JP4379959B2 - Grid interconnection inverter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a grid-connected inverter that converts DC power of a solar cell, a fuel cell, or the like into commercial frequency AC and links it to a power system.
[0002]
[Prior art]
FIG. 4 is a connection diagram showing a configuration of a grid-connected inverter that has been conventionally used. The grid-connected inverter includes a DC power supply 1, a boost converter 2, an intermediate stage capacitor 3, half-bridge inverters 4 and 5, a current limiting coil 6 that removes high-frequency ripple from the output, and an output capacitor 7. ing. As the DC power source 1, a solar cell or a fuel cell is used.
[0003]
With the above configuration, the output of the DC power source 1 is converted to a high frequency high voltage by the boost converter 2, and converted to a commercial frequency sine wave AC by the four switching elements formed by the half bridge inverters 4 and 5. The current is output to the system 10 via the current limiting coil 6 and the output capacitor 7.
[0004]
[Problems to be solved by the invention]
The grid-connected inverter having the conventional configuration has a problem that it is difficult to supply a sine wave voltage having a commercial frequency when the power supply of the grid is interrupted.
[0005]
That is, the grid-connected inverter having the conventional configuration detects the current flowing through the current limiting coil 6 by the current detecting means 12 and compares the waveform of this current with the sine wave signal generated by the sine wave generating means 13. Four switching elements are driven so as to correct the difference. At the time of a power failure, since the current flowing through the current limiting coil 6 varies greatly depending on the type of load connected at the time of the power failure, it is difficult to execute control for correcting the difference from the sine wave signal. .
[0006]
[Means for Solving the Problems]
The present invention bridges a DC power supply, a boost converter that boosts the output of the DC power supply, an intermediate stage capacitor that removes a high-frequency component contained in a voltage boosted by the boost converter, and a plurality of switching elements An inverter connected to the boost converter via the intermediate stage capacitor, a reactor and an output capacitor for removing high frequency components from the output of the inverter, and a commercial frequency with high frequency components removed by the reactor and output capacitors. A system relay that outputs alternating current to the system, a power failure detection means that detects the presence or absence of a power failure in the system, a current detection means that detects a current flowing through the reactor and outputs a signal, and the reactor and the output capacitor generate high-frequency components. A constant obtained by integrating the output voltage of the inverter before being removed Output voltage detection means for outputting a voltage signal having a ripple, sine wave generation means for generating a signal indicating a sine wave waveform, and either the output voltage detection means or the current detection means and the sine wave generation A comparator for driving the plurality of switching elements by hysteresis control from the signal of the means, and when the power failure detection means does not detect a power failure and the system is in a normal state, the comparator The plurality of switching elements are driven by hysteresis control from the signal and the signal of the current detection means. After the power failure detection means detects a power failure of the system, the comparator outputs the signal of the sine wave generation means and the output. by driving with hysteretic control the plurality of switching elements and a signal of the voltage detecting means, an accurate positive even during autonomous operation And a system interconnection inverter capable of supplying a voltage of the wave.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The invention described in claim 1 includes a DC power supply, a boost converter that boosts the output of the DC power supply, an intermediate-stage capacitor that removes a high-frequency component contained in a voltage boosted by the boost converter, and a plurality of capacitors Inverter connected to the boost converter via the intermediate stage capacitor by switching connection, a reactor and an output capacitor for removing a high frequency component from the output of the inverter, and a high frequency component removed by the reactor and the output capacitor System relay for outputting the commercial frequency alternating current to the system, power failure detection means for detecting the presence or absence of power failure of the system, current detection means for detecting the current flowing through the reactor and outputting a signal, the reactor and the output Integrate the output voltage of the inverter before high frequency components are removed by the capacitor. Output voltage detection means for outputting the obtained voltage signal having a constant ripple, sine wave generation means for generating a signal showing a sine wave waveform, and either one of the output voltage detection means or the current detection means And a comparator that drives the plurality of switching elements by hysteresis control from the signal of the sine wave generating means, and when the power failure detection means has not detected a power failure and the system is in a normal state, the comparator The plurality of switching elements are driven by hysteresis control from the signal of the sine wave generation means and the signal of the current detection means. After the power failure detection means detects a power failure of the system, the comparator detects the sine wave generation means. from the signal of the signal of the output voltage detecting means to drive said plurality of switching elements in the hysteresis control, self luck And a system interconnection inverter capable of supplying a voltage of the correct sine wave even when.
[0008]
【Example】
Example 1
The first embodiment of the present invention will be described below. FIG. 1 is a circuit diagram showing the configuration of this embodiment. The grid-connected inverter of the present embodiment uses a DC power source 1 constituted by a solar cell or a fuel cell as an input, converts the power supplied from the DC power source 1 into commercial frequency AC, and is a self-sustained relay. 8 or the system relay 9 via the system relay 9.
[0009]
A boost converter 2 connected to the DC power source 1 boosts the voltage supplied from the DC power source 1 to a voltage higher than the voltage of the system 10 at a high frequency. The intermediate stage capacitor 3 connected to the boost converter 2 uses a capacitor having a capacity of about several hundred μF or less, and acts to remove high frequency components contained in the boosted voltage. The half bridge inverter 4 constituted by two switching elements Q1 and Q2 acts to step down this voltage in a region where the input voltage input from the intermediate stage capacitor 3 is lower than the voltage of the system 10. To do. The half bridge inverter 5 constituted by the two switching elements Q3 and Q4 acts to switch the polarity of the output voltage output from the half bridge inverter 4 between positive and negative. The current-limiting coil 6 is generally called a reactor, and works together with the output capacitor 7 to remove high-frequency ripple from the voltage output by the half-bridge inverters 4 and 5.
[0010]
The four switching elements Q1, Q2, Q3, and Q4 are controlled by a comparator 14. The comparator 14 has a reference value obtained by providing a hysteresis width of a predetermined magnitude to the sine wave signal generated by the sine wave generating means 13, and the reference value and the output current flowing through the current limiting coil 6 are calculated. By comparing the detected signal of the current detection means 12 with one of the output voltage detection means signals for detecting the output voltages of the four switching elements Q1, Q2, Q3, and Q4, four switching elements Q1, Q2, Q3, and Q4 are controlled.
[0011]
The output voltage detecting means includes a second voltage dividing circuit 17 connected to a connection point between the emitter and collector of one arm Q1, Q2 forming four switching elements Q1, Q2, Q3, Q4, and the other The first voltage dividing circuit 16, the subtracting circuit 18, and the integrating circuit 19 are connected to the connection point between the emitters and collectors of the arms Q3 and Q4. The first voltage dividing circuit 16 is constituted by a resistor R1 and a resistor R2, and the second voltage dividing circuit 17 is constituted by a resistor R3 and a resistor R4. The subtracting circuit 18 includes an operational amplifier 18a, a negative input resistor 18b, a positive input resistor 18c, and a feedback resistor 18d. The integrating circuit 19 includes a capacitor 19a and a resistor 19b.
[0012]
Hereinafter, the operation of the grid interconnection inverter of the present embodiment will be described. The voltage of the intermediate stage capacitor 3 must be at least several tens of volts higher than the voltage of the system 10 in order to inject power into the system 10. Therefore, the comparator 14 that controls the four switching elements Q1, Q2, Q3, and Q4 performs the control as shown in FIG. 2 and 3 show driving waveforms for driving the four switching elements Q1, Q2, Q3, and Q4 at each instant. FIG. 2 shows characteristics during normal operation and FIG. 3 shows characteristics during power failure. Show.
[0013]
When the system is in a normal state, that is, when the power is not interrupted, an operation at the time of system interconnection is called. At the time of grid connection, the grid relay 9 is on and the independent relay 8 is off. Therefore, for example, if the input voltage is DC 200V and the system 10 voltage is AC 200V, the switching elements Q1, Q2, Q3, and Q4 constituting the half-bridge inverter 4 and the half-bridge inverter 5 are input with the absolute value of the system voltage. During a period longer than the voltage (4 to 5 ms), the commercial frequency polarity switching operation is performed. By this polarity switching operation, the output current flowing through the current limiting coil 6 is a sine wave. That is, the comparator 14 controls the switching elements QB and QF of the boost converter 2 so that the output current becomes a sine wave. Further, during the period in which the input voltage is equal to or greater than the absolute value of the system voltage, the drive of the boost converter 2 is stopped, and the switching elements Q1 and Q2 constituting the half bridge inverter 4 are switched at a high frequency, thereby Is controlled so that the low frequency component of the current flowing through the sine becomes a sine wave. When Q4 is on and Q1 is on and Q2 is off, the current-limiting coil 6 has a voltage VM-VO obtained by subtracting the voltage VO at both ends of the output capacitor 7 from the voltage VM at both ends of the intermediate capacitor 3. Is applied. For this reason, when Q4 is on, the current flowing through the current limiting coil 6 increases. Further, when Q1 is off and Q2 is on, -VO is applied, so the current flowing through the current limiting coil 6 decreases.
[0014]
The current detection means 12 detects the current flowing through the current limiting coil 6 and transmits it to the comparator 14. The comparator 14 compares this current signal with the command value of the sine wave signal having the upper limit and the lower limit output by the sine wave generating means 13, and the current flowing in the current limiting coil 6 is the upper limit of the command value. When Q1 is exceeded, Q1 is turned off and Q2 is turned on, and when below the lower limit, Q1 is turned on and Q2 is turned off. This control is performed at high speed. As a result, the switching elements Q1 and Q2 are repeatedly turned on and off at a high frequency.
[0015]
When a power failure occurs in the system, the power failure detection means 11 detects that there is a power failure. At this time, the comparator 14 performs a self-sustained operation. That is, when the comparator 14 detects a power failure with the signal from the power failure detection means 11, the signal input to the comparator 14 is switched from the signal of the current detection means 12 to the output voltage Vio of the half bridge inverter 4 and the half bridge inverter 5. At the time of a power failure, the system relay 9 is turned off and the independent relay 8 is turned on, and the outputs of the half bridge inverter 4 and the half bridge inverter 5 are output via the independent relay 8. At this time, the output of the half bridge inverter 4 is divided by the first voltage dividing circuit 16, and the output of the half bridge inverter 5 is divided by the second voltage dividing circuit 17. This divided signal is transmitted to the subtracting circuit 18. The operational amplifier 18a detects a Vio signal using the minus side terminal as a reference potential based on the signal transmitted from the subtracting circuit 18. For example, when Q1 is on and Q2 is off with Q4 on polarity, the pulse train is Vio = input voltage, and when Q1 is off and Q2 is on, Vio = 0. Further, this Vio signal is converted into a voltage signal having a constant ripple by an integrating circuit 19 comprising a resistor 19b and a capacitor 19a. A signal indicating the output voltage Vio of the inverter detected by the voltage detection means is compared with a sine wave-like command value having an upper limit and a lower limit output from the sine wave generation means 13 by the comparator 14. The comparator 14 performs control so that Q1 is turned off and Q2 is turned on when the integral value of the output voltage Vio of the inverter exceeds the upper limit of the command value. When the value falls below the lower limit, control is performed so that Q1 is turned on and Q2 is turned off. For this reason, the outputs of the half-bridge inverter 4 and the half-bridge inverter 5 output a sinusoidal voltage as in the case where the system is in a normal state.
[0016]
As described above, according to the present embodiment, the current flowing through the current limiting coil 6 is compared with the sinusoidal command value having the upper limit and the lower limit, and the on / off of the switching elements Q1, Q2, Q3, Q4 is determined. Thus, when the system 10 fails, the inverter output voltage is detected as an integral value instead of the current flowing through the current limiting coil 6, and this is compared with a sinusoidal command value having an upper limit and a lower limit as in the case of the grid connection. The switching elements Q1, Q2, Q3, and Q4 are determined to be turned on / off, so that most of the control circuit can be shared with the conventional control circuit, and an accurate sine wave voltage can be obtained even in independent operation with an inexpensive configuration. This is to realize a grid-connected inverter that can be supplied.
[0017]
In this embodiment, the inverter is configured to switch the output of the half-bridge inverter that performs high-frequency switching at the commercial frequency. However, it goes without saying that the same applies to a configuration in which all four stones perform high-frequency switching.
[0018]
【The invention's effect】
According to the present invention, a grid-connected inverter capable of supplying an accurate sine wave voltage even during independent operation is realized.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing the configuration of a grid interconnection inverter according to a first embodiment of the present invention. FIG. 2 is a waveform diagram showing the operation of each part during grid interconnection. FIG. Fig. 4 is a waveform diagram showing the operation of each part of the circuit. Fig. 4 is a circuit diagram showing the configuration of a conventional grid-connected inverter.
DESCRIPTION OF SYMBOLS 1 Input power supply 2 Boost converter 3 Intermediate stage capacitor 4 Half bridge inverter 5 Half bridge inverter 6 Current limiting coil 7 Output capacitor 8 Self-supporting relay 9 System relay 10 System 11 Power failure detection means 12 Current detection means 13 Sine wave generation means 14 Comparator 15 detection Signal switching means 16 First voltage dividing circuit 17 Second voltage dividing circuit 18 Subtracting circuit 19 Integrating circuit

Claims (1)

A DC power supply, a boost converter for boosting the output of the DC power source, an intermediate stage capacitor for removing high frequency components contained in the boosted voltage by the boost converter, the result with a plurality of switching elements bridge-connected An inverter connected to the step-up converter via an intermediate stage capacitor, a reactor and an output capacitor for removing high frequency components from the output of the inverter , and a commercial frequency alternating current from which high frequency components have been removed by the reactor and output capacitor Before the high frequency component is removed by the system relay to output , the power failure detection means for detecting the presence or absence of power failure of the system, the current detection means for detecting the current flowing through the reactor and outputting a signal, and the reactor and the output capacitor certain ripple obtained by integrating the output voltage of the inverter One output voltage detecting means for outputting a voltage signal, a sine wave generating means for generating a signal indicative of the sine waveform, either signal of the output voltage detecting means or said current detecting means and the sinusoidal wave generating means And a comparator that drives the plurality of switching elements by hysteresis control from the signal, and when the power failure detection means has not detected a power failure and the system is in a normal state, the comparator and the signal of the sine wave generation means The plurality of switching elements are driven by hysteresis control from the signal of the current detection means. After the power failure detection means detects a power failure of the system, the comparator detects the signal of the sine wave generation means and the output voltage detection. A grid-connected inverter that drives the plurality of switching elements by hysteresis control based on means signals .