JP6958394B2 - Power conditioner and its control method and power storage system - Google Patents

Description

The present invention relates to a power conditioner, a control method thereof, and a power storage system.

The power conditioner connected to the commercial power system has various required protection functions, and one of them has an independent operation detection function (see, for example, Non-Patent Documents 1 to 3). Independent operation refers to a state in which the power conditioner itself is connected to the voltage output to the AC electric circuit immediately after a power failure of the commercial power system. The power conditioner that detects the solitary operation stops the operation and disconnects itself from the commercial power system. At present, in the test of such a solitary operation detection function, it is a substantially essential requirement to satisfy JEM1498 or JEM1505, which is a standard of the Japan Electrical Manufacturers' Association (JEMA).

For example, in the JEM1498 certification test, as the power flow conditions at the interconnection point with the commercial power system, the active power for the load is set to -10%, -5%, 0%, + 5%, + 10%, and the reactive power is set. , -10%, -5%, 0%, + 5%, + 10%, and whether or not independent operation can be detected within a predetermined time under 25 types of conditions in which these are combined in a matrix. test.

The power conditioner used for the test is triggered by, for example, a frequency deviation after a power failure occurs. The frequency deviation is a value obtained by subtracting the latest moving average frequency during 40 ms from the moving average frequency during 320 ms 200 ms before. When the frequency deviation is larger than 0.01 Hz, the reactive power is injected linearly (frequency feedback function), and when the frequency change reaches a predetermined value as a result, it is detected as independent operation.

On the other hand, under the load condition where the active power becomes 0%, the frequency deviation immediately after the independent operation is smaller than 0.01 Hz. In this case, since it is not possible to inject reactive power based on the frequency deviation, instead, we focus on the change in voltage, which is another feature during independent operation. Specifically, based on the increase in the harmonic voltage or the increase in the fundamental wave voltage, the reactive power is injected stepwise for a certain period of time (step injection function). After that, the frequency feedback function is activated for the frequency deviation caused by the ineffective power by this step injection function, and when the frequency deviation becomes large, it is detected as independent operation.

Japan Electric Industry Association JEM1498, JEM1505 Nissin Electric Technical Report Vol. 45, No. 2 "Independent operation detection device by inter-degree harmonic injection method" Nissin Electric Technical Report Vol. 46, No. 2 "Independent operation detection method and product development by inter-degree harmonic injection"

However, if the power flow condition at the interconnection point is 0% for both active power and active power, that is, if the power output by the power conditioner and the power consumption of the load are balanced, a power failure occurs in the commercial power system. Even if it occurs, the frequency deviation does not exceed 0.01 Hz, and the fundamental voltage and the harmonic voltage may hardly change. In particular, in a high-quality power conditioner that originally has a small output of harmonic voltage, the time required for detecting independent operation may be longer than the specified time.

In view of these problems, it is an object of the present invention to enable stable independent operation detection in a power conditioner even under load conditions where independent operation detection is difficult.

The present disclosure includes the following inventions. However, the present invention is defined by the scope of claims.

The power conditioner according to one expression of the present invention is a power conditioner that is grid-connected to a commercial power system, and detects the voltage of a power conversion unit that performs switching operation and an AC electric circuit connected to the commercial power system. The power conversion unit is controlled by the voltage sensor to be used and a control command value based on the voltage of the fundamental wave extracted from the voltage detected by the voltage sensor, and the independent operation is detected based on the voltage detected by the voltage sensor. In this case, it includes a control unit that controls the power conversion unit by a control command value based on a voltage in which a harmonic component is superimposed on the fundamental wave.

The power conditioner control method according to another expression of the present invention is a power conditioner control method including a power conversion unit that is connected to a commercial power system and performs a switching operation, and is the same as the commercial power system. When the voltage of the connected AC electric circuit is detected, the power conversion unit is controlled by the control command value based on the voltage of the fundamental wave extracted from the detected voltage, and the independent operation is detected based on the voltage of the AC electric circuit. The power conversion unit is controlled by a control command value based on a voltage in which a harmonic component is superimposed on the fundamental wave.

According to the present invention, in a power conditioner, stable independent operation detection is possible even under load conditions where independent operation detection is difficult.

It is a circuit diagram which shows an example of a power conditioner, and its input / output circuit. It is a functional block diagram of the independent operation detection existing as an internal function of a control unit. This is the processing procedure for detecting independent operation shown in the flowchart. For comparison, it is a waveform diagram which shows the example of the isolated operation detection at the time of not executing steps S7, S8, S9 of FIG. It is a waveform diagram of the AC voltage before and after the power failure. As shown in FIG. 3, it is a waveform diagram which shows the example of the independent operation detection at the time of executing | execution including steps S7, S8, S9. It is a figure explaining the mutual interference of harmonics.

[Summary of Embodiment]
The gist of the embodiment of the present invention includes at least the following.

(1) This is a power conditioner that is grid-connected to a commercial power system, and includes a power conversion unit that performs switching operation, a voltage sensor that detects the voltage of an AC electric circuit connected to the commercial power system, and the above. The fundamental wave is used when the power conversion unit is controlled by a control command value based on the voltage of the fundamental wave extracted from the voltage detected by the voltage sensor and the independent operation is detected based on the voltage detected by the voltage sensor. It is a power conditioner including a control unit that controls the power conversion unit by a control command value based on a voltage on which a harmonic component is superimposed.

In such a power conditioner, it is possible to generate a high-quality sine wave waveform by eliminating the influence of harmonics by a control command value usually based on the voltage of the fundamental wave. When detecting the solitary operation, the control command value based on the voltage in which the harmonic component is superimposed on the fundamental wave can make it easy to generate the voltage due to the harmonics during the solitary operation. In this way, it is possible to provide a power conditioner capable of stably detecting independent operation even under load conditions where it is difficult to detect independent operation.

(2) Further, in the power conditioner of (1), when the control unit detects the independent operation, the harmonic voltage included in the voltage detected by the voltage sensor reaches the first threshold value. At this time, a control command value in which a harmonic component is superimposed on the fundamental wave may be generated, and the power conversion unit may be controlled by the control command value.
In this case, when there is a sign of independent operation that the harmonic voltage reaches the first threshold value, so to speak, by positively superimposing the harmonic components, the voltage due to the harmonics is quickly generated during the independent operation. Can be.

(3) Further, in the power conditioner of (2), for example, the first threshold value is a value lower than the second threshold value at which invalid power should be injected into the output of the power conversion unit.
In this case, signs of isolated operation can be detected early.

(4) Further, in the power conditioner of (2) or (3), the control unit may change the harmonic component to be superimposed in proportion to the harmonic voltage.
In this case, as the harmonic voltage increases, the control command value also increases, so that the timing of the ineffective power injection can be reached quickly.

(5) Further, in any of the power conditioners (2) to (4), the control unit may superimpose harmonic components of odd-numbered orders.
In this case, for example, even when a plurality of power conditioners are connected in parallel to the load, it is possible to suppress a situation in which harmonics are attenuated due to mutual influence.

(6) Further, in the power conditioner according to any one of (2) to (5), if the frequency deviation is larger than a predetermined value before the harmonic component is superposed by the control unit, the control unit may use the power conditioner. It is preferable to avoid superimposition of harmonic components.
In this case, since it is no longer necessary to superimpose the harmonic components, unnecessary operation can be avoided.

(7) Further, in the power conditioner of (1), when the control unit detects the independent operation, the control unit uses the voltage detected by the voltage sensor including harmonics as it is according to the control command value. The power conversion unit may be controlled.
In this case, in the case of independent operation, it is possible to utilize the AC voltage of the AC electric circuit which may contain harmonics without removing the harmonics.

(8) Further, the power storage system may include a DC power supply and a power conditioner according to any one of (1) to (7) connected to the DC power supply.
In this case, it is possible to provide a power storage system with the action and effect of the power conditioners (1) to (7).

(9) On the other hand, this is a control method of a power conditioner including a power conversion unit that is connected to a commercial power system and performs a switching operation, and detects a voltage of an AC electric circuit connected to the commercial power system. Then, when the power conversion unit is controlled by a control command value based on the voltage of the fundamental wave extracted from the detected voltage and the independent operation is detected based on the voltage of the AC electric circuit, a harmonic is applied to the fundamental wave. This is a power conditioner control method in which the power conversion unit is controlled by a control command value based on a voltage on which components are superimposed.

In such a power conditioner control method, it is usually possible to eliminate the influence of harmonics by a control command value based on the voltage of the fundamental wave and generate a high-quality sine wave waveform. When detecting the solitary operation, the control command value based on the voltage in which the harmonic component is superimposed on the fundamental wave can make it easy to generate the voltage due to the harmonics during the solitary operation. In this way, it is possible to provide a control method of a power conditioner capable of stably detecting independent operation even under a load condition in which it is difficult to detect independent operation.

[Details of Embodiment]
Hereinafter, the power conditioner according to the embodiment of the present invention will be described with reference to the drawings.

<< Configuration example of power conditioner >>
FIG. 1 is a circuit diagram showing an example of a power conditioner 100 and an input / output circuit thereof. First, to explain from the main circuit elements, the power conditioner 100 includes a DC / DC converter 1 and an inverter 2 as power conversion units. A DC power source 3 (for example, a storage battery, a solar power generation panel, etc.) is connected to the DC side (left side of the figure) of the power conditioner 100. Further, an AC electric circuit 4 is connected to the AC side (right side of the figure) of the power conditioner 100.
The DC power supply 3 and the power conditioner 100 constitute a power storage system.

The two lines of the AC electric circuit 4 are usually single-phase three-wire voltage lines (U line, W line). In reality, a neutral line (O line) with an intermediate potential (0V) is often created in the power conditioner 100 and connected to the commercial power system 7 of a single-phase three-wire system, but here it is simplified. It is shown in the figure.
The load 5 of the consumer is connected to the AC electric line 4. Further, the AC electric circuit 4 is provided with an interconnection relay 6. The interconnection relay 6 is connected to the commercial power system 7.

Here, the simplest example is shown in which the DC system from the DC power supply 3 to the DC / DC converter 1 is one system, but the present invention is not limited to this, and there are a plurality of systems, which are connected to each other by the DC bus 8. The circuit configuration may be connected in parallel.

A DC side capacitor 9 is provided between the DC power supply 3 and the DC / DC converter 1. The DC / DC converter 1 is configured by connecting a DC reactor 10, a low-side switching element Q1 and a high-side switching element Q2 as shown in the figure. Diodes d1 and d2 are connected in antiparallel to each of the switching elements Q1 and Q2, respectively. The DC / DC converter 1 can also operate as a step-up chopper or in the opposite direction as a step-down chopper.

The switching elements Q1 and Q2 shown in the figure are IGBTs (Insulated Gate Bipolar Transistors). The same applies to the other switching elements Q3 to Q6. However, a switching element such as a MOS-FET (Metal-Oxide-Semiconductor Field-Effect Transistor) can be used instead of the IGBT.

An intermediate capacitor 11 is provided between the two wires of the DC bus 8. The inverter 2 is connected to the DC bus 8. The inverter 2 includes switching elements Q3, Q4, Q5, and Q6 that form a bridge circuit. Diodes d3, d4, d5, and d6 are connected in antiparallel to the switching elements Q3, Q4, Q5, and Q6, respectively. An AC reactor 12 and an AC side capacitor 13 are provided on the AC side of the inverter 2.

Regarding the elements related to measurement and control, first, the voltage sensor 14 detects the voltage across the DC side capacitor 9 and sends the detected output to the control unit 20. The current sensor 15 detects the current flowing through the DC / DC converter 1 and sends the detected output to the control unit 20. The voltage sensor 16 detects the voltage between the two wires of the DC bus 8 and sends the detection output to the control unit 20. The current sensor 17 detects the current flowing through the AC reactor 12 and sends the detected output to the control unit 20. The voltage sensor 18 detects the voltage between the two lines of the AC electric circuit 4 and sends the detection output to the control unit 20.

The control unit 20 controls the switching elements Q1 to Q6 based on the detection output from each sensor. Further, the control unit 20 controls the opening and closing of the interconnection relay 6. During normal operation of the power conditioner 100, the interconnection relay 6 is closed. When it is detected that the commercial power system 7 has a power failure and the power conditioner 100 is in a state of independent operation, the control unit 20 opens the interconnection relay 6.
The control unit 20 includes, for example, a computer, and the computer executes software (computer program) to realize a necessary control function. The software is stored in a storage device (not shown) of the control unit 20.

The power conditioner 100 is bidirectional, and in addition to power conversion from DC to AC, when the DC power source 3 is a storage battery, power conversion from AC to DC is performed to charge the storage battery. You can also do it.

<< Example of normal control >>
During normal operation, as described above, the control unit 20 can perform grid interconnection operation of the power conditioner 100 by controlling the switching elements Q1 to Q6 based on the detection output from each sensor.

When the power conditioner 100 is provided between the commercial power system 7 and the DC power supply 3 having a voltage lower than the peak value of the absolute value of the AC voltage thereof, an example of a preferable known control is an AC half cycle. Within, one of the DC / DC converter 1 and the inverter 2 is made to perform a switching operation according to the phase of the alternating current, and the other causes a period of rest. Then, the control unit 20 is based on the voltage of the AC power, the current flowing through the AC reactor 12, the voltage change due to the impedance of the AC reactor 12, the invalid current flowing through the intermediate capacitor 11 and the AC side capacitor 13, respectively, and the voltage of the DC power. Then, the current command value of the DC / DC converter 1 is set to be synchronized with the current of the AC power. Further, as the voltage of the AC power, a voltage whose phase is supplemented in consideration of the delay of the detection and the control system can be used for the fundamental wave extracted based on the AC voltage detection value of the commercial power system 7.

In such a power conditioner 100, the control unit 20 causes one of the DC / DC converter 1 and the inverter 2 to perform a switching operation in the AC half cycle according to the phase of the AC, and the other period is paused. It is possible to execute the "minimum switching conversion method" of causing it to occur. In order to realize this method with high conversion efficiency, the voltage of AC power, the current flowing through the AC reactor 12, the voltage change due to the impedance of the AC reactor 12, the invalid current flowing through the intermediate capacitor 11 and the AC side capacitor 13, and the DC power. The current command value of the DC / DC converter 1 is set to be synchronized with the current of the AC power based on the voltage of.

Then, as the voltage of the AC power, the phase is supplemented to the fundamental wave extracted based on the AC voltage detection value (AC voltage detected by the voltage sensor 18) of the commercial power system 7 in consideration of the delay of the detection and the control system. By using a voltage, it is possible to suppress a delay in control with respect to the voltage phase, eliminate the influence of disturbance of the system voltage of the commercial power system 7, and obtain a stable and less distorted alternating current.

Specifically, the output current command value to the load 5 is Ia *, the capacitance of the AC side capacitor 13 is Ca, the AC voltage of the AC electric circuit 4 is Va, the voltage of the DC power supply 3 side is _VDC , and the Laplace operator. Let s. In this case, the control unit 20 sets the AC output current command value Iinv * that should flow to the current sensor 17.
Iinv * = Ia * + s CaVa ... (1)
Set to.

Further, when the impedance of the AC reactor 12 is set to Za, the control unit 20 sets the AC output voltage command value Vinv * at the output end of the inverter 2 (the interconnection point between the inverter 2 and the AC reactor 12).
Vinv * = Va + ZaIinv * ・ ・ ・ (2)
Set to.

Further, the control unit 20 sets the _{larger of the absolute values of the voltage VDC} and the AC output voltage command value Vinv * to the output voltage command value Vo * of the DC / DC converter 1, and sets the intermediate capacitor 11 to the output voltage command value Vo *. When the capacitance is C, the current command value Iin * of the DC / DC converter 1 is
Iin * = {(Iinv * × Vinv *) + (s C Vo *) × Vo *} / V _DC
... (3)
Set to. The AC voltage Va has an effective value of _{Va_rms} and a phase of the timing for commanding the switching operation as ωt.
Va = √2 V _{a_rms} × sin (ωt) ・ ・ ・ (4)
Can be.

According to the above control, the current command value Iin * of the DC / DC converter 1 is the voltage of the AC power, the voltage change due to the current flowing through the AC reactor 12 and the impedance of the AC reactor 12, the intermediate capacitor 11 and the AC side capacitor. It reflects all the ineffective current flowing through 13 and the voltage of DC power. Therefore, even when the voltage of the DC power supply 3 or the AC output current changes, it is possible to always output the power synchronized with the AC output current.

By controlling such a minimum switching conversion method, the DC / DC converter 1 and the inverter 2 can perform DC / AC conversion with the minimum number of high-frequency switching required. As a result, the switching loss of the semiconductor switching element and the iron loss of the AC and DC reactors are significantly reduced, and high conversion efficiency can be obtained. Further, by setting the system voltage Va in this way, a low-distortion alternating current can be obtained.

<< Function of independent operation detection >>
Next, the function of the isolated operation detection realized by the control unit 20 will be described.
FIG. 2 is a functional block diagram of the isolated operation detection that exists as an internal function of the control unit 20. In the figure, the detection signal of the AC voltage (system voltage) of the AC electric circuit 4 (FIG. 1) detected by the voltage sensor 18 (FIG. 1) is A / D converted (f1) and detected as an AC voltage (f2). ). Based on this AC voltage, the frequency (f3), the fundamental wave voltage (f4), and the harmonic voltage (f5) are detected, respectively.

The frequency becomes a frequency deviation (f8) after undergoing a moving average process (f6, f7). The frequency deviation is a value obtained by subtracting the latest moving average frequency during 40 ms from the moving average frequency during 320 ms 200 ms before. When the frequency deviation exceeds 0.01 Hz, the frequency feedback function operates (f11), and the command value of the injecting reactive power is determined (f13). On the other hand, if the frequency deviation does not exceed 0.01 Hz, the process goes towards the step injection function (from f8 to f9). Then, the step injection function (f9, f12) operates based on the fundamental wave voltage and the harmonic voltage, and the command value of the reactive power to be injected is determined (f13).

In addition, the command value of the active power is determined separately (f14, f15). The current control (f16) is performed based on the command value of the active power and the command value of the active power. The harmonic voltage participates in the current control via the harmonic adjustment control (f10). Based on the current control (f16), pulse width modulation control (f17, f18) is performed for each of the DC / DC converter 1 and the inverter 2.

FIG. 3 is a processing procedure for detecting independent operation shown in a flowchart.
In the figure, the control unit 20 first determines whether or not 5 ms has elapsed from the reference time (step S1). That is, the determination of the isolated operation detection is performed every 5 ms. Since 5 ms has not passed at first, the process jumps to step S10, and it is determined whether or not the independent operation is detected. If “No”, the process returns to step S1.

When 5 ms has elapsed in step S1, the control unit 20 determines whether or not the frequency deviation is greater than 0.01 Hz (step S2). Here, when the frequency deviation is larger than 0.01 Hz, the frequency feedback function operates, and the control unit 20 executes the injection (A) of the reactive power (step S3). In step S3, the control unit 20 injects the reactive power linearly based on the frequency deviation.

After injecting the reactive power, the control unit 20 determines whether or not the independent operation is detected (step S10). If the frequency change (for example, frequency deviation or frequency itself) has not reached a predetermined value that can be regarded as independent operation, the control unit 20 returns to step S1 and repeats the same process every 5 ms. Then, when the independent operation is detected in step S10, the control unit 20 stops the operation as the power conditioner 100 (step S11).

Further, in step S2, when the frequency deviation is 0.01 Hz or less, the step injection function is activated, and the control unit 20 has increased the harmonic voltage by 2 V (step S4) or the fundamental wave voltage by a predetermined amount. If any one of (step S5) is satisfied, the injection of reactive power (B) is executed (step S6). In step S6, the control unit 20 injects reactive power in steps for a certain period of time.

After injecting the reactive power, the control unit 20 determines whether or not the independent operation is detected (step S10). If the frequency change (for example, frequency deviation or frequency itself) has not reached a predetermined value that can be regarded as independent operation, the control unit 20 returns to step S1 and repeats the same process every 5 ms. Then, when the independent operation is detected in step S10, the control unit 20 stops the operation as the power conditioner 100 (step S11).

The above processing is a processing in accordance with the provisions of JEM1498. However, in the flowchart of FIG. 3, further processing is given. That is, in steps S4 and S5, when the harmonic voltage does not increase by 2V and the fundamental wave voltage does not increase by a predetermined amount (that is, when there is little change), the control unit 20 raises the harmonic. It is determined whether or not the wave voltage has increased slightly (step S7). The threshold value for recognizing "small" or "increased" is, for example, 0.7 V. That is, if this 0.7V is set as the first threshold value, 2V is the second threshold value, and the first threshold value is a value lower than the second threshold value. As described above, since the first threshold value is lower than the second threshold value at which the injection of the reactive power should be started, the sign of the isolated operation can be detected early.

If the harmonic voltage has not reached the first threshold value in step S7, the control unit 20 returns to step S1 through step S10, and the same process is repeated every 5 ms. Then, when the harmonic voltage reaches the first threshold value in step S7, the control unit 20 superimposes the harmonic component on the control command value (step S8). As a result, the power conditioner 100 operates so as to output a voltage in which a harmonic component is superimposed on the fundamental wave. Here, the control unit 20 changes, for example, the harmonic components to be superimposed in proportion to the harmonic voltage. In this case, as the harmonic voltage increases, the control command value also increases, so that the timing of subsequent injecting reactive power can be reached quickly.

After that, the control unit 20 executes the same process every 5 ms until the harmonic voltage increases by 2 V (Yes in step S9), which is the second threshold value, and when the harmonic voltage increases by 2 V in step S9, the control unit 20 executes the same process. , Injecting the reactive power (B) (step S6). Then, when the independent operation is detected in step S10, the control unit 20 stops the operation as the power conditioner 100 (step S11).

If the frequency deviation is larger than 0.01 Hz in step S2 before the next harmonic component is superposed, further superimposition of the harmonic component is avoided. That is, in this case, since it is no longer necessary to superimpose the harmonic components, unnecessary operation can be avoided.

<< Summary of Disclosure >>
As described above, in normal operation, the control unit 20 of the power conditioner 100 is a DC / DC converter that is a power conversion unit based on a control command value based on the voltage of the fundamental wave extracted from the voltage detected by the voltage sensor 18. 1 and inverter 2 are controlled. Further, when the independent operation is detected based on the voltage detected by the voltage sensor 18, the DC / DC converter 1 and the inverter 2 are controlled by the control command value based on the voltage in which the harmonic component is superimposed on the fundamental wave. ..

With such control, it is possible to generate a high-quality sine wave waveform by eliminating the influence of harmonics by a control command value usually based on the voltage of the fundamental wave. When detecting the independent operation, the control command value based on the voltage on which the harmonic component is superimposed on the fundamental wave can make it easy to generate the voltage due to the harmonics during the independent operation.

Then, when the control unit 20 detects the independent operation and the harmonic voltage included in the voltage detected by the voltage sensor 18 reaches the first threshold value (for example, 0.7V), the control unit 20 harmonics with the fundamental wave. A control command value in which wave components are superimposed is generated, and the DC / DC converter 1 and the inverter 2 are controlled by the control command value. In this case, when there is a sign of independent operation that the harmonic voltage reaches the first threshold value, so to speak, by positively superimposing the harmonic components, the voltage due to the harmonics is quickly generated during the independent operation. Can be.

<< Example of waveform >>
FIG. 4 is a waveform diagram showing an example of independent operation detection when steps S7, S8, and S9 of FIG. 3 are not executed for comparison. The waveform diagram shows the AC voltage, the current at the reverse tide point (current detected by the current sensor 17), the gate block confirmation signal confirming that the gate block of the DC / DC converter 1 and the inverter 2 has been performed, and the debugging signal. (It goes high at a harmonic voltage of 2V.) And a step injection confirmation signal is shown. Of the two vertically oriented dotted lines, after a power failure of the commercial power system occurs at the time of the dotted line on the left side, independent operation is detected at the time of the dotted line on the right side. The time interval between these dotted lines is, for example, 180 ms, but there is some variation and may exceed 200 ms.

FIG. 5 is a waveform diagram of the AC voltage before and after the power failure. A power failure occurs at the time of the vertical dotted line in the figure, but it is a good quality waveform with little distortion both before and after the power failure. With such a high-quality waveform, it is difficult to quickly detect the independent operation when steps S7, S8, and S9 of FIG. 3 are not executed.

FIG. 6 is a waveform diagram showing an example of independent operation detection when steps S7, S8, and S9 are also executed as shown in FIG. The waveform diagram shows the AC voltage, the current at the reverse tide point (current detected by the current sensor 17), the gate block confirmation signal confirming that the gate block of the DC / DC converter 1 and the inverter 2 has been performed, and the debugging signal. (It goes high at a harmonic voltage of 2V.) And a step injection confirmation signal is shown. Of the two vertically oriented dotted lines, after a power failure of the commercial power system occurs at the time of the dotted line on the left side, independent operation is detected at the time of the dotted line on the right side. In the case of FIG. 6, since the step injection is performed at a relatively early stage, the time interval between the two dotted lines is 150 ms. There was almost no variation even if the load conditions were such that the frequency change due to a power failure was unlikely to occur, and the frequency was about 150 ms.

Therefore, the detection within 200 ms required by JEM1498 can be ensured.

<< About the order of the harmonic components to be superimposed >>
Next, the order of the harmonic components superimposed on the fundamental wave will be supplemented. When there are three output circuits of the power conditioner, if these three circuits are the first circuit (+ 101V), the second circuit (0V), and the third circuit (-101V) in order, these are U line, O line, and so on, respectively. The case where it is connected to the W line is referred to as "tangent". Further, the case where the first electric line, the second electric line, and the third electric line are connected to the W line, the O line, and the U line, respectively, is referred to as "reverse connection". For example, when two power conditioners 100 are connected to a single-phase three-wire (U line, O line, W line) commercial power system, one may be tangent and the other may be reverse.

FIG. 7 is a diagram illustrating mutual interference of harmonics. The upper left of the figure is the tangent waveform, and the lower left of the figure is the reverse waveform. The solid line is the fundamental wave, the alternate long and short dash line is the second harmonic, and the dotted line is the third harmonic. When the tangent and the tangent are added to each other, the second-order or even-order harmonics are canceled, but the odd-order harmonics are not cancelled.

For this reason, it is preferable that the control unit 20 superimposes harmonic components of an odd-numbered order. By doing so, for example, even when a plurality of power conditioners are connected in parallel to the load, it is possible to suppress a situation in which harmonics are attenuated due to mutual influence.

"others"
In the above power conditioner 100, in the equation (4), an ideal sine wave having an effective value of the system voltage is used instead of the system voltage itself actually detected. This contributes to the effect that in normal operation, the influence of harmonics can be eliminated by the control command value based on the voltage of the fundamental wave, and a high-quality sine wave waveform can be generated. However, in the case of the isolated operation detection, since this may cause a delay in the detection, the processes as in steps S7, S8, and S9 of FIG. 3 are added.

Therefore, apart from the above-described embodiment, the AC voltage Va of the equation (4) is usually used, but when the independent operation is detected every 5 ms, the AC voltage of the AC electric circuit 4 from which the load 5 is hung (detection of the voltage sensor 18). It is also conceivable to use the AC voltage) as it is instead of Va in the equation (4). In this case, step S8 of FIG. 3 may be, for example, "determining the control command value using the AC voltage of the AC electric circuit as it is".

That is, when detecting independent operation, the control unit 20 controls the DC / DC converter 1 and the inverter 2 by a control command value using the voltage detected by the voltage sensor 18 including harmonics as it is. It is possible to utilize the AC voltage of the AC electric circuit 4 which may contain harmonics without removing the harmonics.
In other words, the voltage on which the harmonic component is superposed on the fundamental wave includes both the case of positive superposition (plus) and the case of naturally superimposition (not minus).

<< Supplement >>
It should be noted that the embodiments disclosed this time are exemplary in all respects and are not considered to be restrictive. The scope of the present invention is indicated by the scope of claims, and it is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 DC / DC converter 2 Inverter 3 DC power supply 4 AC electric circuit 5 Load 6 Interconnection relay 7 Commercial power system 8 DC bus 9 DC side capacitor 10 DC reactor 11 Intermediate capacitor 12 AC reactor 13 AC side capacitor 14 Voltage sensor 15 Current sensor 16 Voltage sensor 17 Current sensor 18 Voltage sensor 20 Control unit 100 Power conditioner d1, d2, d3, d4, d5, d6 Diode Q1, Q2, Q3, Q4, Q5, Q6 Switching element

Claims (7)

A power conditioner that connects to a commercial power system
A power converter that performs switching operation and
A voltage sensor that detects the voltage of the AC electric circuit connected to the commercial power system, and
And a to that control section controls the power conversion unit in response to the control instruction value based on the extracted fundamental voltage from the detection to the voltage of the voltage sensor,
When the control unit detects independent operation based on the voltage detected by the voltage sensor,
(A) When the frequency deviation is less than a predetermined value and the harmonic voltage increases to the first threshold value.
(B) When the frequency deviation is equal to or less than the predetermined value and the fundamental wave voltage increases by a predetermined amount, and
(C) When the frequency deviation is equal to or less than the predetermined value and the fundamental wave voltage increases by less than the predetermined amount, the harmonic voltage increases to the first threshold value when a harmonic component is superimposed. if you did this,
A power conditioner that confirms the success or failure of all of the above, and if any one of them is satisfied, performs step injection of reactive power. The power conditioner according to claim 1, wherein the control unit changes a harmonic component to be superimposed in proportion to the harmonic voltage. The power conditioner according to claim 1 or 2, wherein the control unit superimposes harmonic components of an odd order. The control unit avoids superimposition of harmonic components when the frequency deviation is larger than a predetermined value before superimposing the harmonic components, according to any one of claims 1 to 3. The power conditioner described in. The power according to claim 1, wherein the control unit controls the power conversion unit by a control command value using the voltage detected by the voltage sensor including harmonics as it is when detecting the independent operation. Conditioner. A power storage system including a DC power supply and the power conditioner according to any one of claims 1 to 5, which is connected to the DC power supply . It is a control method of a power conditioner including a power conversion unit that connects to a commercial power system and performs switching operation.
Detecting the voltage of the AC electric circuit connected to the commercial power system,
The power conversion unit is controlled by a control command value based on the fundamental wave voltage extracted from the detected voltage.
In the case of detecting independent operation based on the voltage of the AC electric circuit ,
(A) When the frequency deviation is less than or equal to a predetermined value and the harmonic voltage increases to the first threshold value.
(B) When the frequency deviation is equal to or less than the predetermined value and the fundamental wave voltage increases by a predetermined amount, and
(C) When the frequency deviation is equal to or less than the predetermined value and the fundamental wave voltage is increased by less than the predetermined amount and the harmonic component is superimposed, the harmonic voltage is increased to the first threshold value. if you did this,
A power conditioner control method in which the success or failure of all of the above is confirmed, and if any one of them is satisfied, step injection of reactive power is performed .

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