JP4462390B2 - Inverter using current source - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power conversion device, and more particularly, to a so-called inverter device that converts a DC power source obtained by rectifying and smoothing an AC power source to pulse width modulation by high-speed switching using a semiconductor switch and converts the DC power into an alternating current of an arbitrary frequency.
[0002]
[Prior art]
The single-phase or three-phase inverter device converts a DC voltage into an AC voltage using a semiconductor switching element, and belongs to a so-called power conversion device. The power conversion is performed by intermittently switching a DC voltage serving as a source of conversion by periodic high-speed switching, and thus a pulsed voltage is applied to the output (load). By changing the pulse width (so-called PWM modulation), the output voltage can be changed from zero to the maximum value of the source voltage. When this method is used and the change in pulse width is compared with the switching period and changed to a low frequency sine wave with a sufficiently low period, the output voltage waveform is pulsed but effective at the low frequency time level. This is a so-called sinusoidal modulation voltage waveform inverter in which the voltage is a sinusoidal voltage. On the other hand, in applications where the switching speed cannot be increased (for example, applications using a large capacity thyristor), an equivalent current source is provided by providing an inductor between the DC power source and the switching element in addition to the same configuration as above. In addition, so-called current source inverters that enable power conversion even at low-speed switching by switching the current are applied.
[0003]
However, in order to realize a high-efficiency power converter, either voltage or current is output in pulses. These pulses cause harmful effects such as torque ripple and abnormal vibration on the load due to its harmonics and high frequency components. In addition, the dV / dt or dI / dt noise causes leakage current to the ground (which results in noise current to the power line) and unwanted radiation to the space, causing noise interference in various devices. This is one of the major social problems.
[0004]
As one means for avoiding these problems, conventionally, a filter including an inductor is inserted into the output of the inverter. As a requirement of the filter, it is necessary to remove the pulse frequency component of the output (referred to as a carrier frequency), but the frequency is generally several k to several tens of kHz, which is a relatively low frequency, and the output current Therefore, the L (inductor) and C (capacitor) of the filter components are usually very large, which is a level that cannot be ignored with respect to the inverter price. (Sometimes the price is equivalent or higher.)
A proposal for reducing the size of the filter is disclosed in Japanese Patent Publication No. 61-500198.
[0005]
[Problems to be solved by the invention]
In the conventional inverter described in Japanese Patent Laid-Open Publication No. 61-500198, as shown in FIG. 6, an internal current source is made constant so that an inductor and a capacitor required for an output filter can be obtained. It can be expected to reduce the value of. However, even in this proposal, three large inductors that do not saturate with the output current are required. If the value of the inductor is too small, a short circuit occurs between the phases through the capacitor of the filter. For example, when the switch Q4 is turned on in the figure, a short circuit occurs along the path of the switch Q4, the diode D6, and the capacitors C2 and C1. Therefore, in this proposal, there is a limit to reducing the inductors L1, L2, and L3 in the output filter.
[0006]
The first object of the present invention is to provide a low-cost linear voltage inverter using a current source that does not use an inductor for the inverter output as means for removing the voltage or current pulse of the carrier frequency component from the output of the inverter. It is to be.
[0007]
The second object of the present invention is to provide an inverter using a current source that makes it possible to obtain an output voltage higher than that of a DC power supply.
[0008]
[Means for Solving the Problems]
A voltage inverter using a current source according to the present invention includes a current source that generates a constant current pulse by an inductor connected to a DC power source and a first semiconductor switch, and N being a positive integer, N sets of second semiconductor switches that have a backflow prevention function for the negative electrode and can select them, and an output capacitor that connects the outputs of the second semiconductor switches to each other. The control means for comparing each of the output voltages with the corresponding N sets of command voltages and selecting the second semiconductor switch so that the output voltage is proportional to the command voltage and outputting the generated constant current pulse possess bets, the other terminal of the output capacitor having one terminal connected to respective N sets of said second semiconductor switch, to the negative or positive electrode side or an intermediate potential of the DC power source It is continued, the output capacitor integrating the output voltage.
[0009]
With the above configuration, the output voltage and current of the inverter can be simultaneously output as a continuous waveform (for example, a sine wave waveform).
[0011]
A peak value of the output voltage of the N sets of second semiconductor switches is detected and compared with an average value of the command voltage to adjust the current of the current source.
[0012]
The output capacitor includes a terminal voltage set higher than the voltage of the DC power supply.
[0013]
When the terminal voltage of the output capacitor is higher than a predetermined voltage, the current source output is circulated to the DC power source, and the output terminal voltage is controlled so as not to become abnormally high.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0015]
(First embodiment)
FIG. 1 is a principle diagram of an inverter using a current source according to a first embodiment of the present invention, and shows a case of three-phase output. Current source 1, backflow prevention elements (diodes or the like) 5 to 10, semiconductor switches 2, 3, 4 that can select positive or negative of current source 1, and capacitor 11 that integrates the outputs of semiconductor switches 2, 3, 4 , 12, 13 constitute a main circuit, and the semiconductor switch control circuits 14, 15, 16 detect the output voltage or output current of each semiconductor switch, and the target value Sig. u, Sig. v, Sig. The semiconductor switches 2, 3, and 4 are controlled so as to be similar to w. Since the output voltage is integrated by the capacitors 11 to 13, even if the semiconductor switches 2, 3, and 4 are not switched at high speed, the output voltage and current waveform are smooth. For example, the specified voltage, that is, the target value is sine. If it is a wave, the output voltage and current waveform are sine waves.
[0016]
Although the current source 1 is composed of a semiconductor switch and an inductor, since it is provided inside the inverter, a very high frequency switching (for example, several hundred kHz) can be applied, and a small inductor is also used for generating the current source. I can do it. Conventionally, in a normal inverter, in order to prevent short-circuiting of elements, a period in which two upper and lower semiconductor elements are paused, called dead time, is required, and high-speed switching cannot be performed. In the present embodiment, since an internal current source is used, dead time is unnecessary, and control becomes easy. Further, since the capacitors 11, 12, and 13 attached to the output side for integrating the current can be applied for high frequency, there is an advantage that a very small capacitor can be applied.
[0017]
For load fluctuations, an average voltage / current detection circuit 19 is provided to detect whether the output voltage or current has reached a target magnitude, and the current source control circuit 18 determines the current value of the current source 1. By controlling, it is possible to cope with the fluctuation of the load 17.
[0018]
According to the present invention, the output voltage and current of the inverter can be simultaneously output as a continuous waveform (for example, a sine wave waveform).
[0019]
(Example)
FIG. 2 shows a block diagram of an embodiment of the inverter of FIG. 1 using a current source .
[0020]
In this embodiment, in FIG. 2, the semiconductor switches 20 and 21 and the inductor 22 constitute a current source, a DC voltage is obtained by the power supply rectifier diode 38 and the capacitor 39, and then the inductors are switched simultaneously by the semiconductor switches 20 and 21. A current is generated in 22 and supplied to the semiconductor bridge 27 through the diodes 24 and 25 when the semiconductor switch is turned off. Since it is the energy of the inductor 22, a current source action occurs. The semiconductor bridge 27 includes semiconductor switches 32-37 and diodes 40-45. The semiconductor bridge 27 charges the same current to the output capacitors 11 to 13 by turning on and off each semiconductor switch. By controlling the capacitor voltage to a predetermined voltage, an output waveform with greatly reduced switching noise can be obtained. That is, the switch control unit 31 detects the terminal voltages (peak values of the output voltages) of the capacitors 11, 12, and 13, and the U phase waveform command unit 28, the V phase waveform command unit 29, and the W phase waveform command unit, respectively. The command output by 30 is controlled so that the error from the value is within a predetermined range. When the load 17 is connected to the U, V, and W terminals, the output voltage / current is determined by the terminal voltage of the capacitor, so the dV / dt and dI / dt noise output to the outside is extremely Less.
[0021]
When a thyristor is used for the semiconductor switch of the semiconductor bridge 27, backflow can be prevented, and a backflow preventing diode is not necessary. When an IGBT or MOSFET is used for the semiconductor switch, the switch element itself cannot prevent backflow due to a parasitic diode or insufficient withstand voltage. Therefore, as shown in the semiconductor bridge 27 ′ in FIG. 4, backflow preventing diodes 52 to 57 are required.
[0022]
In FIG. 2, the terminal on the opposite side of the output capacitor 11, 12, 13 from the semiconductor bridge 27 side is connected to the negative electrode of the DC power source as indicated by the broken line 48. Sometimes connected.
[0023]
Next, the operation will be described with reference to FIG.
[0024]
First, a single-phase or three-phase power supply is rectified by the power supply rectifier diode 38 and smoothed by the capacitor 39. Now, when the semiconductor switches 20 and 21 are simultaneously turned on, a current is generated in the inductor 22. When the semiconductor switches 20 and 21 are turned off at this time, the current in the inductor 22 circulates to the capacitor 39 via the diodes 23, 24, 25 and 26. When the semiconductor switches 20 and 21 are repeatedly turned on and off at high frequencies ((1) in FIG. 3), the current value of the inductor 22 can be maintained in a pulse shape or a constant value. (FIG. 3-2) When the capacitor 11 is not charged, when the semiconductor switch 32 is turned on (FIG. 3-3), the voltage at the U terminal is lower than the positive side of the inductor 22. The current of the inductor 22 is not circulated to the capacitor 39 but is charged to the capacitor 11 ((4) in FIG. 3). When the switch 32 is turned off and the semiconductor switch 33 is turned on ((6) in FIG. 3), the charge of the capacitor 11 flows to the inductor 22 and the voltage at the terminal U can be reduced (FIG. 3- (). 7 ▼). By repeating this, the voltage of the capacitor 11, that is, the terminal U can be set to a predetermined voltage. (For example, when the on / off ratio of the semiconductor switches 32 and 34 is changed linearly, the terminal voltage of U also becomes a linear waveform.) These are also performed by charging / discharging the capacitor 11 (FIG. 3). Therefore, if the oscillation frequency of the current source is sufficiently high, a smooth voltage waveform is obtained. For this reason, the current to the load also has a smooth waveform (FIG. 3-12).
[0025]
The inverter using the current source of this embodiment has a smooth output voltage and current waveform, so that it is not necessary to use an expensive filter on the output side in order to remove the pulse component.
[0026]
(Second embodiment)
FIG. 5 shows a block diagram of an inverter using a current source according to the second embodiment of the present invention.
[0027]
The inverter using the current source of FIG. 5 has the same configuration as FIG. 2 except that the semiconductor switch 46 and the control circuit 47 are provided instead of the diode 23 in the linear voltage inverter of FIG. Function. Here, the control circuit 47 controls ON / OFF of the semiconductor switch 46.
[0028]
The inverter using the current source of FIG. 2 can obtain an output waveform with greatly reduced switching noise by controlling the terminal voltage of the output capacitors 11 to 13 to a predetermined voltage. However, when the output voltage becomes higher than the DC power supply voltage (rectified DC voltage), the internal current source is not output to the output but is circulated to the DC power supply. Since the current source generates an abnormal voltage when its load becomes high impedance, recirculation to the DC power supply is a means for avoiding this, but as a result, the output voltage is also made higher than the DC voltage. I couldn't.
[0029]
In the inverter using the current source of FIG. 5 , in order to make it possible to obtain an output voltage higher than the DC power supply, when the output voltage is lower than a predetermined voltage, the current source is prevented from circulating to the power supply. The semiconductor switch 46 is provided, and the control circuit 47 turns the semiconductor switch 46 on and off according to the value of the output voltage.
[0030]
If the energy of the inductor current is larger than the energy supplied to the load 17 connected to U, V, W, and the output switch (semiconductor switch in the semiconductor bridge 27) selects the positive current source, the output The output voltage integrated into the capacitors 11, 12, and 13 increases. Since this value is theoretically unlimited, it can be made larger than the power supply voltage. If it becomes too high, the switch element is destroyed. When the value becomes a certain value, the semiconductor switch 46 circulates the current source to the power source and cuts the supply to the output. In order to control this switch 46, the voltage of the output capacitor is monitored by the control circuit 47, and when it becomes larger than a certain value, the switch 46 is turned on, and vice versa.
[0031]
The inverter using the current source of this embodiment is a low-noise inverter and can output a voltage higher than that of the power supply. Therefore, for example, the low-noise inverter can be applied to a double voltage application. In addition, since a stable output voltage can be obtained in areas where power supply is unstable, the motor design is simplified, and as a result, the inverter can also be designed optimally, for example, with a low current, resulting in low cost and low loss. Contribute. In the conventional inverter, an output higher than the input DC voltage could not be obtained. However, in the present invention, for example, a smoothing capacitor for input rectification uses 100V, and 200V can be obtained as an output.
[0032]
【The invention's effect】
Although the present invention has, as described, by comparing the output voltage of the N sets of switches and command voltage determines the selection direction of the switch by integrating a capacitor, the pulse waveform is divided from the output, the inverter A low-cost inverter using a current source can be realized without using an expensive filter to eliminate the output voltage and current pulse components. Unnecessary power ripple to the load and noise emission to the outside The adverse effect of the inverter such as the above can be greatly reduced, and since there is a current source inside, the switching element does not need the function of preventing the upper and lower short-circuits, and has the effect of greatly improving the reliability against malfunction or the like.
[0033]
Furthermore, by setting the terminal voltage of the output capacitor higher than the voltage of the DC power supply, it becomes possible to apply a low-noise inverter for voltage doubler applications and obtain a stable output voltage in areas where power supply is unstable. As a result, the motor design is simplified, and as a result, the inverter can be optimally designed to reduce the current, which contributes to low cost and low loss.
[Brief description of the drawings]
FIG. 1 is a principle diagram of a linear voltage inverter according to a first embodiment of the present invention.
FIG. 2 is a block diagram of an embodiment of an inverter using a current source in FIG. 1;
FIG. 3 is a waveform diagram of each part of an inverter using a current source in FIG. 2;
FIG. 4 is a block diagram of another embodiment of the semiconductor bridge 27 of FIG.
FIG. 5 is a block diagram of an inverter using a current source according to a second embodiment of the present invention.
FIG. 6 is a block diagram of a conventional example of an inverter using a current source .
[Explanation of symbols]
1 Current source 2-4 Semiconductor switch 5-10 Backflow prevention element (diode)
11-13 Output capacitor 14-16 Semiconductor switch control circuit 17 Load 18 Current source control circuit 19 Output voltage detection circuit 20, 21 Semiconductor switch for current source generation 22 Inductor for current source 23-26, 40-45 Diode 27, 27 ′ Semiconductor bridge 28-30 Waveform command unit 31 Switch control unit 32-37, 46 Semiconductor switch (transistor)
38 Power supply rectifier diode 39 Smoothing capacitor 47 Control circuit 48 Broken line

Claims (4)

In the so-called inverter device that converts the DC power source obtained by rectifying and smoothing the AC power source to pulse width modulation by high-speed switching by a semiconductor switch, and converting it to AC of an arbitrary frequency,
A current source for generating a constant current pulse by an inductor connected to the DC power source and a first semiconductor switch;
N sets of second semiconductor switches that have a backflow prevention function with respect to the positive electrode or the negative electrode of the current source and can select them, where N is a positive integer,
An output capacitor for connecting the outputs of the second semiconductor switch to each other is provided, each output voltage of the second semiconductor switch is compared with a corresponding N sets of command voltages, and the output voltage is compared with the command voltage. Control means for selecting the second semiconductor switch to output the generated constant current pulse so as to be proportional;
Have,
The other terminal of the output capacitor having one terminal connected to each of the N sets of second semiconductor switches is connected to the negative electrode side, the positive electrode side, or the intermediate potential of the DC power supply,
An inverter using a current source, wherein the output capacitor integrates the output voltage . Detecting a peak value of the N sets of the output voltage of the second semiconductor switch, compared with the average value of the command voltage adjusting the current of the current source, with a current source according to claim 1 Symbol placement inverter. Inverter the terminal voltage of the output capacitor, said set higher than the voltage of the DC power source, using a current source according to claim 1 or 2 wherein. When the terminal voltage of the output capacitor is higher than a predetermined voltage, the current source output refluxed to the DC power source, the output terminal voltage is controlled not abnormally high, using a current source according to claim 3, wherein Inverter.

Images