CN217787250U - Frequency converter input phase loss detection circuit - Google Patents

Abstract

The utility model relates to a converter technical field specifically is a converter input lacks looks detection circuitry, and it can make things convenient for accurate detection to lack looks, simple structure, and is with low costs, and it includes three-phase circuit module, a serial communication port, two arbitrary sides are provided with first magnetic switch and second magnetic switch respectively in the diode of three anodal altogether of three-phase circuit module, first magnetic switch with first detection module and second detection module are connected respectively to second magnetic switch, first detection module with second detection module all includes RC low pass filter, reverse amplifier and stabiliser, the output time chart of stabiliser.

Description

Frequency converter input phase loss detection circuit

Technical Field

The utility model relates to a converter technical field specifically is a converter input lacks looks detection circuit.

Background

In the current general frequency converter, in the industrial application occasion, the input power supply of the frequency converter adopts the design of three-phase alternating-current voltage. For example, 380V alternating voltage is pulled out through a transformer on site and then connected to the input end of the frequency converter to enable the frequency converter to operate.

In normal use, a transformer needs to satisfy several conditions. First, the output capacity must be sufficient; for example: when a 7.5kW inverter is driven, the transformer must have a capacity of 25KVA or more, and the effective value of the voltage output from the transformer must be controlled to be within. + -. 10% of the rated voltage 380V, and the variation in the voltage frequency must be controlled to be 50 Hz. + -. 5Hz. And the balance rate of the three-phase voltage can be preferably maintained within 5%, and the specifications are met, so that the normal operation of the frequency converter can be ensured.

However, in actual conditions, the field transformer rarely works with only one frequency converter, and more than a few devices are connected in parallel, and even 220V ac power is drawn out through zero + one phase output and provided for other 220V devices, as shown in fig. 1.

The stable output of the transformer is easily influenced as a result of the use under the complex working conditions. For example, the voltage of the transformer may generate many harmonics along with the impedance of different loads, or cause voltage fluctuation, frequency oscillation, etc., which may cause the transformer to burn, cause the output voltage of the transformer to be unbalanced for a long time, and finally cause phase-loss fault. Fig. 2 is a graph comparing the voltage waveforms of the normal output of the transformer and the L3 phase loss.

When the transformer is out of phase, a three-phase power supply becomes a single-phase power supply, the frequency converter can still operate, but the direct-current voltage after full-wave rectification and filtering is only 67% of the original three phases, the current distribution of a rectifier bridge inside the frequency converter and the ripple factor of a filter capacitor are greatly changed, the two devices of the frequency converter are directly heated seriously, and the service life of the frequency converter is greatly influenced for a long time. When the transformer 7.5kw is operated with a full load 15A, fig. 3 is a graph comparing a current waveform of the rectifier bridge when the input voltage is normal when the three-phase voltage 380v is input with a current waveform of the rectifier bridge after L3 phase loss, and fig. 4 is a graph comparing a ripple waveform of the bus voltage during normal with a ripple waveform of the bus voltage during L3 phase loss.

It can be observed from fig. 3 and 4 that after L3 is out of phase, the input currents of L1 and L2 are significantly increased from 45A, 40A to 122A, 120A, respectively; the voltage ripple value of the direct current bus is increased from 44V to 160V; the ripple ac cycle also changes from 3.3ms to 10ms. It can be seen that the input phase loss is quite detrimental to the frequency converter. The generally damaged devices almost generate heat for a long time due to large ripples of the main capacitor, so that the service life is shortened; or the rectifier bridge is damaged due to the fact that the rectifier bridge is large in current and generates heat for a long time. Therefore, a normal inverter usually has some measures to protect the input phase loss.

The general frequency converter on the market mainly has 2 kinds to the detection mode of inputing the open-phase, and the scheme is as follows:

firstly, the following steps: detecting the input three-phase power signal.

The traditional method for detecting the phase loss of the input power supply adopts a hardware circuit to detect, samples a three-phase input power supply signal through a sampling circuit, and judges whether the input is in phase loss or not through waveform comparison after a series of processing, but the scheme has the following defects:

1. the cost and complexity of the circuit is high. 3 voltage sensors and partial detection circuits are required to be installed, and the scheme is not suitable for a low-power or compact and economical universal frequency converter;

2. when the three-phase voltage source has harmonic waves, the problems of interference and input phase loss are easily caused by misjudgment; if the input voltage has a relatively serious harmonic component, the detection of the hardware circuit is easy to be misjudged.

II, secondly: and detecting the voltage harmonic value of the direct current bus.

Under normal conditions, where no phase loss of the input voltage occurs in the frequency converter, the ripple value variation within 10% is normal.

Namely 380V alternating current condition, when the direct current bus voltage is 540VDC, the full-load operation can accept 50V change, and the detection flow chart shown in the figure 5 has the following defects:

1. when the load is light or medium, the input phase loss is not easy to be detected by the DC bus ripple. When the load is not large, the input phase loss is small, and the capacitor ripple is also small. But the current distribution of the rectifier bridge is not relatively problematic, the heating phenomenon still exists, and the service life of the rectifier bridge is also reduced after a long time;

2. the frequency converter is applied to variable torque load, and detection misjudgment is easily caused. The variable torque load, such as a mixer and other loads, is widely applied, the capacitance ripple becomes large when the torque is changed, and if the mechanism is adopted to judge whether the input phase is missing, the detection misjudgment is easily caused.

Disclosure of Invention

In order to solve the problem that misjudgment easily appears in the detection that current converter lacks the looks to the input, with high costs, the rate of accuracy is low, the utility model provides a converter input lacks looks detection circuit, its detection that can make things convenient for the accuracy lacks looks, simple structure, it is with low costs.

The technical scheme is as follows: the utility model provides a converter input phase failure detection circuitry, its includes three phase circuit module, its characterized in that, arbitrary two sides are provided with first magnetic switch and second magnetic switch respectively in the three anodal diode altogether of three phase circuit module, first magnetic switch with first detection module and second detection module are connected respectively to second magnetic switch, first detection module with second detection module all includes RC low pass filter, inverting amplifier and stabiliser, the output timing diagram of stabiliser.

It is further characterized in that, first detection module includes reverse amplifier U1, reverse amplifier U1's inverting input connecting resistance R5 one end, electric capacity C3 one end, electric capacity C6 one end, electric capacity R7 one end, the resistance R5 other end is connected first magnetic switch, reverse amplifier U1's normal phase input connecting resistance R6 one end, the resistance R6 other end with electric capacity C3 other end ground connection, reverse amplifier U1's output connecting resistance R8 one end the electric capacity C6 other end the resistance R7 other end, electric capacity C4 one end, zener diode D4's negative pole are connected to the resistance R8 other end and are good IO _1 output of chronology, second detection module includes reverse amplifier U2, reverse amplifier U2's inverting input connecting resistance R1 one end, electric capacity C5 one end, electric capacity R2 one end, the resistance R1 other end is connected second magnetic switch, normal phase amplifier U2's input connecting resistance R3 one end, the resistance R3 other end with electric capacity C1 other end ground connection, electric capacity C2 one end, electric capacity R2 one end the negative pole connecting resistance R4 one end of the negative pole connecting resistance R2 one end and the signal output are good IO _1 output.

Adopt the utility model discloses afterwards, can produce the magnetic field in the twinkling of an eye when the diode is flowed through to the electric current, through magnetic switch output voltage, the voltage is again through low pass filter, reverse amplifier, stabiliser, obtains two sets of sequential signal, confirms whether takes place to lack the looks according to sequential signal, circuit structure is simple, and output signal is reliable and stable, and the detection that can make things convenient for the accuracy lacks looks and with low costs.

Drawings

Fig. 1 is a diagram illustrating an operating state of a conventional multi-converter;

FIG. 2 is a graph comparing the voltage waveforms of the transformer after normal output and (L3) phase loss;

FIG. 3 is a comparison of a rectifier bridge current waveform plot when the input voltage is normal at a three-phase voltage 380v input and a rectifier bridge current waveform plot after L3 phase loss;

FIG. 4 is a waveform diagram of the bus voltage ripple in normal operation compared with the waveform diagram of the bus voltage ripple in phase loss L3;

FIG. 5 is a flow chart illustrating a conventional method for detecting a harmonic value of a DC bus;

FIG. 6 is a schematic circuit diagram of the present invention;

FIG. 7 is a timing diagram of diode conduction when the three-phase voltage is normal;

FIG. 8 is a comparison chart of the conduction of 3 diodes sharing a positive electrode when the input voltage is normal and the input voltage is open;

fig. 9 is a phase loss determination flowchart.

Detailed Description

As shown in fig. 6, a converter input phase loss detection circuit, it includes three-phase circuit module, arbitrary two sides in the three anodal diodes of three-phase circuit module are provided with first magnetic switch Fe1 and second magnetic switch Fe2 respectively, select diode D4 and diode D2 in this embodiment, first magnetic switch Fe1 and second magnetic switch Fe2 are connected first detection module and second detection module respectively, first detection module and second detection module all include RC low pass filter, inverting amplifier and stabiliser, the output timing diagram of stabiliser.

The first detection module comprises a reverse amplifier U1, the reverse phase input end of the reverse amplifier U1 is connected with one end of a resistor R5, one end of a capacitor C3, one end of a capacitor C6, one end of a capacitor R7, the other end of the resistor R5 is connected with a first magnetic switch Fe1, the normal phase input end of the reverse amplifier U1 is connected with one end of a resistor R6, the other end of the resistor R6 is grounded with the other end of the capacitor C3, the output end of the reverse amplifier U1 is connected with one end of a resistor R8, the other end of the capacitor C6 is connected with the other end of a resistor R7, the other end of the resistor R8 is connected with one end of a capacitor C4, the cathode of a voltage stabilizing diode D4 is connected with the output end of IO _1 with good timing sequence, the second detection module comprises a reverse amplifier U2, the reverse phase input end of the reverse amplifier U2 is connected with one end of a resistor R1, one end of a capacitor C5, one end of a capacitor R2, the other end of the resistor R1 is connected with the other end of a capacitor C2, one end of a cathode of a capacitor R2 is connected with the output end of a voltage stabilizing diode IO _2, and the output end of a signal of the capacitor C2.

The three-phase alternating current is rectified by a rectifier bridge to obtain direct current voltage, and the three-phase alternating current positive rotation voltage with 120-degree phase difference is connected to an input point of the rectifier bridge in the rectifying process. In different phase angles, the diodes D1 to D6 are determined to be on or off according to the amplitudes and the positive and negative of the voltages L1, L2 and L3, fig. 7 is a continuous period, and when the three-phase voltage is normal, the diodes D1 to D6 are turned on in a timing chart, the diodes D1 and D4 define the (1) th group, the diodes D3 and D6 define the (2) th group, and the diodes D5 and D2 define the (3) th group.

Fig. 8 is a graph showing the comparison of the conduction of 3 diodes which share the positive when the input voltage is normal and open phase, and it can be seen that the comparison result is:

from the table, it can be known that when the power supply has any phase loss, the 3 diodes sharing the anode will not conduct in the group with the phase loss, and the conduction time of the other 2 diodes conducting is increased from 120 ° to 180 °.

At 50Hz power system, the 120 ° conduction time is 6.7ms; the on-time of 180 deg. is 10ms.

In a 60Hz power system, the conduction time of 120 degrees is 5.6ms; the on-time of 180 deg. is 8.3ms.

In the utility model, when the diode D4 is turned on, the first magnetic switch Fe1 is turned on by the instant current until the diode D4 is turned off, and the first magnetic switch Fe1 is also turned off; the diode D4 is turned on for a time that the first magnetic switch Fe1 is turned on in synchronization with the off time.

The first magnetism switches on the switch of Fe1, the physical quantity is the voltage output of fixed pulse width, and the voltage passes through the RC filter and the operational amplifier, before entering the IO pin of CPU, through a zener diode steady voltage, protects the highest voltage limit of CPU, avoids damaging the CPU device. IO _1 is responsible for receiving the on/off signal of the D2 diode; IO _2 is responsible for receiving the on/off signal of the D4 diode, and after 2 signals enter the CPU pin, whether the open phase exists or not can be judged according to the comparison chart of the table.

The logic of the decision is given in fig. 9, taking the 50Hz system as an example:

1: in the cycle time (20 ms), IO _1 and IO _2 have conducting signals, and the conducting time is 6.7ms, which is normal;

2: in the period time (20 ms), IO _2 has a signal, IO _1 has no signal, and L1 is in phase failure;

3: in the cycle time (20 ms), IO _1 has a signal, IO _2 has no signal, and L3 is in phase failure;

4: the cycle time (20 ms), IO _1 and IO _2 have ON signals, and the ON time is 10ms, and L2 is out of phase.

Claims (2)

1. The utility model provides a converter input phase failure detection circuitry, its includes three-phase circuit module, its characterized in that, arbitrary two sides are provided with first magnetic switch and second magnetic switch respectively in the diode of three anodal altogether of three-phase circuit module, first magnetic switch with first detection module and second detection module are connected respectively to second magnetic switch, first detection module with second detection module all includes RC low pass filter, inverting amplifier and stabiliser, the output timing diagram of stabiliser.

2. The input open-phase detection circuit of a frequency converter according to claim 1, wherein the first detection module comprises a reverse amplifier U1, the reverse input end of the reverse amplifier U1 is connected to one end of a resistor R5, one end of a capacitor C3, one end of a capacitor C6 and one end of a capacitor R7, the other end of the resistor R5 is connected to the first magnetic switch, the normal input end of the reverse amplifier U1 is connected to one end of the resistor R6, the other end of the resistor R6 is grounded to the other end of the capacitor C3, the output end of the reverse amplifier U1 is connected to one end of a resistor R8, the other end of the capacitor C6 and the other end of the resistor R7, the other end of the resistor R8 is connected to one end of a capacitor C4 and the cathode of a voltage regulator diode D4 and is the output end of IO _1 with good timing, the second detection module includes reverse amplifier U2, reverse amplifier U2's inverting input connecting resistance R1 one end, electric capacity C5 one end, electric capacity R2 one end, the resistance R1 other end is connected the second magnetic switch, reverse amplifier U2's normal phase input connecting resistance R3 one end, the resistance R3 other end with electric capacity C1 other end ground connection, reverse amplifier U2's output connecting resistance R4 one end the electric capacity C5 other end the resistance R2 other end, electric capacity C2 one end, zener diode D1's negative pole is connected to the resistance R4 other end and IO _2 output is good for the chronology.

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