JPH0767352A - Current loop control type pwm inverter - Google Patents

Abstract

PURPOSE:To miniaturize an AC filter by keeping the hysteresis frequency of a semiconductor switching element constituting a PWM inverter constant. CONSTITUTION:A current loop control type PWW inverter is composed of a bridge circuit 1 consisting of a semiconductor switching element, a DC power supply 2, a hysteresis width setter 16, to which the output voltage of the bridge circuit 1 is input through a voltage detector 6, adders 9 and 10, in which the output signal of the hysteresis width setter 16 is added to a current command value and subtracted from the current command value, and two comparators 7 and 8, to which the output signals of the two adders 9 and 10 and the output currents of the bridge circuit 1 are input through a current detector 3. The hysteresis width setter 16 is constituted of an A/D converter 15, a ROM 14, a D/A converter 13, a set resistor 12 and an adder 11, and adds hysteresis current width consisting of a fixed current component proportional to TE/L and a current component proportional to TV<2>/EL to the current command value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current loop control type PWM inverter which constitutes a UPS.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram of a current loop control type PWM inverter according to the prior art, which comprises a single-phase half bridge circuit 101 composed of semiconductor switching elements S ₁₁ and S ₁₂ and DC voltages E ₁ and E _2. DC power supply 102,
Two comparators 107 and 108, two adders 10
9 and 110, the hysteresis width setting device 111 is a hysteresis comparator type current loop control type PWM
It constituted the converter. Note that E ₁ = E ₂ (= E)
And A consisting of reactor 104 and capacitor 105
AC power is supplied to the load 112 via the C filter.

Two current command values (i ^* + i _T ) and (i) generated by adding and subtracting the hysteresis width current signal i _T from the hysteresis width setting device 111 to and from the current command value i ^* in the adders 109 and 110. ^* -I _T ) and the current detector 10 provided on the output side of the single-phase half-bridge circuit 101.
The output current signal i detected from
And 108. Hysteresis comparator 1
The output signal from _{^{07 (i * + i T)}} -i semiconductor switching element S ₁₁ is output currents turned on increased by, and the output signal i- (i ^* -i _T) by a semiconductor switching hysteresis comparator 108 Element S
₁₂ turns on and the output current decreases. The waveform of the output current signal i which is controlled by the hysteresis comparator 107 and 108 described above, as shown in FIG. 3, the output current i is the error between (i ^* + i _T) and (i ^* -i _T) The vibrational follow-up control is performed within the threshold value (hysteresis width) i _T.

[0004]

The above-mentioned threshold value i _T
Is a constant value set by the hysteresis width setting unit 111 and keeps the hysteresis width of the current command value constant, so that the hysteresis frequency (the switching frequency of the semiconductor switching elements S ₁₁ and S ₁₂ ) greatly fluctuates. For this reason, the high-order frequency generated from the bridge circuit 101 also largely fluctuates, so that there is a drawback that the effect of the AC filter constituted by the reactor 104 and the capacitor 105 is lost. The present invention has been made in order to eliminate the defects of the current loop control type PWM inverter according to the prior art described above, and provides a current loop control type PWM inverter including a hysteresis setter having a substantially constant hysteresis frequency. The purpose is to do.

[0005]

In order to achieve the above-mentioned object, the current loop control type PWM inverter according to the present invention uses a hysteresis width setter which constitutes a hysteresis comparator to output a current component proportional to the square of the output voltage. Output a hysteresis current width consisting of a constant current component, and input a current command value with this hysteresis current width to the hysteresis comparator to alternately turn on / off the semiconductor switching elements that form the bridge circuit. The hysteresis current width of the current command value is controlled so that the hysteresis frequency of the semiconductor switching element becomes substantially constant.

[0006]

The constant current component (TE / L) determined by the hysteresis period (reciprocal of the switching frequency) T,
When a current command value having a hysteresis current width composed of a current component (TV ² / EL) proportional to the square of the hysteresis period T and the output voltage V is input to the hysteresis comparator, the output signal from this hysteresis comparator causes The hysteresis frequency of the semiconductor switching element that is on / off controlled is constant.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a circuit configuration of a current loop control type PWM inverter comprising a single-phase half bridge circuit according to the present invention. Except for a hysteresis width setting device and an accompanying voltage detector, a current loop control type device in the prior art is shown. Since it is the same as the PWM inverter, the description of the same components will be omitted.

A voltage detector 6 detects the load-side output voltage of the reactor 4 provided in the AC output circuit of the single-phase half-bridge circuit 1 composed of the semiconductor switching elements S ₁₁ and S ₁₂ , and forms a hysteresis width setting device 16. The A / D converter 15 converts the signal into a digital signal and inputs it into the ROM 14. The ROM 14 inputs the digitized output voltage signal V to generate a current component proportional to T · V ² / EL, further converts it into an analog signal in the D / A converter 13, and then inputs it into the adder 11. To do. Where T
Is the hysteresis period, V is the output voltage, E is the DC power supply voltage, and L is the inductance of the reactor 4. The hysteresis setting resistor 12 provided in the hysteresis width setting device 16 outputs a current component proportional to T · E / L and is added to the output signal of the D / A converter 13 in the adder 11. When the hysteresis period T is constant, the current component from the setting resistor 12 is constant, and the ROM 1
The current component output from 4 has a value proportional to the square of the output voltage V. Therefore, the output signal i _T from the hysteresis width setting unit 16 output from the adder 11 is (T · E /
L) − (T · V ² / EL), which is a current component and has a hysteresis current width with respect to the current command value i ^* . The output signal i _T from the hysteresis width setter 16 is added to and subtracted from the current command value i ^* in the adders 9 and 10, and is input to the comparators 7 and 8 together with the current signal i detected by the current detector 3, Semiconductor switching element S ₁₁
And a control signal for alternately controlling S ₁₂ are output.

Next, the relationship between the current command value having a hysteresis characteristic in the hysteresis comparator and the hysteresis frequency will be described. FIG. 4 is a block diagram for explaining the operating characteristics of a single-phase half-bridge PWM inverter equipped with a hysteresis comparator. now,
When a signal A to turn on the semiconductor switching element 33 is inputted to the operational amplifier 38, the voltage across V _L of the reactor 36 by the output current i flowing through the reactor 36 is _{V L = E-V = L} · di / dt dt = T 1 Then, T ₁ = L · di / (E−V) (1) Next, when the signal B is input to the operational amplifier 39 to turn on the semiconductor switching element 34, the voltage −V _L across the reactor 36 is − If V _L = − (E + V) = − L · di / dt dt = T ₂ , then T ₂ = L · di / (E + V) (2) FIG. 5 is an enlarged view of the modeled output current waveform. , The hysteresis period T of the semiconductor switching element is (T ₁ +
Since T ₂ ), T = T ₁ + T ₂ = [1 / (E−V) + 1 / (E + V)] × L · di = 2ELdi / (E ² −V ² ) from the equations (1) and (2). ) Therefore, di = (T / 2EL) · (E ² −V ² ) …… (3)

[0010] The hysteresis current width of the current command value to the hysteresis comparator i ^* i _T is _{i T = (1/2) · di} = T / 4EL · (E 2 -V 2) = TE / 4L- (T / 4EL) · V ² (4) If the DC power supply voltage E and the inductance L are constant and the hysteresis period T is set to a desired value, the first term on the right side of the equation (4) becomes constant and the second term Is the output voltage V 2
It becomes a value proportional to the power. Therefore, in order to make the hysteresis period T constant, the hysteresis current width i _T determined by the equation (4) may be given to the current command value i ^* . The current component proportional to L is output and the ROM 14
To output a current component proportional to TV ² / EL. Although the above description relates to the hysteresis comparator provided in the single-phase half bridge circuit, the current loop control type PWM inverter having a constant hysteresis frequency is also provided for the three-phase bridge circuit by providing the above-mentioned hysteresis comparator for each phase. Can be realized.

[0011]

As described above, the current loop control type PWM inverter according to the present invention sets the hysteresis width of the output voltage signal detected from the load side of the reactor provided in the AC output circuit of the bridge circuit composed of semiconductor switching elements. Input to the hysteresis comparator and generate a current command value having a hysteresis characteristic consisting of a current component proportional to the square of the output voltage signal and the hysteresis period and a constant current component determined by the hysteresis period, and input to a hysteresis comparator. When the semiconductor switching elements forming the bridge circuit are alternately turned on and off, the hysteresis frequency of the semiconductor switching elements becomes substantially constant. Therefore, the high-order harmonics generated from the PWM inverter have a certain frequency or higher, and the AC filter can be downsized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a current loop control type PWM inverter according to the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a conventional current loop control type PWM inverter.

FIG. 3 is an output current waveform diagram.

FIG. 4 is a block diagram of a single-phase half-bridge type PWM inverter having a hysteresis comparator.

FIG. 5 is a modeled output current waveform diagram.

[Explanation of symbols]

 1 bridge circuit 2 DC power supply 3 current detector 4 reactor 6 voltage detector 7,8 comparator 9,10,11 adder 12 setting resistance 13 D / A converter 14 ROM 15 A / D converter 16 hysteresis width setting device

Claims (1)

[Claims] 1. A bridge circuit comprising a semiconductor switching element for inputting a DC power supply and converting into AC, and a comparator for inputting a current signal detected from an AC output circuit of the bridge circuit and a current command value having a hysteresis characteristic. In a hysteresis-comparator current loop control type PWM inverter that alternately turns on and off the semiconductor switching elements that form the bridge circuit by the output signal of the comparator, a reactor provided in the AC output circuit of the bridge circuit The output voltage signal detected from the load side is input to the ROM constituting the hysteresis width setting device to generate a current component proportional to the square of the output voltage signal, and a separate current setting device generates a constant current component. , A hysteresis consisting of the two current components A hysteresis characteristic is added to the current command value input to the comparator according to the flow width, and the hysteresis current width of the current command value is controlled so that the hysteresis frequency of the semiconductor switching element forming the bridge circuit becomes constant. Current loop control type PWM inverter.