RU2327276C1 - Method of control of tetrasquare converter with computation of switching phases and microprocessor device to implement method - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering and may be used to control the electric train AC. The invention increases the accuracy in control of the converter and eliminates alarm operating conditions. The method of control of tetrasquare converter with computation of switching phases includes generating the data on the dependency of the gate switching intervals on the depth of modulation and inputting this data into the memory of the converter control system for the range of tolerable operating frequencies in compliance with the number of the PWM-intervals. The control system is used to preset the current voltage value at the converter output, the current circuit value and the value of phase difference between the circuit voltage and current. The circuit current value id regulated by varying the voltage modulation at the converter input. The intervals of the controlled gates switching are calculated and the voltage modulation value is varied by setting the control signal for cutting in- cutting off the gates. The method features the correction of the gates cutting in interval values allowing for certified data on controlled gates, operating conditions and the converter load nature. Here, in every half-cycle of the supply voltage, the maximum modulation frequency is limited by the gate switching duration. The microprocessor device to control the said converter incorporates a timer, a processor, an operating memory, a permanent memory, ANC, drivers' unit, current sender, synchroniser and the input current amplitude generator, timer inputs-outputs, those of the processor, permanent memory, operating memory. The drivers' unit inputs are coupled by the data-address bus. It also includes the converter operation parameters generator, voltage sender, gate switching phase computation unit, the unit of limiting switching intervals, the time interval I/O unit, the unit of communication with the converter load.

EFFECT: higher accuracy of control over converter, ruling our abnormal operating conditions.

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Description

The invention relates to electrical engineering, to the control of input converters of electric rolling stock of alternating current, can be used to improve the shape of current consumption by a traction drive with four-quadrant converters, to reduce the risk of emergency operation.

A known method of controlling a four-quadrant converter, which consists in setting the switching frequency of the semiconductor switches of the converter and measuring the current at the input of the converter. Using the measured current values, using the analytical dependences for the predicted current value, the energy-optimal switching phases are determined (German Patent No. 4,129,261 of October 8, 1992. The method of digital regulation of a four-quadrant converter connected to an alternating voltage network via a transformer).

The disadvantage of this method is the existence of a significant accumulation error that occurs when empirical coefficients are used in determining the predicted current, depending on the impedance and resistance of the AC side of the converter, as well as on the length of the reading period of the instantaneous values of current and voltage.

A microprocessor-based control device for a four-quadrant converter is known, comprising a set of current and voltage sensors, a processor, a pulse-width modulator of voltage, a setpoint for the amplitude of the consumed current, and a device for interfacing with a four-quadrant converter. The control commands for the valves of the four-quadrant converter are set in the indicated device in digital form by signals coming from the interface devices of the control system with the four-quadrant converter (see ibid.).

The device has functional limitations in determining the phases of switching due to the lack of operational information about load changes.

The use of this device on an electrically rolling stock does not guarantee control accuracy, in particular, it does not provide the optimal switching times for switching on-off power semiconductor devices (valves) in the current half-cycle, taking into account the dependence of the width of the modulating voltage pulses at the input of the converter on the modulation depth.

The closest in technical essence is the method of controlling a four-quadrant converter with calculation of switching phases, which consists in forming and storing into the memory of the converter control system for the range of admissible operating frequencies of the converter arrays of arrays of dependences of the lengths of the switching intervals of power semiconductor devices (SPP) on the modulation depth in according to the number of PWM intervals, the effective voltage value at the output is converted using the control system The actual value of the mains current and the value of the phase shift between the mains voltage and the mains current, the mains current value is controlled by changing the duration of the application at the input of the voltage converter of the AC voltage source and the voltage difference between the AC voltage source and the capacity of the output filter, while the duration of the application of the source voltage AC voltage and voltage difference between the AC voltage source and the output filter capacity lyayut ratio modulating sine wave signal and the triangular clock signal is shifted relative to the angle-voltage AC voltage source

where X is the inductive resistance of the mains current flow path when an AC voltage source is applied to the input of the voltage converter;

I is the effective value of the mains current; U is the actual value of the voltage of the AC voltage source, measured for each half-cycle using current sensors and voltage sensors, the actual values of the mains current and voltage at the converter output, determine the integrated mismatch of the output voltage, limit the integral mismatch by the maximum and minimum, determine the modulation depth by the formula μ = μ ₀ -Δμ, where μ ₀ is the modulation value in the nominal operating mode of the converter; Δμ is the correction value of the control signal for switching valves on and off, the switching intervals of controlled power semiconductor devices are calculated. (Algorithms for controlling a four-quadrant converter / A.V. Belyaev, K.P. Soltus, M.Yu. Kapustin // Electric locomotive construction: Collection of scientific papers / JSC "All-Russian scientific and research and design-engineering t electric locomotive building "(OJSC" VELNII "). - Novocherkassk, 2003. T.45. S.341-354).

With this control method, the switching time of power semiconductor devices is not taken into account, i.e. the time during which the valve (thyristor, transistor) opens or, conversely, closes. Depending on the type and dynamic properties of the devices, due to their passport data, the nature of the load, and other conditions and operating modes of the converter, the duration of the switching process can reach unacceptable values under the conditions of trouble-free operation. That is (especially in the field of high modulation frequencies) when the valves are turned on in one of the converter arms and the current flows in the other arm simultaneously, moments of overlapping switching current circuits are possible, leading to emergency operation of the converter.

The closest in technical essence is a microprocessor control device of a four-quadrant converter that implements the specified control method, containing a timer, a processor, random access memory, read-only memory, analog-to-digital converter, a driver block controlling a four-quadrant converter having an input current sensor, the output of which is connected with a synchronizer and with one of the ADC inputs, the other ADC input is connected to the input current amplitude adjuster. The inputs and outputs of the timer, processor, random access memory and read-only memory, the output of the analog-to-digital converter and the inputs of the driver unit are connected by the data-address bus. The four-quadrant converter and synchronizer are powered by alternating voltage. The input of the synchronizer is connected to the timer reset input and the processor interrupt bus (Soltus K.P. Formation of the control logic of a four-quadrant converter // News of Universities. North-Caucasus Region. Technical Sciences. - 2004. - No. 1. - P.37-40 )

Such a device does not allow to ensure the accuracy of the converter control when the load changes due to the lack of information channels of communication with the load control units (inverter). In addition, the device does not provide simultaneous switching control at all shoulders of the converter. The specified disadvantage creates the risk of emergency processes in the event of through-currents flowing in the converter.

The objective of the invention is to develop a method of controlling a four-quadrant converter with the calculation of the switching phases, eliminating emergency conditions, in particular, the coincidence of the on-off time of the valves in the adjacent (parallel) arms of the converter. Another objective of the invention is the development of a microprocessor device that implements the specified control method and provides the expansion of information functions for better controllability of adjustable parameters.

The problem is solved in that in a method for controlling a four-quadrant converter with calculation of switching phases, which consists in forming and storing in the memory of the converter control system for the range of acceptable working frequencies of the converter arrays of dependences of the lengths of the switching intervals of power semiconductor devices on the modulation depth in accordance with by the number of PWM intervals, set the actual voltage value at the converter output, using the control system, The value of the mains current and the phase shift value between the mains voltage and the mains current, the mains current value is controlled by changing the duration of the application at the input of the voltage converter of the AC voltage source and the difference between the voltages of the AC voltage source and the capacity of the output filter, while the duration of the application of the voltage of the AC voltage source the current and voltage differences of the AC voltage source and the capacity of the output filter determine the ratio We have a modulating sinusoidal signal and a triangular clock signal, shifted relative to the voltage of the AC voltage source by an angle

where X is the inductive resistance of the mains current flow path when an AC voltage source is applied to the input of the voltage converter;

I is the effective value of the mains current; U is the actual value of the voltage of the AC voltage source, measured for each half-cycle using current sensors and voltage sensors, the actual values of the mains current and voltage at the converter output, determine the integrated mismatch of the output voltage, limit the integral mismatch by the maximum and minimum, determine the modulation depth by the formula μ = μ ₀ -Δμ, where μ ₀ is the modulation value in the nominal operating mode of the converter; Δμ is the correction value of the control signal for turning the valves on and off, the switching intervals of the controlled power semiconductor devices are calculated, new signs are introduced - the values of the switching intervals of the valves are adjusted taking into account the switching time of the converter valves based on the passport data of the controlled valves, operating modes and the nature of the converter load. Moreover, in each half-cycle of the supply voltage, the maximum modulation frequency is limited by the duration of the switching of the valve.

To implement the described method, a microprocessor control device for a four-quadrant converter is proposed, consisting of a timer, a processor, random access memory, read-only memory, an analog-to-digital converter, a driver block controlling a quadrant converter with an input current sensor, the output of which is connected to a synchronizer and with one from the inputs of the ADC, the other input of the ADC is connected to the input current amplitude adjuster, the inputs and outputs of the timer, processor, RAM, The memory, the ADC output and the driver block inputs are connected by a data-address bus, while the four-quadrant converter and synchronizer are powered by an alternating voltage, the synchronizer input is connected to the timer reset input and the processor interrupt bus, it additionally contains a block for calculating the switching phases of power semiconductor devices, a software block for switching switching interval, communication unit with the load of the quadrant converter connected to the processor via the data-address bus, network mode sensor, output sensor the voltage of the converter connected to the ADC, the output of the network mode sensor is connected to the input of the block of synchronizing pulses.

Given the high-frequency switching modes of the valves of the four-quadrant converter, the specified device does not have a deadband to the deviation of the adjustable value.

A positive effect of the proposed method for controlling a four-quadrant converter with calculation of switching phases is the ability to take into account and control the turn-off time of the valves in one arm and the turn-on time in the other arm in order to prevent the occurrence of through-current circuits.

The positive effect of the proposed microprocessor device is to expand the information functions for better controllability of the adjustable parameters of the quadrant converter. The introduction of new blocks into the device provides an implementation of the method of controlling a four-quadrant converter with calculation of switching phases, controlling the energy-optimal switching of the valves along with reducing the risk of an emergency operation (preventing the passage of through currents).

The figures presented to the description show:

Figure 1 presents a block diagram of the proposed control algorithm for a four-quadrant converter with the calculation of the switching phases.

Figure 2 shows a typical dependence of the switching times of a power semiconductor device of a four-quadrant converter on the load voltage for one half-period of the supply voltage.

Figure 3 presents a variant of a microprocessor control device of a four-quadrant converter that implements the proposed control method.

The method is implemented by the algorithm shown in figure 1.

,The operation of the converter begins upon the arrival of a command to start the control system (block 1 (in Fig. 1)). In block 2, the operating parameters and admissible operating values of the converter are loaded into the memory of the control system (for example, the admissible value of the harmonic coefficient K _D (non-linear distortion coefficient)), the voltage at the converter input, the reduced inductance of the input circuit, etc., as well as the input of arrays of lengths switching intervals of valves of converters from modulation for a possible range of modulated frequencies ωt = f (μ). In block 3, the current parameters of the converter are input - the set value of the mains current I _NЗ and the output voltage U _dЗ . In block 4, the instantaneous values of the input current I _N and the output voltage U _{d of the} converter are measured. In block 5, a comparison of the values of a given output voltage U _dЗ and the actual (measured) U _{d is} performed. In the event of a mismatch, go to block 6. In block 6, the voltage modulation μ is changed in accordance with the mismatch between the specified U _dЗ and the actual U _d voltage, followed by transition to block 4. If the value is insufficient, the voltage modulation μ is reduced, and when the actual voltage is excessive, the voltage modulation is increased. In block 5, if the values of the specified output voltage and the actual (measured) match, go to block 7. In block 7, the switching phases ωt of the SPP are calculated without taking into account the dynamic properties of the valves, i.e. present them as “ideal” keys with instant switching. In block 8, the switching phases are adjusted taking into account the dynamic properties of the valves. Based on the obtained pulse sequence as applied to the nearest half-cycle, the network current curve is predicted and laid out in harmonic components (block 9), for example, in Fourier series. In this case, the duration of the voltage pulses determined under the condition of instant switching of the valves accordingly changes. The harmonic coefficient (non-linear distortion coefficient) is determined by the formula

,

where I ₁ is the effective current value of the main harmonic of the network current, n is the number of harmonics analyzed, I _i is the effective current value of the i-th harmonic of the network current. In block 10, the resulting harmonic coefficient K _{G is} compared with a valid K _D. In case of a mismatch in block 11, the phases of the edges of the switching pulses are reduced:

- front (when turned on) ωt _1i according to the formula Δωt _1i = Δωt _i-1 -ε,

where Δωt _i-1 is the switching duration in the previous period of regulation of the leading edge of the same pulse, ε is the step of changing the time of a non-conducting state,

- rear (when turned off) Δωt _2i according to the formula Δωt _2i = Δωt _2i-1 + ε,

where Δωt _2i-1 is the switching duration in the previous period of regulation of the trailing edge of the same pulse, ε is the step of changing the time of the non-conducting state. The value of ε can be taken equal to, for example, 0.1 μs. This time value is acceptable based on the four-quadrant converter operating frequency range traditional for electric rolling stock (no more than 3000 Hz). When calculating K _{G, the} value of n can be taken equal to 60.

When operating at a high frequency, the pause duration (absolute time between adjacent pulses) becomes small and commensurate with the duration of the valve shutdown. In this regard, the duration of the pause between switching is limited by the actual time of closing the valve, since the duration of the pause should not be less than the passport shutdown time. For example, in the case of a sinusoidal PWM (Fig. 2), the central impulses in the half-cycle are most susceptible to the coincidence of the conducting states of the valves.

After these calculations, when changing the half-cycle of the supply voltage, they return to block 5. In block 12, the logic of controlling the valves by the converter is implemented. As an algorithm for generating the converter control logic, one can use, for example, the algorithm described in the publication: K. Soltus Formation of the control logic of a four-quadrant converter // News of Universities. North Caucasus. region. Technical science. - 2004. - No. 1. - S. 37-40.

Further, the control process continues (block 3) until the end of the converter operation. Interruption of the operation algorithm is allowed in any block (figure 1).

Turn-on and turn-off times of the NGN can be determined in advance based on the expected modes and algorithms of the converter according to known parameters.

A preliminary determination of the dynamic properties and the formation of arrays of actual switching pulse durations of power semiconductor devices can be performed according to the methodology (see A. Leshchev. Practical recommendations for the use of IGBT transistors / A.I. Leshchev, V.V. Nikonov, K.P. Soltus , K.N.Suslova // Electric locomotive construction: Collection of scientific papers / All-Russian Scientific Research Institute and Design Electric Locomotive Engineering OJSC (VELNII OJSC). - 1999. - T.41. - S.179-188), based on the reference data of catalogs of manufacturers of power semiconductor devices.

Figure 2 presents a typical dependence of the switching times of a power semiconductor device of a four-quadrant converter from the load voltage. As can be seen from the graph, in the case of neglecting the switching duration U _V = f (ωt), there is a danger of the flow of through currents through the transverse valve arms of the transducer with different half-waves. The dependence U _Ф = f (ωt) reflects the possible forms of voltage pulses applied to the valves.

As a result of these operations for controlling the converter, the emergency operation of the converter is prevented due to the simultaneous switching of valve arms of different periods. Moreover, the specified control method does not impair the quality of the current consumed.

The method is implemented by a microprocessor device (figure 3).

The device comprises: a timer 13, a processor 14, a random access memory 15, a read-only memory 16, an analog-to-digital converter 17, a block of drivers 18 that control the valves of the four-quadrant converter 19, having an input current sensor 20, the output of which is connected to the synchronizer 21 and with one from the inputs of the ADC 17, the other input of the ADC 17 is connected to the input current amplitude selector 23. In addition, the device contains a block for calculating the switching phases 22 of the power semiconductor devices of the converter 19, the output sensor voltage 30, a block of switching interval switching (BOKI) 24, a communication unit (BSN) 25 with a load of 26, a parameter setter 27 of a converter 19, an input-output unit of a time interval 28. The inputs and outputs of a timer 13, processor 14, RAM 15, ROM 16, the ADC output 17 and the inputs of the driver unit 18 are connected by the data-address bus 29. The four-quadrant converter 19 and the synchronizer 21 are powered by alternating voltage, the input of the synchronizer 21 is connected to the reset input of the timer 13 and the processor interrupt bus 14. The output of the network current sensor 20 is connected to the input synchro izatora 21. The instantaneous value of the output voltage measured by the four-quadrant inverter output voltage sensor 30. The output voltage sensor 30 is connected to the output of inverter 19, sensor information output 30 is connected to ADC 17.

The processor 14 is the central computing core that implements the basic protocols for the exchange of information between blocks and elements of the device.

In block 22, logical and arithmetic operations are performed for calculating the switching phases based on the data arrays stored in the ROM 16, depending on the operating frequency of the converter 19. The switching phases calculated in block 22 are addressed to the driver block 18 of the converter 19 valves. The type of driver block 18 is determined by the type of valves mainly transistors.

In the block of switching interval limits (BOKI) 24 monitor and compare the time of the inter-switching intervals with the maximum possible duration of switching valves depending on the value of the load.

The communication unit 25 with the load 26 addresses on the bus 29 operational information about the change in the load 26. This contributes to the speed of regulation of the current consumption by the converter 19.

As a parameter setpoint 27, for example, devices of a remote control of an electric rolling stock driver (handles of a driver’s controller, switches, a keyboard with an indication unit) can be used. As a setpoint for the amplitude of the input current 23 can be one of the manual controls of the electric rolling stock, for example, a handle for setting the traction force.

Block 28 provides the formation of control signals in accordance with the calculated switching phases in block 22, addressed to the driver block 18 of the converter 19.

The calculation unit for the switching phases 22 of the power semiconductor devices, the software unit for limiting the switching interval 24, the communication unit 25 with the load of the quadrant converter are connected to the processor 14 via the data-address bus 29.

In this device, a timer 13, processor 14, RAM 15, ROM 16, BOKI 24, BSN 25 can be integrated into a specialized controller, for example M167-1C (see the catalog of products "On-board industrial electronics" JSC "Kaskod", 105037 Moscow, Izmailovskaya pl., 7).

The device operates as follows.

When the supply voltage U _N passes through a zero value, an impulse appears at the output of the synchronization block 21, through which the processor 14, RAM 15, ROM 16, the input-output unit of the time interval 28 are initialized, and the ADC 17 is started. After that, the microprocessor control device is a quadrant converter operates in accordance with the commands, arrays and constants recorded in the ROM 16, and in the first half-cycle of the supply voltage, the modulation value is set equal to the nominal.

Upon arrival of the clock pulse (block 1), the signals from the network current sensor 20 and the voltage sensor 30 at the output of the converter 19 are supplied to the ADC 17. In accordance with the specified values of the network current and voltage at the output of the converter 17, coming from the master mode 27 on the data bus 29 in the processor 14, determine the necessary voltage modulation. Measure the value of the current supplied to the ADC 17 from the current sensor of the network 20. In accordance with the arrays ωt = f (μ) in the block for calculating the switching phases 22, the necessary switching moments of the valves of the converter 19 are determined. For each switching interval, the duration of the non-conducting state of the valves is compared with the passport switching time pre-recorded and stored in ROM 16. If the passport time is exceeded, the switching time is reduced by limiting the phase of the leading and trailing edges of the pulses sa on commands supplied from the hips 24. In order to reduce the number of computational operations of the processor 14 comparing the duration of a non-conductive state of the switching valve with the certified time is performed only when the load current. The signal about the change in the load current comes from the load 26 through the BSN 25 via bus 29 to the processor 14.

Moreover, the organization of the operation of the communication unit with the load 25 is made in such a way that eliminates the deadband to the deviation of the adjustable value.

Thus, the combination of known and newly introduced in the proposed method actions on material objects allows us to solve the problem that the invention is aimed at, while ensuring the desired technical result. The method is technically feasible and has novelty.

Ways to implement these methods of controlling a four-quadrant converter with the calculation of the switching phases and devices implementing it do not exclude other options for their implementation.

Claims (2)

1. A method for controlling a four-quadrant converter with calculation of switching phases, which consists in forming and storing in the memory of the converter control system for the range of admissible operating frequencies of the converter arrays of arrays of dependences of the lengths of the switching intervals of power semiconductor devices (valves) on the modulation depth in accordance with the number of PWM -intervals, using the control system, set the effective voltage value at the converter output, the effective value of the mains current the phase shift value between the mains voltage and the mains current, the mains current value is controlled by changing the duration of the application at the input of the voltage converter of the AC voltage source and the voltage difference of the AC voltage source and the capacity of the output filter, while the duration of the application of the voltage of the AC voltage source and the voltage difference of the source AC voltage and output filter capacitance is determined by the ratio of the modulating sine wave nogo clock signal and the triangular signal, shifted with respect to the AC voltage source by an angle of voltage

where X is the inductive reactance of the circuit current flow when applying to the input of the Converter, the voltage of the source of alternating voltage; I is the effective value of the mains current; U is the actual value of the voltage of the AC voltage source, measured for each half-cycle using current sensors and voltage sensors, the actual values of the mains current and voltage at the converter output, determine the integrated mismatch of the output voltage, limit the integral mismatch by the maximum and minimum, determine the modulation depth by the formula μ = μ ₀ -Δμ, where μ ₀ is the modulation value in the nominal operating mode of the converter; Δμ is the correction value of the control signal for turning the valves on and off, the switching intervals of controlled power semiconductor devices are calculated, characterized in that the values of the switching intervals of the valves are adjusted taking into account the switching time of the converter valves, based on the passport data of the controlled valves, operating modes and the nature of the converter load, at the same time, in each half-cycle of the supply voltage, the maximum modulation frequency is limited by the duration of the switching of the valve. 2. A microprocessor control device for a four-quadrant converter, consisting of a timer, a processor, random access memory, read-only memory, an analog-to-digital converter, a driver block controlling a four-quadrant converter having an input current sensor, the output of which is connected to a synchronizer and to one of the ADC inputs , the other ADC input is connected to the input current amplitude adjuster, inputs / outputs of the timer, processor, RAM, ROM, ADC output and driver block inputs are combined data bus address, while the four-quadrant converter and synchronizer are powered by alternating voltage, the synchronizer input is connected to the timer reset input and the processor interrupt bus, characterized in that it additionally contains a converter for operating parameters of the converter, an output voltage sensor connected to the output of the converter, information output the output voltage sensor is connected to the ADC input, in addition, the device contains a phase calculation unit connected to the processor via the data-address bus mutation valves, flow restrictions switching intervals, the block of input-output time slot, the communication unit with converter load.

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