which is connected to the reactance element L20 and the anode side of which is connected to the second terminal of the capacitor. Here, the second switching element QD22 has, for example, a structure in which a MOSFET and a parasitic diode are combined.

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

By the way, the configuration of the power conversion device 1E in FIG. 9 is obtained by removing L2, which is one of the reactance elements L1 and L2, in the power conversion device 1 in FIG. is.

Therefore, like the control circuit 100 of the power conversion device 1, the control circuit 100E of the power conversion device 1E maintains the first switching element QD11 off and the second switching element QD11 in the positive half-cycle of the AC voltage. ON/OFF control of QD12 is sufficient. In addition, the control circuit 100D may turn on/off the first switching element QD11 and keep the second switching element QD12 off in the negative half-cycle of the AC voltage. In this manner, the control circuit 100D has a configuration similar to that of the control circuit 100, and acquires the duty ratio of the PWM control near the peak of the AC voltage. DC voltage can be set and adjusted. Note that the power conversion device 1D of FIG. 9 can be applied to a single-phase AC power supply, and can also be applied to a three-phase AC power supply.

(Appendix)
1. A power converter (1, 1B to 1E) for regulating power supplied to a load after conversion from an AC source to DC, comprising:
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 shorting and opening alternating voltage from the alternating current source via the reactance element;
a control unit (100, 100B to 100E) that controls the switching element;
with
The control unit (100, 100B to 100E)
a zero-cross detection unit (112) for detecting the phase of the AC voltage from the AC source;
A substantially sinusoidal alternating current is induced so as to have the same phase as the alternating voltage by performing PWM control on the switching element in a half cycle in which the phase of the alternating voltage is positive or negative, and the terminal voltage of the capacitor is reduced. means (101 to 106) for charging so as to approach the charging target voltage;
means (108) for obtaining a duty ratio in the PWM control in a phase where the AC voltage is near a positive or negative peak;
When the duty ratio is greater than a first reference value, the charging target voltage of the capacitor is decreased from the current value, and when the duty ratio is less than a second reference value which is less than the first reference value, the capacitor is charged. and means (110, 111, 102) for increasing the target voltage from the current value.
2. The power converter,
a full wave rectifier circuit (TD11 to TD14 or QD21, QD22, D21, D22 or D11, QD11, D12, QD12) fed from the AC source, or a full wave rectifier circuit (D1 to D4 or D11 , D12, QD11, QD12) to supply power to the load, and
The switching elements (TD12, TD14, QD1, QD2, QD11, QD12) are elements (TD11, TD13, D5, D6 , D11, D12) connected in parallel with the capacitor (C1),
The elements (TD11, TD13, D5, D6, D11, D12) having a rectifying function are connected to the first terminal on the high potential side of the capacitor (C1) on the cathode side, and the switching elements (TD12, TD14) on the anode side. , QD1, QD2, QD11, QD12) and the load side of the reactance elements (L1, L2, L3, L4, L11, L12).
3. The power converter 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;
elements having a first rectifying function (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 element having the first rectifying function;
The second circuit portion is
a second reactance element (L2, L4, L12) connected to the second terminal of the AC power supply; and an anode side of the second reactance element connected to the first terminal of the capacitor (C1). elements (TD13, D6, D12) having a second rectifying function to which the cathode side is connected;
and second switching elements (TD14, QD2, QD12) connected in parallel to the capacitor via the elements (TD13, D6, D12) having the second rectifying function. A power converter as described.
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 is
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 the 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 the second terminal of the capacitor;
a first rectifying element (D21) having a cathode connected to the first terminal of the capacitor;
a second rectifying element (D22) having a cathode side connected to the anode side of the first rectifying element (D21) and a second terminal of the AC source, and having an anode side connected to the second terminal of the capacitor; 1. The power conversion device according to the above item 1.
and means for increasing the charging target voltage of the sensor from the current value.
5. (missing number)
6. A control method for a power conversion device (1, 1B to 1E) for adjusting power supplied to a load after conversion from an AC source to DC, comprising:
The power converter,
Reactance elements (L1, L
2, L3, L4, L11, L12, L20);
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 shorting and opening the AC voltage from the AC source via the reactance element,
detecting the phase of the alternating voltage from the alternating current source (S1);
A substantially sinusoidal alternating current is induced so as to have the same phase as the alternating voltage by performing PWM control on the switching element in a half cycle in which the phase of the alternating voltage is positive or negative, and the terminal voltage of the capacitor is reduced. charging to approach the charging target voltage (101 to 106);
Acquiring a duty ratio in the PWM control in a phase where the AC voltage is near a positive or negative peak (S2);
If the duty ratio is greater than the first reference value, the charging target voltage of the capacitor is lowered from the current value (S4); A control method for a power converter, the method comprising: increasing a target charging voltage of a capacitor from a current 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 detector 109 duty ratio Threshold register 110 Comparator 111 Target DC voltage adjustment amount register A1 AC current sensor C1 Capacitors D1, D2, D3, D4, D5, D6 Diodes L1, L2, L3, L4, L11, L12, L20 Reactance elements QD1, QD2, QD11 , QD12, QD21, QD22 Switching elements TD1, TD2, TD3, TD4, TD5, TD6 Switching elements V1 AC voltage sensor V2 DC voltage sensor

Claims (6)

A power conversion device that adjusts the power supplied to a load after converting from an AC source to DC,
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 shorting and opening an alternating voltage from the alternating current source via the reactance element;
a control unit that controls the switching element;
with
The control unit
a zero-cross detection unit that detects the phase of the AC voltage from the AC source;
A substantially sinusoidal alternating current is induced so as to have the same phase as the alternating voltage by performing PWM control on the switching element in a half cycle in which the phase of the alternating voltage is positive or negative, and the terminal voltage of the capacitor is reduced. means for charging to approach a charging target voltage;
means for obtaining a duty ratio in the PWM control in a phase where the AC voltage is near a positive or negative peak;
When the duty ratio is greater than a first reference value, the charging target voltage of the capacitor is decreased from the current value, and when the duty ratio is less than a second reference value which is less than the first reference value, the capacitor is charged. and means for increasing the target voltage from the current value. The power conversion device includes a full-wave rectifier circuit that is powered by the AC source, or is a circuit that is powered by the AC source via the 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 contact on the load side of the reactance element,
2. The device according to claim 1, wherein the element having a rectifying function has a cathode side connected to a first terminal on a high potential side of the capacitor, and an anode side connected to a contact point between the switching element and the load side of the reactance element. power converter. The power converter 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;
an element having a first rectifying function, the anode side of which is connected to the first reactance element and the cathode side of which is connected to the first terminal of the capacitor;
a first switching element connected in parallel to the capacitor via the element having the first rectifying function;
The second circuit portion is
a second reactance element connected to the second terminal of the AC source; and a second rectifying function having an anode side connected to the second reactance element and a cathode side connected to the first terminal of the capacitor. an element having
3. The power converter according to claim 1, further comprising a second switching element connected in parallel to said capacitor via said element having said second rectifying function. 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 is
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 the first terminal of the capacitor;
a second switching element having a rectifying function, the cathode side of which is connected to the reactance element and the anode side of which is connected to the second terminal of the capacitor;
a first rectifying element having a cathode connected to the first terminal of the capacitor;
2. A second rectifying element having an anode side of said first rectifying element and a cathode side connected to a second terminal of said alternating current source, and a second rectifying element having an anode side connected to said second terminal of said capacitor. The power conversion device according to . A control unit of a power conversion device that adjusts the power supplied to a load after converting from an AC source to DC,
The power converter,
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 shorting and opening an alternating voltage from the alternating current source via the reactance element;
a control unit that controls the switching element;
with
The control unit
a zero-cross detection unit that detects the phase of the AC voltage from the AC source;
A substantially sinusoidal alternating current is induced so as to have the same phase as the alternating voltage by performing PWM control on the switching element in a half cycle in which the phase of the alternating voltage is positive or negative, and the terminal voltage of the capacitor is reduced. means for charging to approach a charging target voltage;
means for obtaining a duty ratio in the PWM control in a phase where the AC voltage is near a positive or negative peak;
When the duty ratio is greater than a first reference value, the charging target voltage of the capacitor is decreased from the current value, and when the duty ratio is less than a second reference value which is less than the first reference value, the capacitor is charged. and means for increasing the target voltage from the current value. A control method for a power conversion device that adjusts power supplied to a load after conversion from an AC source to DC, comprising:
The power converter,
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 shorting and opening an alternating voltage from the alternating current source via the reactance element,
detecting the phase of an alternating voltage from the alternating source;
A substantially sinusoidal alternating current is induced so as to have the same phase as the alternating voltage by performing PWM control on the switching element in a half cycle in which the phase of the alternating voltage is positive or negative, and the terminal voltage of the capacitor is reduced. charging so as to approach the charging target voltage;
Acquiring a duty ratio in the PWM control in a phase where the AC voltage is near a positive or negative peak;
When the duty ratio is greater than a first reference value, the charging target voltage of the capacitor is decreased from the current value, and when the duty ratio is less than a second reference value which is less than the first reference value, the capacitor is charged. increasing a target voltage from a current value; and controlling a power conversion device.

Images