JPH0199478A - Control device for power converting device - Google Patents

Abstract

PURPOSE:To cause the output voltage of sinusoidal wave to follow the reference signal without stationary deviation, by inserting a sinusoidal wave signal generator into a voltage control loop for a sinusoidal wave voltage output device and into a current control loop for a sinusoidal wave current output device. CONSTITUTION:A power converting device is composed of a DC power source 1, an inverter 2 and an AC filter 3 and feeds the current to a load 4. On the other hand, a control device is composed of an auxiliary transformer 5 to detect output voltage and to step down the voltage level, a sinusoidal wave reference voltage generator 6, a subtractor 7, a pulse generator 9 and a pulse amplifier 10. On this occasion, provided are a sinusoidal wave oscillator 11 to input the difference between the sinusoidal wave reference voltage and the output voltage (limited deviation) and a gain 12 to input the oscillator output and outputs the modulation rate. The stationary deviation thereby becomes zero and the output voltage follows without deviating the amplitude, pulse difference and reference limited wave.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is applicable to power supplies that require a sine wave voltage output, such as PWM inverters for uninterruptible power supplies, or grid-connected PWM inverters, The present invention relates to a control device for a power conversion device such as a power source that requires a sine wave current output.

(Conventional technology) In general, power outage power supplies for computers are required to output a sine wave voltage with a small distortion factor, and grid-connected inverters are required to output a sine wave voltage with a small distortion factor. It is required to output a synchronized sinusoidal current with little ripple. PWM inverters are often used in these devices.

There are various methods to control a PWM inverter, but they can be broadly divided into:

A. A method in which a pulse pattern is determined over one cycle so that the output is as close to a sine wave as possible, and the average value of the output is compared to control the deviation to zero. B. The output reference value is a sine wave, and the instantaneous There are two types of methods: one that compares the instantaneous output value with a reference value and controls the deviation to zero.

Method A has been widely used in the past, but it does not provide a very high-speed response, and method B is becoming more widely used.

An example of method B is shown in FIG. 16 using a single-phase PWM inverter for an uninterruptible power supply as an example.

In Figure 16, 1 is a DC power supply, 2 is an inverter that converts DC to AC, 3 is an AC filter that smoothes the output voltage, 3a is the AC filter glue handle, 3b is the AC filter capacitor, 4 is the load, and 5 is the output An auxiliary transformer that detects the voltage and reduces the voltage level, 6 is a sine wave reference voltage generator,
7 is a subtracter that takes the difference between the auxiliary transformer output voltage and the reference voltage;
8 is a compensator that outputs a modulation rate according to the control deviation; 9 is a pulse generator that generates firing and extinguishing pulses for the semiconductor elements constituting the inverter 2 according to the modulation rate; 10 is a pulse generator pulse It is a pulse amplifier that amplifies the signal.

is often used.

(Problems to be Solved by the Invention) However, in this method, the control deviation, that is, the difference between the sine wave reference signal and the actual output, does not become zero.

A slight difference in amplitude or phase remains. -Generally P
A system using an I controller can follow a step-like target value with zero steady-state deviation, but cannot follow a sinusoidal-like target value without a steady-state deviation. For this reason, for example, voltage accuracy decreases in a single-phase inverter, and voltage 'l?' in a three-phase inverter. IJ! In addition to a decrease in i, an unbalanced output voltage and a shift in phase difference occur due to unbalanced loads, variations in filter constants, etc., resulting in a problem in that the quality of the voltage deteriorates.

An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a device that requires a sine wave voltage output so that the output voltage can follow a reference signal without steady-state deviation even if there is an unbalanced load or variations in circuit constants. In a device that is required to output a wave current, it is an object of the present invention to provide a control device that allows the output current to follow a reference current without steady-state deviation.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention, as shown in FIG. In addition, in a device requiring a sine wave current output, a sine wave signal generator is inserted in series with the current control loop.

(Function) Figure 1 shows an embodiment of the present invention.
Components with the same reference numerals as those in FIG. 6 indicate the same components, and therefore the description thereof will be omitted. In FIG. 1, 11 is a sine wave oscillator which inputs the difference (limited deviation) between the sine wave reference voltage and the output voltage, and 12 is a gain which inputs the output of the sine wave oscillator and outputs a modulation factor. The oscillation frequency of the sine wave oscillator 11 is the same as the oscillation frequency of the sine wave reference voltage generator 6.

Hereinafter, it will be explained that the steady control deviation becomes zero in FIG. 1.

When FIG. 1 is rewritten as a block diagram as a control system, it becomes as shown in FIG. 2. In FIG. 2, reference numeral 13 represents the components from the pulse generator 9 to the auxiliary transformer 5 in FIG. When the transfer function of the controlled object 13 is G(s), the following relationship holds true between the control deviation e(s) and the reference value vFnt(s).

The reference value is Whef(8) = τ-go' VpHf (V
? $1f=amplitude)S+ω According to the final value theorem of Laplace transform, if the closed loop system is stable, Qin e(t)=&lim 5−e(s)t−1oo
s→0 =I2ims” □ s→o s”+ω”+G(s)Kω=0
■It becomes. That is, the steady-state deviation becomes zero, and the output voltage follows the reference limited wave without deviation for both amplitude and phase difference. As is clear from the calculation of equation (2), even if the parameters of the controlled object vary and G (s) varies, as long as the closed loop system is stable, the steady-state deviation will be zero.

The discussion above has proceeded on the assumption that the controlled object 13 is linear and can be expressed by the transfer function G (s), but even if the controlled object is nonlinear, the steady-state deviation will still be zero as long as the closed-loop system is stable. This is because the property that the steady-state deviation is zero is due to the provision of the sine wave oscillator inside the control system, and is not dependent on the properties of the controlled object.

(Example) Other embodiments of the present invention are shown in FIGS. 3 and 4.

FIG. 4 is a diagram showing details of the portion surrounded by the dotted line in FIG. 3. In FIG. 4, 14a and 14b are integrators, and 15a
.

15b are gains with values of -ω and ω, respectively, 16a, 16
b is an adder, and 17a and 17b each have a value of kottl.
This is the gain of caz. Dotted line part 1 on the left side in Figure 4
1a is a sine wave oscillator representing lla in FIG. 3, and the dotted line portion 12a on the right side in FIG. 4 is a gain representing 12a in FIG.

Generally, a sine wave oscillator that receives a control deviation e (t) as an input can be expressed by the following state equation.

Expressing this in terms of area, the embodiment shown in FIG. 2 uses only two of the two states of the sine wave oscillator. 21,2. Using both increases the degree of freedom in design, and can be expected to improve stability and transient response. In that case, the feedback rule is that the control input (modulation rate) is U. The gain of equation 0 is the gain 12a in FIG.
These are gains 17a and 17b in the figure.

FIG. 5 shows another embodiment of the invention. In FIG. 5, a direct route from the control deviation to the control input is added to FIG. 3, further increasing the degree of freedom in design.

Next, another embodiment of the present invention will be described with reference to FIGS. 6 and 7. In FIG. 6, numerals 1 to 7 and 9 to 10 are the same as in FIG. 16. Further, lla and 12a are the same as in FIG. 3. In FIG. 6, 18 is a CT for detecting the current flowing through the AC filter handle 3a, 19a,
19b is a gain for minor feedback of the output voltage and the reactor current, respectively; 20 is an adder;
21 is a subtracter.

When FIG. 6 is rewritten as a block diagram as a control system, it becomes as shown in FIG. 7. The gain □ in FIG. 7 and the gain 11jhl in FIG. Yes, and the minor loop further increases the degree of freedom in design.

Improvements in transient response can be expected.

An embodiment using analog control has been described above, but an embodiment using digital control will be explained using FIGS. 8 to 10. In FIG. 8, the same reference numerals as in FIG. 6 indicate the same components, and therefore the description thereof will be omitted. In FIG. 8, reference numeral 22 is an interface that converts the output voltage and reactor current into digital signals at each sampling period, and is actually composed of a sample hold, an A/D converter, and the like. 23 is a control calculation device that calculates a control law based on the signal obtained from the interface 22 and calculates the pulse width that the inverter should output for each sampling period, and is actually composed of a microprocessor or the like.

The circuit equation for the main circuit portion of FIG. 8 is as follows.

Here, VQ is the output voltage, iL is the saddle current, v
l is the inverter bridge output voltage.

When defined as , the formula ■ can be expressed as follows.

x=Ax+B-vl 1g)
Now, let the sampling period be T, and the interval kT≦t<(k
Suppose that the output pulse pattern of the inverter at ÷1)T (k=o, 1.2...) is determined as shown in FIG. In other words, consider a pulse in which the center of each sampling period coincides with the center of the pulse.

At this time, with x (kT) as the initial value, the differential equation 0 is changed to t
= (k+1)T When solved and linearized approximation is performed, the following is obtained.

x ((k+1) T )” F −x(k) + G
-u(k) (10) Here, A engineering F=e, G=e 2・BE, u(k)=±ΔT
(11) For this PWM inverter, the 10th
The control system shown in the figure can be constructed. In FIG. 10, 24 is the main circuit of the PWM inverter including an AC filter and a load, and is modeled by equation (10).

25 is a discrete time sine wave reference voltage generator, 26 is a discrete time sine wave oscillator to which the control deviation is input, and its pulse transfer function is 'ZsinuT-1.

Z −22CO8(llT+1 27a and 27b are feedback gains, 28a is a subtracter that compares the output voltage with a reference value, and 28b is a subtracter.

Although Fig. 10 is different from Fig. 7 in that it is analog and digital, it is the same in that the sine wave oscillator is inserted vertically into the control loop, and the output follows the reference sine wave without deviation. .

Above, we have described examples of single-phase PWM inverters, but
An embodiment of a three-phase PWM inverter will be described using FIG. 11 and FIG. 12.

In FIG. 11, the same reference numerals as in FIG. 8 indicate the same components, and therefore the description thereof will be omitted. 29 in Figure 11
is a three-phase inverter bridge, 30 is a three-phase AC filter,
31 is a three-phase load, and 32 is an auxiliary transformer.

33a and 33b are CTs for detecting AC filter current.

Generally, the output line voltage of the AC filter of a three-phase inverter is Vcabe, Vcbcy, and Vcea.
+ Vcbe + Vcea: Since there is a relationship of 0,
Of the three voltages, only two are independent. Similarly,
Inverter bridge output voltage Viabt VibQy
Viab + Vtbc + Vtc also between Vtca
Since there is a relationship of a = 0, if the pulse width of each sampling period is controlled for two of the three, the remaining one is automatically determined. Therefore, a three-phase PWM inverter can be considered a two-man crab output system.

Therefore, for example, when controlling Veab and Vcbe, it is sufficient to prepare Vtab and Vr6fbc as sine wave references. FIG. 12 shows a block diagram for digitally controlling a three-phase PWM inverter. In FIG. 12, 34 is a controlled object that includes everything from the pulse generator 9 to the interface 22 in FIG. 11, 35a, 35b
39a and 39b are sine wave signal generators that provide voltage references for the ab and bc phases, respectively; subtracters 36a and 36 that compare the output voltages with the ab and be phase references, respectively;
b is a sine wave oscillator whose input is the control deviation obtained from the comparison, 37.38 is a feedback gain, and 40
is a subtractor.

According to this embodiment, both the AB phase and BC phase output voltages follow their respective reference voltages without deviation, so even if there is unbalanced load or variation in the circuit constants of the AC filter, the three-phase output voltages will be unbalanced. Very good voltage accuracy is maintained without occurrence of Further, the phase difference between the output voltages is also kept constant at almost 120°.

Next, another embodiment of the present invention will be described using FIGS. 13 and 14. FIG. 13 is a diagram showing an example of a grid-connected inverter using a voltage-type PWM inverter. 1 may be any DC voltage source, such as a solar cell, a fuel cell, or a chargeable/dischargeable battery. 29 is a three-phase inverter bridge, 41a, 41b.

41c is a grid interconnection reactor, 42 is a transformer, and 43 is a three-phase AC voltage source indicating a power system.

Generally, in a grid-connected inverter, active power (P) and reactive power (Q) are controlled by following the active power command (Phof) and reactive power command (Q-af) given from a higher-level power dispatch center, etc. required to occur. PrQf
Since the instantaneous value of the current that should flow through the grid-connected reactors 41a, 41b, and 41c can be easily calculated from the instantaneous value of y Qrot and the grid voltage, it is necessary to give the actual control system accelerator current reference value and make the reactor current follow it. FIG. 14 shows an example of a block diagram of a control system that is often configured. System voltage Va
t Vbt From VQ, sine wave current reference 1reta+Qr
46a and 46b are current reference generators that produce efb, subtractors that compare the current references of the a phase and b phase with the actual accelerator current, and 47a and 47b are the a phase and b phase currents, respectively.
A sine wave oscillator receives phase current deviation as input, 48.49 is a feedback gain, and 50 is a subtracter. In this embodiment as well, even if there are variations in the main circuit constants, system a voltage unbalance, etc., the reactor current follows the current reference without deviation, and extremely accurate active/reactive power control is achieved.

Although an embodiment of controlling a grid-connected inverter using a three-phase PWM inverter has been described above, it goes without saying that a similar control system can be configured for a single-phase grid-connected inverter. Further, the control method proposed by the present invention can also be used to control a current source PWM inverter as shown in FIG. Furthermore, this method can also be used when controlling the current supplied from alternating current to a sine wave in a PWM converter.

〔Effect of the invention〕

As explained above, according to the present invention, in a power conversion device provided with a sine wave voltage reference or a sine wave current reference, the output voltage or current can be adjusted to the reference value without deviation even if there are variations in circuit constants or voltage imbalance. It is possible to configure a system with extremely good steady-state characteristics.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a block diagram of the control system shown in FIG. 1, FIGS. 3 and 4 are diagrams showing a second embodiment of the present invention, 5 is a diagram showing a third embodiment of the present invention, FIG. 6 is a diagram showing a fourth embodiment of the present invention, "7
The figure is a block diagram of the control system shown in FIG. 6, FIG. 8 is a diagram showing one embodiment of the digital control of the present invention, and FIG.
10 is a block diagram of the control system of FIG. 8. FIG. 11 is a diagram showing an embodiment of the three-phase PWM inverter of the present invention.
11 is a block diagram of the control system, FIG. 13 is a diagram showing an embodiment of the grid-connected inverter of the present invention, FIG. 14 is a block diagram of the control system of FIG. 13, and FIG. 15 is a block diagram of the control system of FIG. 16 is a diagram showing an example of a current source PWM inverter, and FIG. 16 is a diagram showing an example of a conventional device. 1...DC power supply 2...Inverter 3...
・AC filter 3a...Reactor 3b...
Capacitor 4...Load 5...Auxiliary transformer 6...Sine wave reference voltage generator 7...Subtractor 8...Compensator 9...Pulse generator 10...Pulse amplifier 11. 1 la
- Sine wave oscillator 12, 12a, 12b - Gain 13.
...Controlled object 14a, 14b...Integrator 1
5a, 15b-gain 16a, 16b,
16cm adder 17a, L7b -- gain 18
-CT19a, 19b...Gain 20...Adder 21...Subtractor 22...Interface 23...Control calculation device 24...Controlled object (single-phase PWM inverter) 25...
- Sine wave reference voltage generator 26...Sine wave oscillator 27a, 27b...Gains 28a, 28b...Subtractor 29...
Three-phase inverter 30...AC filter 31...
・Three-phase load 32...Auxiliary transformer 33a, 3
3b...CT34...Controlled object (three-phase PWM inverter) 35a, 35b...Sine wave reference voltage generator 36
a, 36b...Sine wave oscillator 37.38...Gain 33a, 33b...Subtractor 40...Subtractor 41a, 41b, 41cm interconnection reactor 42...
Transformer 43...Power system 44...Controlled object (grid-connected inverter) 45...Sine wave reference current generator 46a, 46b...-Subtractor 47a, 47b...Sine wave oscillator 48, 49 ...
Gain 50...Subtractor 51...DC current source 52...Current source inverter 53...Capacitor agent Patent attorney Noriyuki Chika Kendai Daishimaru Kendai 5 Figure/'/ Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] A power conversion device that compares a sine wave voltage reference value and an output voltage value or a sine wave current reference value and an output current and controls the deviation to reduce the deviation, characterized by connecting a sine wave oscillator in series with the control loop. A control device for a power conversion device.