RU2321147C1 - Method for relay generation of network currents in a three-phased bridge-based network inverter - Google Patents

Abstract

FIELD: electric engineering, possible use in network inverters included in composition of electric motors of constant and alternating current, in electro-technical plants.

SUBSTANCE: method for relay generation of network currents includes cyclic switching of two modes of operation at the frequency of activation of relay regulator. The current for each phase is generated by corresponding phase relay regulator in accordance to the setting which is determined for each phase from a formula, provided in the formula of the invention. Current amplification mode in corresponding network phase is achieved by activation of transistor of anode or cathode group of current phase, collector-emitter direction of which transistor coincides with current setting direction of given phase. To reduce current in network phase, control impulses are not injected into transistors. Closure circuit in consumption and recuperation mode is altered. According to the method, the amplitude for setting effective value of network current is generated on basis of condition of equality of effective power at the input and the output of the network inverter according to the law, which is provided in the formula of the invention. Diodes and transistors of the network inverter participate in generation of network currents. Duration of current flow through diodes and current flow through transistors is determined by speed of reduction and speed of increase of current in corresponding phase of network, which differs for energy consumption and energy recuperation modes. In energy consumption mode, the current through network inverter diodes dominates, and in recuperation mode - the current through transistors.

EFFECT: improved shape of current which is consumed from the network and injected into network, possible management of reactive power consumed from the power system.

2 cl, 10 dwg

Description

The method of relay formation of network currents in a three-phase bridge network inverter relates to the field of semiconductor converter technology and can be used in AC and DC drives for electrical installations.

The closest in technical essence and the achieved result is the method adopted for the prototype according to the invention patent No. 2280310 "Method of relay current generation and device for its implementation", published on July 20, 2006 in the bulletin No. 20 of the Federal Service for Intellectual Property, Patents and Trademarks, authors Mikitchenko A.Ya., Moguchev MV, patent holder of OJSC Rudoavtomatika).

A known method of relay current generation in a three-phase bridge network inverter, which consists in cyclic, with the frequency of operation of the relay controller, connecting the load through a chain consisting of series-connected diodes and transistors of the rectifier and the switch of the consumption channel, to the line voltage of the network, positive with respect to the direction current in the load (consumption mode), while the current in the load increases faster than the rate of change of the current reference signal at the input of the relay controller, turn off the transistors of the switch of the consumption channel, while the current displaced from the disconnected transistors is closed through other diodes and transistors of the rectifier and the inverter of the recovery channel to the line voltage of the network, which is negative with respect to the direction of the current in the load (recovery mode) and the current decreases in the load faster than the signal changes tasks. In the energy recovery mode, the load is connected to the same line voltage of the network as in the consumption mode, in the polarity opposite to the consumption mode. In this case, the transistors of the recovery circuit open in extreme inverter mode without regulation.

The disadvantages of this method is that the shape of the consumed and delivered current is far from the sinusoidal shape due to the presence of higher harmonics of the canonical series ν = 6k ± 1, where k = 0, 1, 2 ... etc. (i.e. 1, 5, 7, 11, 13 ... etc.), and also there is no possibility of the device working with a variable power factor.

The technical result of the invention is to improve the shape of the current consumed from the network and supplied to the network, the ability to control the reactive power consumed from the power system.

The method of relay formation of network currents consists in switching two modes of operation cyclically with the frequency of operation of the relay controller: the mode of increasing current, while the current increases faster than setting it, and the mode of decreasing current, while the current decreases faster than setting it. The current of each phase is generated by the corresponding relay controller in each phase of the network according to the task, which is determined by the amplitude of the current value of the current of the network phase, which is necessary to ensure equal active power at the input and output of the network inverter according to the formula:

where, ifm - the amplitude of the current value of the current phase of the network;

Id is the current of the DC link supplied or received by the load;

Ud is the voltage of the DC link (can be adjustable);

Uf - phase voltage of the network;

Cosφ is the desired power factor;

as well as its shape, obtained from phase voltage sensors of the network or any other source of three-phase voltage having the same frequency as the network, and phase, taking into account the desired power factor.

Tasks for network currents are determined according to the expressions:

for phase A:

for phase B:

for phase C:

where I _f - the effective value of the current phase of the network;

ω is the circular frequency of the network;

t is the time;

φ is the load angle (phase shift between voltage and current of the corresponding phase);

π is a constant number of 3.14159.

Figure 1 shows the structural-schematic diagram of a device for relay formation of network currents containing phase-voltage sensors 1, phase-current sensors 2, a control system with phase relay controllers of network currents 3, network inductances 4, a network inverter made in the form of a three-phase bridge rectifier , the keys of the cathode 5 and anode 6 groups of which consist of counter-parallel connected diodes and transistors, a DC link 7 and a load of 8 as a consumer or source of electric ergii; figure 2 is a structural schematic diagram explaining the operation of the device with increasing current in the phase of the network in the mode of energy consumption; figure 3 is a structural schematic diagram explaining the operation of the device with increasing current in the phase of the network in the energy recovery mode; figure 4 is a structural schematic diagram explaining the operation of the device when the current decreases in the phase of the network in the mode of energy consumption; in FIG. 5 is a structural schematic diagram explaining the operation of the device when the current decreases in the network phase in the energy recovery mode; Fig.6 is an example of a specific implementation of the device, including a control system with relay regulators of network currents; Fig.7 - oscillograms of the EMF of the network transformer, the mains current, the task on it, explaining the processes in the network inverter when working with a leading power factor in the power consumption mode; on Fig - waveforms of currents through the key elements of one phase of the network, explaining the processes in the network inverter when working with a leading power factor in the power consumption mode; figure 9 - oscillograms of the EMF of the network transformer, the mains current, the task on it, explaining the processes in the network inverter when working with a leading power factor in the energy recovery mode; figure 10 - waveforms of the currents through the key elements of one phase of the network, explaining the processes in the network inverter when working with a leading power factor in the energy recovery mode.

An example of the method of relay formation of network currents in a three-phase bridge network inverter and the operation of the device.

By alternately turning on the first (increasing current) and second (decreasing current) modes, the network currents are maintained at the set level: to increase the current in the corresponding phase of the network, the transistor of this phase of the anode 6 or cathode 5 group is activated (Fig. 1), the collector-emitter direction which coincides with the direction of the task for the current of this phase, while in the energy consumption mode (Fig. 2), the current closes in a chain - the inductance of this phase of the network 4 (La), the open transistor of this phase VT4 (or VT1), the diode of the same group is different phase VD2 or VD6 (VD3 or VD5), on the cathode (or anode) of which there is a smaller (or larger) potential, the network inductance 4 of another phase of the network (Lb or Lc). In the energy recovery mode (Fig. 3), an increasing current flows through the chain - the inductance of this phase 4 (La), the open transistor of this phase VT4 (or VT1), the capacitor in the DC link 7 (C), the open transistor of another group and phase VT3 or VT5 (VT6 or VT2), whose circuit potential is lower, the network inductance 4 of another phase of the network (Lb or Lc). To reduce the current in the network phase, control pulses are not supplied to the transistors, while the current in the consumption mode (Fig. 4) and recovery (Fig. 5) is closed in a chain - the network inductance 4 of this network phase (La), the diode of this phase VD1 ( or VD4), the direction of the anode-cathode of which coincides with the direction of the current, the capacitance (C) in the DC link 7, the diode of the other group and phase VD2 or VD6 (VD3 or VD5), on the cathode (or anode) of which there is a smaller (or larger ) potential, network inductance 4 of another phase of the network (Lb or Lc). The control system with relay regulators of network currents in Fig.6 contains relay regulators 9, 10, 11 - according to the number of phases of the network, to the input of which a signal is given for the mismatch of the reference for the current of the corresponding phase and the mains current of the same phase. The current reference signal is shaped according to the sinusoidal phase of the network voltage, according to the phase it is determined by the reference to the required power factor (± φ), the amplitude of the current value of the current reference signal is set by block 12 according to the voltage reference signal and feedback voltage and current feedback links constant voltage.

According to the oscillograms explaining the processes in the network inverter, there are switching modes of the relay controller (current increase mode and current decrease mode) when working with a leading power factor in the energy consumption mode (Figs. 7 and 8) and energy recovery (Figs. 9 and 10 ) The waveforms of the current phase of the network phase (Figs. 7 and 9) contain higher harmonics, but they do not belong to the canonical series ν = 6k ± 1, where k = 0, 1, 2 ... etc., but are determined by the frequency actuation of the relay controller and little effect on the sinusoidal nature of the current shape. In the power consumption mode (Fig. 8), the current prevails through the diodes of the network inverter, the transistors open to increase the current in the phase of the network, and their switching frequency is determined by the rate of increase and decrease of the network current. The rate of increase in the mains current is higher (in this case, the transistor is open in this phase) than the rate of its decrease (in this case, the diode is open in this phase), and the time of the conducting state of the transistor is correspondingly less than the time of the conducting state of the diode. In the energy recovery mode (figure 10), the current prevails through the transistors, the diodes open to reduce the current in the phase of the network. In this mode, the rate of increase in the network current is lower (in this case, the current closes through the open transistor of this phase) than the rate of decrease (in this case, the current is closed through the open diode of this phase), and the time of the conducting state of the transistor is accordingly longer than the time of the conducting state of the diode. Other time intervals during which currents increase and decrease in the network phase (Figs. 7 and 9), which are not directly related to the switching processes of diodes and transistors of this phase (Figs. 8 and 10), are explained by switching processes independently of this phase in other phases of the network according to the ratio:

where Ifa - phase A current;

Iph - phase current B;

Ifc - phase C current.

The current surges during the switching of transistors (Figures 8 and 10) are explained by the presence of snubber circuits included to protect the key elements from overvoltage (conditionally not shown in Figs. 1, 2, 3, 6).

The advantages of the proposed method for generating network currents are that the currents consumed and supplied to the supply network are sinusoidal in nature, and the device can operate with a lagging or leading power factor (when changing the task to φ).

Claims (2)

1. The method of relay formation of network currents consumed and given out by a network inverter made in the form of a three-phase bridge rectifier, the keys of which consist of counter-parallel connected diodes and transistors, consisting in cyclic (with the frequency of operation of the relay controller) switching of two operating modes: increase mode current, while the current increases faster than the task on it, and the current reduction mode, while the current decreases faster than the task on it, characterized in that the current of each phase of the network is formed with corresponding phase relay according to the task for phase A:

for phase B:

for phase C:

where I _f - the effective value of the current phase of the network; ω is the circular frequency of the network; t is the time; φ is the load angle (phase shift between voltage and current of the corresponding phase); π is a constant number of 3.14159, to increase the current in the corresponding phase of the network, the transistor of this phase (anode or cathode group) is triggered, the collector-emitter direction of which coincides with the direction of the task for the current of this phase, while in the energy consumption mode, the current is closed in the circuit inductance of this phase of the network, an open transistor of this phase, the diode of the same group of another phase (at the cathode or anode of which there is a smaller or larger potential, respectively), the inductance of the other phase of the network, in the energy recovery mode, the current closes kidney, inductance of this phase, open transistor of this phase, capacitor in the DC link, open transistor of another group and phase (the circuit potential of which is lower), network inductance of another phase, to reduce the current in the network phase, control pulses are not supplied to the transistors, while the current in the consumption and recovery mode, the inductance of this phase, the diode of this phase, the direction of the anode-cathode of which coincides with the direction of the current, the capacitance in the DC link, the diode of another group, are closed in a chain phase (at the cathode or anode of which there is a smaller or greater potential, respectively), the network inductance of the other phase. 2. The method according to claim 1, characterized in that the amplitude of the task on the effective value of the mains current is formed based on the condition of equality of the active power at the input and output of the network inverter according to the formula

where ifm - the amplitude of the current value of the current phase of the network; Id is the current of the DC link supplied or received by the load; Ud is the voltage of the DC link (can be adjustable); Uf - phase voltage of the network; Cosφ is the desired power factor, and the form and phase of the task is formed either from the sensors of the phase voltage of the network (with Cosφ = 1), or from an independent three-phase source of the same frequency (with Cosφ ≠ 1).

Images