JPH054781U - Current limit circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To suppress commutation failure due to AC voltage drop during regenerative operation in a reversible thyristor leonard, and to facilitate commutation even at that voltage. [Structure] In a reversible thyristor Leonard device, an AC voltage detector and a current limit correction circuit are provided for the current control function with current limit, and even if the power supply voltage drops (power failure) during regenerative operation, the correction circuit operates according to the voltage. The current limit value is lowered to prevent commutation failure.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a DC motor control device for controlling speed and current of a reversible and regenerative thyristor Leonard device.

[0002]

[Prior Art]

In a three-phase pure-bridge thyristor leonard that uses an AC power supply voltage as a commutation means without a forced commutation circuit, the relationship between the _AC voltage E _AC and the DC average voltage E _DC is generally well known. The calculation formula of the maximum no-load voltage of the wave rectifier circuit is as shown in the equations (1) and (2).

[0003]

[Equation 1]

In particular, it is well known that during regeneration, the decrease in the AC power supply voltage in the power supply commutation means is a cause of overcurrent due to commutation failure, and a protective operation is required. For this reason, when used at the power receiving end where power supply conditions are unfavorable, the power supply fluctuation range is large and it may be used in a range that does not lead to power failure detection.Therefore, it is unavoidable to use power down with a reduced rated DC output voltage, Regardless of whether or not there is a flow failure, a power cutoff operation is intentionally performed at low voltage, and an overcurrent cutoff after assuming a commutation failure is performed by a circuit breaker provided on the DC side to disconnect the circuit and protect the equipment from stoppage. I was doing it. In this case, there was a drawback in that the low current during regeneration = immediate, commutation failure → overcurrent caused a deliberate DC cutoff protection operation, and the equipment was often stopped.

[0005]

[Problems to be solved by the device]

 Even though the commutation operation depends on the power supply as described above, the control information was only the power failure detection and the protection operation after the commutation failure was performed, but it was positive when the AC voltage dropped. It was lacking in suppressing commutation failure.

FIG. 4 is a block diagram of a conventional example. An OR circuit 13 is provided by detecting a power failure by the signals of the AC voltage detector 8 and the power failure detector 9 by the DC blocking circuit 14 and the DC breaking breaker 4. The power was cut off during a power outage. Here, 1 is a three-phase AC power supply, 2 is an ACCT, 3 is a reversible converter, 5 is a DC motor, 6 is a gate circuit, 7 is a current control circuit, 10 is a current limit correction circuit, 11 is a signal priority diode, and 12 Is a current limiting setter, and I _S is a current command.

The present invention defines the commutation limit at the time of voltage drop by a simple method and suppresses commutation failure at the time of regeneration. In the regenerative mode, the main power source is only on the DC side, and the commutation margin angle γ is determined by the magnitude of the DC average voltage E _DC . This is E _DC = -1.35E _AC · COS γ, as is clear from the equation (2) of the above equation 1, and γ becomes smaller as the DC average voltage E _DC becomes larger when the AC voltage E _DC is constant. , E _DC = -1.35E _AC , γ becomes 0 °. This means that E _DC <1.35E _AC during regeneration means the commutation limit, but in reality, the commutation overlap angle μ caused by circuit reactance and circuit current occurs during commutation, and the period of γ = μ or more It is necessary to consider the voltage that has seen the margin. In general, the commutation overlap angle μ is given by the equation (3) of Equation 2, or is known from the calculation formula of the three-phase bridge rectifier, and may be a value proportional to the DC average current and the commutation reactance. Are known.

[0008]

[Equation 2]

Therefore, γ> μ is a necessary condition for commutation, but it is usually limited to γ = 180 ° and is set so that the overlapping angle due to the magnitude of the DC average current does not matter. However, as the DC current decreases, the commutation margin is increased accordingly. Also, when regenerative braking is performed at a relatively high E _DC , γ is set so that E _DC = -1.35E _AC · COS γ, as described above, and the current is current limited because it is necessary to pass an effective current. Γ approaches 0 ° until it reaches (It tends to cause commutation loss.) Since E _AC is generally set at 200V or 400V, the direct current output voltage is high (high speed), and the larger the DC current, the smaller the commutation margin. In other words, the commutation limit is mainly influenced by the _AC voltage E _AC and the DC average current, and the commutation failure can be suppressed by reducing the current limit value so that γ does not approach 0 °. You can do it.

FIG. 5A is a basic circuit diagram, and FIG. 5B is a diagram for explaining the commutation operation of FIG. 5A. Since the content is known, the operation of FIG. those described which omitted, the three-phase alternating current E _AC and a DC voltage E _DC, illustrating the circuit reactance X _L, the load current I commutation overlapping angle μ and corners at that flow inversion to R-phase from T phase _D gamma Is. 1'and 2'show the load current flow at that time. FIG. 6 is an explanatory diagram illustrating the commutation limit zone described above between the _AC voltage E _AC and the DC average voltage E _DC . It is also important to consider the commutation reactance drop. The present invention was devised in view of the above-mentioned points, and its purpose is to prevent commutation failure that occurs at low power during regeneration and to reduce the number of stoppages of the device due to unnecessary protection operation. It provides a current limiting circuit that eliminates the need for a simpler configuration.

[0011]

[Means for Solving the Problems]

In other words, the means for achieving the purpose is to provide a detection circuit for the _AC voltage E _AC and a correction circuit for decreasing the current limit value by that value in order to know the above-mentioned commutation limit. is there.

[0012]

[Action]

The effect is that the AC voltage detector operates normally with the current limit value that is normally set when the AC voltage is at the specified value, and through the correction circuit when the _AC voltage E _AC decreases. It is designed to work to lower the regular current limit value in accordance with the decrease. An embodiment of the present invention will be described below in detail with reference to the drawings.

[0013]

【Example】

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a concrete circuit diagram of FIG. 1, and FIG. 3 is an explanatory diagram of its internal operation level. It has components. In FIGS. 1 and 3, the current command I _s set by the current control circuit 7 and the gate circuit 6 is output to the current limit setter 12 and the current limit correction circuit 10 of the present invention through the signal priority diode 11. Each of them is compared as a level priority, and the current to be actually flown is connected so as to be commanded by the smallest value of these three. Therefore, no matter how large the current command I _s or the current limit set value V _L shown in FIG. 3, the output V _AX of the correction circuit 10 will work at that value if it is small.

In FIG. 2, the value E _AC detected by the AC voltage detector 8 in FIG. 1 is configured by the operational amplifier 16 and the gain adjustment VR 17 so that the output V _AX of the correction circuit 10 becomes smaller, When the AC voltage E _AC is normal (100%), the priority output 15 is the current limit set value _VL , and when E _AC is lower than the specified value (100%), the correction circuit output V _AX is at a low level. Therefore, the priority output 15 with a value lower than the current limit set value V _L is possible, the current limit value is narrowed, the commutation current is reduced, and the commutation margin is increased to prevent commutation failure. Guide to suppress. In addition, the current adjustment pattern can be changed by adjusting the gain adjustment VR17 of the operational amplifier 16 in response to a constant that slightly changes depending on the magnitude of the circuit reactance and the power supply fluctuation.

[0015]

[Effect of the device]

 As described above, according to the present invention, the commutation limitation is simply assumed by the value of the AC voltage, and in the event of an abnormality, the current is swiftly reduced to a small current that allows commutation, and the commutation margin is increased to regenerate the regeneration. It is possible to suppress commutation failures that occur when the power is low, and the number of stoppages of the device due to unnecessary protection operations is reduced. It is also common to design and configure an accurate commutation allowance angle γ by measuring and calculating the output waveform and ignition phase, and to perform control correction, but it is complicated including hardware and software. Become. In this respect, the present invention is effective in that a simple and equivalent purpose can be obtained.

[0016]

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a specific circuit diagram of FIG.

FIG. 3 is an explanatory diagram of its internal operation level.

FIG. 4 is a configuration diagram of a conventional example.

FIG. 5 (a) is a basic circuit diagram.

5 (b) is a diagram for explaining the commutation operation of FIG. 5 (a).

FIG. 6 is an explanatory diagram of a commutation limiting voltage.

[0017]

[Explanation of symbols]

 1 3 Phase AC Power Supply 2 ACCT 3 Reversible Thyristor Converter 4 DC Breaker 5 DC Motor 6 Gate Circuit 7 Current Control Circuit 8 AC Voltage Detector 9 Power Failure Detector 10 Current Limit Correction Circuit 11 Signal Priority Diode 12 Current Limit Set Device 13 OR circuit 14 DC cutoff circuit 15 Priority output 16 Operational amplifier 17 Gain adjustment VR

Claims (1)

[Claims for utility model registration] Claims: 1. A thyristor Leonard device for reversible regeneration, which has current control and current limiting functions, and which controls and protects overcurrent.
Equipped with a current limit correction circuit, the current limit value during regeneration is lowered according to the detected voltage value of the AC power supply voltage, and the commutation current is made small to facilitate commutation, thus suppressing the occurrence of overcurrent due to commutation failure. A current limiting circuit characterized by being configured to perform.