JPH04285473A - Dc/ac power source - Google Patents

Abstract

PURPOSE:To provide a power source which can cope with any power factor by improving a waveform and efficiently use a load by not PWM-controlling in a predetermined period near a maximum value of an AC voltage but PWM- controlling only in the other zone. CONSTITUTION:An inverter controller 4 controls an inverter bridge 18 and outputs an AC voltage VAC, and PWM-controls to maintain a switching command to be output from a PWM circuit 40a ON in a predetermined period near a maximum value of the voltage VAC by a voltage V17 or -V17 and becoming a trapezoidal wave in the other period. A filter is provided at the output of the bridge 18 to remove high frequency components. Since the PWM is not conducted in a period in which a current mainly flows when such a control is executed, a switching loss is eliminated, and an efficiency is raised.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC/AC power supply device that obtains alternating current power from a battery power source.

0002

[Prior Art] As a recent leisure trend, people go out by car and use the car's battery power source (generally DC12V).
There is an increasing demand to obtain alternating current voltage (100 V) from a large number of sources (of which there are many) and use it in general home televisions, refrigerators, microwave ovens, etc.

This type of conventional DC/AC power supply is shown in FIG.
Shown below.

FIG. 3 is an example of a DC/AC power supply device that obtains 100 V AC from 12 V DC. The power to the battery 1 is turned on and off by the circuit breaker 2. When the battery power is turned on, the smoothing capacitor 4 is charged via the current limiting resistor 3, and then the current limiting resistor 3 is short-circuited by the relay 5.

The DC power smoothed by the capacitor 4 is applied to both terminals of the transformer 6 via the center tap of the transformer 6 and MOSFETs 7 and 8, and the MOSFETs 7 and 8 are alternately switched so that the AC power is transferred to the transformer. 6.

MOSFETs 7 and 8 are provided with diodes 9 and 12, capacitors 10 and 13, and discharge resistors 11 and 12, respectively.
A surge absorption circuit consisting of 14 is provided to prevent the MOSFET from deteriorating due to overvoltage.

The alternating current voltage obtained on the secondary side of the transformer 6 is rectified by a diode bridge 15 and then passed through a reactor 16.
, the second DC voltage V17 is obtained by removing the high frequency component by the capacitor 17. This V17 is inverter bridge 1
8, it is converted into an alternating current voltage VAC of 50 Hz or 60 Hz and output.

[0008] The DC/DC converter 19 has a capacitor 4
A control power supply VC is obtained from the voltage of the chopper control circuit 20.
and the inverter control circuit 21. The chopper control circuit 20 performs PWM control on the MOSFETs 7 and 8 to control the voltage V17 of the capacitor 17. Inverter control circuit 2
1 controls the FET of the inverter bridge 18.

There are various control systems for chopper control and inverter control, one example of which is shown in FIG. 4(a). In this method, the voltage V17 of the capacitor 17 is subjected to chopper control so as to have a double-wave rectified waveform, and the inverter bridge 18 is inverter controlled to invert the polarity every 180 degrees (half wave) to obtain the alternating current voltage VAC.

As another control, the capacitance of the capacitor 17 is increased to keep V17 constant through chopper control, and as shown in FIG.
Inverter control may also be performed to generate the pseudo square wave shown in (b). Note that id is the chopper input current.

[0011]

The method shown in FIG. 4(a) is highly efficient because PWM is not performed on the secondary side of the transformer. However, since there is no circuit for flowing the reactive power of the AC output (because the capacitance of the capacitor 17 is small), it cannot be used with a load with a lagging power factor or a leading power factor.

Among home appliances, radios, TVs, VTRs, etc. are loads with capacitor input type rectifier circuits, so method (a) can be applied, but for refrigerators, electric fans, etc. that use motors, method (a) can be applied. The motor does not rotate smoothly and is unusable.

The method shown in FIG. 4(b) can process the reactive power of the load with the capacitor 17, so it can be used for lagging power factor and leading power factor loads, but the distortion of the output voltage is large and harmonic components cause damage to motors and capacitors. may cause overheating.

Furthermore, if the inverter bridge 18 is PWM controlled so that the output voltage VAC becomes a sine wave, the problems of power factor and distortion factor can be solved, but there is a drawback that efficiency is reduced due to switching loss. Especially in loads with capacitor input type rectifier circuits, the peak current of the load is high, so switching losses tend to increase.

Furthermore, when a load having a capacitor input type rectifier circuit is applied, there is a problem in that the applied current becomes large and overcurrent is likely to occur, and it is often impossible to apply a large load.

As described above, in conventional devices, when improving efficiency, there are problems such as not being able to cope with the load power factor or deteriorating the output waveform. This had the disadvantage that it was easy to trip and the load could not be used effectively.

An object of the present invention is to provide a power supply device that has a good waveform, can handle any power factor, is efficient, and can suppress current when turned on to utilize up to 100% of the load. do.

[Configuration of the invention]

[0019]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention includes an inverter unit bridge-connected between the positive and negative sides of a DC power supply, and connects the inverter bridge to the PW.
In a device that converts DC voltage to AC voltage by controlling M, a predetermined section near the maximum value of this AC voltage is P
P that does not perform WM control and only performs PWM control on other sections
A WM control means is provided.

Further, current limiting means is provided for turning off either the positive side or the negative side circuit of the inverter bridge when the current in the inverter section exceeds a predetermined current.

[0021]

[Operation] By the PWM control means, the DC voltage is output as is in the predetermined section near the maximum value of the AC voltage, resulting in a trapezoidal wave-shaped AC voltage, and since PWM control is not performed in the predetermined section, switching loss does not occur and efficiency is increased. gets better. Further, the current limiting means suppresses overcurrent such as inrush current even when a load having a capacitor input type rectifier circuit is applied.

[0022]

[Embodiment] An embodiment of the present invention is shown in FIG. Components that are the same as those in FIG. 3 are given the same reference numerals and their explanations will be omitted.

[0023] The chopper control circuit 20 controls the MOSFETs 7 and 8 so that the voltage V17 of the capacitor 17 is constant.
M control.

The inverter control circuit 40 controls the inverter bridge 18 to output an alternating current voltage VAC.
Control so that the waveform is as shown in . That is, P
In the switching command output from the WM circuit 40a, PWM control is performed so that a predetermined section near the maximum value of VAC remains on and constant at V17 or -V17, and a trapezoidal wave is generated in other sections.

A filter consisting of a reactor 32 and a capacitor 33 is provided at the output of the inverter bridge 18 to remove high frequency components. The load current is detected by the current transformer 34, converted to direct current by the rectifier 40d, and then the level is detected by the hysteresis comparator 40c. Logic is set such that when the load current becomes overcurrent, the FETs 18b and 18d of the inverter bridge 18 are turned off. Configure. FET18a and 18b
, 18c and 18d are operated as inverters.

The waveform 18a in FIG. 2 is a PWM waveform that turns the FET 18a on and off, and its average value is a trapezoidal wave as shown by the broken line. FET 18b is driven by the inverted waveform of 18a. F
ET18c also has a phase difference of 180° and similarly performs PWM with a trapezoidal wave, and FET18d is driven with an inverted waveform of FET18c.

By performing such control, the filtered AC output VAC has the waveform shown in the figure.

In the sections a to d that are divided into one cycle of the output voltage VAC, there is a constant slope between the sections a and c,
PWM control is performed only in this section, and PWM control is performed between sections b and d.
The voltage V17 of the capacitor 17 is output without performing this step.

When such control is performed and a capacitor input type rectifier load (which is the load in most household and OA equipment) is connected, a current as shown by iac in FIG. 2 flows.

In this case, the period during which current flows is mainly in sections b and d, and since PWM is not performed in this section, no switching loss occurs.

Even when the load is of a resistance type, the efficiency is high because PWM is not performed near the peak value of the current.

Furthermore, according to this embodiment, when a capacitor input type rectifying load is applied, overcurrent due to inrush current of the capacitor is limited.

Now, when FETs 18a and 18d in section b are on and an overcurrent flows, the hysteresis comparator 40c detects this and turns off FET 18d.
The current flowing in the reactor 32 is → load → FET1
It flows through the closed circuit of diode 8c and FET 18a, and attenuates while charging the load capacitor. Then, when the hysteresis comparator 40c is reversed, the FET 18d is turned on again.
turns on.

While repeating this operation, the current is limited and the load capacitor is charged. In the case of section d, FET18
Since c and 18b are on, 18b similarly controls the current limit.

In sections a and c, in addition to the above modes, FET
There is a mode in which both 18a and 18d are turned off. In this case, the energy of reactor 32 is equal to the load and capacitor 1.
7, the energy transferred to the load decreases, but the effect of limiting the current remains the same.

As explained above, according to the present invention, in a capacitor input type rectified load, switching is not performed in the range where current flows, so there is no switching loss and high efficiency is achieved.

The distortion factor of the trapezoidal wave is less than 5%, which is very close to that of a sine wave, and the torque ripple is low even when the load is a motor.
It is also highly effective.

Furthermore, the current limiting action of turning on and off only one side makes it possible to limit the current while effectively supplying energy to the capacitor input type rectifying load.

Note that the hysteresis comparator 2 in FIG.
1c has a level detector and an off-delay timer,
It may be configured such that one FET is turned off for a certain period of time in the event of an overcurrent.

Although the sections b and d in FIG. 2 are each about 60 degrees, they can be widened if the waveform rate permits. The longer this section is, the higher the inverter efficiency is.

Furthermore, the circuit of the capacitor 17 and inverter bridge 18 in FIG. 1 may be a half-wave type inverter in which the output is between the midpoint of two capacitors 17 connected in series and the midpoint of a half-bridge inverter bridge. It can be applied similarly.

Further, the output voltage waveform does not need to be an accurate trapezoidal wave; a part of a sine wave may also be used, but the output voltage remains on near the peak and is not subjected to PWM control.

[0043]

According to the present invention, an AC output with a low distortion factor can be obtained with high efficiency even for a load with a lagging power factor or a leading power factor.

Furthermore, when a load that causes an overcurrent is applied, the current is limited, so even a load with a capacitor input type rectifier circuit can be applied safely, resulting in a highly reliable DC/AC power supply. can be provided.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the operation of the present invention.

FIG. 3 is a configuration diagram of a conventional device.

FIG. 4 is an explanatory diagram of the operation of the conventional device.

[Explanation of symbols]

4...Smoothing capacitor
6...Transformer 7, 8...MOSFET
15...Diode bridge 16...Reactor
17...Capacitor 18...Inverter bridge
20...Chopper control circuit 40...Inverter control circuit 40a
...PWM circuit 40b...logic circuit 4
0c...Hysteresis comparator

Claims (2)

[Claims] Claim 1: An inverter unit is provided with a bridge connection between the positive and negative sides of a DC power source, and this inverter bridge is connected to a PW
In a device that converts DC voltage to AC voltage by controlling M, a predetermined section near the maximum value of this AC voltage is P
P that does not perform WM control and only performs PWM control on other sections
A DC/AC power supply device characterized by being provided with WM control means. 2. The apparatus according to claim 1, further comprising current limiting means for turning off one of the positive and negative circuits of the inverter bridge when the current in the inverter section exceeds a predetermined current. DC/A characterized by
C power supply device.