JP3965622B2 - Power converter - Google Patents

Description

電力変換器出力電圧補正器３２では、出力電流と関数Ｆを乗じて得た出力の平均値を求め、偏磁状態を検出するとともに、検出値を基に電力変換器出力電圧指令の補正値を出力する。
【００１２】
本実施形態では、変圧器３の直流偏磁に伴うピーク電流と関数Ｆが振幅１である位相が一致しているので、ピーク電流に対する相関が強く、効率よくピーク電流を検出でき、変圧器３の偏磁方向および偏磁の大きさを精度良くかつ確実に検出することができる。
一方で、関数Ｆは直流成分を含まないので、出力電流検出値に直流成分が含まれていても、直流成分は偏磁成分の検出値、すなわち出力電流検出値と関数Ｆとの積の平均値には全く影響を与えない。同様に、関数Ｆは電力変換器１の基本波成分を含まないから、偏磁電流の検出値には全く影響を与えない。
これにより、検出系に直流成分が含まれていても、また、基本波成分が含まれていても、直流偏磁に伴うピーク電流を誤差なく、確実に検出することができる。
勿論、高調波を発生する負荷が変圧器の二次側に接続されていたとしても、これらの負荷に起因する高調波成分を含まないように関数Ｆを設定すれば、同様の効果が得られる。例えば、ダイオードやサイリスタのような半導体素子からなる整流負荷は、３次、５次、７次、９次といった低次の高調波を多く含むことが知られており、これらを含まないように関数Ｆを設定すればよい。また、三相の場合には３の整数倍の高調波は含まず、５次、７次といった高調波を多く含むので、これらを含まないように関数Ｆを設定すればよい。
【００１３】
なお、変圧器の入力電流を直接検出できる場合には、電力変換器の出力電流に代えて変圧器の入力電流を用い、変圧器の偏磁状態の検出に用いても同様の効果が得られる。
また、直流成分および基本波成分との相関が低く、偏磁電流との相関が高ければ、変圧器の偏磁検出に用いる関数Ｆの波形は、図３に示す波形でなくても良い。
上述した実施形態においては、電力変換器出力電流と関数Ｆを乗じることにより、偏磁方向および強さを検出しているが、図３に示したように、１、０、−１の三つのレベルからなる比較的簡単な関数の場合には、電力変換器出力電流と関数Ｆを乗じるに及ばず、積算バッファーを設け、電力変換器出力電流をＦ＝１の場合には、サンプリングした出力電流を加算し、Ｆ＝−１の場合にはサンプリングした出力電流を減算することでも同様の結果が得られる。
本発明の実施形態として、直流を単相交流に変換する電力変換器を用いて出力電圧を制御する電力変換装置を例にとって説明したが、本発明は、三相交流を含む多相交流の変圧器にも容易に適用可能である。また、直流を交流に変換する電力変換器を用いて交流出力電流を制御する電力変換装置や、交流を直流に変換する電力変換装置を用いて交流入力電流および直流電圧を制御する電力変換装置にも容易に適用可能である。
【００１４】
【発明の効果】
以上説明したように、本発明によれば、直流成分および基本波成分との相関が低く、偏磁電流との相関が高い関数Ｆと電力変換器の出力電流とを乗じることにより、検出系に含まれるオフセット成分の影響、負荷電流の影響を受けることなく、簡単かつ確実に変圧器の偏磁方向および強さを検出することができ、また、検出系のオフセット成分の影響、負荷電流の影響を受けることなく、変圧器の偏磁現象を確実に抑制することができ、安定かつ歪のない良質な交流出力電圧を得ることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態である電力変換装置の構成図
【図２】変圧器の直流偏磁に伴い発生するピーク電流を示す図
【図３】本発明の変圧器の直流偏磁に伴い発生するピーク電流を検出するための関数の一例を示す図
【符号の説明】
１…電力変換器、２…フィルタ回路、３…変圧器、４…負荷、５…電圧検出器、６…電流検出器、１１…二次電圧指令発生器、１２…二次電圧制御器、１３…電力変換器出力電流制御器、１４…パルス発生器、１５…減算器、３１…関数発生器、３２…電力変換器出力電圧補正器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power conversion device, and more particularly to a DC converter that is constituted by a switching element and that is connected to an AC side of a power converter that converts DC to AC and a power converter that converts AC to DC. TECHNICAL FIELD OF THE INVENTION
[0002]
[Prior art]
In general, on the AC side of a power converter that converts AC to DC and a power converter that converts DC to AC, in order to insulate the power converter from the power source and load, and to obtain the required AC voltage and current Is connected to the transformer.
A power converter can obtain direct current from alternating current, or conversely from direct current, but it constitutes a direct current component (offset component) included in the voltage detection system, current detection system and control system, and a power converter. A DC component may be included in the AC output voltage due to variations in switching speed of the switching elements.
When a DC component is included in the input voltage of the transformer, the excitation inductance is extremely reduced due to saturation of the magnetic material constituting the transformer, and (1) an excessive excitation current flows. (2) the transformer Are distorted, and (3) the magnetic noise is increased.
Japanese Patent Laid-Open No. 2000-231269 discloses a method for suppressing direct current magnetic polarization of a transformer connected to a power converter. By limiting the period for accumulating the current of the transformer, drift of the current detection system ( A method for reducing the influence of the DC deviation due to the offset and the time variation of the offset is described.
[0003]
[Problems to be solved by the invention]
In the known example, the influence of the offset can be reduced, but in principle the influence of the offset cannot be made zero. For this reason, when the offset is large, a sufficient demagnetization suppressing effect cannot be expected.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to provide a power converter in which a transformer is connected to the AC terminal of a power converter, and reliably detect the biased state of the transformer without being affected by the offset of the detection system. This is to suppress the magnetic demagnetization.
[0005]
[Means for Solving the Problems]
In order to solve the above problem, the output current of the power converter is multiplied by a function that has a strong correlation with the bias magnetic current and has no correlation with the direct current component, the fundamental wave component, and the harmonics caused by the load. From the output current of the power converter, the intensity and direction of the magnetic bias of the transformer are detected, the AC output of the power converter is corrected based on the detected value, and the DC magnetic bias of the transformer is suppressed.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a power conversion apparatus according to an embodiment of the present invention. In the present embodiment, a DC voltage source 20 and a DC power source 21 are used as a DC voltage source. The power converter 1 includes a switching element, converts DC to AC, a reactor, and a capacitor. Filter circuit 2 for removing high-frequency components contained in the output voltage to be output, transformer 3 having the output voltage of filter circuit 2 as a primary input voltage, load device 4 connected to the secondary side of transformer 3, The voltage detector 5 for detecting the secondary voltage of the voltage generator 3 and the output current command of the power converter 1 are generated so that the output of the voltage detector 5 matches the output voltage command output by the secondary voltage command generator 11 The secondary voltage controller 12 that detects the output current of the power converter 1, the output of the secondary voltage controller 12 and the output of the current detector 6 so that the output of the current detector 6 matches. The power to adjust the output voltage Converter output current controller 13, function generator 31 that outputs function F used to detect the biased magnetic current, and power conversion that calculates an output voltage correction value from the output of current detector 6 and the output of function generator 31 Based on the output of the subtractor 15, the subtractor 15 that subtracts the output of the power converter output voltage corrector 32 from the power converter output voltage command generated by the power converter output current controller 13, and the subtractor 15. This is a power conversion device comprising a pulse generator 14 that outputs a control pulse for controlling the switching state of the switching elements constituting the power converter 1.
[0007]
In FIG. 1, in order to supply a stable AC voltage to the load device 4, the secondary voltage of the transformer 3 is detected, and the output of the voltage detector 5 is output by the secondary voltage controller 12 to the secondary voltage command generator 11. The power converter output current command is output so as to match the output voltage command output by the power converter 1, the output current of the power converter 1 is detected, and the power converter output current controller 13 outputs the power of the current detector 6 to the power. The output voltage of the power converter 1 is adjusted so as to coincide with the converter output current command.
Further, in the power converter output voltage corrector 32, the function F having a strong correlation with the peak current generated when the transformer 3 is dc-biased by the function generator 31 and the output of the power converter 1 are generated. While detecting the direction and strength of the magnetism of the transformer 3 from the current, the output voltage correction value of the power converter 1 is output based on the detection result. By subtracting the output voltage correction value from the output of the power converter output current controller 13, the DC bias of the transformer 3 is suppressed.
[0008]
The secondary output voltage command of the secondary voltage command generator 11, the output current command of the secondary voltage controller 12, and the output of the power converter output current controller 13 are only alternating current components that do not include direct current components. However, the output voltage and current of the power converter 1 and the secondary output voltage and current of the transformer 3 are also controlled only by the AC component. That is, the direct current component is controlled to be zero. For this reason, a DC voltage is not applied to the transformer 3.
However, the current detector 6 constituting the output current detection system and the controllers 12 and 13 constituting the control system contain a small amount of DC component, and the detected component does not exist as an offset component, that is, originally. Various quantities are detected with the DC component superimposed. When a direct current component is superimposed on the detection system and the control system, it appears as if the direct current component exists even though the direct current component is not included in the output current of the power converter 1. Therefore, the current control system controls the output voltage of the power converter 1 so that the superimposed offset component becomes zero. Since the DC component is not removed in the filter circuit 2, the DC component output from the power converter 1 is applied to the primary winding of the transformer 3. As a result, a DC component is also superimposed on the primary input voltage of the transformer, and the iron core of the transformer 3 causes DC demagnetization. When the iron core of the transformer 3 is DC-biased, the excitation inductance is extremely reduced, so that an excessive peak current (dotted line) flows near the zero cross of the transformer voltage as shown in FIG.
In order to suppress such a phenomenon, the peak current component generated by the DC bias of the transformer core included in the output current of the power converter 1 is detected, so that this is suppressed, that is, the power converter 1. The output voltage may be controlled in the direction in which the DC component included in the output voltage decreases. However, the output current of the power converter 1 includes the current superimposed on the current flowing through the filter circuit 2 and the load current (secondary current multiplied by the transformer turns ratio) in addition to the peak current due to the DC bias. Become. In particular, since the load current varies depending on the state of the load, it is extremely difficult to reliably detect only the peak current associated with the DC bias from the output current of the power converter 1.
As a method for detecting the presence / absence of DC bias in the transformer 3, a method of detecting a DC component included in the output current of the power converter 1 is conceivable. However, since the current detection system is affected by offset, It is virtually impossible to accurately detect the components.
There is the above-mentioned known example as a direction in which the influence of the offset is eliminated and the magnetic bias current is detected. However, this method only reduces the influence of the offset component, and depending on the magnitude of the offset component, Current may not be detected. Or it may be detected as if it is demagnetized even though it is not demagnetized.
[0009]
Therefore, in the present embodiment, the function F and the inverter output current, which have no correlation with the direct current component and the fundamental wave component and have a strong correlation with the peak current component due to the direct current magnetization, are multiplied by the average value of the multiplication results. Detect the magnitude and direction of the magnetic current.
Here, the correlation between functions will be described. A case where the frequency components included in a certain function G (t) and H (t) and the phases of the frequency components are dense is called a strong correlation (having a common frequency component and the same phase), and these are sparse. There is a case where there is no correlation (no relationship at all: frequency and phase do not match). That is, the function having the strongest correlation with a certain function G (t) is G (t) itself, and the function having no correlation with G (t) is a function composed of frequency components not included in G (t), or The frequency components included in G (t) are functions that are orthogonal to each other.
Ideally, there is no correlation between the function F and the DC component of the function F and the fundamental component of the function F, but if the intensity of the correlation with the peak current component due to the DC bias is negligible or sufficiently small. It is possible to suppress demagnetization.
For example, the DC component (including offset and error) detected by the power converter output current detection system is A, the effective value of the fundamental wave (including error) is B, and the effective value of the peak current associated with DC bias is When H is H, the correlation strength with respect to the DC component of the detection function F is AF, the correlation strength with respect to the fundamental wave is BF, and the correlation strength with respect to the peak current associated with the demagnetization is HF, the direction and strength of the demagnetization. The value that represents
A x AF + B x BF + H x HF
It is represented by
In order to suppress the demagnetization, Am × AF and Bm × BF need only be ignored or sufficiently smaller than H × HF. However, Am is the maximum offset value (determined by the accuracy of the controller and detector) possessed by the control device of the power converter, and Bm is the maximum output current (determined by the output capacity) of the power converter. For example, if the level that can be ignored is X (depending on the scale of the device and the object to be controlled, it is considered to be about 5 to 10%), and the minimum detection level of the bias current (bias current detection accuracy) is Hm.
X × (Hm × HF)> Am × AF
X × (Hm × HF)> Bm × BF
That is, the correlation for each component is AF <X × Hm × HF / Am
BF <X × Hm × HF / Bm
If this is satisfied, detection of the bias current is not affected.
Therefore, it is sufficient to use a function F that satisfies the above-mentioned correlation with respect to the DC current, the fundamental wave component, and the peak current caused by the bias.
[0010]
Based on the magnitude and direction of the bias current, an output voltage correction value for correcting the output voltage of the power converter 1 is generated from the power converter output voltage corrector 32 so that the bias current is attenuated or zero. By subtracting from the output of the power converter output current controller 13, the DC component included in the output voltage of the power converter 1 is suppressed. Examples of means for generating the output voltage correction value from the bias current include a proportional controller and a proportional-integral controller widely used in feedback control.
[0011]
The operation will be described below by taking as an example the case where a function as shown in FIG. 3 is used as the function F satisfying the above conditions.
The function F shown in FIG. 3 is a phase in which the peak current is generated and a pulse having an amplitude of 1 and a width W (W is 90 ° or less) so that the correlation with the peak current associated with the DC bias of the transformer 3 is high. , A function having a pulse with an amplitude of −1 and a width W within a half period (T / 2) of the period T of the pulse and the fundamental wave. That is, the function F shown in FIG. 3 can be expressed as (1).
In FIG. 3, one cycle of the output voltage is 2π,
0 ≦ θa, θb, θc, θd, θe, θf, θg, θh ≦ 2π
Also, θe = θa + π, θf = θb + π, θg = θc + π, θh = θd + π
Then,
[Expression 1]

The power converter output voltage corrector 32 obtains an average value of the output obtained by multiplying the output current and the function F, detects the biased state, and calculates a correction value of the power converter output voltage command based on the detected value. Output.
[0012]
In the present embodiment, the peak current associated with the DC bias of the transformer 3 and the phase where the function F has an amplitude of 1 coincide with each other, so that the correlation with the peak current is strong and the peak current can be detected efficiently. It is possible to accurately and reliably detect the demagnetization direction and the magnitude of the demagnetization.
On the other hand, since the function F does not include a direct current component, even if the output current detection value includes the direct current component, the direct current component is the detected value of the bias component, that is, the average of the product of the output current detection value and the function F. The value is not affected at all. Similarly, since the function F does not include the fundamental wave component of the power converter 1, it does not affect the detected value of the bias current.
As a result, even if the detection system includes a direct current component or a fundamental wave component, it is possible to reliably detect the peak current associated with the direct current bias without error.
Of course, even if a load generating harmonics is connected to the secondary side of the transformer, the same effect can be obtained if the function F is set so as not to include harmonic components caused by these loads. . For example, a rectifying load made of a semiconductor element such as a diode or a thyristor is known to contain many low-order harmonics such as third order, fifth order, seventh order, and ninth order. F may be set. In the case of three phases, harmonics that are integer multiples of 3 are not included, and many harmonics such as the fifth and seventh orders are included. Therefore, the function F may be set so as not to include them.
[0013]
If the input current of the transformer can be directly detected, the same effect can be obtained by using the input current of the transformer instead of the output current of the power converter and detecting the biased state of the transformer. .
Further, if the correlation between the direct current component and the fundamental wave component is low and the correlation with the magnetic bias current is high, the waveform of the function F used for detecting the magnetic bias of the transformer may not be the waveform shown in FIG.
In the above-described embodiment, the demagnetization direction and the strength are detected by multiplying the power converter output current and the function F, but as shown in FIG. In the case of a relatively simple function consisting of levels, it is not necessary to multiply the power converter output current and the function F, but an integration buffer is provided. When the power converter output current is F = 1, the sampled output current The same result can be obtained by subtracting the sampled output current when F = −1.
As an embodiment of the present invention, a power conversion device that controls an output voltage using a power converter that converts direct current to single-phase alternating current has been described as an example, but the present invention is a multiphase alternating current transformer including three-phase alternating current. It can be easily applied to vessels. In addition, a power converter that controls AC output current using a power converter that converts DC to AC, and a power converter that controls AC input current and DC voltage using a power converter that converts AC to DC Is also easily applicable.
[0014]
【The invention's effect】
As described above, according to the present invention, the detection system is multiplied by multiplying the output current of the power converter by the function F having a low correlation with the DC component and the fundamental wave component and a high correlation with the bias current. It is possible to easily and reliably detect the direction and strength of the transformer's magnetism without being affected by the offset component and load current included. Also, the influence of the offset component of the detection system and the effect of the load current Without being subjected to this, it is possible to reliably suppress the magnetic demagnetization phenomenon of the transformer, and to obtain a stable and distortion-free high quality AC output voltage.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a power conversion apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a peak current generated due to DC bias of a transformer. FIG. Diagram showing an example of a function for detecting the peak current generated by the
DESCRIPTION OF SYMBOLS 1 ... Power converter, 2 ... Filter circuit, 3 ... Transformer, 4 ... Load, 5 ... Voltage detector, 6 ... Current detector, 11 ... Secondary voltage command generator, 12 ... Secondary voltage controller, 13 ... Power converter output current controller, 14 ... Pulse generator, 15 ... Subtractor, 31 ... Function generator, 32 ... Power converter output voltage corrector

Claims (6)

In a power converter comprising a power converter, a transformer connected to the AC terminal of the power converter, and a control device that controls at least one of the current or voltage of the AC terminal of the power converter,
Function generation that generates a function that has a strong correlation with the peak current generated when the transformer is magnetically saturated and the excitation inductance decreases, and that has no correlation between the DC component and the fundamental component of the AC output from the power converter. And multiplying the output of the function generating means by either one of the current at the AC terminal of the power converter or the input current of the transformer, and detecting the demagnetization state of the transformer from the result of multiplication , Power converter output voltage correction means for calculating an output voltage correction value of the power converter according to the detected biased state of the transformer is provided, and the power converter output voltage is determined from an output voltage command of the power converter. A power conversion apparatus, wherein the output voltage correction value calculated by the correction means is subtracted to correct the AC output of the power converter and suppress DC bias magnetism of the transformer. In a power converter comprising a power converter, a transformer connected to the AC terminal of the power converter, and a control device that controls at least one of the current or voltage of the AC terminal of the power converter,
Strongly correlated with the peak current generated when the transformer is magnetically saturated and the excitation inductance is reduced, and compared with the correlation with the peak current, the direct current component and the alternating current fundamental wave component output from the power converter A function generating means for generating a function having a sufficiently weak correlation, and multiplying the output of the function generating means by either the current at the AC terminal of the power converter or the input current of the transformer. A power converter output voltage correction means for detecting a biased state of the transformer and calculating an output voltage correction value of the power converter according to the detected biased state of the transformer; this AC output of the power converter by correcting the output voltage command by subtracting the calculated output voltage correction value of the power converter output voltage correcting unit suppresses the DC magnetic deviation of the transformer Power converter according to claim. In a power converter comprising a power converter, a transformer connected to the AC terminal of the power converter, and a control device that controls at least one of the current or voltage of the AC terminal of the power converter,
Function generating means for generating a function having a strong correlation with the peak current generated when the transformer is magnetically saturated and the excitation inductance is reduced, and having no correlation between the DC component and the AC fundamental wave component output from the power converter And multiplying the output of the function generating means by either the current at the AC terminal of the power converter or the input current of the transformer, and calculating the average value of the results of the multiplication, And a power converter output voltage correction means for calculating an output voltage correction value of the power converter according to the detected biased state of the transformer, and from the output voltage command of the power converter, A power conversion device, wherein the output voltage correction value calculated by the power converter output voltage correction means is subtracted to correct the AC output of the power converter and suppress DC bias magnetism of the transformer. In a power converter comprising a power converter, a transformer connected to the AC terminal of the power converter, and a control device that controls at least one of the current or voltage of the AC terminal of the power converter,
Strongly correlated with the peak current generated when the transformer is magnetically saturated and the excitation inductance is reduced, and compared with the correlation with the peak current, the direct current component and the alternating current fundamental wave component output from the power converter and function generating means for correlation to generate a sufficiently weak function, multiplied by the output of the function generator means to one of the input current of the current or the transformer of the AC end of the power converter, the average value of the multiplied result A power converter output voltage correction means for calculating the output voltage correction value of the power converter according to the detected magnetic bias state and calculating the biased state of the transformer The output voltage command of the power converter is subtracted from the output voltage correction value calculated by the power converter output voltage correction means to correct the AC output of the power converter, and the DC bias of the transformer is corrected. Power converter, characterized in that the braking.   5. The function generated by the function generating means according to claim 1, wherein the function generated by the function generating means has a strong correlation with a peak current generated when the exciting inductance decreases, and a direct current component, an alternating current output from the power converter. The power conversion device is a function that has no correlation with the fundamental wave component of and the harmonic component caused by the load device connected to the other end of the transformer.   5. The function generated by the function generating means according to claim 1, wherein the function generated by the function generating means has a strong correlation with a peak current generated when the excitation inductance is reduced, and is a direct current compared with the correlation with respect to the peak current. A power converter characterized by a sufficiently weak correlation between a component, an AC fundamental wave component output from the power converter, and a harmonic component caused by a load device connected to the other end of the transformer .

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