JP5733558B2 - Output control method of photovoltaic power generation system - Google Patents

Description

  The present invention relates to an output control method for a solar power generation system that controls the output power of a power conditioner based on the generated power of a solar battery in a solar power generation system in which a solar battery is connected to a power system using a power conditioner. .

  In recent years, a photovoltaic power generation system using sunlight is attracting attention as one of clean natural energy from the viewpoint of environmental protection. This solar power generation system has a configuration in which a solar cell is connected to a power system such as a commercial power source by a power conditioner (power converter) including an inverter.

  The power conditioner of a photovoltaic power generation system that links this solar cell and a power system converts the DC power generated by the solar cell into AC by a switching operation by an inverter and supplies the AC power to a load. is there. The output of this solar cell generally has a convex PV characteristic. In this PV characteristic, when the operating voltage is increased from the lowest voltage (0 V), the output power gradually increases and reaches a maximum point at which the output power reaches the maximum power at a predetermined operating voltage. Thereafter, as the operating voltage is raised, the output power gradually decreases, and when the operating voltage finally reaches the open voltage, the output power becomes zero.

  Based on such PV characteristics, in the photovoltaic power generation system, in order to efficiently use the output of the solar cell, the maximum power that appropriately controls the operating voltage so that the output power of the solar cell always becomes the maximum power. A tracking control method is employed (see, for example, Patent Document 1).

  In the power conditioner in this photovoltaic power generation system, a DC voltage control command value is generated by the maximum power tracking control based on the output voltage and output current of the solar cell, and the DC voltage control command value is obtained by PI control. The inverter is switched by PWM control based on the current control command value, and the output power of the inverter is supplied to the load.

JP-A-8-44446

  By the way, in the conventional photovoltaic power generation system described above, when the generated power of the solar cell increases and the output power of the inverter of the power conditioner exceeds the power consumption required by the load, the surplus power is transferred to the power system. Reverse current. When such a reverse power flow occurs, power fluctuations and voltage frequency fluctuations of the power system are caused, which is not desirable.

  Therefore, in the power conditioner, a limiter upper limit value is set for the current control command value, and even when the generated power of the solar cell becomes large, the output power of the inverter is set by the limiter upper limit value set for the current control command value. By suppressing it, the occurrence of reverse power flow is prevented in advance.

  However, the maximum power follow-up control of the power conditioner generates a DC voltage control command value every 3 seconds, for example. Therefore, when the load fluctuates in a time shorter than 3 seconds, current control is performed as in the conventional case. The current situation is that if the limiter upper limit value provided in the command value is a fixed value, it cannot cope with the load fluctuation.

  That is, when the power consumption required by the load decreases due to such a short-time load fluctuation, the output power of the inverter of the power conditioner exceeds the power consumption required by the load. As a result, surplus power flows backward to the power system.

  When such reverse power flow occurs, power fluctuations and voltage frequency fluctuations of the power system are caused. Thus, it has been difficult for the conventional solar power generation system to cope with a load fluctuation in a shorter time than the maximum power tracking control of the power conditioner.

  Therefore, the present invention has been proposed in view of the above-mentioned problems, and the object of the present invention is to provide an output of a photovoltaic power generation system that can easily cope with a short-time load fluctuation and reliably prevent reverse power flow. It is to provide a control method.

As a technical means for achieving the above-mentioned object, the present invention provides a photovoltaic power generation system in which a solar cell is connected to a power system by a power conditioner, wherein the power conditioner includes an output voltage and an output of the solar cell. A DC voltage control command value is generated by maximum power tracking control based on the current, the DC voltage control command value is converted to a current control command value by PI control, and the inverter is switched by PWM control based on the current control command value An output control method of operating and supplying the output power of the inverter to a load, wherein a limiter upper limit value is set to a current control command value by the PI control, and limiter control is performed according to load fluctuation input by an external signal The upper limit value of the limiter is variable.

In the present invention, a limiter upper limit value is provided for the current control command value by PI control, and the limiter upper limit value is varied by limiter control in accordance with load fluctuations input by an external signal, thereby reducing power consumption required by the load. If the output power of the inverter exceeds the power consumption required by the load, the limiter upper limit value is lowered. By reducing the limiter upper limit value in this way, the reverse power flow is prevented beforehand by suppressing the output power of the inverter.

  On the contrary, when the power consumption required by the load increases and the output power of the inverter falls below the power consumption required by the load, the limiter upper limit value is increased. By increasing the limiter upper limit value in this way, the power consumption required by the load can be supplied by increasing the output power of the inverter.

Thus, in the present invention, even if there is a load fluctuation in a shorter time than the maximum power tracking control of the power conditioner, the limiter upper limit value is varied by the limiter control according to the load fluctuation inputted by the external signal. The output power of the inverter can be adjusted, and it is easy to cope with a load fluctuation for a short time and the response can be improved.

According to the present invention, by providing a limiter upper limit value for the current control command value by PI control and varying the limiter upper limit value by the limiter control according to the load fluctuation input by an external signal , the power consumption required by the load When the output power of the inverter exceeds the power consumption required by the load, the limiter upper limit value is lowered. By reducing the limiter upper limit value in this way, the reverse power flow is prevented beforehand by suppressing the output power of the inverter.

  Thus, by varying the limiter upper limit value, the output power of the inverter can be suppressed even when there is a load change, and reverse power flow can be reliably prevented. As a result, it is possible to provide a highly reliable photovoltaic power generation system that can easily cope with load fluctuations for a short time, improve responsiveness, and reliably prevent reverse power flow.

In embodiment of this invention, it is a block diagram which shows schematic structure of a solar energy power generation system. 2 is a flowchart for explaining limiter control in the power conditioner of FIG. 1.

  The embodiment of the operation control method of the photovoltaic power generation system according to the present invention will be described in detail below. FIG. 1 is a block diagram showing a schematic configuration of a photovoltaic power generation system according to this embodiment.

  The solar power generation system in the embodiment shown in FIG. 1 includes a configuration in which a solar battery 20 is linked to a power system 30 such as a commercial power source by a power conditioner 10 (power converter) including an inverter 11. The power conditioner 10 in this solar power generation system converts DC power generated by the solar battery 20 into AC by a switching operation by the inverter 11 and supplies the AC power to a load (not shown).

  The power conditioner 10 includes an MPPT control unit 12 that generates a DC voltage control command value by maximum power tracking control based on the output voltage Vdc and the output current Idc of the solar cell 20, and a direct current output from the MPPT control unit 12. A PI control unit 13 that converts a voltage control command value into a current control command value by PI control, a limiter control unit 14 that sets a limiter upper limit value for the current control command value output from the PI control unit 13, and its limiter control The PWM control unit 15 that performs switching operation of the inverter 11 by PWM control based on the current control command value output from the unit 14, that is, the current control command value for which the limiter upper limit value is set, constitutes a main part.

  In addition, the code | symbol 40 in a figure is a connection transformer for connecting the power conditioner 10 and the electric power grid | system 30, and the code | symbol 50 is for disconnecting the solar cell 20 from the electric power grid | system 30 at the time of a system power failure, etc. AC switch.

  The limiter control unit 14 in the power conditioner 10 of this embodiment sets a limiter upper limit value for the current control command value by PI control, and sets the limiter upper limit value by the limiter control according to load fluctuations input by an external signal. Variable.

  In the power conditioner 10, the output voltage Vdc of the solar battery 20 is detected by an instrument transformer, and the output current Idc is detected by a current transformer. Based on the output voltage Vdc and the output current Idc of the solar battery 20, MPPT The control unit 12 generates a DC voltage control command value by maximum power tracking control.

  Here, the output of the solar cell 20 generally has a convex PV characteristic. In this PV characteristic, when the operating voltage is increased from the lowest voltage (0 V), the output power gradually increases and reaches a maximum point at which the output power reaches the maximum power at a predetermined operating voltage. Thereafter, as the operating voltage is raised, the output power gradually decreases, and when the operating voltage finally reaches the open voltage, the output power becomes zero. On the basis of such PV characteristics, the MPPT control unit 12 uses the output of the solar cell 20 efficiently, so that the output power of the solar cell 20 is always the maximum power so that the direct current voltage is controlled by the maximum power tracking control. Generate control command values.

  The PI control unit 13 converts the DC voltage control command value output from the MPPT control unit 12 into a current control command value by PI control. Further, the limiter control unit 14 sets a limiter upper limit value for the current control command value output from the PI control unit 13. The PWM control unit 15 switches the inverter 11 by PWM control based on the current control command value output from the limiter control unit 14, that is, the current control command value for which the limiter upper limit value is set. Output power generated by the switching operation of the inverter 11 is supplied to a load (not shown).

  Here, the limiter control unit 14 can vary the limiter upper limit value by limiter control in accordance with load fluctuations input by an external signal. That is, as shown in FIG. 2, a variable limiter upper limit value is set for the output of the PI control unit 13, that is, the current control command value (STEP 1). When the power consumption required by the load decreases and the output power of the inverter 11 exceeds the power consumption required by the load (STEP 2), the limiter upper limit value set in the current control command value is lowered (STEP 3). . In this way, with the output of the limiter control unit 14 with the limiter upper limit value lowered (STEP 4), the output power of the inverter 11 is suppressed to prevent the reverse power flow.

  Conversely, when the power consumption required by the load increases and the output power of the inverter 11 falls below the power consumption required by the load (STEP 5), the limiter upper limit value set in the current control command value is increased. (STEP 6). In this way, with the output of the limiter control unit 14 that has increased the limiter upper limit value (STEP 4), the power consumption required by the load can be supplied by increasing the output power of the inverter 11.

  The maximum power follow-up control of the power conditioner 10 generates a DC voltage control command value every 3 seconds, for example. Even if the load fluctuates in a time shorter than 3 seconds, the limiter control unit 14 In this case, the output power of the inverter 11 can be suppressed or increased by changing the limiter upper limit value so as to decrease or increase with respect to the load fluctuation input by the external signal. It is easy to cope with fluctuations, and responsiveness can be improved.

  Here, when determining whether the output power of the inverter 11 is higher or lower than the power consumption required by the load, a predetermined hysteresis width is provided to prevent hunting and to output the inverter 11. The power is kept from becoming unstable. Note that the rate of change to decrease or increase the limiter upper limit value is that reverse power flow occurs based on the DC voltage control command value output from the MPPT control unit 12 or the current control command value output from the PI control unit 13. It is decided in the range not to.

  The present invention is not limited to the above-described embodiments, and can of course be implemented in various forms without departing from the gist of the present invention. It includes the equivalent meanings recited in the claims and the equivalents recited in the claims, and all modifications within the scope.

DESCRIPTION OF SYMBOLS 10 Power conditioner 11 Inverter 20 Solar cell 30 Electric power system

Claims (2)

In a photovoltaic power generation system in which a solar cell is connected to a power system by a power conditioner, the power conditioner generates a DC voltage control command value by maximum power tracking control based on the output voltage and output current of the solar cell. In the output control method, the DC voltage control command value is converted into a current control command value by PI control, the inverter is switched by PWM control based on the current control command value, and the output power of the inverter is supplied to the load. A limiter upper limit value is set to a current control command value by the PI control, and the limiter upper limit value is varied by limiter control according to load fluctuations input by an external signal . Output control method.   The output control method of the photovoltaic power generation system according to claim 1, wherein when the output power of the inverter exceeds the power consumption required by the load, the limiter upper limit value is decreased.

Images