Power Conversion Equipment

Abstract

To suppress the biased magnetization while preventing overcompensation of the biased magnetism and low resolution due to closeness between the switching cycle and the control cycle due to high frequency switching.SOLUTION: A power conversion device 1 includes an inverter 3 that bridge-connects semiconductor switching elements 31 to 34, converts DC power to AC power, and applies the AC power to the primary winding of a transformer 4, a forward converter 5 that converts AC power between terminals of other windings of the transformer 4 into DC power, a current detector 7 that detects a primary winding current flowing through the primary winding, and a control unit 20 that adjusts the output power of the inverter 3, and the control unit 20 includes a command value calculation unit 21 that calculates a duty command value, a magnetic bias detection unit 24 that detects the magnetic bias amount of the transformer 4 from a value obtained by sampling the primary winding current, a magnetic bias compensator 25 that obtains a magnetic bias compensation command value by adjusting the duty command value according to the amount of magnetic bias, and a gate driver unit 23 that compares the carrier wave and the bias compensating command value to generate a gate signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device, and more particularly to a power conversion device that performs power transformation using a transformer. [Background technology]

[0002] The density of the magnetic flux passing through the iron core of a transformer has an upper limit that depends on the cross-sectional area and the material, and if the magnetic flux increases above the allowable magnetic flux density, magnetic saturation occurs, generating an overcurrent in the winding.

[0003] In addition, since the magnetic flux generated in the iron core is proportional to the integral of the voltage applied to the windings, if the positive and negative AC voltages applied to the windings are unbalanced, biased magnetism will occur to either the positive or negative side, causing an overcurrent.

[0004] DC / AC conversion using semiconductor switching elements and power transformation using transformers are widely used. In addition, by increasing the switching frequency of semiconductor switching elements, the iron core is less likely to become magnetically saturated, which allows the transformer to be made smaller.

[0005] However, as switching frequencies become higher, the proportion of the switching period that is occupied by the positive and negative imbalance in the on / off time due to factors such as individual differences in the switching elements themselves or drive circuits increases, and the positive and negative imbalance in the switching leads to biased magnetism. If an overcurrent occurs due to biased magnetism, there is a risk of damage to the semiconductor switching elements or peripheral circuits.

[0006] In response to this, techniques have been proposed for suppressing magnetism bias in power conversion devices that use transformers.For example, Patent Document 1 discloses a technique for suppressing magnetism bias by detecting the amount of magnetism bias in a transformer and varying the duty ratio of an on / off signal of a switching element of an inverter unit that applies AC power to the primary winding of the transformer in accordance with the magnitude of the magnetism bias. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-103200 A Summary of the Invention [Problem to be solved by the invention]

[0008] In the technology disclosed in Patent Document 1, when biased magnetism occurs, the on / off times of the switching elements are corrected in each switching period. Therefore, if the amount of biased magnetism is small or if the control period is not sufficiently short compared to the switching period, overcompensation may occur, causing biased magnetism in the reverse direction and resulting in an overcurrent.

[0009] In view of the above circumstances, an object of the present invention is to provide a power conversion device that can suppress biased magnetization while preventing over-compensation of biased magnetization and a decrease in resolution due to the proximity of the switching period and the control period associated with higher switching frequencies. [Means for solving the problem]

[0010] In order to solve the above problems, a power conversion device according to the present invention includes an inverter that bridge-connects semiconductor switching elements to convert DC power to AC power and applies the AC power to a primary winding of a transformer, a forward converter that converts AC power between terminals of another winding of the transformer into DC power, a current detector that detects a primary winding current flowing through the primary winding, and a control unit that controls on / off of the semiconductor switching elements to adjust the output power of the inverter, wherein the control unit includes: a command value calculation unit that calculates a duty command value for controlling the output voltage of the forward converter, a magnetic bias detection unit that detects an amount of magnetic bias of the transformer from a sampled value of the primary winding current detected by the current detector, a magnetic bias compensation unit that calculates a magnetic bias compensation command value by adjusting the duty command value in accordance with the amount of magnetic bias detected by the magnetic bias detection unit, and a gate driver unit that generates a gate signal for the semiconductor switching elements by comparing a carrier wave that determines a switching period of the inverter with the magnetic bias compensation command value. The magnetic bias detection unit samples the primary winding current at a constant sampling period that is longer than the carrier period of the carrier wave or a half period of the carrier period by a small predetermined value in the time dimension, and calculates the amount of magnetic bias of the transformer by performing an operation on the sampled value of the primary winding current and a value obtained by delaying the sampled value. do.

[0011] Moreover, in the power conversion device according to the present invention, the magnetic bias detection unit includes a sampling unit that outputs a value of the primary winding current for each sampling period that is longer than a carrier period of the carrier wave by a predetermined value, a plurality of delay units connected in series, and a plurality of adder units and subtractor units that are provided corresponding to each of the plurality of delay units other than a rearmost delay unit and are connected in series, wherein the first delay unit among the plurality of delay units delays an output of the sampling unit by the sampling period and outputs the delayed output to the rear-stage delay unit and the corresponding adder unit, and the delay units among the plurality of delay units other than the first delay unit and the rearmost delay unit delay an output of the preceding-stage delay unit by the sampling period and output the delayed output to the rear-stage delay unit and It is preferable that the output of the previous stage adder is delayed by the sampling period and output to the corresponding adder, the last delay unit delays the output of the previous stage delay unit by the sampling period and outputs it to the subtraction unit, the first adder among the multiple adder units adds the output of the sampling unit and the output of the first delay unit and outputs it to the subsequent adder unit, the adder units among the multiple adder units other than the first adder unit and the last adder unit add the output of the previous stage adder unit and the output of the corresponding delay unit and outputs it to the subsequent adder unit, the last adder among the multiple adder units adds the output of the previous stage adder unit and the output of the corresponding delay unit and outputs it to the subtraction unit, and the subtraction unit subtracts the output of the last delay unit from the output of the last adder unit and outputs it as the amount of magnetic bias.

[0012] Furthermore, in the power conversion device of the present invention, it is preferable that the magnetic bias detection unit includes a sampling unit that outputs the value of the primary winding current for each sampling period that is a predetermined value longer than half the carrier period of the carrier wave, a delay unit that delays the output of the sampling unit by the sampling period and outputs the delayed output, an adder unit that adds the output of the sampling unit and the output of the delay unit and outputs the sum, and a low pass filter that removes high frequency components from the output of the adder unit and outputs the sum as the amount of magnetic bias. Effect of the Invention

[0013] According to the power conversion device of the present invention, it is possible to suppress asymmetric magnetization while preventing over-compensation of asymmetric magnetization and a decrease in resolution caused by the switching period and the control period becoming closer together as the switching frequency increases. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram illustrating an example of the configuration of a power conversion device according to a first embodiment of the present invention. [Diagram 2] 2 is a diagram illustrating an example of the configuration of a magnetic bias detection unit illustrated in FIG. 1; [Figure 3A] 2 is a diagram showing an example of an observation target waveform, a triangular wave, and sampling timings by the magnetic bias detection unit shown in FIG. 1 when no magnetic bias occurs; FIG. [Figure 3B] FIG. 3B is a diagram showing waveforms of values ​​obtained at the sampling timings shown in FIG. 3A. [Figure 3C] FIG. 3C is a diagram showing a waveform obtained by recording the waveform in FIG. 3B over a long period of time. [Figure 4A] 2 is a diagram showing an example of an observation target waveform, a triangular wave, and sampling timings by the magnetic bias detection unit shown in FIG. 1 when magnetic bias occurs; FIG. [Figure 4B] FIG. 4B is a diagram showing waveforms of values ​​obtained at the sampling timings shown in FIG. 4A. [Figure 4C] FIG. 4C is a diagram showing a waveform obtained by recording the waveform in FIG. 4B over a long period of time. [Diagram 5] 1 is a diagram illustrating an example of the configuration of a power conversion device according to a first embodiment of the present invention. [Figure 6] 6 is a diagram illustrating an example of the configuration of a magnetic bias detection unit illustrated in FIG. 5. [Figure 7A] 6 is a diagram showing an example of an observation target waveform, a triangular wave, and sampling timings by the magnetic bias detection unit shown in FIG. 5 when no magnetic bias occurs. FIG. [Figure 7B] FIG. 7B is a diagram showing waveforms of values ​​obtained at the sampling timings shown in FIG. 7A. [Figure 7C] FIG. 7C is a diagram showing a waveform obtained by recording the waveform of FIG. 7B for a long period of time. [Figure 7D] FIG. 7D is a diagram showing a waveform obtained by adding each value shown in FIG. 7C to the value immediately preceding that value. [Figure 8A] 6 is a diagram showing an example of an observation target waveform, a triangular wave, and sampling timings by the magnetic bias detection unit shown in FIG. 5 when magnetic bias occurs. [Figure 8B] FIG. 8B is a diagram showing waveforms of values ​​obtained at the sampling timings shown in FIG. 8A. [Figure 8C] FIG. 8C is a diagram showing a waveform obtained by recording the waveform of FIG. 8B for a long period of time. [Figure 8D] FIG. 8D is a diagram showing a waveform obtained by adding each value shown in FIG. 8C to the value immediately preceding that value. [Figure 9] FIG. 1 is a diagram illustrating a configuration example of a conventional power conversion device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] 9 shows an example of the configuration of a conventional power conversion device 100 for comparison with the present invention. The conventional power conversion device 100 includes a control unit 200, an inverter 3, a transformer 4, a forward converter 5, an input smoothing capacitor 6, a current detector 7, an output reactor 8, an output smoothing capacitor 9, and an output voltage detector 91.

[0017] The control unit 200 includes a command value calculation unit 21, a triangular wave generation unit 22, and a gate driver unit .

[0018] The command value calculation unit 21 calculates the output voltage V Out The duty command value P ref ,N ref and outputs it to the gate driver unit 23.

[0019] The triangular wave generating unit 22 generates a carrier wave (triangular wave) Vtri that determines the switching period of the inverter 3, and outputs it to the gate driver unit .

[0020] The gate driver unit 23 receives the triangular wave V tri and the duty command value P output from the command value calculation unit 21. ref ,N ref By comparing these signals, PWM (Pulse Width Modulation) controlled gate signals G31, G32, G33, and G34 are generated and output to the inverter 3.

[0021] <First embodiment> 1 is a diagram showing an example of the configuration of a power conversion device 1 according to a first embodiment of the present invention. The power conversion device 1 includes a control unit 2, an inverter 3, a transformer 4, a forward converter 5, an input smoothing capacitor 6, a current detector 7, an output reactor 8, an output smoothing capacitor 9, and an output voltage detector 91. The configuration of the control unit 2 of the power conversion device 1 differs from that of a control unit 200 of a conventional power conversion device 100.

[0022] The power conversion device 1 insulates and transforms DC power input from a DC power source 10 and outputs the power to a load 11 .

[0023] The input smoothing capacitor 6 smoothes the DC power input from the DC power supply 10 .

[0024] The inverter 3 has semiconductor switching elements 31, 32, 33, and 34 bridge-connected, and intermediate points a and b are connected to the primary winding of the transformer 4. As a result, the inverter 3 converts the DC power smoothed by the input smoothing capacitor 6 into AC power and applies it to the primary winding of the transformer 4.

[0025] The transformer 4 has a plurality of windings, and the primary winding is independent of the other windings. The transformer 4 insulates the AC power generated by the inverter 3, and in the example of FIG. 1, generates AC power between the terminals of the secondary winding and outputs it to the rectifier 5.

[0026] Transformer 4 is not limited to the two-winding transformer shown in Fig. 1, and may be a three-winding transformer. When transformer 4 is a three-winding transformer, power conversion device 1 further includes a forward converter 5 that shares the iron core of transformer 4, an output reactor 8, and an output smoothing capacitor 9. The output voltage detector 91 and control unit 2 may remain as one unit.

[0027] The rectifier 5 converts the AC power between the terminals of the other winding of the transformer 4 into DC power. Note that the other winding of the transformer 4 refers to the secondary winding if the transformer 4 is a two-winding transformer, and refers to the secondary winding and the tertiary winding if the transformer 4 is a three-winding transformer.

[0028] The output reactor 8 and the output smoothing capacitor 9 adjust the quality of the DC power generated by the rectifier 5 and output it to a load 11 external to the power conversion device 1.

[0029] The current detector 7 detects the primary winding current I Pri and outputs it to the control unit 2.

[0030] The output voltage detector 91 detects the output voltage V Out and outputs it to the control unit 2.

[0031] The control unit 2 includes a command value calculation unit 21, a triangular wave generation unit 22, a gate driver unit 23, a magnetic bias detection unit 24, and a magnetic bias compensation unit 25. The control unit 2 receives the output voltage V Out and the primary winding current I detected by the current detector 7. Pri By generating gate signals G31, G32, G33, and G34 based on the above, the on / off of the semiconductor switching elements 31, 32, 33, and 34 is controlled to adjust the output power of the inverter 3.

[0032] The command value calculation unit 21 calculates the output voltage V Out The duty command value P ref ,N refand outputs the duty command value P ref ,N ref Calculate the following.

[0033] The triangular wave generating unit 22 generates a carrier wave (triangular wave) V that determines the switching period of the inverter 3. tri and outputs it to the gate driver section 23. The carrier wave may be a sawtooth wave.

[0034] The magnetic bias detection unit 24 detects the primary winding current I Pri The value obtained at each sampling period Ts (primary winding current I Pri The value of one period obtained from the sampled value of the transformer 4 is integrated to obtain the amount of magnetic bias I Sat and outputs it to the magnetic bias compensation unit 25.

[0035] The magnetic bias compensation unit 25 detects the magnetic bias amount I Sat Depending on this, the duty command value P ref ,N ref Adjust the value of the magnetic field compensation command value P refComp ,N refComp In this specification, "adjusting the value" includes not changing the value. That is, the magnetic field bias compensation command value P refComp ,N refComp is a triangular wave V tri In a certain period, the duty command value P ref ,N ref In another period, the duty command value P ref ,N ref It does not have to change from

[0036] The gate driver unit 23 receives the triangular wave V tri and the magnetic bias compensation command value P generated by the magnetic bias compensation unit 25. refComp ,N refComp By comparing these, PWM-controlled gate signals G31, G32, G33, and G34 are generated and output to the inverter 3.

[0037] <Magnetic bias detection unit> 2 is a block diagram showing a configuration example of the magnetic bias detection unit 24. The magnetic bias detection unit 24 shown in FIG. 2 includes a sampling unit 240, a scale adjustment unit 241, a plurality of delay units 242 (delay units 242-1 to 242-(n+1)), a plurality of adders 243 (adder units 243-1 to 243-n), and a subtracter 244.

[0038] The sampling unit 240 detects the primary winding current I Pri Specifically, the sampling unit 240 outputs a sampled value of the carrier wave carrier period T (triangular wave V tri A small predetermined value in the time dimension Δt The primary winding current I Pri The value of is held and output to the scale adjustment unit 241.

[0039] The scale adjustment unit 241 adjusts the primary winding current I Pri The scale adjustment unit 241 adjusts the value of the sampled primary winding current I Pri The output level of the sampling unit 240 is adjusted so that the output level does not overflow as a result of being added by the adder 243 described later. Note that, in practical use, it is preferable to provide the scale adjustment unit 241, but the primary winding current I Pri Therefore, the scale adjustment unit 241 is not an essential component.

[0040] Delay units 242-1 to 242-(n+1) are connected in series. Only (T / Δt)+1 delay units 242 are provided. Adder units 243-1 to 243-n are connected in series. Adder units 243-1 to 243-n are provided corresponding to delay units 242-1 to 242-n, respectively. In other words, a plurality of ((T / Δt)) adders 243 are provided corresponding to each of the delay units 242 other than the last delay unit 242-(n+1), and are connected in series.

[0041] Of the multiple delay units 242 connected in series, the delay unit 242-1 (the first delay unit) receives the primary winding current I Pri The delay unit 242-1 delays the output of the sampling unit 240 by the sampling period Ts and outputs the delayed signal to the delay unit 242-2 (the subsequent delay unit) and the adder unit 243-1 corresponding to the delay unit 242-1. As described above, the scale adjustment unit 241 is not an essential component. Therefore, if the scale adjustment unit 241 is not provided, the delay unit 242-1 delays the output of the sampling unit 240 by the sampling period Ts and outputs the delayed signal to the delay unit 242-2 and the adder unit 243-1.

[0042] Of the multiple delay units 242, delay units 242-2 to 242-n other than delay unit 242-1 (the first delay unit) and delay unit 242-(n+1) (the last delay unit) delay the output of the preceding delay unit 242 by the sampling period Ts and output it to the subsequent delay unit 242 and the corresponding adder 243.

[0043] Of the multiple delay sections 242, a delay section 242-(n+1) (the last delay section) delays the output of a delay section 242-n (the preceding delay section) by the sampling period Ts and outputs the delayed output to a subtraction section 244.

[0044] Among the multiple adders 243, the adder 243-1 (the first adder) receives the primary winding current I Priand the output of delay unit 242-1 (first delay unit), and outputs the result to addition unit 243-2 (next-stage addition unit). As described above, scale adjustment unit 241 is not an essential component. Therefore, if scale adjustment unit 241 is not provided, addition unit 243-1 adds the output of sampling unit 240 and the output of delay unit 242-1, and outputs the result to addition unit 243-2.

[0045] Of the multiple adder units 243, adder units 243-2 to 243-(n-1) other than adder unit 243-1 (the first adder unit) and adder unit 243-n (the last delay unit) add the output of the previous adder unit 243 to the output of the corresponding delay unit 242 and output the result to the adder unit 243 in the subsequent stage.

[0046] Of the multiple adders 243, adder 243-n (the last adder) adds the output of adder 243-(n-1) (the previous adder) and the output of corresponding delay unit 242-n, and outputs the result to subtraction unit 244.

[0047] The subtraction unit 244 subtracts the output of the delay unit 242-(n+1) (the last delay unit) from the output of the addition unit 243-n (the last addition unit) to obtain the magnetic bias amount I Sat The output is as follows:

[0048] <Magnetic bias detection method> Next, a magnetic bias detection method by the magnetic bias detection unit 24 will be described with reference to Figures 3A to 3C and 4A to 4C. In Figures 3A to 3C and 4A to 4C, the horizontal axis indicates time.

[0049] 3A and 4A are diagrams showing waveforms of the observation target waveform target, the triangular wave tri for sampling timing, and the sampling timing command value ref. FIG. 3B and 4B are diagrams showing waveforms of values ​​obtained by reading the observation target waveform target at the sampling timing. FIG. 3C and 4C are diagrams showing waveforms obtained by recording the waveforms shown in FIG. 3B and 4B for a long period of time. FIG. 3A to FIG. 3C show a case where no biased magnetism occurs, and FIG. 4A to FIG. 4C show a case where biased magnetism occurs. In addition, in FIG. 3A to FIG. 3C and FIG. 4A to FIG. 4C, the frequency of the observation target waveform target is 50 Hz, the frequency of the triangular wave tri is 49 Hz, the carrier period T is 20 ms, and Δt is 0.408 ms. Therefore, the sampling period Ts is 20.408 ms. The phase of the triangular wave tri may or may not be synchronized with the phase of the observation target waveform target.

[0050] 3A and 4A, the sampling unit 240 samples the value of the observation target waveform target at the moment when the triangular wave tri coincides with the sampling timing command value ref. As described above, the sampling period Ts is set to be longer than the carrier period T. Δt Therefore, as shown in Figures 3B and 4B, the sampling timing shifts little by little. This allows the value of the observation target waveform (target) to be read with high resolution.

[0051] The carrier period T is 20 ms and Δt is 0.408 ms, so to sample one period of the target waveform, T / Δt pieces of data are required. Since the frequency of the triangular wave tri is 49 Hz, one period of the target waveform target can be sampled in 1 second.

[0052] When bias is occurring (FIG. 4C), the positive peak value of the observation target waveform TARGET changes nonlinearly (circled portion in FIG. 4C) compared to when bias is not occurring (FIG. 3C). Therefore, when the sum of the sampled values ​​for one period of the observation target waveform TARGET shown in FIGS. 3C and 4C is calculated, the sum is 0 when bias is not occurring, and a deviation occurs when bias is occurring. Therefore, the amount of bias I Sat can be detected.

[0053] In this embodiment, the primary winding current I Pri From the sampled values ​​(sampled at a sampling period that is a predetermined value Δt greater than the carrier period T), the magnetic bias amount I of the transformer 4 is calculated. Sat Therefore, the amount of bias magnetism I Sat can be detected with high accuracy. As a result, it is possible to suppress the magnetism bias while preventing overcompensation of the magnetism bias and a decrease in resolution due to the approach of the switching period and the control period accompanying the high frequency switching. Moreover, the power conversion device 1 according to this embodiment can be configured by simply adding the magnetism bias detection unit 24 and the magnetism bias compensation unit 25 to the conventional power conversion device 100.

[0054] <Second embodiment> Fig. 5 is a diagram showing an example of the configuration of a power conversion device 1a according to a second embodiment of the present invention. In Fig. 5, the same components as those in Fig. 1 are given the same reference numerals, and the description thereof will be omitted.

[0055] 5, the power conversion device 1a according to this embodiment is different from the power conversion device 1 according to the first embodiment in that the control unit 2 is changed to a control unit 2a. The control unit 2a is different from the control unit 2 in that the magnetic bias detection unit 24 is changed to a magnetic bias detection unit 24a.

[0056] <Magnetic bias detection unit 24a> FIG. 6 is a diagram showing an example of the configuration of the magnetic bias detection unit 24a.

[0057] As shown in FIG. 6, the magnetic bias detection unit 24a includes a sampling unit 240a, a scale adjustment unit 241a, a delay unit 242a, an addition unit 243a, and a low pass filter (LPF) 245.

[0058] The sampling unit 240a detects the primary winding current I Pri Specifically, the sampling unit 240a outputs a sampled value of a small predetermined value in the time dimension every half period (T / 2) of the carrier period T of the carrier wave. Δt The primary winding current I Pri The value is held and output to the scale adjustment unit 241a.

[0059] The scale adjustment unit 241a adjusts the primary winding current I Pri The scale adjustment unit 241 adjusts the value of the sampled primary winding current I Pri The output level of the sampling unit 240a is adjusted so that the output level does not overflow as a result of being added by the adder 243a described later. Note that, in practical use, it is preferable to provide the scale adjustment unit 241a, but the primary winding current I Pri Therefore, the scale adjustment unit 241a is not an essential component.

[0060] The delay unit 242a receives the primary winding current I Pri The delay unit 242a delays the output of the sampling unit 240a by the sampling period Ts and outputs the delayed output to the adding unit 243a. As described above, the scale adjustment unit 241a is not an essential component. Therefore, if the scale adjustment unit 241a is not provided, the delay unit 242a delays the output of the sampling unit 240a by the sampling period Ts and outputs the delayed output to the adding unit 243a.

[0061] The adder 243a receives the primary winding current I Pri and the output of the delay unit 242 a are added together and output to the LPF 245 .

[0062] The LPF 245 removes high-frequency components from the output of the adder 243a and outputs only low-frequency components as the magnetic bias amount I Sat The output is as follows:

[0063] <Magnetic bias detection method> Next, a magnetic bias detection method by the magnetic bias detection unit 24a will be described with reference to Figures 7A to 7D and 8A to 8D. In Figures 7A to 7D and 8A to 8D, the horizontal axis indicates time.

[0064] 7A and 8A are diagrams showing waveforms of the observation target waveform target, the triangular wave tri for sampling timing, and the sampling timing command value ref. FIG. 7B and 8B are diagrams showing waveforms of values ​​obtained by reading the observation target waveform at the sampling timing. FIG. 7C and 8C are diagrams showing waveforms obtained by recording the waveforms shown in FIG. 7B and 8B for a long time. FIG. 7D and 8D are diagrams showing waveforms obtained by adding the values ​​obtained in FIG. 7C and 8C to the previous value. FIG. 7A to FIG. 7D show a case where biased magnetization does not occur, and FIG. 8A to FIG. 8D show a case where biased magnetization occurs. In addition, in FIG. 7A to FIG. 7D and FIG. 8A to FIG. 8D, the frequency of the observation target waveform target is 50 Hz, the frequency of the triangular wave tri is 99 Hz, the carrier period T is 20 ms, and Δt is 0.101 ms. Therefore, the sampling period Ts is 10.101 ms. The phase of the triangular wave tri may or may not be synchronized with the phase of the observation target waveform target.

[0065] 7A and 8A, the sampling unit 240a samples the value of the observation target waveform target at the moment when the triangular wave tri coincides with the sampling timing command value ref. As described above, the sampling period Ts is set to be shorter than a half period (10 ms) of the carrier period T. ΔtTherefore, as shown in Figures 7B and 8B, the sampling timing shifts little by little. This allows the value of the observation target waveform (target) to be read with high resolution.

[0066] The sampling period Ts by the sampling unit 240a is longer than half the carrier period T by Δt ( T / 2+Δt 7C and 8C, the sampling section 240a can sample positive and negative values ​​alternately.

[0067] When no biased magnetism occurs, as shown in FIG. 7D, adding each value shown in FIG. 7C to the value immediately preceding it results in a value of almost 0 at most sampling timings, since positive and negative values ​​are sampled alternately.

[0068] On the other hand, when biased magnetism occurs, as indicated by a circle in FIG. 8D, a DC component appears on the positive side where biased magnetism occurs.

[0069] By passing the amount of change per half cycle obtained in Figs. 7D and 8D through the LPF 245, the amount of biased magnetism I Sat can be detected.

[0070] In this embodiment, the primary winding current I Pri From the sampled values ​​(sampled at a sampling period that is a predetermined value Δt greater than half the carrier period T), the magnetic bias amount I of the transformer 4 is calculated. Sat Therefore, the amount of bias magnetism I Sat It is possible to detect the bias magnetization with high accuracy. As a result, it is possible to suppress the bias magnetization while preventing overcompensation of the bias magnetization and a decrease in resolution due to the closeness of the switching period and the control period accompanying the high frequency switching. Moreover, the power conversion device 1a according to this embodiment can be configured by simply adding the bias magnetization detection unit 24a and the bias magnetization compensation unit 25 to the conventional power conversion device 100.

[0071] Furthermore, in the technology disclosed in Patent Document 1, a simple LPF is used for magnetic bias detection, so when discrete values ​​are used, the accuracy of magnetic bias detection is affected by the sampling period. Also, when continuous values ​​are used to implement an LPF using an analog circuit, hardware that constitutes the analog circuit is required. On the other hand, in the power conversion devices 1 and 1a according to the present invention, the carrier period T and a minute difference ( Δt ) or a small difference between the half period of the carrier period T ( Δt ) in the sampling period Ts Δt By adjusting the sampling timing period, it is possible to detect magnetic bias with high accuracy at a period of about the carrier period T or a half period of the carrier period T. Furthermore, since the magnetic bias detection method according to the present invention can be realized by software on a control unit included in a general power conversion device, there is no need to provide separate hardware.

[0072] Moreover, the power conversion device 1, 1a according to the present invention realizes magnetic bias compensation by the independently existing magnetic bias detection unit 24 or magnetic bias detection unit 24a and magnetic bias compensation unit 25. Therefore, magnetic bias compensation can be easily realized by simply adding components equivalent to the magnetic bias detection unit 24 or magnetic bias detection unit 24a and magnetic bias compensation unit 25 to an existing power conversion device that does not perform magnetic bias compensation.

[0073] Although the above-mentioned embodiment has been described as a representative example, it is obvious to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the above-mentioned embodiment, and various modifications and changes are possible without departing from the scope of the claims. [Explanation of symbols]

[0074] 1,1a Power conversion device 2,2a Control part 3. Inverse converter 4. Transformers 5. Forward converter 6 Input smoothing capacitor 7 Current Detector 8 Output reactor 9 Output smoothing capacitor 10 DC power supply 11 Load 21 Command value calculation unit 22 Triangle wave generator 23 Gate driver section 24, 24a Magnetic bias detection unit 25 Unbalanced magnetic compensation section 240,240a Sampling section 241,241a Scale adjustment section 242,242a Delay section 243,243a Addition section 244 Subtraction section 245 LPF

Claims

1. an inverter that converts DC power into AC power by connecting semiconductor switching elements in a bridge and applies the AC power to a primary winding of a transformer; a converter for converting AC power between terminals of the other winding of the transformer into DC power; a current detector for detecting a primary winding current flowing through the primary winding; A control unit that controls on / off of the semiconductor switching element to adjust the output power of the inverter, The control unit is a command value calculation unit that calculates a duty command value for controlling an output voltage of the converter; a magnetism bias detection unit that detects an amount of magnetism bias of the transformer from a sampled value of the primary winding current detected by the current detector; a magnetic bias compensation unit that obtains a magnetic bias compensation command value by adjusting the duty command value in accordance with the amount of magnetic bias detected by the magnetic bias detection unit; a gate driver unit that generates a gate signal for the semiconductor switching element by comparing a carrier wave that determines a switching period of the inverter with the magnetic bias compensation command value, the magnetic bias detection unit samples the primary winding current at every fixed sampling period that is longer in time dimension than the carrier period of the carrier wave or a half period of the carrier period by a small predetermined value, and calculates the amount of magnetic bias of the transformer by performing an operation on the sampled value of the primary winding current and a value obtained by delaying the sampled value.

2. 2. The power conversion device according to claim 1, The magnetic bias detection unit includes: a sampling unit that outputs a value of the primary winding current for each sampling period that is longer than a carrier period of the carrier wave by a minute predetermined value in a time dimension; A plurality of delay units connected in series; a plurality of adders connected in series, the adders being provided corresponding to the delay units other than the last delay unit among the plurality of delay units; A subtraction unit, Among the plurality of delay units, a leading delay unit delays the output of the sampling unit by the sampling period and outputs the delayed output to a subsequent delay unit and a corresponding adding unit; Among the plurality of delay units, delay units other than the first delay unit and the last delay unit delay the output of the preceding delay unit by the sampling period and output the delayed output to the subsequent delay unit and the corresponding adder unit; the last delay unit delays the output of the preceding delay unit by the sampling period and outputs the delayed output to the subtraction unit; a first adder among the plurality of adders adds an output of the sampling unit and an output of the first delay unit, and outputs the sum to a subsequent adder; Among the plurality of adders, each adder other than the first adder and the last adder adds an output of a previous adder and an output of a corresponding delay unit, and outputs the result to the adder in the subsequent stage; Among the plurality of adders, the last adder adds an output of a previous adder and an output of a corresponding delay unit, and outputs the result to the subtracter; The subtraction unit subtracts the output of the last delay unit from the output of the last addition unit, and outputs the result as the amount of magnetic bias.

3. 2. The power conversion device according to claim 1, The magnetic bias detection unit includes: a sampling unit that outputs a value of the primary winding current for each sampling period that is longer than a half period of the carrier period of the carrier wave by a small predetermined value in a time dimension; a delay unit that delays the output of the sampling unit by the sampling period and outputs the delayed output; an adder unit that adds an output of the sampling unit and an output of the delay unit and outputs the result; a low-pass filter that removes high-frequency components from the output of the adder and outputs the result as the amount of magnetic bias.

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