JP2010028977A - Power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable power supply unit capable of solving the distortion of an inverter output voltage without increasing control load, irrespective of carrier signal frequencies. <P>SOLUTION: When a switching PWM signal for a single-phase inverter 20 is generated by comparison in voltage between a carrier signal and a command signal, the power supply unit applies a correction bias V3 to each of a positive level voltage of the command signal and a negative level voltage thereof. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a converter that converts a level of a DC voltage by switching, and a power supply device that includes an inverter that converts an output of the converter to AC by switching.

  As a power supply device that takes out the generated power of the solar cell (PV), boosts it (level conversion) with a converter, converts the boosted DC voltage into AC by the inverter, and supplies it to the load, the inverter is connected to the commercial AC power system. Some have a grid-connected operation function that operates in a system and a self-sustained operation function that operates the inverter regardless of the commercial AC power supply system (for example, Patent Document 1).

  In this power supply device, during independent operation, a switching PWM signal for the inverter is generated by voltage comparison between the carrier signal (triangular wave signal voltage) and the sine wave command signal Vrms_ST_REF (effective value). The switching element of the inverter is turned on / off by the generated PWM signal, and an AC voltage Vinv_ad_rms (effective value) of a level corresponding to the on / off duty is output from the inverter. Furthermore, a difference ΔVrms between the actually output AC voltage Vinv_ad_rms and the voltage of the command signal Vrms_ST_REF is obtained, and a correction voltage Vrms_refpi obtained by PI control of the voltage difference ΔVrms is added to the command signal Vrms_ST_REF. With this addition, a new command signal Vac_Ref shown in FIG. 10 is obtained, and by generating a PWM signal based on the command signal Vac_Ref, a sine wave voltage with small distortion is output from the inverter.

here,

It is.

Ksoft is a soft start coefficient from “0” to “1” for starting the software when the inverter is started. ωt = ωt + Δωt. Δωt = 2πHz / fc. Hz is the frequency of the commercial AC power system (50/60 Hz). fc is a carrier signal frequency for generating an inverter PWM signal.
JP 2001-37246 A

  In the case of the power supply device described above, the effective level of the command signal Vac_Ref decreases near the zero cross of the inverter output voltage, so that distortion occurs near the zero cross of the AC voltage Vinv_ad_rms output from the inverter, as shown in FIG. There's a problem. In general, the output voltage distortion rate in a resistive load is designed to be 5% or less in a self-sustained operation, but the above power supply device has no margin near the zero cross.

  Further, as described above, if the difference ΔVrms between the actually output AC voltage Vinv_ad_rms and the voltage of the command signal Vrms_ST_REF is fed back to the command signal, the distortion reduction effect is small unless the carrier signal frequency is relatively high. There is a problem that the control load becomes heavy.

  The present invention has been made in consideration of the above circumstances, and its purpose is to provide a highly reliable power source that can eliminate distortion of the inverter output voltage without increasing the control load regardless of the carrier signal frequency. Is to provide a device.

  The power supply device of the invention according to claim 1 is a converter for converting a DC voltage level by switching, an inverter for converting an output of the converter to AC by switching, a PWM signal for switching for the converter and the inverter, a carrier signal and a command signal The control means generates a switching PWM signal for the inverter by generating a voltage comparison between the carrier signal and the command signal. A correction bias is added to each of the positive level voltage and the negative level voltage.

  According to the power supply device of the present invention, the distortion of the inverter output voltage can be eliminated irrespective of the carrier signal frequency and without increasing the control load, and the reliability is improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a solar cell (PV), which outputs a DC voltage by receiving light. This output voltage is applied to the capacitors 3 and 4 via the switch 2, and the voltage of the capacitors 3 and 4 is supplied to a converter, for example, a boost chopper 5. The step-up chopper 5 includes a DC reactor 6, a switching element such as an IGBT 7, a backflow prevention diode 8, and a capacitor 9. The input voltage (DC voltage) is boosted to a predetermined level (level conversion).

  The output voltage of the boost chopper 5 is supplied to the single-phase inverter 20. The single-phase inverter 20 includes a full bridge circuit composed of four switching elements, for example, IGBTs 21, 22, 23, and 24, a freewheeling diode D connected in reverse parallel to each of the IGBTs, and a gate drive circuit 31 connected to the gate of each IGBT. , 32, 33, and 34, and each IGBT is turned on and off (switching) in accordance with the PWM signal supplied from the control unit 60, thereby converting the input voltage (DC voltage) into an AC voltage having a predetermined frequency. .

  A series circuit of capacitors 45 and 46 is connected to the output terminal of the single-phase inverter 20 via a noise reducing LC filter including an AC reactor 41 and a capacitor 42 and further via relay contacts 43 and 44. A commercial AC power supply system (single-phase AC200V) 47 is connected to the series circuit of the capacitors 45 and 46. Further, a capacitor 49 is connected to the output terminal of the single-phase inverter 20 through a noise reducing LC filter including the AC reactor 41 and the capacitor 42 and further via a relay contact 48. The voltage generated in the capacitor 49 is output to the outside as the voltage of the AC power supply (single-phase AC100V) 50 for independent operation. The relay contacts 43, 44 and 48 are controlled by the control unit 60.

  The control unit 60 is used to generate a PWM signal for the MCU 61 which is the center of control, a nonvolatile memory (EEPROM) 62 for data storage, an A / D converter 63 for voltage / current detection, the boost chopper 5 and the single-phase inverter 20. A PWM generator 64 and an A / D converter 65 for voltage / current detection are included. The detection lines for the voltage of the solar cell 1 (referred to as PV voltage), the current of the solar cell 1 (referred to as PV current), the ground fault of the PV current, and the output voltage (referred to as boosted voltage) of the boost chopper 5 are A / D. Connected to converter 63, output voltage of single-phase inverter 20 (referred to as inverter output voltage), output current of single-phase inverter 20 (referred to as inverter output current), DC component of inverter output current, commercial AC power supply system (single-phase AC 200V) Each of the voltage (and frequency) detection lines is connected to the A / D converter 65.

The MCU 61 monitors the state of each part through each detection line, and controls the generation of the PWM signal by the PWM generator 64 according to the monitoring result, and has the following (1) to (3) as main functions. .
(1) Control means for system interconnection operation that turns on the relay contacts 43 and 44 and turns off the relay contact 48 to operate the single-phase inverter 20 in conjunction with the commercial AC power supply system 47.

  (2) Self-sustained operation control means for turning off the relay contacts 43 and 44 and turning on the relay contact 48 to operate the single-phase inverter 20 irrespective of the commercial AC power supply system 47.

  (3) A PWM signal for switching for the boost chopper 5 and the single-phase inverter 20 is generated by voltage comparison between a carrier signal (for example, a triangular wave signal voltage) and a command signal, and in particular, a PWM signal for the single-phase inverter 20 during independent operation. Control means for adding a correction bias to each of the positive level voltage and the negative level voltage of the command signal when generating.

The operation will be described.
First, the relay contact 44 is turned on to monitor the voltage and frequency of the commercial AC power supply system 47 and the PV voltage. When a certain standby time (for example, about 300 seconds) elapses when the system voltage / frequency and PV voltage are below the specified values, the relay contact 43 is turned on, and the single-phase inverter 20 is connected to the commercial AC power system 47. A grid-connected operation is started. During the standby time until the start, the frequency of the system voltage (referred to as system frequency) is recognized and stored in the nonvolatile memory 62.

  A switching PWM signal for the single-phase inverter 20 is generated by voltage comparison between the carrier signal (triangular wave signal voltage) and the sine wave command signal Vac_Ref (effective value). The sine wave command signal Vac_Ref is set to the same frequency as the system frequency stored in the nonvolatile memory 62. Then, the switching element of the single-phase inverter 20 is turned on / off by the generated PWM signal, and the AC voltage Vinv_ad_rms (effective value) having a level corresponding to the on / off duty is output from the single-phase inverter 20.

  In this grid-connected operation, when power is consumed by the load on the commercial AC power supply system 47 side and the output voltage of the boost chopper 5 drops, the on / off duty of the PWM signal for the boost chopper 5 is controlled in an increasing direction, The output voltage of boost chopper 5 rises to a predetermined level. In this process, MPPT (mountain climbing) control for obtaining maximum power from the solar cell 1 is executed.

  When the system voltage rises above a predetermined value, reactive power injection control is performed to inject reactive power and suppress the increase in system voltage. In addition, when the commercial AC power supply system 47 is shut off, it is necessary to detect that it is an independent operation. This is one of the important control functions in grid interconnection operation. That is, there are a passive method and an active method as an isolated operation detection function, and both are often used together. The passive method monitors and detects a frequency variation rate, a phase jump (abrupt phase change), and the like. In the active method, there is a frequency shift in which the phase angle of the inverter output voltage is slightly advanced with respect to the system voltage, zero cross detection is performed on the system voltage, and the inverter output voltage is generated at the previous zero cross detection cycle. To go. Therefore, the inverter output voltage is generated in synchronization with the frequency of the system voltage until the commercial AC power supply system 47 is shut off. However, when the commercial AC power supply system 47 is shut off, the cycle of the inverter output voltage is cycled. Decreases by the above-mentioned advance phase angle and is detected as a frequency abnormality. Further, when the frequency and voltage deviate from a predetermined range during the transition period when the commercial AC power supply system 47 is cut off, active detection is performed at that time (UVR: low voltage, OVR: high voltage, UFR: low frequency, OFR: high). Frequency).

  Inverter output overvoltage, inverter output overcurrent, inverter output current DC component excess, PV voltage excess, PV current excess, PV ground fault (PV current unbalance detection via zero-phase CT), boost voltage, etc. are monitored When an abnormality occurs in any of these monitoring results, an error is notified on the operation display unit (not shown) and the operation is stopped.

  On the other hand, in the self-sustained operation, a switching PWM signal for the single-phase inverter 20 is generated by voltage comparison between the carrier signal (triangular wave signal voltage) and the sine wave command signal Vac_Ref (effective value). The sine wave command signal Vac_Ref is set to the same frequency as the system frequency which is recognized during the standby time of system interconnection operation and stored in the nonvolatile memory 62. Then, the switching element of the single-phase inverter 20 is turned on and off by the generated PWM signal, and the AC voltage Vinv_ad_rms (effective value 100 V) is output from the single-phase inverter 20.

  When the independent operation is performed from the beginning without performing the grid interconnection operation, the frequency of the command signal Vac_Ref is set to the default frequency stored in advance in the nonvolatile memory 62.

  In particular, in this self-sustained operation, as shown in FIG. 2, the correction bias V3 is added to the positive level voltage and the negative level voltage of the command signal Vac_Ref, respectively.

That is, when the command signal Vac_ref ≧ 0, the command signal Vac_ref is set as follows.

When the command signal Vac_ref <0, the command signal Vac_ref is set as follows.

  Ksoft is a soft start coefficient from “0” to “1” for starting the software when the inverter is started. ωt = ωt + Δωt. Δωt = 2πHz / fc. Hz is the frequency of the commercial AC power system (50/60 Hz). fc is a carrier signal frequency for generating an inverter PWM signal.

  In this way, by adding the correction bias V3 to the positive level voltage and the negative level voltage of the command signal Vac_Ref, respectively, it is possible to suppress a decrease in the effective level of the command signal Vac_Ref near the zero cross, as shown in FIG. As described above, the AC voltage Vinv_ad_rms from which distortion is eliminated over the entire waveform as well as near the zero cross is output from the single-phase inverter 20.

The output voltage distortion rate THD can be obtained by the following equation as the ratio of the second to 40th harmonic components with respect to the amplitude V1 when the amplitude of the target output voltage of the single-phase inverter 20 is V1, which is a significant improvement. An effect is obtained.

  The output voltage distortion rate of the present invention and the conventional output voltage distortion rate are shown in FIG. In particular, when the difference between the actual inverter output voltage and the voltage of the command signal is fed back to the command signal as in the prior art, the distortion reduction effect is small and the control load is heavy unless the carrier signal frequency is relatively high. In contrast, in the case of the present invention, the distortion of the inverter output voltage can be greatly reduced regardless of the carrier signal frequency and without increasing the control load.

By the way, as shown in FIGS. 5 and 6, the amplitude of the original command signal Vac_Ref is V1, the correction bias added to the command signal Vac_Ref is V3, and the carry amplitude of the command signal Vac_Ref due to the addition of the correction bias V3 is When V2, the correction bias V3 is set as follows.

  By setting the correction bias V3, the effective value of the output voltage Vinv_ad_rms of the single-phase inverter 20 does not change depending on whether the correction bias V3 is added or not. An example of the setting of the correction bias V3 is shown in FIG.

That is, it is assumed that the effective value of the output voltage Vinv_ad_rms of the single-phase inverter 20 is the same when the correction bias V3 is added and when it is not added.

Next, it is assumed that both sides of the above formula are squared and equal.

The first term on the right side is

The two terms on the right side are

Right side = 1 term on the right side + 2 terms on the right side,

From these equations, when the amplitude V2 of the output voltage of the single-phase inverter 20 obtained when the correction bias V3 is added, a quadratic equation of the correction bias V3 as shown in the following equation is obtained.

The solution of the quadratic equation of the correction bias V3 is as follows from the formula of the solution of the quadratic equation.

From the conditions of V3> 0 and V2> 0, V3 is determined by the following equation.

here,

An example of the solution in the case of is shown in FIG.

An example of the solution in this case is shown in FIG.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

The block diagram which shows the structure of one Embodiment of this invention. The figure which shows the waveform of the state in which the correction bias was added to the command signal in one Embodiment. The figure which shows the waveform of the inverter output voltage in one Embodiment. The figure which compares and shows the output voltage distortion rate of this invention, and the conventional output voltage distortion rate. The figure which shows the waveform of the command signal in one Embodiment. The figure which shows the carry amplitude of a command signal when correction bias is added to the command signal in one Embodiment. The figure which shows an example of the setting of the correction bias in one Embodiment. The figure which shows the waveform of one solution of the correction bias in one Embodiment. The figure which shows the waveform of the other solution of the correction bias in one Embodiment as a reference. The figure which shows the waveform of the new command signal by the feedback of a conventional apparatus. The figure which shows the waveform of the inverter output voltage of a conventional apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Solar cell, 5 ... Boost chopper (converter), 7 ... IGBT, 20 ... Single phase inverter 21, 22, 23, 24 ... IGBT, 31, 32, 33, 34 ... Gate drive circuit, 47 ... Commercial AC power supply System, 50 ... AC power supply for autonomous operation, 60 ... Control unit, 61 ... MCU

Claims (3)

A converter for converting the level of DC voltage by switching, an inverter for converting the output of the converter to AC by switching, and a control means for generating a PWM signal for switching for the converter and the inverter by voltage comparison between the carrier signal and the command signal In the power supply
The control means adds a correction bias to each of a positive level voltage and a negative level voltage of the command signal when generating a PWM signal for switching to the inverter by voltage comparison between the carrier signal and the command signal. Power supply. A grid connection operation means for operating the inverter in conjunction with a commercial AC power supply system; and a self-sustained operation means for operating the inverter independently of the commercial AC power supply system,
The control means executes the addition of the bias during the independent operation.
The power supply device according to claim 1. When the amplitude of the command signal is V1, the correction bias added to the command signal is V3, and the carry amplitude of the command signal by adding the correction bias V3 is V2, the correction bias V3 is set as follows:

A grid-connected inverter characterized in that the effective value of the output voltage of the inverter does not change depending on whether the correction bias V3 is added or not.
The power supply device according to claim 2, wherein:

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