JPS60128515A - Controller of power converter - Google Patents

Abstract

PURPOSE:To control stably the entire region of load state by compensating the gain variation of a control system produced by the impedance change of a load circuit by means of a correction signal operating device. CONSTITUTION:Plural inverters are connected to the output side of a common converter and each inverter drives an induction motor individually. A DC voltage is inputted to the inverter via a main circuit contactor 23 and an input capacitor 22, the voltage is converted into a variable voltage/variable frequency and the result is fed to the said motor. In this case, a voltage feedback signal VFBK, a current feedback signal IFBK and an operating signal 6 representing the on/off state of the contactor 23 are inputted to a correction signal operating device 5 so as to operate the load resistance component of the converter and also the load capacitor component is operated from the capacitor 22. Then a function cancelling the main circuit transfer function is operated and the result is inputted to a gain correction signal 7 as a voltage controlling operator VC.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a power conversion method that performs negative feedback control of a controllable power converter that converts AC power to DC power so that the output DC voltage matches a set value. This relates to a control device for a device.

[Technical background of the invention]

This type of power converter (hereinafter referred to as a converter) is widely used in applications that require a stably controlled DC voltage and a wide range of load fluctuations, such as power supplies for variable-speed motors. There is. In particular, the method of guiding the curved output of the converter mentioned above through a smoothing circuit to an inverter (hereinafter referred to as inverter 9), where it is converted into variable voltage, variable frequency AC power to drive an AC motor, is widely used. It is being FIG. 1 shows a device for implementing such a drive method.

Figure 1 shows a device configuration in which a plurality of inverter devices 2 are connected to the output side of a common converter device, and an AC motor, for example an induction motor 3, is individually driven by each impedance. I'll go. The convergence device l is
The input AC power is converted to DC power with a DC sound pressure vTHY by the anti-parallel connected converter/l, and then the reactor/
LO smoothing circuit k' consisting of 2 and core capacitor 13
The FIJ is performed to generate electric power as a DC voltage Vc with less pulsation.

The inverter device 2 converts the DC power of the voltage Vc into variable voltage, variable frequency AC power by the voltage type inverter 21 via the main circuit contactor 23 and the input capacitor 22, and supplies it to the induction motor 3. This is then controlled at variable speed. Each of the innovators 2/ is equipped with a control device for controlling variable voltage and variable frequency. Here, the voltage reference signal vRF, F is the capacitor 1
It is compared with the voltage feedback signal ■FBK obtained from both ends of 3, that is, the output terminal of the converter device/through the lightning voltage detector VD, and the deviation thereof is amplified by the voltage control calculator ■0 and sent to the voltage reference signal generator R1I. , F.

This current reference signal ■R11;F is further converted to a converter/
It is compared with the voltage feedback signal generator FBK obtained through the current detector IDi provided on the AC input side of
The firing phase of the converter // is controlled through the converter.

FIG. 2 is an equivalent circuit representation of the main circuit section extending from the LO smoothing circuit to the load in FIG. 1, that is, the load circuit as seen from the converter/l. The load resistance ≠ expressed as a variable resistance is expressed by assuming that the induction motor 3 serving as a load via the inverter device 2 is isometrically considered as a resistance component. This equivalent circuit connects reactor /2 in a plane row to the power supply input terminal of voltage vTHY, and capacitor 13 is connected to the output side.
, capacitor n, and load resistance≠ are connected in parallel.

The frequency transfer function G(jω) in the above-mentioned equivalent circuit is as follows: ffi ""'resonant frequency tF=ζ damping coefficient R0, which is an element of second-order lag.

From FIGS. 1 and 2, a block diagram of the control system of the converter device 1 is shown in FIG. 3. This control system has a so-called current minor-7'' OML, and the transfer function of this current minor loose is approximated to a first-order lag element and expressed simply as G.0 in Figure 3. , GAvR is the transfer function of the voltage control calculator Va, and similarly, GAOR is the transfer function of the current control calculator c'a, GI + G2
rGR is the transfer function of each main circuit portion, GVD is the voltage detector VD, and G is the transfer function of the current detector.

The transfer function Gs in FIG. , that is, the gain of the control system changes depending on the resistance value R of the load resistance l and the number of connected inverter devices 2, that is, the combined capacitance C.

[Problems with background technology]

From what has been stated above, the apparatus shown in FIG. 1 has the following disadvantages.

(1) Since the gain of the control system changes significantly depending on the load condition (the values of the toe 9, R and C), it is extremely difficult to perform stable control with fast response over the entire range.

(2) Stability can be increased by slowing down the response, but recovery is slow when the load suddenly changes, and this can cause overvoltage and voltage generation if regenerative operation is in progress.

(Since the JJLO smoothing circuit originally has resonance characteristics, the gain increases significantly at a certain frequency,
Tends to be unstable.

To solve this problem, there is a method of inserting a damping resistor in series with the LO smoothing circuit or a dummy load resistor in parallel with the 9-load resistor, but these methods have a number of drawbacks.

a) The damping resistor or dummy resistor consumes a large amount of power, so it is large in size and expensive.

b) The damping resistor or dummy resistor all consumes energy as loss, resulting in a decrease in conversion efficiency.

[Purpose of the invention]

An object of the present invention is to provide an entire control device for a power converter that can supply a stably controlled DC voltage with a quick response even to large fluctuations in unbalanced loads.

[Outline of the invention]

In order to achieve the above object, the present invention includes an impedance detection means for detecting the impedance of the load circuit, and a gain correction signal formed based on the impedance detected by the impedance detection device, to detect changes in the impedance of the load circuit. The main feature is that a correction signal calculator is provided to compensate for fluctuations in gain of the control system caused by the above.

[Embodiments of the invention]

FIG. 5 shows the main structure of an embodiment of the present invention. It is assumed that the main circuit portion is the same as that in FIG. The special features of this device are the voltage feedback signal and the lightning current return signal F.
BK and main circuit contactor included in each in/2-input device
A gain correction signal 7 obtained as a result of the performance is input to a correction signal calculator j.
The circuit configuration is such that the voltage is input to the voltage control calculator Va.

Correction signal calculator in the device shown in Figure 5! is the voltage feedback signal vFBK,! : Calculates the load resistance R of the converter installation l from the current feedback signal IFBK, and determines the number of connected capacitors n of known capacitance from the contactor operation signal 6, and calculates it as seen from the converter installation W/. Calculate cl for the added load capacitor. Then, the main circuit transfer function a mentioned above is
, (s)=FV(/+OR9) is calculated and input as a gain correction signal 7 to the voltage control calculator Va.

The functions of the device shown in FIG. 5 will be further explained with reference to the control block diagram shown in FIG.

Figure 6 is based on the one in Figure 6.

Transfer function G added as a gain correction signal. This corresponds to the one with omp added. As is clear from this control block diagram, the control system always has a constant gain regardless of load fluctuations in both open-loop and closed-loose systems.

Note that in the above embodiment, the load current is detected by the converter/
Although this is done on the AC input side of /, it is of course possible to do it on the DC output side. Further, when controlling the DC voltage Vc to be constant, the voltage feedback signal vFBK input to the correction signal calculator j can be omitted.

〔Effect of the invention〕

As described above, according to the present invention, by adding a correction signal calculator, the following effects can be obtained.

(1) Since the gain of the control system does not change depending on the load condition and is always constant, it is possible to stably control the entire range by making the best adjustment without considering load fluctuations, and as a result, this control system It will be possible to always demonstrate the maximum response of your ability.

(, 2) Due to the fast response, recovery is quick when the load suddenly changes, and the risk of overvoltage during regenerative operation is significantly reduced.

(3) A damping resistor or a load dummy resistor is not required, so the conversion efficiency does not decrease and the external size can be made small and lightweight.

[Brief explanation of drawings]

FIG. 1 is an abstract diagram of the device to which the present invention is applied, and FIG.
3 is a control block diagram of the converter shown in FIG. 1, and FIG. 3 is a control block diagram simplified by equivalent exchange and approximation of FIG. FIG. 5 is a diagram showing the main parts of an embodiment of the present invention, and FIG. 6 is a control block diagram obtained from FIG. 5 and corresponding to FIG. ...Inverter device, 3
...Induction electric @+ machine, Hiro...Load resistance, j...Correction signal calculator, 6...Main circuit contactor operation signal, 7...
Gain correction signal, l/... converter (flit converter), /2... react) #, /J... capacitor,
VC...Voltage control calculator, CC...Current control calculator, VD...Voltage detector, ID...Current detector, ■
...Voltage reference signal, ■FBK...Electric EF positive feedback signal, IR1! iF'...Standardization issue, 1F
BK...Current feedback signal 1.2/...Voltage source inverter 1. ! K...Input capacitor, U3...Main circuit contactor, GAVR...Voltage control operator transfer function, GAo
R...Current control operator transfer function, Gl + G2 +
Gs...Main circuit transfer function, Gaa...Current minoruso transfer function, G...Gain correction calculation Omp device transfer function. Dispatch agent Kiyoshi Inomata

Claims (1)

[Claims] In a control device for a power converter that performs negative feedback control of a controllable power converter that converts AC power into DC power so that the output DC voltage matches a set value, the impedance of the load circuit is controlled. an impedance detection means to detect, and a gain correction signal formed based on the impedance detected by the impedance detection means;
A power converter control device O characterized by being provided with a correction signal calculator for compensating for fluctuations in gain of the control system caused by changes in impedance of the load circuit.