JP5134263B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device including a converter that adjusts the voltage of a DC voltage supplied from a DC power source and outputs an intermediate voltage, and an inverter that converts the intermediate voltage into AC.

  A solar cell, a fuel cell, or the like generates a DC voltage, but an AC voltage is suitable for transmission of electric power and driving of a motor, and a power conversion device that converts the DC voltage into an AC voltage is used.

  A power conversion device includes, as a basic configuration, a converter that adjusts the voltage of a DC voltage supplied from a DC power source and outputs an intermediate voltage, an inverter that converts the intermediate voltage into AC, and a control unit that controls the inverter Is provided.

  The intermediate voltage is generated by the converter so as to be a constant direct current having a sufficient potential as an input of the inverter, and the potential is always maintained at a potential equal to or higher than the peak value of the alternating voltage.

  The inverter forms a bridge circuit including a switching element. These switching elements are repeatedly turned on and off in a minute cycle so that the output voltage becomes a sine waveform by PWM control under the action of the control unit.

  By the way, when the AC voltage has a peak value, the difference from the intermediate voltage is sufficiently small and the loss of the switching element (switching loss and conduction loss) is small. Is larger than the peak value of the AC voltage, and the loss of the switching element also increases.

  This increase in loss is due to the fact that the intermediate voltage generated by the converter is maintained at a constant value.

  On the other hand, Patent Document 1 proposes that the intermediate voltage generated by the converter changes in synchronization with the output AC voltage. In the system described in Patent Literature 1, it is assumed that the generation of harmonics can be reduced by suppressing distortion of the output current.

JP-A-10-155280 (FIG. 5)

  In the system described in Patent Document 1, the intermediate voltage is changed in synchronization with the output AC voltage, but the intermediate voltage is always maintained at or above the peak value of the AC voltage. That is, when the AC voltage is 0 or a value in the vicinity thereof, the difference from the intermediate voltage is equal to or greater than the peak value of the AC voltage, and the loss of the switching element is still large.

  Further, in the system described in Patent Document 1, the change in the intermediate voltage is linear, and is composed of a constant slope section and a constant value section. In order to obtain an AC voltage having a smooth sine waveform from the intermediate voltage having such a waveform, the switching element of the inverter must be controlled on and off in a complicated procedure.

  The present invention has been made in consideration of such problems, and an object of the present invention is to provide a power converter that can be easily controlled and has low loss.

A power converter according to the present invention controls a converter that adjusts the voltage of a DC voltage supplied from a DC power source and outputs an intermediate voltage, an inverter that converts the intermediate voltage into AC, the converter, and the inverter It includes a control unit, wherein the inverter comprises a first switching element pair energizing the first direction of the current to the load, and a second switching element pair energizing the second direction of current flow opposite wherein the control unit, when outputting the intermediate voltage by the converter, the intermediate voltage, generates a periodic of certain voltage full-wave rectified waveform for converting the alternating current, the zero crossing of the AC corresponding to the timing, most of each timing as a low voltage, the first switching element pair and the second switching element pair group for switching the control of the intermediate voltage And timing, in every period of the full-wave rectified waveform, shorter than the first Rutotomoni the switching element pair is turned on at least a predetermined time, and turning off the second switching element pairs or the first switching element pair time to turn, in other every other cycle of the full-wave rectified waveform, as well as at least a predetermined time on the second switching element pairs, and turns off the first switching element pair or the second switching element pairs It is turned on for a shorter time, and the voltage at which the intermediate voltage is the lowest is set smaller than the peak value of the output voltage of the inverter.
In this case, the converter includes an input side capacitor provided between a positive electrode and a negative electrode of the DC power supply, a switching element that turns on and off a current flowing from the positive electrode side of the DC power supply, and the switching element and the negative electrode. An inductor provided in between, a backflow prevention diode having a cathode connected to a connection point between the output side of the switching element and the inductor, and an output side capacitor provided between the anode and the negative electrode of the diode And the control unit reduces the ON signal width when the full-wave rectified waveform value is small, and increases the ON signal width when the full-wave rectified waveform value is large. By chopping driving so that the voltage on the anode side of the diode for backflow prevention becomes the minimum of the intermediate voltage The side of the potential, the voltage of the negative electrode side, it is preferable to maximize value side potential of the intermediate voltage.

Thus, the intermediate voltage generated voltage with a periodicity corresponding to the timing of the zero crossing of the AC, based on the respective timing as the lowest voltage of the intermediate voltage, the first switching element pair and the second switching element energizing direction is switched in pairs, the output voltage of the AC is obtained conveniently.

  In addition, by setting the voltage that is the lowest of the intermediate voltages to be smaller than the peak value of the output voltage, the voltage applied to both ends of the switching element is reduced, and the loss that occurs in the switching element can be suppressed. .

  It should be noted that the timing at which the intermediate voltage is the lowest is a location where the intermediate voltage is substantially reduced and does not include a location where the intermediate voltage is instantaneously reduced due to the influence of noise or the like.

In this case, the so the intermediate voltage is full-wave rectified waveform, the output voltage of the sine wave is conveniently obtained by exchange.

  A command signal to the first switching element pair and the second switching element pair of the inverter circuit may be controlled by a square wave voltage to output an alternating current. Thereby, an intermediate voltage is reduced moderately and the output voltage of a desired peak value or effective value is obtained.

  By reducing the duty ratio of the command signal in the vicinity of the zero cross, the influence of the offset superimposed on the intermediate voltage is suppressed, and an output voltage having an appropriate shape can be obtained.

  Voltage detection means for detecting the output voltage of the inverter or the voltage value of the intermediate voltage is provided, so that the output voltage becomes a predetermined peak value or a predetermined effective value based on the voltage value detected by the voltage detection means. The inverter or the converter may be controlled. As a result, a more accurate peak value or effective value output voltage can be obtained.

The control unit corresponds to the timing of the zero crossing of the AC at each timing when the lowest voltage of the intermediate voltage, in every other period, the always-on said first switching element pair, the second switching The element pair may be always turned off, and at every other period, the first switching element pair may be always turned off, and the second switching element pair may be always on. As a result, an AC output voltage can be obtained with a simple configuration.

According to the power conversion device according to the present invention, the intermediate voltage generated voltage with a periodicity of the full-wave rectified waveform, corresponding to the timing of the zero crossing of the AC, the reference each time the most a low voltage of the intermediate voltage As described above, the AC output voltage can be easily obtained by switching the energization direction between the first switching element pair and the second switching element pair.

  In addition, by setting the voltage that is the lowest of the intermediate voltages to be smaller than the peak value of the output voltage, the voltage applied to both ends of the switching element is reduced, and the loss that occurs in the switching element can be suppressed. .

  Hereinafter, the first to fourth embodiments of the power conversion device according to the present invention will be described with reference to the accompanying FIGS.

  As shown in FIG. 1, the power conversion device 10 a according to the first embodiment includes a converter 14 that adjusts the voltage of a DC input voltage Vi supplied from a DC power supply 12 and outputs an intermediate voltage Vm, and an intermediate voltage The inverter 16 which converts Vm into alternating current, the stabilization circuit 18 which stabilizes the output of the inverter 16, and the control part 20 which controls the converter 14 and the inverter 16 are provided.

  The DC power source 12 is, for example, a solar cell or a fuel cell, and the input voltage Vi to be output can vary, but the output voltage Vo becomes a stable AC due to the action of the power converter 10a.

  The converter 14 includes an input-side capacitor 24, an inductor 26, an output-side capacitor 28, a switching element 30, and a diode 32 that prevents backflow. The input side capacitor 24 is connected in parallel to the DC power supply 12 and smoothes fine fluctuations of the input voltage Vi.

  The switching element 30 (and the switching elements 22a to 22d) is a semiconductor element, and examples thereof include a power transistor, an IGBT, and a switching element.

  The switching element 30 is inserted in series on the plus side line of the DC power supply 12 and is chopper-driven under the action of the control unit 20. A parasitic diode 34 is formed in parallel with the switching element 30.

  The inductor 26 is inserted in parallel downstream of the switching element 30 and generates an electromotive force based on the chopper operation of the switching element 30. The electromotive force generated by the inductor 26 is generated so that the negative line of the DC power supply 12 has a high potential, and the voltage can be controlled by the chopper signal of the switching element 30 and is controlled by the control unit 20.

  The diode 32 prevents the power generated by the action of the inductor 26 from flowing backward.

  The output side capacitor 28 is for stabilizing the voltage generated by the action of the inductor 26.

  The intermediate voltage Vm generated by the converter 14 has a high potential on the negative line of the DC power supply 12. In FIG. 1, in the connection to the inverter 16, the line is crossed so that the high potential side is upward and the blackout side is downward. It is shown as follows.

  The inverter 16 forms a bridge circuit 22 including four switching elements 22a, 22b, 22c and 22d. These switching elements 22 a to 22 d are on / off controlled under the action of the control unit 20. Parasitic diodes 23 are formed in the switching elements 22a to 22d, respectively. The switching element of the inverter 16 is not limited to a switching element, and may be a transistor, an IGBT (Insulated Gate Bipolar Transistor), or the like.

  The drains of the switching element 22a and the switching element 22c are connected to the plus side line 34a, and the sources of the switching element 22b and the switching element 22d are connected to the minus side line 34b. The connection point between the source of the switching element 22a and the drain of the switching element 22b branches to the first output line 36a, and the connection point of the source of the switching element 22c and the drain of the switching element 22d branches to the second output line 36b. doing.

  The stabilization circuit 18 includes an inductor 38 inserted in series with the first output line 36 a and the second output line 36 b, and a capacitor 40 provided on the downstream side of the inductor 38. The output voltage Vo stabilized by the stabilization circuit 18 is supplied to the load R.

  The control unit 20 includes a converter control unit 42 that performs chopper control of the converter 14 and an inverter control unit 44 that controls the inverter 16. Converter control unit 42 and inverter control unit 44 control converter 14 and inverter 16 in synchronization.

  The converter control unit 42 includes a sine wave generation unit 46, an absolute value circuit 48, an amplifier 50, a carrier wave generation unit 52, and comparators 54 and 56. The sine wave generation unit 46 generates a sine waveform Vs having the same frequency and the same peak value (that is, peak value) as the AC waveform to be obtained as the output voltage Vo in real time.

  The absolute value circuit 48 obtains the absolute value of the sine waveform Vs supplied from the sine wave generator 46 and obtains a full-wave rectified waveform.

  The amplifier 50 amplifies the full-wave rectified waveform supplied from the absolute value circuit 48. This amplification factor is small, for example, about 1.1 times. The amplification by the amplifier 50 is performed in order to set a certain margin in order to obtain a desired output voltage Vo.

  The carrier wave generation unit 52 generates a high-frequency triangular wave that is a basis for chopper-driving the converter 14. The triangular wave generated by the carrier wave generation unit 52 has a waveform with a minimum value of 0 and an amplitude on the plus side.

  The comparator 54 compares the amplified full-wave rectified waveform supplied from the amplifier 50 with the triangular wave supplied from the carrier wave generation unit 52, and outputs an on signal or an off signal according to the magnitude of both waveforms, and the switching element The switching element 30 is chopper driven by supplying it to the gate 30. That is, when the value of the full-wave rectified waveform is small, the width of the ON signal of the comparator 54 is shortened and the electromotive force of the inductor 26 is reduced. When the value of the full-wave rectified waveform is large, the ON signal of the comparator 54 is reduced. The width becomes longer and the electromotive force of the inductor 26 becomes larger. In this way, the converter 14 generates the intermediate voltage Vm of the sine wave full-wave rectified waveform under the action of the converter control unit 42.

  That is, the converter in the conventional power converter outputs a constant DC voltage as the intermediate voltage Vm, but the converter 14 in the power converter 10a according to the present embodiment generates a full-wave rectified waveform of a sine wave. It has the feature to do.

  The comparator 56 determines whether the sine waveform Vs supplied from the sine wave generator 46 is positive or negative, outputs 1 when the sine wave is positive, and outputs -1 when the sine waveform Vs is negative. To supply.

  The inverter control unit 44 includes a carrier wave generation unit 60, comparators 62 and 64, an inverter 66, and output inverters 68 and 70.

  The carrier generation unit 60 is a part that generates a high-frequency (for example, 20 kHz) triangular wave that serves as a reference for PWM control of the inverter 16. The triangular wave generated by the carrier wave generation unit 60 has a waveform with a median value of 0 and an amplitude of 1 or more on the positive side and the negative side. The carrier wave generation unit 60 may use the triangular wave obtained from the carrier wave generation unit 52 by shifting it so that the positive side and the negative side have the same peak value.

  The comparator 62 compares the positive / negative signal (1 or -1) supplied from the comparator 56 of the converter control unit 42 with the triangular wave supplied from the carrier wave generation unit 60, and turns on or off according to the magnitude of both waveforms. An off signal is output and supplied to the gate of the switching element 22a. The output inverter 68 inverts the output of the comparator 62 and supplies it to the gate of the switching element 22b. That is, the switching element 22a and the switching element 22b are driven in opposite phases.

  The inverter 66 inverts the positive / negative signal supplied from the comparator 56 of the converter control unit 42 and supplies the inverted signal to the comparator 64.

  The comparator 64 compares the positive / negative signal supplied from the inverter 66 with the triangular wave supplied from the carrier wave generation unit 60, and outputs an on signal or an off signal according to the magnitude of both waveforms, and the gate of the switching element 22c. To supply. The output inverter 70 inverts the output of the comparator 64 and supplies it to the gate of the switching element 22d. That is, the switching element 22c and the switching element 22d are driven in opposite phases.

  Since the switching element 22a and the switching element 22d are synchronized and the switching element 22b and the switching element 22c are synchronized, the switching element 22d is driven by the output signal of the comparator 62, and the switching element 22d is output by the output signal of the output inverter 68. May be driven (see FIG. 6).

  According to the inverter control unit 44, when the sine wave generated by the sine wave generation unit 46 of the converter control unit 42 is a positive value, the switching element 22a and the switching element 22d are PWM-driven with a constant duty ratio of a high value, The switching elements 22b and 22c are PWM driven with a constant duty ratio of a small value. The inverter 16 is driven by so-called complementary PWM.

  Thereby, the peak value of the intermediate voltage Vm is somewhat suppressed, and the output voltage Vo having a desired peak value is obtained. The peak value of the intermediate voltage Vm is adjusted by the amplifier 50 to about 1.1 times the peak value of the output voltage Vo. However, since there is actually a loss, the peak value of the full-wave rectified waveform is input to the inverter 16. Is, for example, about 1.05 times the desired output voltage Vo. In this case, the duty ratio is set so that the peak value of the output voltage Vo is 1 / 1.05 with respect to the peak value of the full-wave rectified waveform.

  Thereby, according to the duty ratio, the current passes from the plus line to the minus line through the switching element 22a, the first output line 36a, the load R, the second output line 36b, and the switching element 22d (first direction).

  When the sine wave has a negative value, the switching element 22b and the switching element 22c are PWM-driven with a constant duty ratio of a high value, and are PWM-driven with a constant duty ratio of a low value of the switching elements 22a and 22d. Thereby, according to the duty ratio, the current passes from the plus line to the minus line through the switching element 22c, the first output line 36a, the load R, the second output line 36b, and the switching element 22b (second direction).

That is, on the basis of the timing at which the intermediate voltage Vm of the full-wave rectified waveform output from the converter 14 becomes zero, the switching elements 22a and 22d of the first switching element pair are turned on with a high constant duty at every other period. Then, the switching elements 22b and 22c of the second switching element pair are turned on with a small constant duty . In every other period, the switching elements 22a and 22d of the first switching element pair are turned on with a constant value of a small value, and the switching elements 22b and 22c of the second switching element pair are turned on with a constant value of a high value. turn on. Thereby, the output voltage Vo which is a desired peak value is obtained.

  In the inverter in the conventional power converter, a constant DC voltage is input as the intermediate voltage Vm, and the duty ratio is controlled in real time to generate a sine waveform. The power converter according to the present embodiment The switching elements 22a to 22d of the inverter 16 in the device 10a may be simply controlled so as to be driven with a constant duty according to the sign waveform.

  As shown in FIG. 2, when compared in absolute value, the difference between the intermediate voltage Vm and the output voltage Vo is always sufficiently small, and the loss of the inverter 16 due to the current passing through the four switching elements 22a to 22d is sufficiently small. . Further, the fluctuation of the electric power to be supplied from the converter 14 to the inverter 16 is small, and the output side capacitor 28 only needs to have a small capacity.

  In the power conversion device 10a, loss may occur in the switching element 30 of the converter 14. However, since the chopper operation in the converter is an essential configuration in order to generate an appropriate intermediate voltage Vm, the conventional technology Of course, the loss does not increase in the converter 14 as compared with the above.

  FIG. 3 shows signal waveforms of respective parts of the power conversion device 10a. That is, the sine waveform Vs, the intermediate voltage Vm, the source-drain voltage Vds, the current Ic flowing through the inductor 38, and the output voltage Vo are shown. Waveform A is an on / off signal for switching elements 22a and 22d, and waveform B is an on / off signal for switching elements 22b and 22c. Waveforms A and B are on at the top and off at the bottom.

  As understood from FIG. 3, according to the power conversion device 10a, the AC output voltage Vo can be obtained with a fairly accurate sine waveform.

  FIG. 4 shows an enlarged waveform at time t1 in FIG. Time t1 is a time at which the intermediate voltage Vm reaches a peak value.

Here, each loss in the inverter 16 of the power conversion device 10a is obtained. The switching loss P _{SW # OFF} when the switching element 22a (hereinafter, the other switching elements 22b to 22d are off) is P _{SW # OFF} = Vds × Ic × Toff × f = 127.0 [V] X 15.6 [A] x 270 [ns] x 20 [kHz] = 10.7 [W]. Here, Toff is the turn-off time, and f is the frequency of the carrier wave.

The switching loss P _{SW # ON} when the switching element 22a is on is P _{SW # ON} = Vds × Ic × Ton × f = 166.6 [V] × 13.7 [A] × 60 [ns] × 20 [kHz] ] = 2.7 [W]. Here, Ton is a turn-on time.

  The conduction loss Pds of the switching element 22a is Pds = r × Iave × (T− (Ton + Toff)) × f = 0.052 [Ω] × (15.6 + 13.7) / 2 [A] × (50 [μs]. − (270 + 60) [ns]) × 20 [kHz] = 11.1 [W]. Here, r is a conduction resistance of the switching element 22a.

On the other hand, when the intermediate voltage Vm is maintained at a constant value as in the prior art, illustration is omitted, but by performing the same calculation, P _{SW # OFF} = 12.7 [W], P _{SW # ON} = 2.7 [W] and Pds = 10.3 [W].

  Thus, at time t1, there is no significant difference in the loss of the switching element in the inverter between the power conversion device according to the conventional technique and the power conversion device 10a according to the present embodiment.

  Next, FIG. 5 shows an enlarged waveform at time t2 in FIG. Time t2 is a time at which the intermediate voltage Vm becomes a value close to zero.

Similarly to the time t1, each loss of the inverter 16 of the power conversion device 10a at the time t2 is obtained. The switching loss P _{SW # OFF} when the switching element 22a is _OFF is P _{SW # OFF} = Vds × Ic × Toff × f = 16.6 [V] × 0.8 [A] × 270 [ns] × 20 [kHz] ] = 0.07 [W].

The switching loss P _{SW # ON} when the switching element 22a is on is P _{SW # ON} = Vds × Ic × Ton × f = 18.7 [V] × 0.6 [A] × 60 [ns] × 20 [kHz] ] = 0.01 [W].

  The conduction loss Pds of the switching element 22a is Pds = r × Iave × (T− (Ton + Toff)) × f = 0.052 [Ω] × (0.8 + 0.6) / 2 [A] × (50 [μs]. − (270 + 60) [ns]) × 20 [kHz] = 0.03 [W].

On the other hand, when the intermediate voltage Vm is maintained at a constant value as in the prior art, illustration is omitted, but by performing the same calculation, P _{SW # OFF} = 5.9 [W], P _{SW # ON} = 1.3 [W] and Pds = 2.3 [W].

  Thus, at time t2, it can be confirmed that the loss is significantly reduced in the power conversion device 10a according to the present embodiment as compared with the power conversion device according to the related art. In the power conversion device 10a, Vds is 16.6 [V] or 18.7 [V] at time t2, whereas in the power conversion device according to the related art, the intermediate voltage is low. This is because Vds is always about 160 [V] because Vm is always equal to or higher than the peak value of the output voltage Vo.

  Such an effect is remarkable because Vds becomes sufficiently small because the lowest voltage of the intermediate voltage Vm having periodicity is set to a voltage lower than the peak value of the output voltage Vo.

  Next, the power converter device 10b according to the second embodiment will be described. Hereinafter, about the power converter device 10b-10d, about the location of the same structure as the power converter device 10a which concerns on 1st Embodiment, the same code | symbol is attached | subjected and the detailed description is abbreviate | omitted.

  As shown in FIG. 6, the power converter 10b includes a sensor 80 that detects the voltage of the output voltage Vo, a peak detector 82 that detects a peak value of the output voltage Vo from the signal of the sensor 80, and a peak value. And a duty control unit 84 that adjusts the positive / negative signal of the comparator 56 of the converter control unit 42 based thereon.

  When the peak value is lower than the desired value, the duty control unit 84 sets the positive / negative signal (1 or −1) of the comparator 56 higher (for example, 0.9 or −0.9) according to the peak value. And supplied to the comparator 62. As a result, the output voltage Vo increases in peak value, approaches a desired value, and matches. On the contrary, when the peak value is higher than the desired value, the positive / negative signal (1 or -1) of the comparator 56 is set lower (for example, 1.1 or -1.1) according to the peak value, and the comparison is made. Supply to the device 62. As a result, the peak value of the output voltage Vo decreases, approaches the desired value, and matches. That is, the duty control unit 84 has a feedback action. The duty control unit 84 does not necessarily perform processing based on the peak value, but may perform similar processing based on, for example, the effective value. In this case, the sensor 80 may be an AC voltmeter. The sensor 80 does not necessarily detect the output voltage Vo, but the output voltage Vo with considerably high accuracy can be obtained, for example, by detecting the intermediate voltage Vm.

  Next, the power converter device 10c which concerns on 3rd Embodiment is demonstrated.

  As shown in FIG. 7, in the power conversion device 10c, the duty control unit 84 is connected to the amplifier 50 of the converter control unit 42, and adjusts the amplification factor of the amplifier 50 based on the peak value of the output voltage Vo. .

  The power conversion device 10 c includes a buffer 86 that converts the positive / negative signal (1 or −1) of the comparator 56 into a 1 or 0 signal. The output signal of the buffer 86 drives the switching elements 22 a and 22 d and drives the switching elements 22 b and 22 c via the output inverter 68. That is, the power conversion device 10c uses the timing at which the intermediate voltage Vm of the full-wave rectified waveform output from the converter 14 becomes 0 as a reference, and in every other cycle, as shown in waveforms A and B in FIG. The switching elements 22a and 22d of one switching element pair are always turned on, and the switching elements 22b and 22c of the second switching element pair are always turned off. In every other period, the switching elements 22a and 22d of the first switching element pair are always turned off, and the switching elements 22b and 22c of the second switching element pair are always turned on.

Within the inverter 16 of the power converter 10c, rather than the ability to adjust the peak value, the waveform of the intermediate voltage Vm ing to be output as the output voltage Vo is adjusted only polarity, the detection signal of the sensor 80 Based on this, the intermediate voltage Vm of the full-wave rectified waveform is adjusted, so that the output voltage Vo having a desired peak value can be obtained.

  Further, the inverter control unit 44 does not require the carrier wave generation unit 60 and the comparator 62 (see FIG. 6), and the configuration is simple. Note that the sensor 80 and the duty control unit 84 may be omitted when the output of the DC power supply 12 is stable to some extent or the accuracy of the output voltage Vo is not particularly required.

  Next, a power conversion device 10d according to a fourth embodiment will be described.

  As shown in FIG. 9, the power conversion device 10 d is provided with an offset detector 90 in addition to the power conversion device 10 b (see FIG. 6). The offset detector 90 detects the effect of the intermediate voltage Vm due to the offset Vf (see FIG. 10) based on the signal from the sensor 80 and supplies the detected effect to the duty control unit 84. The sensor 80 may be configured to directly detect the intermediate voltage Vm.

  When the duty control unit 84 recognizes that the offset Vf exists in the intermediate voltage Vm under the action of the offset detector 90, it is in the vicinity of the time when the intermediate voltage Vm becomes the lowest voltage, that is, at the time of the zero crossing of the output voltage Vo. The duty ratio is set small in the vicinity, and control is performed so that distortion due to the offset Vf does not appear in the output voltage Vo.

  That is, the intermediate voltage Vm is ideally a full-wave rectified waveform having a minimum value of 0, but in reality, a slight offset Vf may be superimposed as shown in FIG. In this case, if the intermediate voltage Vm is decreased at a constant ratio in the inverter 16, the output voltage Vo may be distorted due to the influence of the offset Vf.

  In the power conversion device 10d, in order to suppress such distortion and set the output voltage Vo with an appropriate waveform, the duty control unit 84 sets a period close to the zero cross of the output voltage Vo as shown by the waveforms A and B. Thus, the duty ratio D is continuously changed, and the duty ratio is set sufficiently small particularly in the vicinity of the zero cross. Thus, conceptually, it is equivalent to the intermediate voltage Vm being limited as shown by the phantom line to have a substantially sine waveform, and distortion due to the offset Vf can be sufficiently suppressed.

  For example, when the duty ratio D is changed linearly in the vicinity of the zero cross as shown in FIG. 10, the control procedure becomes simple.

  In the power converter 10d, when it is known in advance that the intermediate voltage Vm includes the offset Vf, the offset detector 90 may be omitted, and the duty control unit 84 may autonomously control the duty ratio. .

  As described above, according to the power conversion devices 10a to 10d according to the present embodiment, the intermediate voltage Vm is generated as a periodic voltage, and the timing at which the intermediate voltage Vm is in phase with the previous cycle (in each of the above embodiments) The AC output voltage Vo can be easily obtained by switching the energization direction between the switching elements 22a and 22d and the switching elements 22b and 22c with reference to the timing at which the voltage is lowest.

  Further, the voltage Vds applied to both ends of the switching elements 22a to 22d is reduced by setting the lowest voltage of the intermediate voltage Vm to be at least smaller than the peak value Vp (see FIG. 2) of the output voltage Vo. Therefore, it is possible to suppress the loss generated in the switching elements 22a to 22d.

  The power conversion device according to the present invention is not limited to the above-described embodiment, but can of course adopt various configurations without departing from the gist of the present invention.

It is a block diagram of the power converter device concerning a 1st embodiment. It is a figure which shows an intermediate voltage and an output voltage. It is a time chart of the waveform of each part of the power converter concerning a 1st embodiment. It is a time chart of the waveform of each part in the vicinity of a peak value. It is a time chart of the waveform of each part in the vicinity of a zero cross. It is a block diagram of the power converter device which concerns on 2nd Embodiment. It is a block diagram of the power converter device which concerns on 3rd Embodiment. It is a time chart of the waveform of each part of the power converter concerning a 3rd embodiment. It is a block diagram of the power converter device which concerns on 4th Embodiment. It is a time chart of the waveform of each part of the power converter concerning a 4th embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10a-10d ... Power converter 12 ... DC power supply 14 ... Converter 16 ... Inverter 18 ... Stabilization circuit 20 ... Control part 22 ... Bridge circuit 22a-22d, 30 ... Switching element 42 ... Converter control part 44 ... Inverter control part 80 ... Sensor 82 ... Peak detector 84 ... Duty control unit 90 ... Offset detector L ... Load Vds ... Source-drain voltage Vf ... Offset Vi ... Input voltage Vm ... Intermediate voltage Vo ... Output voltage

Claims (6)

A converter that adjusts the voltage of the DC voltage supplied from the DC power supply and outputs an intermediate voltage;
An inverter that converts the intermediate voltage into alternating current;
A control unit for controlling the converter and the inverter;
Have
It said inverter comprises a first switching element pair energizing the first direction of the current to the load, and a second switching element pair energizing the second direction of the current reversed,
The controller is
When the intermediate voltage is output by the converter , the intermediate voltage is generated as a periodic voltage of a full-wave rectified waveform for converting to the alternating current ,
Each timing at which the intermediate voltage is the lowest corresponding to the AC zero-cross timing is set as a reference timing for switching control of the first switching element pair and the second switching element pair . 1 in every cycle, the first Rutotomoni the switching element pair is turned on at least a predetermined time, and turning off the second switching element pair or in the first shorter on than the switching element pairs,
The full wave In another every other period of the rectified waveform, as well as at least a predetermined time on the second switching element pairs, and turns off the first switching element pair or the second switching element pairs shorter than Turn on
A voltage that is the lowest of the intermediate voltages is set to be smaller than a peak value of an output voltage of the inverter. The power conversion device according to claim 1,
The converter is
An input side capacitor provided between a positive electrode and a negative electrode of the DC power supply;
A switching element for turning on and off the current flowing from the positive electrode side of the DC power supply;
An inductor provided between the switching element and the negative electrode;
A backflow preventing diode having a cathode connected to a connection point between the output side of the switching element and the inductor;
An output-side capacitor provided between the anode and the negative electrode of the diode;
The controller is
When the switching element is chopped to reduce the width of the on signal when the value of the full-wave rectified waveform is small, and to increase the width of the on signal when the value of the full-wave rectified waveform is large, A voltage on the anode side of the diode for preventing backflow is set to a potential on the minimum value side of the intermediate voltage, and a voltage on the negative electrode side is set to a potential on the maximum value side of the intermediate voltage. Power conversion device. In the power converter device according to claim 1 or 2,
The controller is
Power converter and outputting the alternating current command signal to said first switching element pair and the second switching element pairs of said inverter circuit is controlled by the square-wave voltage. In the power converter device according to any one of claims 1 to 3 ,
The controller is
A power conversion device, wherein the duty ratio of the command signal is reduced in the vicinity of the zero cross of the alternating current . In the power converter device according to any one of claims 1 to 4,
Voltage detecting means for detecting a voltage value of the output voltage or the intermediate voltage of the inverter;
It said voltage based on the voltage value detected by the detection means, the power converter in which the output voltage is characterized Rukoto Gyosu control the inverter or the converter to a predetermined peak value or the predetermined effective value. In the power converter device according to any one of claims 1 to 5 ,
The controller is
Prior SL every other period, the first switching element pair always turned on, the normally-off the second switching element pairs,
Wherein in the other every other period, the first to normally-off switching element pairs, the power conversion device, characterized in that said second switching element pair always Tokio down.

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