RU2517199C1 - Method to arrange grouped operation of reversible converters - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: clock frequency synchronisation of a slave converter is made with the master one, balance of output currents for the converters at the permitted unbalance is attained by recording of the load characteristic for each separate device where by means of a control system an initial value of load current is set, load resistance is changed at the recorded current setting, values of voltage and current are measured at the selected point and compared, the phase shift and pulse duty cycle are also measured at the output of these devices at a stage of their designing. After that they are compared and tuned in order to ensure identical load characteristics, phase and pulse duty cycle of the output current values with error not exceeding 2-5%.

EFFECT: increase of the output power and reliability.

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Description

The invention relates to the field of electrical engineering and can be used in the construction of devices for electric arc welding with alternating current of increased frequency, as well as sources for induction heating of metals and sources for dielectric drying, in which to achieve a technical result is to increase the output power of the power supply, transistor inverter sources of electrical energy are connected in parallel to the total load.

There is a method of controlling static stabilized DC or AC voltage sources operating in parallel for a total load (RU No. 2379812, НОМ 7/5387, published January 20, 2010), which consists in the fact that for each source built on the basis of static converters, generating a control signal by comparing the voltage amplitude of this source with the voltage amplitude at the total load; in addition, a signal is generated for comparing the voltage phase of one source with the voltage phase of another source by integrating the difference between the reference phase signal and the total signal corresponding to the difference of the reactive components of the currents, and these difference voltages of the active and reactive components of the currents are formed as the difference of the corresponding component of the currents of the two sources. When combining the output sensors of current and voltage of individual sources, the total current at the load is measured and the average current is calculated to form the task of the share of the current of each converter in the load current.

The disadvantage of this control method is that it implements proportional control both by the instantaneous values of currents and by the instantaneous value of the output voltage in each of the parallel sources, and therefore has static errors when stabilizing the total voltage and the distribution of the load current between the sources. In addition, when using this method, additional functional elements are used - phase detectors, measurement schemes for the active and reactive components of the source currents, additional combinations of output sensors, which complicates and increases the cost of the source circuit.

The known method (RU No. 2275280, B23K 9/09, published April 27, 2006), in which the electric arc welding system includes several parallel-connected power sources operating on a single electrode for performing electric arc welding with current pulses with a frequency of 18 kHz, controlled by oscillation generators and a circuit that synchronizes power sources on a master-slave basis. Due to synchronization by a high-precision interface of parallel connected power sources, the alternating current output is the sum of the currents from parallel connected sources combined after the polarity switches. Synchronization between sources is precisely coordinated by the interface board with an accuracy of less than 10 μs, preferably in the range of 1-5 μs. This synchronization accuracy coordinates and coordinates the switching operation in parallel connected power supplies to provide AC output.

The disadvantage of this invention is that when synchronizing power sources, the requirements for accuracy in synchronization time are set, but the requirements for unbalance of duty cycle, non-identical load characteristics of welding sources and phase delay of control pulses in communication circuits are taken into account, which in parallel operation will affect the accuracy of the unbalance currents between welding sources. In addition, it is contemplated that the present invention can be used with any standard AC power source with switches to change the output polarity. An additional output current polarity switching unit increases the dimensions, weight and reduces the efficiency of the source for welding.

The technical result is that, with minimal circuitry changes to the devices, based on pre-setting the control system of each device according to the parameters of the load characteristics, phase and duty cycle of the output current pulses, to ensure, in group operation of inverter converters to increase their output power and increase technological reliability, equality of currents in the static and dynamic mode of converters with their permissible imbalance.

The technical result is achieved by synchronizing the slave converter at the clock frequency of the master converter. The equality of the output currents of the converters with their permissible imbalance is achieved by removing its load characteristics for each individual device. In this case, with the help of the control system, the initial value of the load current is established, the load resistance changes at a fixed value of the current setting and the values of voltages and currents at the selected points are measured and compared. The phase shift and duty cycle of the pulses at the output of the devices at the design stage are also measured, and then they are compared and adjusted to ensure the identical load characteristics, phase and duty cycle of the output current pulses with an error of not more than 2-5%.

Figure 1 shows a diagram of the organization of the group work of inverter converters, with which it is possible to implement the proposed method.

Figure 2 shows:

a) load characteristics of two power sources for electric arc welding;

b) the phase difference of the current pulses at the output of the sources;

c) the duty cycle difference of the current pulses at the output of the sources.

Figure 3 shows a generalized dependence of the imbalance of currents between sources on the difference in load characteristics, phase imbalance and duty cycle of the output current pulses

The synchronization circuit of the slave converter A is carried out according to the clock frequency of the master converter B (Fig. 1), consisting of rectifiers with output storage capacities 1, connected in series with inverters 2, which are connected in series with power transformers 3, on the secondary side of which current sensors 4 are installed. Slave converter A and master converter B are controlled by control systems 5.

The method is as follows. When synchronizing parallel-connected converters A, B at the clock frequency, in order to ensure equality of the output currents of the converters with their permissible unbalance, their load characteristic is removed for each individual device, at which the initial value of the load current is set using the control system. Then, the load resistance is changed at a fixed value of the current setting and the voltage and current values at the selected points are measured. They are compared. Also measure the phase shift and duty cycle of the pulses at the output of the devices at the design stage. Then they are compared and adjusted to ensure the identity of the load characteristics, phase and duty cycle of the output current pulses with an error of not more than 2-5%. This is necessary, since in real conditions it is not possible to ensure complete identity of the parameters of the converters, and even with tight synchronization by clock pulses, there will be a certain imbalance in the load currents. When specifying stringent and justified requirements for the identity of the parameters of converters A, B, which most strongly affect the current imbalance, it is possible to ensure that this imbalance does not exceed a predetermined allowable value. By computer simulation of processes and experiments on physical mock-ups with parallel connection of converters A and B for operation on one common load, results were obtained that made it possible to ensure an imbalance of currents not exceeding a given maximum permissible value.

The following factors are set as factors that can influence the current imbalance:

- The difference in the load characteristics of the converters (figa.)

- The phase shift between the current pulses associated with the delay of the clock pulses arriving at the slave Converter (fig.2b.)

- The difference in the duty cycle of the current pulses due to differences in transmission coefficients and time constants in the control circuits of active keys (transistors of converters) (figv.).

The results of the influence of these factors on the imbalance of the currents of the converters are reflected in figure 3. Thus, when setting the permissible value of the unbalance of the load currents in the limit of 10%, it is necessary to ensure the identity of the load characteristics, phase and duty cycle of the output pulses with an error of no more than 2-5%.

Compared with the known solutions, the proposed method allows, with minimal circuitry changes to the devices, based on the preliminary adjustment of the control system of each device according to the parameters of the load characteristics, phase and duty cycle of the output current pulses, to ensure, in group operation, inverter converters to increase their output power and increase technological reliability , equality of currents in the static and dynamic mode of the converters with their permissible imbalance.

Claims (1)

A method of providing group operation of inverter converters for supplying consumers with alternating current pulses of increased frequency by synchronizing the slave converter according to the clock frequency of the leading converter, characterized in that the output currents of the converters with their permissible imbalance are achieved by removing its load characteristic for each individual device, in which using the control system set the initial value of the load current, change from load resistance at a fixed value of the current setting, measure the values of voltages and currents at selected points and compare them, and also measure the phase shift and duty cycle of the pulses at the output of the devices at the design stage, then compare and fine-tune them to ensure the identical load characteristics, phase and the duty cycle of the output current pulses with an error of not more than 2-5%.

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