JPH05227793A - Heating value regulating method for converter main circuit element - Google Patents

Abstract

PURPOSE:To suppress magnetic noise while suppressing the heating value of converter main circuit subjected to PWM control. CONSTITUTION:When a motor 3 is driven through a PWM control circuit 2 based on comparison results between 6 carrier signal fed from a carrier generator 1 and a control signal, magnetic noise decreases as the frequency of carrier signal increases but heating value of a switching element 21 in converter main circuit increases. In the invention, the converter is normally operated while selecting the frequency of carrier signal such that the heating value of the switching element 21 does not exceed an allowable value although some level of magnetic noise is allowed and when an overload detector 4 detects an overload state, the converter is operated while lowering the frequency of carrier signal thus satisfying both suppression of heating value and reduction of magnetic noise simultaneously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting the heat generation amount of a converter main circuit element when a motor is driven through the converter, and more particularly to the heat generation of a pulse width modulation (PWM) controlled converter main circuit element. Regarding the quantity adjustment method.

[0002]

2. Description of the Related Art In the case of controlling a motor by PWM control, the higher the switching carrier frequency (hereinafter, also simply referred to as the carrier frequency), which is a cycle for turning on and off the switching element of the main circuit, the loss of the switching element. It is known that the amount of heat generation increases and the amount of heat generation increases.
However, there is no one that adjusts the heat generation amount of the converter main circuit element so far, but by lowering the thermal resistance of the cooling body that cools the switching element (this means that the cooling body becomes large and the cost is low). It leads to up), so that the switching element is kept within the rated specifications. Specifically, the junction temperature of the switching element is kept within a predetermined value. On the other hand, when controlling the motor by PWM control, since a pulsed voltage having a carrier frequency is applied to the motor, the current flowing through the motor contains harmonic components,
This causes the motor to generate magnetic noise. by the way,
It has been pointed out that the carrier frequency may be increased to reduce the magnetic noise.

[0003]

As described above, miniaturization and cost reduction of the converter (cooling body thereof) and noise reduction of the motor are in conflict with each other, and both cannot be satisfied at the same time. There is a problem. Therefore, an object of the present invention is to satisfy the requirements of downsizing and cost reduction of a converter (its cooling body) and noise reduction of a motor almost at the same time.

[0004]

In order to solve such a problem, according to the present invention, a carrier signal and a control signal are compared with each other, and the converter main circuit element is subjected to pulse width modulation (PWM) according to the comparison result. ) In controlling and driving the motor, the frequency of the carrier signal is normally operated at a predetermined value, and when the motor is judged to be in an overload state, the carrier frequency is set to a predetermined time according to the state. It is characterized in that the heat generation amount of the converter main circuit element does not exceed the rated value by operating by lowering it only by a certain amount.

[0005]

The thermal resistance of the cooling body of the switching element of the converter main circuit is generally designed in consideration of the worst condition (maximum overload condition, etc.). (It is assumed that the motor exceeds the rated load) is a special case, and attention is paid to the fact that it occurs extremely rarely. In an emergency such as time, the carrier frequency is lowered to suppress the heat generation amount of the switching element, so that the switching element can be kept within the rated specification range.

[0006]

1 is a block diagram for explaining an embodiment of the present invention, and FIG. 2 is a block diagram showing a concrete example of the overload detector shown in FIG. As shown in FIG. 1, this type of system is a carrier generator 1 for generating a carrier signal CA.
And the carrier signal CA and the control signal are compared, and the switching element 21 of the converter main circuit is selected according to the comparison result.
It is composed of a PWM control circuit 2 for performing PWM control of the, and a motor 3 driven by its output. In such a configuration, when the carrier frequency is increased to operate in order to reduce magnetic noise, the amount of heat generated by the switching element 21 increases, so that the cooling body must be upsized, which leads to cost increase. is there. Therefore, in this embodiment, although some magnetic noise is usually tolerated, the switching element is operated by appropriately selecting the frequency of the carrier signal so that it falls within the rating, and whether or not an overload state is detected is detected. The frequency of the carrier signal CA is reduced when the overload condition occurs. The load state is monitored here by, for example, the output current of the PWM control circuit 2, and when it exceeds a predetermined level, it is determined to be an overload state.

That is, as shown in FIG. 2, a comparator 41, a filter 42, etc. are provided, and first, the comparator 41
In, the load state detection signal DE is compared with the reference signal S00, and when DE> S00, the switch SW is turned on as an overload state. On the other hand, since the difference between the detection signal DE and the reference signal S00 is obtained via the adder / subtractor AD1, the signal of this difference is input to the filter 42 via the switch SW. The time constant T1 of the filter 42 is set such that T1> T2 when the acceleration / deceleration time of the motor 3 is T2. This is because a current corresponding to the overload level is generally flowed for the time T2 during the acceleration / deceleration of the motor, so that the filter 42 secures a constant time T1. That is, the filter in this case acts as a kind of delay element. The output S1 of the filter 42 is given to the adder / subtractor AD2, where a difference S2 from a set value S01 preset so as to be in the rated load state is obtained, and the frequency of the carrier signal CA is reduced according to the difference S2. It

[0008]

According to the present invention, by allowing a little magnetic noise, there is an advantage that the cooling body can be downsized and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an embodiment of the present invention.

FIG. 2 is a block diagram showing a specific example of the overload detector of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Carrier generator, 2 ... PWM control circuit, 3 ... Motor, 4 ... Overload detector, 21 ... Switching element, 41
... Comparator, 42 ... Filter, SW ... Switch, A
D1, AD2 ... Adder / subtractor.

Claims (1)

[Claims] 1. A carrier signal and a control signal are compared with each other, and when a motor is driven by pulse width modulation (PWM) controlling a converter main circuit element according to the comparison result, the frequency of the carrier signal is usually used. Is operated at a predetermined value, and when the motor is judged to be in an overload state, the carrier frequency is lowered by a predetermined time in accordance with the state, and the amount of heat generated by the converter main circuit element is reduced. A method for adjusting the amount of heat generated by the converter main circuit element, characterized in that the voltage does not exceed the rating.