Patent Description:
Circuits for rectifying an AC wave are known, such as a class-E rectifier circuit as disclosed in Patent Document <NUM>.

Prior art document <CIT> discloses a semiconductor integrated circuit that is used for a stabilizing power supply circuit which supplies an output power supply voltage to a parallel connection of a smoothing capacitor and a load, from an input power supply voltage, includes an error amplifier that detects an error of the output power supply voltage, an output control circuit that is connected between the input terminal and the output terminal, a phase compensation circuit that is connected to the error amplifier, and a detection control circuit that is connected to the phase compensation circuit.

Prior art document <CIT> refers to a method of power converter regulation, in particular regulation of very high frequency (VHF) power converters operating at frequencies in the MHz range, wherein accurate output regulation utilizes inherent delays in the regulation loop, whereby, contrary to hysteresis on/off control, the new method does not require immediate responses to comparisons of a sense voltage to two reference voltages; rather, according to the new method, only one reference voltage is used, and delays in the feedback loop are allowed to cause some variation of an output of the power converter.

However, in the conventional class E-rectifier circuit described above, the capacitance value of the capacitor constituting the rectifier circuit changes depending on the temperature characteristics. For example, since the capacitance of the capacitor decreases as the temperature increases, a peak value of a voltage waveform subjected to half-wave rectification in the rectifier circuit increases in association with the decrease in the capacitance, leading to a decrease in impedance. After that, since the temperature of the capacitor rises further, the same phenomenon is repeated, and there is a problem that over temperature occurs beyond a rated temperature of components.

In view of the foregoing problem, the present invention provides a power conversion device capable of suppressing a change in impedance of a capacitor included in a rectifier circuit to prevent over temperature, and a method for controlling the power conversion device.

The object underlying the present invention is achieved by a method for controlling a power conversion device according to independent claim <NUM> and by a power conversion device according to independent claim <NUM>. Preferred embodiments are defined in the respective dependent claims
To solve the above problem, an aspect of the present invention provides a power conversion device and a method for controlling the power conversion device which are inter alia configured to regulate an alternating-current wave input to a rectifier capacitor depending on a change in impedance of the rectifier capacitor so as to suppress the change in the impedance of the rectifier capacitor.

The present invention can suppress a change in impedance of a rectifier capacitor included in a rectifier circuit to prevent over temperature in the rectifier capacitor.

A first embodiment to which the present invention is applied is described below with reference to the drawings. The same elements illustrated with reference to the drawings are indicated by the same reference numerals, and overlapping explanations are not repeated below.

<FIG> is a circuit diagram illustrating a configuration of a power conversion device according to the present embodiment. As illustrated in <FIG>, the power conversion device <NUM> according to the present embodiment includes an input power supply <NUM>, an alternating-current (AC) wave generation circuit <NUM>, a rectifier circuit <NUM>, a detector <NUM>, a controller <NUM>, and a load <NUM>. The power conversion device <NUM> converts direct current (DC) power input from the input power supply <NUM> into AC power, and supplies DC power rectified by the rectifier circuit <NUM> to the load <NUM>.

The AC wave generation circuit <NUM> includes a choke coil <NUM>, a resonant coil <NUM>, a resonant capacitor <NUM>, a switching element <NUM>, and a shunt capacitor <NUM>. The AC wave generation circuit <NUM> is a class-E inverter circuit that generates an AC wave from the DC power from the input power supply <NUM> depending on a drive frequency of the switching element <NUM>.

As illustrated in <FIG>, the choke coil <NUM> is connected between the input power supply <NUM> and the switching element <NUM>. The resonant coil <NUM> and the resonant capacitor <NUM> form a resonant circuit connected to a connection point between the choke coil <NUM> and the switching element <NUM>. The switching element <NUM> turns on/off the input to the resonant circuit. The shunt capacitor <NUM> is connected in parallel to the switching element <NUM>.

The rectifier circuit <NUM> is a class-E circuit that includes a diode <NUM>, a rectifier capacitor <NUM>, a filter coil <NUM>, and a filter capacitor <NUM> to rectify an AC wave with a configuration in which the diode <NUM> and the rectifier capacitor <NUM> are connected in parallel.

The rectifier circuit <NUM> causes the diode <NUM> to subject the AC wave generated in the AC wave generation circuit <NUM> to half-wave rectification to charge the rectified energy to the rectifier capacitor <NUM>. The rectifier circuit <NUM> transfers the charged energy to an LC filter implemented by the filter coil <NUM> and the filter capacitor <NUM> to transmit the power in a DC waveform to the load <NUM>. As illustrated in <FIG>, while a voltage waveform of the rectifier capacitor <NUM> has a shape subjected to half-wave rectification, the voltage waveform to be supplied to the load <NUM> via the LC filter becomes direct current, as illustrated in <FIG>.

The detector <NUM> detects a change in impedance of the rectifier capacitor <NUM>. The detector <NUM> detects a current value or a voltage value of the rectifier capacitor <NUM>, and detects a degree of change in impedance of the rectifier capacitor <NUM> according to a change in the current value or the voltage value. The detector <NUM> may detect a temperature of the rectifier capacitor <NUM> so as to detect a degree of change in the impedance of the rectifier capacitor <NUM> according to a change in the temperature. The detector <NUM>, when provided with any of an ammeter, a voltmeter, or a thermometer, may detect a change in the impedance by calculating the amount of change in the value of any of the current, the voltage, or the temperature. The impedance of the rectifier capacitor <NUM> has a set value set so that the power conversion device <NUM> can execute optimum operations. The detector <NUM> thus detects how much the impedance of the rectifier capacitor <NUM> is changed from the set value.

The controller <NUM> regulates the AC wave input to the rectifier capacitor <NUM> so as to suppress the change in the impedance of the rectifier capacitor <NUM>, depending on the change in the impedance of the rectifier capacitor <NUM> detected by the detector <NUM>. In particular, when the impedance of the rectifier capacitor <NUM> is increased above the set value, the controller <NUM> regulates the AC wave input to the rectifier capacitor <NUM> so as to decrease an output voltage of the power conversion device <NUM>. When the impedance of the rectifier capacitor <NUM> is decreased below the set value, the controller <NUM> regulates the AC wave input to the rectifier capacitor <NUM> so as to increase the output voltage of the power conversion device <NUM>. For example, the controller <NUM> changes the drive frequency of the switching element <NUM> to regulate a frequency of the AC wave generated in the AC wave generation circuit <NUM>, so as to regulate the AC wave input to the rectifier capacitor <NUM>.

The controller <NUM> is fabricated by a multi-purpose electronic circuit including a microcomputer, a microprocessor, and a CPU, and peripheral components such as a memory, and has a function of controlling the AC wave generation circuit <NUM> and the rectifier circuit <NUM>. The respective functions of the controller <NUM> can be implemented in single or plural processing circuits. The respective processing circuits include a programmed processing device, such as a processing device including an electric circuit, for example, and also include an application-specific integrated circuit (ASIC) configured to execute the functions described herein, and conventional circuit components.

A method for controlling the power conversion device <NUM> according to the present embodiment is described below. A capacitance of the rectifier capacitor <NUM> included in the rectifier circuit <NUM> has the temperature characteristics as illustrated in <FIG>, and a capacitance value of the rectifier capacitor <NUM> thus decreases as the temperature of the rectifier capacitor <NUM> increases.

A voltage V of the rectifier capacitor <NUM> is inversely proportional to a capacitance value C of the rectifier capacitor <NUM>, as given by the following formula (<NUM>): <MAT> where I is a current of the rectifier capacitor <NUM>, ω = 2πf, and f is a frequency of an AC wave, which is the same as the drive frequency of the switching element <NUM>.

According to the formula (<NUM>), since the voltage V of the rectifier capacitor <NUM> increases as the capacitance value C of the rectifier capacitor <NUM> decreases, a peak value of the voltage waveform of the rectifier capacitor <NUM> increases in association with the decrease in the capacitance, as illustrated in <FIG>. The output voltage of the power conversion device <NUM> output to the load <NUM> then increases, as illustrated in <FIG>.

At this time, since the input current of the power conversion device <NUM> also increases, an input impedance of the power conversion device <NUM> decreases. The temperature of the rectifier capacitor <NUM> further increases in association with the increase in the input current and the output voltage, and the similar phenomenon is repeated accordingly. Therefore, in the conventional case, the input impedance of the power conversion device <NUM> decreases with the passage of time, as illustrated in <FIG>, and both the input current and the output voltage of the power conversion device <NUM> increase, as illustrated in <FIG>. As a result, the temperature of the circuit components increases with the time, causing over temperature due to thermal runaway accordingly.

However, according to the present embodiment, the power conversion device <NUM> regulates the AC wave input to the rectifier capacitor <NUM> depending on the change in the impedance of the rectifier capacitor <NUM> detected by the detector <NUM> so as to suppress the change in the impedance of the rectifier capacitor <NUM>. In particular, when the impedance of the rectifier capacitor <NUM> is increased above the set value, the controller <NUM> regulates the AC wave input to the rectifier capacitor <NUM> so as to decrease the output voltage of the power conversion device <NUM>. On the other hand, when the impedance of the rectifier capacitor <NUM> is decreased below the set value, the controller <NUM> regulates the AC wave input to the rectifier capacitor <NUM> so as to increase the output voltage of the power conversion device <NUM>.

The controller <NUM> changes the drive frequency of the switching element <NUM> to regulate the frequency of the AC wave generated in the AC wave generation circuit <NUM>, so as to regulate the AC wave input to the rectifier capacitor <NUM>.

More particularly, when the capacitance of the rectifier capacitor <NUM> is decreased because of the increase in the temperature, the impedance of the rectifier capacitor <NUM> is increased above the set value, and the voltage of the rectifier capacitor <NUM> is also increased, as given by the formula (<NUM>). In this case, when the drive frequency of the switching element <NUM> is caused to increase above a predetermined value to increase the frequency of the AC wave generated by the AC wave generation circuit <NUM>, the frequency of the AC wave input to the rectifier circuit <NUM> is also increased. As a result, the value ω in the formula (<NUM>) is then increased, and the impedance of the rectifier capacitor <NUM> is decreased accordingly. This leads the peak value of the voltage waveform of the rectifier capacitor <NUM> to be decreased as illustrated in <FIG>, and also leads the output voltage of the power conversion device <NUM> output to the load <NUM> to be decreased as illustrated in <FIG>. The predetermined value set for the drive frequency may be a frequency obtained upon the execution of an optimum operation so that the load <NUM> has a design value.

When the capacitance of the rectifier capacitor <NUM> is increased because of the decrease in the temperature, the impedance of the rectifier capacitor <NUM> is decreased below the set value, and the voltage of the rectifier capacitor <NUM> is also decreased, as given by the formula (<NUM>). In this case, when the drive frequency of the switching element <NUM> is caused to decrease below the predetermined value to decrease the frequency of the AC wave generated by the AC wave generation circuit <NUM>, the frequency of the AC wave input to the rectifier circuit <NUM> is also decreased. As a result, the value ω in the formula (<NUM>) is then decreased, and the impedance of the rectifier capacitor <NUM> is increased accordingly. This leads the peak value of the voltage waveform of the rectifier capacitor <NUM> to be increased, and also leads the output voltage of the power conversion device <NUM> output to the load <NUM> to be increased.

As described above, regulating the frequency of the AC wave input to the rectifier capacitor <NUM> suppresses the change in the impedance of the rectifier capacitor <NUM>. This can control the input impedance, the input current, and the output voltage of the power conversion device <NUM> each to be constant, so as to prevent over temperature of the components caused by thermal runaway.

If the drive frequency of the switching element <NUM> is increased, a switching loss is increased. In view of this, the AC wave generation circuit <NUM> is the class-E inverter circuit that can achieve zero-voltage switching (ZVS) due to voltage resonance, so as to greatly suppress the switching loss. This can reduce the influence which increases the drive frequency to a small level accordingly.

The rectifier circuit <NUM> according to the present embodiment is the class-E circuit in which the diode <NUM> and the rectifier capacitor <NUM> are connected in parallel. However, other rectifier circuits, such as full-wave rectifier circuits with diode, do not have a rectifier capacitor to charge energy. The rectifier circuit <NUM> thus does not cause a change in the output voltage, the input current, or the input impedance because of a change in the temperature of the rectifier capacitor, so as to prevent over temperature that is the problem to be solved by the present embodiment.

While typical snubber circuits also employ a configuration in which a diode and a capacitor are connected in parallel, the snubber circuits execute an operation of absorbing a surge voltage derived from high-speed switching by the capacitor, and thus have a different function from the rectifier circuit <NUM> according to the present embodiment.

The AC wave generation circuit <NUM> may have any configuration that generates and outputs the AC wave, instead of the configuration illustrated in <FIG>, and may be a resonant circuit including a plurality of switches, such as a class-D inverter circuit. The filter of the rectifier circuit <NUM> is not limited to the LC filter, and may have any structure. In addition, a transformer for isolation may be arranged between the AC wave generation circuit <NUM> and the rectifier circuit <NUM>.

As described in detail above, the power conversion device <NUM> according to the present embodiment regulates the AC wave input to the rectifier capacitor <NUM> so as to suppress a change in the impedance of the rectifier capacitor <NUM>, depending on the change in the impedance of the rectifier capacitor <NUM>. This can suppress the change in the input current, the output voltage, and the input impedance of the power conversion device <NUM>, so as to prevent over temperature of the rectifier capacitor <NUM>.

The power conversion device <NUM> according to the present embodiment regulates the AC wave input to the rectifier capacitor <NUM> so as to decrease the output voltage of the power conversion device <NUM> when the impedance of the rectifier capacitor <NUM> is increased above the set value. The power conversion device <NUM> regulates the AC wave input to the rectifier capacitor <NUM> so as to increase the output voltage of the power conversion device <NUM> when the impedance of the rectifier capacitor <NUM> is decreased below the set value. Thus the power conversion device <NUM> can suppress the change in the impedance of the rectifier capacitor <NUM>, so as to prevent over temperature of the rectifier capacitor <NUM>.

The power conversion device <NUM> according to the present embodiment increases the frequency of the AC wave generated by the AC wave generation circuit <NUM> when the impedance of the rectifier capacitor <NUM> is increased above the set value. The power conversion device <NUM> decreases the frequency of the AC wave generated by the AC wave generation circuit <NUM> when the impedance of the rectifier capacitor <NUM> is decreased below the set value. The power conversion device <NUM> can suppress the change in the impedance of the rectifier capacitor <NUM> by regulating the frequency of the AC wave input to the rectifier capacitor <NUM>, so as to prevent over temperature of the rectifier capacitor <NUM>.

The power conversion device <NUM> according to the present embodiment detects the change in the impedance of the rectifier capacitor <NUM>. Since the power conversion device <NUM> directly detects the change in the impedance of the rectifier capacitor <NUM>, the power conversion device <NUM> can immediately suppress the change in the impedance of the rectifier capacitor <NUM>, so as to prevent over temperature of the rectifier capacitor <NUM> with a high accuracy.

The power conversion device <NUM> according to the present embodiment includes the AC wave generation circuit <NUM> that includes the resonant circuit including the resonant coil <NUM> and the resonant capacitor <NUM>, and the switching element <NUM> that turns on/off the input to the resonant circuit. Thus, the power conversion device <NUM> can easily regulate the AC wave input to the rectifier capacitor <NUM> by regulating the drive frequency of the switching element <NUM>. This can suppress the change in the impedance of the rectifier capacitor <NUM>, so as to prevent over temperature of the rectifier capacitor <NUM>.

The power conversion device <NUM> according to the present embodiment includes the AC wave generation circuit <NUM> that further includes the choke coil <NUM> connected between the input power supply <NUM> and the switching element <NUM>, and the shunt capacitor <NUM> connected in parallel to the switching element <NUM>. The resonant circuit is connected to the connection point between the choke coil <NUM> and the switching element <NUM>. Since the AC wave generation circuit <NUM> can be implemented as the class-E inverter circuit, a switching loss can be reduced to a small level. This can not only suppress an influence caused by an increase in switching loss upon the increase in the drive frequency of the switching element <NUM> but also prevent over temperature of the rectifier capacitor <NUM>.

A second embodiment to which the present invention is applied is described below with reference to the drawings. The same elements illustrated with reference to the drawings are indicated by the same reference numerals, and overlapping explanations are not repeated below.

<FIG> is a circuit diagram illustrating a configuration of a power conversion device according to the present embodiment. As illustrated in <FIG>, the power conversion device <NUM> according to the present embodiment differs from the first embodiment in further including a rectifier switch <NUM> as a switching element which turns on/off the AC wave input to the rectifier capacitor <NUM>. The rectifier switch <NUM> is connected in series to the rectifier capacitor <NUM>.

A method for controlling the power conversion device <NUM> according to the present embodiment is described below. According to the present embodiment, when the detector <NUM> detects a change in the impedance of the rectifier capacitor <NUM>, the controller <NUM> controls the on/off operation of the rectifier switch <NUM> so as to regulate the AC wave input to the rectifier capacitor <NUM>.

In particular, when the impedance of the rectifier capacitor <NUM> is increased above the set value, the controller <NUM> controls the rectifier switch <NUM> so as to decrease the period of time during which the AC wave is input to the rectifier capacitor <NUM>. When the impedance of the rectifier capacitor <NUM> is decreased below the set value, the controller <NUM> controls the rectifier switch <NUM> so as to increase the period of time during which the AC wave is input to the rectifier capacitor <NUM>.

For example, when the capacitance of the rectifier capacitor <NUM> is decreased in association with an increase in the temperature of the rectifier capacitor <NUM>, the impedance of the rectifier capacitor <NUM> is increased as given by the formula (<NUM>), and the voltage of the rectifier capacitor <NUM> is increased. In this case, an input stop period is provided at a point at which the voltage of the rectifier capacitor <NUM> starts increasing as illustrated in <FIG>. The input stop period is a period during which the rectifier switch <NUM> is turned off so as not to input the AC wave to the rectifier capacitor <NUM>. After this period, the rectifier switch <NUM> is turned on so as to input the AC wave to the rectifier capacitor <NUM> (an AC wave input period). The AC wave input period is shorter as the input stop period is set to be longer, so as to set the period of time during which the AC wave is input to the rectifier capacitor <NUM> to be shorter than a predetermined time. The power to be charged to the rectifier capacitor <NUM> is thus reduced, so as to decrease the output voltage of the power conversion device <NUM> output to the load <NUM>, as illustrated in <FIG>. The predetermined time may be set to a time upon the execution of an optimum operation so that the load <NUM> has a design value.

When the capacitance of the rectifier capacitor <NUM> is increased in association with a decrease in the temperature of the rectifier capacitor <NUM>, the impedance of the rectifier capacitor <NUM> is decreased as given by the formula (<NUM>), and the voltage of the rectifier capacitor <NUM> is decreased. In this case, the input stop period as illustrated in <FIG> is decreased so as to set the period of time during which the AC wave is input to the rectifier capacitor <NUM> to be longer than the predetermined time. The power to be charged to the rectifier capacitor <NUM> is thus increased, so as to increase the output voltage of the power conversion device <NUM> output to the load <NUM>.

The rectifier switch <NUM> may be connected in parallel to the rectifier capacitor <NUM>, as illustrated in <FIG>. In this case, the operation of turning on/off the rectifier switch <NUM> is controlled reversely to the case of being connected in series as illustrated in <FIG>. In particular, when the rectifier switch <NUM> is connected in parallel to the rectifier capacitor <NUM>, by turning on the rectifier switch <NUM>, the input stop period during which the AC wave is not input to the rectifier capacitor <NUM> is set. The AC wave is input to the rectifier capacitor <NUM> when the rectifier switch <NUM> is turned off.

As described above, the power conversion device <NUM> according to the present embodiment decreases the period of time during which the AC wave is input to the rectifier capacitor <NUM> when the impedance of the rectifier capacitor <NUM> is increased above the set value. The power conversion device <NUM> increases the period of time during which the AC wave is input to the rectifier capacitor <NUM> when the impedance of the rectifier capacitor <NUM> is decreased below the set value. The power conversion device <NUM> can suppress the change in the impedance of the rectifier capacitor <NUM> by regulating the period of time during which the AC wave is input to the rectifier capacitor <NUM>. As a result, the power conversion device <NUM> can prevent over temperature of the rectifier capacitor <NUM>.

A third embodiment to which the present invention is applied is described below with reference to the drawings. The same elements illustrated with reference to the drawings are indicated by the same reference numerals, and overlapping explanations are not repeated below.

<FIG> is a circuit diagram illustrating a configuration of a power conversion device according to the present embodiment. As illustrated in <FIG>, the power conversion device <NUM> according to the present embodiment differs from the first and second embodiments in detecting an input voltage, an input current, an output voltage, and an output current of the power conversion device <NUM>. The detector <NUM> detects the input voltage Vi, the input current li, the output voltage Vo, and the output current Io of the power conversion device <NUM>, instead of the change in the impedance of the rectifier capacitor <NUM>. Since a typical power conversion device detects an input voltage, an input current, an output voltage, and an output current, these values may be detected by a general method such as installing a voltmeter or an ammeter in this embodiment,.

A method for controlling the power conversion device <NUM> according to the present embodiment is described below. According to the present embodiment, the power conversion device <NUM> is controlled based on the input voltage Vi, the input current li, the output voltage Vo, and the output current Io of the power conversion device <NUM>. In particular, the controller <NUM> first acquires the input voltage Vi, the input current li, the output voltage Vo, and the output current Io from the detector <NUM>, and calculates an input impedance Zi according to the following formula (<NUM>): <MAT>.

After calculating the input impedance Zi, The controller <NUM> determines whether the impedance of the rectifier capacitor <NUM> is increased above the set value or decreased below the set value, while referring to a table as illustrated in <FIG> illustrates upward arrows indicating an increase, downward arrows indicating a decrease, and sideways arrows indicating no change.

As illustrated in <FIG>, when the input impedance Zi is decreased below the set value, and the output voltage Vo and the output current Io are increased above the set value, the controller <NUM> determines that the capacitance of the rectifier capacitor <NUM> is decreased and the impedance is increased above the set value. When the input impedance Zi is increased above the set value, and the output voltage Vo and the output current Io are decreased below the set value, the controller <NUM> determines that the capacitance of the rectifier capacitor <NUM> is increased and the impedance is decreased below the set value. The set value for each of the input impedance, the output voltage, and the output current is a value when the power conversion device <NUM> executes an optimum operation.

When a change in the input/output power of the power conversion device <NUM> is caused, not only a change in the capacitance of the rectifier capacitor <NUM> but also a fluctuation in the load <NUM> and the input voltage are presumed. Therefore, the controller <NUM> distinguishes between the case where the load <NUM> fluctuates and the case where the input voltage fluctuates based on the input impedance Zi, the output voltage Vo, and the output current Io.

The case of the fluctuation in the load <NUM> is described first. As illustrated in <FIG>, when the input impedance Zi and the output voltage Vo is increased above the set value, and the output current Io is decreased below the set value, the controller <NUM> determines that this case corresponds to "change A" in which a resistance value of the load <NUM> is increased above the design value. For example, as illustrated in <FIG>, the power conversion device <NUM> sets and determines the resistance value of the load <NUM> in optimum operation to <NUM>Ω as the design value, for example. The "change A" is a case in which the resistance value of the load <NUM> is increased in a direction away from the design value determined.

Further, as illustrated in <FIG>, when the input impedance Zi and the output current Io is increased above the set value, and the output voltage Vo is decreased below the set value, the controller <NUM> determines that this case corresponds to "change B" as illustrated in <FIG>. The "change B" is a case in which the resistance value of the load <NUM> is decreased in the direction away from the design value.

Further, as illustrated in <FIG>, when the input impedance Zi and the output current Io is decreased below the set value, and the output voltage Vo is increased above the set value, the controller <NUM> determines that this case corresponds to "change C" as illustrated in <FIG>. The "change C" is a case in which the resistance value of the load <NUM> is increased in the direction approaching the design value. Further, as illustrated in <FIG>, when the input impedance Zi and the output voltage Vo is decreased below the set value, and the output current Io is increased above the set value, the controller <NUM> determines that this case corresponds to "change D" as illustrated in <FIG>. The "change D" is a case in which the resistance value of the load <NUM> is decreased in the direction approaching the design value.

The case of the fluctuation in the input voltage is described next. As illustrated in <FIG>, when the input impedance Zi has no change from the set value, the controller <NUM> determines that this case corresponds to an input fluctuation, and determines that the input voltage is increased when the output voltage Vo and the output current Io are increased above the set value. When the output voltage Vo and the output current Io are decreased below the set value, the controller <NUM> determines that input voltage is decreased.

As described above, when any of the change in the impedance of the rectifier capacitor <NUM>, the fluctuation in the load <NUM>, or the fluctuation in the input voltage is determined, the controller <NUM>, when determining the change in the impedance, controls the drive frequency of the switching element <NUM>. In particular, the controller <NUM>, when determining that the impedance of the rectifier capacitor <NUM> is increased above the set value, increases the drive frequency of the switching element <NUM> to decrease the impedance of the rectifier capacitor <NUM>. The controller <NUM>, when determining that the impedance of the rectifier capacitor <NUM> is decreased below the set value, decreases the drive frequency of the switching element <NUM> to increase the impedance of the rectifier capacitor <NUM>.

While <FIG> illustrates the case in which the power conversion device according to the present embodiment is applied to the power conversion device according to the first embodiment illustrated in <FIG>, the power conversion device according to the present embodiment may be applied to the power conversion device according to the second embodiment illustrated in <FIG> or <FIG>.

As described above, the power conversion device <NUM> according to the present embodiment can determine all of the change in the impedance of the rectifier capacitor <NUM>, the fluctuation in the load <NUM>, and the fluctuation in the input voltage by use of the input impedance, the output voltage, and the output current of the power conversion device <NUM>. It could be presumed that the impedance of the rectifier capacitor <NUM> is not necessarily changed even though the input impedance is changed, but the input impedance may be changed in response to the fluctuation in the load <NUM>. In view of this, the power conversion device <NUM> according to the present embodiment accurately makes a determination of which case is caused, the change in the impedance of the rectifier capacitor <NUM>, or the fluctuation in the input voltage or the fluctuation in the load <NUM>, according to the table as illustrated in <FIG>.

Another method could also be used that measures the temperature of the rectifier capacitor <NUM> and estimates the amount of change in the capacitance value according to the change in the temperature. This method, however, needs to add a measurement device for measuring the temperature at a specific point. Still another method could be used that accurately estimates the change in the capacitance value according to the value of the increase in the temperature. This method also needs to preliminarily measure the characteristics including a variation in each of capacitors, and further needs to add a checking process of acquiring a relationship between the temperature and the capacitance value for each of devices to be manufactured. This requires additional components for estimating the amount of change in the capacitance value according to the change in the temperature of the rectifier capacitor <NUM>, impeding a reduction in size of the device or a reduction in cost.

On the contrary, the power conversion device <NUM> according to the present embodiment detects the input voltage, the input current, the output voltage, and the output current of the power conversion device <NUM>. Therefore, the power conversion device <NUM> only uses the voltage and the current of the input/output power which are typically detected. Thus, the power conversion device <NUM> can determine the change in the impedance of the rectifier capacitor <NUM> with no additional components provided for measuring the temperature. The power conversion device <NUM> thus can suppress the change in the impedance of the rectifier capacitor <NUM> with no addition of components or devices to prevent over temperature of the rectifier capacitor <NUM>.

The power conversion device <NUM> according to the present embodiment also calculates the input impedance according to the input voltage and the input current, and determines that the impedance of the rectifier capacitor <NUM> is increased above the set value when the input impedance is decreased below the set value and the output voltage and the output current are increased above the set value. The power conversion device <NUM> determines that the impedance of the rectifier capacitor <NUM> is decreased below the set value when the input impedance is increased above the set value and the output voltage and the output current are decreased below the set value. The power conversion device <NUM> can determine whether the impedance of the rectifier capacitor <NUM> is increased above or decreased below the set value, with no addition of components or devices. The power conversion device <NUM> thus can suppress the change in the impedance of the rectifier capacitor <NUM> based on this determination, so as to prevent over temperature of the rectifier capacitor <NUM>.

Claim 1:
A method for controlling a power conversion device (<NUM>),
the power conversion device (<NUM>) comprising:
- an alternating-current wave generation circuit (<NUM>) comprising a switching element (<NUM>) and configured to convert input power into an alternating-current wave,
- a controller (<NUM>) configured to control the switching element (<NUM>) to regulate the alternating-current wave, and
- a rectifier circuit (<NUM>)
- which is configured to rectify the alternating-current wave generated by the alternating-current wave generation circuit (<NUM>) with a configuration in which a rectifier capacitor (<NUM>) and a diode (<NUM>) to subject the alternating-current wave to half-wave rectification are connected in parallel, and
- which comprises a filter (<NUM>; <NUM>) that is implemented by a filter coil (<NUM>) and a filter capacitor (<NUM>), characterized in that
the method comprises detecting an impedance of the rectifier capacitor (<NUM>),
the method further comprises
- by controlling a drive frequency of the switching element (<NUM>) -
- regulating the alternating-current wave input to the rectifier capacitor (<NUM>) by the controller (<NUM>) to increase a frequency of the alternating-current wave generated by the alternating-current wave generation circuit (<NUM>) so as to decrease an output voltage of the power conversion device (<NUM>) when the impedance of the rectifier capacitor (<NUM>) is increased above a set value; and
- regulating the alternating-current wave input to the rectifier capacitor (<NUM>) by the controller (<NUM>) to decrease the frequency of the alternating-current wave generated by the alternating-current wave generation circuit (<NUM>) so as to increase the output voltage of the power conversion device (<NUM>) when the impedance of the rectifier capacitor (<NUM>) is decreased below the set value,
and thereby suppressing a change in the impedance of the rectifier capacitor (<NUM>) by regulating the period of time during which the AC wave is input to the rectifier capacitor (<NUM>).