JP2016116350A - Inverter control device interconnected to ac system via transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter control device interconnected to an AC system via a transformer, the inverter control device being configured to reduce DC magnetic deflection using a low-priced current sensor.SOLUTION: The inverter control device comprises: an adder which adds a detection current of a current sensor 3 for detecting a primary current outputted from an inverter 2 to a transformer 4 and a delay current obtained by delaying the detection current by an odd multiple of 0.5 cycle of the detection current and extracts a DC excitation current component; a magnetic deflection detector which detects the presence/absence and a direction of magnetic deflection of the transformer from the DC excitation current component extracted by the adder and obtains a magnetic deflection correction amount; a subtractor which subtracts the magnetic deflection correction amount of the magnetic deflection detector from an inverter drive signal and obtains an inverter drive correction signal; and a gate signal generation circuit 11 which obtains a gate signal of the inverter based on the inverter drive correction signal. Thus, the DC magnetic deflection of the transformer is reduced.SELECTED DRAWING: Figure 1A

Description

  The present invention relates to an inverter control device linked to an AC system via a transformer, and more particularly to an inverter control device linked to an AC system via a transformer that reduces the DC bias of the transformer. .

  In an inverter controller connected to an AC system through a conventional transformer, DC magnetic flux (DC magnetic flux is generated by a minute DC component generated on the primary side of the transformer, and overcurrent is caused by saturation of the transformer core. In order to reduce this phenomenon, a method of detecting a minute DC component included in the primary side of the transformer from the transformer primary current via an analog or digital filter has been proposed (Patent Document 1).

  In addition, the instantaneous value of the transformer primary current is piecewise integrated in synchronization with the output period, and the leveling process is performed to detect the presence and direction of the DC bias of the transformer, and calculate the correction amount to suppress the bias. Was. Also, a method has been proposed in which the calculated correction amount is injected into the inverter drive signal to reduce the DC bias of the transformer (Patent Document 2).

Japanese Patent Laid-Open No. 4-121062 (pages 3-4, FIG. 1) Japanese Patent Laid-Open No. 10-229682 (paragraphs 0015 to 0019, FIGS. 1 to 5)

In an inverter control device linked to an AC system via a conventional transformer, the DC current flowing to the primary side of the transformer is measured with a high-accuracy current sensor, and an analog or digital filter is installed after the current sensor. The DC component was detected, and the inverter drive signal was corrected from the detected DC component to prevent DC bias. However, in order to detect a DC current of several A level from an AC current of several hundred A level with high accuracy, an expensive current sensor is necessary, and there is a problem in terms of cost.
The present invention has been made to solve the above-described problems, and obtains an inverter control device linked to an AC system via a transformer that reduces DC bias using an inexpensive current sensor. It is.

  An inverter control apparatus linked to an AC system via a transformer according to the present invention includes a transformer, an inverter linked to an AC system via the transformer, and the transformer output from the inverter to the transformer A current sensor for detecting a primary current, an adder for adding a detected current of the current sensor and a delay current delayed by an odd multiple of 0.5 cycles of the detected current to extract a DC excitation current, and the adder A magnetism detector that detects the presence and direction of magnetism of the transformer from the DC excitation current extracted in step 1 to obtain a magnetism correction amount, and subtracts the magnetism correction amount of the magnetism detector from the inverter drive signal of the inverter A subtractor for obtaining an inverter drive correction signal, and a gate signal generation circuit for obtaining a gate signal of the inverter by the inverter drive correction signal, so as to reduce the DC bias of the transformer. One in which the.

  According to the inverter control device linked to the AC system through the transformer of the present invention, the detected current of the transformer primary current and the delay current delayed by an odd multiple of 0.5 cycles of the detected current are added, Since the DC excitation current is extracted, and the presence and direction of the DC bias generation of the transformer is detected from the extracted DC excitation current to obtain the bias correction amount, the DC bias magnetism can be obtained using an inexpensive current sensor. Can be reduced.

It is a figure which shows the structure of the inverter control apparatus linked to an alternating current system via the transformer in Embodiment 1 of this invention. It is a figure which shows the internal structure of the exciting current extraction block contained in the inverter control apparatus linked to an alternating current system via the transformer in Embodiment 1 of this invention, and a magnetization presence / absence / direction detection block. In Embodiment 1 of this invention, it is a figure which shows transition of each signal. (A) is a figure which shows transition of each signal in the case of positive electrode bias magnetism generation | occurrence | production, (b) is a figure which shows transition of each signal in the case of negative electrode bias magnetism generation | occurrence | production. It is a figure which shows the structure of the inverter control apparatus linked with an alternating current system via the transformer in Embodiment 2 of this invention. It is a figure which shows the internal structure of the exciting current extraction block contained in the inverter control apparatus linked to an alternating current system via the transformer in Embodiment 2 of this invention, and a magnetization presence / absence / direction detection block. It is a figure which shows the structure of the inverter control apparatus linked with an alternating current system via the transformer in Embodiment 3 of this invention. It is a figure which shows the internal structure of the exciting current extraction block contained in the inverter control apparatus linked with an alternating current system via the transformer in Embodiment 3 of this invention, and a magnetization presence / absence / direction detection block.

Embodiment 1 FIG.
In FIG. 1A, 1 is an inverter DC bus voltage smoothing capacitor, 2 is a three-phase inverter (inverter), 3 is a current sensor for detecting primary currents Ia and Ic (detected currents) of the transformer 4, and 4 is a transformer. Thus, the three-phase inverter 2 is linked to the AC system via the transformer 4.

  5 is an exciting current extracting block for extracting DC exciting current components Ima, Imb, and Imc from the primary currents Ia and Ic of the transformer, 6 is a biased presence / absence / direction detection block, and 7 is a biasing presence / absence / direction detection block 6 The counter block 8 counts the presence / absence / direction signal 20 (Xa, Xb, Xc), and the gain block 8 amplifies the output signal of the counter block 7 and calculates the amount of magnetization. The demagnetization presence / absence / direction detection block 6, the counter block 7 and the gain block 8 constitute a demagnetization detector.

  9 is a subtraction block (subtractor) for obtaining an inverter drive correction signal by subtracting the bias correction amount 34 (Xa2, Xb2, Xc2) from the inverter drive signal 10 (Ma, Mb, Mc), and 11 is an inverter drive correction signal. 3 is a gate signal generation circuit for generating a gate signal 31 for driving the three-phase inverter 2.

  In FIG. 1B, 12 is a calculation block for calculating the remaining one-phase current Ib (t) from the two-phase components Ia (t) and Ic (t) of the transformer primary current, and 13 is the transformer primary current Ia (t ), Ib (t), Ic (t) are time delay blocks for delaying Td (an odd multiple of 0.5 cycles of the primary current (excitation current waveform)), and 14 is the primary current Ia (t) of the transformer. , Ib (t), Ic (t) and Ia (t-Td), Ib (t-Td), Ic (t-Td) obtained by delaying the transformer primary current by Td time, It is an addition block (adder) for calculating Ima.

  15 is a comparator that outputs +1 (0 at steady state) when the DC excitation currents Ima, Imb, and Imc exceed the upper limit (Upper Limit), and 16 is the lower limit (Lower Limit) of the DC excitation current. Is a comparator that outputs -1 (zero in steady state), 17 is a latch circuit that latches outputs 0 and +1 of the comparator 15 (UL), and 18 is a comparator 16 (LL) output 0 and -1. The latch circuit 19 adds the outputs of the latch circuits 17 and 18, and outputs information on the presence / absence of the demagnetization and the demagnetization direction (0: no demagnetization, -1: demagnetization on the negative side, +1: positive side) Adder that demagnetizes the magnetic field.

  Denoted at 20 is a demagnetization presence / absence / direction signal (Xa, Xb, Xc) output to the counter block 7, and this signal includes the demagnetization presence / absence and direction information of the transformer 4. The latch circuits 17 and 18 are reset in one cycle period.

  Next, the operation in the first embodiment will be described with reference to FIGS. 1A, 1B, and 2. FIG. The excitation current extraction block 5 adds the primary current Ia (t) of the real-time transformer and the signal Ia (t−Td) (delay current) delayed by Td time by the time delay block 13, thereby exciting the direct current. The current component 33 (Ima) is extracted.

  When the magnetization is generated, the DC excitation current is excessively increased only on one side. In the presence / absence detection / direction detection block 6, the DC excitation current Ima is compared with the comparator 15 (UL) and the comparator 16 (LL. ) To determine whether there is a deviation from the upper limit or lower limit. The determination of whether or not there is a deviation is synonymous with the determination of whether or not there is a bias. The comparator 15 (UL) is for detecting the presence / absence of bias on the positive electrode side, and outputs +1 when the bias is generated. Similarly, the comparator 16 (LL) is for detecting the presence / absence of the negative side magnetism, and outputs −1 when the magnetism occurs.

  Further, latch circuits 17 and 18 are provided at the subsequent stage of the comparator 15 (UL) and the comparator 16 (LL), the biased magnetic signal +1 or −1 is latched, and the signals of the latch circuits 17 and 18 every cycle. Is added by the adder 19 to indicate whether there is a magnetization or direction signal 20 (Xa, Xb, Xc) (0: no magnetization, -1: generation of magnetization on the negative electrode side, +1: generation of magnetization on the positive electrode side) Is output. Also, the latch information of the latch circuit is cleared (zeroed) in one cycle period.

  Further, the counter block 7 at the subsequent stage counts up (integrates) the presence / absence of the demagnetization / direction signal 20 every cycle, and the demagnetization correction amount of the count-up signal 32 (Xa1, Xb1, Xc1) by the gain block 8. 34 (Xa2, Xb2, Xc2). In the subtraction block 9, by subtracting the bias correction amount 34 (Xa2, Xb2, Xc2) from the inverter drive signal 10 (Ma, Mb, Mc), an inverter drive correction signal 30 for driving the inverter while reducing the bias. And the gate signal generation circuit 11 generates a gate signal 31 based on the generated inverter drive correction signal 30 to drive the three-phase inverter 2. As a result, when the magnetization is generated on the positive electrode side and the negative electrode side, the magnetization correction amount 34 is generated, and it is possible to finally make the DC voltage not generated in the transformer 4.

Embodiment 2. FIG.
FIG. 3A is a diagram showing a configuration of an inverter control device linked to an AC system via a transformer according to Embodiment 2 of the present invention. FIG. 3B is a diagram illustrating an internal configuration of an excitation current extraction block and a biased presence / absence / direction detection block. In the first embodiment, since the demagnetization correction amount 34 is increased or decreased at a constant level, it may take time until the DC demagnetization is reduced after the demagnetization abnormality is detected. It may be difficult to apply to transformers that need to be reduced to a certain level.

  Therefore, as shown in FIGS. 3A and 3B, a block for detecting the maximum value of the direct current excitation current Ima, that is, an absolute value calculation block 22 and a maximum value calculation block 23 are added to the biased magnetism presence / absence / direction detection block 6A. The degree of bias is calculated in the form of a bias degree signal 21 (Xag, Xbg, Xcg). Further, the demagnetization degree signal 21 is input to the gain variable unit 8A (amplification degree changes), and the gain value is changed according to the degree of demagnetization. As a result, when the degree of magnetic anomaly is large, the increase / decrease value of the magnetic demagnetization correction amount 34 can be increased. Therefore, the present invention is applied to a transformer that has a low anti-magnetization tolerance and needs to reduce the magnetic demagnetization at high speed. be able to.

Embodiment 3 FIG.
In the first and second embodiments, the processing for detecting and reducing the magnetic anomaly has been described. However, this embodiment does not support the detection of bipolar magnetic saturation that occurs in both the positive and negative directions. Therefore, in addition to the configuration of the first embodiment, as shown in FIGS. 4A and 4B, an absolute value calculation block 24 and an adder 25 are added to the biased presence / absence / direction detection block 6B to obtain the latch circuit 17. From the absolute value of the positive pole magnetism detection output and the negative pole magnetism detection output obtained from the latch circuit 18 via the absolute value calculation block 24, the adder 25 detects the magnetism presence / absence / magnetic saturation detection signal 26 (Asat, Bsat). , Csat).

  The presence / absence of demagnetization / magnetic saturation detection signal 26 (Asat) changes to 0 when there is no demagnetization, +1 when the demagnetization occurs, and +2 when the magnetic saturation occurs. As a result, in addition to detecting the presence / absence / direction of magnetic demagnetization, it is also possible to monitor the occurrence of magnetic saturation in both polarities and to detect abnormal magnetic saturation, thereby enhancing the protection function of the device.

  It should be noted that within the scope of the present invention, the embodiments can be freely combined, or the embodiments can be appropriately modified or omitted.

DESCRIPTION OF SYMBOLS 1 Capacitor 2 Three-phase inverter 3 Current sensor 4 Transformer 5 Excitation current extraction block Ia, Ic Primary current 6 Demagnetization presence / absence / direction detection block 7 Counter block 8 Gain block 8A Gain variable 9 Subtraction block 10 Inverter drive signal 11 Gate signal Generation circuit 12 Computation block 13 Time delay block 14 Addition block 15 Comparator 16 Comparator 17 Latch circuit 18 Latch circuit 19 Adder 20 Demagnetization presence / absence / direction signal 21 Demagnetization degree signal
22 Absolute value calculation block 23 Maximum value calculation block
24 Absolute value calculation block 25 Adder
26 Signal for detecting presence / absence of magnetic demagnetization / magnetic saturation 30 Inverter drive correction signal 31 Gate signal 32 Count-up signal 33 DC excitation current 34 Demagnetization correction amount

Claims (4)

  A transformer, an inverter linked to an AC system via the transformer, a current sensor for detecting a primary current of the transformer output from the inverter to the transformer, a detection current of the current sensor, and the detection current Add the delay current that is delayed by an odd multiple of 0.5 cycles, adder that extracts the DC excitation current, and detect the presence and direction of the magnet of the transformer from the DC excitation current extracted by the adder A demagnetization detector for obtaining a demagnetization correction amount, a subtractor for subtracting a demagnetization correction amount of the demagnetization detector from an inverter drive signal of the inverter, and obtaining an inverter drive correction signal, and a gate of the inverter by the inverter drive correction signal An inverter control device comprising a gate signal generation circuit for obtaining a signal and connected to an AC system via a transformer configured to reduce DC bias of the transformer.   2. The bias correction detector obtains the bias correction amount by integrating the output obtained by detecting the presence and direction of bias of the transformer from the DC excitation current extracted by the adder with a counter. An inverter control device linked to an AC system via the described transformer.   A gain variable device whose amplification degree changes in accordance with the DC excitation current extracted from the adder is provided, and the bias variable correction amount obtained by the magnetic bias detector is amplified by the gain variable device, from the inverter drive signal The inverter control apparatus linked to an AC system via a transformer according to claim 1 or 2, wherein the inverter drive correction signal is obtained by subtracting the amplified bias correction amount.   In the above-mentioned magnetic field detector for detecting the presence and direction of magnetic bias of a transformer and obtaining a magnetic field correction amount, a magnetic field detector for detecting that both the positive direction and the negative direction are generated at the same time is provided. An inverter control device linked to an AC system via the transformer according to any one of claims 1 to 3.

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