JP2001209439A - Voltage phase detector for photovoltaic power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage phase detector detecting that phase and voltage become same by monitoring an output voltage of power converter and the phase of the voltage and the voltage of a power transmission system and suppresses an overcurrent at the time when the converter and the power transmission lines are connected with each other. SOLUTION: The voltage phase detector has transformers 18 and 33 at each side of the power converter 12 and the power transmission system 16, which monitor the voltage at the both transformers with a start and stop unit 32. On the other hand, a phase monitoring unit 50 monitors a relative phase. The phase monitoring unit detects each of zero cross points and judges that the output voltage of the power converter and the power transmission system voltage are the equal phase if both zero cross points are overlapped, calculates output voltage for the power converter and voltage for the power transmission and judges that both phases are equal if the calculated values are less than a prescribed threshold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output voltage waveform of a power conversion device and a voltage waveform of a power transmission system when a photovoltaic power generation system is connected to a solar cell whose power supply is limited by the amount of solar radiation or the like. And a device for detecting phase synchronization.

[0002]

2. Description of the Related Art In a photovoltaic power generation system in which DC power of a solar cell is converted into AC power by a power converter and power is supplied to a load in connection with a power transmission system, a difference in power transmission system frequency (eg, 50 Hz Or 60 Hz) is disclosed in Japanese Patent Laid-Open No. 8-1.
26343.

[0003] The control of the power converter uses a bimodal bandpass filter in the control system of the output current feedback loop, and the output current of the power converter is in phase with the voltage of the transmission system by the phase of the output of the bimodal bandpass filter. Control so that When the power converter is connected to the power transmission system, the frequency of the power transmission system is confirmed by a transformer for detection, and the center frequency and the Q value of the band filter constituting the bimodal band filter, A system control circuit for determining a constant of the system protection circuit is provided. Thus, the output current control of the power converter is automatically switched according to the frequency of the power transmission system.

[0004]

In the above prior art, an overcurrent always occurs when the power converter is connected to the power transmission system. The inrush current flows from the power transmission system side to the low-pass filter at the moment when the power converter and the power transmission system are connected, and gradually decreases as the control becomes stable.

[0005] Such an overcurrent applies stress to switching elements and filters, etc., leading to destruction and shortened life of the elements, and also causes noise to flow into the system side, so that a load connected to the system is imposed on the load. It has an adverse effect and is not preferred for safety. Further, the overcurrent will continue until the control is stabilized.

SUMMARY OF THE INVENTION It is an object of the present invention to reliably suppress an overcurrent at the time of interconnection between a power converter and a transmission system.

[0007]

In order to achieve the above object, the present invention provides a phase monitor for monitoring the relative phase between the output voltage of the power converter and the voltage of the power transmission system. The phase monitoring unit detects the zero-cross point of each voltage, and determines that the output voltage of the power conversion device and the voltage of the power transmission system are in phase because the zero-cross points overlap each other.
Further, the output voltage of the power converter and the voltage of the power transmission system are calculated, and if the calculation result is equal to or less than a predetermined threshold value, it is determined that both are in phase. On the other hand, the output voltage of the power converter and the voltage of the power transmission system are individually monitored by providing a transformer for detection.

As described above, the phase monitoring unit determines whether or not the phase of the output voltage of the power converter and the phase of the voltage of the power transmission system are the same, and can determine that the voltages are equal by the individually provided detection transformers. Therefore, overcurrent can be reliably suppressed during interconnection.

[0009]

FIG. 1 is a block diagram of a system interconnection operation according to the present invention. The solar power generation system is a solar cell 1
0, a diode 11 for preventing a reverse voltage from being applied to the solar cell, a power converter 12 for converting a DC voltage to an AC voltage
And a switch 15 for connecting and disconnecting the power transmission system 16 and the power converter 12 from each other, and a capacitor 22 for suppressing the pulsation of the DC voltage.

The power conversion control unit 21 controls the system interconnection operation of the power conversion device 12. Power conversion control unit 21
Are the maximum power follow-up controller 26, the power factor 1 controller 27, the PW
M signal generator 30, modulated wave generator 28, carrier wave generator 2
9, protection unit 31, start / stop unit 32, and phase monitoring unit 5
0.

The maximum power follow-up controller 26 controls the solar cell 10
Since the generated power greatly depends on the temperature and the amount of sunshine, the voltage Vdc of the solar cell 10 is read from the insulating amplifier 19, and the operation is performed at the voltage point at which the maximum output power is obtained at the present time.

When the solar cell 10 generates more power than is consumed by the load 17 at the interconnection point, the power factor 1 control unit 27 sells the power by causing the power to flow backward in the power transmission system 16. The reverse power flow reads the transmission system voltage Vac and the power converter output current Iac from the transformer 18 and the current transformer 14, respectively, and controls the current Iac to a power factor of 1 with respect to the transmission system voltage Vac. The current value of the reverse power flow is determined by the current command value Iac * of the maximum power tracking control unit 26.

The PWM signal is obtained by converting the modulated wave generated by the modulated wave generating unit 28 and the carrier generated by the carrier generating unit 29 by the voltage command value Vc * of the power factor 1 control unit 27 into PWM signals, respectively.
It is created by giving it to the signal generator 30. The PWM signal of the power converter 12 is a sine wave from which high-frequency components have been cut by the low-pass filter 13.

Further, the protection unit 31 shown in FIG. 1 constantly monitors the output current Iac of the power converter 12, the voltage Vac at the interconnection point, and the solar cell voltage Vdc, and monitors the overcurrent, over / under voltage, over / under frequency. When an abnormality such as an overvoltage of the solar cell occurs, a stop command signal 25 is immediately issued, the switch 15 is opened, the power transmission system 16 is separated from the power converter 12, and the power converter 12 is stopped. The method of stopping the power converter 12 is based on the pulse signal 2 generated by the PWM signal generator 30.
Since 3 and the gate signal 24 are ANDed and given to each arm, the gate signal 24 is invalidated and the switching operation of each arm of the power converter 12 is stopped.

The phase monitor 50 converts the output voltage of the power converter 12 and the voltage Vac of the power transmission system 16 into transformers 33 and 1.
8 and outputs a connection permission command 51 when both voltage waveforms have the same phase.

The start / stop unit 32 issues a start command 34 to the protection unit 31 after the output voltage of the power converter 12 and the voltage Vac of the power transmission system 16 are equal and the interconnection permission command 51 becomes effective. The power conversion device 12 is activated by enabling the gate signal 24. The power factor 1 control unit 27 operates the power converter 12 as a voltage source with the current command Iac * set to zero, reads the voltage Vac of the power transmission system 16 from the transformer 18, and outputs the output voltage of the power converter 12 and Vac. The voltage command value Vc * is adjusted to be equal. Start / stop unit 32
Reads the output voltage of the power converter 12 and the voltage Vac of the power transmission system 16 from the transformer 33 and the transformer 18, and connects to the protection unit 31 if the voltages become the same and the connection permission signal 51 becomes valid. A command 34 is issued, and the switch 15 is closed to interconnect.

As described above, according to the present invention, the power converter 12
Output voltage and the voltage Vac of the transmission system 16 are controlled by the start / stop unit 3
2 monitors the relative phase of both voltage waveforms.
0 is monitoring. Start / stop unit 32 and phase monitoring unit 50
When both of the conditions are satisfied, the interconnection can be performed at the same voltage and the same phase by interconnecting, so that the overcurrent can be surely suppressed.

FIG. 2A is an embodiment showing an internal block of the phase monitoring unit 50. As described above, the phase monitoring unit 50 outputs the output voltage of the power converter 12 and the voltage of the power transmission system 16.
Vac is read. For example, at the zero point of the voltage Vac of the power transmission system 16, a rising signal is generated at the point A by the zero point detection unit 100 as shown in (b). On the other hand, since the zero point detection unit 101 is the same as 100, the power conversion device 12
A rising signal is generated at the point B at the zero point of the output voltage. Further, in the logical operation unit 102, an output signal Y is obtained from the signals at the points A and B as shown in (c). That is, A
When the point and the point B become the same signal, the signal at the point Y is held at a low level. The time monitoring unit 103 outputs a connection permission command after confirming that the signal at the point Y has been kept at the low level for a predetermined time.

As described above, according to the present embodiment, the power converter 1
2 and the voltage Vac of the power transmission system 16 can be determined to be in phase.

FIG. 3 is another embodiment showing an internal block diagram of the phase monitoring unit 50. First, the operation unit 200 subtracts the output voltage of the power converter 12 and the voltage Vac of the power transmission system. Here, assuming that the output voltage of the power converter 12 is Vac ',

[0021]

Vac−Vac ′ = 2 · Cos (θ + φ) / 2 · Sin (θ−φ) / 2 (1) where θ is the angular frequency of Vac and φ is the angular frequency of Vac ′.

If there is no phase difference between Vac and Vac 'in equation (1) (θ = φ), it becomes zero. If there is a phase difference between Vac and Vac ', a sine wave output waveform appears in the arithmetic unit 200. The phase calculation unit 201 calculates the transmission system voltage Vac and the calculation unit 20
The phase difference of the output waveform of 0 is calculated, and the threshold value is
If the result of the operation is equal to or smaller than the threshold value A, the output is enabled. Further, the comparison unit 203 compares the peak value of the output waveform of the calculation unit 200 with the threshold value B, and when the calculation result is equal to or smaller than the threshold value B, enables the output. The outputs of the comparators 202 and 203 are logically ANDed 204, and an interconnection permission command is output only when the outputs of both comparison units are valid.

As described above, according to the present embodiment, if there is a phase difference between Vac and Vac ', a sine wave appears in the output of the arithmetic unit 200. A threshold value is provided for the phase difference between the output waveform and Vac, and the peak value of the output waveform is compared with Vac and Va.
Phase synchronization with c ′ can be reliably detected.

[0024]

According to the present invention, the power converter and the power transmission system are interconnected at the time of startup by checking the voltage and phase relationship between the output voltage waveform of the power converter and the voltage waveform of the power transmission system. The generation of overcurrent can be reliably suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a system interconnection operation according to the present invention.

FIG. 2 is a diagram showing an embodiment of a phase monitoring unit of the present invention.

FIG. 3 is a diagram showing another embodiment of the phase monitoring unit of the present invention.

[Explanation of symbols]

10 solar cell 11 reverse voltage prevention diode 12
Power converter, 13 ... filter, 14 ... current transformer for detection,
Reference numeral 15: switch, 16: power transmission system, 17: load at interconnection point, 18: detection transformer, 19: isolation amplifier, 20 and 35: logical product, 21: power conversion control unit, 22: capacitor, 23: PWM Signal, 24 gate signal, 25 stop command signal, 26 maximum power follow-up control unit, 27 power factor 1
Control unit, 28: modulated wave generation unit, 29: carrier wave generation unit, 3
0: PWM signal generation unit, 31: protection unit, 32: start / stop unit, 33: detection transformer, 50: phase monitoring unit, 51:
Interconnection permission signal, 100 and 101... Zero point detector, 1
02: logical operation unit, 103: time monitoring unit, 200: operation unit, 201: phase operation unit, 203 and 204: comparison unit.

Continued on the front page (72) Inventor Manabu Fujimoto 7-1-1 Higashi-Narashino, Narashino-shi, Chiba Industrial Machinery Group, Hitachi, Ltd. (72) Inventor Kunihiko Fuji 7-1-1, Higashi-Narashino, Narashino-shi, Chiba Co., Ltd. F-term in Hitachi Industrial Machinery Group (reference) BB16 CC03 DD03 EA10 EB09 EB16 EB39 FF03 FF04 FF11 FF25 FF26 LL04 LL10 NB04 NE15 5J039 JJ02 JJ07 KK10 MM11 5J055 AX59 AX64 AX66 BX12 BX40 CX07 CX09 DX61 FX10 FX12 FX19 FX21 FX31 FX31 FX31 GFX

Claims (1)

[Claims] 1. A power conversion device comprising: a solar cell; a power conversion device for converting DC power supplied from the solar cell into AC power; and a filter, a switch for connecting and disconnecting the power transmission system and the power conversion device, and a power conversion device and a power transmission device. Detects the output voltage of the power converter when the output voltage of the power converter and the voltage of the power transmission system are connected at the same voltage and in the same phase when starting the photovoltaic power generation system that supplies the required AC power to the load together with the grid. And a transformer for detecting a transmission system voltage, and issuing a start command signal when it is determined that the phases of the voltage waveforms are synchronized.