JPH06197552A - Power conversion device - Google Patents

Abstract

PURPOSE:To obtain a power conversion device which consumes a less amount of power and generates less noise by providing a carrier distributing rate changing means which changes the occupying rates of a plurality of carriers to be compared with a modulated wave given to a PWM circuit in a prescribed period of time by means of a control signal. CONSTITUTION:Of a plurality of carriers, the carrier 7 which can reduce noise is set at a frequency near the upper limit of the audible frequency range of human beings and the carrier 8 which can reduce the power consumption of a power converter is set at a carrier frequency nearly equivalent to that of the power converter. A carrier distributing rate changing means 9 outputs the occupying rates of the carriers 7 and 8 by changing the rates in accordance with the magnitude of the output signal 10 of a load current detecting means and a PWM circuit 5 outputs a pulse-like gate signal to a gate circuit 4 by performing PWM-control and drives an induction motor 3 at a prescribed voltage and prescribed frequency by switching the self-extincting element of an inverter 2. As a result, low noise can be attained while the emphasis is laid upon at the saving of the power consumption when the load current is large and saving of power consumption can be attained while the emphasis is laid upon the low noise when the load current is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter, and more particularly to a power converter composed of a field effect type self-extinguishing element.

[0002]

2. Description of the Related Art Generally, in a pulse width modulation (hereinafter referred to as PWM) power converter composed of a field effect type self-extinguishing element or the like, a carrier frequency thereof is set to an audible frequency range or higher to reduce noise generated from an induction motor, It is designed to be almost the same as when driven by a commercial power source. However, since the carrier frequency is high, the generated loss due to switching is increased and the power consumption is increased.

In view of this, the conventional device takes the above into consideration, and sets the upper limit frequency determined by the generated loss and the lower limit frequency determined by the noise as the variable range of the carrier wave as described in JP-A-3-82396. The carrier frequency is variably controlled in conjunction with the magnitude of the load current so that the carrier frequency is lowered as the load current of the device increases and the carrier frequency is increased as the load current decreases.

[0004]

Since the above conventional device performs variable control of the carrier frequency linked to the load current, continuous operation with a large load current results in continuous operation at the lower limit (lower) carrier frequency. A loud noise continues. In addition, continuous operation with a small load current results in continuous operation with the upper limit (higher) carrier frequency,
High power consumption continues.

An object of the present invention is to provide a power converter that consumes less power and produces less noise even when continuously operated in a state where the load current of the power converter is large or small.

[0006]

To achieve the above object, in the present invention, a power converter constituted by a field effect type self-extinguishing element, a gate circuit for driving a gate of the self-extinguishing element, In a power converter configured by a PWM circuit that PWM-controls the gate circuit, a plurality of carrier frequencies to be compared with a modulation wave given to the PWM circuit are provided, and a ratio (allocation ratio) of the plurality of carriers in a predetermined time is controlled. A carrier distribution ratio varying unit that changes according to a signal is provided, and the control signal inputs a signal output from a unit that detects a load current or a current command that specifies the magnitude of the load current.

[0007]

Function: A signal output from the means for detecting the load current,
Alternatively, the control signal is increased as the current command designating the magnitude of the load current increases. Receiving this signal,
When the control signal is large, that is, when the load current is large, the carrier wave distribution ratio changing means increases the carrier wave distribution ratio of the frequency that can suppress the power consumption. Further, when the control signal is small, that is, when the load current is small, it acts to increase the distribution rate of the carrier wave of the frequency that can suppress noise.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a power converter according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a power converter according to the present invention, FIG. 2 is a block diagram of a carrier distribution ratio varying means, FIG. 3 is a characteristic diagram showing a relationship between a control signal and a distribution ratio, and FIG. 4 is a carrier distribution ratio varying. It is explanatory drawing which shows the carrier wave output from a means.

In FIGS. 1 and 2, 1 is a DC voltage power source, 2 is an inverse converter composed of a field effect type self-extinguishing element,
3 is an induction motor, 4 is a gate circuit, 5 is a PWM circuit, 6
Is a modulated wave, 7 is an A carrier having a frequency capable of reducing noise among a plurality of carriers, 8 is a B carrier having a frequency capable of reducing power consumption among the plurality of carriers, 9 is a carrier allocation ratio varying means, 9
-1 is a peak detector for detecting the peak of the carrier wave, 9-2
Is a timer for counting the output time of the A carrier, 9-3 is a timer for counting the output time of the B carrier, 9-4 is a time setter for setting the time in timers 9-2 and 9-3, 9
Reference numeral -5 is a carrier wave switch, and 10 is an output signal of the load current detecting means which serves as a control signal.

The basic operation of the power converter in this embodiment will be described with reference to FIG.

First, of the plurality of carrier waves, the carrier wave 7 having a frequency capable of realizing noise reduction is set to a frequency near the upper limit of the human audible frequency range, for example, 16000 Hz. In addition, the carrier wave 8 having a frequency capable of realizing the power elimination among the plurality of carrier waves is a conventional BJT (bipolar transistor).
The carrier frequency almost equal to that of the power converter configured in, for example, 3000 Hz is set. Next, in the carrier wave distribution ratio changing means 9, the ratio of the carrier wave 7 and the carrier wave 8 to the predetermined time is output signal 10 of the load current detecting means which becomes a control signal.
It changes according to the size of and outputs. The carrier wave outputted from the carrier wave distribution ratio changing means 9 and the modulated wave 6 are PWM-controlled by the PWM circuit 5, and a pulsed gate signal is outputted to the gate circuit 4. Then, the gate circuit 4 includes the inverse converter 2
The self-arc-extinguishing element is switched to drive the induction motor 3 at a predetermined voltage and a predetermined frequency.

Further, the operation of the carrier distribution rate changing means 9 will be described in detail with reference to FIG.

First, the peak detector 9-1 detects the upper and lower peaks of the carrier wave output to the PWM circuit 5,
The peak detection signal designating the timing of switching the carrier wave of the carrier wave switch 9-5 is output.

The time setter 9-4 has a predetermined distribution ratio and a distribution ratio obtained from the relationship between the distribution ratio and the control signal shown in FIG. 3 depending on the magnitude of the control signal 10 which is the output signal of the load current detecting means. From the time, the time calculated by the formula 1 and the formula 2 is calculated.
-2, and the output time of the carrier wave 8 is set in the timer 9-3.

[0016]

[Equation 1]

[0017]

[Equation 2]

In the relationship between the distribution rate and the control signal shown in FIG. 3, the maximum value Rmax and the minimum value Rmin of the distribution rate are set so that a plurality of preset carrier waves can always output at least one cycle within a predetermined time. Set.

The timers 9-2 and 9-3 are supposed to start counting by the other timer after the time set by one timer is reached, and to determine which carrier wave is output when the timer is switched. And outputs the carrier designation signal to the carrier switch 9-5.

The carrier switching unit 9-5 switches the carrier according to the peak detection signal and the carrier designation signal.
The carrier wave whose distribution ratio is changed as shown in (3) is output to the PWM circuit.

According to the power converter configured as described above, when the load current is large, a large proportion of the carrier wave that can suppress the generated loss is output, so that noise reduction can be achieved while focusing on power saving. In addition, when the load current is small, a large proportion of carrier waves that can suppress noise can be output, so that the power converter can achieve power saving while focusing on low noise.

Further, in the present embodiment, the power converter constituted by the inverse converter has been described, but the same effect can be obtained by placing the power converter constituted by the forward converter.

[0023]

According to the present invention, the ratio of a plurality of carrier frequencies to a predetermined time can be changed. Therefore, when the load current is large, the generated loss can be suppressed to be low and a large ratio of carrier waves can be output. Therefore, low noise can be achieved while focusing on power saving.Moreover, when the load current is small, a large proportion of carrier waves that can keep noise low is output, so low noise is emphasized. However, power saving can also be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram of a power converter according to the present invention.

FIG. 2 is a block diagram of a carrier distribution ratio changing unit.

FIG. 3 is a characteristic diagram showing a relationship between a control signal and a distribution rate.

FIG. 4 is an explanatory diagram of a carrier wave output by a carrier wave distribution ratio varying unit.

[Explanation of symbols]

1 ... DC power supply voltage, 2 ... Inverse converter, 3 ... Induction motor, 4
... Gate circuit, 5 ... PWM circuit, 6 ... Modulated wave, 7, 8 ...
Carrier wave, 9 ... Carrier wave distribution ratio varying means, 10 ... Control signal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiromi Inaba 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Shunsuke Mine 1070 Ichige, Katsuta-shi, Ibaraki Stock Hitachi, Ltd. Mito factory

Claims (6)

[Claims] 1. An inverse converter composed of a field effect type self-extinguishing element for converting a DC voltage power supply into AC power of a predetermined frequency and a predetermined voltage, and an induction motor connected to the output side of the inverse converter. A power converter comprising a gate circuit for driving the gate of the self-extinguishing element and a pulse width modulation circuit for controlling the pulse width modulation of the gate circuit. An electric power converter comprising a carrier frequency and a carrier distribution ratio varying means for changing a ratio of the plurality of carriers in a predetermined time by a control signal. 2. A forward converter composed of a field effect type self-extinguishing element for converting a three-phase AC power supply into a predetermined DC voltage, and a filter capacitor for smoothing the output voltage of the forward converter.
In a power converter composed of a gate circuit for driving the gate of the self-extinguishing element and a pulse width modulation circuit for controlling the pulse width modulation of the gate circuit, a plurality of carrier waves to be compared with a modulation wave given to the pulse width modulation circuit. Equipped with frequency
A power converter comprising: a carrier distribution ratio varying means for changing a ratio of the plurality of carriers in a predetermined time by a control signal. 3. The power converter according to claim 1, wherein the carrier distribution ratio changing means sets the distribution ratio so that each of the plurality of carriers can be output for at least one cycle. 4. The carrier distribution ratio varying means according to claim 3, wherein a signal output from a means for detecting a load current or a current command designating a magnitude of the load current is inputted as a control signal, Power converter that sets the distribution rate. 5. The power converter according to claim 3, wherein a signal output from a means for measuring the power consumption of the power converter is input as a control signal to the carrier distribution ratio varying means to set the distribution ratio. 6. The control means of claim 1, wherein the carrier distribution ratio varying means uses a signal output from a means for measuring the torque of the induction motor or a torque command designating the magnitude of the induction motor torque as a control signal. A power converter that inputs and sets the allocation rate.