Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
  • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
  • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
  • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
  • H02M7/145—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
  • H02M7/155—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
  • H02M7/1555—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only with control circuit

Definitions

• the invention relates to a method and an apparatus according to the preambles of independent claims 1 and 5.
• High-power frequency converters provided with a voltage intermediate circuit conventionally comprise a rectifier, which is separate from the inverter part and implemented as an n-phased half-controlled diode bridge.
• a capacitor battery of a DC intermediate circuit is fed by the rectifier to produce direct voltage in the intermediate circuit.
• the lower branches of such a rectifier bridge are diodes, and the upper branches are controllable components, most typically thyristors.
• the rectifier When the rectifier is switched on, it must be ensured before the thyristors are controlled into the diode mode that the capacitor battery of the intermediate circuit has been charged nearly up to its final voltage, because otherwise a high current pulse taken from the network may burn protective fuses.
• the charging may be implemented by using either a resistor or adjusting the phase angle of the thyristors. The purpose is to charge the capacitor battery up to its maximum voltage by restricting the magnitude of the current flowing into the capacitor of the intermediate circuit.
• the components in the upper branch cannot be controlled with full control until the voltage of the intermediate circuit is at its maximum or close to it, in which case the components functionally correspond to diodes, i.e. they are conductive always when this is enabled by the voltage acting over the component. If the components in the upper branch are implemented as diodes, current has to be restricted re- sistively.
• US 6,038,155 discloses an integrated circuit intended to control the phase angles of the thyristors in the upper branch of the rectifier for charging the capacitor battery.
• a problem associated with prior art is that the rectifier control is bound to a certain voltage level which is to be reached in the DC voltage circuit.
• the rectifier bridge has to be adapted for each line voltage and information on the voltage to be reached has to be provided for the rectifier bridge controller.
• the size of the capacitor battery of the intermediate circuit, the frequency of the supply network and the order and number of phases have to be taken into account in the rectifier bridge control. This limits the versatility of the controller and its adaptability to changing conditions since the changes have to be always accounted for in the commissioning stage.
• the object of the invention is to provide a method and an apparatus which avoid the disadvantages described above and enable production of direct voltage in a more flexible manner by means of simple circuit solutions. This object is achieved by a method and an apparatus which are characterized by what is stated in the characterizing parts of the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.
• auxiliary intermediate circuit which is fed by a normal uncontrolled n-phased diode bridge, is connected via isolating diodes to a DC intermediate circuit fed by a half-controlled rectifier bridge.
• the auxiliary intermediate circuit is employed in the control to produce a reference voltage level up to which the DC intermediate circuit is charged.
• the method and apparatus according to the invention provide a complete independence of the frequency and amplitude of the supply voltage. Controls are implemented on the basis of the voltage level of the auxil- iary intermediate circuit, in which case it is unnecessary to determine or know any absolute voltage.
• the auxiliary intermediate circuit and its converter bridge can also be used for feeding a power source, which produces auxiliary voltage for circuits requiring it.
• the auxiliary intermediate circuit can also be provided with a transient voltage limiter, in which case one limiter can be utilized for cutting voltage peaks from all supply phases.
• Figure 1 is a block diagram illustrating implementation of a method according to the invention
• Figure 2 illustrates a circuit solution for a charging mode
• FIG. 3 illustrates curve forms of the charging mode
• Figure 4 illustrates a circuit implementing switch from the charging mode into the diode mode
• Figure 5 illustrates a circuit solution for the diode mode
• Figure 6 illustrates a circuit solution for controlling gate current.
• the method according to the invention can be divided into two operation modes on the basis of its operation: a charging mode, where the rectifier bridge is controlled to charge the capacitor battery of the voltage intermediate circuit, and a diode mode, where the rectifier bridge is controlled to feed the full voltage into the capacitor battery of the DC intermediate circuit.
• FIG. 1 shows a schematic block diagram illustrating the operation of the solution according to the invention and the structure in respect of one phase.
• the main part of the rectifier circuit consists of bridge-connected rectifier components V21 and V22.
• V21 is a component which in triggered from the gate, in particular a thyristor, and V22 is a diode.
• the phase input Uin is fed between these components as shown in Figure 1.
• the supply voltage is rectified by the bridge circuit to the DC intermediate circuit, and the voltage is stored in a capacitor or a capacitor battery CB connected between the positive bus DC+ and the negative bus DC- of the intermediate circuit.
• Figure 1 illustrates the structure in respect of only one phase. It is, however, clear that as the number of phases increases, the bridge circuits of all phases are connected to the same intermediate circuit.
• the positive busbar DC+ of the DC intermediate circuit is further connected to the positive busbar Aux+ of the auxiliary intermediate circuit by means of an isolating diode V23.
• the negative busbar DC- of the DC intermediate circuit is connected to the negative busbar Aux- of the auxiliary intermediate circuit by means of a second isolating diode V24.
• Rectified voltage is generated in the auxiliary intermediate circuit by diodes V25 and V26, which form an uncontrolled bridge circuit to rectify the phase voltage Uin.
• all phases of the voltage to be rectified feed the same auxiliary intermediate circuit.
• rectified voltage can be generated in the usual manner in the auxiliary intermediate circuit, the voltage being a six- pulse voltage in connection with a three-phase voltage, for example.
• One purpose of the isolating diodes V23 and V24 is to isolate the DC intermediate circuit from the auxiliary intermediate circuit so that current cannot flow from the auxiliary intermediate circuit to the DC intermediate circuit. Had the intermediate circuits not been isolated from each other, current would flow from the auxiliary intermediate circuit to the DC intermediate circuit and possibly to its large capacitor. In that case, current would be considerably high and damage the components of the electric circuit.
• the voltage of the DC intermediate circuit is increased in a controlled manner to the target level.
• the capacitor battery or the capacitor of the intermediate circuit is typically totally or nearly uncharged.
• the capacitor charging rate is adjusted by controlling the triggering instant of the components to be triggered from the gate and connected to the DC intermediate circuit, i.e. thyristors, with respect to the network cycle.
• the thyristor may be triggered in a known manner when the anode voltage is higher than the cathode voltage.
• the thyristor cannot be switched off actively, but it is quenched when current stops flowing though it. This quenching situation is called natural commutation.
• the circuits of the charging mode are switched on by activating a 'System Enable' signal, which is transmitted to the charging circuit 10.
• This circuit feeds short pulses through an optoisolator 11 and a drive circuit 12 to the thyristor gate at instants when the thyristor is triggered slightly before it is quenched by natural network commuta- tion.
• a current pulse cut from a network cycle is transmitted from the DC intermediate circuit to the capacitor battery of the DC intermediate circuit, which increases the terminal voltage of the battery.
• the amplitude of the current pulse is dependent on the inductance limiting the current and on how long before the commutation moment a gate pulse is given.
• phase current is measured by a current transformer T, and if the current pulse is too high, the instant of giving the gate pulse is delayed, and thus the amplitude of the following current pulse no longer increases. This method enables charging of a previously unknown and very large capacitor battery while restricting current. On the other hand, burning of feed fuses is avoided even when the DC intermediate circuit is in short circuit.
• the instant of the gate pulses is advanced all the time, and thus the voltage of the capacitor battery approaches the rectified voltage of the auxiliary intermediate circuit.
• the voltage difference between these voltages is sufficiently small, a switch to the diode mode takes place, and the signal informing the user of the switch, 'System Ready', is activated.
• the thyristors are controlled to the conductive state for the maximum period, i.e. to function as diodes would function in place of the thyristors.
• the momentous phase voltage i.e. the anode voltage of the thyristor V21
• the voltage of the positive busbar Aux+ in the auxiliary intermediate circuitry 14 is compared to the voltage of the positive busbar Aux+ in the auxiliary intermediate circuitry 14 according to the invention.
• gate current is given to the thyristor via the optoisolator 13 and drive circuit 12 according to Figure 1.
• Current is supplied until the difference between the voltages exceeds the predetermined limit. Due to continuous gate voltage, the thyristor is triggered immediately when its anode voltage exceeds the cathode voltage.
• gate current is thus produced from the instant the anode voltage has increased to a maximum threshold voltage lower than the voltage of the positive busbar of the auxiliary intermediate circuit until the anode voltage drops below the same threshold.
• a maximum threshold voltage lower than the voltage of the positive busbar of the auxiliary intermediate circuit until the anode voltage drops below the same threshold.
• 12 V can be selected as the limit voltage.
• the thyristor is quenched due to natural network commutation and gate voltage stops from flowing when the anode voltage of the thyristor is 12 V lower than the voltage of the positive busbar of the auxiliary inter- mediate circuit. Thanks to the isolating diodes, the voltage of the positive busbar in the auxiliary intermediate circuit follows the voltage of the DC intermediate circuit regardless of the load of the auxiliary intermediate circuit. According to this feature of the invention, no gate voltage is fed into the thyristor when they are biased in the reverse direction, which prevents back current losses from increasing.
• the thyristor may also be quenched by short notches in the line voltage if they are so deep that the thyristor becomes biased in the reverse direction.
• the voltage in the reverse direction is higher than the 12 volts given as an example, the flow of gate current stops according to the invention. However, gate current starts to flow immediately when the voltage in the reverse direction drops below 12 volts. Thus the thyristor is ready to be triggered immediately when the anode voltage exceeds the cathode voltage. Consequently, it functions as a diode in these cases, too.
• a transient suppressor is connected to the auxiliary intermediate circuit to cut overvoltage in all supply phases.
• the solution according to the embodiment requires only one transient suppressor for protecting all phases.
• the auxiliary intermediate circuit is arranged to feed voltage into a power source 15.
• a power source can be used for feeding all circuits requiring auxiliary voltage.
• the power resource receives rectified voltage from the auxiliary intermediate circuit, and the voltage can be processed further in the power source in a desired manner.
• FIG. 2 illustrates an embodiment of the invention describing operation in connection with the charging mode, in particular.
• a charging synchronization circuit is formed by two integrators, whose function is to filter all interfering factors from the network voltage.
• the instant when the gate pulse is given to the thyristor with respect to the phase voltage is determined by a ramp comparator, which controls gate current through the led of the optoisolator and the drive circuit.
• phase voltage is led to a first integrator R1-C1 , at whose output, point B, there is a dampened cosine wave form, i.e. a wave form which is nearly 90° behind the phase voltage.
• the comparator A1 detects the zero-crossing points of the wave form B, from which the square wave at point C is obtained by inversion.
• the integrator R1-C1 is connected to the comparator A1 via a protective resistor R6.
• the square wave of point C is nearly 270 degrees behind the phase voltage of point A.
• the square wave is supplied to a second integrator R2-C2, at whose output, point D, there is a wave form resembling a triangular wave.
• the wave form of point D is very pure, having no trace of any interference peaks or notches of line voltage.
• a ramp wave increasing slowly in the positive direction is formed at point E by means of integrator R3- C3 in Figure 2.
• the integrator is controlled by switch S1 from reference potentials Lref and Href. Lref is negative and Href positive.
• the component values of the integrator R2-C2 have been selected so that the wave form of point D stays within the whole frequency area defined for input voltages between the above-mentioned reference potentials.
• the switch S1 is controlled by signals 'System Enable' and 'Diode Mode' via an AND member D1 and by signal 'Current Sense' via comparator A3.
• the switch turns to position Href and the ramp wave of point E starts to increase from potential Lref. If the latter signal becomes active, the switch turns back to position Lref. In that case the ramp wave starts to decline.
• the first intersection thus takes place in the descending portion of the triangular wave, close to its minimum point, which is nearly at the same point as the minimum of the line voltage. It is, however, behind the natural network commutation point.
• the first gate pulse occurs at an instant when the thyristor has been biased in the reverse direction for a while. This means a negative ignition advance and the thyristor cannot be triggered.
• Figure 3 illustrates the wave forms explained above graphically. It can be seen from Figure 3 how the starting instant of the gate pulses advances as the intersection point of the wave forms D and E moves towards the positive direction of the triangular wave form. Figure 3 also shows a commutation instant CP and a first pulse FP.
• the drain electrode of the FET switch V9 is connected to potential J, i.e. to potential K which is 12 volts more negative than the positive busbar of the auxiliary intermediate circuit.
• potential J i.e. to potential K which is 12 volts more negative than the positive busbar of the auxiliary intermediate circuit.
• the gate control of the FET switch is ended due to the influence of the above-mentioned voltage division and zener diode V11.
• the operating point is typically set at approximately 50 volts, for example. Current can flow via the resistance R8 and led V10 and the light of the led V10 goes on to indicate that the necessary charging state has been reached.
• the optosiolator generates the 'Enable' signal shown in Figure 5 and an external 'Ready' signal to indicate that the rectifier is ready for charging.
• the voltage of the positive busbar of the auxiliary intermediate circuit is stored in a memory and used as a reference voltage instead of the voltage of the positive busbar.
• Storing of the voltage level is advantageous in particular when the mains supply to a rectifier in the diode mode is interrupted for a while due to high-speed automatic reclosing, for example.
• the inverter load may very rapidly drop the intermediate circuit voltage below the level at which it is safe to continue in the diode mode in respect of fuses when mains supply is restored.
• a digitally adjustable potentiometer may function as the memory element.
• Figure 5 illustrates a schematic circuit solution for the diode mode.
• One of the significant parts in respect of the circuit is transistor B6, whose emitter is in potential K, which is 12 volts more negative than the positive busbar J of the auxiliary intermediate circuit. This requires, however, that the 'Enable' signal should be active and thus control switch V50.
• the transistor's collector is provided with an optoisolator V7, whose output controls the thyristor gate current.
• the transistor base is connected to the point between the diodes V25 and V5 that form the upper branch of the auxiliary intermediate circuit bridge.
• the diode V26 is the lower branch of this bridge.
• Figure 5 further illustrates resistances R6 and R7.
• the transistor V6 base current can be generated only when the potential at point H sufficiently exceeds the potential of point K. This happens when the voltage level of the phase output exceeds level K by a few volts. Due to the base current, the led V7 of the optoisolator is lit up and it generates gate current for the thyristor.
• the thyristor gate current is controlled by the basic circuit shown in Figure 6.
• Transistor V8 whose emitter is connected to voltage M which is 16 volts higher than the transistor auxiliary cathode potential, functions as the gate current switch.
• the gate current is limited by gate resistance R8.
• the circuit also includes resistance R9 in a known manner.
• the transistor V8 base current is controlled by optoisolators V1 ( Figure 2) and V7 ( Figure 5). Since the optoisolators are connected in parallel, either of them may generate a gate pulse when activated.

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Citations (3)

• 2003
  • 2003-04-25 FI FI20030632A patent/FI115575B/fi not_active IP Right Cessation
• 2004
  • 2004-04-20 WO PCT/FI2004/000241 patent/WO2004098038A1/en active Application Filing
  • 2004-04-20 EP EP04728361A patent/EP1537646A1/en not_active Withdrawn

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