JP2012080666A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device capable of achieving three-phase balancing of a converter output current without need for installing a DC voltage detector of each unit power converter circuit.SOLUTION: A power conversion device 100 in at least one embodiment includes: a power converter having a plurality of unit power converter circuits 1a, 1b, 1c, 2a, 2b, 2c, 3a, 3b, 3c and a plurality of power storage means 4a, 4b, 4c, 5a, 5c, 6a, 6b, 6c provided for each phase; current detection means 13, 14, 15 for detecting an AC current of the power converter; and controller 19 that detects a three-phase AC current unbalanced component from a three-phase AC current value obtained from the current detection means 13, 14, 15 and corrects an output AC voltage command value to the power converter so that a three-phase AC current is balanced for each phase.

Description

Embodiments described herein relate generally to a power conversion apparatus.

In recent electric power systems, the introduction of natural energy such as solar power and wind power generation is progressing. Natural energy always generates fluctuating electric power, but in order to make effective use of generated electric power, a power storage system is needed to charge the power storage device when power generation is excessive, and to discharge when power generation is insufficient. Become.

  When connecting to a power system, the power storage system configuration using a single power converter requires the power converter to have a high withstand voltage and the power storage device to have a high withstand voltage and a large capacity. In addition, a filter circuit that suppresses harmonic components is required at the output portion of a general two-level or three-level power converter, and there are problems such as an increase in the volume of the entire power storage system and a reduction in efficiency. .

In view of this, multistage power converters in which a plurality of unit power conversion circuits having power storage devices are connected in series and parallel are being studied. Since a plurality of power converters are connected in series and parallel in multiple stages, the withstand voltage and capacity of each power converter and power storage device can be reduced by increasing the number of connections.

  In addition, since the number of output voltage levels of the entire power converter system can be increased by increasing the number of connections, the output voltage waveform approaches a sine wave, and the filter circuit can be reduced in size, or can be filtered only with a connected reactor. Can be realized.

JP 2010-110120 A

"6.6kV transformerless power storage system using cascaded PWM converter and secondary battery" (Shigenori Inoue, Mahaljan Luxman, Satoshi Asakura, Yasufumi Akagi: IEEJ Transactions D 129 No. 1 2009)

However, since it is necessary to control a large number of power converters, the system may become complicated and large. Therefore, for the detection of each current and voltage, a configuration is desired in which only the system voltage detector and the converter output current detector are used, and no DC voltage detector or the like of each unit power conversion circuit is installed. However, if the DC voltage of each power converter is different, the converter output voltage becomes three-phase unbalanced because there is no means for detecting the DC voltage value or converter output voltage value of each unit power converter circuit, and the converter There is a concern that the output current may be adversely affected by the three-phase imbalance.

The present invention has been made in order to solve the above technical problems. The power that enables three-phase balancing of the converter output current without installing the DC voltage detector of each unit power conversion circuit. The object is to obtain a conversion device.

The power conversion device of the embodiment includes a power converter having a plurality of unit power conversion circuits and power storage means for each phase, a current detection means for detecting an alternating current of the power converter, and three obtained from the current detection means. A control device that detects a three-phase AC current unbalanced component from the phase AC current value and corrects the output AC voltage command value to the power converter for each phase so that the three-phase AC current is balanced. Yes.

It is a figure showing the electric power storage system of a 1st embodiment. It is a figure which shows the converter control apparatus of 1st Embodiment. The figure of the calculation model of the converter output voltage excess-deficiency amount of 2nd Embodiment. The internal block diagram of the converter current control calculating part of 2nd Embodiment. The figure which shows the converter output voltage excess-deficiency calculation part of 2nd Embodiment. The figure which shows the converter output voltage correction amount calculation part and converter output voltage command value correction | amendment part of 3rd Embodiment. The figure which shows the converter output voltage correction amount calculation part and converter output voltage command value correction | amendment part of 4th Embodiment.

Hereinafter, the power converter of an embodiment is explained with reference to drawings.

(First embodiment)
The first embodiment will be described in detail with reference to FIGS.

(Constitution)
In the power storage system 100 of this embodiment, the single-phase converters 1a to 1c are connected in series, the U phase, 2a to 2c are connected in series, the V phase, and 3a to 3c are connected in series to form the W phase. And it is connected with the electric power grid | system 20 via the interconnection reactors 10-12. Power storage devices 4a to 6c and filter capacitors 7a to 9c are connected to the direct current portions of the single-phase converters.

  Moreover, it has the current detectors 13-15 which detect the electric current of a power converter, and the voltage detectors 16-18 which detect an electric power system voltage, Each information is transmitted to the converter control apparatus 19, and the semiconductor of each single phase converter An element switching command is calculated and transmitted to each single-phase converter.

(Function)
For the power storage devices 4a to 6c, for example, a secondary battery such as a lithium ion battery is used. In the secondary battery, the output terminal voltage, that is, the single-phase converter DC voltage varies depending on the internal resistance and the SOC. If the internal resistance value and SOC are uniform, the DC voltage fluctuation is the same even when the DC voltage value is not detected. Therefore, the excess / deficiency of the converter output voltage should be corrected by PI control of the current control unit. However, if the internal resistance value or SOC of each secondary battery varies, there will be a difference in the DC voltage of each converter, the output voltage command value cannot be calculated properly, and the converter current will be There is a risk of a three-phase imbalance.

  As shown in FIG. 2, a three-phase system voltage is converted into a biaxial rotational coordinate system by a dq converter 24 (hereinafter referred to as dq conversion) from the system voltage phase detected by the phase detector 26, and the system is connected to the d axis. The dq transformation is defined so that the line-to-line effective value of voltage and the q-axis are zero. Also, a converter current command value is calculated from a command value of active power and reactive power, and a current control unit 21 that calculates a dq axis converter output voltage command value based on a deviation from the detected value of the converter current, a dq axis converter output voltage command value is calculated. Inverse dq converter 22 for converting to a three-phase converter output voltage command value, converter output voltage command value normalization 23 for normalizing the converter output voltage command value with a constant DC voltage standard value, and dq converter for dq converting the converter current 25. A triangular wave comparison unit 30 that compares the obtained modulated wave with a triangular wave is provided. Further, a converter output voltage excess / deficiency calculation unit 27, a converter output voltage correction amount calculation unit 28, and a converter output voltage command value, which are features of the present invention, are provided. The correction unit 29 has a converter by correcting the converter output voltage according to the calculated converter output voltage excess / deficiency To achieve three-phase equilibrium of forces voltage. For example, when the U-phase converter output voltage is excessive, the amplitude of the U-phase output voltage command value is reduced. Conversely, when the U-phase converter output voltage is insufficient, the U-phase output voltage command value Increase the amplitude.

(effect)
According to the power conversion device of the embodiment described above, when the converter output voltage is excessive, the amplitude of the output voltage command value is reduced according to the converter output voltage excess / deficiency calculated from the converter current. Conversely, if the converter output voltage is insufficient, the DC voltage detector for each unit power conversion circuit is installed by correcting the converter output voltage command value so that the amplitude of the output voltage command value is increased. Without this, it is possible to realize three-phase balancing of the converter output voltage and the converter current only by detecting the converter current value.

(Second Embodiment)
The second embodiment will be described in detail with reference to FIGS. 3 to 5. FIG. 3 is a calculation model of the converter output voltage excess / deficiency, and FIG. 4 is an internal configuration of the current control calculation unit 21. The calculation formula of the converter output voltage excess / deficiency calculation unit 27 is derived from FIGS. In addition, about the thing which has the same structure as FIG. 1 thru | or 2, the same code | symbol is attached | subjected and description is abbreviate | omitted.

(Constitution)
In FIG. 3, the single-phase converters 1a to 1c of FIG. 1 are one U-phase single-phase converter 40, the single-phase converters 2a to 2c are one V-phase single-phase converter 41, and the single-phase converters 3a to 3c are one W-phase. Treated as a single-phase converter 42. The converter output voltage is regarded as a sine wave, and the direction of the current is positive in the direction input to the converter.

(Function)
Here, the difference between the converter output voltage command value and the actual value of the converter output voltage is set as Δu, Δv, Δw (DC value) as the excess / deficiency of the modulation rate. This excess / deficiency occurs in the converter output voltage command value normalization 23 of FIG. Also, the difference between the converter output voltage and the actual value that should be output in order to obtain the desired converter current is Δu ′, Δv ′, Δw ′ (DC value) as the excess or deficiency of the modulation rate, and in a steady state, as follows: Define.

The sum of Δu ′, Δv ′, and Δw ′ becomes 0, as will be described later, the converter output voltage that should be output and the actual output voltage according to the integral control terms of the PI controllers 62 and 67 of the current control unit 21. This is because it is considered that the sum of the amplitudes is equal in the steady state.

When the system voltages 47 to 49 are three-phase balanced and the line voltage effective value Vg and the frequency f (ω = 2πf), the respective system phase voltages are given as follows.

vid_ref and viq_ref are dq-axis converter output voltage command values calculated by the current control calculation unit 21.

By inverse dq conversion, each phase converter output voltage command value is given as follows.

Here, considering the excess and deficiency of the modulation rate of the converter output voltage command value, the actual phase converter output voltage is as follows.

Further, since the converter output voltage is unbalanced, the following zero-phase voltage v 0 is generated at the converter neutral point 51.

Therefore, the voltage between the converter output voltage and the converter neutral point 51 is as follows.

Here, when Δu ′, Δv ′, and Δw ′ are each 0,

Therefore, the converter output voltage is balanced, and the deviation between the desired converter voltage value and the actual converter output voltage value due to Δd is compensated by the integral control terms of the PI controllers 62 and 67 of the current control unit 21. That is, if the amplitude of the converter output voltage command value is increased or decreased so that Δu ′, Δv ′, and Δw ′ are 0, the converter voltage approaches three-phase equilibrium. Here, if the actual value of the converter output voltage obtained above is dq converted,

Since the zero phase voltage cancels out, the dq axis converter voltage is

As described above, when the converter output voltage is unbalanced, the vibration of the fundamental frequency component twice as much as the value on the dq axis is generated, and the vibration of the fundamental frequency component twice as much as that occurs in the dq axis converter current. The vibration of the dq-axis converter output voltage and the dq-axis converter current depends on the excess / deficiency Δu ′, Δv ′, Δw ′ of each converter voltage value. In the present invention, vibration of the dq-axis converter current due to the converter current three-phase imbalance is detected, and Δu ′, Δv ′, and Δw ′ are derived from the vibration components.

 Hereinafter, a process of calculating Δu, Δv, Δw and Δu ′, Δv ′, Δw ′ from the dq-axis converter current from the calculation model of the converter output voltage excess / deficiency in FIG.

If the inductance value of the interconnected reactors 44 to 46 in FIG. 3 is L [H], the u-phase converter current can be obtained by the following equation.

Here, when the converter output voltage is three-phase unbalanced, as described above, the dq-axis converter current is also superposed with twice the vibration of the fundamental frequency component. The control system of the current control is configured as shown in FIG. 4, and the dq-axis converter output voltage command value is calculated by feeding back the dq-axis converter current value. Therefore, the dq-axis converter output voltage command value is also doubled. Frequency component vibrations are superimposed. The formulation is as follows.

(Vd, Vq are dq axis system voltage, Vg = Vd, Vq = 0, respectively) dq axis converter voltage command values vid_ref, viq_ref in the steady state are DC components Vid_dc and Viq_dc and twice the vibration component of the fundamental frequency component. Assuming that the viq_ref is 90 degrees ahead of the vid_ref, the following can be defined as follows.

The partial integration is as follows.

When the partial integration results are returned to the partial integration expressions of vid_ref and viq_ref, respectively.

Therefore, the u-phase current can be defined as follows.

Similarly for v and w phases,

Therefore, the dq axis converter current is given as follows.

When calculation is performed by substituting each, the integral term of the zero-phase voltage is canceled and becomes as follows.

In the above equations for the d-axis converter current and the q-axis converter current, the first term and the second term on the right side are both 2 ωt sine waves × (DC value −2 ωt sine waves). In the following, the product of 2ωt sine waves is ignored, and the second term is ignored, assuming that the d-axis converter voltage is sufficiently larger than the q-axis converter voltage. The dq axis converter voltages necessary for outputting the command value current are as follows.

Since the direct current value of the dq-axis converter voltage is considered to be equal to the desired dq-axis converter voltage in the steady state, the following equation is established from the dq-axis converter voltage obtained above.

By performing the above approximation, the dq axis converter current equation can be simplified as follows.

Further, from FIG. 4, vid_ref and viq_ref are respectively set as follows.

When divided into DC component and vibration component respectively,

Since Kd_dc and Kq_dc work to eliminate the deviation of the direct current due to Δu + Δv + Δw, they are approximated as follows.

For Δid and Δiq, assuming that 3 + Δu + Δv + Δw≈3,

By substituting the above results, the relationship between Δid and Δiq and Δu, Δv, and Δw can be obtained.

From the above formula, if only Δu ′ is left,

Similarly, if only Δv ′ and Δw ′ are left,

Therefore, Δu ′, Δv ′, and Δw ′ are summarized as follows.

Using the above equation, the excess or deficiency of the modulation rate that causes the difference between the converter output voltage to be output and the actual value can be obtained from the converter output current value.

FIG. 5 shows a converter output voltage excess / deficiency calculation unit 27 for obtaining an excess / deficiency of the modulation rate from the obtained equation. In addition, although it converts into a modulation factor by multiplying with Kdelta, even when not multiplying with Kdelta, the relative value of the excess / deficiency between the three-phase converter voltages does not change. Therefore, if the PI control gain of the converter output voltage compensation amount calculation unit 28 is adjusted, it is not necessary to multiply by Kdelta.

(effect)
According to the power conversion device of at least one embodiment described above, the amplitude of the output voltage command value when the converter output voltage is excessive according to the converter output voltage excess / deficiency calculated from the converter current. If the converter output voltage is insufficient, the converter output voltage command value is corrected so as to increase the amplitude of the output voltage command value, thereby detecting the DC voltage of each unit power conversion circuit. Without installing a converter, it is possible to achieve three-phase balancing of the converter output voltage and the converter current only by detecting the converter current value.

(Third embodiment)
The third embodiment will be described in detail with reference to FIG. In addition, about the thing which has the same structure as FIG. 1 thru | or 5, the same code | symbol is attached | subjected and description is abbreviate | omitted.

The converter output voltage excess / deficiency obtained by the converter output voltage excess / deficiency calculator 27 is a deviation between the ideal converter output voltage and the current converter output voltage. Therefore, it is possible to perform proportional integration control on the deviation and increase or decrease the modulation rate so that the deviation becomes zero.

(Function)
As shown in FIG. 6, proportional integral control is performed by the PI controllers 111, 114, and 117 with respect to the derived excess / deficiency of the converter output voltage to calculate a corrected DC amount. Further, in order to convert the corrected DC amount into an AC waveform synchronized with the converter output voltage command value, the multipliers 112, 115 and 118 integrate the corrected DC amount and the converter output voltage command value, and the integrated value is converted into the converter output voltage command value. Is subtracted by subtracting sections 113, 116, and 119, so that the modulation factor decreases when the converter output voltage is excessive, and the modulation factor increases when the converter output voltage is insufficient. As the excess / deficiency of each converter output voltage approaches zero, the DC amount held in the integral terms of the PI controllers 111, 114, and 117 becomes dominant as the corrected DC amount, and the converter voltage becomes three-phase balanced. That is, the converter current operates to approach three-phase equilibrium.

Further, since the actual converter voltage and converter current include low-order harmonics and harmonics resulting from switching, it is conceivable that vibration components are superimposed on the converter voltage excess / deficiency. Therefore, in practical use, as shown in FIG. 7, the corrected DC amount is calculated by using the values obtained by removing the harmonic components through low-pass filters 121, 125 and 129 through the excess and deficiency of the derived converter output voltage. The vibration of the corrected DC amount can be prevented.

(effect)
According to the power conversion device of at least one embodiment described above, the amplitude of the output voltage command value when the converter output voltage is excessive according to the converter output voltage excess / deficiency calculated from the converter current. If the converter output voltage is insufficient, the converter output voltage command value is corrected so as to increase the amplitude of the output voltage command value, thereby detecting the DC voltage of each unit power conversion circuit. Without installing a converter, it is possible to achieve three-phase balancing of the converter output voltage and the converter current only by detecting the converter current value.

1a: U-phase first stage single-phase converter 1b: U-phase second-stage single-phase converter 1c: U-phase third-stage single-phase converter 2a: V-phase first-stage single-phase converter 2b: V-phase second Stage single phase converter 2c: V phase third stage single phase converter 3a: W phase first stage single phase converter 3b: W phase second stage single phase converter 3c: W phase third stage single phase converter 4a ˜6c: power storage devices 7a-9c: filter capacitors 10-12: interconnection reactors 13-15: converter current detectors 16-18: system voltage detector 19: converter controller 20: power system 21: converter current control calculation Unit 22: dq axis converter voltage command value reverse dq conversion unit 23: Three-phase converter output voltage command value standard unit 24: System voltage dq conversion unit 25: Converter current dq conversion unit 26: System voltage phase detection unit 27: Data output voltage excess / deficiency calculation unit 28: converter output voltage correction amount calculation unit 29: converter output voltage command value correction unit 30: triangular wave comparison unit 41: u-phase converter 42: v-phase converter 43: w-phase converters 44 to 46 : Interconnection reactors 47 to 49: Power system 50 Power system ground point 51: Converter neutral point 61: Subtractor 62: PI controller 63: Subtractor 64: Adder 65: Gain 66: Subtractor 67: PI controller 68: Subtractor 69: Adder 71: Adder 72: Subtractor 73-75: Gain 76: Subtractor 77: Subtractor 78-80: Gain 81-82: Multiplier 83: Sin wave generator 84: Cosine wave Generator 85: Adder 86: Subtractors 87-88: Multiplier 89: Sine wave generator 90: Cosine wave generator 91-92: Multiplier 93: Sin wave generator 94: Cosine wave generator 95 97: Adder 98: Gain 100: Power storage system 111: PI controller 112: Multiplier 113: Subtractor 114: PI controller 115: Multiplier 116: Subtractor 117: PI controller 118: Multiplier 119: Subtraction Unit 121: Low-pass filter 122: PI controller 123: Multiplier 124: Subtractor 125: Low-pass filter 126: PI controller 127: Multiplier 128: Subtractor 129: Low-pass filter 130: PI controller 131: Multiplier
132: Subtractor

Claims (4)

A power converter having a plurality of unit power conversion circuits and power storage means for each phase;
Current detecting means for detecting an alternating current of the power converter;
The three-phase alternating current unbalanced component is detected from the three-phase alternating current value obtained from the current detecting means, and the output alternating voltage command value to the power converter is set for each phase so that the three-phase alternating current is balanced. A control device to correct,
Power conversion device having The three-phase alternating current unbalanced component is an alternating voltage command value output to the power converter from the vibration component in the rotating coordinate system by converting the three-phase alternating current into a rotating coordinate system synchronized with the power system voltage. The power conversion device according to claim 1, wherein an excess or deficiency of a certain output AC voltage command value is calculated 3. The power converter according to claim 1, wherein an excess / deficiency amount of the output AC voltage command value is proportional-integral-controlled and an amplitude value of a correction amount superimposed on the output AC voltage command value of the power converter is calculated. The power conversion device according to claim 3, further comprising a low-pass filter for shaping an excess / deficiency of the output AC voltage command value.

Images