FI121293B - Control of a brake function - Google Patents

Description

BRAKE FUNCTION CONTROL

TECHNICAL FIELD The present invention relates to the control of an electric braking function in an electric drive comprising a permanent magnet motor driven by a frequency converter. In particular, the invention relates to controlling a braking function in a situation where the voltage of the mains supplying the frequency converter is broken.

10 Prior Art

The permanent magnet motor is a commonly used type of motor in many industrial applications such as modern elevators. Such an engine typically has a three-phase winding on the stator and permanent magnets mounted on the surface of the root-15 market. Such a motor is by nature a synchronous machine whose rotor rotates without leaving at the speed determined by the frequency of the voltage applied to the stator winding. The rotation speed control is preferably implemented with a frequency converter.

A mechanical brake is applied to ensure the safe operation of the elevator system or similar electric motor driven equipment 20 in the event of a malfunction, such as a power failure. In order to ensure safety also in the event of failure of the mechanical brake, it is known to use a so-called "brake" according to WO 2008/031915. dynamic braking, which means short-circuiting the motor supply connections. Short-circuiting can be achieved, e.g., in contact-25 drives or inverter drives, preferably also by conducting all of the output semiconductors of the downstream phases of the inverter supplying the motor, or alternatively only the negative power semiconductors of phases where the motor current is away from the motor. If the rotor starts to rotate during such a short-circuit, a voltage is generated in the stator winding which causes a short-circuit current, which in turn causes a resistance to the rotor rotation. Thus, the engine speed is limited to a reasonable amount, which is intended to prevent damage, for example, when the elevator car collides with the motion limiter.

Ko. in the patent arrangement, the braking current of the drive controlled by the frequency converter 35 is controlled by connecting the inverter changeover contacts of the frequency converter. In the method, the motor phases are short-circuited by either inverter negative or positive inverter contacts. The braking current then begins to increase, controlled by the source voltage of the 2 motors. When the changeover contacts are opened, the braking current tends to pass through the resistor-connected diodes adjacent to the positive changeover contacts to the intermediate circuit. Then the capacitor in the intermediate circuit starts to charge and the intermediate circuit voltage starts to increase. When the short-circuited changeover contacts 5 are opened and closed with short pulses, the braking power is transmitted via the motor to the intermediate circuit of the drive in a pulsed manner. Ko. according to the patent, the braking power is transmitted via the motor to the intermediate circuit of the frequency converter and further to the control system of some equipment controlling the frequency converter so that said control system receives its power from the braking power of the motor. 10 Engine braking power can also be supplied, for example, to an engine movement monitor which is controlled by the engine braking power. When used as a stroke engine, the aforesaid. According to the patent, the permanent magnet motor and the brake control operating voltage are made by rectifying the source voltage of said motor, the dynamic braking can be achieved completely without additional power supply.

In this case, the dynamic braking control devices draw their control power directly from the intermediate circuit voltage, and the braking control is automatically activated when the intermediate circuit voltage reaches a predetermined value. As the intermediate circuit voltage begins to increase as the rotor begins to rotate, the control means 20 is engaged and begins to brake the motor. Thus, there is no need for a separate energy reserve for the dynamic braking control system, but the dynamic braking also works, for example, in situations where the system's control electricity is cut off.

As current, such as the aforementioned short-circuit current, passes through the power semiconductors of the frequency converter 25, there is a large loss of power therein, which is why it is conventional to attach them to a lattice cooler. Cooling can be known to be enhanced by using a fan to accelerate the flow of air through the lining.

The fan supply voltage may be formed by a transformer from the supply voltage of the frequency converter or preferably by a converter from the voltage of the inverter circuit. In the former case, an AC fan or an AC / DC converter and a DC fan can be used, in the latter case it is normal to use a DC / DC converter and a DC fan. In both cases, it is natural that the fan and the enhanced cooling of the power semiconductors 35 provided by it do not work when the supply voltage to the drive is interrupted and consequently the intermediate circuit voltage is lowered.

The short-circuit current required by the dynamic brake may be of the same order as the nominal output current of the drive. The braking situation can last for a long time, up to several minutes, which may be longer than the time constant of the fin cooler. In such a situation, there is a risk of component damage due to overheating when short-circuiting is made by short-circuiting the power semiconductors of the drive downstream phases.

5

SUMMARY OF THE INVENTION It is an object of the present invention to provide a solution to the prior art problem where dynamic braking is accomplished by short-circuiting the power semiconductors of the output phases of the upstream or downstream phases of the frequency converter supplying the permanent magnet motor.

In the invention, the supply voltage of the fan is formed by a converter from the voltage of the frequency converter circuit.

According to the invention, the drive uses a first auxiliary voltage source which wakes up to operate when the intermediate circuit voltage rises to a first level, which may be e.g. 20 V. This auxiliary voltage co. for upper or lower gate guides.

According to said simple pulse pattern, the power semiconductors of the upper or lower arms are pulsed to conduct the motor poles to a short circuit, thereby increasing the short circuit current to the level determined by the internal impedances of the motor. Further, according to the same pulse pattern, the short circuit is intermittently removed, whereby the inductive current of the motor charges the intermediate circuit capacitor. In this way, the braking power is pulsed to the intermediate circuit of the drive. The operation corresponds to a known so-called. step-up converter operation.

When the voltage of the intermediate circuit has risen sufficiently, for example to 200 V, the second main auxiliary voltage source of the frequency converter wakes up, supplying power to the whole system and, in the case of the invention, also to the cooling fan. Thus, as the dynamic braking situation continues, all power semiconductors are henceforth well cooled, so that there is no time limit for the situation to continue.

The arrangement of the invention increases the reliability of the device when the dynamic brake is implemented by short-circuiting the power semiconductors. Especially if the short-circuit current 4 is significant, for example, more than 30% of the rated current of the device, the arrangement according to the invention is necessary to prevent damage.

Brief Description of the Drawings

The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which:

Figure 1 shows the main circuit and motor of the drive,

Figure 2 shows the frequency-converter and motor components essential for dynamic braking,

Figure 3 shows the control signals of the downstream IGBTs and the voltage curves of the motor short circuit current and the drive intermediate circuit,

Fig. 4 shows the control signals of the downstream IGBTs, the waveform of the frequency converter intermediate circuit and the wakeup of the auxiliary voltage sources.

15

Detailed Description of the Invention

Fig. 1 shows an example of a main circuit of a standard three-phase PWM frequency converter with a three-phase supply voltage L1, L2, L3, 20 diodes mains bridge 10 for rectifying the three-phase alternating voltage of the supply network to a dc voltage dcd. a load bridge 11 consisting of three power semiconductor phase switches, which provides an intermediate circuit for supplying a three-phase output voltage U, V, W to motor 13, and a control unit 12. In modern frequency converters, the so-called. free-wheeling diodes. The inductive component normally used to filter the mains current taken by the drive on either side of the network bridge is insignificant for purposes of the present invention, not drawn in the figure.

Figure 2 shows the drive and motor components essential to the operation of the present invention. In this example, the invention is described solely by means of short-circuit short circuits, but it is also possible to use a list of short-circuit short circuits. In practice, the control of the lower arms is simpler, since all the power semiconductor control circuits of the lower arms are located at the same potential.

5

The short-circuit required for dynamic braking operation is formed when the gate controller GD drives all the downstream IGBT power semiconductors V4, V5, V6. The short-circuit current of the motor then passes through these components or through the neutral diodes D4, D5, De5 connected to them, depending on the direction of the phase current. When the IGBTs are driven to a nonconductive state by the control signals G4i G5, G6, the motor current travels, depending on the direction of the phase current, through either the uplink zero diodes D1, D2, D3 or the downstream zero diodes D4, D5, De to charge the intermediate capacitor which wakes up at a very low intermediate circuit voltage Udc, provides 10 operating voltages only for a portion of the control circuits that are capable of controlling the downstream IGBT power semiconductors. The PS2 is the main auxiliary voltage source which supplies the supply voltage to the entire control system and also to the cooling fan F according to the present invention. Z m. With a permanent magnet motor, the voltage Um is known to be proportional to the rotational speed. The series impedance Zm consists of a resistive and an inductive component. At low frequencies, the resistive component is dominant, so that when the dynamic braking succeeds in deliberately limiting the rotation speed, the short circuit current will remain at its set value, regardless of the duration of the short circuit.

Fig. 3 shows the characteristic behavior of the motor short-circuit current iM and the intermediate loop pin 25 udc during dynamic braking. Signal G4 G5 G6 illustrates the control of the lower branch IGBT switches, where the upper position of the signal corresponds to the fact that all IGBTs are wired and the lower position means that they do not conduct current. In the short-circuit situation, before the times h and t3, the current Im increases with the constant constant of the motor impedance towards its final value 30, and at the same time the intermediate circuit voltage drops under the auxiliary voltage supply. When there is no short circuit, at time intervals t1 ... t2 and t3 ... t4, the inductive current of the motor charges the intermediate circuit capacitor whose voltage rises. Since the auxiliary power source power consumption during a short circuit is typically much less than the current pulse charging current of one intermediate circuit capacitor, the voltage of the intermediate circuit capacitor increases with each cycle (e.g., cycle t3).

By adjusting the proportion of the short-circuiting time to the total duty cycle, it is possible to achieve a situation where the auxiliary power source energy consumption 6 is the same as the charge current pulses, whereby the intermediate circuit voltage no longer rises;

Figure 4 illustrates how the dynamic brake-5 actuation of the invention begins. The assumption here is that before the time t0, the permanent magnet motor has started to rotate at an accelerating rate, whereby its internal voltage (Um in Fig. 2) increases by charging the intermediate circuit capacitor through the zero diodes D ^ .De. When the capacitor voltage udc reaches the first limit UDC (iim). the first auxiliary voltage source PS1 is started, whereupon the dynamic brake 10 control logic and the gate controller GD wake up, and the IGBTs of the lower branch are short-circuited at t0. In accordance with the operation shown in Figure 3, the short circuit current of the motor then begins to increase and the intermediate circuit voltage decreases. The voltage drop during the first short-circuit can be assumed to be so small that the auxiliary voltage source PS1 remains operational at all times. When the short circuit 15 k ends at t1, the intermediate circuit voltage rises rapidly until a new short circuit begins at t 2. The operation thus continues until the intermediate circuit voltage rises to the second limit uDc (iim2) at time tx, whereupon the actual auxiliary voltage source PS2 of the drive starts. The PS2 also supplies the drive voltage to the frequency converter cooling fan, so from this point on, the cooling of the power semiconductors will work as intended, which in turn is a prerequisite for braking the motor for a long time at a reasonable current.

It will be apparent to one skilled in the art that various embodiments of the invention are not limited to the above example, but may vary within the scope of the following claims. For example, within the concept of the invention, it may be possible to arrange the auxiliary voltage source of the frequency converter to operate upwards from the first voltage limit value uDc (iim), whereby two voltage sources with different dimensions are not required. It is also possible to arrange the required short circuits of the dynamic braking action including the uplink controlled power semiconductors, or the upstream and downstream power semiconductors alternately, which compensates for losses and reduces the risk of overheating prior to the fan-enhanced cooling arrangement.

Claims (3)

A method by which the braking of a permanently magnetized motor (13) controlled by a drive is arranged, wherein the dynamic braking is performed such that the power semiconductors (V4, 5 V5, Ve) in the upper and / or lower branches of the phases (U, V, W) in the drive which feeds the permanently magnetized motor pulse-controlled to short-circuit so that the capacitor in the intermediate conduit is charged and the voltage across the intermediate conduction rises, where the control of the power semiconductors is started when the voltage across the intermediate conduit when a predetermined value (uDc) the supply voltage to the drive connected to the drive is dynamically formed by the voltage across the intermediate link during braking, characterized in that the device is the drive's cooling fan (F) arranged to cool the upper and / or lower branches power semiconductor, used in the procedure, a first n first limit value (uocoimi)) and a second upper limit value (uDC (iim2)), and that when the DC voltage across the intermediate link exceeds the first limit value (uDc (iimi)), a first auxiliary voltage source (PS1) is started, by means of which the controllable the power semiconductors in the upper and / or lower branches of the output phases are simultaneously pulse-controlled to a conductive state, and when the DC voltage across the second limiter rises above the second limit value (uDC (iim2)) a second auxiliary voltage source (PS2) is started, which in turn starts the frequency converter F ). 2. A method according to claim 1, characterized in that the short-circuit portion of the entire operating period is regulated such that a state of the nose where the auxiliary voltage source's energy consumption is the same as the energy in the charging current pulses, whereby the voltage across the intermediary no longer increases. 3. Arrangement by which the braking of a permanently magnetized motor (13) controlled by a drive is arranged, the drive being provided with a load bridge (10) connected to the AC network, a load bridge (11) connected to the motor, between them a capacitor (Cdc ) in the DC link and a control unit (12), where the dynamic braking is effected such that the control unit (12) is arranged to pulse-control the power semiconductors (V4, V5, V6) in the upper and / or ned lower branches of the phases (U, V, W) in the drive which feeds the permanently magnetized motor to short circuit such that the capacitor in the intermediate conductor is charged and the voltage across the intermediate conductor rises, where the control unit (12) is arranged to start the control of the power semiconductors when the voltage across the intermediate conductor reaches a predetermined value (UDC). And where the drive is provided with a drive whose supply voltage during braking can be dynamically generated by the voltage over medium reason, characterized in that: the device is the drive fan (F) cooled to cool the upper and / or lower branches power semiconductors, and the system has two auxiliary voltage sources (PS1, PS2) which use two predetermined limit values for the voltage across the intermediate, first lower limit value (uDc (iimi)) and a second upper limit value (UDC (iim2)), where the auxiliary voltage sources are arranged to operate, so that when the DC voltage across the intermediate link rises above the first limit value (uDC (iimi)), the first auxiliary voltage source is started (PS1), by means of which the controllable power semiconductors in the upper and / or lower branches of the phases are simultaneously pulse-controlled to the conductive state, and when the DC voltage across the intermediate link rises above the second limit value (uDC («m2)) the second auxiliary voltage source ( PS2) which in turn starts the drive's cooling fan (F).