JPS5943920B2 - Variable speed control method for AC motor using cycloconverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable speed control method for an AC motor using a cycloconverter that has both direct drive and cycloconverter variable speed drive functions.

When driving an AC motor at variable speed with a cycloconverter, the upper limit of the frequency is approximately 1/2 to 1/3 of the power supply frequency, and for commutation purposes, the power supply voltage must be sufficiently large compared to the motor voltage, which reduces the power factor. It is not completely satisfactory either.

Therefore, when the AC motor is at low speed, the cycloconverter variable speed drive is used. At high speeds, a method is used in which a specific element of the cycloconverter is ignited to switch the AC motor to direct-on drive, which connects the AC motor directly to the power source. An example is shown in Figure 1. This block diagram shows a drive system that controls an induction motor with a fixed primary voltage/primary frequency ratio at low speeds, a cycloconverter variable speed drive, and a direct drive at high speeds. 11 is an 18-arm thyristor element (RUP-'IW
N) and 3 windings (DC-Li, DC-L2, DC-L3)
2 is a cycloconverter composed of a DC reactor and a DC reactor that are closely magnetically coupled; 2 is an induction motor 13 driven by the cycloconverter 1; 4 is a current transformer 3 that detects the input current; 5 is a voltage detector that detects the terminal voltage of the induction motor 2; 6 is a reference setting device that sets the motor voltage and frequency standards when driving the cycloco/verter at variable speed; ,7
8 is a voltage control amplifier that amplifies the deviation between the voltage reference signal provided from the reference setter 6 and the motor voltage signal provided from the voltage detector 5; a current control amplifier 9 that amplifies the deviation from the applied current detection signal; 9 a phase controller that controls the firing phase of the thyristor element of the cycloconverter 1 with respect to the power supply according to the output signal of the current control amplifier 8; 10 is a V-F converter that converts the frequency reference signal given from the standard setter 6 into a digital signal; 11 is a ternary counter that converts the digital signal from the 5V-F converter 10 into a three-phase signal for the induction motor; 12 is phase control 9
130 is a gate logic circuit that generates a gate signal to the thyristor element RUP-TWN from the phase control signal from the ternary counter/coupler 11 and the three-phase signal from the ternary counter 11; A gate logic circuit 5 selectively provides a gate signal to the thyristor element according to the output signals of the phase detector 9 and the ternary counter 11 when the cycloconverter is driven at variable speed by the switching signal generator that provides the switching signal generator.
12, during direct drive, the cycloco/verter 1 is
A gate signal is applied to a specific element of C, which acts on a gate logic circuit.

In this configuration, the cycloconverter variable speed drive is generally y-order control (; motor voltage. F; motor primary frequency)
This control method detects the terminal voltage of the motor and attempts to control the motor by keeping the ratio of the motor voltage to the motor frequency constant.

In addition, direct-on drive is a method in which a gate signal is given to a specific element among the 18-arm thyristor elements of the cycloconverter to drive the motor by directly connecting it to the power source. For example, thyristor RUP/RUN-SVP-SvN-'Iw
If a continuous gate signal is applied to P-'RwN, the power R phase will be connected to the motor U phase, the power S phase will be connected to the motor V phase, the power T phase will be connected to the motor W phase, and the motor will be driven at the power frequency. Become. The specific element is RUP-RUN-SVP-S
VN-Not limited to Sugaboshi/TWN, but power supply R-
If a thyristor element is selected to connect the motor U-V-w phase one-to-one with the S-T phase, six types of specific elements can be selected. In this drive system, when switching from direct-on drive to cycloconverter variable-speed drive, conventionally, the gate is cut off for a certain period of time, and during the gate cut-off period, a specific element that was lit during direct-on drive is turned off. Assuming that the arc was extinguished, I switched to cycloco Y-verter variable speed drive.

However, even if the gate is turned off for a specific element that was lit during direct-on operation, the current flowing at that time will continue to flow through the DC reactor in the U phase as shown in Figure 2, due to the action of the DC reactor in the main circuit. It continues to flow while being attenuated in the circulation loop of DC-L1 winding → thyristor RUN → thyristor RUP. The specific number of this circulating loop is usually large, and if the circulating current continues to flow even after a certain gate period has elapsed (C is the case where, for example, the phase gate signal to SUP is applied when switching to variable speed cycloconverter drive) If this happens, the S and R phases of the power supply will be short-circuited in the path of thyristor SUP → DC reactor DC-L1 → thyristor RUN, resulting in an overcurrent flow.Therefore, the cycloconverter variable speed from direct-on drive will be short-circuited. If the switching to drive is dependent on gate opening or disconnection for a certain period of time, the above-mentioned concerns are unavoidable.Also, there are drawbacks such as the gate opening or disconnection period being long. This was developed to eliminate the above drawbacks, and it is a cycloconverter that can safely switch to variable speed cycloconverter drive by extinguishing specific elements that are lit during direct drive in a very short time. An object of the present invention is to provide a variable speed control method for an AC motor using a converter.An embodiment of the present invention is shown in FIG.

21 is a power supply side commutation command signal generation circuit for RP to TN; 22
23 is a load side commutation command signal generation circuit that generates load side commutation commands for UP and UN, and 23 is a switching signal i signal generator that switches between direct drive and cycloconverter variable speed drive. This corresponds to the switching signal generator 13.

Numerals 24 to 29 are NAND circuits which output a signal of 0 when the output signals of the power supply side commutation command signal generation circuit 22 and the switching signal generator 23 are 1.

30 is a gate pulse amplifier that receives the output signal 0 from the NAND circuits 24 to 29 and generates a gate pulse to the thyristor element. 31 is a one-shot pulse generator. When the output signal of the switching signal generator 23 changes from "O" to "1", that is, when switching from direct-on drive to cycloconverter variable speed drive, the signal "1" is output for a certain period of time, and the load side shift is performed. Output signal UP of flow command signal generation circuit 22
, UN are forcibly locked to 1 and act on the phase controller 32 to narrow down the ignition phase angle to the r side.

Now, from direct input 1 drive. The manner in which the switching to the variable speed drive of the cycloconverter at frequency 14 of the power supply frequency is performed will be explained with reference to FIG. During the period shown in FIG. 4A, the output signal of the switching signal generator 23 is 0 during direct power-on and driving. Therefore, the outputs of the NAND circuit and the NAND circuit 27 become 0, and the output from the gate pulse amplifier 30 to RUP 1.
A signal of RUN〃1〃 is output and a gate signal is given to thyristor RUP and thyristor RUN. Now, if you switch from direct drive to cycloconverter variable speed drive. The output signal of the switching signal generator 23 becomes "L", the one shot pulse generator 31 outputs the signal "1" for a certain period (period shown in FIG. 4B), and the load side commutation command signal generation circuit 2
The output signals RUP and RUN of 2 are locked to 1, and the power supply side commutation command signal generation circuit 21 outputs a signal RP-T'N which restricts the power commutation to the r side. Therefore, the NAND circuits 24 to 29 output a signal inverted from the output signal of the power supply side commutation command signal generation circuit 21, that is, the thyristor RU
For P~TUN. Since an r-phase gate signal matching the power commutation command signal RP-TN is given, the three-phase G-V-connected thyristors RUP to TUN are fired in the regeneration mode with respect to the U phase. If the v-phase and w-phase thyristors are fired in regeneration mode in the same way, the energy stored in the DC reactor and motor during direct-on operation will be quickly regenerated to the power supply side, and the energy will be ignited during direct-on operation. The specific element that was arcing is extinguished, the above-mentioned circulation loop is not created, the main circuit current becomes zero, and the cycloconverter can be safely switched to variable speed drive. FIG. 5 shows the gate signal period given to the 18-arm thyristor at this time, and shows A&'! ．． U phase. B indicates phase, and C indicates w phase. In other words, regarding the U phase, the specific element RUP&'! during direct drive! ．． When the SUP is ignited, it is extinguished by the S-R line voltage. RUN is extinguished by the R-S line voltage when SUN fires, so at the firing timing of SUP or SUN, thyristor RUP → DC reactor DC-L1
→The circulation loop of thyristor RUN is broken. Similarly, regarding the phases, TVP, TVN. For W phase, RWP, R
The circulation loop can be broken at the ignition timing of WN. Further, FIG. 6 shows the DC side voltage of the three-phase Gretz connection made up of thyristors RUP to TUN when regeneration is performed after r=30 for the U phase, and regeneration is performed by the voltage surrounded by the solid line in the figure. As explained above, when switching from direct-on drive to cycloconverter variable speed drive, the present invention
Specific elements during direct-on-line driving by igniting the cycloconverter element on the r side for a short period of time and regenerating the energy stored in the motor or DC reactor to the power supply side during direct-on-on driving to quickly reduce the main circuit current to zero It is possible to provide a variable speed control method for an AC motor using a cycloconverter, which simultaneously extinguishes the arc and switches from direct-on drive to cycloconverter variable speed drive safely and in a short time.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the conventional method, Fig. 2 is a reference diagram for explaining the conventional method, Fig. 3 is a connection diagram showing an embodiment of the present invention, and Figs. 4 to 6 are diagrams of the present invention. It is a reference diagram for explanation. 1; cycloconverter, 2; induction motor, 3; CT,
4; Current detector, 5; Voltage detector, 6: Reference setter, 7
: Voltage control amplifier, 8: Current control amplifier, 9, 32; Phase controller. 10: 1F converter, 11: ternary counter. 1
2: Gate logic circuit, 13, 23; Switching signal generator, 2
1: Power supply side commutation command signal generation circuit, 22: Load side commutation command signal generation circuit, 24 to 29: NAND circuit, 30: Gate pulse amplifier, 31: One shot pulse generator.

Claims (1)

[Claims] 1. In a variable speed control device for an AC motor using a cycloconverter, which has a direct drive function that applies power supply voltage directly to the AC motor by igniting a specific element of the cycloconverter, from direct drive to cycloconverter variable speed drive. 1. A variable speed control method for an AC motor using a cycloconverter, characterized in that when switching, an element of the cycloconverter is fired on the r side for a short period of time.