# The use of ionistra for regenerative braking in the subway

Many of you have noticed that the subway is very hot in the summer and there is an unpleasant smell. So I once thought about how this heat and this smell come from. In fact, the metro smells 4 smells: the smell of the composition to protect the tree of sleepers from decay, the smell of heated wires, the smell of fine dust from the brake pads and the smell of burnt fine iron. I thought it was bad for my health.

Another time, leaving the car, I noticed that a warm stream of air rises from under the car. And I thought, where is he from. And then I remembered that the cars are electric and that when braking, braking occurs due to engines (electrodynamic braking). But, why not use this energy? After all, then there will be no heating of the wires, there will be no dust from the brake pads. This requires a recovery system.

Recovery allows you to return energy back. A similar system is implemented on the Toyota Prius Hybrid.

But here is the problem, where is it to be returned? There are 2 options: either back to the power grid or store it somewhere. Return back to the power grid - the other necessary traction substations and the other cars themselves are needed. Plus, you can not make recovery between trains that are powered from different traction substations. As a result, the recovery effect reaches 15%, which is quite small. And to convert the traction substations expensively and for a long time. 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 re-equip the train and the efficiency can reach 80%.

To store energy, it is better to use not batteries, but ionistra.

Advantages:

1. Traction substations for the conversion of trains are not required.

2. The train can independently travel to the nearest station for disembarking passengers in case of power failure.

3. You can convert existing trains.

4. There is no problem transferring energy from one train to another. That is, there is no need for an additional power supply network in the case of a very uneven load of trains at metro stations.

Disadvantages:

1. The cost of the ionist.

2. The increase in train mass due to ionistra (not so much in relation to the mass of the train and passengers).

Advantages of ionisters compared to batteries:

1. High charge / discharge speed - high discharge current.

2. The simplicity of the charger.

3. Small degradation after hundreds or even thousands of charge / discharge cycles.

4. Charge / discharge capability at low temperatures.

Disadvantages:

1. Less specific energy.

2. The dependence of voltage on the degree of charge.

Thus, ionisters are more suitable for recovery than batteries as a mobile energy source.

And what is an ionistr? The ionister is a supercapacitor, it is essentially an electric capacitor, but with a double electric layer. In fact, it is a hybrid of a battery and a capacitor. In an electrolyte (like in a battery), charges (like in a capacitor) float, which are attracted to each other. In order for these floating charges not to collide with each other and not to neutralize each other, there is a delectric between them. Thus, the double electric layer form the

Ionistra used in the E-mobile.

But there is still the problem of regulating the supply of energy from the ionistra to the engines and vice versa.

For this, pulse-width modulation paired with an inverter circuit is well suited. Pulse Width Modulation (PWM) is now used in absolutely all power circuits, be it computer power supplies, voltage regulators of the processor on the motherboard, or some other power device. The essence of PWM is that the pulse width (width) varies with a frequency of several tens - hundreds of kHz, and due to this, the amount of energy transmitted to the consumer changes. The alternating signal is smoothed by the capacitor and can become constant if necessary. Usually in a PWM there is a high-frequency transformer, to which control pulses are applied.

And the inverter is a circuit where the constant voltage becomes variable (inverted) and can then be converted back to constant - this is done by the rectifier if necessary. Conversion to AC is necessary to obtain the desired voltage and its adjustment. Direct current can be converted into alternating current and further obtain the desired voltage using a transformer. But using not just alternating current, but alternating current of a higher frequency (tens of hundreds of kHz), you can get a transformer with better mass-dimensional indicators, efficiency and low cost. What is being successfully done, for example, in a welding machine or a computer power supply unit.

But the problems do not end there. It is still 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 2 technologies of transistors, for a long time competing with each other, in one element. At the input is a field effect transistor that controls a bipolar transistor. Thus, the advantages of both transistors are achieved and their disadvantages are removed:

1. A small voltage drop in the saturation mode.

2. Quick switch.

A small voltage drop makes it possible to increase the efficiency and reduce heating, as well as to pass more current.

A quick switch allows you 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, usually they are placed on radiators for better cooling. One such unit is capable of switching huge power. A current of hundreds of amperes and a voltage of hundreds of volts. That is, the total switching power of tens - hundreds of kW. Just such a power in the engines of subway cars. Usually there are 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 wagon capacity: 330 passengers.

Metrovagonmash

Average passenger weight: 70 kg.

The speed of the train, for example: 60 km / h.

Electricity cost: 4 rubles / kW * h.

Number of cars: 10

Wagon Walking Interval: 30 seconds.

Landing time: 30 seconds.

Number of metro lines: 12 The

average length of a trip on each line is from end to opposite end: one hour.

Schedule of the metro: from 5 to 01 hours.

Ticket price on average: 20 rubles.

The number of all person trips per day: 8 million.

We calculate the kinetic energy that the train gains during acceleration and will lose when braking

E = m * v ^ 2/2 = (34000 kg + 330 * 70 kg) * (60 / 3.6 ) ^ 2/2 = 8 * 10 ^ 6 J = 8 MJ (1)

Whether it is a lot or a little, consider it yourself. But the car with a mass of 1,500 kg and moving at a speed of 614 km / h has the same energy. It is clear that he does not move at that speed. But a comparison gives an idea of how much energy it is.

We do not consider potential energy, 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, brake pads are erased and there is possible rheostatic braking - a set of powerful resistors that are connected to traction motors and thus slow down the motors. Braking is stepwise. There is no smooth braking - increased wear of wheelsets and rails and sharp negative acceleration (jerking of the train), which is inconvenient for passengers. And the operation of the pneumatic brake creates dispersion dust in the brake pads in the air. Regeneration eliminates all these problems.

8 MJ /3.6 MJ = 2.22 kWh * 4 rubles / kWh = 8.88 rubles.

For one composition: 8.88 * 10 = 88 rubles.

The train makes at least 60 minutes / (30 + 30 seconds) / 60 = 60 starts / stops per hour.

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 electricity consumed: 60 * 12 * 5280 rubles = 3,801,600 rubles per hour.

But rush hour is morning 2 hours and evening 2 hours.

Total at rush 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 at rush hour 16 * 420 = 6.7 million rubles.

Total: 20.9 million rubles. in a day.

The cost per person is 2.61 rubles. And if a ticket costs 20 rubles on average, then this is 13% of the ticket price, not so much.

627 million rubles a month.

Another time, leaving the car, I noticed that a warm stream of air rises from under the car. And I thought, where is he from. And then I remembered that the cars are electric and that when braking, braking occurs due to engines (electrodynamic braking). But, why not use this energy? After all, then there will be no heating of the wires, there will be no dust from the brake pads. This requires a recovery system.

Recovery allows you to return energy back. A similar system is implemented on the Toyota Prius Hybrid.

But here is the problem, where is it to be returned? There are 2 options: either back to the power grid or store it somewhere. Return back to the power grid - the other necessary traction substations and the other cars themselves are needed. Plus, you can not make recovery between trains that are powered from different traction substations. As a result, the recovery effect reaches 15%, which is quite small. And to convert the traction substations expensively and for a long time. 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 re-equip the train and the efficiency can reach 80%.

To store energy, it is better to use not batteries, but ionistra.

Advantages:

1. Traction substations for the conversion of trains are not required.

2. The train can independently travel to the nearest station for disembarking passengers in case of power failure.

3. You can convert existing trains.

4. There is no problem transferring energy from one train to another. That is, there is no need for an additional power supply network in the case of a very uneven load of trains at metro stations.

Disadvantages:

1. The cost of the ionist.

2. The increase in train mass due to ionistra (not so much in relation to the mass of the train and passengers).

Advantages of ionisters compared to batteries:

1. High charge / discharge speed - high discharge current.

2. The simplicity of the charger.

3. Small degradation after hundreds or even thousands of charge / discharge cycles.

4. Charge / discharge capability at low temperatures.

Disadvantages:

1. Less specific energy.

2. The dependence of voltage on the degree of charge.

Thus, ionisters are more suitable for recovery than batteries as a mobile energy source.

And what is an ionistr? The ionister is a supercapacitor, it is essentially an electric capacitor, but with a double electric layer. In fact, it is a hybrid of a battery and a capacitor. In an electrolyte (like in a battery), charges (like in a capacitor) float, which are attracted to each other. In order for these floating charges not to collide with each other and not to neutralize each other, there is a delectric between them. Thus, the double electric layer form the

Ionistra used in the E-mobile.

But there is still the problem of regulating the supply of energy from the ionistra to the engines and vice versa.

For this, pulse-width modulation paired with an inverter circuit is well suited. Pulse Width Modulation (PWM) is now used in absolutely all power circuits, be it computer power supplies, voltage regulators of the processor on the motherboard, or some other power device. The essence of PWM is that the pulse width (width) varies with a frequency of several tens - hundreds of kHz, and due to this, the amount of energy transmitted to the consumer changes. The alternating signal is smoothed by the capacitor and can become constant if necessary. Usually in a PWM there is a high-frequency transformer, to which control pulses are applied.

And the inverter is a circuit where the constant voltage becomes variable (inverted) and can then be converted back to constant - this is done by the rectifier if necessary. Conversion to AC is necessary to obtain the desired voltage and its adjustment. Direct current can be converted into alternating current and further obtain the desired voltage using a transformer. But using not just alternating current, but alternating current of a higher frequency (tens of hundreds of kHz), you can get a transformer with better mass-dimensional indicators, efficiency and low cost. What is being successfully done, for example, in a welding machine or a computer power supply unit.

But the problems do not end there. It is still 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 2 technologies of transistors, for a long time competing with each other, in one element. At the input is a field effect transistor that controls a bipolar transistor. Thus, the advantages of both transistors are achieved and their disadvantages are removed:

1. A small voltage drop in the saturation mode.

2. Quick switch.

A small voltage drop makes it possible to increase the efficiency and reduce heating, as well as to pass more current.

A quick switch allows you 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, usually they are placed on radiators for better cooling. One such unit is capable of switching huge power. A current of hundreds of amperes and a voltage of hundreds of volts. That is, the total switching power of tens - hundreds of kW. Just such a power in the engines of subway cars. Usually there are 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 wagon capacity: 330 passengers.

Metrovagonmash

Average passenger weight: 70 kg.

The speed of the train, for example: 60 km / h.

Electricity cost: 4 rubles / kW * h.

Number of cars: 10

Wagon Walking Interval: 30 seconds.

Landing time: 30 seconds.

Number of metro lines: 12 The

average length of a trip on each line is from end to opposite end: one hour.

Schedule of the metro: from 5 to 01 hours.

Ticket price on average: 20 rubles.

The number of all person trips per day: 8 million.

We calculate the kinetic energy that the train gains during acceleration and will lose when braking

E = m * v ^ 2/2 = (34000 kg + 330 * 70 kg) * (60 / 3.6 ) ^ 2/2 = 8 * 10 ^ 6 J = 8 MJ (1)

Whether it is a lot or a little, consider it yourself. But the car with a mass of 1,500 kg and moving at a speed of 614 km / h has the same energy. It is clear that he does not move at that speed. But a comparison gives an idea of how much energy it is.

We do not consider potential energy, 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, brake pads are erased and there is possible rheostatic braking - a set of powerful resistors that are connected to traction motors and thus slow down the motors. Braking is stepwise. There is no smooth braking - increased wear of wheelsets and rails and sharp negative acceleration (jerking of the train), which is inconvenient for passengers. And the operation of the pneumatic brake creates dispersion dust in the brake pads in the air. Regeneration eliminates all these problems.

8 MJ /3.6 MJ = 2.22 kWh * 4 rubles / kWh = 8.88 rubles.

For one composition: 8.88 * 10 = 88 rubles.

The train makes at least 60 minutes / (30 + 30 seconds) / 60 = 60 starts / stops per hour.

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 electricity consumed: 60 * 12 * 5280 rubles = 3,801,600 rubles per hour.

But rush hour is morning 2 hours and evening 2 hours.

Total at rush 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 at rush hour 16 * 420 = 6.7 million rubles.

Total: 20.9 million rubles. in a day.

The cost per person is 2.61 rubles. And if a ticket costs 20 rubles on average, then this is 13% of the ticket price, not so much.

627 million rubles a month.