Causes of inverter overvoltage

(1) The overvoltage of the breaking transformer is based on the theory of intercepting overvoltage. When the transformer is disconnected, the current in the transformer inductance cannot be abrupt, and the magnetic field energy stored therein oscillates between the transformer magnetizing inductance and the ground capacitance. An overvoltage has occurred.

(2) Overvoltage generated by transformer with load closing In the actual test, the combined no-load transformer has detected several times the overvoltage of the power supply voltage. The physical principle is that the no-load transformer can still be equivalent to a magnetizing inductance and Parallel connection of the equivalent capacitance of the transformer itself. If the neutral point of the transformer is not grounded, the switch is aperiodic closing (one phase or two phase first), due to the inductance of the feeder, the capacitance of the transformer to the ground, the longitudinal capacitance and the inductance of the transformer. As a result, a higher overvoltage is generated, especially in the transformer neutral point overvoltage. Although the transformer is basically loaded with a load, the transformer will also generate an overvoltage when it is loaded with a load, but it is smaller when it is relatively empty. There is a relatively large capacitance in the real load, because the storage of the capacitor does not suddenly increase, and the transmission cable has a distributed capacitance to the ground when transmitting a high frequency oscillating voltage, and these capacitors have an absorption effect on the overvoltage. The combination of the two causes the overvoltage of the transformer during the closing process to be suppressed, but sometimes the value is still high and may even be higher than the withstand voltage of the component, which is very dangerous.

(3) The commutation overvoltage rectifying element of the rectifying element is high in steering, and therefore the steering overvoltage is also high. This not only damages components, but also creates electromagnetic interference.

Frequency converter overvoltage processing method

(1) For the breaking overvoltage of the phase shifting transformer of the frequency converter, the overvoltage absorption circuit is formed by the RC absorption network and the zinc oxide arrester, and good results are obtained.

(2) For the overvoltage generated by the transformer with load closing, a switch with good cycle performance can be selected (the switch will have different periods after long-term operation); a good resistance-capacitance absorption circuit or active suppressor technical solution is adopted; The shielded transformer can also effectively suppress the closing overvoltage. However, the difficulty of making a high-power transformer in the formation of an electrostatic shielding layer will be considerable.

(3) For the overvoltage generated by the commutation of the rectifying element, the point of attention is: the reverse withstand voltage of the rectifying element is sufficient, and the second is that the absorption circuit and the freewheeling circuit must be properly controlled. Otherwise, the rectifier device may be broken down by an overvoltage. (4) Since the overvoltage during the operation of the inverter is basically generated when the transformer is opened, it is necessary to start from the transformer to find a way to suppress the overvoltage of the inverter. Can be used:

1 Increase the magnetizing inductance of the transformer and the capacitance to the ground, increase the excitation inductance to reduce the no-load current, which will increase the cost of the transformer.

2 increase the capacitance of the transformer to the ground: in principle, it is easy to analyze, but in fact, due to the structure and material limitations of the transformer itself, it is impossible to make a transformer with any insulation method or high insulation level, so it is necessary to increase it greatly. The capacitance to ground C of the transformer is also quite difficult.

Air compressor frequency conversion modification notes and advantages


In the current operation of many air compressors, a large part of the time is carried out under non-full load conditions, so that waste of energy is generated by conventional control, resulting in inefficiency. But now there is a new generation of air compressor products, because it passes through the speed controller, so that it has the opportunity to save energy and improve efficiency when running at full load. This air compressor has a built-in speed controller VSD as part of the overall machine equipment.

In this article, we will mainly introduce the basic situation of the air compressor using the speed controller (especially the inverter), and briefly explain some small points after the air compressor uses the inverter. When the air compressor is running and the power frequency is controlled, the system is loaded for pressure control, and the motor is always in the power frequency running state. After the inverter device is modified, the pipe network pressure can be controlled under any constant pressure, and the frequency conversion system automatically controls the motor speed regulation.

The pressure sensor device is used to detect the pressure of the pipe network, and an analog signal is given to the frequency converter through the PID adjustment. The frequency converter gives the appropriate voltage and frequency to the air compressor motor, adjusts the motor speed and output power, thus forming a closed loop feedback. The system maintains a constant pressure on the pipe network and can be automatically adjusted by the internal PLC.

In the actual application, the required supply power is different depending on the usage time, day and night, depending on the amount of gas supplied. The traditional adjustment method is to load through the adjustment of the pressure valve.

It is relatively simple to install the inverter when the air compressor is installed. Remove the motor from the original AC, install it into the inverter cabinet, and take the cable from the power supply open side to the inverter cabinet. The external sampling signal is connected to the control AC to automatically adjust the motor speed to achieve constant voltage control (PID adjustment). The frequency converter itself has various protections (overvoltage, overcurrent, overload, overheating and undervoltage protection).

The advantages of using frequency conversion: easy to start without impact current, automatic adjustment, constant pressure, low noise, less wear and tear on the machine, and stable operation of the machine.

1) Startup method:

The air compressor is a large moment of inertia load. This kind of starting characteristic can easily cause the inverter of V/F control mode to skip flow protection during startup. It is recommended to use a speed sensorless vector inverter with high starting torque. To ensure the continuity of constant pressure gas supply, and to ensure reliable and stable operation of the equipment.

The air compressor is not allowed to run at low frequencies for a long time. When the speed of the air compressor is too low, the working stability of the air compressor will be deteriorated on the one hand, and the lubrication of the cylinder will be deteriorated on the other hand, which will accelerate wear. Therefore, the lower limit of the working frequency should be no less than 25Hz.

The start and stop of the motor with frequency converter speed regulation cannot be directly operated by the circuit breaker and the contactor, and the control terminal of the frequency converter is used for operation. Otherwise, the frequency converter may be out of control and may cause serious consequences.

When using the inverter to control the motor speed, the temperature rise and noise of the motor will be higher than when using the grid power (power frequency); at low speed, due to the low speed of the motor blades, attention should be paid to ventilation cooling and proper load reduction to avoid motor temperature. Rise exceeds the allowable value.

The start signal of the inverter is controlled by the delta connection AC contactor KM1, that is, the inverter does not start without output when the star type; the setting time of the air compressor time relay JS is greater than or equal to the startup time of the inverter, which ensures that the inverter is empty. The inverter starts.

The designed system is preferably equipped with two sets of control loops of frequency conversion and power frequency to ensure that the inverter has abnormal jump protection without affecting production.

Before the motor is used for the first time or after being placed for a long time before being connected to the inverter, the insulation resistance measurement of the motor must be performed (using a 500V or 1000V megohmmeter, the measured value should be not less than 5M ohm). If the insulation resistance is too low, the inverter will be damaged. When the inverter is connected to the motor, it is not allowed to measure the insulation resistance of the motor with a megohmmeter. Otherwise, the high voltage output of the megohmmeter will damage the inverter.

2) Air compressor modification inverter selection and installation environment

It is recommended to use a general-purpose inverter with a higher power than the air compressor or a special-purpose inverter of the same type as the southern Lixin air compressor, so as to avoid the frequency trip when the air compressor starts.

If the inverter is not used for more than one year, the capacitor must be recharged for one hour per year.

The frequency converter should be installed vertically, leaving room for ventilation and controlling the ambient temperature not to exceed 40 °C.

3) Air compressor frequency conversion transformation wiring installation:

When carrying out the air compressor frequency conversion transformation, care should be taken to maintain the integrity of the original equipment main circuit and control circuit as much as possible, and the less changes to its circuit are better; this is beneficial to the air pressure in the event of fault or maintenance of the inverter. The machine can be easily changed back to the original control mode, which ensures that the air compressor can be operated under both variable frequency and power frequency conditions, and the PLC program can be rewritten without modification.

The lower limit operating frequency of the inverter is set at 25-30HZ. If the HZ number is too low, it may cause the separator to be unable to effectively separate the oil and gas, resulting in oil leakage of the air compressor. However, it is necessary to consider the setting of the lower limit according to the actual situation, because the mechanical wear and the efficiency of different air compressors are not the same, and the lower limit frequency of the oil leakage is not necessarily the same.

The impedance of the power supply line should not be too small. The inverter is connected to the voltage grid. When the capacity of the distribution transformer is greater than 500KVA or the capacity of the distribution transformer is greater than 10 times the capacity of the inverter, or when the inverter is connected close to the distribution transformer, due to the loop impedance. Small, the input moment will cause a large surge to the inverter, which will damage the rectifier components of the inverter. When the line impedance is too small, an AC reactor should be installed between the grid and the inverter.

When the three-phase voltage unbalance rate of the power grid is greater than 3%, the peak value of the input current of the inverter is very large, which may cause the inverter and the connection to overheat or damage the electronic components. At this time, an AC reactor is also required. Especially when the transformer is V-shaped, it is more serious. In addition to installing a reactor on the AC side, it is necessary to install a DC reactor on the DC side.

It is not possible to install an excessively large capacitor on the incoming side because of increasing the power factor, and it is no longer possible to install a capacitor between the motor and the inverter. Otherwise, the line impedance will drop and overcurrent will be generated to damage the inverter.

It is generally not advisable to install an AC contactor between the inverter and the motor to avoid overvoltage generated in the current interruption and damage the inverter. If it needs to be installed, the output contactor should be closed before the inverter runs.

The sensor is installed on the main air supply pipe. Some gas supply systems use a check valve at the air outlet of the air compressor. The position of the sensor should be after the check valve, that is, away from the end of the air outlet. Otherwise, the pressure will drop suddenly when the air compressor is unloaded, and the frequency converter will oscillate frequently when loading and unloading frequently.

Pay attention to the thermal protection of the motor. If the motor is adapted to the drive capacity, the thermal protection inside the drive can effectively protect the motor. If the capacity of the two does not match, the protection value must be adjusted or other protective measures should be taken to ensure the safe operation of the motor. The electronic thermal protection value of the inverter (motor overload detection) can be set within the range of 25%-105% of the rated current of the inverter.

4) How to deal with interference from air compressor frequency conversion?

Some air compressor controllers have high requirements on system grounding. If the system is not reliably grounded, it will inevitably cause interference to the detection signal during frequency conversion operation. I have encountered it several times. The control line must be shielded and grounded reliably. It is best to separate it from the output cable. The grounding of the inverter cabinet must be reliable. It is best to ground independently and the air compressor should be grounded reliably. This ensures that the interference is effectively suppressed. It can also prevent the inverter from causing electric shock due to leakage.

In order to effectively filter out the higher harmonic components in the inverter output current and reduce the electromagnetic interference caused by higher harmonics, it is recommended to use the output AC reactor to reduce the motor running noise and temperature rise and improve the stability of the motor. Sex.

5) Use of braking resistor

For the case of lifting the load and frequent start and stop, there will be a large torque, and the appropriate braking resistor needs to be selected. Otherwise, the inverter will often trip due to overcurrent or overvoltage fault.

For the case where the inverter drives the ordinary motor for constant torque operation, long-term low-speed operation should be avoided as much as possible, otherwise the heat dissipation effect of the motor will be worse and the heat will be severe. If you need to run at low speed and constant torque for a long time, you must use a variable frequency motor. When the motor has another brake, the inverter should work in the free stop mode, and the brake action signal will be issued after the inverter issues a stop command. The braking resistor connected to the inverter must not be less than the braking resistor required by the inverter. Under the premise of meeting the braking requirements, the braking resistor should be larger. Do not short-circuit the terminals that should be connected to the braking resistor. Otherwise, a short-circuit accident will occur through the switch when braking.

Correctly handle the speed increase and deceleration problems. The acceleration and deceleration time set by the inverter is too short, and it is easy to be affected by “electric shock” and may damage the inverter. Therefore, when using the inverter, the acceleration and deceleration time should be extended as much as possible under the premise of the load device. If the load is heavy, the acceleration and deceleration time should be increased; otherwise, the acceleration and deceleration time can be appropriately reduced. If the load equipment needs to be added or decelerated in a short time, it must be considered to increase the capacity of the inverter to avoid too much current and exceed the rated current of the inverter. If the load equipment requires a short acceleration and deceleration time (such as within 1S), then consider using a brake system on the inverter. Generally, larger inverters are equipped with a brake system.

Summary: After the air compressor is modified by using the AC inverter, it is not only easy to operate, simple, and has a small amount of maintenance, but also has significant energy-saving effects and high-automatic adjustment to achieve high energy-saving requirements. The air compressor constant pressure air supply uses the frequency converter and pressure control to form a closed-loop control system, which reduces the pressure fluctuation to 1.5%, reduces noise, reduces vibration and ensures stable operation of the equipment. After using the frequency converter, the air compressor can be started freely under any pressure, breaking the rule that the pressure start is not allowed before, and the starting current is greatly reduced compared with the previous one. After using the frequency converter, the power saving rate is generally about 20%, which is lower than that of the fan and the pump type. However, the motor power is relatively large, and its power saving value is large, and the economic benefits are relatively significant.

Advantages and Principles of Energy Saving for Asynchronous Servo Drives of Injection Molding Machines

Advantages; power saving and prolonging the service life of the injection molding machine. The original oil circuit is slightly modified. The maintenance cost is low. The soft start of the motor is faster. The vector control method does not extend the product cycle time.
1. Asynchronous servo driver Why can the power saving rate reach 10%-60%? How does it achieve power saving?
A: Because the injection molding machine is a typical cyclically variable load device, a complete production cycle includes stages of clamping, injection, melting, cooling, and mold opening. For its hydraulic system, each stage is pressure-dependent. The flow rate is matched differently, and the power of the oil pump motor is equipped according to the maximum load during the operation. However, in the production cycle of the injection molding machine, only the high-voltage mold clamping and the furnace rubber section load are large, and the motor load in other working stages is generally Smaller, especially during the cooling process, the load is almost zero. During the whole working process of the injection molding machine, the power consumption of the oil pump motor is severe, and the power utilization rate is only 30%–70%. Therefore, the power saving space is relatively large. AC asynchronous servo is a high-efficiency power saver developed for injection molding machine. It uses the flow signal of the injection molding machine as its own control signal to realize soft start and stepless speed regulation, so that the output power of the motor matches its load, and the whole process of the injection molding machine It is completely consistent and achieves high efficiency and energy saving without affecting production efficiency. The power saving rate can reach 30%–65%.

2. Why can we reduce the number of maintenance of the injection molding machine and reduce the oil temperature while saving electricity?
Answer: Because the oil pump motor realizes the variable frequency variable voltage and stepless speed regulation under the control of the power saver during the power saving process, the motor can be completely stopped during the cooling of the injection molding machine. The running frequency of the motor is lower than the whole power saving process. The frequency (50HZ) in the power frequency (ie non-power saving) state, that is, the rotational speed of the injection pump oil pump motor is relatively reduced, so that the friction degree of the oil pump is lowered, the oil temperature is lowered, and the bearing temperature of the motor is lowered, so during the power saving process Not only achieves high efficiency and energy saving, but also prolongs the service life of the motor, slows down the degree of oil quality degradation, and prolongs the aging time of the oil seal, thereby reducing the maintenance cost and reducing the number of maintenance.

3. Does the frequent start of the motor during the power saving process affect the motor?
A: No adverse effects! AC asynchronous servo drive is a special power-saving device for injection molding machine. The software has designed the motor-specific “S”-type starting curve, 21 kinds of V/F torque lifting mode, and stepless speed regulation during operation. 0.02 seconds – 3200 seconds width adjustable acceleration time selection, can choose the appropriate acceleration time according to different power motors, thus avoiding the large inrush current when the motor is directly started. In fact, any starting process of the motor under the control of the AC asynchronous servo drive is actually a “soft start” process without current surge. In addition, the AC asynchronous servo also includes various protection functions such as over current, over voltage, overload, under voltage, over temperature, CPU protection and so on. Therefore, even if the motor is frequently started and stopped, there is no adverse effect on the motor itself, and on the contrary, the service life of the motor can be extended.

Photovoltaic (MPPT ) solar inverter water pump system

Photovoltaic water pump system is also called photovoltaic lift water system, which consists of photovoltaic solar panels, special inverters for photovoltaic, water pumps, and water storage devices. The principle is to use semiconductors to absorb solar radiation energy, and convert it into direct current, and then convert it into alternating current through a photovoltaic inverter to drive the pump to lift water.

 

Photovoltaic pump system features:
Clean Energy: Solar energy is driven as a power source and has zero pollution to the environment;
Affordable: No need to lay power lines, greatly reducing system construction costs;
Safe and reliable: automatic operation, no need to be on duty, to replace water storage power storage, direct drive pump water, to avoid large-scale laying of the hidden safety problems caused by the cable, high reliability, significantly reduce the system’s construction and maintenance costs.
Intelligent adjustment: adjust the speed of the pump according to the change of the sunshine intensity so that the output power is close to the maximum power of the solar array; when the sunshine is sufficient, the rotation speed of the water pump does not exceed the rated rotation speed; when the sunshine is insufficient, according to the set conditions, automatic Stop or switch to commercial power to ensure the system continues to operate economically.
Widely used: The water pump is driven by a three-phase AC motor, pumping water from a deep well, injecting a water storage tank/pool, or directly accessing an irrigation system. According to actual system requirements and installation conditions, different types of pumps can be used for work. And can provide economical and effective solutions based on the needs of different regions and customers.

 


Photovoltaic water pump to inverter requirements
1. With MPPT algorithm, adjust the pump speed according to the change of sunshine intensity so that the output power is close to the maximum power of the solar array. Due to the non-linearity of the output characteristics of the photovoltaic array, its output is affected by the light intensity, ambient temperature and load conditions. Under a certain light intensity and ambient temperature, the photovoltaic array can work at different output voltages, but only at a certain output voltage value. At this time, the output power of the photovoltaic cell can reach its maximum value. Therefore, in the solar photovoltaic pump system, to improve the system efficiency, the output power of the photovoltaic array must be detected in real time and the operating point of the photovoltaic cell must be adjusted so that it always operates near the maximum power point, so as to satisfy the solar energy requirement under different solar illumination conditions. More is converted into electrical energy to enable the pump to work efficiently and stably. Therefore, Maximum Power Point Tracking (MPPT) is the core function of the PV Pump Frequency Converter.
2, with a dry burning detection, automatic protection of the pump. The working environment of the water pump is in the water. The water pump motor is used to radiate heat by water. It is forbidden to run under broken water. However, the water level of the water pump is very different according to the amount of water supply and the change of the water source. Burning the pump motor affects the reliability of the system.
3, according to changes in light intensity, automatic sleep wake up. In order to meet the requirements of the system’s automatic work, the system should have the function of self-diagnosis and automatic start-up. The control system should conduct self-testing and pre-judgment before the pump work, and start the photovoltaic pump work or charge the lighting battery after the conditions are met; In cloudy and thundery weather, the system can stop the work of the photovoltaic pump according to the detected data. When the light meets the working requirements of the photovoltaic pump, the system can automatically resume operation.
4, the system has lightning protection and other functions, when the over-voltage, under voltage, over-current, overload, overheating, water tank full of water, water pump and other failures have been lifted, the system can automatically resume working after self-diagnosis.
5. It can cooperate with water level switch and water tower to store water and improve water use efficiency.

9600B series wiring diagram and technical standards

一、 9600B series

Features: functional, high-end use
Voltage level: 220V, 380V, 440V, 660V four voltage levels
Frequency range: 0-650Hz, 0-3200Hz
Features: Upgrade based on 9600A series,supports the three phase AC synchronous motor and supports vector control of permanent magnet synchronous motor without absolute position feedback.

二、Wiring diagram

三、Technology standard

9600A series wiring diagram and technical standards

一、 9600A series

Features: functional, high-end use
Voltage level: 220V, 380V, 440V, 660V four voltage levels
Frequency range: 0-650Hz, 0-3200Hz
Features: Asynchronous motor vector inverter in the 9000 series based on the increase in pulse input control, fast current limit, instantaneous stop non-stop, multi-motor switching and other functions.

二、Wiring diagram

三、Technology standard

9100 series wiring diagram and technical standards

一、9100 series

Features: special customization, powerful function .
Voltage rating: 220V, 380V, DC voltage.
Frequency range: 0-650Hz
Features: Customized constant pressure water supply: support direct display pressure value, up and down key regulator, water protection, sleep function, auxiliary pump control, etc .; Solar frequency converter: support DC wide voltage input, maximum power point tracking function (MPPT) .

二、Wiring diagram

  • Notes :X5,X6,DO2 andA,B is reset terminals of 485 communication port,parameters switched by P9.07 and wire jumpered by JP6,JP7,JP8.

三、Technology standard

9000 series wiring diagram and technical standards

一、9000 series

Features: easy to use, easy debugging
Voltage level: 110V, 220V, 380V three voltage levels
Frequency range: 0-650Hz
Features: support a variety of control methods, analog input and output, PID control, simple PLC, multi-speed, RS485 communication, zero speed detection, etc., widely applicable to various occasions.

二、Wiring diagram

三、Technology standard

 

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