High-voltage converter employing IGCT switches (
Nowadays, most suburban trains in Russia have 2 head carriages, 5 or 6 motor carriages, and 3 or 4 auxiliary carriages [
Each traction drive contains contactor equipment and 18-item power circuit breakers and power starting resistors, which carry out start-up and regulation of the train speed. Numerous efforts to use semiconductor power traction drive instead of obsolete and unserviceable 18-item power circuit breakers with power starting resistors were not successful.
The difficulties of designing semiconductor power high-voltage converter for suburban trains in Russia are the following: The wide range of input voltages (from 2000 V up to 4000 V DC) with possible short single impulses up to 5000 V DC and with duration up to 10 ms. The wide range of environment temperature (from minus 50°C up to plus 45°C) and presence of high humidity, frost, and hoarfrost. The absence of high-frequency high-voltage power semiconductor devices and capacitors and other elements, which are required to solve these problems.
It is known that using the high-frequency principle of the electrical energy transformation is an effective and attractive mean for the power converters. It provides the advantage of reducing their weight, sizes, and cost. However, the use of high operating frequency for the power converters leads to the number of simultaneous problems. The important problem is related to the defence circuits of the power switches where the power losses are increasing in conformity with the frequency rise.
It should be noted that total losses in defence circuits for the converters of the Russian suburban trains are much higher because of the high supply voltage
Thus, the development of the defence circuits in such converter application is prime importance. Thereto, during the design process of defence circuits design, it is necessary to solve two conflicting problems. The first one is to provide normal operation for the semiconductor devices and could be solved by increasing of the components of the snubber circuit. The second problem is to minimize the losses in the protection circuit and should be solved by reducing the values of the parameters of the snubber circuit. The authors suggest a compromise solution of these problems.
Thus the described difficulties in designing a power traction drive require unusual approaches and decisions in designing high-voltage converter as a system, as well as in choosing power device and snubber circuits, control systems, and so forth. In this paper the authors are offered new power high-voltage high-frequency converter for traction drive employing IGCT switches (
As noted, the required output power of the high-voltage converter is 1200 kW. However the maximum power of the traction drive, which is equal to the multiplication of the peak current after the input smoothing filter and maximum input voltage, must be not less than 1700 kW because of the wide range of voltages in the contact network (from 2000 V up to 4000 V DC). It is obvious that the design of highly reliable and relatively cheap traction drive for such power and high-voltage can be conducted only on the base of high-frequency power IGCT switches.
To get the high level of traction drive responsibility, it is necessary to specify very rigid requirements for the reliability of the power converter operation. Therefore it is thought to be reasonable to choose such principle of the work of the power circuit, which could provide the following: The power semiconductor devices will have the best working conditions, particularly during transient processes. The control of the power high-voltage converter based on the rigid algorithm (independent from input voltage level, load value, etc.) must have a much higher fraction than control based on the flexible algorithm.
After careful consideration of existing decisions and methods, a power Pulse Width Modulation (PWM) high-voltage converter was chosen [
The first one is to provide normal operation for the semiconductor devices and could be solved by increasing of the components of defence circuits. The second problem is to minimize the losses in the protection circuit and should be solved by reducing the values of the parameters of defence circuits. The parameters of the defence circuits depend on choosing the power self-commutated devices. Therefore specific technical requirements and properties of the power semiconductor devices are considered [ High current (rms, average, peak, and surge) and voltage (peak repetitive, surge, and DC-continuous). Low losses (conduction and switching). High reliability (low random failures, high power and temperature cycling, and high blocking stability).
An important quality is improved robustness and low device coast.
By output current (
The best parameters of considered power semiconductor devices are in bold font. According to the above-described requirements IGCT devices are selected for traction high-voltage converter of suburban trains.
Properties and parameters of power high-voltage semiconductor devices.
Ratings | GTO | IGCT | ETO | IGBT |
---|---|---|---|---|
3000 A |
4000 A |
1000 A |
1200 A | |
|
1.7 |
|
2.6 | 2.4 |
|
1.20 | 1.08 | 0.96 |
|
|
0.12 | 0.11 |
|
0.12 |
|
High | Middle |
|
|
As a result of the completed analysis and design procedures the original basic power circuit of the traction driver for Russian suburban train is created. Only last improvements in modern semiconductor technique have given possibilities to design and create this scheme in real conditions. This circuit can realize as well drive mode as a mode of dynamic break for train.
In Figure
At the driver mode the control system of high-voltage converter commutes power semiconductor switches
The basic power circuit for the drive mode.
When power semiconductor switches
The first way: the positive potential EMF of the excitation winding
The second way: the positive potential EMF of excitation winding
In order to increase or decrease the rotational frequency of traction brushed electric DC motors
If the suburban train has to move backwards, then the control system of high-voltage converter has to open switches
When power semiconductor switches
The first way: the positive potential EMF of the excitation winding
The second way: the positive potential EMF of the excitation winding
In Figure
The basic power circuit for the brake mode.
If the suburban train has to stop, then the control system of high-voltage converter has to close switches
It is clear that changing switches
In this situation traction motors
At the brake mode the control system high-voltage converter commutes power semiconductor switches
The first way: the positive potential EMF of the traction motor
The second way: the positive potential EMF of the traction motor
When power semiconductor switches
By reducing the speed of the train the control system of high-voltage converter increases the pulse width of the semiconductor switches
The first way: the positive potential EMF of the traction motor
The second way: the positive potential EMF of the traction motor
When power semiconductor switches
Thus the train stops without using the brake pads.
The important advantage of the proposed power circuit of the high-voltage converter is that power semiconductor switches
As a result of the analysis and design procedures the basic power circuit of modules
The basic power circuit of modules
It contains two power semiconductor switches (
As power semiconductor switches
The clamping inductor
The snubber capacitors
The snubber capacitors
The accuracy of simulation results is achieved due to careful study of real transients in power semiconductor devices
The comprehensive analysis of the transient is carried out for a wide range of different values of supply voltage, load, clamping inductor
The maximum values of the surge current
The analysis of the transient shows that in case of a rise of the supply voltage and load current almost all parameters for the transient have got a tendency to change the conditions for the power semiconductor switch
The surge current.
During its turn, the energy losses in the clamping resistance
For the proper synthesis of the energy efficient snubber circuits it is desirable to select the minimum possible inductor The auxiliary variable is calculated: where The maximum value of the The inductor
where
The obtained values of the clamping inductance allow maintaining the minimum losses over one period in the clamping resistance
The obtained value of the clamping inductance
The analysis of the transient shows that maximum peak voltage
The maximum peak voltage.
In order to select optimal clamping resistor the following design procedure is used. The auxiliary variables are calculated: where The minimum value of the
The parameters of the
The analysis of the transient shows that the increase of snubber capacitor values leads to the power loss growth in the discharging resistors
For selecting the minimum possible capacitors values the following design strategy is recommended. The auxiliary variable is calculated: The auxiliary variables are calculated: where The optimum of the Dependencies of the maximum values of the instantaneous surge current The dependencies of the maximum values of the instantaneous repetitive peak voltage on the off-state power semiconductor switch
The values of snubber capacitor
The obtained values of the defence circuits allow maintaining the minimum losses over one period in the resistor
Transients, quasi-steady-states and emergency mode of the operation are passed using CASPOC software. The comprehensive analysis of the transient is considered out for a wide range of the supply voltage and parameters variation of the load, clamping inductor, clamping resistance, snubber capacitors and discharging resistances. The current and voltage curves of the proposed high-voltage converter are received and analyzed as a result of computer simulation. For example, the simulation results of the current waveform (
The current waveform.
As the simulation result, the suburban train speed (
The speed waveform of the train.
Also CASPOC was used for examination of the interference of proposed high-voltage converter into the central railways emergency system and wire communications. Computer simulation of electromagnetic processes show that the maximal amplitudes of the input current harmonic components appear at the maximal permissible loads (400 A) and the input voltage (4000 V). The maximal values of the harmonic component amplitudes (equal to 77 mA, 2790 Hz) are not exceeding the permissible values.
As a result of the comprehensive analysis the optimum parameters of elements of snubber circuits of semiconductor switches
Parameters of elements of snubber circuits.
|
|
|
|
|
|
---|---|---|---|---|---|
0.9 mH | 9.1 Om | 0.03 mF | 91 Om | 0.02 mF | 120 Om |
The skilled sample of the power module for Russian suburban trains is designed. In the design sample was decided to be applied to power fast IGCT devises 5SHY35L4505 (as semiconductor switches
Clamping inductors
The design power module of the proposed converter is shown in Figure
The power module.
Complete tests of the power module are conducted in the high-voltage experimental laboratory for checking the accuracy of the mathematical model. As an example, the test results of the voltage waveforms of the power switches
The voltage waveforms of the power switches
The surface temperatures of electrical components of the power module are also measured. The maximum surface temperature excess over the ambient temperature is fixed for the clamping inductor
As a result of the completed analysis and design procedures the original high-voltage converter of the traction driver for Russian suburban train is proposed. The authors developed the detailed algorithm for the calculation and selection of the elements of the low-loss snubber circuits for considered converter. This algorithm is used during the preliminary design stage of the traction converters with nominal output power 1200 kW (maximum power 2100 kW) at the unstable input voltage
The important advantage of the proposed power circuit of the high-voltage converter is that power semiconductor switches
Extensive tests of the designed converter conducted in the high-voltage laboratory demonstrated the high accuracy of the used software, and the correctness of the chosen basic power elements. The complex tests have shown that the considered high-voltage converter operates stably at steady-state conditions over a whole range of the input voltages and permissible loads (including their discrete variations) and at the starting mode and turn-off of the loads.
The presented results are very interesting for the designers of power high-voltage converters and traction drive.
The authors declare that there are no competing interests regarding the publication of this paper.