JP6167337B2 - Power converter - Google Patents

Description

  The present invention relates to a protection operation of a power converter that converts DC power based on renewable energy into AC power.

  The conventional power conversion device is configured to allow input from a plurality of solar cell strings, detects the output current for each input, that is, for each solar cell string, and mutually outputs the output current for each solar cell string. Compared to the above, there is a case where the abnormality is judged when the output current of the other solar cell string is far from the output current. (Patent Document 1)

Japanese Patent No. 3474711

In the thing of patent document 1, when the rated value of each solar cell string is substantially the same, it is an abnormal state by comparing the output currents of solar cell strings with each other (when the output greatly exceeds the rated value). Or when the output is abnormally low compared to others, etc.), but when all or most of the solar cell strings are defective, the abnormal state is falsely detected. There was a case.

In particular, when each solar cell string generates a large amount of sunlight and the power generation exceeds the rating, the protection operation is activated if the total power generation exceeds the design capacity of the converter that converts DC power to AC power. The power converter sometimes stopped.

  The power conversion device of the present invention is configured to be able to connect a plurality of solar cell strings that are connected together by electrically connecting a plurality of solar cells, and converts DC power obtained from these solar cell strings into AC power. A booster circuit that boosts DC power obtained from the solar cell string corresponding to each solar cell string, and at least a current value, a voltage value, or the DC power value of DC power input to the booster circuit A detection unit that obtains any one of the above, a first protection operation unit that detects an abnormality from the detection value of the detection unit and a predetermined value, and reduces the output power of the booster circuit, all or effectively operating The output power of each of the booster circuits that are operating effectively by judging abnormality from at least one value of the total output power or the total current of the booster circuit that is operating In which and a second protection operation section decreasing.

The power conversion device according to the present invention includes a first protection operation unit for each booster circuit and a second protection operation unit for the entire booster circuit or the booster circuit that is operating effectively. It is to suppress.

FIG. 1 is an explanatory view showing an embodiment of the present invention. FIG. 2 is an explanatory diagram showing the operation of the embodiment shown in FIG.

  The present invention performs a protection operation by including a first protection operation unit for each booster circuit of a power converter and a second protection operation unit for an entire booster circuit or an effective booster circuit. .

  FIG. 1 is an explanatory view showing an embodiment of the present invention, wherein A to E are solar cell strings, and a plurality of solar cells are electrically connected in series / parallel to form a single module. Alternatively, this module is electrically connected in series / parallel to form a single string. Hereinafter, the embodiments will be described simply as strings A to E. In FIG. 1, reference numeral 1 denotes a power converter, and the output of the power converter 1 is superimposed on the grid G.

  The strings A to E are configured by connecting a plurality of solar cell panels in parallel and / or in series so as to meet the specifications (ratings) of the corresponding input circuits 2a to 2e. The specifications (rating) of the input circuit are maximum DC voltage = 450 V, maximum DC current = 10 A, maximum power = 1.5 kW, and the like. The number of strings to be connected is not limited to five from A to E, and is not limited to this specification.

  Since the same circuit can be used for the input circuits 2a to 2e, the input circuit 2a will be described and the description of the input circuits 2b to 2e will be omitted. A string A of solar cells is connected to the input circuit 2a via positive and negative input terminals, and a (direct current) input voltage (corresponding to the output voltage of the string A) of the input circuit 2a is detected by the voltage detector 3. A (direct current) input current (corresponding to the output current of the string A) of the input circuit 2a is detected by the current detector 4.

  The voltage detector 3 divides the applied voltage as necessary, performs A / D (analog / digital) conversion, and supplies it to the control unit 5 as a digital voltage value. In the case where the control element such as the control unit 5 or the microprocessor of the control unit 5 has an A / D conversion unit, the voltage detector 3 may be configured as a voltage dividing unit by resistance voltage division.

  The current detector 4 detects a supplied current, and there are a detector that detects a voltage drop due to a shunt resistor, a non-contact type that uses the Hall effect, and the like, and outputs a voltage corresponding to the detected current amount. Is. This voltage is supplied to the control unit 5 in the same manner as the output of the voltage detector 3.

  The input circuit 2a includes a DC voltage boosting unit (boosting circuit). The boosting unit includes at least a reactor 6, a switching element 7, a diode 8, and a capacitor 9. The terminal voltage of the capacitor 9 becomes a target voltage. A general DC / DC converter that feedback-controls the on-duty ratio of the switching element 7 (for example, the switching period is 1 to 3 kHz) can be used. The diode 10 is used to prevent backflow when a plurality of input circuits are used.

  The DC power output through the diode 10 is combined with the outputs of the other input circuits 2b to 2e and supplied to the capacitor 11 that supplies an intermediate voltage. This intermediate voltage is supplied to an inverter unit 12 that performs D / A (digital / analog) conversion by connecting four switching elements in a single-phase bridge shape.

  The inverter unit 12 turns on / off each switching element based on a switching signal obtained by comparing the magnitude of a modulated wave having a frequency equivalent to the frequency of the system G and the carrier wave, so that the frequency is substantially the same as that of the system G. The pseudo sine wave AC power is output. The pseudo sine wave is superposed on the system G after the high frequency component is attenuated by the filter circuit including the reactors 13 and 14 and the capacitor 15. The waveform shaping of the pseudo sine wave is not limited to this method, and other methods such as a neutral point clamping method can be used.

Reference numeral 16 denotes a display unit that can display numbers, symbols, characters, etc., such as a general-purpose 7-segment / 8-segment display or a liquid crystal display. Based on a signal from the control unit 5, numbers, symbols, A specific code is displayed by combining characters.

  The control unit 5 has a maximum (or near or maximum) AC power for superimposing the target voltage of the boosting unit, the peak value of the AC voltage superimposed on the system G (or an effective voltage or an average voltage), etc. on the system G. Value). At this time, the generated power of the string A is calculated from the detection values of the voltage detector 3 and the current detector 4 and is added to the control. That is, control is performed so that the total generated power of the strings A to E does not exceed the power supplied from the inverter unit to the system G.

For example, the power generation amount of string A usually increases as the amount of sunshine increases, but does not exceed the maximum power generation amount in terms of characteristics. This maximum power generation amount does not all become the same value due to individual differences for each solar cell. It is generally known that the power generation characteristics of each solar cell are represented by P = V (V) × I (A), where P (W) is the power generation amount. Therefore, modules and strings using a plurality of such solar cells are also substantially represented by this characteristic.

  The power generation characteristic of the solar cell is a characteristic in which the power generation amount (W) usually has a single peak value with respect to the change of the voltage (V), and the power generation amount at this peak is also P = V × I = R × I. When the output voltage of the solar cell deviates up and down from the peak voltage V, the current I decreases and the power generation amount P also decreases. The control unit 5 controls the target voltage of the boosting unit so that the power generation amount P (the product of the detection value of the voltage detector 3 of the input circuit 2a and the detection value of the current detector 4) is always maximized. That is, the boosting ratio of the boosting unit is controlled. Since this step-up ratio changes with the on-duty ratio of the switching element 7, the impedance R of the input circuit 2a seen from the string A changes, and the output of the string A can be changed.

By making the target voltage smaller than the value at which the power generation amount P becomes maximum, the power generation amount of the string A can be controlled to be smaller than the maximum power generation amount.
When the voltage detected by the voltage detector 3 exceeds the specification of the input circuit 2a (the upper limit voltage of the input voltage), the control unit 5 (operation of the first protection operation unit) receives the current detected by the current detector 4 When the specification of the circuit 2a (the upper limit current of the input current) is exceeded, the product of the voltage value detected by the voltage detector 3 and the current value detected by the current detector 4 is the specification of the input circuit 2a (upper limit of the input capacity). Is exceeded, the target voltage of the booster (the on-duty ratio of the switching element 7) is decreased by a predetermined value. If these conditions continue further, the target voltage is further lowered.

  For example, when the current value detected by the current detector 4 exceeds a predetermined value (a value according to the specification, a value obtained by multiplying this value by a predetermined value) exceeds a predetermined time (0.05 to 0.20 sec) The protection operation is started. The protection operation is canceled when the value falls below a value obtained by adding a differential to the predetermined value.

Also, this protection operation is based on the detected current value in multiple zones (zone that does not perform protection operation, zone that protects without increasing current value, zone that protects to reduce current value, protection that greatly reduces current value) It is also possible to perform zone control using a zone to be performed and the like, and there is no particular limitation. Note that the protective operation can be performed in the same manner when using the voltage value and the product of the voltage value and the current value (corresponding to the generated power).

  The detection of voltage and current can be replaced with the voltage value and current value on the output side (output side of the diode 8) of the input circuit 2a, and in this case, it can also be used to determine the current value and input capacitance. Similarly, the input circuits 2b to 2e also control the target voltage of the boosting unit so that the power generation amount of the corresponding string becomes large, and if the power generation amount of the string exceeds the specification of each input circuit, the corresponding string Protection control to reduce the amount of power generation.

  When such protection control is performed, the control unit 5 outputs a specific code to the display unit 16 for display.

The control unit 5 (the operation of the second protection operation unit) is a sum of the output powers of the respective input circuits 2a to 2e (however, the input power that is not effective such as the fact that the power generation amount of the connected strings is small and the boosting operation is not performed) The output power of the circuit is not added, or the output power can be added as 0. The set value (allowable capacity based on the specification of the inverter unit 12 or a predetermined value multiplied by this value) When a value exceeds a specified value, a protective action is taken.

  This protection operation is an operation for reducing the output substantially simultaneously to the input circuits 2a to 2e (only valid input circuits may be used). The specific protection operation is a constant operation of the first protection operation unit. Detailed description will be omitted. The difference in operation between the first protection operation unit and the second protection operation unit is that the first protection operation unit individually corresponds to each input circuit, whereas the second protection operation unit simultaneously applies to all the input circuits. It is a thing to correspond.

  The operation of the second protection operation unit is based on the input power of each of the input circuits 2a to 2e. In addition, a voltage detector and a current detector are provided on the input side of the inverter unit 12, and values of input power and input current by these detectors are provided. It is also possible to use. It is also possible to detect and replace the amount of power supplied (superimposed or sold) to the grid G by the power meter 17, but in this case, setting is made in consideration of conversion loss of the input circuit, the inverter unit 12, etc. What is necessary is just to correct | amend a value. If the system voltage is assumed to be constant, the current value can be calculated from this electric energy and used.

  FIG. 2 is an explanatory diagram showing the operation of the embodiment shown in FIG. 1. In step S1, the current I and the voltage V supplied to the respective input circuits 2a to 2e are detected. In step S2, the input power (generated power of the corresponding string) of each input circuit is calculated from the current I and voltage V detected in step S1. In step S3, a power generation amount Σ that is the sum of the input power (power generation amount) of each input circuit is calculated.

  In step S4, it is determined whether or not there is an input circuit in an abnormal state (a state where the current exceeds the set value) in the current I detected in step S1, and if this condition is satisfied (in the case of Yes), the process proceeds to step S5. Then, the first protection operation is performed.

  In step S6, it is determined whether or not the power generation amount Σ calculated in step S3 is in an abnormal state (a state exceeding the set value). If this condition is satisfied (in the case of Yes), the process proceeds to step S7. 2 The protection operation is performed.

  Thus, in this invention, the capacity | capacitance excess of a power converter device is suppressed using a 1st protection operation and a 2nd protection operation.

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.

DESCRIPTION OF SYMBOLS 1 Power converter 2a-2e Input circuit 3 Voltage detector 4 Current detector 5 Control part 16 Display part 17 Electric power meter

Claims (2)

  In the power conversion device configured to connect a plurality of solar cell strings electrically connected to a plurality of solar cells and to convert DC power obtained from these solar cell strings into AC power, A booster circuit that boosts DC power obtained from the solar cell string corresponding to the solar cell string, and at least one of a current value, a voltage value, or the DC power value of the DC power input to the booster circuit A detection unit that obtains, a first protection operation unit that detects an abnormality from the detection value of the detection unit and a predetermined value and reduces the output power of the booster circuit, and a booster circuit that is operating all or effectively Second, the abnormality is judged from at least one of the total output power and the total current, and the output power of each of all the booster circuits that are operating effectively is reduced. Power converter, characterized in that it comprises a protection operation unit.   In the power conversion device configured to connect a plurality of solar cell strings electrically connected to a plurality of solar cells and to convert DC power obtained from these solar cell strings into AC power, A booster circuit that boosts DC power obtained from the solar cell string corresponding to the solar cell string, and at least one of a current value, a voltage value, or the DC power value of the DC power input to the booster circuit A detection unit that obtains, a first protection operation unit that detects an abnormality from the detection value of the detection unit and a predetermined value, and reduces the output power of the booster circuit; and at least the total output power of the converted AC power Or a second protection operation unit that determines abnormality from any one value of the total current and reduces the output power of each of the booster circuits that are operating effectively or all. Power conversion apparatus characterized by obtaining.

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