Abstract: Inverter supply
The energy-saving analysis of frequency conversion speed regulation technology is introduced. The basic composition of the frequency conversion constant pressure water supply system and the selection of control parameters and the operating parameters of the frequency converter are described. The advantages of the frequency conversion constant pressure water supply system are analyzed.
I. Overview of inverter supply
AC motor frequency control technology is a widely used energy-saving technology. Due to the rapid development of electronic technology, the performance of the inverter has been greatly improved. It can realize the soft start and soft stop of the control equipment, which can not only reduce the equipment failure rate, but also significantly reduce the power consumption to ensure the system is safe, stable, and long-term operation. .
For a long time, the district's water supply system has been used by the municipal pipe network after the secondary pressure and the water tower or sky pool to meet the user's requirements for water supply pressure. In a residential water supply system, the booster pump usually uses the water pressure requirements of the most unfavorable water point to determine the corresponding head design. The pump group then selects the pump according to the change in flow rate and determines the operating mode of the pump. Since the residential water has obvious changes in season and time, the daily water supply operation control often uses the adjustment of the water pump operation mode plus the outlet valve opening to adjust the water supply water pressure, a large amount of energy is wasted in the outlet valve, and there is a pool "Secondary pollution" problem. Frequency conversion speed control technology applied to the feed pump station, successfully solved the two major problems of energy consumption and pollution.
Second, frequency conversion energy-saving theory of frequency converter supply
1, the principle of AC motor speed control
AC motor speed characteristics: n = 60f (1-s) / p, where n is the motor speed, f is the frequency of the alternating current, s is the slip rate, p is the number of pole pairs.
After the motor is selected, s and p are fixed values, and the motor speed n is proportional to the AC frequency f. Using the inverter to change the AC frequency can realize the stepless speed regulation of the motor.
2, according to the working principle of centrifugal pump load can be seen:
The flow is proportional to the speed: the supply torque of the QâˆN inverter is proportional to the square of the speed: TâˆN2
The power is proportional to the third power of the speed: PâˆN3
And the energy loss of the frequency conversion speed regulation itself is extremely low, and the input power of the inverter is almost equal to the motor shaft power at various speeds. It can be seen that the relationship between the flow rate change and the power in the system when using the frequency conversion speed regulation technology water supply:
P variable = N3P amount = Q3P amount using the outlet valve to control the flow, the motor in the power frequency operation, the relationship between the flow changes in the system and power: P valve = (0.4 + 0.6 Q) P amount where P is The power N is the rotational speed Q as the flow rate
For example, if the current flow rate is set to 60% of the rated flow rate of the water pump, the P variable = Q3P amount = 0.216P when the variable frequency speed control is adopted, and the P valve = (0.4 + 0.6Q) P = 0.76P, power saving = (P valve - P change) / P valve * 100% = 71.6%.
Flow % 100 90 80 70 60 50
Saving rate % 0 22.5 41.8 61.5 71.6 82.1
It can be seen from the theoretical calculation results that the energy-saving effect is very significant, and in the actual operation of the community frequency conversion constant pressure water supply technology than the traditional pressurized water supply system has automatic control of constant pressure, no pollution and other obvious advantages.
And the new residential frequency conversion constant pressure water supply system can automatically control the operation of one or more main pumps and a dormant pump. When the water consumption of the pipe network is reduced to about 1/6-1/8 of the flow rate of a single main pump, the system will automatically stop the main pump and start a low-power dormant pump to ensure that the system provides a small flow of water and solves the problem of small-flow or even zero-flow water supply. When a large amount of electric energy is wasted, further energy-saving is realized from the operation control.
Third, constant pressure water supply system and control parameters selection
1, frequency conversion constant pressure water supply system composition inverter supply
The frequency conversion constant pressure water supply system is usually composed of a pool, a centrifugal pump (main pump + dormant pump), a pressure sensor, a PID regulator, a frequency converter (main pump + dormant pump), and a pipe network (see FIG. 1). The work flow is to use the pressure sensor set on the pipe network to change the water pressure caused by the change of water consumption in the pipe network system, and feed back the signal (4-20mA or 0-10V) to the PID regulator in time, and the PID regulator contrasts the setting control. After the pressure is calculated, the corresponding frequency conversion instruction is given, and the operation or rotation speed of the water pump is changed so that the water pressure of the pipe network is consistent with the control pressure.
2, the frequency conversion constant pressure water supply system parameter selection frequency changer supplies
(1) Reasonably select the pressure control parameters to realize the system of low energy consumption and constant pressure water supply. The key to the realization of this purpose lies in the selection of pressure control parameters. Usually there are two pressure control point selections in the pipe network: one is the pressure control of the most unfavorable point of the pipe network, and the other is the constant pressure control of the pump outlet pressure. How to choose the two, let's analyze briefly.
When the pressure at the most unfavorable point of the pipe network is constant, the water consumption of the pipe network is reduced from QMAX to Q1. The water pump reduces the rotation speed, intersects the characteristic curve A (invariant) of the water pipe at point C, and the pump characteristic curve shifts downward. The most unfavorable point of the pipe network is Pressure H0. When the pressure at the outlet of the pump is controlled under constant pressure, Ha is not changed. The water consumption is reduced from QMAX to Q1 and Ha at point B. The characteristic curve A of the water pipeline moves upwards and passes through point B. The pressure at the most unfavorable point of the pipe network becomes Hb. The difference of lift between Hb and H0 is energy waste, so the minimum head of the most unfavorable point of the pipe network is selected as the pressure control parameter to form a closed-loop pressure automatic control system, which makes the speed of the water pump match the set pressure of the PID regulator and can reach the maximum. Energy-saving effect, but also achieve the purpose of constant pressure water supply.
(2) The commissioning of the inverter after it is put into operation is a necessary means to ensure that the system reaches its optimum operating state. Inverter according to the size of the moment of inertia of the load, the time required to start and stop the motor is not the same. If the set time is too short, the inverter will over-current during acceleration and over-voltage protection during deceleration; setting time is too long. It will lead to slow adjustment of the system when the frequency converter is running at a variable speed, with a slow response, poor adaptability, and the system is vulnerable to short-term instability.
In order to protect the inverter from tripping, the acceleration and deceleration time settings of many inverters in the field are too long. The problems it brings can easily be masked by the normal appearance of the device, but the inverter cannot reach the optimal operation state. Therefore, according to the nature of the load that is driven during field use, test the minimum allowable acceleration/deceleration time of the load and set it. For the water pump motor, the acceleration/deceleration time is selected between 0.2-20 seconds.
Fourth, the advantages of frequency conversion constant pressure water supply system
Compared with traditional pressurized water supply methods, the advantages of variable frequency and constant pressure water supply systems are prominently reflected in the following aspects:
1ã€Efficient and energy-saving inverter supply
The most significant advantage of frequency conversion constant pressure water supply system is that it saves electricity, and the energy saving is usually 10-40%. From the point of view of energy saving of a single pump, the smaller the flow, the greater the amount of energy savings.
2, constant pressure water supply inverter supply
The frequency conversion constant pressure water supply system achieves stable system water supply pressure and the flow rate can continuously change over a large range, which can guarantee the user's water pressure at any time, and it will not occur when the water heater cannot be used normally during the peak of water use.
3, safety and health frequency converter supply
After the closed-loop water supply system was implemented, the user's water was supplied directly by pipelines, water towers, sky pools, and pressure tanks were eliminated, water “secondary pollution†was avoided, and the pool’s regular cleaning work was cancelled.
4, automatic operation, easy management, inverter supply
The new community frequency conversion constant pressure water supply system has the functions of over-current, over-voltage, under-voltage, under-phase, short-circuit protection, instantaneous power failure protection, overload, stall protection, low liquid level protection, main pump timing rotation control, password setting and other functions , Full-featured, fully automatic control, automatic operation, pump station without a post, just send regular inspection and maintenance.
5, extend equipment life, protect the stability of the power grid
After the inverter is used, the speed of the pump is no longer maintained for a long period of time to maintain the rated speed, which reduces mechanical wear and reduces the pump failure rate. In addition, the main pump timing rotation control function automatically alternates the main pump operation to ensure uniform wear of the pumps. The stainless die, extending the pump life. The stepless speed regulation operation of the frequency converter realizes the soft start of the pump, avoids the impact of the large current when the motor starts and stops on the motor coil and the power grid, and eliminates the water hammer effect of the water pump.
6, less land, short investment recovery period supply
The new residential frequency conversion constant pressure water supply system uses a vertical pump installed directly on the pool. If only one or two control cabinets are placed between the control rooms, the volume is small and the entire system occupies a very small area, which can save investment. In addition, no water towers or sky pools, no special management of control rooms, and extremely low equipment failure rates have achieved further reductions in investment. The low operating and management fees, coupled with the energy-saving advantages of variable frequency water supply, have all determined the frequency of cell conversion. The investment recovery period of the constant pressure water supply system is short, generally about 1 year.
The energy-saving analysis of frequency conversion speed regulation technology is introduced. The basic composition of the frequency conversion constant pressure water supply system and the selection of control parameters and the operating parameters of the frequency converter are described. The advantages of the frequency conversion constant pressure water supply system are analyzed.
I. Overview of inverter supply
AC motor frequency control technology is a widely used energy-saving technology. Due to the rapid development of electronic technology, the performance of the inverter has been greatly improved. It can realize the soft start and soft stop of the control equipment, which can not only reduce the equipment failure rate, but also significantly reduce the power consumption to ensure the system is safe, stable, and long-term operation. .
For a long time, the district's water supply system has been used by the municipal pipe network after the secondary pressure and the water tower or sky pool to meet the user's requirements for water supply pressure. In a residential water supply system, the booster pump usually uses the water pressure requirements of the most unfavorable water point to determine the corresponding head design. The pump group then selects the pump according to the change in flow rate and determines the operating mode of the pump. Since the residential water has obvious changes in season and time, the daily water supply operation control often uses the adjustment of the water pump operation mode plus the outlet valve opening to adjust the water supply water pressure, a large amount of energy is wasted in the outlet valve, and there is a pool "Secondary pollution" problem. Frequency conversion speed control technology applied to the feed pump station, successfully solved the two major problems of energy consumption and pollution.
Second, frequency conversion energy-saving theory of frequency converter supply
1, the principle of AC motor speed control
AC motor speed characteristics: n = 60f (1-s) / p, where n is the motor speed, f is the frequency of the alternating current, s is the slip rate, p is the number of pole pairs.
After the motor is selected, s and p are fixed values, and the motor speed n is proportional to the AC frequency f. Using the inverter to change the AC frequency can realize the stepless speed regulation of the motor.
2, according to the working principle of centrifugal pump load can be seen:
The flow is proportional to the speed: the supply torque of the QâˆN inverter is proportional to the square of the speed: TâˆN2
The power is proportional to the third power of the speed: PâˆN3
And the energy loss of the frequency conversion speed regulation itself is extremely low, and the input power of the inverter is almost equal to the motor shaft power at various speeds. It can be seen that the relationship between the flow rate change and the power in the system when using the frequency conversion speed regulation technology water supply:
P variable = N3P amount = Q3P amount using the outlet valve to control the flow, the motor in the power frequency operation, the relationship between the flow changes in the system and power: P valve = (0.4 + 0.6 Q) P amount where P is The power N is the rotational speed Q as the flow rate
For example, if the current flow rate is set to 60% of the rated flow rate of the water pump, the P variable = Q3P amount = 0.216P when the variable frequency speed control is adopted, and the P valve = (0.4 + 0.6Q) P = 0.76P, power saving = (P valve - P change) / P valve * 100% = 71.6%.
Flow % 100 90 80 70 60 50
Saving rate % 0 22.5 41.8 61.5 71.6 82.1
It can be seen from the theoretical calculation results that the energy-saving effect is very significant, and in the actual operation of the community frequency conversion constant pressure water supply technology than the traditional pressurized water supply system has automatic control of constant pressure, no pollution and other obvious advantages.
And the new residential frequency conversion constant pressure water supply system can automatically control the operation of one or more main pumps and a dormant pump. When the water consumption of the pipe network is reduced to about 1/6-1/8 of the flow rate of a single main pump, the system will automatically stop the main pump and start a low-power dormant pump to ensure that the system provides a small flow of water and solves the problem of small-flow or even zero-flow water supply. When a large amount of electric energy is wasted, further energy-saving is realized from the operation control.
Third, constant pressure water supply system and control parameters selection
1, frequency conversion constant pressure water supply system composition inverter supply
The frequency conversion constant pressure water supply system is usually composed of a pool, a centrifugal pump (main pump + dormant pump), a pressure sensor, a PID regulator, a frequency converter (main pump + dormant pump), and a pipe network (see FIG. 1). The work flow is to use the pressure sensor set on the pipe network to change the water pressure caused by the change of water consumption in the pipe network system, and feed back the signal (4-20mA or 0-10V) to the PID regulator in time, and the PID regulator contrasts the setting control. After the pressure is calculated, the corresponding frequency conversion instruction is given, and the operation or rotation speed of the water pump is changed so that the water pressure of the pipe network is consistent with the control pressure.
2, the frequency conversion constant pressure water supply system parameter selection frequency changer supplies
(1) Reasonably select the pressure control parameters to realize the system of low energy consumption and constant pressure water supply. The key to the realization of this purpose lies in the selection of pressure control parameters. Usually there are two pressure control point selections in the pipe network: one is the pressure control of the most unfavorable point of the pipe network, and the other is the constant pressure control of the pump outlet pressure. How to choose the two, let's analyze briefly.
When the pressure at the most unfavorable point of the pipe network is constant, the water consumption of the pipe network is reduced from QMAX to Q1. The water pump reduces the rotation speed, intersects the characteristic curve A (invariant) of the water pipe at point C, and the pump characteristic curve shifts downward. The most unfavorable point of the pipe network is Pressure H0. When the pressure at the outlet of the pump is controlled under constant pressure, Ha is not changed. The water consumption is reduced from QMAX to Q1 and Ha at point B. The characteristic curve A of the water pipeline moves upwards and passes through point B. The pressure at the most unfavorable point of the pipe network becomes Hb. The difference of lift between Hb and H0 is energy waste, so the minimum head of the most unfavorable point of the pipe network is selected as the pressure control parameter to form a closed-loop pressure automatic control system, which makes the speed of the water pump match the set pressure of the PID regulator and can reach the maximum. Energy-saving effect, but also achieve the purpose of constant pressure water supply.
(2) The commissioning of the inverter after it is put into operation is a necessary means to ensure that the system reaches its optimum operating state. Inverter according to the size of the moment of inertia of the load, the time required to start and stop the motor is not the same. If the set time is too short, the inverter will over-current during acceleration and over-voltage protection during deceleration; setting time is too long. It will lead to slow adjustment of the system when the frequency converter is running at a variable speed, with a slow response, poor adaptability, and the system is vulnerable to short-term instability.
In order to protect the inverter from tripping, the acceleration and deceleration time settings of many inverters in the field are too long. The problems it brings can easily be masked by the normal appearance of the device, but the inverter cannot reach the optimal operation state. Therefore, according to the nature of the load that is driven during field use, test the minimum allowable acceleration/deceleration time of the load and set it. For the water pump motor, the acceleration/deceleration time is selected between 0.2-20 seconds.
Fourth, the advantages of frequency conversion constant pressure water supply system
Compared with traditional pressurized water supply methods, the advantages of variable frequency and constant pressure water supply systems are prominently reflected in the following aspects:
1ã€Efficient and energy-saving inverter supply
The most significant advantage of frequency conversion constant pressure water supply system is that it saves electricity, and the energy saving is usually 10-40%. From the point of view of energy saving of a single pump, the smaller the flow, the greater the amount of energy savings.
2, constant pressure water supply inverter supply
The frequency conversion constant pressure water supply system achieves stable system water supply pressure and the flow rate can continuously change over a large range, which can guarantee the user's water pressure at any time, and it will not occur when the water heater cannot be used normally during the peak of water use.
3, safety and health frequency converter supply
After the closed-loop water supply system was implemented, the user's water was supplied directly by pipelines, water towers, sky pools, and pressure tanks were eliminated, water “secondary pollution†was avoided, and the pool’s regular cleaning work was cancelled.
4, automatic operation, easy management, inverter supply
The new community frequency conversion constant pressure water supply system has the functions of over-current, over-voltage, under-voltage, under-phase, short-circuit protection, instantaneous power failure protection, overload, stall protection, low liquid level protection, main pump timing rotation control, password setting and other functions , Full-featured, fully automatic control, automatic operation, pump station without a post, just send regular inspection and maintenance.
5, extend equipment life, protect the stability of the power grid
After the inverter is used, the speed of the pump is no longer maintained for a long period of time to maintain the rated speed, which reduces mechanical wear and reduces the pump failure rate. In addition, the main pump timing rotation control function automatically alternates the main pump operation to ensure uniform wear of the pumps. The stainless die, extending the pump life. The stepless speed regulation operation of the frequency converter realizes the soft start of the pump, avoids the impact of the large current when the motor starts and stops on the motor coil and the power grid, and eliminates the water hammer effect of the water pump.
6, less land, short investment recovery period supply
The new residential frequency conversion constant pressure water supply system uses a vertical pump installed directly on the pool. If only one or two control cabinets are placed between the control rooms, the volume is small and the entire system occupies a very small area, which can save investment. In addition, no water towers or sky pools, no special management of control rooms, and extremely low equipment failure rates have achieved further reductions in investment. The low operating and management fees, coupled with the energy-saving advantages of variable frequency water supply, have all determined the frequency of cell conversion. The investment recovery period of the constant pressure water supply system is short, generally about 1 year.