JP2005130589A - Inverter controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an inverter controller in which a voltage balance of respective capacitors connected in series is suppressed to a desired range even if there is not a special circuit, such as a resistor, etc., a device can be remarkably reduced in size, a loss at the resistor is eliminated, and energy-saving can be performed. <P>SOLUTION: The inverter controller includes a plurality of the capacitors 5 connected in series, a voltage across which is operated as a DC bus bar between a converter 4 for converting a three-phase AC into a DC and an inverter 8 for converting the DC into the AC, and a preliminarily charging circuit 10 for charging the respective capacitors by the same constant voltage before the inverter device is started. Thus, the preliminarily charging circuit can be operated even during the operation of the inverter device. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inverter control device.

  In a conventional inverter control device, when a DC voltage is applied to both ends of a capacitor series body, the shared voltage of each capacitor becomes unbalanced due to the deviation of the parallel resistance component inside the capacitor due to leakage current. Therefore, a voltage dividing resistor that is sufficiently smaller than the internal parallel resistance of the capacitor is connected in parallel to each capacitor to correct the deviation caused by the leakage current of the capacitor. In this case, since the loss at the resistor is large, a configuration by a combination of a transistor complementary connection body and a resistor has been proposed (for example, see Patent Document 1).

Japanese Patent Laid-Open No. 10-295081

In the conventional inverter control device, in the case of the configuration using the combination of the transistor complementary connection body and the resistor, the loss of resistance is small, but when the capacitance of the capacitor increases, it is necessary to select a smaller resistance value for the resistor. , Loss increases. At the same time, it is necessary to increase the rated current of the transistor. As a result, the apparatus becomes larger and the power supply capacity of the precharging circuit for precharging the capacitor before starting the inverter also increases, leading to an increase in the size and cost of the precharging circuit.
In addition, since a transistor is used, the failure rate is higher than that of only a resistor. For example, when one transistor is on-failed, the voltage across one capacitor is reduced by the parallel connection of two resistors. At this time, since the voltage at the connection point between the emitters of the transistors becomes higher than the voltage at the connection point between the bases of the transistors, this time, the other transistor continues to be turned on, and the two connected to the collector of the transistor Current always flows with both resistors, and loss occurs in the resistors and transistors. This is a problem because the resistance is large and the voltage balancing capability is insufficient. Although it is necessary to detect this abnormality, the number of circuits is further increased for this purpose, resulting in an increase in the size and cost of the equipment.
Usually, when the power supply voltage is AC400V system, two capacitors with a rated voltage of DC400V are connected in series and used as a DC bus. In this case, the PNP transistor constituting the transistor has a rated voltage of 400V As described above, since the rated current also increases depending on the capacitance of the capacitor, there are very few types of transistors that satisfy the rating, the availability is low, and it is difficult to realize at high cost.

  The present invention has been made to solve the above-described problems, and a first object is to bring the voltage balance of each capacitor connected in series within a desired range without a special circuit such as a resistor. It is possible to provide an inverter control device that can be suppressed, the device can be greatly reduced in size, loss in resistance can be eliminated, and energy can be saved.

  The inverter control device according to the present invention operates a voltage across a plurality of capacitors connected in series as a DC bus between a converter that converts three-phase AC to DC and an inverter that converts DC to AC. A precharge circuit for charging each capacitor with the same constant voltage before starting the inverter device is provided, and the precharge circuit is operated even during operation of the inverter device.

  The present invention operates a plurality of capacitors connected in series as a DC bus between a converter that converts three-phase AC to DC and an inverter that converts DC to AC. A pre-charge circuit that charges each capacitor with the same constant voltage is provided, and the pre-charge circuit is operated even during operation of the inverter device. The voltage balance of each capacitor can be suppressed to a desired range. As a result, the device can be greatly reduced in size and energy can be saved because there is no loss in resistance. Also, the power supply capacity of the precharging circuit can be reduced. In other words, if the power supply capacity is the same, fast charging is possible. Even if the battery is discharged, it can be quickly charged at high speed, the time until the inverter is started can be greatly shortened, and service deterioration can be prevented.

Embodiment 1 FIG.
FIG. 1 is an overall configuration diagram of an inverter control apparatus according to Embodiment 1 of the present invention.
In the figure, 1 is a three-phase AC power source, 2 is a power-on switch such as a no-fuse breaker, 3 is an electromagnetic contactor, 4 is a converter that converts three-phase AC into DC power, and a diode converter comprising a combination of a plurality of diodes Alternatively, it is a high power factor transistor converter formed by combining a plurality of diodes and transistors connected in parallel. Reference numeral 5 denotes a DC smoothing capacitor, which is composed of a series connection of a capacitor 6 and a capacitor 7 in order to eliminate the insufficient withstand voltage of the capacitor. 8 is an inverter that converts direct current to alternating current, and 9 is a motor. Reference numeral 10 denotes a precharging circuit for precharging the smoothing capacitor 5, which includes a first charging circuit 11 for charging the capacitor 6 and a second charging circuit 12 for charging the capacitor 7. As for the wiring of the pre-charging circuit 10, one wiring that connects the + line of the first charging circuit 11 and the + line of the capacitor 6, and one wiring that connects the − line of the second charging circuit 12 and the − line of the capacitor 7. And the -line of the first charging circuit 11 and the + line of the second charging circuit 12 are connected in common and connected to one intermediate portion of the series smoothing capacitor 5. A control circuit 13 controls the opening / closing of the magnetic contactor 3 based on a signal from the voltage detection circuit 14.
FIG. 2 is a block diagram showing an example of internal circuits of the preliminary charging circuit 10a, the first charging circuit 11a, and the second charging circuit 12a. The first charging circuit 11a and the second charging circuit 12a are composed of insulated DC / DC converters 16 and 17 using a switching power supply technology. A rectifier bridge 15 rectifies an AC power supply and supplies a DC voltage to the inputs of the DC / DC converters 16 and 17.
FIG. 3 is a block diagram showing another example of internal circuits of the preliminary charging circuit 10b, the first charging circuit 11b, and the second charging circuit 12b. The first charging circuit 11b and the second charging circuit 12b are composed of boosting commercial transformers 18, 19, rectifier bridges 20, 21, and charging current limiting resistors 22, 23.

Next, the operation of the present invention will be described. Here, the case where the three-phase AC power supply 1 is AC440V is considered. Capacitors 6 and 7 have a full-wave rectified voltage of the three-phase AC power supply AC440V of about DC620V, so that a margin is added to the half and a capacitor rated for DC400V is used. When the power-on switch 2 is operated and the control circuit 13 outputs an operation start command to the preliminary charging circuit 10, the preliminary charging circuit 10 starts operating the first charging circuit 11 and the second charging circuit 12 therein simultaneously. The capacitors 6 and 7 are charged to a desired voltage, respectively. According to the DC / DC converter system of FIG. 2, the voltage can be adjusted to an arbitrary voltage by setting the turn ratio and circuit constants of a switching transformer constituting a circuit (not shown). Here, it is assumed that both the first DC / DC converter 16 and the second DC / DC converter 17 are set to output DC 325V. Capacitors 6 and 7 increase in voltage until reaching DC 325 V on a charging curve determined by an output limiting function which is a protection function of the DC / DC converter. The voltage detection circuit 14 detects and checks the voltage across the series body of the capacitors 6 and 7, and when detecting that the voltage has risen to a voltage at which no inrush current flows even when the electromagnetic contactor 3 is turned on, for example, DC 620V, The magnetic contactor 3 is turned on so that the inverter can be started. The purpose of the preliminary charging is to suppress the inrush current when the electromagnetic contactor 3 is turned on. Originally, when the operation of the charging circuit is stopped after the electromagnetic contactor 3 is turned on, power is supplied to the inverter via the charging circuit. It is preferable from the viewpoint that the charging circuit can be prevented from being overloaded. However, in the present invention, the operation command of the precharging circuit is continuously output even after the electromagnetic contactor 3 is turned on. Thereby, during the operation of the inverter, the voltage sharing between the capacitors 6 and 7 becomes unbalanced due to the deviation of the capacitor internal parallel resistance component due to the leakage current of the capacitor, and the voltage across one capacitor, for example, the capacitor 6 is When the voltage is lower than DC 325 V, the capacitor 6 is instantaneously charged to DC 325 V by supplying power from the preliminary charging circuit 11. As a result, both the capacitors 6 and 7 are always secured at DC 325 V or more, and the capacitor exceeds the rated DC 400 V only when the bus voltage exceeds DC 725 V (= DC 325 V + DC 400 V). When the converter 4 is a diode converter, the normal bus voltage is about DC 620V and does not exceed DC 725V when the rectified voltage of the AC power supply voltage, for example, AC 440V is used. When the converter 4 is a transistor converter, it can be boosted to a desired bus voltage. However, if the bus voltage is controlled to DC 725 V or less, the capacitors 6 and 7 do not exceed the rated voltage of 400 V as described above.
In the case of a transistor converter, the bus voltage can always be controlled to be constant, for example, DC 700 V. Therefore, when the output of the preliminary charging circuit 10 is DC 650 V (= DC 325 V + DC 325 V), power is supplied from the preliminary charging circuit 10. Only when the voltage sharing between the capacitors 6 and 7 is unbalanced and one voltage falls below DC325V, power is not consumed unnecessarily. On the other hand, in the case of a diode converter, the bus voltage changes according to the AC power supply voltage. For example, when it is AC440V, it becomes about DC620V. Therefore, when the precharge circuit output is set to DC650V, the inverter is always connected from the precharge circuit. Electric power is supplied to. In FIG. 2, there is no particular problem by appropriately setting the output limiting function, but this is not very preferable from the viewpoint of energy saving.
In the case of a diode converter, after the electromagnetic contactor 3 is turned on, unnecessary power consumption of the precharge circuit is avoided by lowering the output voltage of the precharge circuit from the rectified voltage of the AC power supply voltage. be able to.
In the case of a diode converter, when the bus voltage changes according to the AC power supply voltage and the output of the precharge circuit is set higher than the rectification level of the AC power supply voltage to prevent inrush current, the precharge circuit is operated during the inverter operation. Therefore, power is always supplied to the inverter, and unnecessary power consumption occurs, which can be avoided.
As described above, by operating the precharge circuit 10 even after the electromagnetic contactor 3 is turned on, a special circuit such as a voltage balancing resistor is not necessary. Loss in resistance can be greatly reduced, and downsizing and low loss of equipment can be achieved. Also, for the precharge circuit 10, the load is reduced by the amount of resistance, and the precharge of the capacitor can be speeded up. As a result, when the inverter does not operate for a long time, if the inverter power supply is shut off and the standby mode is set, the time until the inverter starts becomes faster when the power is turned on again when necessary. Energy saving can be realized without causing service degradation.
In the above description, the method of FIG. 2 has been described as an example, but basically the same effect can be obtained in the case of FIG. The difference is that the DC / DC converter system of FIG. 2 can easily change the output voltage by changing circuit constants or electrical switching, whereas in the case of FIG. 3, the boost ratio of the commercial transformers 18 and 19 for boosting is different. It is charged with the rectified voltage determined by In FIG. 2, the output can always be kept constant even when the input voltage changes. In FIG. 3, if the input voltage changes, the output changes at the same ratio. Further, FIG. 2 has an output limiting function by the switching control circuit, or the output can be easily stopped, whereas in FIG. 3, only the current is limited by the limiting resistors 22 and 23, and the output is stopped. It is necessary to add a semiconductor switch to the AC side or the DC side. (For example, refer to JP 2001-261245 A)

Embodiment 2. FIG.
FIG. 4 is an all-off configuration diagram of the inverter control apparatus according to Embodiment 2 of the present invention.
In the figure, reference numerals 1 to 14 are the same as those in the first embodiment, but the output of the precharge circuit 10 is wired to the DC smoothing capacitor 5 comprising the series connection body of the capacitors 6 and 7. Two wires from the first charging circuit 11 and two wires from the second charging circuit are wired.

Next, the operation of the present invention will be described. The normal operation of the precharge circuit is not changed after the power-on switch 2 is operated, and the voltage balance function is the same as in the first embodiment. Here, the operation in the case where a failure of the precharging circuit 10, disconnection of wiring, or poor contact occurs will be described. In the wiring of the preliminary charging circuit in FIG. 1, the − line of the first charging circuit 11 and the + line of the second charging circuit 12 serve as a common line and are wired to the capacitor 5. Even if this occurs, the bus voltage detected by the voltage detection circuit 14 is apparently normal. Therefore, this abnormality cannot be detected even though the voltage balance function described in the first embodiment does not work. When the output of the first charging circuit 11 or the second charging circuit 12 is stopped, the voltage of the voltage detection circuit 14 does not rise to a predetermined value, so that the control circuit 13 can recognize an abnormality.
On the other hand, in the second embodiment shown in FIG. 4, the −line of the first charging circuit 11 and the + line of the second charging circuit 12 are wired independently to the capacitor 5. As long as the wirings are not disconnected at the same time or contact failure is not caused, the control circuit 13 can recognize the abnormality by the voltage check of the voltage detection circuit 14.
With the above configuration, since the inverter does not continue to operate without recognizing an abnormal state in which the voltage balance function does not operate, a highly reliable inverter device can be realized.
When the output line of the precharge circuit is disconnected for some reason, or when contact failure occurs, or when the precharge circuit itself breaks down and stops output, the voltage across the capacitors connected in series is checked. Therefore, an abnormality can be easily detected. Since the inverter does not continue to operate without a failure being recognized, a highly reliable inverter device can be realized.

1 is an overall configuration diagram of an inverter device according to a first embodiment of the present invention. It is a block diagram which shows an example of the precharging circuit of the inverter apparatus in Embodiment 1 of this invention. It is a block diagram which shows the other example of the precharging circuit of the inverter apparatus in Embodiment 1 of this invention. It is a whole block diagram of the inverter apparatus in Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Three-phase alternating current power supply 2 Power-on switch 3 Magnetic contactor 4 Converter 5 DC smoothing capacitor 6, 7 Capacitor 8 Inverter 9 Motor 10 Precharge circuit 11, 11a, 11b 1st charge circuit 12, 12a, 12b 2nd Charging circuit 13 Control circuit 14 Voltage detection circuit 15, 20, 21 Rectifier bridge 16, 17 Insulated DC / DC converter 18, 19 Booster commercial transformer 22, 23 Charging current limiting resistor

Claims (4)

  In an inverter device in which a voltage across a capacitor connected in series is operated as a DC bus between a converter that converts three-phase AC to DC and an inverter that converts DC to AC, before starting the inverter device, A control device for an inverter, comprising: a precharging circuit for charging the capacitor at a constant voltage; and operating the precharging circuit even during operation of the inverter device.   2. The inverter control device according to claim 1, wherein the output voltage of the precharging circuit is controlled to be equal to or lower than a rectified voltage level of the AC power supply voltage during operation of the inverter device.   The output line of the precharging circuit is wired by one + line and −line of each capacitor connected in series, and one common line of the −line and + line of each capacitor. The inverter control device according to Item 1.   2. The inverter control device according to claim 1, wherein two output lines of the precharging circuit are wired to each of the capacitors connected in series.

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