JPH06141402A - Controller for inverter - Google Patents

Abstract

(57) [Abstract] [Purpose] To suppress the amount of heat generated under heavy load and enable downsizing of the entire device. The inverter control device of the present invention variably sets the switching frequency command to a low value when the load condition is large, and conversely, when the load condition is small, the switching frequency command exceeds the audible range and is high. By variably setting the value and controlling the switching of the switching element of the inverter according to these switching frequency commands, when the load is large, the switching element is switched at a low switching frequency so that the thermal loss in the inverter becomes small. When the load gets smaller, the switching element is switched to a higher switching frequency to operate the switching element, keeping the amount of heat generated almost constant regardless of the size of the load as a whole, and without using a large radiator. Heat dissipation can be performed, the overall size of the device can be reduced, and quietness is maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter controller for controlling an inverter such as that used in a vehicle power converter.

[0002]

2. Description of the Related Art Conventionally, in an inverter that performs power conversion by a semiconductor switching element such as used in a vehicle power conversion apparatus, the switching frequency of the switching element is used as the purpose of the apparatus, the characteristics of the semiconductor switching element, and external restrictions. An appropriate frequency is selected based on the above, and the switching gate control device performs switching control at a constant frequency.

[0003]

However, such a conventional inverter control device has the following problems.

Generally, in the switching by the semiconductor switching element, the higher the frequency is, the more excellent the power characteristic after conversion becomes, and the human cannot hear the operation sound at the frequency beyond the audible range, so that the quiet operation can be obtained. . Further, the capacity of the reactor and the capacitor for smoothing the converted power output can be reduced by high-frequency switching, and the device can be downsized.

However, by increasing the switching frequency, heat is likely to be generated due to electrical loss due to switching of the semiconductor switching element, and in order to perform large-capacity power conversion by high frequency switching, the semiconductor switching element is cooled. However, since a large radiator is required, it is inevitable that the device as a whole becomes large, and if this is taken into consideration, there is a restriction that the switching frequency cannot be increased indefinitely.

Therefore, in order to increase the switching frequency of the semiconductor switching element to achieve miniaturization, quietness, and high performance of the inverter device, it is necessary to consider the treatment of thermal loss of the semiconductor switching element due to switching. . As a means for processing this thermal loss, a method of radiating the heat generated from the semiconductor switching element by a radiator is common, and it is structurally easy.

By the way, since this radiator is increased in size in accordance with the capacity, infinitely increasing the capacity will increase the size of the entire apparatus, so that heat can be effectively radiated within the limited capacity. Is desired.

On the other hand, when the load is light, the amount of current flowing through the semiconductor switching element is small, so heat generation does not increase even at high frequency switching. However, when the load increases, the current also increases, and heat is generated by the load and switching occurs. The heat generated by this increases the load on the radiator and may exceed the capacity of the radiator.

Therefore, switching at a low frequency may be considered, but thermal loss due to switching at a low frequency is small, but the switching operation is performed within the audible range, so that it is generated from a device such as a transformer or a reactor. The noise becomes loud and the silence cannot be maintained.

From the above, conventionally, in order to reduce the size, noise and performance of the inverter device, the heat generation of the semiconductor switching element is taken into consideration from the switching frequency and the relatively small radiator is effectively used. However, there has been a challenge to improve performance.

The present invention has been made in view of the above-mentioned conventional technical problems. By variably controlling the switching frequency according to the size of the load, the overall size of the apparatus can be reduced and the noise and performance can be improved. It is an object of the present invention to provide an inverter control device that can be realized.

[0012]

According to the present invention, there is provided an inverter control device for controlling an inverter for converting a DC power into an AC power by switching a semiconductor switching element and supplying the AC power to a load, and a state of a load connected to the inverter. When the load state detected by the load state detection means and the load state detected by the load state detection means is large,
Switching frequency control means for variably setting the switching frequency command of the inverter to a low value, and gate signal generation means for giving a switching gate signal of a frequency corresponding to the switching frequency command output by the switching frequency control means to each switching element of the inverter. It is equipped with.

[0013]

In the inverter control device of the present invention, the load condition is detected by the load condition detecting means, the switching frequency command is variably set to a low value when the load condition is large, and conversely when the load condition is small. The switching frequency command is variably set to a high value exceeding the audible range, and switching control of the switching element of the inverter is performed according to these switching frequency commands.

Thus, when the load is large, the switching element is switched at a low switching frequency so that the thermal loss in the inverter is small, and when the load is small, the switching element is switched to a high switching frequency to switch the switching element. By keeping the amount of heat generation substantially constant regardless of the size of the load as a whole, sufficient heat dissipation processing can be performed without using a large radiator, and quietness can be maintained.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a circuit block diagram of an embodiment of the present invention. The inverter control device of this embodiment is
A three-phase output inverter based on the PWM modulation method is used to perform variable control of the switching frequency according to the load state, and an inverter 1 that performs a switching operation of the semiconductor switching element G by the PWM modulation method for overhead line DC power; A current detector 2 for the output current of the inverter 1 used as a means for detecting
A filter 3 for smoothing the output of the inverter 1 and shaping it into a sine wave, and a load 4 are provided. The power consumption of the load 4 changes frequently.

The inverter control device of this embodiment further includes a switching gate control device 5 for controlling the switching of the semiconductor switching element G, an output current calculation unit 6 for calculating a load current from the detection signal of the current detector 2,
For the current value output by the output current calculation unit 6, as shown in FIG.
A switching frequency control unit 7 that gives a small switching frequency when the output current is large and a large switching frequency when the output current is small, and a switching frequency output by the switching frequency control unit 7 based on the characteristic curve shown in FIG. A gate signal generation circuit 8 for generating a switching gate signal in response to a command and giving it to each semiconductor switching element G of the inverter 1 to control the switching operation.

The above-mentioned switching frequency control section 7 is for variably controlling the switching frequency according to the magnitude of the load current because the load current increases as the output power to the load 4 increases. As shown in the characteristic curve of FIG. 2, when the load current (output current) is heavy, the switching frequency is a low audible frequency, and when the load current is small, the load is small. It has the characteristic of outputting a high frequency that exceeds the audible frequency as the switching frequency.

Next, the operation of the inverter control device having the above configuration will be described.

The inverter 1 converts DC power into AC power by the switching operation of the semiconductor switching element G, smoothes it through the filter 3 and shapes it into a sine wave, and supplies it to the load 4.

Therefore, the current detector 2 detects the output current of the inverter 1 in order to know the load state, and inputs the detection signal to the output current calculator 6 of the switching gate controller 5. The output current calculation unit 6 calculates the output current value from the input current detection signal and supplies it to the switching frequency control unit 7.

The switching frequency control unit 7 judges whether the load condition is light or heavy based on the magnitude of the output current value, and outputs a low switching frequency command that is in the audible range under heavy load based on the characteristic curve shown in FIG. Conversely, when the load is light, it outputs a high switching frequency command that exceeds the audible range.

The gate signal generation circuit 8 receives the switching frequency command from the switching frequency control section 7, generates a gate signal corresponding to the frequency, and outputs the gate signal to each semiconductor switching element G of the inverter 1. Then, each semiconductor switching element G is switched in a cycle corresponding to the switching frequency command.

As a result, the inverter 1 is subjected to variable frequency control in accordance with the lightness or heavyness of the load state, and performs a switching operation at a low switching frequency when the load is heavy, and a switching operation at a high switching frequency when the load is light.

As a result, at the time of light load, high frequency switching beyond the audible range realizes silence, and
It becomes possible to output an output waveform with a low distortion rate.
Although switching loss of semiconductor switching elements increases due to high-frequency switching, in the case of a light load, the load current is small, so the amount of heat generated is small and the load on the radiator is small, so it is necessary to enlarge the radiator. There is no.

On the contrary, when the load is heavy, the switching frequency is lowered to reduce the switching loss of the semiconductor switching element, so that the heat generation amount of the semiconductor switching element is prevented from being superposed on the heat generation of the semiconductor switching element due to the load current. It is possible to reduce the burden of. Note that when the switching frequency is set to a low frequency, noise in the audible range is generated, but especially in the case of electric vehicles, the heavy load is due to mechanical loads such as compressors and air conditioners that generate relatively large noise. Due to the large number of noises, the noise emitted from the inverter is canceled by it, and the passengers are less likely to feel discomfort.

The present invention is not limited to the above-described embodiments, and the inverter may have another type, and the load state detection is not limited to the current detection. Further, the characteristic curve of the switching frequency control unit is not limited to that of the embodiment, and the curvature may be changed, the linear characteristic may be used, and the optimum characteristic may be experimentally determined.

[0028]

As described above, according to the present invention, when the load condition is large, the switching frequency command is variably set to a low value, and conversely, when the load condition is small, the switching frequency command is set in the audible range. Is variably set to a high value exceeding the above, and switching control of the switching elements of the inverter is performed according to these switching frequency commands.Therefore, when the load is large, thermal loss in the inverter is reduced. If the switching element is operated at a low switching frequency and the load becomes small, the switching element is switched to a high switching frequency to operate the switching element, and as a whole, the heat generation amount can be kept almost constant regardless of the size of the load. , Sufficient heat dissipation can be performed without using a large radiator, and the overall size of the device can be reduced. Quietness can be maintained.

[Brief description of drawings]

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

FIG. 2 is a graph showing a switching frequency command-output current characteristic provided in the switching frequency control unit in the above embodiment.

[Explanation of symbols]

 1 inverter 2 current detector 3 filter 4 load 5 switching gate controller 6 output current calculator 7 switching frequency controller 8 gate signal generation circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Ujiie No. 1 Toshiba-cho, Fuchu-shi, Tokyo Toshiba Corporation Fuchu factory

Claims (1)

[Claims] 1. An inverter control device for controlling an inverter that converts DC power into AC power by switching a semiconductor switching element and supplies the AC power to a load, and load state detection means for detecting a state of a load connected to the inverter. When the load state detected by the load state detecting means is large, a switching frequency control means for variably setting the switching frequency instruction of the inverter to a low value, and a switching frequency instruction output by the switching frequency control means And a gate signal generating means for applying a switching gate signal having a different frequency to each switching element of the inverter.