JP3050976B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter that includes a power converter that operates in synchronization with a commercial power supply and supplies stable power to a load. The present invention relates to a power converter configured to be able to stably operate in synchronization and to quickly detect an abnormality and disconnect a commercial power supply from a power converter when an abnormality occurs.

[0002]

2. Description of the Related Art A power supply system using a power converter, particularly a new energy power generation system using a fuel cell, a solar cell, or the like as a power source, needs to be operated in synchronization with a commercial power supply. The capabilities of the synchronous control circuit and the abnormality detection circuit of the commercial power supply system directly affect the performance of the power supply system and the reliability of power supply to the load. FIG. 2 is a block diagram showing a control circuit of this type of conventional power converter.

[0003] 1 is a DC power supply such as a fuel cell, a solar cell, a battery, etc., 2 is a DC capacitor, 3 is an inverter for converting DC power from the DC power supply 1 into AC power, and 4 is an inverter 3 for a system of a commercial power supply 12. Interconnection reactor for interconnecting and shaping the output waveform, 5 is a transformer for transforming the AC voltage of the inverter 3 and insulating it from the AC system, 6 is a load, 7 is a connection between the commercial power supply 12 and the inverter 3 / Circuit breaker for disconnection.

On the other hand, the control device of the power converter is a voltage detector (instrument transformer) for detecting the voltage of the commercial power supply 12.
8, a synchronous control circuit 9A for following the phase and frequency of the commercial power supply 12, and an inverter control circuit 10 for operating the inverter 5 in synchronization with the commercial power supply 12.

The synchronous control circuit 9 is disclosed in Japanese Patent Publication No. 60-3771.
It is known as shown in Japanese Patent Publication No. 1 and is generally configured as follows. That is, a three-phase to two-phase conversion circuit 91 that separates a three-phase commercial power supply by a phase detector into orthogonal two-phase components, and converts them into a sine, which is the output of the synchronization control circuit 9A,
A phase difference calculation circuit 92 for calculating a phase difference from a cosine, a filter circuit 93 for performing a calculation such as a proportional integration with an output of the calculation circuit 92, and an oscillation circuit for outputting a pulse having a frequency proportional to the output of the filter circuit 93 It comprises a (VCO) 94, a frequency dividing circuit 95 for counting pulses, and a data table circuit 96 for outputting sine and cosine data stored in advance with the count value as a phase angle. Since the output count value of the frequency dividing circuit 95 in the synchronous control circuit 9A is the phase angle data of the commercial power supply 12, the inverter control circuit 1
0 is based on the phase data.

The inverter control circuit 10 operates in accordance with a command from the synchronization control circuit 9A, performs output voltage or output current control, and outputs a gate signal as a command to the inverter 3.

With this configuration, the inverter 3 can operate in synchronization with the commercial power supply 12. or,
To detect a frequency abnormality of the commercial power supply 12, a frequency detection relay 11 is provided at a stage subsequent to the voltage detector 8, and the output of the relay 11 operates the circuit breaker 7 to disconnect the inverter 3 from the commercial power supply 12. The inverter 3 can be supplied to the load 6 even when the commercial power supply 12 is abnormal by operating in an isolated manner.

[0008]

However, in the power converter having the configuration shown in FIG. 2, if there is an error in the synchronous control circuit 9A or the voltage detector 8, the output of the power converter has a lower harmonic. Will be mixed. This is because if there is an error in the voltage detector 8 and the synchronization control circuit 9A, the three-phase detection value of the voltage becomes unbalanced, and a ripple occurs in the output of the three-phase to two-phase conversion circuit 91 in the synchronization control circuit 9A. . That is, even if the average frequency value of the output of the synchronization control circuit 9A is constant, fluctuation occurs within one cycle, and low-order harmonics are generated. This tendency becomes more remarkable when the control gain of the synchronization control circuit 9A is increased in order to enhance the response.

If the power converter is connected to the system load 6 in this state, the lower-order harmonics adversely affect the system or the load. Accordingly, in order to suppress the fluctuation within one cycle, the filter circuit 9 in the synchronization control circuit 9A is used.
The time constant of 3 had to be increased.

Further, in the configuration shown in FIG. 2, when a system disturbance or a power failure occurs due to a ground fault or the like, the response of the synchronous control is slow, so that operation corresponding to the system state cannot be performed, and If the detection delay of the detection relay 11 is large, an emergency stop operation of the power conversion device may be caused, and the power supply to the load 6 may be interrupted, or the system may be adversely affected.

Therefore, the present invention detects a system disturbance or a power failure due to a ground fault or the like immediately, shuts off a commercial power supply, and continues operation without being affected by a change in a system state. An object is to provide a power conversion device that continuously supplies power to a load.

[0012]

According to the present invention, a DC power source such as a battery and the power of the DC power source are converted into AC power in order to achieve the above object. A first synchronization control circuit that follows the commercial power supply at a predetermined following speed and detects a frequency and a phase of the commercial power supply; a monitoring circuit for outputting the detected command the frequency abnormality of the commercial power at the output, the first
The function of synchronizing with the output of the first synchronization control circuit and the function of operating at a fixed frequency in advance in accordance with a command from the monitoring circuit, and the power converter A second synchronization control circuit serving as an operation reference, and switching means provided between the power converter and the commercial power supply for disconnecting the power converter from the commercial power supply when the commercial power supply is abnormal. It is a power conversion device.

[0013]

According to the present invention, when the commercial power supply is normal, the opening / closing means remains closed, so that the operation can be stably continued in synchronization with the system. If the commercial power supply is abnormal,
Since the opening / closing means is opened, the operation can be continued without being affected by the fluctuation of the system state, and the power can be continuously supplied to the load of the device.

The first synchronization control circuit always follows the commercial power supply as a synchronization reference, operates at the same frequency as the commercial power supply,
Outputs a signal synchronized with the phase of the commercial power supply. The first synchronization control circuit is designed with an emphasis on the speed following the synchronization reference, and can respond quickly to changes in the commercial power supply.

The second synchronization control circuit has a function of synchronizing with an output signal of the first synchronization circuit or of synchronizing with a preset reference cycle or frequency. Also, unlike the first synchronization control circuit, the second synchronization control circuit is designed with emphasis on output stability and does not emit low-order harmonics.

The switching of the synchronization reference of the second synchronization control circuit is performed by a commercial power supply monitoring circuit. The monitoring circuit is the first
Monitoring the output of the first synchronization control circuit, and if the output of the first synchronization control circuit is out of the determination reference range, the control reference of the second synchronization control circuit is changed from the output of the first synchronization control circuit to the internal A switching command is output to the reference cycle or frequency, and a disconnection command is output to an opening / closing unit that disconnects the power converter from the commercial power supply.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 1. Here, the same parts as those in FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. State.

The configuration of the first synchronization control circuit 9 of FIG. 1 is the same as that of the synchronization control circuit 9A of FIG. 2, but the filter time constant of the synchronization control circuit 9 used here is different from that of FIG. It is small enough and has good responsiveness and good tracking.

The second synchronization control circuit 13 includes a phase comparison circuit 131 comprising a counter for detecting a time difference (phase difference) between the output of the first synchronization control circuit 9 and the output of the second synchronization control circuit 13; An arithmetic circuit 132 for performing control arithmetic such as proportional integration using the output value of the phase comparison circuit 131;
For example, TI can set the frequency by the output value of 32
Oscillator circuit 133 composed of a rate multiplier circuit such as SN7497, frequency divider circuit 134 that divides the output of oscillator circuit 133 and outputs a fixed phase of synchronous control circuit 9, and TTL on the system side. An oscillator 135 having an internal reference frequency when the synchronization control to the first synchronization control circuit 9 is cut off.

The monitoring circuit 14 has a counter circuit 141 for counting the output period of the first synchronization control circuit 9, and monitors the count value to provide an abnormality detection circuit 142 for detecting a frequency abnormality of the commercial power supply 12 as soon as possible. have.
The control state of the second synchronization control circuit 13 is changed from the synchronization control to the output of the first synchronization control circuit 9 to the reference cycle or frequency inside the second synchronization control circuit 13 by the output of the monitoring circuit 14. And an open command signal is output to an opening / closing means such as the circuit breaker 7 for disconnecting the commercial power supply 12 and the power converter such as the inverter 3.

Next, the operation of the power converter device configured as described above will be described. In the circuit configuration of the present embodiment, due to the use of two synchronous control circuit 9 and 13, a first synchronization control circuit 9 to the power supply abnormality detection, control of the second synchronization control circuit 13 power conversion device to be selected response, stability individually.

First, the operation when the commercial power supply 12 is normal will be described. The first synchronization control circuit 9 outputs a signal synchronized with the commercial power supply. However, the filter time constant of the synchronous control circuit 9 used here is the synchronous control circuit 9A of FIG.
And the response and follow-up are good. Since the commercial power supply 12 is normal, the output of the first synchronization control circuit 9 is
When the value falls within the reference value, the monitoring circuit 14 outputs a command to select synchronization with the commercial power supply. Therefore, the second synchronization control circuit 13 synchronizes with the output of the first synchronization control circuit 9, and the inverter 3 continues to operate in synchronization with the commercial power supply 12.
In the second synchronization control circuit 13, the phase comparison circuit 131
And the arithmetic circuit 132 are configured to operate only once in one cycle, and have a synchronous circuit system that does not include low-order harmonics obtained by equally dividing one cycle. Therefore, low-order harmonics do not mix with the output of the power converter. Next, an operation when the commercial power supply 12 becomes abnormal will be described.

In order for the first synchronization control circuit 9 to reproduce the state of the commercial power supply with good responsiveness and follow-up, the monitoring circuit 14 for monitoring the output of the first synchronization control circuit 9 operates in response to the abnormal frequency of the commercial power supply 12. Detect quickly. According to this abnormality detection,
The monitoring circuit 14 outputs a switching command to the second synchronous control circuit 13 to operate independently with the oscillator in the own circuit and a disconnection command to the circuit breaker 5. Therefore, the second synchronization control circuit 13
Is smoothly switched to the fixed frequency held in its own circuit, and the circuit breaker 5 disconnects the inverter 3 from the commercial power supply 12.

Conversely, when the commercial power supply 12 recovers from the abnormality, the first synchronization control circuit 9 captures the state of the commercial power supply 12 and monitors the output of the first synchronization control circuit 9. I do. The monitoring circuit 14 detects that the frequency of the commercial power supply 12 has returned to normal. Therefore, the monitoring circuit 14
Outputs a switching command so that the second synchronization control circuit 13 synchronizes with the output of the first synchronization control circuit 9. Therefore, the second synchronization control circuit 13 switches the control so that the output of the first synchronization control circuit 9, that is, the commercial power supply 12 synchronizes. The monitoring circuit 14 outputs a closing command to the circuit breaker 5 after confirming that the inverter 3 is completely synchronized with the commercial power supply 12. In this way, the inverter 3 is connected to the commercial power source 1
It returns to the original state linked to 2.

As described above, according to this embodiment described above,
Even if an abnormality occurs in the commercial power supply 12, this is immediately detected, the inverter 3 including the load 6 is disconnected from the commercial power supply 12, and the operation is continued, so that the power is continuously supplied to the load 6 safely. When the commercial power supply 12 returns to the normal state, the state in which the power supply 12 is connected to the original state can be returned.

The present invention is not limited to the embodiment described above, but may be, for example, as follows. That is, the same effect can be obtained even if the control calculation after the phase comparison performed for each cycle and the setting of the oscillation circuit 133 including the rate multiplier are replaced with an analog filter having a large time constant and a voltage-controlled oscillation circuit (VCO). Can be

[0027]

According to the power converter of the present invention, even if a system disturbance due to a ground fault occurs, it is detected immediately and the power converter including the load is disconnected from the commercial power supply.
By continuing the operation, power can be safely supplied to the load.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a power conversion device according to the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a conventional power converter.

[Explanation of symbols]

1 DC power supply 2 DC capacitor 3 Inverter
4 ... interconnection reactor, 5 ... transformer, 6 ... load, 7 ... breaker, 8 ... voltage detector, 9 ... first synchronous control circuit, 91 ...
3-phase to 2-phase conversion circuit, 92: phase difference calculation circuit, 93: filter circuit, 94: oscillation circuit, 95: frequency dividing circuit, 96: data table circuit, 10: inverter control circuit, 11 ...
Frequency detection relay, 12 commercial power supply, 13 second synchronization circuit, 131 phase comparison circuit, 132 arithmetic circuit, 13
3 oscillation circuit, 134 frequency divider circuit, 14 monitoring circuit, 1
41: count circuit, 142: abnormality detection circuit.

Claims (1)

(57) [Claims] 1. A power conversion apparatus comprising : a DC power supply such as a battery; and a power converter that converts power of the DC power supply into AC power and operates in synchronization with a commercial power supply. A first synchronization control circuit that detects the frequency and phase of the commercial power supply, and detects an abnormality in the frequency of the commercial power supply based on the output of the first synchronization control circuit and outputs a command. A monitoring circuit and a tracking speed lower than the tracking speed of the first synchronization control circuit.
Thus, the function of synchronizing with the output of the first synchronization control circuit and the function of operating at a fixed frequency in advance can be switched in accordance with a command from the monitoring circuit, and the second synchronization control circuit serving as an operation reference of the power converter And a switching unit provided between the power converter and the commercial power supply, wherein the switching unit disconnects the power converter from the commercial power supply when the commercial power supply is abnormal.