JPS61177170A - Control circuit of ac/dc converter - Google Patents

Abstract

PURPOSE:To maintain a DC output voltage constant by obtaining a difference between a command value of a DC voltage and a detected voltage, and a difference between a current command value obtained from the momentary voltage of each phase and a momentary current, and controlling a switching element through a hysteresis comparator. CONSTITUTION:The difference between the DC output voltage Ed and a command value Ed deg. is obtained, multiplies by a multiplier X by the momentary values eR'-eT' of AC voltages of the respective phases to obtain DC command values iR*-iT*. Momentary current iR'-iT' are obtained from a current detector 12. The differences between the values iR*-iT* and the momentary values iR'-iT' are obtained for the phases. This phase signal is input to hysteresis comparators 3-5, and switching element TR1-TR3 and TR4-TR6 are alternately driven through amplifiers 6-8, 9-11. Thus, the power factor of the AC input can be always held 1 to maintain the DC output voltage constant.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a control circuit for an AC-DC converter using a three-phase PWM (Pulse Width Modulation) converter.

Generally, the method of rectifying alternating current with a diode to obtain direct current is widely used, but it has the following problems. That is, (1) The current flowing through the AC power source is a pulse wave (when using a capacitor input) or a square wave (when using a square input), which is far from an ideal sine wave and has a very poor power factor.

■ There is pulsation in the DC voltage at the AC power frequency or an integral multiple thereof, and a large choke coil or capacitor filter is required to smooth it.■ Power flows only in one direction, from the AC side to the DC side. Even if surplus power occurs on the DC side, power cannot be regenerated on the AC side.

Therefore, there is a three-phase PWM converter as an AC-DC converter that eliminates the above-mentioned drawbacks. Another feature of this converter is that the voltage on the DC side can be changed freely, but in the conventional three-phase PWM converter control method, the voltage on the DC side can be changed while keeping the power factor on the AC side at 1. A complex control system was required to keep it constant.

<Summary of the Invention> The present invention provides a control method for a three-phase AC-DC converter that facilitates control of AC side power factor and DC side voltage in an AC-DC converter using a three-phase PWM converter. It is something to do.

<Prior Art> FIG. 4 is a connection diagram of a general three-phase PWM converter. e
R+ e S+ 87 indicates the three-phase voltage of the AC power supply.

L beam axle, T Rr - T R6 are switching elements, D1 to D6 are anti-parallel diodes of the switching elements, and C is a capacitor that absorbs high frequency components. The voltage on the DC side is Ed. Switching element T R+ −
The control signal generation circuit that determines on/off of T Rs is:
The configuration is shown in FIG. 5, and the voltage waveforms at each point are shown in FIG. 6.

The three-phase signal generator 1 generates a sine wave signal VB r v5* having the same frequency as the AC power supply and a predetermined voltage and phase.

Generates vo*. VR+V5 and V7 are command values for the AC side voltage VR+V5+V7 of the AC-DC converter.

Sine wave signal VR+V5+VT is triangular wave generator 2
The output eB of is compared with each comparator 3, 4.5,
The comparator output is "1" if the signal is larger.

If the signal is smaller, the switching elements TRr to TR3 on the positive side are turned on and off by the outputs passed through the amplifiers 6 and 7.8, and are turned on when the comparator output is 1, and the switching elements on the negative side are turned on and off when the comparator output is 1. Switching elements TR4 to TR6
Since the signal is supplied through the inverting amplifier 9.10°11, it is turned on when the comparator output is "0".

Therefore, switching elements TR+, TR4, TR2
The pairs of TRs, TR3 and TRs are turned on alternately and do not turn on or off at the same time. Connection points R, S.

The instantaneous voltage value VR' + V5' + V7' of T has a pulse waveform similar to the comparator output, the amplitude is Ed, and the pulse frequency is equal to the frequency of the triangular wave. Instantaneous voltage value V
Average voltage VR+V related to R', v5', , l
51 The amplitude and phase of V7 are sinusoidal signal VR+ V5 +
Follow V7. The average voltage TRI V 5 + VT is the duty factor of the pulse where αR: duty factor α5 of T Rr : duty factor α7 of TR2 * duty 7 actor of T Rs. The phase current IRI 1sI IT is smoothed by each reactor L, and the ripple caused by switching is an if factor α. ,
α8. α is the average voltage VR + v5 according to equation (1)
r It is expressed as the ratio between VT and voltage Ed.

The current 11+12+13 flowing through each element TR+ to TRa is It is expressed as

Now, suppose that each phase voltage eR1e5+ 67 of the AC power supply is expressed as , assuming that their p-p value is smaller than voltage Ed, and each phase current IRI 15+ 17. Average voltage vR9
vS and vT are obtained by subtracting the impedance voltage of the handle L from the AC power supply voltage. That is to say.

However, R is a series resistance component of the reactor, and the DC side current Id is the sum of 11 to i3.

That is, I d ” i + + i 2 + i 3
(6) (2), (51+6) The stain flow Id is expressed by the equation and is determined by the active power of the AC power source. Note that e05ψ is the power factor. Since equation (7) is not a function of wt, there is no alternating current frequency pulsation on the direct current side. Pulse frequency pulsations are absorbed by the capacitor C on the DC side, and if the frequency is increased, the capacitor C only needs to be small.

Also, since the DC power supply voltage Eo is not included in equation (7),
No matter what value Eo has, it can operate in a range larger than the peak value of the AC-DC converter voltage. In order to keep the voltage Ed constant, the current Id in FIG. Adjust IcoBψ to match. The voltage vector t at both ends of the reactor L has the relationship shown in FIG. 7, and it is necessary that the current vector f and the torque t move on the dotted line.

The three-phase signal generator 1 shown in FIG. 5 is specifically configured as shown in FIG. The sinusoidal signal VR+V5!
Outputs V□.

<Problems to be solved by the invention> However, actually configuring a circuit that changes the phase and amplitude according to Ed - Ed is extremely complicated, and when the characteristics change due to reactor saturation or temperature, etc. It was difficult to obtain the value VR+VB+VT.

<Objective of the Invention> The present invention solves these problems and provides a control method for an AC-DC converter that can always operate accurately at a power factor angle of 0.

<Embodiment> FIG. 1 shows an embodiment of the AC-DC converter and its control circuit of the present invention.

The main circuit (the circuit through which power flows) is the same as in Figure 4, but
Here, a current detection circuit 12 on the AC side and a voltage detection circuit on the DC side are added.

FIG. 2 depicts the R-phase operating waveform. To explain the operation for the R phase, first, a command value iR* of the R phase current is obtained by setting the amplitude of the voltage eR' in the same phase as the phase voltage peak to a predetermined value. The difference between the command value IR and the detected instantaneous current value iR', R*.

ip is added to the hysteresis converter 3. now,
Assuming that switching element TRr is off and TR4 is on, the reactor L has a lower potential on the switching element TRd side, so the current iR' gradually increases and becomes larger than the command value iR*. When the difference becomes larger than Δi//2, the comparator output becomes "1", switching element TR+ is turned on and TR4 is turned off. When the switching element TR4 is turned off, the current 4' becomes D! The potential at the R point becomes Ed, and the reactor L
Since the voltage on the right side is higher, the current iR' decreases. The current iR' decreases by the command value iR*, and the difference is Δ
It becomes larger by i/2. and the comparator output is rOJ
Then, switching element TR1 is turned off, switching element TR4 is turned on, and this operation is repeated. The magnitude of Δi is determined by the hysteresis width of the comparator 3. The current iR' is the second
As shown in the figure, it pulsates within a width of Δi around the command value IR, and its average value IR always has a waveform equal to the command value iR*. Since the command value IR is in phase with the voltage eR, that is, ψ=0, the power factor co5ψ on the AC side is always 1.

The operation of the S phase and T phase is the same as that of the R phase described above.

Equations (1) to (7) expressing the relationship between various quantities with respect to the average value are exactly the same as those in the conventional method, but in the conventional method, R
, S, and T points to make the phase current waveform a predetermined phase and amplitude, the method of the present invention does not directly control the phase current waveform to a predetermined one. , R, S, and T points VR+VB+V7 are dependently determined as a result of current control. Therefore, even if saturation of reactor L, temperature change, etc. occur, the current waveform will be accurately controlled according to the command value, and as a result, only the waveform of voltage VB + VB + V□ will change, and the current waveform will not change in the AC system. has no effect.

In order to maintain the power factor at 1 for an AC power source with the present invention, it is sufficient to always set the current command value to be in phase with the phase voltage. In other words, the phase angle is manipulated to create the command value as in the conventional method shown in Fig. 7. There's no need to do that at all. Further, the triangular wave eB shown in FIG. 6 is not required. As a result, the control circuit according to the present invention has a simple configuration. Current command value IR+15. 17
The amplitude of DC I increases, Id increases, and Ed rises. Conversely, when the voltage Ed is large, Id decreases, and when power is regenerated from the load such as in regenerative braking of a load motor, the phase current has an amplitude with the opposite polarity to the phase voltage, and the power is on the DC side. It starts to flow to the alternating current side.

FIG. 3 is a modification of the control circuit in FIG. 1.

First, using the fact that iR+i5+17=O...(8) from equation (4), -t7*-1(I Rs-Is*)...
...The command value lT of the current 11 is created as shown in (9). With this method, one calculator can be omitted for multiplication.

Next, the error amplifier for the voltage Ed is changed from a proportional type to a proportional-integral type to prevent a steady error from occurring in the voltage Ed.

<Effects of the Invention> As described above, according to the present invention, the power factor of AC input is always 1.
The DC bus does not include power frequency ripple, and the load is large,
An AC-DC converter that maintains the voltage on the DC side at a constant value even for small or power generation loads can be easily realized.

[Brief explanation of drawings]

Fig. 1 shows one of the AC-DC converter and its control circuit according to the present invention.
A connection diagram of the embodiment, FIG. 2 is an explanatory diagram of operating waveforms of the control circuit shown in FIG. 1, FIG. 3 is a connection diagram of a modified embodiment of the control circuit of the present invention, and FIG. 4 is a conventional general three-phase PWM. A connection diagram of a converter, FIG. 5 is a conventional current control phase relationship diagram, and FIG. 8 is a configuration diagram of a three-phase signal generator. 3.4.5...Hysteresis comparator, 12...
・Current detection circuit, T Rr - T Rs...Switching element agent Patent attorney Aihiko Fukushi (and 2 others) Figure 1 ，? ) J-fu T0 bowl q dedication map 3rd picture PWM moat 1 ryoshi f7 #F wood grain decoy 4th picture 埒'it*, yki, U-cho mutual map each - Aro, 2 black diagram 5

Claims (1)

[Claims] 1. The command value for each phase current is obtained by multiplying the phase voltage of the AC system by the difference between the command value and the detected value of the DC voltage or its integral value, and if the difference between the command value and the detected value of the phase current is positive or It has a switching means that causes the phase current to flow to the positive or negative terminal on the DC side each time it reaches a certain negative value, and when the DC load fluctuates, it automatically changes the amplitude of the AC phase current to reduce the DC voltage. An alternating current characterized by maintaining a constant value.
DC converter control circuit.