JPH04289730A - Reactive power compensator - Google Patents

Abstract

PURPOSE:To provide a rapid response characteristic by installing separately a controlling system which keeps a dc voltage of a smoothing capacitor constant for PWM-controlling an output voltage of a PWM inverter in obedience to a reactive power command. CONSTITUTION:An output voltage of an inverter (IV) 2 is PWM-controlled. In order to generate a pulse width command signal of a PWM, reactive power is detected by a reactive power detector 8 and using a deviation of the detected reactive power from a reactive power reference signal, an output voltage command signal of the IV 2 is generated by a reactive power controller 10. Then, when an output signal of a dc voltage detector 9 fluctuates, a dc voltage controller 17 detects a deviation of a dc voltage reference signal and sends out a dc voltage correction signal. When this command signal is positive, an output phase of a PLL circuit 18 is allowed to lag synchronously with an ac power system 5 and thereby the phase of the PWM is allowed to lag for running active power into the smoothing capacitor 1 and increasing a dc voltage.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] This invention relates to a reactive power compensator that compensates for reactive power by converting DC input into AC output using an inverter and flowing a predetermined amount of reactive power into and out of an AC power system. It is.

0002

[Prior Art] FIG. 2 shows, for example, Mitsubishi Electric Technical Report Vol. 5
6, No. 6, P47 (published June 1982), this is a configuration diagram showing a conventional reactive power compensator of this kind. In the figure, 1 is a smoothing capacitor that serves as a DC voltage source, 2 is a 36-phase inverter that converts DC input from smoothing capacitor 1 into AC output, 3 is a multi-configuration output transformer that connects inverter 2 to the grid, and 4 is a system breaker inserted between the output transformer 3 and the AC power system 5. 6
is a current transformer that detects the output current to the grid, 7 is an instrument transformer that detects the grid voltage, and 8 is a current transformer 6 and an instrument transformer 7.
9 is a DC voltage detector that detects the voltage of the smoothing capacitor 1. 10 is a reactive power controller that outputs an output voltage command signal based on the deviation between the reactive power detection signal from the reactive power detector 8 and the reactive power reference signal from the reactive power setting device 11; A DC voltage controller outputs a phase signal based on the deviation between the output voltage command signal and the DC voltage detection signal from the DC voltage detector 9, and 13 outputs a phase difference signal from the output voltage phase of the inverter 2 and the grid voltage phase. a phase comparator; 14 is a phase controller that outputs a phase command signal from the phase signal from the DC voltage controller 12 and the phase difference signal from the phase comparator 13; 15 is a phase controller 1;
This is a gate pulse generation circuit that sends gate pulses to each element of the inverter 2 based on the phase command signal from the inverter 4.

Next, the operation will be explained. Inverter 2
converts the DC voltage of the smoothing capacitor 1 into an AC voltage synchronized with the system voltage of the AC power system 5. When the output voltage of the inverter 2 is made higher than the system voltage, leading reactive power flows in due to the difference voltage and the reactance of the output transformer 3 (capacitor operation). Also, inverter 2
When the output voltage is lower than the grid voltage, delayed reactive power flows in (reactor operation). In this way, the reactive power is continuously adjusted by raising and lowering the output voltage of the inverter 2, but the output voltage of the inverter 2 is further adjusted by raising and lowering the voltage of the smoothing capacitor 1.

The conventional reactive power compensator employs a method of controlling the DC voltage of the smoothing capacitor 1 by controlling the phase of the output voltage of the inverter 2. That is, after the inverter 2 and the output transformer 3 are connected to the grid, the losses of the inverter 2 and the output transformer 3 are supplied from the AC power system 5, but the inverter 2
When the phase of the output voltage is delayed from the phase of the system voltage, the active power supplied from the system becomes larger than the loss of the inverter 2 and the output transformer 3, and the DC voltage of the smoothing capacitor 1 increases. Conversely, when the phase of the output voltage of the inverter 2 is advanced from the phase of the grid voltage, the active power supplied from the grid becomes smaller than the loss of the device, and the DC voltage decreases.

In the circuit shown in FIG. 2, a reactive power controller 10 outputs an output voltage command signal based on the deviation between the reactive power detection signal from the reactive power detector 8 and the reactive power reference signal from the reactive power setting device 11. , and the DC voltage detection signal from the DC voltage detector 9, the phase controller 14 operates to eliminate this difference, outputs a phase command signal to the gate pulse generation circuit 15, and adjusts the output voltage of the inverter 2. The DC voltage of the smoothing capacitor 1 is adjusted to a desired value by controlling the phase of the smoothing capacitor 1.

[0006]

[Problem to be Solved by the Invention] Since the conventional reactive power compensator is constructed as described above, the following steps are required: control of the phase of the output voltage of the inverter 2 → control of the DC voltage by charging and discharging the smoothing capacitor 1 → control of the output voltage of the inverter 2 The problem was that a high-speed response could not be obtained as a whole.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a reactive power compensator having high-speed response characteristics.

[0008]

[Means for Solving the Problems] A reactive power compensator according to the present invention employs a PWM control method for an inverter, and a DC voltage controller that outputs a DC voltage correction signal from a DC voltage detection signal and a DC voltage reference signal. a reactive power controller that outputs an output voltage command signal of the inverter from the power detection signal and the reactive power reference signal; a pulse width controller that outputs the pulse width command signal from the DC voltage reference signal and the output voltage command signal; P which controls the phase of the PWM so that the DC voltage is constant at its reference value based on the DC voltage correction signal, and controls the pulse width of the PWM based on the pulse width command signal.
It is equipped with a WM circuit.

[0009]

[Operation] The DC voltage is controlled to always maintain its reference value constant by adjusting the phase of the output voltage of the inverter. For fluctuations in the reference value of reactive power, the inverter's P
WM pulse width control quickly changes the inverter output voltage.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a reactive power compensator according to an embodiment of the present invention. In the figure, numerals 1 to 11 are the same as or equivalent to the conventional case, and their explanation will be omitted. 16 is a DC voltage setting device; 17 is a DC voltage controller that outputs a DC voltage correction signal based on the deviation between the DC voltage detection signal from the DC voltage detector 9 and the DC voltage reference signal from the DC voltage setting device 16; 18 is a DC voltage controller; This is a PLL circuit that outputs a phase command signal φ from a DC voltage correction signal. 19 is a pulse width command signal θ obtained from the deviation between the output voltage command signal from the reactive power controller 10 and the DC voltage reference signal from the DC voltage setting device 16.
The pulse width controller 20 is a PWM circuit that sends gate pulses to each element of the inverter 2 from the phase command signal φ and the pulse width command signal θ.

Next, the operation will be explained. In order to adjust the reactive power of the grid, the output voltage of the inverter 2 is increased or decreased as in the past. And the output voltage of inverter 2 is
Adjustments are made by performing so-called PWM control that widens or narrows the pulse width. In order to create a PWM pulse width command signal, the reactive power of the grid is detected by a reactive power detector 8, and an output voltage command signal for the inverter 2 is created by a reactive power controller 10 from the deviation between this and a reactive power reference signal. do. When this command signal is positive, the output voltage is increased by widening the pulse width, and when this command signal is negative, the output voltage is decreased by narrowing the pulse width. The actual pulse width command signal θ is created by the pulse width controller 19 using the following formula.

[Equation 1] Here, Vref is an output voltage command, and Vdref is a DC voltage reference. That is, in this embodiment, control is adopted in which the DC voltage is assumed to have a constant reference value Vdref, and the output power of the inverter 2 follows changes in the reactive power reference at high speed by pulse width control.

[0012] Therefore, a control system for keeping the DC voltage constant is required, which will be explained below. That is, when the DC voltage detection signal from the DC voltage detector 9 fluctuates, the DC voltage controller 17 detects the deviation from the DC voltage reference signal and outputs a DC voltage correction signal. When this command signal is positive, it is necessary to increase the DC voltage, so by delaying the output phase of the PLL circuit 18 that operates in synchronization with the AC power system 5, the PWM phase is delayed and active power is allowed to flow into the smoothing capacitor 1. to increase its DC voltage. vice versa,
When the command signal is negative, the phase of the PWM is similarly advanced to cause the smoothing capacitor 1 to release active power to the grid, thereby lowering its DC voltage. As described above, in this embodiment, the control system for keeping the DC voltage of the smoothing capacitor 1 constant at its reference value is provided independently from the control system for the output voltage of the inverter 2. This enables responsive output voltage control.

[0013] As the PWM control type inverter, specifically, a GTO inverter, a transistor inverter, a thyristor inverter, etc. can be used, and a multi-pulse PWM control type may also be used.

Furthermore, in the above embodiment, reactive power is detected and the output voltage command is created from the deviation between this detected value and the reactive power reference value, but reactive current is detected and the detected value and the reactive current The output voltage command may be created from the deviation from the reference value. In practical circuits, control is often performed using the latter method. Therefore, the term reactive power in this specification can be directly replaced with reactive current.

[0015]

[Effects of the Invention] As described above, the present invention provides a separate control system to keep the DC voltage of the smoothing capacitor constant, and directly controls the output voltage of the PWM inverter by pulse width control in response to the reactive power command. Therefore, high-speed response characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a reactive power compensator according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a conventional reactive power compensator.

[Explanation of symbols]

1 Smoothing capacitor, 2 Inverter 5　AC power system 8 Reactive power detector 9 DC voltage detector 10　Reactive power controller 11 Reactive power setting device 16 DC voltage setting device 17 DC voltage controller 19 Pulse width controller 20 PWM circuit

Claims (1)

[Claims] [Claim 1] In an apparatus that compensates for reactive power by converting DC input from a smoothing capacitor serving as a DC voltage source into AC output using an inverter and flowing predetermined reactive power into and out of an AC power system, The above inverter is
A DC voltage controller that uses a WM control method, receives the DC voltage detection signal of the smoothing capacitor and the DC voltage reference signal, and outputs a DC voltage correction signal from the deviation of these two signals, and the reactive power detection signal and the reactive power reference signal. A reactive power controller inputs the DC voltage reference signal and the output voltage command signal and outputs the output voltage command signal of the inverter from the deviation of these two signals, and outputs the pulse width command signal from the deviation of these two signals. A PWM circuit that controls the phase of the PWM so that the DC voltage becomes constant at its reference value based on the DC voltage correction signal and the pulse width of the PWM based on the pulse width command signal. A reactive power compensator characterized by: