JPH0488886A - Inverter - Google Patents

Abstract

PURPOSE:To eliminate feeling of a leakage even if a high carrier frequency is used by insulating a commercial power source from the output of an inverter by magnetically coupling, and chopping a DC power source by an inverter. CONSTITUTION:If switching frequency is high, energy necessary for a capacitor 19 is continuously supplied and a DC power source necessary for an inverter 6 is supplied. However, since primary side coil 14 and secondary side coil 17 of a switching transformer 13 are magnetically coupled, the two coils are not electrically coupled. Accordingly, both terminals of the capacitor 19, i.e., power terminals (c), (d) of the inverter 6 are not coupled to a commercial power source 5, and insulated from the ground. The inverter 6 controls a DC voltage by a converter 11 to open or close switching element group of an inverter switching element 8 based on the signal of an inverter controller 7, converts it into 3-phase equal width or unequal width PWM voltage, and supplies it to a motor 9 of a load.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an inverter device operated by the output of a converter section connected to a commercial power source.

2. Description of the Related Art In recent years, inverter devices that are operated by the output of a converter unit connected to a commercial power source have become widespread for, for example, controlling the speed of a motor.

Conventionally, this type of inverter device generally had a configuration as shown in FIG. The configuration will be explained below.

As shown in the figure, the converter section 1 includes a rectifying section 2 and a capacitor 3, and is connected to a commercial power source 5 via a noise removing section 4. The inverter 6 includes an inverter control section 7 and an inverter switching element section 8, and is operated by inputting the output of the converter section 1 to drive a motor 9 as a load.

To explain the operation in the above configuration, AC voltage from the commercial power supply 5 is converted to DC voltage by the converter section 1,
It is supplied to the inverter 6. In the inverter 6, an inverter control section 7 generates a PWM signal of equal width or unequal width, and drives an inverter switching element section 8 with the signal. As a result, the inverter switching element section 8 converts the DC voltage into a uniform-width or unequal-width PWM voltage and supplies it to the motor 9.

Problems to be Solved by the Invention In such conventional inverter devices, the higher the carrier frequency of the equal-width or unequal-width PWM voltage, the closer the waveform becomes to a sine wave (smoother), which improves load efficiency and equipment safety. However, as the carrier frequency increases, the motor 9, which is originally an insulating load, is desirable.
The impedance between the stator coil and the casing gradually decreases due to stray capacitance. On the other hand 1. One end of the commercial power source 5 is grounded, so if a person touches the casing of the motor 9 with their hand, current will leak through the person. Moreover, if the carrier frequency becomes higher than about 15 KHz, there is a problem that electric shock may occur.

In addition, since the DC power of the inverter 6 is obtained by rectifying the aftereffects from the commercial power supply 5 by the rectifier 2 and charging the capacitor 3 as shown in FIG. 4(a), the current waveform at that time is as shown in FIG. As shown in b), it contains many harmonic components,
This has the problem of affecting the commercial power supply 5 and other devices connected to it.

The present invention solves these conventional problems, and aims to provide a safe inverter device that does not cause electrical leakage even when using a high carrier frequency.

Means for Solving the Problems In order to achieve the above object, the present invention provides a means for solving the problems by making the converter section an input/output isolated type.

The present invention uses the above-mentioned problem-solving means to insulate the commercial power source and the output of the inverter by magnetic coupling, and to transmit the high frequency power through the ground in response to the high frequency power generated by chopping the DC power source with the inverter. The route can be eliminated, and even if the carrier frequency of the inverter is set to a high frequency and the insulation impedance decreases, the effects of electric shock on the human body can be eliminated.

Embodiment An embodiment of the present invention will be described with reference to FIG. Note that components having the same configuration as those of the conventional example are given the same reference numerals, and description thereof will be omitted.

As shown in the figure, the noise removal unit 10 is for preventing the noise generated in the converter unit 11 from leaking to the commercial power supply 5, and the converter unit 11 is of an input/output isolated type and is used to prevent the noise generated in the converter unit 11 from leaking to the commercial power supply 5. Electrically isolated from voltage.

Both ends of the commercial power supply 5 are connected to two terminals on the input side of the noise removal section 10, and two terminals on the output side of the noise removal section 10 are connected to two terminals on the input side of the rectification section 2. The output side of the rectifier section 2 is connected to the input side of the converter main circuit section 12. The input side of converter main circuit section 120 basically consists of a series circuit of primary coil 14 of switching transformer 13 and switching element 15, and further has a current value detection section 16 connected in series. In addition to the current detection resistor, the current value detection section 16 includes a combination of a coil and a magnetoresistive element, a combination of a light emitting diode and a light receiving element, and the like. A series circuit of a diode 18 and a capacitor 19 is connected to both ends of the secondary coil 170 of the switching transformer 13 . capacitor 19
Both ends are the output side of the converter section 11. The output side of the converter section 11 is connected to the input side of the inverter 6. The a power terminal of the inverter 6 is connected to the load motor 9 and supplies three-phase power.

The switching transformer 13, the switching element 15, the diode 18, and the capacitor 19 constitute a converter main circuit section 12. Further, converter main circuit section 12, rectifier section 2, and converter control section 20 constitute converter section 11.

The converter control unit 20 converts the voltage signal of the capacitor 19, which is the input voltage of the inverter 6, and the switching transformer 13.
The signal of the primary coil current value and the signal of the power supply voltage waveform of the commercial power supply 5 are used as input signals, and a control signal for controlling opening/closing of the switching element 15 is generated and sent. converter section 11
There are load current limit and other input signals for the input signal, but they will not be considered here. The converter control unit 20 includes a DC voltage setting unit 21 that sets the input DC voltage of the inverter 6, an inverter voltage detection unit 22 that detects the input DC voltage to the converter 6, and a signal of the inverter voltage detection unit 22 and a DC voltage setting unit. A deviation signal generating section 23 receives the signal from the deviation signal generating section 21 and outputs the error signal thereof, and a primary coil of the switching transformer 13 receives the output signal from the deviation signal generating section 23 and the current value detecting section 16. A conduction period control section 25 receives a signal of the flowing current value and sends a signal to the switching element control section 24, a voltage waveform detection section 26 detects the voltage waveform of the commercial power source 5, and the signal from the voltage waveform detection section 26 is input. and a voltage-responsive conduction start signal generator 27 that generates a signal indicating when to start conduction of the switching element 15 so that the input current from the commercial power supply 5 to the inverter 6 has a desired waveform; The switching element control section 24 receives the signal from the conduction period control section 25 and generates a switching element 150 control signal.

To explain the operation in the above configuration, the sine wave AC voltage supplied from the commercial power supply 5 is applied to the input terminal of the rectifier 20 via the noise removing unit 10, and as a result, the entire sine wave is applied to the output terminal of the rectifier 2. A rectified waveform is output. This output voltage is applied to a series circuit of the primary coil 14 of the switching transformer 13 and the switching element 15. Since the switching element 15 is opened and closed by a signal from the converter control unit 20, the energy stored in the primary coil 14 when it is turned on is
A capacitor 19 is connected through a diode 18 from the secondary coil 17 of the instantaneous switching transformer 13 that has been cut off.
supplied to If the frequency of this switching is high, the necessary energy is continuously supplied to the capacitor 19, and the necessary DC power is supplied to the inverter 6. However, the primary coil 14 and the secondary coil 1 of the switching transformer 13
7 is a magnetic coupling, so there is no electrical coupling between the two coils. Therefore, both terminals of this capacitor 19, that is, power supply terminals c and d of the inverter 6, are not coupled to the commercial power supply 5 (and are insulated from the ground). Based on the signal from the inverter control unit 7, the switching elements of the inverter switching element unit 8 are controlled to open and close, and the voltage is converted into a three-phase equal width or unequal width PWM voltage and supplied to the motor 9, which is the load. Even if the carrier frequency of the equal-width or unequal-width PWM voltage is high and the impedance between the energizing wire of the motor 9 and the case or holding part is small, there is a possibility that current may leak through a person to the ground and cause an electric shock. If the carrier frequency of the inverter 6 is selected to be 8K)Iz or higher, the abnormal noise generated from the motor 9 will be rapidly reduced. If the carrier frequency is set above an inaudible frequency around 20 KHz, for example, abnormal noise becomes completely inaudible.The inverter device according to the present invention is effective when the carrier frequency is set in such a high frequency region. Unequal-width PWM inverters have a wider frequency bandwidth than equal-width inverters, so they can be used in this inverter device.

Next, the operation of the converter section 11 will be explained. The DC voltage setting section 21 mainly sets a voltage value suitable for the inverter switching element section 8. On the other hand, the actual DC voltage is detected by the inverter voltage detection section 22 from terminals c and d.

A deviation signal between the set value of the DC voltage and the actual DC voltage value is detected by the deviation signal generating section 23. This deviation signal is compared with the current value of the pulse current flowing through the primary coil 14 of the switching transformer 13 detected by the resistance of the current value detection section 16 in the conduction period control section 25 to determine the conduction time of the pulse current. That is, when the load on the inverter 6 becomes heavy and the DC voltage is about to decrease, the conduction period control section 25 increases the pulse current conduction time (by doing so, suppressing the decrease in the DC voltage. The energization time of the pulse current is shortened (to suppress the increase in DC voltage. In this way, the DC voltage of the inverter 6 is kept constant. Furthermore, the voltage waveform of the commercial power supply 5 is detected by the voltage waveform detection unit 26. The opening/closing period of the switching element 15 is determined by the voltage responsive conduction start signal generating section 27 in accordance with the voltage value.

Therefore, if the characteristics of the voltage-responsive conduction start signal generator 27 are set so that the voltage and the period of the pulse current are compared, if the voltage waveform of the commercial power source 5 is a sine wave as shown in FIG. 2(a), the converter The pulse current shown in FIG. 2(C) generated by the action of the section 11 is smoothed by the noise removing section 10, and the input current from the commercial power supply 5 becomes a nearly sinusoidal wave as shown in FIG. 2(b), with high harmonics. The wave components are suppressed.

In the above explanation, the converter section 11 uses a blocking method that utilizes the flyback voltage generated when the current flowing through the coil is interrupted, but instead, a forward converter that uses a transformer action and a smoothing filter is used. The same effect can be obtained.

Effects of the Invention As is clear from the above embodiments, according to the present invention, since the converter section is of an input/output isolated type, electric shock to the human body through the load from the high frequency power supply generated by chopping DC voltage by the inverter is prevented. The possibility of this can be completely eliminated, and safety against high frequency earth leakage can be improved.

Furthermore, even if the voltage of the commercial power source is changed, the operation of the load is not affected and can operate normally. In other words, 10 identical devices
It can be used normally for both 0V voltage and 200V voltage.

Furthermore, harmonic components of the input current from the commercial power source can be suppressed, reducing the influence on the waveform of the power source and other devices connected to the power source.

In addition, since the DC power supply is connected to the commercial power supply via a switching transformer, external surges and noise from the commercial power supply cannot reach the DC power supply of the inverter (<, therefore, the switching elements connected to the DC power supply are also affected. Kotona (Naru)

Furthermore, since the DC voltage of the inverter hardly fluctuates, no margin is required for the switching elements of the inverter, and as a result, the inverter output can be improved or the inverter can be made smaller.

Further, the filter used to chop the commercial power supply voltage at high frequency may be a small filter for high frequency.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an inverter device according to an embodiment of the present invention,
Figures 2 (a) to (C) are voltage and current waveform diagrams of main parts of the same inverter, Figure 3 is a circuit diagram of a conventional inverter, and Figures 4 (a) and (b) are main parts of the same inverter. FIG. 5...Commercial power supply, 6...Inverter,
10... Noise removal section, 11... Converter section. f: Figure 52

Claims (1)

[Claims] An inverter device comprising: a converter section connected to a commercial power supply via a noise removal section; and an inverter into which the output of the converter section is input, the converter section being of an input-output isolated type.