JP4757663B2 - Voltage source current control inverter - Google Patents

Description

  The present invention relates to a voltage-type current control inverter that is mainly used as a grid-connected inverter in a grid-connected power generation system that is connected to a commercial power system and supplies power to a system load, and more particularly to a technique for current control thereof. About.

In the above voltage source current control inverter, by superimposing a voltage waveform with three times the fundamental frequency on the output voltage waveform, the interphase voltage of the inverter output can be output as a sine wave even when the inverter input voltage is low. It is known that can be improved. The superposition of the voltage waveform of the triple frequency can be realized by superimposing the third harmonic signal directly on the voltage command signal in a general voltage control inverter. In the voltage source current control inverter, a signal obtained by amplifying an error signal between a sine wave target signal having a predetermined frequency and a current feedback signal and a third harmonic signal (three times the frequency of the target signal) are added in synchronization. There has been proposed a method of superimposing third-order harmonic components on the three-phase output of the inverter without distorting the output current by inputting the signal to a pulse width modulation signal generation circuit (for example, Patent Documents). 1).
JP-A-6-133558

  However, in the above conventional technique, a third harmonic signal is generated by calculating the maximum value, the minimum value, and the intermediate value of the signal obtained by amplifying the error signal for three phases, and the generated third harmonic signal is A method of adding in synchronization with the error signal has been proposed, but the method of generating the third harmonic signal is complicated. As another method, a signal obtained by amplifying an error signal between a sine wave target current signal having a predetermined frequency and a current feedback signal, and a third harmonic signal synchronized with the sine wave target current signal (three times the frequency of the target signal) However, if there is a large delay element in the error calculator and the amplifier, the third harmonic cannot be effectively superimposed.

  The present invention has been made in view of the above-described circumstances, and provides a voltage-type current control inverter that can effectively superimpose a third-order harmonic even if the feedback system calculator has a delay element. For the purpose.

  The voltage source current control inverter of the present invention includes a voltage detector that detects a voltage of a commercial power system, a current command waveform generator that generates a current command waveform having the same frequency as the frequency of the voltage detected by the detector, , An error calculator having a delay element for calculating an error between a current target value output from the generator and a current feedback value detected from the output line of the inverter, and the voltage detected by the voltage detector. A third harmonic waveform generator for obtaining a third harmonic signal having a frequency three times the frequency, and a phase shifter for delaying the phase of the output of the third harmonic waveform generator by the delay time of the error calculator And an addition calculator for adding the output of the error calculator and the output of the phase shifter, inputting the output of the addition calculator to a pulse width modulator, generating a pulse width modulation signal, Invar The is characterized in that operating by the pulse width modulation signal.

  In the present invention, when superimposing the third harmonic, the third harmonic is superimposed in consideration of the delay element of the error calculator of the feedback system. The phases of the output signals can be matched, and the third harmonic can be effectively superimposed. As a result, even if there is a delay element in the error calculator of the feedback system, the 3rd harmonic can be put on the proper phase, so a high voltage utilization factor of the DC input voltage of the inverter can be secured and the inverter can be used efficiently can do.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, in each figure, the same code | symbol is attached | subjected to the member or element which has the same effect | action or function, and the overlapping description is abbreviate | omitted.

  FIG. 1 shows a grid-connected power generation system using a voltage source current control inverter according to an embodiment of the present invention. The AC power output of the generator 11 is rectified by a converter 12 such as a full-wave rectifier circuit, and DC power stored in a capacitor (DC power supply) 13 is converted into AC power that can be connected to the grid by an inverter 15 to be commercial power. It is supplied to a load connected to the grid 16. The voltage-type current control inverter 15 is a device that converts the DC power of the DC power supply 13 into an AC current having an amplitude of a current command value, and sends the AC current of the command value to a system load. Synchronizes with voltage and outputs AC power. Then, an actual inverter output current is detected so as to output a command value of alternating current, and feedback control is performed using an error calculator.

  The inverter 15 is a power conversion device that converts DC power into AC power by ON / OFF control of the power switching element according to the pulse width modulation signal, and the input DC voltage is pulse-width modulated and output. For this reason, the basics as an inverter device such as a system voltage detector 18 for detecting a system voltage, a current detector 19 for detecting a current sent to the system, a system reactor 20, a filter circuit for removing a high frequency component including a capacitor 21 and the like. It has a typical configuration.

  The inverter 15 includes a control device having the following configuration that outputs the waveform of the third harmonic superimposed on the waveform of the fundamental frequency for each phase. That is, a frequency detector (phase detector) 23 that detects a waveform of the fundamental frequency from the system voltage, a current command waveform of the fundamental wave from the current command value and the waveform of the fundamental frequency detected by the frequency detector 23. A current command waveform generator 24 for forming a signal, and a delay element for obtaining an error between the current command waveform signal (target value) and the current signal (feedback value) detected from the output line of the inverter by the current detector 19 An error calculator (PID calculator) 25, a third harmonic waveform generator 26 that forms a third harmonic waveform signal having a frequency three times the commercial system voltage detected by the voltage detector 18, and the above 3 A phase shifter 27 for delaying the phase of the output of the second harmonic waveform generator by the delay time of the error calculator (PID calculator) 25, the output of the error calculator 25, and the phase shifter 27 And an adder 28 for adding operation on the power inputs an output of the adder 28 to the pulse width modulator 29 generates a pulse width modulated signal to a pulse width modulation control of the inverter 15.

  According to the control device, the current command waveform generator 24 forms a current command waveform (target value) of the system voltage frequency according to the current command value. Then, an operation for obtaining an error from the actual current waveform (feedback value) detected from the output line of the inverter 15 is performed by the error calculator 25 so that the error becomes zero (the feedback value matches the target value). A current command waveform signal having a fundamental frequency is output from the error calculator 25. A phase shifter 27 delays the phase of the current command waveform signal of the fundamental frequency by the delay time of the error calculator 25 by the phase shifter 27, and the adder 28 Superimposed. As a result, even if the error calculator 25 has a delay time, the phase of the fundamental signal of the error calculator having the delay element can be matched with the third harmonic signal, and the third harmonic can be effectively applied. Waves can be superimposed.

  Therefore, the output current for each phase is obtained by accurately superimposing the third harmonic in phase with the fundamental wave, increasing the voltage utilization factor of the input DC voltage in the inverter and operating the inverter efficiently. Can do. Since the superimposed third harmonic component is canceled in the line voltage, only the fundamental frequency component is output to the commercial AC power system 16 side.

The phase shift amount in the phase shifter 27 of the voltage source current control inverter is set by any one of the following methods.
(A) Predict the output phase delay of the error calculator 25 and set a predetermined value (time or phase angle substantially equal to the delay time).
(B) The output phase of the error calculator 25 is actually detected, and the phase shift amount is set so as to synchronize with the output of the error calculator 25.

  Next, a specific configuration example of the control device is shown in FIG. In this embodiment, the error calculator 25 and the adder 28 are constituted by analog circuits using operational amplifiers. Since the error calculator 25 includes an integration circuit composed of a resistor (R) and a capacitor (C), the output phase delay occurs as described above. Here, the terminal A is connected to the current command waveform generator 24, and the current command waveform (target value) of the system voltage frequency according to the current command value is input. The terminal B is connected to the current detector 19, the actual current waveform (feedback value) detected from the output line of the inverter 15 is input, and the error calculator 25 performs error calculation (PID calculation). The third harmonic waveform generator 26 and the phase shifter 27 are realized by digital arithmetic processing by a microprocessor using a program stored in the memory, and a third harmonic analog waveform with a predetermined amount of output phase delay is added to the adder 28. Is added to the output of the error calculator 25, and a current command waveform on which the third harmonic is superimposed is output from the terminal C to the pulse width modulator (triangular wave comparison circuit) 29.

  Next, the phase shift of the third harmonic in this control apparatus will be described with reference to FIG. First, a time T1 from the rising zero cross of the U phase voltage waveform (a), which is a system voltage waveform, to the next rising zero cross is measured by the timer 1 in the microprocessor (b). Next, the output phase of the current command waveform generator 24 is the type of the timer 2 (c) in which, for example, 1/360 time (time corresponding to an electrical angle of 1 °) measured from the above rising timing is set. Can be created using the app. Specifically, a time 1/360 of the time measured by the timer 1 is set in the timer 2 having the interval timer function. In response to an interrupt that occurs every time the timer 2 expires (interval time), the sine waveform table data reference pointer divided into 360 parts used for output is incremented. When the rising zero cross occurs, the sine waveform table data reference pointer is reset to zero (the start point of the zero cross point is set). Thereby, the current command waveform shown in FIG. 3D can be created.

  Here, when outputting the triple frequency waveform of the above-described current command waveform, the sine waveform table data for the triple frequency is prepared, and the triple frequency sine waveform is obtained every time the timer 2 (e) is timed up. By incrementing the table data reference pointer, the triple frequency waveform (f) synchronized with the current command waveform can be output. Further, in order to delay the phase of the triple frequency waveform with respect to the current command waveform, the pointer for reference of the triple frequency reference table is set when the sine waveform table data reference pointer is reset to zero when a rising zero cross occurs. By setting to an arbitrary value (phase shift amount T3), the phase of the triple frequency can be changed by an arbitrary value with respect to the current command value. In the case of the illustrated embodiment, the time T2 is delayed by three times at the rising zero cross timing, thereby delaying the current command waveform by 3 °. The above description is an explanation when one period is divided into 360, and the number of divisions in one period may be an arbitrary value. When the fundamental wave output waveform (g) of the error amplifier is added to the phase-shifted triple frequency waveform (f) by the adder 28, a trapezoidal adder output waveform (h) in which the phases are accurately matched is obtained.

  The above-described embodiment can be implemented by hardware without using a microprocessor, but the configuration with a microprocessor becomes simpler and the change when changing the phase shift amount becomes easier. Therefore, it can be configured at a low cost.

  In the above embodiment, the error calculator 25 and the adder 28 are configured by hardware. However, the error calculator 25 and the adder 28 may be configured by software using a microprocessor and a memory.

  Although one embodiment of the present invention has been described so far, the present invention is not limited to the above-described embodiment, and may of course be implemented in various forms within the scope of the technical idea.

It is a block diagram which shows the voltage type current control inverter of one Embodiment of this invention. It is a circuit diagram which shows the structural example of the control apparatus of the said inverter. It is a wave form diagram which shows the operation example of the said inverter.

Explanation of symbols

11 Generator 12 Converter 13 DC Power Supply 15 Voltage Source Current Control Inverter 16 Commercial AC Power System 18 Voltage Detector 19 Current Detector 20 Reactor 21 Capacitor 23 Frequency Detector 24 Current Command Waveform Generator 25 Error Calculator (PID Calculator)
26 Third harmonic waveform generator 27 Phase shifter 28 Adder 29 Pulse width modulator

Claims (2)

A voltage detector for detecting the voltage of the commercial power system;
A current command waveform generator that generates a current command waveform having the same frequency as the frequency of the voltage detected by the detector;
An error calculator having a delay element for calculating an error between the current target value output from the generator and the current feedback value detected from the output line of the inverter;
A third harmonic waveform generator for obtaining a third harmonic signal having a frequency three times the frequency of the voltage detected by the voltage detector;
A phase shifter that delays the output of the third harmonic waveform generator by the delay time of the error calculator;
An adder that adds the output of the error calculator and the output of the phase shifter, input the output of the adder to a pulse width modulator, generate a pulse width modulation signal, and A voltage-type current control inverter which is operated by the pulse width modulation signal.   2. The voltage-type current control inverter according to claim 1, wherein the current command waveform generator, the third harmonic waveform generator, and the phase shifter are configured by software using a microprocessor and a memory.