JP2013215075A - Photovoltaic power generation control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photovoltaic power generation control system capable of achieving optimum power of a solar battery in a short time after an AC power system which had caused a power failure has been restored.SOLUTION: Being accompanied with stopping of a commercial power supply system 5, for a DC-DC converter 2 and a DC-AC inverter 3 which have stopped the operation and MPPT control, the time of MPPT control which starts with power restoration of the commercial power supply system 5 is shortened by using a DC voltage of the DC-DC converter 2, and the time required for a solar cell 1 to obtain optimum power is shortened by synchronizing a voltage phase of the commercial power system 5 at power restoration with a phase of an output voltage of the DC-AC inverter 3.

Description

  The present invention relates to a photovoltaic power generation control system that operates by connecting power generated by a solar cell to a commercial power supply system.

  The technology to connect the power generated by solar cells to the commercial power system and to reverse the power flow to the commercial power system is defined in the “System Interconnection Rules” issued by the Japan Electric Association. It must be done under the specified conditions. For this reason, development of a photovoltaic power generation control system in accordance with the “system interconnection regulations” is underway.

  The power generation capacity of the solar cell is affected by the amount of sunlight irradiated to the solar cell and the temperature at which the solar cell operates. Maximum power point tracking (MPPT) control is known as a method for constantly optimizing the power generation capacity of a solar cell in an environment where the weather changes every day. (See Patent Document 1)

  In order to ensure the quality of power generated by the photovoltaic power generation system when the voltage of the commercial power system connected to the photovoltaic power generation control system decreases and when the frequency fluctuates, It is required to satisfy the operation continuation requirement at the time of accident (FRT requirement (FRT: Fault Ride Through)). (See Non-Patent Document 1)

JP 2011-101455 A

“Grid-Interconnection Code JEAC 9701-2010 [2011 supplement (Part 1)], Japan Electric Association

  Hereinafter, the phase (frequency) of the commercial power system voltage that is connected to the grid is referred to as an external frequency, and the phase of AC power that is output from the power converter of the photovoltaic power generation control system is referred to as an internal frequency. When the power generated by the solar cell is grid-connected to the commercial power supply system, the “system interconnection regulations” require that the phases of the external frequency and the internal frequency be synchronized. FIG. 3 shows conventional phase synchronization control. When the phases of the internal frequency and the external frequency are not synchronized as in (a), it is detected how much the internal frequency is different from the external frequency. After detecting the phase difference, PI control is performed on the internal frequency using the phase difference as shown in (b). The operations of (a) and (b) were repeated until the internal frequency was synchronized with the external frequency as shown in (c). In this method, a time equivalent to five cycles of the external frequency is required until the internal frequency and the external frequency are synchronized, and therefore a faster synchronization method is required.

  Further, in MPPT control for optimizing the power generation capacity of a solar cell, Patent Document 1 describes a method for starting MPPT control starting from a voltage stored immediately before a commercial power supply system fails. No reference is made to a method for quickly obtaining optimum AC power from a solar power generation system by synchronizing the internal frequency with an external frequency when recovering from a voltage drop accompanied by a state in which AC frequency cannot be obtained from the power supply system.

  The purpose of the present invention is to meet the FRT requirements for ensuring the quality of the power generated by the photovoltaic power generation system, and to shorten the time required for the power output from the power converter to recover from power reduction to active power. To provide a control system.

  In order to achieve the above object, a photovoltaic power generation control system according to the present invention includes a solar cell, a power conversion unit that converts DC power generated by the solar cell into AC power, and is connected to a commercial power system, and A power follow-up control unit that performs follow-up control to the optimum operating point of the solar cell while minutely changing a set of output voltage and output current of the solar cell, a voltage detection unit that detects a voltage of the commercial power supply system, and the voltage detection A system state determination unit that determines whether the commercial power system is in an instantaneous voltage drop state based on the voltage detected by the unit, a phase detection unit that detects a voltage phase of the commercial power system, and the power conversion A phase synchronization unit that synchronizes the output AC voltage phase of the unit with the voltage phase of the commercial power supply system, and an instantaneous voltage drop when the commercial power supply system is determined to be in an instantaneous voltage drop state by the system state determination unit An operation storage unit that stores a set of output current and output voltage generated by the previous solar cell, and when the commercial power state determination unit determines that the commercial power supply system is in a return state, After the instantaneous voltage drop recovery of the power supply system, the voltage phase of the power conversion unit is preset at the timing of zero crossing in the first detected voltage phase, synchronized with the voltage phase of the commercial power supply system, and further stored in the operation storage unit The tracking control is performed to the optimum operating point of the solar cell starting from the set of the output voltage and output current of the solar cell immediately before the instantaneous voltage drop.

  According to the present invention, after the recovery from the instantaneous voltage drop on the commercial power supply system side, it is possible to shorten the time until the phase of the external frequency and the internal frequency is synchronized, and in addition, the timing for starting the MPPT control by phase synchronization. Therefore, the recovery time of the output power required by the FRT requirement can be further shortened.

The block diagram of the photovoltaic power generation control system which concerns on embodiment of this invention. The relationship diagram of AC power supply system voltage and the counter in the microcomputer. FIG. 6 is a diagram illustrating conventional phase synchronization control. Explanatory drawing of phase-synchronization control of this invention. The conceptual diagram of the electric current-voltage characteristic of a solar cell.

  Embodiments of the present invention will be described below. FIG. 1 is a configuration diagram of a photovoltaic power generation control system according to an embodiment of the present invention. The direct current generated by the solar cell 1 is subjected to voltage adjustment in a power converter 4 composed of devices including a DC / DC converter 2 and a DC / AC inverter 3, and then converted into alternating current. Grid connected.

  The system power supply voltage detector 9 transmits the voltage of the commercial power supply system 5 to the system state determination device 10, and the system state determination device 10 determines whether or not the commercial power supply system 5 is in an instantaneous voltage drop state. The system power supply phase detector 12 detects the voltage phase of the commercial power supply system 5 and transmits it to the phase synchronization device 13. The phase synchronizer 13 always synchronizes the voltage phase of the power converter 4 and the commercial power supply system 5 (PLL: Phase Locked Loop) and enables system interconnection with the commercial power supply system 5.

  Here, an outline of the PLL control will be described. For example, when the voltage drops to 0% due to the instantaneous voltage drop of the commercial power system, the voltage phase of the commercial power supply system 5 cannot be detected by the system power supply phase detector 12, and the PLL control stops. When the commercial power supply system 5 recovers from the instantaneous voltage drop, the PLL control is started in order to link the output voltage phase of the power converter 5 and the voltage phase of the commercial power supply system. When performing PLL control, as shown in FIG. 2, one cycle 0 [rad] to 2π [rad] of the commercial power system voltage is treated as a counter value such as 0 [cnt] to 3,000,000 [cnt]. As shown in FIG. 3, using this count number, (a) the phase difference between the internal frequency and the external frequency is detected, and the phase difference at this time becomes the count number. (B) PI control is performed using the number of phase difference counts for the internal frequency, and the phase difference between the internal frequency and the external frequency is gradually reduced by repeating the operations (a) and (b). (C) The internal frequency and the external frequency are synchronized.

  A state in which the output phase of the power converter 4 and the power of the commercial power supply system 5 can be reversely flowed by the operation shown in FIG. 3 and the voltage phase is synchronized within a certain range is referred to as a PLL lock. The control method leading to this PLL lock state is called PLL control.

  In the PLL control of the present embodiment, the system power supply phase detector 12 detects the frequency (external frequency) of the commercial power supply system 5 that has recovered from the power failure as shown in FIG. When the external frequency recovers from the power failure and becomes the first zero cross as shown in FIG. 4A, the phase synchronizer 13 presets the frequency (internal frequency) of the DC / AC inverter in the power converter 4 (b ), The phase of the internal frequency and the external frequency is synchronized (PLL lock). Therefore, the output power of the power converter 4 and the commercial power supply system 5 can be interconnected by phase synchronization.

  By completing the PLL lock as described above, the power converter 4 can use the frequency of the commercial power supply system 4 as a reference sine wave for PWM control, so that the MPPT control for the solar cell 1 can be started. MPPT control is a method of optimizing the power generation capability of the solar cell 1 by inputting the voltage (VDC) detected by the voltage detector 6 and the current (IDC) detected by the current detector 7 to the power follow-up control device 8. It is.

  Here, an outline of MPPT control will be described. As described above, the characteristics of the output power P (P = I × V) of the solar cell 1 vary depending on the amount of sunlight irradiated to the solar cell 1 and the temperature at which the solar cell 1 operates, and are generally as shown in FIG. It is known to draw a simple curve. This is commonly called “IV characteristic curve”. Therefore, in order to obtain the maximum output of the solar cell, a combination of Imax and Vmax on the “IV characteristic curve” where the area (I × V) indicated by the oblique line shown in FIG.

  In order to find a combination of Imax and Vmax, the combination of I and V is minutely changed and the combination is input to the power follow-up control device 8. In the power tracking device, the output power of the solar cell 1 is calculated from the input combination of I and V, the increase or decrease of the power is determined, and the “IV characteristic curve” is small so as to approach the combination of Imax and Vmax. Repeat the change. This control method is MPPT control.

  The operation storage device 11 stores and holds the direct current (IDC) and the direct current voltage (VDC) received from the power follow-up control device 8 when the commercial power supply system fails. When the power is restored from the power failure, the DC current (IDC) and the DC voltage (VDC) that are stored are input to the power tracking control device 8.

  Here, it is assumed that the output power of the power converter 4 is connected to the commercial power supply system 5. In this state, when the commercial power supply system 5 causes a momentary voltage drop, the power converter 4 performs PWM control on the DC / AC inverter 3 using the voltage waveform of the commercial power supply system 5. With the voltage drop of 5, the output voltage of the DC / AC inverter 3 is lowered. In this state, the voltage input from the DC / DC converter 2 to the DC / AC inverter 3 is too high for the DC / AC inverter 3. Therefore, it is necessary to reduce the output of the solar cell 1 and also reduce the output voltage of the DC / DC converter 2. If the output of the solar cell 1 is reduced once, it is necessary to perform the MPPT control from the initial state before returning to the original output. Therefore, it takes time for the output of the solar cell 1 to return to the original state.

  A method for shortening this time is shown below. The system state determination device 10 detects a power failure of the commercial power supply system 5 based on the AC power supply monitoring signal from the system power supply monitoring device 9. When a power failure is detected, the system state determination device 10 transmits a power failure signal to the power tracking control device 8. When the power follow-up control device 8 receives the power failure signal, it stores the DC voltage (VDC) and DC current (IDC) immediately before the power failure in the operation storage device 11. When the system state determination device 10 detects the power recovery of the commercial power system 5, the power phase detector 12 detects the first zero cross of the external frequency after the power recovery and supplies the voltage phase (VRN) to the phase synchronization device 13. Then, the phase angle of the internal frequency is preset as shown in FIG. By performing this operation, the phases of the external frequency and the internal frequency are synchronized, and the time until the PLL lock state is reached can be shortened.

  In addition, the system state determination device 10 transmits a power recovery signal to the power follow-up control device 8. The power follow-up control device 8 instructs to output the direct current voltage (VDC) and direct current (IDC) stored in the operation storage device 11. The direct current voltage (VDC) and direct current (IDC) output from the operation storage device 11 are input to the power tracking control device 8. The power follow-up control device 8 can start MPPT control using the input DC voltage (VDC) and DC current (IDC).

  In the photovoltaic power generation control system of this embodiment that operates in this way, when the AC power supply recovers from an instantaneous power failure, the phase of the output voltage of the DC / AC inverter 3 is the zero cross point of the commercial power supply system 5. Since the preset is preset, the phase synchronization is completed after the frequency of the commercial power supply system is about 5 cycles in the conventional method. However, in this embodiment, the phase synchronization is completed in the half cycle of the commercial power supply system at the maximum. Can be shortened.

  Furthermore, the MPPT control can be resumed using the DC power supply (VDC) and DC current (IDC) stored at the moment of a power failure while the output voltage of the DC / AC inverter 3 and the voltage phase of the commercial power supply system 5 are synchronized. Therefore, the time until the power generation of the solar cell 1 is optimized can be shortened.

  Therefore, when the commercial power supply system 5 recovers from the momentary power failure, the time until the grid connection between the photovoltaic power generation control system and the commercial power supply system 5 is shortened, so that the FRT requirement can be satisfied. .

DESCRIPTION OF SYMBOLS 1 Solar cell 2 DC / DC converter 3 DC / AC inverter 4 Power converter 5 Commercial power supply system 6 Voltage detector 7 Current detector 8 Power tracking control apparatus 9 System power supply voltage detector 10 System state determination apparatus 11 Operation | movement memory apparatus 12 System power supply phase detector 13 Phase synchronization device

Claims (1)

Solar cells,
A power conversion unit that converts the DC power generated by the solar cell into AC power and interconnects with a commercial power supply system;
A power follow-up control unit that performs follow-up control to the optimum operating point of the solar cell while minutely changing the set of output voltage and output current of the solar cell;
A voltage detector for detecting the voltage of the commercial power system;
A system state determination unit that determines whether the commercial power supply system is in an instantaneous voltage drop state based on the voltage detected by the voltage detection unit;
A phase detector for detecting a voltage phase of the commercial power system;
A phase synchronization unit that synchronizes the output AC voltage phase of the power conversion unit to the voltage phase of the commercial power supply system; and
An operation storage unit for storing a set of output current and output voltage generated by the solar cell immediately before the instantaneous voltage drop when the commercial power supply system is determined to be in an instantaneous voltage drop state by the grid state determination unit; Prepared,
When it is determined by the system state determination unit that the commercial power supply system is in a return state, the voltage phase of the power conversion unit at the timing of zero crossing in the voltage phase first detected after the instantaneous voltage drop recovery of the commercial power supply system Is preset to synchronize with the voltage phase of the commercial power system, and the optimum operating point of the solar cell using the set of output voltage and output current of the solar cell immediately before the instantaneous voltage drop stored in the operation storage unit A photovoltaic power generation control system characterized by following control.

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