JPH09182450A - Overvoltage protecting circuit for inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to drive the switching element for the conduction of a resistor with a simple constitution by comparing the output of a differential amplifier and a reference value, and controlling the switching element. SOLUTION: When a PWM inverter 1 is operating at present under the power running state, a signal Sb remains zeroed and compared with a reference value Sc. Here, when the signal Sb is smaller than the reference value Sc, it is not necessary to operate a switching element 42 for conducting a regenerative current through a resistor 41. Next, when the PWM inverter 1 is operated under the regenerative state, the DC voltage VDC of a DC charging part 12 quickly rises up, and the output of a voltage detector 43' also rises up quickly. In the meantime, a signal Sa as the output of a first-order lag device 47 does not rise up quickly. Therefore, the difference is generated in the inputs of a differential amplifier 48, and the signal Sb is no longer zero. Therefore, when the signal Sb becomes larger than the reference value Sc, a driving signal Sd by a comparator 46' is given to the switching element 42, and the regenerative current is not conducted through the resistor 41.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention protects an inverter device from being overvoltage by regenerative power by energizing a resistor with the regenerative power generated when decelerating or stopping in driving an induction motor by the inverter device and performing heat conversion. The present invention relates to an overvoltage protection circuit for an inverter device.

[0002]

2. Description of the Related Art FIG. 3 is a view for explaining the prior art, 1 is a PWM inverter, 2 is an input power source, 3 is an induction motor (hereinafter simply referred to as an electric motor), and 4 is an overvoltage protection circuit. That is, this is an example in which the PWM inverter 1 obtains the input power source 2 and drives the electric motor 3, and has the function of protecting the inverter device from being overvoltage by regenerative power by providing the overvoltage protection circuit 4. . In the PWM inverter 1, 11 is a DC smoothing unit that smoothes the three-phase AC supplied to the inverter device into DC, 12 is a DC charging unit that charges the power smoothed by the DC smoothing unit 11, and 13 is optional. It is an AC power output unit that supplies the three-phase AC power to the electric motor 3.

In the overvoltage protection circuit 4, 41 is a resistor connected to the input side of the AC power output section 13 by a switching element 42 to consume regenerative power, and 43 is a voltage for detecting the voltage of the DC charging section 12. A detector, 44 is a voltage detector that detects the input power supply voltage of the PWM inverter 1, 45 is a reference value generator that gives a reference value proportional to the output of the voltage detector 44, and 46 is a comparator. In the overvoltage protection circuit 4, the comparator 46 compares the output of the reference value generator 45 with the output of the voltage detector 43, and when the voltage of the DC charging unit 12 is larger than the reference value, the switching element 42 causes the DC charging unit 12 to operate. Is used to flow the electric power of 1 to the resistor 2.

Generation of regenerative power will be described below. When attempting to decelerate or stop the driving of the electric motor 3 or when the electric motor 3 is rotated by a load machine, the electric motor 3 enters the power generation region, so that the flow of electric power is reversed and the kinetic energy becomes regenerative electric power. Flows into the inverter device side. At this time, the DC charging unit 12 is charged with electric power and its voltage rises. The voltage of the DC charging unit 12 is applied to each unit that constitutes the inverter device,
In particular, if the withstand voltage of the switching element used for the AC power output section 13, which is the inverter section, is exceeded, the switching element may be damaged, so the voltage of the DC charging section 12 needs to be accurately controlled. Therefore, there is a need for the overvoltage protection circuit 4 that consumes regenerative power.

The reference value generator 45 is provided for obtaining the output of the voltage detector 44 and controlling the operation level of the overvoltage protection circuit 4 in accordance with the level of the input power supply voltage.
If this generator is not provided, the operation level of the overvoltage protection circuit 4 is set to a constant value in advance. Since the operation level at that time is set in consideration of the fluctuation of the input power supply voltage, the voltage at which the overvoltage protection circuit 4 actually operates is set to about 120% of the rated voltage of the electric motor 3. During the regenerative operation in this situation, the electric motor is operated in the overexcited state, the control characteristics of the electric motor are deteriorated, and the voltage pulsation of the DC charging unit 12 is increased due to the operation of the overvoltage protection circuit. Since the control characteristic may be deteriorated, it is necessary to have a function of changing the operation level of the overvoltage protection circuit 4 according to the input power supply voltage.

[0006]

As described above, in the conventional technique, the overvoltage protection circuit of the inverter device needs to have a function of changing the operation level of the overvoltage protection circuit according to the fluctuation of the input power supply voltage. Therefore, a circuit for detecting the input power supply voltage of the inverter device is provided. Furthermore, if the input power supply voltage is detected in a single phase instead of in three phases, a contradiction may occur between the voltage of the DC charging unit and the output of the input power supply voltage detector. For example, if only the voltage of the phase detecting the input power supply voltage is reduced due to power source imbalance or the like, the detection level is evaluated to be lower than the voltage of the DC charging unit of the inverter device. In this case, the overvoltage protection circuit performs overvoltage protection operation even when the inverter device is not in regenerative operation, and the resistor that consumes regenerative power is constantly energized to cause overheating of the resistor. Become.

Therefore, an object of the present invention is to provide an overvoltage of an inverter device capable of driving a switching element driven by a resistor with a simple structure without providing an input power supply voltage detector and an output side reference value generator thereof. The point is to provide a protection circuit.

[0008]

The present invention has been made in view of the above points, and is as follows. (B) A resistor that consumes the power regenerated in the DC charging section of the inverter device and a switching element that energizes the resistor with regenerative power are connected in series, and this series circuit is connected in parallel to the DC charging section. To configure. (B) The switching element that controls the period during which the regenerative power is supplied is the signal output obtained by the first-order delay calculation and the voltage detector that inputs the output of the voltage detector that detects the voltage of the DC charging unit to the first-order delay device. Input the output of and to the differential amplifier,
The comparator compares the output of the differential amplifier with a preset reference value, and operates by the output signal of the comparator.

With such a solution, it is not necessary to detect the input power supply voltage and set the comparison reference value, and the input power supply voltage detector and the output side reference value generator thereof are unnecessary. This is composed of a path for directly inputting the voltage detector output of the DC charging unit and a differential amplifier for inputting the voltage signal of the DC charging unit that has once become a primary delay signal via the primary delay device. The difference between the output signal and the first-order lag signal does not occur because the electric power is supplied from the inverter device to the electric motor side in the steady state, that is, when the load or the like is being driven. However, when the electric motor is decelerated or stopped, or when it is rotated by the load machine, the electric motor enters a regenerative state, regenerative electric power flows from the electric motor side into the inverter device, and a difference occurs between the two signals. In this case, the voltage rises only on the side where the voltage detection value of the DC charging unit is directly input. Further, a signal for controlling the switching element is obtained by comparing the difference with a reference value set in advance by the comparator. Therefore, the switching element is driven by the obtained signal, and regenerative power is supplied to the resistor to be consumed as heat.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A concrete embodiment is constructed as follows. That is, it comprises a voltage detector that detects the voltage of the DC charging unit, a first-order delay device that calculates the first-order delay of the voltage detector output, and a differential amplifier that receives the voltage detector output and the first-order delay device output. In addition, the input signal of the comparator is configured to compare the output of the differential amplifier with a preset reference value, and a switching element connected in series with the resistor that consumes regenerative power using the output of the comparator is connected. It comes to control. Further, the present invention will be described in detail with reference to the accompanying drawings.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the construction of the essential part of an embodiment of the present invention in a manner similar to FIG. 3, in which 4'is an overvoltage protection circuit. In the overvoltage protection circuit 4 ', 43' is a voltage detector, 46 'is a comparator, 47 is a first-order delay device, 48 is a differential amplifier,
49 is a setting standard. That is, in particular, the first-order delay device 47
Is a voltage detector 4 for detecting the DC voltage VDC of the DC charging unit 12.
First-order delay calculation of the detected value by 3'is performed. Differential amplifier 48
Generates a signal Sb with the signal Sa of the voltage detector 43 'output and the output of the primary delay device 47 as an input, and the setting reference device 49 generates a reference value Sc set in advance, and the comparator 46'.
Are configured to be supplied with these signals Sb and the reference value Sc.

Now, when the PWM inverter 1 is operated in the power running state, there is no difference between the inputs of the differential amplifiers 48, so the signal Sb remains zero and the reference value Sc.
Is compared to Here, if the signal Sb is smaller than the reference value Sc, it is not necessary to operate the switching element 42 for supplying the regenerative power to the resistor 41, and the comparator 46 ′ outputs the drive signal Sd for the switching element 42. Is not output. Next, when the PWM inverter 1 is operated in the regenerative state, the DC voltage VDC of the DC charging unit 12 suddenly rises. Therefore, the output of the voltage detector 43 'also rises sharply. On the other hand, the signal Sa of the output of the first-order lag device 47 does not rise sharply with respect to the output of the voltage detector 43 ', and is maintained at a substantially constant value. Therefore, a difference occurs at the input of the differential amplifier 48, and the signal Sb is not zero. Therefore, when the signal Sb becomes large as compared with the reference value Sc, the drive signal S by the comparator 46 ′ is
d is given to the switching element 42, and regenerative power is supplied to the resistor 41 and consumed. This is shown as in FIG.

FIG. 2 shows the operation signal levels of the respective parts in FIG. 1, and shows how the PWM inverter 1 is operated in the regenerative state. In FIG. 2, from time T0 to P
The WM inverter 1 is in the regenerative state, and the DC voltage VDC of the DC charging unit 12 is rising. At this time, since the signal Sa of the output of the first-order delay device 47 has a substantially constant value, the signal Sb of the output of the differential amplifier 48 rises in accordance with the detected value of the DC voltage VDC, and the setting reference device preset at time T1. It becomes larger than the reference value Sc of 49 outputs. Here, the comparator 46 'outputs the drive signal Sd for the switching element 42. Therefore, during the period (T1 -T2) during which the regenerative power is supplied to the resistor 41, the DC voltage VDC does not increase and power is consumed on the contrary, and thus decreases toward the voltage value in the powering state. At time T2, the DC voltage VDC becomes a certain value or less, the output of the comparator 46 'is automatically stopped, and the switching element 42 stops energizing the resistor 41. In the comparator 46 ', the hysteresis voltage is provided at the operating level and the level at which the operation is stopped. This is because the operation cycle of the switching element 42 is limited. Next, at the time T2, if the PWM inverter 1 is in the regenerative state, the DC voltage V
DC rises, and the operation in the period (T1-T2) is repeated in the periods (T3-T4), (T5-T6), and (T7-T8). After time T8, the direct-current voltage VDC of the direct-current charging unit 12 at the time of shifting from the regenerative state to the power running state is naturally reduced to the normal operation level.

[0014]

As described above in detail, according to the present invention, a circuit and an input power source for generating a reference value for comparison with a voltage detection value of a DC charging unit of an inverter device in proportion to an input power source voltage. It is possible to provide a device having a simple structure in which the voltage detector is removed, the trouble due to the circuit failure is reduced, the wiring work error is reduced, and the like, and the reliability of the protection operation is improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram showing operating signal levels of respective parts of FIG.

FIG. 3 is a circuit diagram shown for explaining the prior art.

[Explanation of symbols]

 1 PWM inverter 11 DC smoothing unit 12 DC charging unit 13 AC power output unit 2 Input power supply 3 Induction motor (motor) 4 Overvoltage protection circuit 4'Overvoltage protection circuit 41 Resistor 42 Switching element 43 Voltage detector 43 'Voltage detection 44 Voltage detector 45 Reference value generator 46 Comparator 46 'Comparator 47 First-order lag device 48 Differential amplifier 49 Setting reference device

Claims (1)

[Claims] 1. An overvoltage protection circuit for an inverter device, wherein a regenerative power is supplied to a resistor connected in parallel to a DC charging unit by using a switching element to protect the inverter device from overvoltage due to the regenerative power. A voltage detector that detects the voltage of the charging unit, a first-order delay device that calculates the first-order delay of the voltage detector output, and a differential amplifier that receives the voltage detector output and the first-order delay device output are provided. An inverter characterized in that an input signal of a comparator is configured to compare the output of the differential amplifier with a preset reference value, and the switching element is controlled using the output of the comparator. Device overvoltage protection circuit.