POWER CONVERTING APPARATUS

Abstract

A power converting apparatus used as an active filter includes single-phase multiplex inverter unit for converting DC power into AC power and a control unit for controlling the single-phase multiplex inverter unit. The single-phase multiplex inverter unit includes a first single-phase inverter and a second single-phase inverter. The first single-phase inverter to which a maximum DC voltage is supplied outputs voltage pulses at a rate of one pulse per half the period of an AC voltage fed from an AC source. The control unit includes a pair of hysteresis comparator circuits for driving the second single-phase inverter such that an AC source current follows a sinusoidal target current.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing the configuration of a principal part of a power converting apparatus according to a first embodiment of the invention;

FIG. 2 is a diagram showing how the power converting apparatus of the first embodiment used as an active filter works;

FIG. 3 is a diagram showing output voltage waveforms of a single-phase multiplex inverter unit and first and second single-phase inverters of the first embodiment;

FIG. 4 is a diagram showing a waveform of a source current output from a power supply according to the first embodiment;

FIG. 5 is a diagram showing output pulse voltage generation timing of the first single-phase inverter of the first embodiment;

FIG. 6 is a diagram showing the waveform of the source current output from the power supply and on/off timing of the second single-phase inverter when an output voltage thereof is switched between 0 and a positive voltage according to the first embodiment;

FIG. 7 is a diagram showing the waveform of the source current i_s output from the power supply and on/off timing of the second single-phase inverter when the output voltage thereof is switched between 0 and a negative voltage according to the first embodiment;

FIG. 8 is a circuit diagram of an inverter driving circuit for controlling the power converting apparatus of the first embodiment;

FIG. 9 is a timing chart showing signals including gate driving signals for the first single-phase inverter of the first embodiment;

FIG. 10 is a timing chart showing signals including gate driving signals for the second single-phase inverter of the first embodiment;

FIG. 11 is a diagram showing waveforms of a source voltage and an output voltage of a first single-phase inverter according to a second embodiment of the invention;

FIG. 12 is a diagram showing output voltage waveforms of a single-phase multiplex inverter unit and the first and second single-phase inverters of the second embodiment;

FIG. 13 is a diagram showing waveforms of a source voltage and an output voltage of a first single-phase inverter according to a third embodiment of the invention;

FIG. 14 is a diagram showing output voltage waveforms of a single-phase multiplex inverter unit and the first and second single-phase inverters of the third embodiment;

FIG. 15 is a diagram showing a waveform of the source current output from a power supply and on/off timing of a second single-phase inverter when an output voltage thereof is switched between 0 and a positive or negative voltage according to a fourth embodiment;

FIG. 16 is a diagram showing the waveform of the source current output from the power supply and on/off timing of the second single-phase inverter when the output voltage thereof is switched between 0 and a negative or positive voltage according to the fourth embodiment;

FIG. 17 is a circuit diagram of an inverter driving circuit for controlling the power converting apparatus of the fourth embodiment;

FIG. 18 is a timing chart showing signals including gate driving signals for the second single-phase inverter of the fourth embodiment;

FIG. 19 is a circuit diagram showing the configuration of a principal part of a power converting apparatus according to a fifth embodiment of the invention;

FIG. 20 is a circuit diagram showing the configuration of a power converting apparatus according to a sixth embodiment of the invention; and

FIG. 21 is a circuit diagram showing the configuration of a power converting apparatus according to a seventh embodiment of the invention.

Claims

1. A power converting apparatus comprising: a single-phase multiplex converter connected to a load via a reactor to provide electric power to the load, said single-phase multiplex converter including a plurality of single-phase inverters connected in series at AC output sides of said single-phase inverters, wherein the single-phase inverters convert DC power fed from a DC power supply into AC power; anda control unit for controlling said single-phase multiplex converter to produce an output voltage having a quasi-sinusoidal waveform simulated by the sum of output voltages of respective single-phase inverters, said control unit including a current controller for regulating an output current of said single-phase multiplex converter to follow a target current which is determined in accordance with the load.

2. The power converting apparatus according to claim 1, wherein said plurality of single-phase inverters include a first single-phase inverter to which a maximum DC source voltage is supplied and at least one second single-phase inverter, said first single-phase inverter outputting voltage pulses at a rate of one pulse per half period of a reference AC voltage, andsaid current controller drives said second single-phase inverter such that the output current of said single-phase multiplex converter follows the target current.

3. The power converting apparatus according to claim 2, wherein a ratio V/Vm of a total DC source voltage V, supplied to said at least one second single-phase inverter, to the DC source voltage Vm, supplied to said first single-phase inverter, is within a range of 0.5 to 1.0.

4. The power converting apparatus according to claim 2, wherein said control unit includes a central processing unit having a mathematical processing capability and a control circuit including an analog circuit and a digital signal processing circuit,said central processing unit outputs a current signal corresponding to the target current, andsaid current controller regulates the output current by using said control circuit.

5. The power converting apparatus according to claim 4, wherein said control circuit of said control unit includes a hysteresis comparator circuit having an ordinary range of hysteresis, andsaid current controller of said control unit generates a control signal which is supplied to said second single-phase inverter so that the output current of said single-phase multiplex converter increases and decreases within the ordinary range of hysteresis.

6. The power converting apparatus according to claim 5, wherein said hysteresis comparator circuit has a marginal range of hysteresis encompassing the ordinary range of hysteresis and, if the output current of said single-phase multiplex converter goes out of the ordinary range of hysteresis, said control unit makes a correction so that the output current to said second single-phase inverter varies within the ordinary range of hysteresis.

7. The power converting apparatus according to claim 5, wherein the ordinary range of hysteresis of said hysteresis comparator circuit is determined based on amplitude of output voltage of said second single-phase inverter and a maximum switching frequency of switching devices constituting said second single-phase inverter.

8. The power converting apparatus according to claim 2, wherein said first single-phase inverter is controlled such that output voltage of said first single-phase inverter produces a stepwise waveform inscribed in each half-wave portion of the reference AC voltage and absolute value of the output voltage of said first single-phase inverter is equal to or smaller than absolute value of the reference AC voltage at all times.

9. The power converting apparatus according to claim 2, wherein said first single-phase inverter is controlled such that output voltage of said first single-phase inverter produces a stepwise waveform circumscribed about each half-wave portion of the reference AC voltage and absolute value of the output voltage of said first single-phase inverter is equal to or larger than absolute value of the reference AC voltage at all times.

10. The power converting apparatus according to claim 2, wherein the DC source voltage supplied to said first single-phase inverter is variable, andsaid control unit controllably drives said second single-phase inverter in such a manner that amounts of electric power supplied to and discharged from the DC power supply of said second single-phase inverter through said second single-phase inverter are balanced.

11. The power converting apparatus according to claim 2, wherein said plurality of single-phase inverters include said first single-phase inverter and only one second single-phase inverter.

12. The power converting apparatus according to claim 1, wherein said single-phase multiplex converter is connected between an AC power supply and the load in parallel with the load via the reactor, andsaid single-phase multiplex converter is used as an active filter which outputs a harmonic compensation current for canceling harmonics generated by the load.