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Method of output voltage control in multi-cell frequency converter

IPC classes for russian patent Method of output voltage control in multi-cell frequency converter (RU 2331151):

H02M7/493 - Conversion of ac power input into dc power output; Conversion of dc power input into ac power output

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Semi-bridge thyristor inverter / 2321942
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Method of providing power supply of electrodynamic flying vehicles / 2335060
Invention relates to remote transfer and conversion of super-high-frequency energy into DC electrical power. The proposed method consists in fitting an aluminium foil enclosure on over the entire surface of the vehicle airframe skin. The super-high-frequency converter is made in a material representing a mix of two chemical solid-state components with grain size not over 30 to 50 microns, taken in equal proportion but different atomic numbers, and forming, when combined, a dipole solid-state matrix. Note that the said bi-component mix is applied uniformly onto the said skin enclosure, the like poles of the dipole matrix being combined and connected to appropriate terminals of the vehicle flight control components.

FIELD: electricity.

SUBSTANCE: invention refers to electric engineering and may be used in inductive heating systems with semi-conducting frequency converters when control system are designed. Method is intended for controlling output voltage of converter containing several inverters and multi-elements matching transformer with primary windings being connected to proper inverters and secondary windings being connected serially forming voltage summation circuit. Output voltage of one inverter is controlled by means of DC voltage converter connected to inverter input within the range defined by low and high thresholds. Other non-controlled inverters connected in parallel or fed from rectifiers are actuated into one of two states: "boosting voltage" or "short circuit". Output voltages of non-controlled inverters are set to be proportional to weight coefficient of bit pattern (1, 2, 4, 8, 16, ...). Different combinations of non-controlled inverters states form several levels of output voltage further creating several sub-ranges (zones) of output voltage controlling. Control is conducted by controlled inverter within those sub-ranges. Therefore, if output voltage of controlled inverter achieves proper range of controlling, states of non-controlled inverters are changed so that sum of non-controlled inverters weight coefficients being in "voltage boosting" mode could change by one. It results in control range shifting in controlled inverter by the voltage value assigned for lowest weight coefficient.

EFFECT: increase of energy indicators for conversion, creation of favourable switching conditions for converter transistors and increase of conversion power coefficient; improvement of energy indicators for conversion and provision of favourable switching modes for converter transistors.

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The invention relates to electrical engineering and can be used in induction heating systems with solid state frequency converters when creating control systems.

Known way to control the resonant inverter with anti-parallel diodes (patent RU 2152683), which consists in forming and alternately applying control pulses to the transistors forming the forward and reverse half-wave current in the load, and changing the time interval of the supply of control pulses as a function of time-conductive state of the key and the counter-parallel diode.

The disadvantages of the method are: small range and low accuracy regulation that does not meet a number of technological processes, inflated overall power of the keys, due to the high amplitude value of a current with a small current value.

Another way to control the frequency Converter is pulse-width regulation of the output voltage of the inverter (patent RU 2061292). Converter comprises a rectifier connected in series, capacitive filter and push-pull bridge transistor inverter, each transistor which is shunted by a capacitor and a counter-parallel diode. During operation of the inverter formed and alternately fed to the transistors Opera the bearing and the locking pulses; the duration of the enabling pulse set in the range of 0.15-0.3 period of the output voltage, the control voltage on the capacitors, and the inclusion of another pair of transistors is carried out in a time equal to the voltage on the capacitor to a level of less than 0.2 of the maximum voltage level.

This method reduces the switching losses in the transistors by providing switching at zero current and voltage values, which increases the reliability of the Converter. The control voltage on the commutating capacitor can be carried out by determining the discharge time of the switching capacitors on the model of the Converter or by measuring.

The disadvantages of this method of regulation can be attributed to the limited control range of the pulse width - 0,15-0,3 period of the output voltage, in addition, clearly excessive reactive current through the transistors and low power factor due to the phase shift of the fundamental harmonic voltage and current.

Output power converters described methods of control limited power characteristics of the transistors used.

The closest to the technical nature of the claimed invention is a method of regulating the output voltage of the Converter, sotoyama what about multiple inverters and multi-element matching transformer, described in SU 754635. The primary winding of the transformer connected to respective inverters made in a bridge circuit, and the secondary is connected in series and form a loop of the summation voltage. The Converter also includes a control unit that generates pulses with adjustable angles delays and timing, arriving at the control inputs of the inverters. When all the inverters in the "bootstrap", which consists in alternating circuit of the transistors forming the diagonal of the inverter, the output voltages of all of the transformers included in the summation circuit, and is formed on the load maximum voltage equal to the sum of the voltage of the secondary winding. To regulate the output voltage of the Converter of any of the inverters is introduced in the phase regulation mode, which is the phase shift control pulses of one pair of transistors of the inverter relative to another. As a result, part of the half-cycle is in phase with the inclusion of adjacent transistors, which leads to "shortages" in these intervals the primary winding of the transformer. A further increase of the phase shift leads to an increase in the duration of the "shorted" state of the transformer, and regulating the output voltage conversions the user. At some point of time interval "Takoradi primary winding occupies the entire half-cycle, i.e. the inverter is in the status of Takoradi", and the load current through the transformer is shorted open adjacent transistors and reverse diodes. A further increase of the phase shift leads to antiphase to enable the controlled inverter with respect to the other part of the period. If there is insufficient adjustment range, which can provide a phase adjustment of one inverter, the phase regulation mode is entered the following inverter. Thus, all the inverters of the inverter can be entered in the phase regulation mode.

The main disadvantage of the prototype is the negative mode of the switching transistors of all of the inverters when operating in a resonant mode, in which cases both lead and lag switching commute a non-zero current, resulting in significant dynamic losses and degrades performance and power characteristics. In addition, the phase shift of the fundamental harmonic of the output voltage and current leads to a decrease of the power factor of the system.

The aim of the invention is to increase the energy parameters of the transformation, enabling modes switching transistors of the inverter, increasing the giving power factor of the Converter.

This goal is achieved by the fact that, unlike the prototype, the method of regulating the output voltage of the Converter containing multiple inverters and multi-element matching transformer, the primary windings of which are connected to respective inverters, and the secondary winding are connected in series and form a loop summation voltage, the output voltage of one of the inverters regulate by means of the inverter DC voltage, is included at the input of the inverter, in the range defined by lower and upper threshold levels. The remaining unregulated inverters, connected in parallel and fed from a rectifier, is entered in one of two States: "bootstrap" or "Takoradi". The output voltage of the unregulated inverters set proportional to the weights of the binary code(1, 2, 4, 8, 16,...). Various combinations of States of unregulated inverters form multiple levels of output voltage, forming, in turn, several sub-bands (zones) regulation of output voltage, in which the regulation is made adjustable by inverter. Therefore, if the output voltage of the regulated inverter reaches the boundaries of its own regulation range, change the state of the unregulated inverter is in so to the sum of the weights of unregulated inverters located in the "bootstrap"has been changed to one. This leads to the displacement of the control range of the controlled inverter voltage younger weighting factor.

The technical result of the invention is no need for phase control in inverters of the inverter, which significantly reduces the dynamic loss switching power switching devices, it is essential with this method of control, especially at high frequency conversion, and provides high energy and operational performance indicators. In addition, the elimination of the need for phase regulation increases the power factor of the system.

The essence of the method is illustrated by reference to the drawings, on which: figure 1 - functional Converter circuit that implements this method; figure 2 - timing diagram of operation of the transducer that implements the method.

Functional diagram of the device for implementing the method of controlling a resonant Converter in figure 1 includes a rectifier with R-shaped filter 1, the power supply Converter DC voltage 2 and several resonant inverters 3, 4, 5, n, unregulated inverters 4, 5, n included a pair of the parallel input, adjustable inverter 3 is fed from the inverter DC voltage 2. The inverter is loaded on the transformers 6, the secondary windings are connected in series and form a loop summation of voltage applied to the load as a series resonant circuit comprising a resonant capacitor and inductor with the heated part. The control pulses of the transistors are formed by the control circuit 7, which receives signals about changing the combination of unregulated inverters, in the direction of increasing the amount of weights the video signal from the comparator 8, downward from the comparator 9, the Comparators compare the signal from the sensor voltage controlled inverter 10 with the threshold levels of PI+ and PI-.

Figure 2: U - output voltage adjustable inverter; U₂- output voltage unregulated inverter with a weight of 2; U₁- output voltage unregulated inverter with a weight of 1; U - the total voltage at the Converter output, IDN - sensor output voltage, PI - and PI+ -, respectively, the upper and lower threshold levels.

The method is as follows. The inverter 3 is connected to the Converter output DC voltage 2 and is controlled by the Converter range, the op is Delaema upper and lower threshold levels of PI+ and PI-. The inputs of the remaining unregulated inverters 4, 5, n from a rectifier fed DC voltage, these inverters operate synchronously with adjustable and can be in one of two steady States: "bootstrap", in which the corresponding output of the transformer is formed of a rectangular voltage, or "Takoradi", in which the output voltage of the transformer is zero (Figure 2). Various combinations of States of unregulated inverters form several discrete levels of output voltage, between these levels is continuous regulation using adjustable inverter. In other words, the output of the inverter formed several sub-bands (zones) regulation. The condition for the transition from zone to zone (from one subband to another) is to achieve an adjustable inverter 3 (and hence the supply of its inverter DC voltage 2) limit values its own range of voltage regulation. To do this, the output voltage of the regulated inverter 3 U measured by sensor 10 and serves the measured voltage to the Comparators 8, 9, continuously comparing the sensor signal IDN with two threshold levels of Fe+ and Fe-determining the allowable control range. One of the Comparators determines the upper limit of the range, i.e. the fo who creates the signal to the add zone regulation, the other defines the lower boundary, i.e. generates a signal to subtract the area of regulation.

Consider, for example, the process of increasing the output voltage of the Converter. In this case, by increasing the output voltage of the regulated inverter 3 U at some point in time t the sensor signal output voltage IDN exceeds the upper threshold level of Fe+, these signals are compared by the comparator 8, which generates a signal transition in the next area, entering the control circuit 7. On this signal to further increase the output voltage of the Converter control circuit produces a change of state of unregulated inverters. Suppose that the original combination of States of unregulated inverters located in the "bootstrap", included only the 2-th weighting factor, i.e. the inverter 5 with the output voltage U2, then to increase the output voltage must be translated into "bootstrap" inverter with 1-th weight coefficient (inverter 4), resulting in its output will appear rectangular voltage U1, the sum of weights is equal to 3.

The transition from the state "Takoradi" status to "bootstrap" inverter with a weight of 1 (Figure 2) occurs by changing the circuit adjacent transistors 11,13-12,14-diagonal circuit t is ancestoral 11,14-13,12, resulting in the windings of the transformer appears rectangular voltage. Simultaneously there is a reduction of the output voltage of the regulated inverter 3 (figure 2) inverter DC voltage 2, the same total output voltage of the Converter remains unchanged. Thus, the output voltage of the regulated inverter 3 again falls within the defined operating range. It is important to note that the control range of the controlled inverter must overlap the magnitude of the area of regulation, i.e. the voltage difference defined threshold levels must exceed the output voltage of the inverter with the younger weight.

The method of control can significantly improve the energy performance of the conversion and provide a favorable modes switching transistors of the Converter, which is proof of the effectiveness of the invention.

The method of regulating the AC output voltage of the Converter, consisting of several inverters and multi-element matching transformer, the primary windings of which are connected to respective inverters, and the secondary are connected in series and form a summation circuit voltage, which by the phase shift control impulse the inverters installed either in a state of "bootstrap", when the voltage of the secondary winding of the corresponding transformer is applied to the load, or in a state of "Takoradi"during which the voltage of the secondary winding of the corresponding transformer is excluded from the summation circuit, wherein one of the inverters is introduced into the mode of regulation of the output voltage enabled by the input of the inverter DC voltage in the range defined by lower and upper threshold levels; when the specified voltage controlled inverter of one of these thresholds further regulation is carried out by changes in these conditions "bootstrap" or "Takoradi" other inverters so that the sum of the weights of inverters that are in the mode "bootstrap"has changed on the unit, while the output voltages of the respective transformers these other inverters ask proportional to the weights of the binary code.