JPH0974771A - Inverter apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inverter apparatus in which a DC component generated in an AC output is suppressed so as to be corrected, in a feed-forward manner, by the difference between the voltage in the neutral point of DC power supplies and that across their positive pole and their negative pole. SOLUTION: An inverter apparatus is provided with DC power supplies 1, 2 comprising a neutral point, with half-bridge inverters 3, 4 composed of a series circuit of two switching elements connected across the positive pole and the negative pole of the DC power supplies, with PWM control means 14a, 14b by which the half-bridge inverters are pulse-width-modulated and controlled on the basis of a control signal and with a correction means 17 which outputs a correction signal on the basis of the voltage in the neutral point of the DC power supplies and that across their positive pole and their negative pole. Then, an AC voltage is output across the neutral point and the series connection point of the two switching elements, a control signal is corrected by the correction signal, and a DC component which is contained in the AC voltage is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for converting an unstable DC voltage such as solar power generation into an AC voltage.

[0002]

2. Description of the Related Art An inverter device for converting a DC voltage into an AC voltage is shown in FIG. 4 (a). In this device, DC power supplies 1 and 2 are connected in series, and this connection point is connected to the neutral point of the system power supply as the neutral point of the DC voltage, and the voltage E1 and E2 of the DC power supplies 1 and 2 are added. Half-bridge inverters 3 and 4 consisting of IGBTs 3a, 3b and IGBTs 4a, 4b are connected between the positive and negative sides of the voltage, and the output terminals of each half-bridge inverter 3 and 4 are respectively connected via current detectors 5a, 5b and reactors 6a, 6b. It is connected to the single-phase 3-wire system power supplies 8a and 8b. The capacitors 7a and 7b are connected in parallel with the system power supplies 8a and 8b as filters.

The host controller 10 outputs a signal Im which determines the magnitude of the current reference, and the current reference circuit 11 detects the signal Im and the system power supply 8a or 8b detected via the transformer 9.
An AC current reference I ^* having the same phase as the voltage of the system power supply is output based on the voltage detection signal va. Inverting amplifier 12 outputs a current reference I ^{* 'having} a phase difference of 180 ° relative to I ^* inverts the polarity of the I ^*. These current references I ^* and I ^{* '} are input to current control amplifiers 13a and 13b, respectively, and are detected via current detectors 5a and 5b.
The output current detection values Ia and Ib of 3 and 4 are compared, and the current control signals Sa and Sb are output so that the respective errors are zero. The PWM control circuits 14a and 14b are triangular wave generators.
The pulse width modulation signal Sc of the triangular wave output from 15 and the current control signals Sa and Sb are respectively compared and the PWM signal Pa
, Pb are output, and the IGBTs 3a, 3b and the IGBTs 4a, 4b of the half-bridge inverters 3 and 4 are switching-controlled to control the output current detection values Ia, Ib to match the current references I ^* and I ^{* '} . By this control, DC power supply
The DC powers 1 and 2 are converted into AC currents having a phase difference of 180 ° and supplied to the system power supplies 8a and 8b.

[0004]

However, the above-mentioned conventional device has a problem that a DC component is generated in the inverter output when the voltages of the DC power supplies 1 and 2 and the values of E1 and E2 are different. For example, when a solar cell is used as a DC power source, when a part of the solar cell is in the shade, a state of E1 ≠ E2 occurs. FIG. 4 (b) shows the current control signal Sa or S
Half-bridge inverter 3 when b is at zero level
Or, it shows the PWM controlled voltage waveform output from 4. When (1) is E1 = E2, (2) is E1 ≠ E
The case of 2 is shown. In the case of (1), the PWM signal has the same on and off periods, the positive side IGBTs 3a, 4a and the negative side IGBTs 3b, 4b are on for the same period of time, and the average value of the output voltage becomes zero and the DC component Does not occur. In the case of (2), the average value of the output voltage (the figure shows the case of E1 = 2E2) does not become zero (shifts to the E1 side), and the DC component Ed is generated. If this DC component flows into the AC system, it may adversely affect the transformer by saturating it and causing waveform distortion or overheating.

The present invention has been made to solve the above problems, and its purpose is to generate an AC output of a half-bridge inverter due to a difference between a neutral point of a DC power source and a voltage between a positive electrode and a negative electrode. An object of the present invention is to provide an inverter device in which a direct current component is corrected in a feedforward manner and suppressed so that the direct current component does not flow out to a load side.

[0006]

SUMMARY OF THE INVENTION An inverter device of the present invention includes a DC power source having a neutral point and a half-bridge inverter composed of a series circuit of two switch elements connected between the positive and negative electrodes of the DC power source. , PWM for controlling pulse width modulation of the half bridge inverter based on a control signal
A control means and a correction means for outputting a correction signal based on a voltage between a neutral point of the DC power source and a positive electrode and a negative electrode are provided, and between the neutral point and a series connection point of two switch elements. The AC voltage is output to and the control signal is corrected by the correction signal to suppress the DC component included in the AC voltage. (Claim 1) Further, the PWM control means compares the control signal with the pulse width modulation signal formed of a triangular wave having a peak value Em to generate a PWM signal, and the correction means generates a neutral point of the DC power supply. The voltage between the positive and negative electrodes is E1 and E2, and (E1
-E2) / (E1 + E2) * Em is calculated to generate the correction signal, and the correction signal is added to the control signal for feedforward correction. (Claim 2) Further, a current control system for connecting the AC voltage output from the half bridge inverter to the AC system and comparing the current reference with the output current of the half bridge inverter to output the control signal is provided. This current control system is provided with an integral control element to control the DC component to zero. (Claim 3) Further, two sets of the half bridge inverters are provided, two sets of the current control systems are provided, and the AC system is a single-phase three-phase system.
Connected as a line type, connecting the neutral point of the DC power source and the neutral point of the single-phase three-wire type, and supplying AC power from each of the two sets of half bridge inverters. (Claim 4) Further, based on a control signal, PWM control means for performing pulse width modulation control of the two sets of half-bridge inverters as full-bridge inverters, an AC voltage reference, and an AC output voltage output from the full-bridge inverters. And second correction means for detecting the DC component of the AC current of the output of the full-bridge inverter and correcting the control signal so that this DC component becomes zero. It is operated as an independent power source by disconnecting from the AC system. (Claim 5)

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment corresponding to claims 1 to 4 of an inverter device according to the present invention. In FIG.
16a and 16b are voltage detectors that detect the voltage of DC power supplies 1 and 2,
Reference numeral 17 is an arithmetic circuit that generates a correction signal based on the detected voltage value. Others are the same as the conventional one (FIG. 4 (a)), the same reference numerals are given and the description thereof is omitted. The arithmetic circuit 17 outputs the correction signal C based on the voltages E1 and E2 of the DC power supplies 1 and 2 detected via the voltage detectors 16a and 16b, and outputs the PW
The current control signals Sa and Sb are input to the M control circuits 14a and 14b.
Is corrected in a feedforward manner.

In the above structure, the pulse width modulation signal Sc output from the triangular wave generating circuit 15 is given as a triangular wave signal of the modulation period T0 in which the amplitude changes from the zero level to the positive or negative at the peak value Em, and the PWM control circuit 14a operates. Current control signal S
The pulse width modulation of the output voltage V1 of the half bridge inverter 3 is performed as shown in FIG. 2 by changing the PWM signal Pa at the time when a and the pulse width modulation signal Sc cross. In this case, when the value of the current control signal Sa is ei, the period t1 when the output voltage V1 becomes the positive voltage E1 and the period t2 when the output voltage V1 becomes the negative voltage E2 are given by the equations (1) and (2).

[0009]

## EQU1 ## t1 = (T0 / 2) (1 + ei / Em) (1) t2 = (T0 / 2) (1-ei / Em) (2) Further, the output voltage V1 in the modulation period T0 is expressed by the equation (3). It can be expressed by Eq. (4) by substituting Eqs. (1) and (2) for transformation.

[0010]

[Equation 2] V1 = E1 * t1−E2 * t2 (3) V1 = (T0 / 2) (E1-E2) + (T0 / 2) (ei / Em) (E1 + E2) (4) Current control signal Since Sb is given in the opposite polarity of the current control signal Sa, the output voltage V of the half-bridge inverter 4
In the case of 2, the second term of the equation (4) has a reverse polarity, and the output voltage has a reverse polarity of V1.

The first term of the equation (4) is a DC component generated by the difference between the voltages E1 and E2 of the DC power sources 1 and 2 regardless of the current control signal, and the second term of the equation (4) is the current. It is a voltage output in proportion to the control signal ei. Therefore, the current control signal is given as an alternating current to output an alternating voltage, and when a difference occurs between the voltages E1 and E2 of the direct current power sources 1 and 2, the direct current component is superimposed and output.

However, in the present invention, when a difference occurs between the voltages E1 and E2 of the DC power supplies 1 and 2, the arithmetic circuit 17 outputs the correction signal C for canceling the DC component shown in the equation (5), and the current control signal. It is added to Sa and Sb and is corrected in a feedforward manner.

[0013]

## EQU3 ## C = (-E1 + E2) (E1 + E2) .Em (5) That is, by adding C of equation (5) to ei of equation (4), the first term of equation (4) becomes They are canceled and the direct current component is canceled, and the output voltages V1 and V of the half bridge inverters 3 and 4 are canceled.
The DC component of 2 is suppressed. Since the peak value Em of the pulse width modulated signal Sc is constant and does not change, the correction signal C is equal to E1 and E.
It can be calculated easily from 2.

The current control amplifiers 13a and 13b are of the proportional-integral (PI) type, and the current control signal Sa output from them is output.
, Sb are adjusted so that the DC component is zero.
According to the present embodiment, when a difference occurs between the voltages of the DC power supplies 1 and 2, the control signal is corrected in a feedforward manner, so that the DC component of the output voltage of the half bridge inverter can be reduced at high speed.

FIG. 3 shows an embodiment corresponding to claim 5 of the inverter device of the present invention. This embodiment further shows an additional element for functioning as an emergency independent power source when the system power source fails due to a disaster or the like.

In FIG. 3, a half bridge inverter
3 and 4 act as a full bridge inverter without using the neutral point of the single-phase two-wire type output as an output, and supply an AC voltage to the load 19. A voltage reference circuit 20 outputs an AC voltage reference V ^* . Reference numeral 21 is an amplifier for voltage control, which is a voltage reference V
^The control signal Sa is output by comparing ^* with the output voltage of the full bridge inverter detected via the transformer 9. twenty two
Is a PWM control circuit, which controls the control signal Sa and the triangular wave generation circuit 15
PWM signal P by comparing with the modulation signal Sc output from
It outputs a and Pb and controls the half bridge inverters 3 and 4 to perform switching as a full bridge inverter. A DC component detection circuit 23 detects a DC component Id from the output current Ia of the full-bridge inverter detected via the current detector 5a. A DC amplifier 24 amplifies the DC component Id to generate a correction signal C and corrects the control signal Sa.

In the above structure, the half-bridge inverters 3 and 4 operate as full-bridge inverters by the PWM signals Pa and Pb output from the PWM control circuit 22, and the DC voltage of the sum of the voltages of the DC power sources 1 and 2 is used as the voltage reference. V ^*
Is supplied to the load 19 after being converted into an AC voltage according to the above. In this case, when a direct current component is generated in the alternating current output current, the direct current component detecting circuit 23 detects the direct current component Id, the direct current amplifier 24 outputs the correction signal C, and the direct current component Id becomes zero so that the control signal Sa becomes zero. to correct.

According to this embodiment, when the AC power is output from the DC power supplies 1 and 2 and the system is operated in an interconnected manner, the single-phase two-wire system is used when the system power fails due to a disaster or the like. The neutral point of the formula output is not used as an output, but it works as a full-bridge inverter, and it functions as an emergency independent power supply.
An AC voltage can be supplied to the load 19, and in this case as well, the DC component contained in the AC voltage can be reduced.

The DC amplifier 24 may be omitted, and the output Id of the DC component detecting circuit 23 may be input to the amplifier 21 for voltage control to correct the voltage reference V ^* . In this case, the amplification factor for the direct current of the amplifier 11 is limited to prevent control abnormality due to overcompensation at light load.

[0020]

According to the present invention, in the case of operating as a half-bridge inverter by being connected to the system, a correction signal is calculated based on the neutral point of the DC power source and the voltage between the positive electrode and the negative electrode, and the control signal is obtained. By canceling the direct current component of the AC output by correcting, and operating as a full-bridge inverter by disconnecting it from the system and using it as an independent power supply, a correction signal is generated based on the DC component contained in the AC output current, and the control signal is generated. It is possible to provide a safe inverter device against a load by canceling the DC component of the AC output and suppressing the outflow of the DC component by correcting the above.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment corresponding to claims 1 to 4 of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the embodiment.

FIG. 3 is a configuration diagram of essential parts of an embodiment corresponding to claim 5 of the present invention.

4A is a configuration diagram of a conventional device, and FIG. 4B is a waveform diagram for explaining a problem of the conventional device.

[Explanation of symbols]

1,2 ... DC power supply 3,4 ... Half bridge inverter 3a, 3b, 4a, 4b ... Switch element 5a, 5b ... Current detector 6a, 6b ... Reactor 7a, 7b ... Capacitor 8a, 8b ... Grid power supply 9 ... Transformer 10 ... Host controller 11 ... Current reference circuit 12 ... Inversion amplifier 13a, 13b ... Current control amplifier 14a, 14b ... PWM control circuit 15 ... Triangle wave generation circuit 16a, 16b ... Voltage detector 17 ... Arithmetic circuit 20 ... Voltage reference circuit 21 ... Voltage control amplifier 22 ... PWM control circuit 23 ... DC component detection circuit 23 ... DC amplifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Kimoto No. 1 Toshiba-cho, Fuchu-shi, Tokyo Toshiba Corporation Fuchu factory

Claims (5)

[Claims] 1. A half-bridge inverter comprising a series circuit of a DC power supply having a neutral point and two switch elements connected between the positive and negative poles of the DC power supply, and the half-bridge inverter based on a control signal. PWM control means for pulse width modulation control and correction means for outputting a correction signal based on the voltage between the neutral point of the DC power supply and the positive and negative electrodes are provided, and the neutral point and the two switch elements are provided. An inverter device which outputs an AC voltage between a series connection point and corrects the control signal by the correction signal to suppress a DC component contained in the AC voltage. 2. The inverter device according to claim 1, wherein the PWM control means generates a PWM signal by comparing a pulse width modulation signal composed of a triangular wave having a peak value Em with the control signal, and the correction means , The voltages between the neutral point of the DC power source and the positive and negative electrodes are E1 and E2, and (E1 −
An inverter device characterized in that E2) / (E1 + E2) * Em is calculated to generate the correction signal, which is added to the control signal to perform feedforward correction. 3. The inverter device according to claim 1, wherein the AC voltage output from the half-bridge inverter is connected to an AC system, and the control is performed by comparing a current reference with an output current of the half-bridge inverter. An inverter device comprising a current control system for outputting a signal, the current control system including an integral control element. 4. The inverter device according to claim 3, wherein the half bridge inverter is provided in two sets, the current control system is provided in two sets, and the AC system is a single-phase three-phase system.
An inverter device characterized by being interconnected as a wire system. 5. The inverter device according to claim 4, wherein PWM control means for performing pulse width modulation control of the two sets of half bridge inverters as full bridge inverters based on a control signal, an AC voltage reference and the full bridge. Voltage control means for comparing the AC output voltage output from the inverter and outputting the control signal, and detecting the DC component of the AC current of the full bridge inverter output,
An inverter device comprising a second correction means for correcting the control signal so that the DC component becomes zero, and operating as an independent power source separated from the AC system.