The use of ionistrov for regenerative braking in the subway
Many of you noticed that the subway is very hot in the summer and there is an unpleasant smell. So I once wondered, but where did this heat and this smell come from? In fact, the metro smells like four smells: the smell of wood to protect the sleepers from rotting, the smell of heated wires, the smell of fine dust from brake pads and the smell of burnt iron. I thought it was unhealthy.
Another time, leaving the car, I noticed that a warm stream of air rises from under the car. And I thought, where did he come from? And then I remembered that electric cars and that when braking the braking occurs due to the engines (electrodynamic braking). But, why not use this energy? After all then there will be no heating of wires, there will be no dust from brake shoes. For this you need a recovery system.
Recovery allows you to return energy. A similar system is implemented on the Toyota Prius Hybrid.
')
But what is the problem, where to return it? There are 2 options: either back to the grid or somewhere to store it. Return back to the grid - the necessary other traction substations and other cars themselves are needed. Plus, you can not produce recovery between trains that are powered by different traction substations. As a result, the recovery effect reaches 15%, which is quite small. And the traction substation to convert expensive and long. And the cars themselves are updated every 30 years. So this option is quite long.
The second option is to return energy back to the train. Then it is enough to retool the train and the efficiency can reach 80%.
For energy storage, it is better to use ionistra, rather than batteries.
Benefits:
1. Traction substations are not required for re-equipment of trains.
2. The train can independently move to the nearest station for disembarking passengers in case of a power failure.
3. You can retrofit existing trains.
4. There is no problem transferring energy from one train to another. That is, there is no need for an additional power grid in the case of a highly uneven train load in the metro stations.
Disadvantages:
1. The cost of ionistra.
2. The increase in train mass due to ionistr (not so much in relation to the mass of the train and passengers).
The advantages of ionisters compared to batteries:
1. High charge / discharge rate - high discharge current.
2. Easy charger.
3. Small degradation after hundreds or even thousands of charge / discharge cycles.
4. The possibility of charge / discharge at low temperatures.
Disadvantages:
1. Less specific energy.
2. Voltage dependence on charge state.
Thus, ionistry more suitable for recovery than batteries as a mobile energy source.
What is ionistr? Ionistr - he is a supercapacitor, it is essentially an electrical capacitor, but with a double electric layer. In fact, it is a hybrid of battery and capacitor. In the electrolyte (as in the battery) float charges (as in a capacitor), which are attracted to each other. So that these floating charges do not collide with each other and do not neutralize each other, there is a dilector between them. Thus a double electric layer form
Ionistra are used in the E-mobile.
But there is still the problem of regulating the supply of energy from ionistrov to the engines and back.
For this, pulse-width modulation paired with an inverter circuit is well suited. Pulse width modulation (PWM) is used now absolutely in all power schemes, whether they are computer power supplies, processor voltage regulators on the motherboard, or any other power devices. The essence of PWM is that the duration (width) of a pulse changes with a frequency of several tens to hundreds of kHz and due to this the amount of energy transmitted to the consumer changes. The variable signal is smoothed by the capacitor and can become permanent if necessary. Usually in PWM there is a high-frequency transformer, to which control pulses are applied.
And the inverter is a circuit where the DC voltage becomes variable (inverted) and can then be converted back to DC - this is what the rectifier does if necessary. Conversion to AC is necessary to obtain the desired voltage and its adjustment. Direct current can be converted to alternating current and then get the desired voltage using a transformer. But using not just alternating current, but alternating current of higher frequency (tens of hundreds of kHz), one can get a transformer with better mass-size indicators, efficiency and low cost. What is successfully done, for example, in a welding machine or a computer power supply.
But the problems do not end there. It is also necessary to find a suitable switching element. The ideal option is IGBT (Insulated Gateway Bipolar Transistor) technology. The essence of this technology is that they combined two transistor technologies, which have been competing for a long time, into one element. At the entrance there is a field-effect transistor, which controls the bipolar transistor. Thus, the advantages of both transistors are achieved and their disadvantages are removed:
1. Small voltage drop in saturation mode.
2. Fast switching.
A small voltage drop makes it possible to increase efficiency and reduce heat, as well as to skip more current.
And fast switching makes it possible to use this transistor for circuits operating at relatively high frequencies (tens to hundreds of kHz).
In real devices, whole blocks of such transistors are used; they are usually placed on radiators for better cooling. One such unit is capable of switching huge powers. The current in the hundreds of amps and the voltage in the hundreds of volts. That is, the total switching power of tens - hundreds of kW. Just such power at the engines of subway cars. There are usually 4 engines of 110 kW each.
Now let's calculate how much electricity can be saved.
Initial data:
Tare weight of the car: 34 tons.
Maximum car capacity: 330 passengers.
Metrowagonmash
Passenger weight on average: 70 kg.
The speed of movement of the composition, for example: 60 km / h.
Electricity cost: 4 rubles per kW * h.
Number of cars: 10
The interval of walking cars: 30 seconds.
Landing time: 30 seconds.
Number of metro lines: 12
The average trip length on each branch from end to opposite end is one hour.
Schedule subway: from 5 to 01 hours.
Ticket price on average: 20 rubles.
The number of all man-trips per day: 8 million.
Calculate the kinetic energy that the train acquires during acceleration and loses when braking
E = m * v ^ 2/2 = (34000 kg + 330 * 70 kg) * (60 / 3.6) ^ 2/2 = 8 * 10 ^ 6 J = 8 MJ (1)
A lot or a little, consider yourself. But the car has the same energy, weighing 1500 kg and moving at a speed of 614 km / h. It is clear that he does not move with such speed. But the comparison gives an idea of how much energy it is.
Potential energy is not considered, because when the train moves down, it returns. And dissipative forces - energy losses due to friction in moving mechanisms and air resistance cannot be returned, it can only be reduced.
When braking, all this energy turns into heat and is spent in empty. Plus, the brake pads are erased and there it is possible, rheostatic braking - a set of powerful resistors that are connected to the traction motors and the motors thus slow down. Braking is stepped. There is no smooth braking - increased wear of wheelsets and rails and a sharp negative acceleration (train jerking), which is inconvenient for passengers. And the air brake operation creates dispersive dust of brake pads in the air. Recovery also eliminates all these problems.
8 MJ / 3.6 MJ = 2.22 kW * h * 4 rubles / kW * h = 8.88 rubles.
For one composition: 8.88 * 10 = 88 rubles.
At one hour the train makes at least 60 minutes / (30 + 30 seconds) / 60 = 60 starts / stops.
Maybe more if you need to wait for another train. There are also partial speed reductions.
Per hour 60 * 88 = 5280 rubles per hour.
On one line 60 trains.
Total consumed electricity: 60 * 12 * 5280 rubles = 3 801 600 rubles per hour.
But the rush hour is the morning 2 hours and the evening 2 hours.
Total for the peak hour 4 * 3.8 million rubles = 14.2 million rubles.
The rest of the time, the walking interval is 3 minutes, which is 9 times less than start / stops and trains on the line, i.e. 3.8 million rubles / 9 = 420 thousand rubles. at one o'clock.
So, the cost of electricity is not in peak hours 16 * 420 = 6.7 million rubles.
Total: 20.9 million rubles. in a day.
Costs per person-trip 2.61 rub. And if the ticket costs 20 rubles on average, it is 13% of the ticket price, not so much.
In the month of 627 million rubles.
Another time, leaving the car, I noticed that a warm stream of air rises from under the car. And I thought, where did he come from? And then I remembered that electric cars and that when braking the braking occurs due to the engines (electrodynamic braking). But, why not use this energy? After all then there will be no heating of wires, there will be no dust from brake shoes. For this you need a recovery system.
Recovery allows you to return energy. A similar system is implemented on the Toyota Prius Hybrid.
')
But what is the problem, where to return it? There are 2 options: either back to the grid or somewhere to store it. Return back to the grid - the necessary other traction substations and other cars themselves are needed. Plus, you can not produce recovery between trains that are powered by different traction substations. As a result, the recovery effect reaches 15%, which is quite small. And the traction substation to convert expensive and long. And the cars themselves are updated every 30 years. So this option is quite long.
The second option is to return energy back to the train. Then it is enough to retool the train and the efficiency can reach 80%.
For energy storage, it is better to use ionistra, rather than batteries.
Benefits:
1. Traction substations are not required for re-equipment of trains.
2. The train can independently move to the nearest station for disembarking passengers in case of a power failure.
3. You can retrofit existing trains.
4. There is no problem transferring energy from one train to another. That is, there is no need for an additional power grid in the case of a highly uneven train load in the metro stations.
Disadvantages:
1. The cost of ionistra.
2. The increase in train mass due to ionistr (not so much in relation to the mass of the train and passengers).
The advantages of ionisters compared to batteries:
1. High charge / discharge rate - high discharge current.
2. Easy charger.
3. Small degradation after hundreds or even thousands of charge / discharge cycles.
4. The possibility of charge / discharge at low temperatures.
Disadvantages:
1. Less specific energy.
2. Voltage dependence on charge state.
Thus, ionistry more suitable for recovery than batteries as a mobile energy source.
What is ionistr? Ionistr - he is a supercapacitor, it is essentially an electrical capacitor, but with a double electric layer. In fact, it is a hybrid of battery and capacitor. In the electrolyte (as in the battery) float charges (as in a capacitor), which are attracted to each other. So that these floating charges do not collide with each other and do not neutralize each other, there is a dilector between them. Thus a double electric layer form
Ionistra are used in the E-mobile.
But there is still the problem of regulating the supply of energy from ionistrov to the engines and back.
For this, pulse-width modulation paired with an inverter circuit is well suited. Pulse width modulation (PWM) is used now absolutely in all power schemes, whether they are computer power supplies, processor voltage regulators on the motherboard, or any other power devices. The essence of PWM is that the duration (width) of a pulse changes with a frequency of several tens to hundreds of kHz and due to this the amount of energy transmitted to the consumer changes. The variable signal is smoothed by the capacitor and can become permanent if necessary. Usually in PWM there is a high-frequency transformer, to which control pulses are applied.
And the inverter is a circuit where the DC voltage becomes variable (inverted) and can then be converted back to DC - this is what the rectifier does if necessary. Conversion to AC is necessary to obtain the desired voltage and its adjustment. Direct current can be converted to alternating current and then get the desired voltage using a transformer. But using not just alternating current, but alternating current of higher frequency (tens of hundreds of kHz), one can get a transformer with better mass-size indicators, efficiency and low cost. What is successfully done, for example, in a welding machine or a computer power supply.
But the problems do not end there. It is also necessary to find a suitable switching element. The ideal option is IGBT (Insulated Gateway Bipolar Transistor) technology. The essence of this technology is that they combined two transistor technologies, which have been competing for a long time, into one element. At the entrance there is a field-effect transistor, which controls the bipolar transistor. Thus, the advantages of both transistors are achieved and their disadvantages are removed:
1. Small voltage drop in saturation mode.
2. Fast switching.
A small voltage drop makes it possible to increase efficiency and reduce heat, as well as to skip more current.
And fast switching makes it possible to use this transistor for circuits operating at relatively high frequencies (tens to hundreds of kHz).
In real devices, whole blocks of such transistors are used; they are usually placed on radiators for better cooling. One such unit is capable of switching huge powers. The current in the hundreds of amps and the voltage in the hundreds of volts. That is, the total switching power of tens - hundreds of kW. Just such power at the engines of subway cars. There are usually 4 engines of 110 kW each.
Now let's calculate how much electricity can be saved.
Initial data:
Tare weight of the car: 34 tons.
Maximum car capacity: 330 passengers.
Metrowagonmash
Passenger weight on average: 70 kg.
The speed of movement of the composition, for example: 60 km / h.
Electricity cost: 4 rubles per kW * h.
Number of cars: 10
The interval of walking cars: 30 seconds.
Landing time: 30 seconds.
Number of metro lines: 12
The average trip length on each branch from end to opposite end is one hour.
Schedule subway: from 5 to 01 hours.
Ticket price on average: 20 rubles.
The number of all man-trips per day: 8 million.
Calculate the kinetic energy that the train acquires during acceleration and loses when braking
E = m * v ^ 2/2 = (34000 kg + 330 * 70 kg) * (60 / 3.6) ^ 2/2 = 8 * 10 ^ 6 J = 8 MJ (1)
A lot or a little, consider yourself. But the car has the same energy, weighing 1500 kg and moving at a speed of 614 km / h. It is clear that he does not move with such speed. But the comparison gives an idea of how much energy it is.
Potential energy is not considered, because when the train moves down, it returns. And dissipative forces - energy losses due to friction in moving mechanisms and air resistance cannot be returned, it can only be reduced.
When braking, all this energy turns into heat and is spent in empty. Plus, the brake pads are erased and there it is possible, rheostatic braking - a set of powerful resistors that are connected to the traction motors and the motors thus slow down. Braking is stepped. There is no smooth braking - increased wear of wheelsets and rails and a sharp negative acceleration (train jerking), which is inconvenient for passengers. And the air brake operation creates dispersive dust of brake pads in the air. Recovery also eliminates all these problems.
8 MJ / 3.6 MJ = 2.22 kW * h * 4 rubles / kW * h = 8.88 rubles.
For one composition: 8.88 * 10 = 88 rubles.
At one hour the train makes at least 60 minutes / (30 + 30 seconds) / 60 = 60 starts / stops.
Maybe more if you need to wait for another train. There are also partial speed reductions.
Per hour 60 * 88 = 5280 rubles per hour.
On one line 60 trains.
Total consumed electricity: 60 * 12 * 5280 rubles = 3 801 600 rubles per hour.
But the rush hour is the morning 2 hours and the evening 2 hours.
Total for the peak hour 4 * 3.8 million rubles = 14.2 million rubles.
The rest of the time, the walking interval is 3 minutes, which is 9 times less than start / stops and trains on the line, i.e. 3.8 million rubles / 9 = 420 thousand rubles. at one o'clock.
So, the cost of electricity is not in peak hours 16 * 420 = 6.7 million rubles.
Total: 20.9 million rubles. in a day.
Costs per person-trip 2.61 rub. And if the ticket costs 20 rubles on average, it is 13% of the ticket price, not so much.
In the month of 627 million rubles.
Source: https://habr.com/ru/post/166387/
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