JPH0767281B2 - Control device for PWM converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a control device for a PWM conversion device such as a motor variable speed.

(Prior Art) Conventionally, as a control method of a PWM converter, in order to reduce a ripple current due to a carrier wave, a DC power supply 16 is provided as shown in FIG.
, And the primary windings of the first transformer 4A connected to the first PWM converter 1A and the second winding of the second transformer 4B connected to the second PWM converter 1B are connected in series. With the configuration, the phases of the carrier waves CAR1 and CAR2 for PWM controlling the first PWM converter 1A and the second PWM converter 1B are shifted by 90 °. First
Output currents i ₁ , i ₂ of the PWM converter 1A and the second PWM converter 1B
Is detected by current detectors 5A and 5B respectively, and the average value Is compared with the current reference i ^* as a feedback amount. The difference is input to the current control circuit 8 and amplified, then added as a disturbance, and the voltage reference e ^* which is the sum thereof and the carrier wave CAR1 are compared by the comparator 9A, and the output thereof is the first PW.
ON / OFF control the transistor 2 of the M converter 1A. The disturbance here depends on the purpose of use of the PWM converter, but when the primary side of the transformers 4A and 4B is connected to the system, it is a control amount corresponding to the voltage. Similarly for the second PWM converter 1B, the carrier wave CAR2 and the voltage reference e ^* are compared by the comparator 9B, and the output is the second PWM converter 1B.
Control the B transistor 2. Since the primary side of transformers 4A and 4B are connected in series, transformers 4A and 4B, first and second
If the circuit constants of PWM converters 1A and 1B are equal,
The output currents i ₁ and i ₂ of the second PWM converters 1A and 1B are exactly the same, and the currents are balanced. However, in reality, the leakage impedance, the excitation impedance, the transformation ratio, the saturation characteristics of the iron core, the ON voltage of the transistor 2 and the diode 3 of the transformers 4A and 4B cannot be said to be completely equal, and the output current must be i ₁ and i _{2 make} a difference. Current control is the average value of the currents i ₁ and i ₂ . Is controlled so as to be equal to the reference value i ^* , the currents i ₁ and i as shown in FIG.
_{Even if 2} changes, the control for setting the respective currents to the reference value i ^* does not work, and current imbalance occurs.

(Problems to be Solved by the Invention) As described above, in the conventional technology, due to the difference in the circuit constant,
Current imbalance occurs, the capacitance of the transistor must be increased, and it also affects cooling.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a control device of a PWM conversion device for balancing current.

[Structure of the Invention] (Means for Solving Problems) In order to achieve the above object, the present invention, as shown in FIG. 1, controls the current of one PWM converter 1A of two PWM converters. In parallel with the conventional average value current control circuit 8, a control circuit 8B for controlling the individual current i ₁ with the current reference i ^* is provided, and the sum of the output and the conventional voltage reference e ^* is added. PWM
Transistor 2 is used as the voltage reference e ^* to control converter 1A.
ON / OFF control is performed.

(Operation) By adding the individual current control circuit 8B, even if the output currents i ₁ and i ₂ of the PWM converters 1A and 1B are unbalanced due to the difference in the circuit constants, the current i ₁ remains the reference current i. Controlled to become ^* . On the other hand, the output current i ₂ of the PWM converter 1B
Is Is controlled so as to, to be controlled so that i ₁ becomes the reference i ^*, equivalently i ₂ is also controlled to the reference i ^*. Therefore, both i ₁ and i ₂ are controlled to be equal to the reference i ^* .

(Embodiment) FIG. 1 shows a block diagram of the present invention. 1 to 9 are exactly the same as in FIG. The current control circuit 8B includes the first PWM converter 1A
Output current i ₁ is individually matched with the current reference value i ^*, and the difference is input, and the amplified output is added to the voltage reference e ^* of the conventional method. The first PWM with the sum voltage reference e ₁ ^*
Since the converter 1A is controlled, the current i ₁ is controlled so as to have the reference value i ^* even if the circuit constant is different or a disturbance element is added.

On the other hand, the second PWM converter 1B is Is controlled so that it becomes the reference current i ^* , but since i ₁ is controlled so that it becomes i ^* as described above, i ₂ also becomes i _2.
Controlled to become ^* .

[Advantages of the Invention] From the above, the currents i ₁ and i ₂ can be balanced and the capacitance of the transistor can be reduced even if there is a difference in circuit constant between parallel circuits or the influence of disturbance. The cooling of the device can also be averaged.

[Brief description of drawings]

FIG. 1 is a control block diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a control block diagram showing a conventional example, and FIG. 3 is a current waveform diagram for explaining the operation of the conventional example. 1A, 1B ... PWM converter, 2 ... Transistor, 3 ... Diode, 4A, 4B ... Transformer, 5A, 5B ... Current detector, 6 ...
... DC power supply, 7 ... Division circuit, 8A, 8B ... Current control circuit, 9A, 9B ... Comparator.

Claims (1)

[Claims] 1. A first and second transformer in which secondary windings are respectively connected to the AC output sides of first and second PWM converters, and the primary windings are connected in series to an AC system. In the PWM converter, the first and second current detectors for detecting the AC output currents of the first and second PWM converters, and the outputs of the first and second current detectors are applied. Means for calculating an average value, a first current control circuit to which the average value and the reference value of the AC output current of the first and second PWM converters are applied, and the first and second PWM conversions A second current control circuit to which the reference value of the AC output current of the power supply and the output of the first current detector are applied, and the outputs of the first and second current control circuits and the voltage of the AC system. Means for controlling the PWM of the first PWM converter by using the added value of the signals as a reference value of the output voltage of the first PWM converter, And a means for PWM-controlling the second PWM converter with the added value of the signal corresponding to the output of the flow control circuit and the voltage of the AC system as the reference value of the output voltage of the second PWM converter. Converter control device.