JP3392939B2 - Voltage converter for 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 voltage control device of a power converter for load compensation of an example of a thyristor converter of an input power source of an inverter circuit for driving an induction motor.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a thyristor converter as an input current of a motor drive device using an inverter.
FIG. 3 shows the configuration of the main part of the conventional example and its control system.
1 is an AC power supply, 2 is a power converter, 3 is a reactor, 4 is a capacitor, 5 is an inverter circuit, and 6 is an induction motor (hereinafter simply referred to as an electric motor). 7 is a voltage detector,
Reference numeral 8 is a current detector, 9 is a voltage setting device, 10a and 10b are addition / subtraction devices, 11 is a voltage controller, 12 is a current controller, and 13 is a gate controller.

That is, in the power converter shown in FIG. 3, the power converter 2 converts the AC power supply 1 into a DC power supply,
It serves as a power supply for the inverter circuit 5. Further, when it is necessary to absorb the load side power, that is, the power of the inverter circuit 5, the power converter 2 has a function of converting the power from the load side and controlling the regenerated power thereof. The reactor 3 and the capacitor 4 play a role of providing a DC power source in which the pulsating current component of the output of the power converter 2 is smoothed. The inverter circuit 5 is
It converts direct current into a three-phase alternating current power source of variable voltage and variable frequency, and drives the electric motor 6.

The voltage detector 7 obtains an output voltage VDC for controlling the voltage supplied to the inverter circuit 5. IDC
Is the output current. Further, the current detector 8 is the power converter 2
The input current IAC of Now, the adder / subtractor 10a obtains the difference from the output voltage VDC with respect to the voltage set value by the voltage setter 9, the adder / subtractor 10a gives a control command for the voltage controller 11, and the voltage controller 11 gives a current control command. Is output. Here, the relationship between the input current IAC and the output current IDC of the power converter 2 is represented by the following equation.

[0005]     IAC = 0.816IDC (1)

The input current IA of the output of the current detector 8
In order to control C, the difference between the output of the voltage controller 11 and the current control command is obtained by the adder / subtractor 10b, and the output of this adder / subtractor 10b is given as the control command of the current controller 12, and therefore the gate controller 13 is activated. Through the gate control of a thyristor which is a semiconductor switch of the power converter 2, current control is performed. Also, there is a method of directly detecting the output current of the power converter 2 and controlling the output current, but it is equivalent as shown in the equation (1), and any of them may be used.

[0007]

However, in the case of this type, when a sudden driving / absorption load variation occurs in the electric motor 6, the smoothing circuit of the power converter 2, the reactor 3 and the capacitor 4 is used. Due to the delay of the control response, the DC voltage of the inverter circuit 5 changes greatly. FIG. 4 shows the behavior transition of the output current and the output voltage of the power converter, where IDC is the output current and VDC is the output voltage. That is, when the load of the electric motor 6 fluctuates to drive and absorb, the output current IDC of the power converter 2 fluctuates greatly, and the output voltage VDC also fluctuates greatly. Therefore, such a large voltage fluctuation may cause adverse effects such as fluctuation of the torque of the electric motor, damage to the drive element of the inverter circuit, and generation of overcurrent due to commutation failure during power regeneration.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and the load fluctuation of the motor appears in the magnitude of the input current of the inverter circuit in proportion to the magnitude thereof, that is, in the motor. A sudden change in load is directly taken as a sudden change in the input current of the inverter circuit.By detecting this current and correcting the current control command of the power converter via the disturbance observer, the input voltage of the inverter circuit It is configured to reduce fluctuation. Further, based on the same idea, the current of the smoothing capacitor also changes in accordance with a sudden change in the load of the electric motor, and the capacitor current is detected and similarly compensated.

[0009]

The operation of such a solution means will be described in detail in the following embodiments. Hereinafter, the present invention will be described in more detail with reference to the drawings.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment to which the present invention is applied, similar to FIG. 3, in which 14 is a current detector, 15 is a load compensator, and 10c is an adder / subtractor. In addition, here, the power converter 2
Is an example of a reversible regenerative system of a three-phase bridge using a thyristor switch, but a semiconductor switch using a transistor, an IGBT or the like may be used. The current detector 14 detects the DC power supply current of the inverter circuit 2, detects the output current IDC, and outputs a signal to the load compensator 15.
The output of the load compensator 15 is provided as one input of the adder / subtractor 10c, and the output of the voltage controller 11 is provided as the other input to the adder / subtractor 10c. Further, the output of the adder / subtractor 10c is provided to the adder / subtractor 10b.

From this, in the adder / subtractor 10a (VS-VD
C) is calculated and used as the input signal of the voltage controller 11, and the current command value IS1 is obtained. The current command value IS1 is corrected by the adder / subtractor 10c by the output of the load compensator 15 to obtain the current command value IS2. In the adder / subtractor 10b (IS2-I
AC) is calculated and a control command signal for the current controller 12 is obtained.

When the motor load fluctuates, the current of the DC power source of the inverter circuit fluctuates and the voltage fluctuates.
In order to reduce the fluctuation of the voltage, the voltage controller 11 is operated to control the output voltage VDC to be constant, but the point that the control response cannot follow the sudden change of the motor load can be solved as follows. . Here, the load compensator 15 has the following equation (2).
Alternatively, it is configured by the function represented by the equation (3).

[0013]     (1 + TD ・ s) / (1 + TI ・ s) ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (2)     (TD ・ s) / (1 + TI ・ s) ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (3)

That is, the denominator (1 + TI · s) of the function in the equations (2) and (3) is designed for the purpose of removing the disturbance input and the high frequency pulsation in the high frequency region on the control compensation, and The numerator (1 + TD · s) or the molecule (TD · s) is designed for the purpose of the primary phase advance control of current control. Here, the relationship between TD and TI is designed to be (TD> TI). In this way,
The fluctuation of the input current of the inverter circuit 2 is taken by the functional relation in the load compensator 15, and the compensation output is taken as the current controller 12
By adding the compensation to the control command, the control response to the load fluctuation in the voltage control can be improved and the voltage fluctuation can be reduced. If this is expressed as a behavior of the output current IDC and the output voltage VDC in a manner similar to FIG. 4, it becomes as shown in FIG.

Furthermore, this embodiment can operate as follows. Generally, the thyristor converter has a control function of the output current in the device itself. However, the reactor 3 and the capacitor 4 smooth the fluctuations in the load current, and it is difficult to control the rapid fluctuations in the load current. Here, by applying forward compensation in the function described above as a disturbance observer to the power supply control command of the power converter 2, the capacitor by the power converter responds to the input current of the inverter circuit, that is, the load change of the motor. It is possible to control so as to reduce the fluctuation of the voltage. Obviously, instead of the current detector 14, the current of the capacitor 4 can be obtained, and the same effect can be obtained.

[0016]

As described above, according to the present invention, it is possible to provide a simple device capable of significantly reducing the voltage fluctuation of the input power source of the inverter circuit, and to realize stable operation by the inverter circuit and the inverter due to overvoltage. Circuit damage can be prevented.

[Brief description of drawings]

FIG. 1 is a control block diagram showing a main part configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a behavior transition of a change in output current and output voltage of the power converter according to FIG.

FIG. 3 is a control block diagram showing a conventional example.

FIG. 4 is a diagram showing a behavior transition of fluctuations in output current and output voltage of the power converter according to FIG. 3.

[Explanation of symbols]

1 AC power supply 2 power converter 3 reactor 4 capacitors 5 Inverter circuit 6 induction motor (electric motor) 7 Voltage detector 8 Current detector 9 Voltage setting device 11 Voltage controller 12 Current controller 13 Gate controller 14 Current detector 15 load compensator

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 7/17 H02M 7/155 H02M 7/757 H02P 7/63

Claims (2)

(57) [Claims] 1. A direct current voltage control for a semiconductor power conversion device for converting an alternating current power source into a direct current and supplying power to a motor driving device through a smoothing circuit, or absorbing power from a motor load and returning the power to the alternating current power source. In a voltage control device of a power conversion device having a current control system in a minor loop, a signal corresponding to a DC output current is detected, and a disturbance equivalent to an inverse function of a transfer function leading to a current change at the time of a sudden load change of a motor is detected. A voltage control device for a power conversion device, comprising: a means for observing, and performing negative feedback to an input signal circuit of the current control system via the means. 2. The voltage control device for a power converter according to claim 1, wherein a signal corresponding to a capacitor current of the smoothing circuit is used instead of the DC output current.