JPH07108096B2 - Uninterruptible power supply control method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an uninterruptible power supply device that supplies electric power to a load uninterruptibly, and particularly to a small-capacity uninterruptible power supply device suitable for OA equipment and the like. Regarding control method.

<Technical background of the invention> Recently, OA (office automation) and FA (factory automation) using a computer have been remarkably spread, and in particular, automation by a small personal computer using a microprocessor is advancing.
They are used as stand-alone or large computer terminals.

These OA and FA systems are generally operated with commercial power supplies, but are unprotected against commercial power supply power interruptions and instantaneous power failures, and there is a risk that programs and memory data will be lost even with a slight power failure. . For this reason, large computers use a dedicated generator or have a large constant voltage, constant frequency uninterruptible power supply (CVCF). On the other hand, a small uninterruptible power supply (hereinafter referred to as UPS) has been used in a workstation such as a personal computer. However, since this kind of UPS is generally installed in the office, it is required to be small, low in noise and inexpensive.
There is a demand for a sine wave output with a constant voltage and a constant frequency, which is a CVCF function, and has little distortion.

<Prior Art and Its Problems> Conventionally, as a control method for this type of UPS, there are, for example, those shown in FIGS. 3 to 5. FIG. 3 shows what is usually called an analog DC feedback control system. The output voltage of a pulse width modulation type inverter 111 which connects a plurality of switching elements to a DC power supply 110 in a bridge manner and changes DC to AC for output. Output filter consisting of LC 11
The output voltage of this output filter 112 is sent to a load (not shown) via 2 and is sent to a rectifier circuit 114, which rectifies and smoothes the input through a voltage transformer 113, and outputs the rectified output. Output voltage of circuit 114 and DC reference voltage circuit 115
The difference between both inputs and the reference voltage of the PI controller 1 via the adder 116
17, the PI controller 117 proportionally and integrates the input (hereinafter referred to as PI operation), and outputs a DC level output signal to the sine wave generator 118, which receives the sine wave generator 118. A sine wave signal corresponding to the input signal is sent to the PWM control circuit 119, and the PWM control circuit 119 outputs a pulse width modulation signal (hereinafter referred to as a PWM signal) in which the pulse width is modulated by the sine wave input signal and the triangular wave carrier. The voltage is sent to each switching element of the inverter 111 to control the output voltage of the inverter 111, and feedback control is performed so that the output voltage of the output filter 112 matches the reference voltage.

In this method, alternating current is converted to direct current, rectified and smoothed, and feedback is applied. Therefore, it takes several cycles to respond, a response within one cycle cannot be made, and a transient response is slow,
Further, since the feedback becomes a DC loop, a feedback loop that corrects the waveform distortion is not formed, and in addition, the inverter generally needs to have a dead time (a quiescent period for preventing arm short circuit). The control input signal (PWM signal) is not perfectly proportional to the output voltage, and even if a sinusoidal wave without distortion is input to the PWM control circuit, the output will be distorted and the output waveform distortion will be large. There is. Moreover, in a non-linear load such as OA equipment, a current flows only at the peak of the output voltage, and the output waveform has a so-called distorted waveform with many flattened peaks near the peak. Has the problem of becoming. FIG. 4 shows a so-called digital operation control system, which is an output voltage transformer 1 of the output filter 112.
Input to A / D converter 120 via 13
0 converts the analog value into a digital value and inputs it to the arithmetic unit 121 via an input unit (not shown). The arithmetic unit 121 arithmetically sets the PWM pattern of one cycle of the output power, and the set value Storage unit 1 that stores the PWM pattern based on
The data is read out from 22 and thereby, the inverter is controlled via the output section (not shown), and feedback control is performed so that the output voltage matches the reference value.

In the case of this method, since the value of one cycle is averaged and compared with the reference voltage, it can respond only after one cycle, and it takes two to three cycles to converge to the target reference value. There is a problem that the feedback cannot be performed against the wave distortion and the waveform distortion becomes large.

Further, FIG. 5 is a so-called multi-feedback control system, and in the configuration of FIG.
It is input to the PWM control circuit 119 via 3 and the adder 123, and an instantaneous value feedback loop that instantaneously changes the PWM signal in response to transient voltage fluctuations is added to add transient characteristics and distortion. This is intended to improve the characteristics.

Even in the case of this method, it is difficult to increase the gain of the instantaneous value feedback loop, the transient response cannot be sufficiently improved, and the waveform distortion cannot be suppressed sufficiently. There is a problem that the configuration is complicated and adjustment is time-consuming. That is, in the feedback loop, the gain of the open loop before this feedback loop is closed is
It must be less than 1 (gain OdB) before the phase delay exceeds 180 ° (otherwise it will oscillate). However, as shown in FIG. 5, a phase delay first occurs in the output filter 112 portion consisting of L and C, and this output filter is a second-order delay, so the phase is delayed by 180 °. This indicates that the open loop gain cannot be increased to 1 (OdB) or more above the cutoff frequency fc of the output filter. On the other hand, since the above output filter needs to sufficiently suppress the PWM carrier of the inverter, the cutoff frequency fc has a value (fc << fo which is sufficiently lower than the switching frequency and carrier frequency (hereinafter referred to as switching frequency) fo. ) Must be set. If this is further explained by the Bode diagram shown in FIG. 6, the output filter 112 has the cutoff frequency f
In the vicinity of c, the gain has an LC resonance peak as shown by the solid line A ₁ and the phase changes abruptly as shown by the solid line A ₁ ′. Also,
The output voltage of the inverter has a very large switching frequency component because the DC input voltage is output as it is with its peak value. To sufficiently suppress this, the cutoff frequency fc of the output filter is set to fc <<Must have a relationship of fo.

Generally, the switching frequency fo is 20
The cutoff frequency fc is 1 because it is selected at about 30kHz.
Approximately 2kHz (fc = fo / 10-20) is required.

In order to provide stable feedback to a system including such a transmission element, an open loop is shown in FIG.
It is necessary to adjust the gain and phase so that the characteristics shown by B ₁ and B ₁ ′ are obtained. Looking at this in the block diagram shown in FIG. 7, the transfer relationship G is If GI and H in the above equation are GI = 1 and H = 1, and the open loop becomes -1, the denominator (1 + GC ·
Since GI, GF, H) will be 0 and will oscillate, GC
Stable feedback cannot be realized unless the (PI adjuster) has the characteristics of the dotted lines C ₁ and C ₁ ′ shown in FIG.

Thus, open-loop gain cutoff frequency
Unless the phase is decreased near fc, the gain becomes OdB (1) or more, and the system becomes unstable or becomes oscillating even though the phase delay φ approaches 180 °. For this reason,
The frequency fx at which the gain of the open loop becomes OdB has a relationship of fx <fc. For example, unless fx≈fc / 10 to 3 is set, a sufficiently stable feedback loop cannot be formed. Now, to make it easier to understand, fc is 1.5kHz, fx is
If fc / 5, then fx = 300Hz, and the gain of the open loop for the fundamental wave f ₁ is fx / f ₁ = 300/60 = 5 (provided that f ₁ = 60Hz) for the 3rd harmonic f ₃ . Is fx / f ₃ = 3
Only 00/60 x 3 = 1.7, which means that the open loop gain cannot be increased. This means that for the fundamental wave (eg 60Hz), there is only about 1/5 the ability to suppress disturbances (power supply voltage fluctuations, load fluctuations, etc.) (ability to maintain a constant voltage), and 20% If there is a change 4
% (20% x 1/5) output fluctuation will occur.

As for the distortion, it is possible to suppress the third harmonic to some extent, but for higher harmonics, the open loop gain becomes smaller than 1 (OdB) and the suppression is suppressed. Can not do it. Moreover, since the LC filter (output filter) is sufficiently effective from twice or more the cutoff frequency fc, it can be said that the harmonic distortion is not improved between 300 Hz and 3 kHz.

On the other hand, as for the transient response characteristic, the open loop gain is small in the high frequency range, so the response at the time of sudden load change is poor, and the stability cannot be maintained. For example, the output voltage becomes as shown in FIG. Sufficient performance cannot be obtained. Also, in the case of a device having a capacitor input type rectifier circuit such as an OA device, the output voltage has a distorted waveform with a flat peak as shown in FIG. As described above, the small open-loop gain in the high frequency range is not very effective in improving the characteristics.

Even with respect to the fundamental wave component, the above-described gain cannot satisfy the constant voltage accuracy, so it can be said that the DC feed loop must be used together.

As can be seen from the Bode diagram in Fig. 6, this method cannot be used to increase fx other than increasing fo, as long as the relationship of fx <fc << fo is established. It is difficult to increase fo in view of the increase in operating speed and switching loss of the switching element, and as a result, fx cannot be increased so much that open loop gain cannot be increased.

<Objects of the Invention> The present invention has been made in view of the above points, and a large open loop gain can be obtained with a simple configuration of only an instantaneous value feedback loop without forming a two-system feedback loop. An object of the present invention is to provide a control method capable of achieving a significant improvement in characteristics.

<Outline of the Invention> In order to achieve the above object, the output voltage of the inverter has a phase delay of 90 ° or less, and a deviation from the reference sine wave signal is taken through a voltage feedback circuit including an RC filter.
By inputting this to the PI controller, the open loop gain is increased and instantaneous feedback control is performed without oscillating the system.

<Embodiment of the Invention> An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. 1 is a commercial AC power supply (hereinafter referred to as a commercial power supply), 2
Is a DC power supply unit which is connected to the commercial power supply 1 and supplies a DC power supply without interruption. This is connected to a commercial power supply 1 with a rectifying / smoothing circuit 21 that rectifies and smoothes an input and outputs a direct current, and a charging power supply circuit 22 that has a power transformer and a rectifier and is configured to always float-charge a storage battery 23. Switch the output end of the storage battery 23 to the output end of the rectifying / smoothing circuit 21.
The storage battery 23 is always connected to the storage battery 24 via a float, and when the commercial power supply 1 fails, the switch 24 is closed by the output signal of the control means (not shown) to discharge the charge of the storage battery 23. It is designed to let you. 3 is an inverter, 4 switching elements consisting of MOS FETs Qu and Q
The Qu and Qx drains of Qu and Qv are connected to the input end P, the sources of Qx and Qy are connected to the input end N, and Qu and Qx, Qv and Qy are connected to form a bridge circuit. Pulse width modulation signal (hereinafter referred to as PWM signal) input to the gates of switching elements Qu, Qv, Qx, and Qy with the connection point of Qy and Qy as the output end.
By this, DC is converted into AC and output. In addition, between the drain and source of the switching elements Qu, Qv, Qx, Qy, a free wheel diode D
u, Dv, and Dy are inserted in the opposite directions. 4 is
In the output filter connected to the output terminal of the inverter 3, the reactor L ₁ is inserted between the connection point of the switching elements Qu and Qx of the inverter 3 and one of the output terminals, and the other of the output terminals is connected to the switching element. Connect to the connection point of Qv and Qy, insert a capacitor C ₁ between the output terminals,
A filter is formed, the switching frequency included in the output voltage of the inverter 3 is filtered, and the output is sent to the load (not shown) from both ends of the capacitor C ₁ . 5 is a voltage feedback circuit which is connected from the input end of the output filter 4 and detects and outputs the input voltage. The voltage dividing resistors R ₁ and R ₂ are inserted between the input terminals of the output filter 4. , capacitor C ₂ between the resistor R ₂ terminal
Are connected in parallel to form a CR low-pass filter, and the output filter 4 is connected between the terminals of the capacitor C _2.
The voltage that is proportional to the input voltage of
It is designed to output as a feedback signal.
Reference numeral 6 is a reference sine wave generating circuit for transmitting a reference sine wave signal of a commercial frequency (for example, 60 Hz) of the commercial power source 1 by the reference signal of the crystal oscillator. Reference numeral 7 is a PI adjusting circuit which is connected from the voltage feedback circuit 5 and the reference sine wave generating circuit 6 and proportionally integrates the deviation between both inputs (PI operation) and outputs the result. This is because the input terminal of the inverting amplifier A ₁ is connected to the connection point between the resistors R ₁ and R ₂ of the voltage feedback circuit 5, the other terminal of the resistor R ₂ is grounded, and the non-inverting input terminal is grounded. Connect the output terminal of the inverting amplifier A ₁ to the inverting input terminal of the operational amplifier A ₂ via the resistor R ₃ and the output terminal of the reference sine wave generating circuit 6 via the resistor R _4. , a resistor R ₅ and capacitor C ₃ between the output terminal of the operational amplifier a ₂ and the inverting input terminal is inserted in series, and outputs from the output terminal of the operational amplifier a _2. Reference numeral 8 denotes a PWM control circuit connected to the output terminal of the PI adjustment circuit 7, which has a reference triangular wave carrier generator and a comparator, compares the input signal with the carrier, and modulates the pulse width of the PWM signal to obtain the inverter. It is designed to be sent to the 3rd party. Next, the operation will be described. The DC power supply unit 2 receiving the commercial power supply 1 applies the DC voltage rectified and smoothed by the rectification smoothing circuit 21 to the inverter 3, and the storage battery 23 is float-charged via the charging power supply circuit 22. The inverter 3 outputs the DC voltage to the P of the PWM control circuit 8.
The WM signal sequentially controls the switching elements Qu to Qy to be turned on and off to be converted into an alternating voltage and output. The output filter 4 that receives this filters the switching frequency of the output voltage of the inverter 3 and applies an AC voltage to a load (not shown). Then, the output voltage of the inverter 3 is fed back. At this time, the output voltage of the inverter 3 is PWM
Since it is a wave, direct feedback cannot be applied, so the voltage feedback circuit 5 formed in the low pass filter by RC filters the switching frequency,
Demodulate the above PWM wave and output. PI adjusting circuit 7 that has received this, the input voltage is inverted and amplified by the inverting amplifier A _1, which was sent together with the reference sine wave signal of the reference sine wave generating circuit 6 to the operational amplifier A _2, the operational amplifier A ₂ is The deviations of both inputs are proportionally integrated and output to the PWM control circuit 8. The PWM control circuit 8 compares the input and the carrier and sequentially sends out the PWM signal to each switching element of the inverter 3 to control the output voltage of the inverter 3 to be a constant voltage. In this feedback control operation, the voltage feedback circuit 5 formed in the RC filter sets its cutoff frequency fD to fo / 3 to 5 (where fo: switching frequency). The switching frequency fo is removed and the voltage is output. Since the RC filter of this voltage feedback circuit 5 has a primary delay, the phase delay φ is 90 °. The block diagram of this feedback loop is shown in FIG. 10, and as can be seen by comparing this with FIG. 7 described above,
The GF (output filter) is out of the feedback loop, and the open-loop transfer function Go is Go =
Gc · GI · H, which is explained by the Bode diagram shown in FIG. 11. Solid lines A ₂ and A ₂ ′ show open loop characteristics before the PI operation is applied. From this A ₂ ′, As you can see, the phase delay φ is only 90 °, so
It seems that the open loop gain can be increased as much as possible, but in reality, due to the characteristics of the inverter 3, the phase suddenly lags as shown by the dotted line A ₂ ″ as it approaches the switching frequency fo, which cannot be ignored. Therefore, the gain of the open loop is set such that the frequency fx at which the gain becomes OdB is, for example, about fo / 4.Now, it is assumed that the cutoff frequency fD of the voltage feedback circuit 5 is set to fD = fo / 4. For example, the characteristics of the PI control circuit (GC) set so that fx = fD are shown by dotted lines B ₂ and B ₂ ′, and open loop Go = Gc ·
The characteristics of GI · H are as shown by the one-dot chain lines C ₂ and C ₂ ′. As a result, comparing with the conventional example using the above-mentioned numerical values, the conventional example fo = 20kHz fx = 300Hz This example fo = 20kHz fx = 5kHz, and the gain of the open loop is approximately 17 times (5kHz
/ 300Hz) can be increased. Therefore, the gain of the fundamental wave is 83 times as the gain ratio (5kHz / 60Hz) The gain of the third harmonic is 28 times as the gain ratio (5kHz / 60Hz × 3) The gain of the fifth harmonic is 17 times as the gain ratio (5kHz It becomes / 60Hz × 5), and it is possible to obtain a sufficiently high gain for harmonics as compared with the conventional one.

Further, since the output filter is excluded from the feedback loop, even if the cutoff frequency fD of the voltage feedback circuit 5 is set higher than the cutoff frequency fc of the output filter 4 (fD> fc), the system does not become unstable. The cut-off frequency fc of the output filter 4 can be set so as to sufficiently suppress the harmonics, the appropriate delivery response characteristics can be further improved, and harmonic distortion can be improved.

In addition, the accuracy of the fundamental wave is 0.24% (20% / 83) even if there is a 20% disturbance by using the numerical value of the above-mentioned conventional example.
It appears only as the output fluctuation of, and the accuracy can be further improved.

It goes without saying that the output filter 4 and the voltage feedback circuit 5 in the embodiment can be variously modified without changing the gist.

<Effect of the Invention> According to the present invention, the feedback signal of the inverter output voltage is kept at a phase delay within 90 °, the deviation from the reference sine wave signal is taken, and the PI adjustment is performed. The open-loop gain can be increased in a high frequency range, and the instantaneous voltage control of the inverter output voltage can be performed with high accuracy.

In addition, since the open loop gain can be increased in the high frequency range, the transient response can be further improved, and a good quality power supply can be supplied even for load fluctuations, power failures-power recovery, sudden power changes, etc. be able to. Moreover, since the feedback loop is formed without forming the two systems and excluding the output filter of the inverter, the output filter has its cutoff frequency without destabilizing the system, It can be set so that high frequencies can be controlled sufficiently, harmonic distortion can be further improved, and a sine wave with a low distortion rate can be output.

Furthermore, the feedback signal of the inverter output voltage, which is taken out with a phase delay of 90 ° or less, can be configured simply by adding an RC filter to the output end of the inverter, which simplifies the configuration, facilitates adjustment, and improves reliability. It is possible to provide a highly inexpensive and inexpensive device. Also, since the feedback loop can be configured without coupling with a voltage transformer etc., even if there is a DC component in the output voltage of the inverter, it can be automatically corrected, and an output that does not generate a DC component in the load can be generated. Can be sent out.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram concretely showing the main part of FIG. 1, and FIG.
5 to 5 are block diagrams showing a conventional example, and FIG. 6 is
FIG. 5 is a Bode diagram, FIG. 7 is a block diagram of FIG. 5, FIGS. 8 and 9 are output voltage and load current waveform diagrams in the conventional example, and FIG. 10 is a diagram of FIG. Block diagram, number 11
The figure is a Bode diagram of FIG. 2: DC power supply section, 3: Inverter 4: Output filter, 5: Voltage feedback circuit 6: Reference sine wave generation circuit, 7: PI control circuit 8: PWM control circuit

Claims (1)

[Claims] 1. An uninterruptible power supply unit which is connected to a DC power supply unit for uninterruptible output and which supplies an output voltage of an inverter controlled by a PWM signal to a load through an output filter. To the input terminal of the PWM control circuit that sends the PWM signal to the PI control circuit that sends the output that is proportionally integrated, connect the reference sine wave signal and the voltage feedback circuit consisting of the RC filter to the input terminal of this PI control circuit. By inputting a deviation from the output voltage of the inverter through the output voltage of the inverter, the phase delay of the feedback signal is kept within 90 °, and the instantaneous voltage is controlled. Control system for power failure power supply.