JPS59194669A - Controlling method of single phase pwm inverter - Google Patents

Abstract

PURPOSE:To enhance the output frequency of an inverter by displacing 180 deg. of an electric angle of the carrier for PWM controlling a pair of switching elements connected in series to the carrier for PWM controlling a pair of switching elements connected in series. CONSTITUTION:A compensating current detected value is compared by a comparator C1 with the instruction value, and a deviation is inputted to a control compensator H(S) to obtain a control input signal. This control input signal is inputted to comparators C2, C3, and compared with the output signal which is displaced at 180 deg. from a triangular wave generator TRG. The outputs of the comparators C2, C3 are applied to the GTO of a PWM inverter through Schmitt circuits SH1, SH2 and gate circuits GC1, GC2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method of controlling a voltage-type PWM (pulse width modulation method) inverter that outputs a single-phase alternating current.

[Technical background of the invention]

A voltage-type PWM inverter is known as a power converter that converts DC power to AC power with variable voltage and variable frequency, and is used as a drive power source for an AC variable speed motor or without a power supply system.
It is used in active filters to compensate for dynamic forces, etc.

FIG. 1 shows a configuration diagram of an active filter device using a conventional single-phase PWM inverter.

In the figure, ■s is a single-phase AC power supply (Ls is AC R'),
INV is the PWM inverter body, and co is the DC smoothing capacitor. The PWM inverter INV consists of gate turn-off switches (hereinafter abbreviated as GTO) S1 to S4, wheeling diodes D1 to D, and DC actuators L and -L2 with protrusions in between.

Also, as a control circuit, a current transformer C that detects the compensation current Ic
It consists of T1 comparators C1 and C2, a control compensation circuit H(s), a triangular wave generator TRG, a Schmitt circuit SH, and a gate circuit GC.

The comparator C3 compares the detected value IC of the compensation current with its command value 2, and inputs the deviation ε, -= IC to the next control compensation circuit H(s). The control compensation circuit H(s) is composed of a proportional element or an integral element, and its constant is selected in consideration of stability and responsiveness of the control system.

The output signal e1 of the control compensation circuit H(S) and the output signal a from the triangular wave generator TRG are compared by a comparator C2,
The deviation ε2=e, -a is input to the next Schmitt circuit SR. Schmitt circuit 5H (when d deviation ε2 is positive ゛1
When the deviation ε2 is negative, an output signal of "0" is generated, and an ignition signal is given to the GTOs 81 to S4 via the gate circuit GC.

FIG. 2 shows the relationship between the output signal a of the triangular wave generator TRG, the output signal e1 of the control compensation circuit H(s), and the output signal X of the gate circuit GC, and the output voltage of the inverter INV at that time. e. is expressed in units.

The output signal a of the triangular wave generator TRG serves as a carrier wave for the PWM inverter, and is a triangular wave of about 1 kHz. Furthermore, the output signal e1 of the control compensation circuit H(s) is P
This is the control input signal for the WM inverter.
A voltage e0 proportional to the positive value e is generated from the inverter INV.

When ε2=e, -a is positive, GTO thyristor SI and 8
An on signal is given to S2 and Ss, and an off signal is given to S2 and Ss. Therefore, in the main circuit of Fig. 1, if the current Ic is flowing in the direction of the arrow, the DC capacitor C.

(+) → Thyristor S, -+ DC actor L1 → AC reactor LII → AC power supply Vs → DC reactor L,
Flows through the path of → silice S4 → DC capacitor Co(-). Here, if the voltage Vc of the DC capacitor Co is made larger than the maximum value V++ (m-x) of the power supply voltage VB, the compensation current Ic can be increased in the direction of the arrow when ε2>0. When the direction of current Ic is flowing in the opposite direction to the arrow, the current flows from DC capacitor Co(-) to diode D.
4→DC reactor L2→AC power supply Vs→AC reactor Ls−+DC reactor L1→diode D,→DC capacitor Co(+). In this case the current I
c is decreasing. Therefore, if 62>0, the inverter I
The output voltage Eo of NV is in the direction of the arrow in FIG. 1, and acts to cause the compensation current Ic to flow in the direction of the arrow.

52= When et −a is negative, G T OS, and 5s
A VrC on signal is given, and an off signal is given to S and 84.

Therefore, in the main circuit of Fig. 1, if current Ic is flowing in the direction of the arrow, DC capacitor Co(-) → diode D2
→ DC reactor L1 → AC reactor Ls → AC power supply Vs → DC reactor L2 → diode D3 → DC capacitor Co (+) to reduce the flowing current Ic. In addition, when the current Ic is flowing in the opposite direction to the arrow, DC capacitor Co (+) → Thyristor S → DC actuator L2 → AC power supply vIl → AC reactor Ls → DC reactor L1 → Thyristor S2 → DC capacitor Co
It flows along the (-) path and operates to increase the current in the corresponding direction.

Compensation current command value ■ Set ↑ to a positive value L%I? >Ic, the deviation ε1-1c-Ic becomes a positive value and increases the control input signal e through the control compensation circuit H(s). The output voltage Eo of the PWM inverter INV increases in the direction of the arrow in FIG. 1 in proportion to the value of the input signal e.

As a result, the actual value Ic of the compensation current increases, Ic = I
c.

When Ic<■C, the control input signal e decreases, causing the output voltage Eo of the inverter INV to decrease.

Therefore, the actual current Ic decreases and is controlled so that IC=Ie.

If the current command value IC changes in a sinusoidal manner, the current collection bF I C also changes in a sinusoidal manner following it.

When using the PWM inverter INV-Q as an active filter, the compensation current command value Ic is equal to the voltage Va.
It includes not only active current and reactive current synchronized with the current, but also various harmonic components, so a current control system with good followability is required.

[Problems with background technology]

The response characteristics of the above current control system are PWM inverter INV
It depends on the control frequency f, and the longer fc becomes, the better the control becomes possible.

The control frequency fc is the output frequency itself of the triangular wave generator TRG, and is usually selected to be about 1 kHz.

Therefore, if the frequency fc is made higher, the control response characteristics will be improved accordingly, but the G
Considering the switching characteristics of TO, it is still 1 kHz.
A value of about z is a reasonable value.

Therefore, when a conventional PWM inverter is applied to an active filter device, the fundamental wave component (5
Q Hz or 60 Hz) can be tracked sufficiently, but harmonic components (3rd, 5th, 7th...
), etc., had the disadvantage that satisfactory compensation could not be provided.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object thereof is to provide a control method for a single-phase PWM inverter that can double the output frequency of the inverter without increasing the switching frequency of the GTO that constitutes the PWM inverter. With the goal.

[Summary of the invention]

The present invention provides two pairs in which at least two semiconductor switching elements are connected in series, and connects them in parallel to a DC cylinder and a pressure drop, so that an AC output voltage is obtained from the midpoint of the series connection. In the single-phase PWM inverter, the PWM-controlled carrier waves of the pair of series-connected switching elements are shifted by 180 degrees in electrical angle from the PWM-controlled carrier waves of the other series-connected switching elements.

[Embodiments of the invention]

FIG. 3 is a configuration diagram showing an embodiment of the single-phase PWM inverter of the present invention.

The main circuit configuration is the same as that shown in FIG. C in the control circuit
hC2 and C3 are comparators, H(s) is a control compensation circuit T R
GB triangular wave generator, 5L-(, 5Hzl'j: Schmitt circuit, GCl, GC2H gate control circuit.

The comparator C1 compares the compensation current detection value Ic and its command thread value IC, and inputs the deviation ε+=IcIc to the control compensation circuit n(s), which performs heel proportional amplification or integral amplification to obtain the control input signal e. What you get is the same as before.

The control input signal e1 is input to comparators C2 and C8 and is compared with the output signals a and b from the triangular wave generator TRG.

For output signal a, the output direction (fi is 180° in electrical angle)
only the phase is shifted. Simply, the b signal is obtained by inverting the a signal.

The Schmitt circuit SH outputs a 1" signal when the control input signal el is larger than the carrier wave (triangular wave) a, and outputs a signal of 1" to GT OS via the next gate circuit GCiQ.

An on signal is given to the GTO 82 and an off signal is given to the GTO 82. On the contrary, e.

At the time of <a, the output of SH becomes 0°', giving an on signal to the 5tlC off signal and St.

The Schmitt circuit SH2 outputs a signal of "1" when the control input signal ei is larger than the carrier wave (triangular wave) b,
An off signal G is sent to GTOS through the gate circuit GC2.
Give an off signal to the T OSs. Conversely, when e, (b), the output of SH2 becomes 0'', giving an off signal to S4 and an on signal to S3.

Figure 4 shows the waveforms of each part in Figure 3, with carrier waves a,
By applying the control l input signal ei to [7], the output signals of the gate circuits GC and GC2 are equal to the waveforms of X and y, respectively, and the output and voltage (expressed in units) are e. It will be like this. When the control input signal is still negative 11 like ei, the output signals of GC, 1GC2 are X', y'
The output voltage at that time will be as shown below.

When the control input signal e1 has a positive value, the on period of G T OSl is longer than the on period of G T OSt, and the on period of G T OS
The on period of O84 is longer than the on period of G T OS.

Moreover, the ON period of GT OS occurs only once during the ON period of GT OS, and the ON period of GT OSt occurs only -8 times during the ON period of GTO8. Therefore, the following three modes occur.

B) St on (82 off), 84 on (S, off)
→ SI on (82 off), 83 on (84 off), 82 on (St off), 84 on (S, off) In mode A) above, capacitor voltage VC is generated at the output terminal, E9 = + Vc becomes. In modes ol and 9, the output terminals are short-circuited and Eo==0. Therefore, if the output voltage Eo is unitized, it will have a waveform like e in FIG. 4. The output voltage e is always a positive value, and its average value is a value proportional to the control input voltage e.

Output voltage e. It can be seen that the control frequency fc is twice the on/off frequency of GTO3, ~S4, that is, the carrier wave frequency.

Further, when the control input signal becomes a negative value e/, the on-period of GTO83 becomes longer than the on-period of GTO83, and the on-period of GTO83 becomes longer than the on-period of GTO83.
This is longer than the on period of 84. Furthermore, the ON period of GTO8 occurs only once during the ON period of GTOSt, and the ON period of GTO8 occurs only once during the ON period of GTOS30.

Therefore, in this case, the following three modes are possible.

b) 81 on (82 off), Ss on (84 off) o)
S2 (S, off), Ss (S, off), 982 on (Ss off), 84 on (S3 off) The output terminals of the inverter are short-circuited at The output voltage Eo becomes zero. In the → mode, a voltage of -vc is generated at the output terminal, and Eo==-Vc. Therefore, when the output voltage Eo is expressed in units, it has a waveform like elo in FIG. The output voltage eQ is always a negative value, and its average value is a value proportional to the control input voltage el. It can be seen that in this case as well, the control frequency fc of the output voltage e' is twice the switching frequency of the GTOs 8 to S4, that is, the carrier wave frequency.

〔Effect of the invention〕

As described above, the Ill 1ilt! According to the method, without changing the conventional main circuit layout, the output voltage of impark can be reduced by 11 lbs.
The number of station waves is 2+f of the switching frequency of the constituent elements! Therefore, the response speed of the control is increased, and it can also be used in an active filter that compensates for high-order surface frequency components that were previously impossible.

Furthermore, by increasing the control frequency of the output voltage, the pulsation of the compensation current Ic becomes smaller, and as a result, the AC reactor can also be made smaller.

``Stop! If you compare the output voltage e in Figure 2 (conventional) and Figure 4 (invention), e is 6+1'' in the conventional device.''
-1′′, whereas e of the present invention is “+1” and “
It is controlled in three stages: 0" and "-1". In other words,
Output voltage e. The change in the compensation current Ic becomes smaller, which also has the effect of reducing the pulsation of the compensation current Ic. Furthermore, when the control input signal ei is zero, in the conventional device, the output voltage e is “
The only difference is that the period of “°+1” and the period of “-1” are the same,
It constantly changes between +1" and -1". On the other hand, according to the uninvented control method, when e,=O, Sl is on (
82 off) and *, Ss is on (84 off) and when 82 is on (S, off), 84 is on (ss off) and e becomes 0''. In other words, the output voltage pulsation is zero. Therefore, the pulsation of the output current (compensation current 1.) also disappears.

Note that the single-phase PWM inverter of the present invention can be applied not only to an active filter device but also to the following devices.

For example, if a load is connected to the DC capacitor CO in Figure 3,
It controls the input current Ic from the power supply so that the capacitor voltage Vc becomes almost constant, and the input terminal Ic
i is an AC/DC power converter ji'1 with an input power factor of 1, which is fa-controlled so that a sinusoidal current in phase with the power supply voltage VII flows.
' (converter).

In addition, we are working hard to connect a single-phase load instead of 1jj, jp, and VsO, and to use a DC capacitor Cof DC power supply to control the load current and current Ic-11i. It goes without saying that it is -6.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an example of the application of a conventional single-phase PWM system, Fig. 2 is a time chart diagram for explaining the operation of the device shown in Fig. FIG. 4 is a block diagram showing an embodiment of the PWM inverter, and FIG. 4 is a time chart for explaining the operation of the device shown in FIG. ■8...AC power supply Ls...AC reactor I NV ---P'WM ear Park body Co...
・DC capacitors S1 to S4...GTO thyristors L, L,...DC reactors D1 to D4...Wheeling diode CT...Current transformer CI...C3...Comparator H(s )・
...Control compensation circuit TRG/...Triangular wave generator SH,
, SH2... Schmitt circuit GC11GC2... gate control circuit

Claims (1)

[Claims] In a single-phase PWM inverter, two pairs of at least two semiconductor switching elements connected in narrow plane rows are provided, and the pairs are differentially connected to a DC voltage source, and an AC output voltage is obtained from a midpoint of the series connection. , the control of a single-phase PWM inverter, characterized in that the carrier wave for PWM control of the pair of series-connected switching elements is shifted by 180'' in electrical angle with respect to the carrier wave for PWM control of the other pair of series-connected switching elements. Method.