JPH09247947A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an output voltage waveform with the minimum switching times by making an output frequency of a chopping wave generating means variable according to a deviation signal when the deviation signal which is the deviation of an instantaneous output voltage detected value of a power converter from an instantaneous output voltage reference value exceeds a predetermined value. SOLUTION: A voltage signal of a load 4 and a voltage standard which is an output voltage of a reference voltage setting device 12 are added by an adder 31 and an output signal of the adder 31 is sent to an error amplifier 33 through an absolute value converter circuit 32 which converts a signal to an absolute value and then a signal which has been error-amplified by the error amplifier 33 is sent to a function generating means 34. According to an output signal of the function generating means 34, an output frequency of a chopping wave generating means 15 can be varied. By this method, when a non-linear load is connected, the number of switchings is increased at a point in one cycle where a rate of change in current is large and an output voltage waveform deforms and thereby the output voltage waveform can be improved with the minimum number of switchings.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter including a semiconductor stack in which a semiconductor element is attached to a cooler such as a heat sink, and a converter circuit having pulse width modulation control means or an inverter circuit. In particular, the present invention relates to a power conversion device that can reduce the loss of the power conversion device while improving the output voltage waveform into a sinusoidal waveform, improve the utilization rate of the cooler, and achieve downsizing of the cooler.

[0002]

2. Description of the Related Art In recent years, in power converters, the adoption of high-frequency pulse width modulation control using high-speed switching elements has been applied to both converters and inverters in order to improve the performance of power conversion. Since it can supply high-quality power, it is widely used in uninterruptible power supplies.

A conventional power converter will be described with reference to FIG. In the figure, 1 is a DC power source, 2 is an inverter formed by a semiconductor stack in which semiconductor elements are attached to a cooler, 3 is a reactor, and 4 is a load.

Explaining the operation of the power converter, the DC power supplied from the DC power supply 1 is generated by a self-excited inverter (hereinafter simply referred to as "inverter") composed of semiconductor elements such as transistors with a predetermined voltage and frequency. The AC power is converted into high AC power, and is supplied to the load 4 through a filter circuit that makes the rectangular wave of the pulsed output of the inverter sinusoidal by the reactor 3 and a capacitor (not shown).

Next, the control circuit of the power converter will be described. Reference numeral 11 is an AC voltage detecting means for insulating the AC output voltage of the power converter and converting it into a control level, 12 is a reference voltage setting device for setting a voltage reference, and 13 is an AC voltage detecting means 1
An adder for adding the output signal of 1 and the output of the reference voltage setting unit 12, 14 is an error amplifier for proportional / integrating the error amount generated by the comparison of the reference amount and the feedback amount by the adder 13, and 15 is a pulse width modulation control ( (Hereinafter, referred to as PWM control) is a carrier wave that determines the switching frequency of the semiconductor element by the triangular wave generating means that constitutes the means, becomes one input of the comparator 16, and the control signal that is the output of the error amplifier 14 is the other input. Becomes A base signal waveform of a predetermined pulse train is obtained for the transistor group used in the inverter 2 by the comparator 16, insulated and amplified by the gate drive circuit 17, and supplied to the base of the transistor group.

The advantages of using the high frequency PWM control will be briefly described below. (1) The output voltage waveform can be controlled. (2) High-speed response to load fluctuations is possible. (3) A filter circuit (not shown) for waveform shaping can be miniaturized. (4) Noise reduction of transformer is possible. In recent years, application of high frequency PWM control has advanced to a large capacity area.

However, considering the loss of the semiconductor element, the total loss is P T, the steady on-state loss is Ps, the switching loss at turn-on is Pon, and the switching loss at turn-off is P.
When the switching frequency is f and the switching frequency is f, the following equation is obtained.

[0008]

## EQU1 ## PT = Ps + (Pon + Poff) f (1) In the equation (1), high-frequency switching means that the switching frequency f increases, and that the energizing current is the same. However, since the second term increases in proportion to the switching frequency f, there is a drawback that the loss increases. Therefore, under the present circumstances, the switching frequency f is determined at a trade-off point of both in consideration of control performance and loss to increase the frequency.

[0009]

Now, let us consider the switching frequency of the power converter configured as described above. In a self-excited inverter, it is generally said that the output voltage waveform has a sinusoidal waveform for good power quality.Therefore, if a linear load or a non-linear load is connected to the output of the power converter, the waveform of the load current is sinusoidal. If not, the output voltage waveform must be controlled in a sinusoidal manner.

When the load current waveform is not sinusoidal, that is, when a capacitor input type rectifier load is connected and a current having a high crest factor flows, the output voltage waveform is crushed and distorted by the impedance existing in the inverter.
In order to correct this, switching of the semiconductor element is repeated a plurality of times during one cycle of the output voltage to obtain a required voltage waveform. However, if the number of times of switching is increased more than necessary, the switching loss of the semiconductor element increases, which becomes a factor that hinders the downsizing of the cooler.

Therefore, the object of the present invention is made in view of the above-mentioned points, and a power conversion such as a converter circuit incorporating a semiconductor element for converting AC power into DC power or an inverter circuit for converting DC power into AC power. In the device,
Provided is a power conversion device capable of increasing the number of times of switching and improving the output voltage waveform with a minimum number of times of switching at the point where the rate of change of current is severe and the output voltage waveform is distorted in one cycle when a non-linear load is connected. To do.

[0012]

To achieve the above object, the invention according to claim 1 is constituted by a semiconductor stack in which one or more semiconductor elements are attached to a cooler, and has at least triangular wave generating means. And a pulse width modulation control means for controlling the semiconductor element, the power converter comprising a converter circuit for converting AC power into DC power or an inverter circuit for converting DC power into AC power. A deviation signal between the instantaneous output voltage detection value of the device and the instantaneous output voltage reference value is applied, and when the deviation signal exceeds a predetermined value, the output frequency of the triangular wave generating means is changed according to the deviation signal. It is characterized by comprising a function generating means.

According to a second aspect of the present invention, in the power converter according to the first aspect, temperature detecting means for detecting the temperature of the semiconductor element and outputting a signal according to the temperature, and the temperature detecting means A second function generating means to which an output signal is applied is provided, and the variable amount of the output frequency of the triangular wave generating means is adjusted according to the output of the second function generating means.

Further, the invention described in claim 3 is the same as claim 2
In the power conversion device described in (1), temperature setting means for setting the temperature of the semiconductor element, and a deviation signal between the output signal of the temperature setting means and the output signal of the temperature detecting means is applied, and the deviation signal is applied according to the deviation signal. It is characterized in that limiting means for limiting the upper limit value and the lower limit value of the output signal of the triangular wave generating means is provided.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, one embodiment of the invention described in claim 1 will be described with reference to the block diagram of FIG. This will be described with reference to a characteristic diagram showing the relationship of

It is to be noted that, in FIG. 1, the components denoted by the same reference numerals as those in FIG. 6 have the same functions, and therefore the description thereof will be omitted. 1 is different from the conventional power converter shown in FIG. 6 in that the load voltage signal and the output signal of the voltage reference 12 are added by the adder 31 and the output signal of the adder 31 is converted into an absolute value. Function generating means 3 to which a signal obtained by amplifying the error by the error amplifier 33 is applied via the conversion circuit 32.
4 is provided so that the output frequency of the triangular wave generating means 15 can be variably adjusted according to the output signal of the function generating means 34.

The function generating means 34 is, for example, as shown in FIG.
A value obtained by error-amplifying the output voltage deviation is applied as shown in, and the triangular wave generating means 15 is used until this value reaches a predetermined value A0.
The output frequency of 1 becomes a constant value f0, and when the error amplified value exceeds A0, it increases to f1.

As a result, when a non-linear load is connected and the rate of change in current becomes severe, the switching frequency of the semiconductor element can be increased and waveform improvement can be achieved. Therefore, the switching frequency is increased only when the waveform needs to be improved in one cycle, and when the rate of change of the current is not severe, the switching frequency f of the second term represented by the equation (1) of the loss of the semiconductor element becomes small. The switching loss can be reduced, the improvement of the waveform can be achieved and suppressed with the minimum switching, and a small-sized power conversion device for the cooler can be provided.

The function generating means is not limited to the above-mentioned characteristics. For example, as shown in FIG. 2B, the output of the triangular wave generating means 15 increases as the value obtained by error amplification of the output voltage deviation increases. The frequency f0 may act so as to gradually increase.

Next, an embodiment of the invention described in claim 2 will be described with reference to FIG. 3 in which the same parts as those in FIG. 1 is different from FIG. 1 in that a temperature detecting means 41, a level converter 42 for converting an output of the temperature detecting means 41 into a predetermined signal level, and a function generator 43, an output voltage deviation amount by a multiplier 51. The point is that it is variable.

Thus, for example, in addition to the characteristics shown in FIG.
When the temperature of the semiconductor element is high, the characteristic of the triangular wave frequency f is reversed in the B direction, and when the temperature is low, it is changed in the C direction so that the optimum switching frequency can be selected after monitoring the element temperature. This is especially effective when the effective value and the peak value of the load current differ greatly.

Further, an embodiment of the invention described in claim 3 will be described with reference to FIG. 5 in which the same parts as those in FIG. 5, as in FIG. 3, reference numerals 41 and 42 denote a temperature detecting means for detecting the temperature of the switching element and a level converter 42 for converting the output of the temperature detecting means 41 into a predetermined signal level. 44 is a level converter 4
It is an adder that outputs a deviation signal between the output signal of No. 2 and the output signal of the temperature setting means 45. The deviation signal output from the adder 44 is given to the limiting means 47 via the error amplifier 46.

The limiting means 47 regulates the upper limit frequency of the triangular wave generating means 15 when the deviation signal exceeds a positive predetermined value, and limits the upper limit frequency of the triangular wave generating means 15 when the deviation signal exceeds a negative predetermined value. Regulate the lower limit frequency.

With this structure, the temperature of the semiconductor element is substantially equal to the outside air temperature when the power converter is activated, and the temperature reference T ^* set by the temperature setting means 45 is set ^.
For example, since the deviation signal has a large positive value because it corresponds to the temperature when the load current is large, the limiting means 47 outputs the output frequency fc of the triangular wave generating means 15 as shown in FIG.
To the upper limit. Therefore, the frequency of the carrier wave in PWM control is fc after the power converter is started.

After that, since the load current increases and the detection signal from the temperature detecting means becomes higher than the temperature reference T ^* , the deviation signal increases to the negative side, so that the output frequency of the triangular wave generating means 15 starts to decrease from fc. , Triangular wave generating means 15
In order to prevent the output frequency of the triangular wave generator 15 from decreasing below the lower limit value fB, the limiting means 52, as shown in FIG.
Output frequency is regulated to the lower limit of fB. As a result, the number of times the semiconductor element is switched can be reduced according to the temperature of the semiconductor element, and the cooler can be operated efficiently.

[0026]

As described above, the first to third aspects of the invention are described.
According to the invention described in (1), since the deviation of the load voltage of the power converter is detected and the frequency of the carrier wave of PWM control can be increased or decreased, the improvement of the output voltage waveform is set at the optimum number of switching times. Therefore, the cooler of the semiconductor element can be efficiently used, and the power converter can be downsized and the space can be saved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the invention described in claim 1.

FIG. 2 is a diagram showing characteristics of the triangular wave generating means of FIG.

FIG. 3 is a block diagram showing an embodiment of the invention described in claim 2.

FIG. 4 is a related characteristic diagram for explaining claims 2 and 3.

FIG. 5 is a block diagram showing an embodiment of the invention described in claim 3.

FIG. 6 is a block configuration diagram of a conventional power conversion device.

[Explanation of symbols]

1 ... DC power supply 2 ... Inverter 3 ... Reactor 4 ... Load 11 ... AC current detecting means 12 ... Reference voltage setting device 13 ... Adder 14 ... Error amplifier 15 ... Triangular wave generating means 16 ... Comparator 17 ... Gate drive circuit 31 ... Addition Unit 32 ... Absolute value conversion circuit 33 ... Error amplifier 34 ... Function generating means 41 ... Temperature detecting means 42 ... Level converter 43 ... Function generating means 44 ... Adder 45 ... Temperature setting means 46 ... Error amplifier 47 ... Limiting means 51 ... Multiplier 52 ... Limiting means

Claims (3)

[Claims] 1. A semiconductor stack comprising one or more semiconductor elements attached to a cooler, at least triangular wave generating means, pulse width modulation control means for controlling the semiconductor elements, and alternating current power to direct current. In a power converter including a converter circuit for converting to electric power or an inverter circuit for converting DC power to AC power, a deviation signal between an instantaneous output voltage detection value of the power converter and an instantaneous output voltage reference value is applied. A power conversion device comprising: a function generating means for varying the output frequency of the triangular wave generating means according to the deviation signal when the deviation signal exceeds a predetermined value. 2. The power conversion device according to claim 1, wherein the temperature detecting means for detecting the temperature of the semiconductor element and outputting a signal according to the temperature, and the output signal of the temperature detecting means are applied. The power conversion device is characterized in that the function generating means is provided and the amount by which the output frequency of the triangular wave generating means is varied is adjusted according to the output of the second function generating means. 3. The power converter according to claim 2, wherein temperature setting means for setting the temperature of the semiconductor element, and a deviation signal between an output signal of the temperature setting means and an output signal of the temperature detecting means are applied. The power conversion device is provided with a limiting unit that regulates an upper limit value and a lower limit value of the output signal of the triangular wave generating unit according to the deviation signal.