JP3263962B2 - DC braking system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC braking system for an inverter for driving an AC motor.

[0002]

2. Description of the Related Art Conventionally, as this type of inverter device,
There is a pulse amplitude modulation (PAM) inverter device. FIG. 3 shows a circuit configuration of this PAM system. In FIG. 3, 1 is a diode bridge for rectifying an AC power supply, 2 is an input side smoothing capacitor, 3 is a chopper switching element for converting a rectified DC voltage into a variable DC voltage _VCP , and 4 is a flywheel. Diode, 5
Is a smoothing reactor, and 6 is an output-side smoothing capacitor.
Reference numerals 7 to 12 denote switching elements, each of which constitutes an inverse conversion circuit 13 for converting a DC voltage into an AC voltage. Reference numeral 14 denotes a three-phase induction motor. To simplify the description, the switching elements 3 and 7 to 12 are represented by switch symbols. Reference numeral 15 denotes a DC voltage command generator at the time of normal operation, 16 denotes a DC voltage commander at the time of DC braking, the voltage command value is _VDB , and 17 is a switch for switching these voltage commands. Reference numeral 18 denotes a voltage control circuit that outputs a switching signal to the chopper switching element 3 so that the variable DC voltage V _CP is in accordance with the voltage command. In many cases, feedback control is performed so as not to be affected by fluctuations in the power supply voltage. It consists of a loop. Reference numeral 19 denotes a PAM frequency control circuit, which outputs a switching signal as shown in FIG. A conventional DC braking system of this inverter device will be described. When a stop command is input during the inverter operation and the inverter decelerates to a low frequency immediately before the stop, the voltage command to the voltage control circuit 18 is changed from the voltage command during normal operation to the DC braking voltage command value V _DB. Switch to. Further, the frequency of the PAM frequency control circuit 19 becomes zero, and the switching pattern of the inverse conversion circuit 13 remains in any one of the switching patterns 1 to 6 in FIG. For example, in the case of the switching pattern 2, the switching pattern shown in FIG. The DC braking current I _DB passes through the switch 7 and enters the U phase of the motor 14,
, And flows through switches 10 and 12. This DC current _IDB generates a braking torque in the motor, and the rotating motor can be stopped. The DC current I _DB is determined by the DC braking voltage V _DB and the DC resistance of the motor.

[0003]

However, the value V _DB of the voltage command 16 at the time of DC braking is about several volts to several tens of volts, which is considerably lower than the DC voltage at the time of normal operation. It is very difficult to accurately output this low voltage. As a result, the DC voltage fluctuated, and the braking torque did not become constant.

[0004]

According to the present invention, there is provided a chopper circuit for converting an AC power supply into a variable DC voltage, an inverse conversion circuit (13) comprising six switching elements, and a pulse converter. In an inverter device including a PAM frequency control means for outputting a control signal based on an amplitude modulation method and a PWM control means for outputting a control signal based on a pulse width modulation method to the inverse conversion circuit, the PAM frequency control is performed during normal operation. Means (19), and the PAM frequency control means (19) sends the PWM signal during DC braking.
A first switch (21) for switching to the control means (20) and transmitting the output of the PWM control means (20) to the inverse conversion circuit (13); and a voltage command generating means (15) for DC braking. Switching to voltage command generating means (16) for generating a DC voltage command, the voltage command generating means (1
A second switch (17) for outputting a voltage command output from 6) to a voltage control circuit (18) for outputting a switching signal for the chopper switching element (3) and a stop command for the inverter; After the motor is decelerated, the first switch (21) and the second switch (17) are simultaneously switched, and the reverse conversion circuit (13)
The DC braking method is characterized in that the DC braking voltage at the time of DC braking is set by the difference between the ON duties of the respective switching elements constituting the above.

[0005]

In the normal operation, the inverter operates in the PAM system, the output voltage is controlled by the chopper circuit, and the frequency is controlled by the PAM frequency control circuit. When a stop command is input to the inverter, the inverter decelerates. Immediately before the stop, a DC voltage command set at a higher level is input to the voltage control circuit, and the DC voltage is applied to the inverse conversion circuit. At the same time, the control signal to the inverse conversion circuit is connected to the PWM control circuit, and the inverse conversion circuit
To switch. The PWM duty is determined from the DC braking voltage output to the motor and the DC voltage V _CP .

[0006]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, reference numeral 20 denotes a PWM control circuit during DC braking, and reference numeral 21 denotes a switch for switching between the PAM frequency control circuit 19 and the PWM control circuit 20 during normal operation and during DC braking. I have. During normal operation,
Switches 17 and 21 are connected to a side. When a stop command is input to the inverter, the inverter decelerates, and immediately before the stop, the switches 17 and 21 are connected to the b side. Now, assuming that a DC voltage command of 100 volts is output from the voltage command generator 16 at the time of DC braking, the DC voltage between U and V of the inverter output terminal is 10 volts, and the DC voltage between U and W is Considering the case of 10 volts, the PWM control circuit outputs a control signal in which the on duty of the switches 9 and 11 is 10% shorter than the on duty of the switch 7. Switches 8, 10,
Numeral 12 outputs switching signals having phases opposite to those of the switches 7, 9, and 11, respectively. FIG. 2 shows a control signal of the switch 7 as a 55% ON signal and a 45% OFF signal.
As control signals for the switches 9 and 11, a signal example in which ON is 45% and OFF is 55% is shown. In the case of the embodiment, the DC braking voltage at the time of the DC braking is set to 100 volts DC and is set by the difference between the on duty of the switch 7 and the on duty of the switches 9 and 11, Can be set by making DC constant and changing the DC voltage.

[0007]

As described above, according to the present invention, the DC voltage can be accurately controlled by outputting the DC voltage to the motor at the time of the DC braking by the PWM method, so that the braking torque of the motor is stabilized. However, variation in the time until the motor stops reliably is reduced. Therefore, unlike the related art, it is not necessary to set the braking time longer in anticipation of variation, and the braking time can be reduced particularly in applications where the vehicle is frequently started and stopped.

[0008]

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of the present invention.

FIG. 2 is an example of an output signal from a PWM control circuit.

FIG. 3 is a conventional circuit configuration diagram.

FIG. 4 shows a frequency control circuit 19 for DC operation and DC braking.
Output signal

[Explanation of symbols]

 7-12 Switching element 13 Inverting circuit 15 Voltage command generator during normal operation 16 Voltage command generator during DC braking 18 Voltage control circuit 19 PAM frequency control circuit during normal operation 20 PWM control circuit

────────────────────────────────────────────────── ─── Continuing from the front page Examiner Ichiro Horikawa (56) References JP-A-58-12577 (JP, A) JP-A-61-247292 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) H02P 3/24 H02P 7/63 302

Claims (1)

(57) [Claims] 1. A chopper circuit for converting an AC power supply into a variable DC voltage, an inverse conversion circuit (13) composed of six switching elements, and a control signal output to the inverse conversion circuit by a pulse amplitude modulation method. An inverter device comprising a PAM frequency control means for performing a pulse width modulation method and a PWM control means for outputting a control signal to the inverse conversion circuit by a pulse width modulation method. At the time of DC braking, the PAM frequency control means (19)
Is switched to the PWM control means (20),
The output of the WM control means (20) is converted to the inverse conversion circuit (13)
A first switch (21) for transmitting a DC voltage command to a voltage command generating means (16) for generating a DC voltage command during DC braking;
A second switch (17) that outputs a voltage command output from the voltage command generating means (16) to a voltage control circuit (18) that outputs a switching signal for a chopper switching element (3); After the stop command is input and the motor is decelerated, the first switch (2
1) and the second switch (17) are switched at the same time , and each switching constituting the inverse conversion circuit (13) is performed.
DC braking voltage during DC braking due to the difference in element on duty
DC braking system, characterized in that you set the pressure.