JP2016007122A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power converter capable of preventing erroneous stop of the power converter even when an instantaneous drop occurs.SOLUTION: A power converter 1 includes: a booster circuit 3 that controls the step-up ratio (first operation amount S1) so that the DC power output from a solar cell 8 is a maximum value or adjacent to the maximum value; and an inverter circuit 4 that receives the DC power output from the booster circuit 3 and converts the DC power into an AC power. The power converter 1 also includes a control section that corrects the step-up ratio using a correction value (second operation amount S2) based on the voltage of the DC power input to the inverter circuit 4 and set a larger correction value during the current value of the AC power exceeds a predetermined value.

Description

  The present invention relates to a power conversion device.

2. Description of the Related Art Conventionally, there has been provided a power conversion device that boosts DC power generated by a solar cell with a booster circuit, converts the DC power into AC power synchronized with a commercial power system using an inverter circuit, and superimposes the AC power on the commercial power system.

In a commercial power system, a natural phenomenon such as a lightning strike may cause a voltage to drop instantaneously or a power outage may be caused instantaneously, and a so-called instantaneous drop (instantaneous power failure) occurs. The number of installed power conversion devices is increasing year by year. For example, when an instantaneous drop occurs in a region, the power conversion device may stop due to an abnormality in the power system. In this case, a large power fluctuation may occur in the power system, and the power system itself may become unstable.

In order to prevent the commercial power system from becoming unstable, the power converter continues to operate even during a sag, and when the sag recovers, the function to quickly restore the output to the power system (FRT
(Fault Ride Through function) is demanded.

Patent Document 1 describes a power conversion device that determines a voltage sag when a voltage on a DC line connecting a booster circuit and an inverter circuit exceeds an upper limit value and switches from a normal mode to a voltage sag mode. Patent Document 1 stores the value of the output current of the inverter and the value of the DC input current to the booster circuit when the operation of the power converter shifts from the normal mode to the sag mode, and stores this when the operation returns. What used the value was described.

JP 2012-55036 A

However, in the power conversion device described in Patent Document 1, a control delay occurs when the operation mode is changed after judging the instantaneous drop, and the power conversion device may stop due to erroneous detection or error of the stored value. .

This invention is an invention made | formed in view of such a point, and it aims at providing the power converter device which ensures the stable operation | movement of a power converter device even if a sag occurs.

The power conversion device according to the present invention includes a booster circuit whose boost ratio is controlled so that the DC power output from the solar cell is at or near the maximum value, and the DC power output from the booster circuit is input to the power converter. In a power converter having an inverter circuit for converting DC power to AC power, the boost ratio is corrected with a correction value based on the voltage of DC power input to the inverter circuit, and the current value of AC power exceeds a predetermined value. And a control unit for increasing the correction value when it is in operation.

Further, another power conversion device of the present invention includes a booster circuit in which the boost ratio is controlled so that the DC power output from the solar cell is at or near the maximum value, and the DC power output from the booster circuit is In a power conversion device having an inverter circuit that converts this DC power into AC power that has been input, a correction value based on the voltage of the DC power that is input to the inverter circuit when the current value of the AC power exceeds a predetermined value. A control unit for adding to the boost ratio corrected based on the voltage is provided.

The power conversion device of the present invention can suppress erroneous stop of the power conversion device even when a voltage sag occurs.

FIG. 1 is a diagram illustrating a power conversion apparatus according to the present embodiment. FIG. 2 is a diagram illustrating a control block of the power conversion apparatus according to the present embodiment. FIG. 3 is a flowchart illustrating control of the power conversion apparatus according to this embodiment.

In this embodiment, the DC power output from the solar cell is converted into MPPT (Maximum Power).
The first operation amount that determines the boost ratio of the booster circuit when performing control based on the (r Point Tracking) method, and the second based on the boosted voltage (DC voltage) output from the booster circuit at the time of a sag.
By controlling the boost ratio of the booster circuit using the operation amount (correction value), it is possible to suppress the stop of the power converter due to malfunction.

As shown in FIG. 1, the power conversion device 1 is connected to the solar cell 8, and the DC power output from the solar cell 8 is input to the booster circuit 3 and converted into AC power synchronized with the commercial power system 2. Thereafter, this AC power is superimposed on the commercial power system 2.

The power converter 1 includes a booster circuit 3, an inverter circuit 4, a filter circuit 5, and a boost control circuit 6
(First control circuit) and an inverter control circuit 7 (second control circuit).

The booster circuit 3 is configured by a non-insulated chopper circuit, and includes a DC reactor 31, a boosting switch element 32, a diode 33, and a capacitor 34. Note that this booster circuit is not limited to the non-insulated type, and may be any type that can control the output voltage, such as an isolated type booster circuit.

The booster circuit 3 boosts and outputs the input DC voltage at a desired boost ratio by periodically turning on / off the boost switch element 32 at a predetermined ON duty ratio. Since the boost ratio is determined by the ON duty ratio, controlling the boost ratio is equivalent to controlling the ON duty ratio. By changing the desired boost ratio, the booster circuit 3 controls the voltage of the DC power output from the solar cell 8 and outputs it to the inverter circuit 4.

The inverter circuit 4 is composed of a single-phase bridge circuit in which a series circuit in which switch elements 41 and 42 are connected in series and a series circuit in which switch elements 43 and 44 are connected in series are connected in parallel. These switch elements 41 to 44 are periodically turned on / off by a pulse signal (switching signal) generated based on PWM (pulse width modulation), and DC power output from the booster circuit 3 is supplied to a commercial power system. To AC power (pseudo sine wave) synchronized with. The converted AC power is shaped into a sine wave through a filter circuit 5 (low-pass filter) that attenuates high-frequency components, and then superimposed on the power system 2. This inverter circuit may output not only single-phase alternating current but also three-phase alternating current, and is not limited to a single-phase / multi-phase bridge configuration, and a neutral point clapping method, output clamping method, or multi-level output. A possible circuit configuration may be used.

The boost control circuit 6 performs the following operations (1) to (4). (1) A first manipulated variable S for controlling the booster circuit 3 so that the DC power output from the solar cell 8 is at or near the maximum value.
1 (step-up ratio) is obtained. (2) DC voltage V of boosted DC power output from the booster circuit 3
A second operation amount S2 is obtained based on d. The second manipulated variable S2 becomes a correction value after being multiplied by a variable a2 based on the DC voltage Vd. (3) An operation of correcting the first operation amount S1 with the correction value is performed. This correction is an operation of adding / subtracting the second operation amount S2 (correction value) to the first operation amount S1. (It is also possible to change the algorithm so as to multiply / divide.) In this case, the first manipulated variable S1 may be preliminarily multiplied by a variable a1 based on the DC voltage Vd and used as the boost ratio. (4)
When the output current of the inverter circuit 4 exceeds a predetermined value, the correction value by the variable a2 is increased. That is, at this time, a large correction value is used.

The step-up control circuit 6 performs the operations (1) to (4) above so that when the output current of the inverter circuit 4 exceeds a predetermined value, the DC voltage Vd of the DC power output from the step-up circuit 3 is normally set. The voltage is raised to a target boost voltage Vdt (a constant predetermined voltage) that is not used during operation. Specifically, a control block diagram of the boost control circuit 6 in FIG. In order to obtain a correction value, the boost control circuit 6 inputs the DC voltage Vd output from the booster circuit 3 (DC voltage of DC power input to the inverter circuit 4) and the target boost voltage Vdt to the adder 66a. To obtain the difference. Next, the operation unit 62 obtains a second operation amount S2 for making this difference zero. The operation of the calculation unit 62 may be the difference itself between the target boost voltage Vdt and the DC voltage Vd, or may be obtained by multiplying this difference by a predetermined value. It may be one that has been subjected to (computation) processing, and can be arbitrarily set according to environmental conditions such as the rating of the power conversion device and the prescribed response speed. Second from the calculation unit 62
The manipulated variable S2 is weighted by the weight integrating circuit 67b using the variable a2 and then sent to the adder 66c as a correction value. The target boost voltage Vdt is a value of an upper limit voltage that is higher than the voltage of the power system 2 and set within the operable range of the power converter. That is, when this voltage is exceeded, the protection device is activated and the power converter stops operation.

The boost control circuit 6 further calculates the first manipulated variable S1. The step-up control circuit 6 receives the input voltage Vi and the input current Ii output from the solar cell 8 to the step-up circuit 3 and multiplies these values to obtain the output power P of the solar cell 8. Next, the calculation unit 61 uses the solar cell 8.
The target input voltage Vit is obtained so that the output power P of the output becomes maximum.

The target input voltage Vit is obtained by storing the previous output power Pd of the solar cell 8 and the direction in which the previous target input voltage Vit changes, and the output power P detected this time is larger than the previous output power. If it becomes, the target input voltage Vit is changed in the same direction as the previous time. That is, when the previous target input voltage Vit is decreased, the target input voltage Vit is also decreased this time, and when the previous target input voltage Vit is increased, the target input voltage Vit is also increased this time.
Increase.

Conversely, when the output power P detected this time is smaller than the previous output power Pd, the target input voltage Vit is changed in the opposite direction to the previous time. That is, when the previous target input voltage Vit is decreased, the target input voltage Vit is increased this time, and when the previous target input voltage Vit is decreased, the target input voltage Vit is increased this time. Such an MPPT operation is performed by the calculation unit 61.

After obtaining the target input voltage Vit, the adder 66b and the booster circuit 3
The difference from the input voltage Vi is obtained. Next, the first operation amount S1 is obtained by the calculation unit 63 so that the difference between the target input voltage Vit and the input voltage Vi of the booster circuit 3 becomes zero. This calculation unit 6
3 can perform a predetermined process according to the environmental conditions in the same manner as the calculation unit 62. The first manipulated variable S1 is weighted by the weight integrating circuit 67a using the variable a1, and then sent to the adder 66c as a step-up ratio.

As shown in FIG. 3, the variables a1 and a2 used in the weight integration circuits 67a and 67b are in the range of 0 to 1, and are set so that the sum of these variables a1 and a2 is always 1 (a1 +
a2 = 1). The variables a1 and a2 change according to the DC voltage Vd. When the DC voltage Vd reaches the target boost voltage Vdt, the variable a1 becomes 0 and the variable a2 becomes 1. DC voltage V
When d reaches the target boost voltage Vs, the variable a1 becomes 1 and the variable a2 becomes 0. The weight integrating circuit 67b performs weighting processing by multiplying the second manipulated variable S2 by the variable a2, so that the DC voltage V
The higher the d (corresponding to the boosted voltage output from the booster circuit 3) is, the larger the second manipulated variable S2 (correction value) after weighting becomes. At the same time, the weight integrating circuit 67a performs the weighting process by multiplying the first manipulated variable S1 by the variable a1, and as the DC voltage Vd increases, the first operation amount S1 increases.
The operation amount S1 is reduced. The target boosted voltage Vs corresponds to the DC voltage Vd when the power conversion device 1 outputs the rated power from the inverter circuit 4 to the power system 2 or when the predetermined predetermined power is output. For example, the DC voltage Vd when the power conversion device 1 is operating near the rated output is the target boost voltage Vs, and the target boost voltage Vs is the DC voltage Vd.
It may be a value of + α.

The first manipulated variable S1 and the second manipulated variable S2 sent to the adder 66c are added / subtracted (corrected) to become the manipulated variable Mv. The manipulated variable Mv is a signal indicating the ON duty ratio (boost ratio) of the pulse signal Pa for driving the switch element 32 of the booster circuit 3, and based on this signal, the calculation unit 6
5 generates a pulse signal Pa and supplies it to the switch element 32 of the booster circuit 3.

The inverter control circuit 7 controls the inverter circuit 4 so that the AC power Po output from the inverter circuit 4 becomes the target power Pt, and restricts the output current Io of the AC power Po so as not to exceed a predetermined current. I do.

Specifically, a control block diagram of the inverter control circuit 7 in FIG. The inverter control circuit 7 detects the output voltage Vo of the inverter circuit 4 and obtains the target output current Iot of the inverter circuit required for the AC power output from the inverter circuit 4 to become the target power Pt. The target output current Iot is input to the limiter 72. In the limiter 72, the target output current Io
When t exceeds the predetermined current Ic, the target output current Iot is clamped to the predetermined current Ic. The predetermined current Ic is a value when the target power Pt is set to, for example, the rated output power of the power converter or a predetermined output power, but a value slightly larger than this value is used according to the withstand current of the power converter. You can also. When the output voltage Io is clamped with the predetermined current Ic, the DC voltage Vd exceeds the target boost voltage Vs.

Next, the target output current Iot is input to the adder 73, and the adder 73 obtains a difference from the output current Io. The calculation unit 74 obtains an operation signal Mva that makes this difference zero. Similar to the calculation unit 62 and the calculation unit 63, the calculation unit 74 performs processing according to environmental conditions. The arithmetic unit 75 modulates the carrier wave with this operation signal Mva PWM (P
pulse widths Pi1 and Pi2 for operating the switch elements 41 to 44 of the inverter circuit 4 to generate the switch elements 41 to 4
4 is supplied.

By controlling the power converter 1 by the boost control circuit 6 and the inverter control circuit 7 in this way, the target output obtained by the inverter control circuit 7 is within a normal range where the output current Io does not exceed the predetermined current Ic. Since the current Iot is not limited (clamped), the DC voltage Vd converges to the voltage Vs. Further, the boost control circuit 6 controls the DC voltage Vd up to the vicinity of the voltage Vs when the target output current Iot is not limited. This control has the variable a1 as 1 and the variable a2 as 0, and the MPPT operation is mainly performed. Become control.

When an instantaneous drop (voltage drop) occurs in the power system 2, the inverter control circuit 7 obtains the target output current Iot so that the output power becomes the target power Pt. At this time, the target output current Iot increases (target output current Iot = target power Pt / system voltage) as the system voltage Vo decreases due to the instantaneous drop, but the target output current Iot is clamped (limited) to the predetermined current Ic. The

When the target output current Iot is limited to the predetermined current Ic, the power from the solar cell 8, that is, the power output from the booster circuit 3 becomes larger than the power output from the inverter circuit 4. This difference in power is charged in the capacitor 34 and the DC voltage Vd (the voltage of the capacitor 34) increases.

As the DC voltage Vd increases, the variable a1 decreases and the variable a2 increases. When the DC voltage Vd reaches the target boost voltage Vdt (while the current value of the AC power output to the power system 2 exceeds a predetermined value (for example, the rated current value when the power system 2 is normal)), the variable a1 Is 0 and the variable a2 is 1. The control of the boost control circuit 6 is mainly controlled by a constant voltage that operates the boost circuit 3 so that the DC voltage Vd becomes the target boost voltage Vdt from the control mainly of the MPPT operation. (This is the control when the second operation amount S2 is increased.)

When the instantaneous drop of the electric power system 2 is recovered, the voltage of the electric power system 2 increases, so that the target output current Iot of the current output from the inverter control circuit 7 becomes small. The target output current Iot becomes small and the restriction on the target output current Iot is released.

When the restriction on the target output current Iot is released, the output of the inverter circuit 4 increases, and the charge of the capacitor 34 is discharged correspondingly, and the voltage of the DC voltage Vd decreases.

As the DC voltage Vd increases, the variable a1 decreases and the variable a2 increases. After this, the DC voltage V
When d decreases and reaches the voltage Vs, the variable a1 becomes 1 and the variable a2 becomes 0, and the boost control circuit 6 mainly controls the boost circuit 3 to perform the MPPT operation.

Thus, in this embodiment, the booster circuit performs the MPPT operation by the first operation amount S1, and the second operation amount S1.
When the intermediate voltage increases at the time of the instantaneous drop due to the operation amount S2, the increase can be stopped at the target boost voltage Vdt, and the stop of the power converter due to the increase of the intermediate voltage (terminal voltage of the capacitor 34) can be suppressed.

In addition, after the instantaneous drop recovery, the limitation on the output current of the inverter circuit is released, and the target current value Iot
Since the value becomes the rated output value, the output can be quickly restored.

In addition, since the booster circuit is controlled using the first manipulated variable S1 and the second manipulated variable S2, there is no change in the control block of the booster control circuit 6 regardless of whether or not an instantaneous drop occurs in the power system 2. There is no need to switch control due to a sag (no need to detect sag). Further, it is not necessary to store the control amount before the voltage drop. Accordingly, it is possible to suppress erroneous stop of the power conversion apparatus 1 due to erroneous detection of the output current of the inverter stored due to control delay or the like, or DC input current to the booster circuit, or erroneous detection of instantaneous drop.

As mentioned above, although one Embodiment of this invention was described, the above description is for making an understanding of this invention easy, and does not limit this invention. It goes without saying that the present invention can be changed and improved without departing from the gist thereof, and that the present invention includes equivalents thereof.

For example, the control is performed using both the variables a1 and a2, but either one may be used as long as the corresponding operation can be performed at the time of a sag or normal.

The power conversion device of this embodiment can also be used as a solar cell system including the solar cell 8 or the like. Moreover, although the power converter device of this embodiment outputs single-phase alternating current power, it is applicable also to what outputs three-phase alternating current power.

DESCRIPTION OF SYMBOLS 1 Power converter 2 Power system 3 Booster circuit 4 Inverter circuit 5 Filter circuit 6 Booster control circuit 7 Inverter control circuit 8 Solar cell 31 DC reactor 32 Switch element 33 Diode 34 Capacitor 41-44 Switch element a1 Variable a2 Variable S1 1st operation Amount S2 second manipulated variable Pa pulse signal Pi1 to Pi2 pulse signal Po AC power Vd DC voltage Vdt target boost voltage Vi input voltage Vit target input voltage

Claims (5)

The step-up ratio is controlled so that the DC power output from the solar cell is at or near the maximum value, and the DC power output from the boost circuit is input to convert the DC power to AC power. In a power converter having an inverter circuit,
A controller that corrects the step-up ratio with a correction value based on the voltage of the DC power input to the inverter circuit, and increases the correction value when the current value of the AC power exceeds a predetermined value; The power converter characterized by this. The step-up ratio is controlled so that the DC power output from the solar cell is at or near the maximum value, and the DC power output from the boost circuit is input to convert the DC power to AC power. In a power converter having an inverter circuit,
A controller that adds a correction value based on the voltage of the DC power input to the inverter circuit to the boost ratio corrected based on the voltage when the current value of the AC power exceeds a predetermined value; A power conversion device. The power converter according to claim 1 or 2, wherein the correction value is increased as the voltage of the DC power input to the inverter circuit increases. The power conversion device according to any one of claims 1 to 3, wherein the correction value is calculated so that an output voltage of the booster circuit 3 becomes a predetermined voltage. A first control circuit for controlling the booster circuit;
The power converter according to claim 1, further comprising a second control circuit that controls the inverter circuit.

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