Schematic diagram of electric motor control. Typical control schemes. Electrical circuit installation technology

The electrical circuit diagram for controlling an asynchronous motor using an irreversible magnetic starter is shown in Figure 4. Protection against spontaneous switching on when the lost voltage is restored is carried out using normally open block contacts connected in parallel with the SB2 (start) button. The asynchronous motor is protected from overloads of unacceptable duration by the KK thermal relay, the open contact of which is connected in series to the starter control circuit. Circuit protection from short circuits here it is carried out by fuses FU1; FU2; FU3. To relieve stress when replacing burnt-out fuse links, a Q switch is installed.

Figure 4 – Control circuit for an asynchronous squirrel-cage electric motor using a magnetic starter and a push-button station
Figure 5 shows a circuit diagram for controlling an asynchronous motor from two places using two push-button stations. Such a need may arise when managing a conveyor in long rooms and in other cases. You can control an asynchronous motor with more places

Figure 5 – Scheme for controlling an electric motor from two places with the corresponding number of push-button stations

Figure 6 – Control circuit for an asynchronous motor using a reversible magnetic starter:
a - power circuit; b - control circuit with electrical interlocking by contacts of the magnetic starter and contacts of the push-button station; c - control circuit with electrical interlocking by contacts of the magnetic starter
Reversible magnetic starters are equipped with two non-reversible ones. They are equipped with a mechanical interlock, which prevents the simultaneous activation of two contactors, which could result in a short circuit. Electrical interlocks to prevent the simultaneous activation of two contactors are carried out using break contacts KM1 and KM2 (Figure 6, b).
Similar electrical interlocks are also carried out by the breaking contacts of three push-button stations (Figure 6, c). The starting elements of these stations (“forward” and “backward”) each have two mechanically connected make and break contacts. When you press the button, the normally closed contact is switched off first, and then the normally closed contact is switched on.

The first operating systems were very simple methods memory management. At first, each user process had to fit entirely into main memory, occupying a contiguous memory area, and the system would accept additional user processes until they all fit into main memory at the same time. Then “simple swap” appeared (the system still places each process entirely in main memory, but sometimes, based on some criterion, completely resets the image of some process from main memory to external memory and replaces it in main memory with the image of another process). Schemes of this kind have not only historical value. Currently, they are used in educational and research model operating systems, as well as in operating systems for embedded computers.

Fixed partition scheme

The most in a simple way RAM management is its preliminary (usually at the generation stage or at the time of system boot) partitioning into several sections of a fixed size. Incoming processes are placed in one or another partition. In this case, a conditional partition of the physical address space occurs. Linking the logical and physical addresses of a process occurs at the stage of loading it into a specific section, sometimes at the compilation stage.

Each partition can have its own process queue, or there can be a global queue for all partitions (see Fig. 8.4).

This scheme was implemented in IBM OS/360 (MFT), DEC RSX-11 and a number of other systems.

The memory management subsystem estimates the size of the incoming process, selects a suitable partition for it, loads the process into this partition and configures the addresses.

Rice. 8.4. Scheme with fixed partitions: (a) – with a common process queue, (b) – with separate process queues

The obvious drawback of this scheme is that the number of simultaneously running processes is limited by the number of partitions.

Another significant drawback is that the proposed scheme suffers greatly from internal fragmentation - the loss of part of the memory allocated to the process, but not used by it. Fragmentation occurs because a process does not completely occupy the partition allocated to it or because some partitions are too small for user programs to run.

One process in memory

A special case of the fixed partition scheme is the work of the memory manager of a single-tasking OS. There is one user process in memory. It remains to determine where the user program is located in relation to the OS - in the upper part of the memory, in the lower or in the middle. Moreover, part of the OS may be in ROM (for example, BIOS, device drivers). The main factor influencing this decision is the location of the interrupt vector, which is usually located at the bottom of the memory, so the OS is also located at the bottom. An example of such an organization is the MS-DOS operating system.

Protection of the OS address space from the user program can be organized using a single boundary register containing the address of the OS boundary.

Drive control includes starting the electric motor, regulating the rotation speed, changing the direction of rotation, braking and stopping the electric motor. To control drives, electrical switching devices are used, such as automatic and non-automatic switches, contactors and magnetic starters. To protect electric motors from abnormal conditions (overloads and short circuits), circuit breakers, fuses and thermal relays are used.

Control of electric motors with squirrel-cage rotor. In Fig. Figure 2.8 shows a control diagram for an asynchronous motor with a squirrel-cage rotor using a magnetic starter.

Rice. 2.8. using a magnetic starter: Q– switch; F– fuse;

KM- magnetic switch, KK1, KK2- thermal relay; SBC SBT

Magnetic starters are widely used for motors with power up to 100 kW. They are used in long-term and short-term drive operation. The magnetic starter allows for remote starting. To turn on the electric motor M The switch turns on first Q. The engine is started by turning on the push-button switch SBC. Coil (switching electromagnet) of a magnetic starter KM KM in the main circuit and in the control circuit. Auxiliary contact KM SBC and ensures continuous operation of the drive after removing the pressing load from the push-button switch. To protect the electric motor from overload, the magnetic starter has thermal relays KK1 And KK2, included in two phases of the electric motor. Auxiliary contacts of these relays are included in the coil power circuit KM magnetic starter. To protect against short circuits, fuses are installed in each phase of the main circuit of the electric motor. F. Fuses can also be installed in the control circuit. In real circuits, a non-automatic switch Q and fuses F can be replaced by a circuit breaker. The electric motor is turned off by pressing the push-button switch SBT.

The simplest scheme only a non-automatic switch can control the electric motor Q and fuses F or circuit breaker.

In many cases, when controlling an electric drive, it is necessary to change the direction of rotation of the electric motor. For this purpose, reversible magnetic starters are used.

In Fig. Figure 2.9 shows a control diagram for an asynchronous electric motor with a squirrel-cage rotor using a reversible magnetic starter. To turn on the electric motor M the switch must be on Q. The electric motor is turned on for one direction, conventionally “Forward”, by pressing the push-button switch SBC1 in the coil power circuit KM1 magnetic starter. In this case, the coil (switching electromagnet) of the magnetic starter KM1 receives power from the network and closes the contacts KM1 V

main circuit and control circuit. Auxiliary contact KM1 a push-button switch is bypassed in the control circuit SBC1 and ensures continuous operation of the drive after removing the pressing load from the push-button switch.

Rice. 2.9. using a reversing magnetic starter: Q– switch; F– fuse; KM1, KM2- magnetic switch, KK1, KK2- thermal relay; SBC1, SBC2 – push-button engine start switch; SBT– push-button engine shutdown switch

To start the electric motor in the opposite direction, conditionally

“Back”, you need to press the button switch SBC2. Pushbutton switches SBC1 And SBC2 have an electrical lock, eliminating the possibility of simultaneous activation of the coils KM1 And KM2. To do this, in the coil circuit KM1 starter auxiliary contact turns on KM2, and into the coil circuit KM2– auxiliary contact KM1.

To disconnect the electric motor from the network when it rotates in any direction, you must press the push-button switch SBT. In this case, the circuit of any coil and KM1 And KM2 breaks, their contacts in the main circuit of the electric motor open, and the electric motor stops.

The reverse switching circuit can, in justified cases, be used to brake the engine by back switching.

Control of electric motors with wound rotor. In Fig. Figure 2.10 shows a control diagram for an asynchronous motor with a wound rotor.

>Fig. 2.10. Asynchronous motor control circuit

with wound rotor: QF – switch; KM – magnetic starter in the stator circuit, KM1 – KM3 – magnetic acceleration starter; SBC – push-button switch for turning on the engine; R – starting rheostat; SBT – push-button engine shutdown switch

>In the above diagram, engine protection M protection from short circuits and overloads is carried out by an automatic switch QF. To reduce the starting current and increase the starting torque, a three-stage starting rheostat is included in the rotor circuit R. The number of steps may vary. The electric motor is started by a linear contactor KM and acceleration contactors KM1 – KM3. The contactors are equipped with a time relay. After turning on the circuit breaker QF push-button switch SBC line contactor turns on KM, which instantly closes its contacts in the main circuit and bypasses the contacts of the push-button switch SBC. The engine begins to rotate when the starting rheostat is fully inserted. R(mechanical characteristic 1 in Fig. 2.11). Point P is the starting point.

Rice. 2.11. Mechanical characteristics of an asynchronous motor with a wound rotor: 1 , 2 , 3 –

when the starting rheostat stages are turned on; 4 – natural;

P– starting point;

The KM time relay contact in the KM1 contactor coil circuit with a time delay t1 (Fig. 2.12) turns on the KM1 contactor, which closes the first stage contacts in the starting rheostat circuit. With a time delay t2, the contactor KM2 is turned on. The process of switching the stages of the starting rheostat R proceeds similarly until the electric drive switches to the natural characteristic (curve 4).

The change in stator current I and rotor speed n2 during motor starting is shown in Fig. 2.12.

Rice. 2.12. Change in stator current and rotor speed of an asynchronous motor with a wound rotor during start-up

During the natural characteristic, the stator current and rotor speed reach nominal values.

The electric motor is stopped using the SBT push-button switch.

Electrical interlocking in drives. In multi-motor drives or drives of mechanisms connected by a common technological dependence, a certain sequence of turning on and off electric motors must be ensured. This is achieved by using mechanical or electrical interlocking. Electrical blocking is carried out by using additional auxiliary contacts of switching devices involved in controlling the drives. In Fig. Figure 2.13 shows a diagram for blocking the start and stop sequence of two electric motors.

Rice. 2.13. : Q1, Q2– switch; F1, F2– fuse; KM1, KM2- magnetic switch, KK1, KK2- thermal relay; SBC1, SBC2– push-button engine switch; SBT1, SBT2– push-button engine shutdown switch; Q3– auxiliary switch

The circuit excludes the possibility of starting the electric motor M2 before engine start M1. To do this, in the control circuit of the magnetic starter KM2 that starts and stops the electric motor M2, normally open auxiliary contact is switched on KM1, connected to the starter KM1. If the electric motor stops M1 the same contact will produce automatic shutdown engine M2. If it is necessary to start the electric motor independently when testing the mechanism, there is a switch in the control circuit Q3, which must first be closed. Turning on the electric motor M2 carried out by push-button switch SBC2, and shutdown – SBT2. Turning on the engine M1 carried out by a switch SBC1, and shutdown – SBT1. This also turns off the switch M2.

Regulating the speed of the working body of a machine or mechanism. The speed of the working body of the machine can be changed through the use of gearboxes or by changing the rotation speed of the electric motor. The motor speed can be changed in several ways. In construction machines and mechanisms, gearboxes with gear, belt and chain drives are used, allowing the gear ratio to be changed. In drives that use squirrel-cage motors, the rotational speed of the electric motor is changed by changing the number of pole pairs. For these purposes, either an electric motor with two stator windings is used, each of which has different quantities pairs of poles, or an electric motor with switching sections of stator phase windings.

It is possible to regulate the rotation speed by changing the voltage on the stator winding. For these purposes, autotransformers with smooth voltage regulation, magnetic amplifiers, thyristor regulators voltage.

To provide effective memory control, the OS must perform the following functions:

• display address space process to specific areas of physical memory;
• memory distribution between competing processes;
• access control to address spaces processes;
• unloading processes (in whole or in part) into external memory when random access memory not enough space;
• accounting of free and used memory.

The following sections of the lecture discuss a number of specific memory management schemes. Each scheme includes a specific control ideology, as well as algorithms and data structures, and depends on the architectural features of the system used. First, the simplest schemes will be considered. The dominant virtual memory design today will be described in subsequent lectures.

The simplest memory management schemes

The first operating systems used very simple memory management techniques. At first, each user process had to fit entirely into main memory, occupying a contiguous area of ​​memory, and the system would accept additional user processes until they all fit into main memory at the same time. Then “simple swap” appeared (the system still places each process entirely in main memory, but sometimes, based on some criterion, completely resets the image of some process from main memory to external memory and replaces it in main memory with the image of another process). Schemes of this kind have not only historical value. Currently, they are used in educational and research model operating systems, as well as in operating systems for embedded computers.

Fixed partition scheme

The easiest way to control RAM is its preliminary (usually at the generation stage or at the time of system boot) division into several sections of a fixed size. Incoming processes are placed in one or another partition. In this case, a conditional division of the physical address space. Linking the logical and physical addresses of a process occurs at the stage of loading it into a specific section, sometimes at the compilation stage.

Each partition can have its own process queue, or there can be a global queue for all partitions (see Fig. 8.4).

This scheme was implemented in IBM OS/360 (MFT), DEC RSX-11 and a number of other systems.

The memory management subsystem estimates the size of the incoming process, selects a suitable partition for it, loads the process into this partition and configures the addresses.

Rice. 8.4.

The obvious drawback of this scheme is that the number of simultaneously running processes is limited by the number of partitions.

Another significant drawback is that the proposed scheme suffers greatly from internal fragmentation– loss of part of the memory allocated to the process, but not used by it. Fragmentation occurs because a process does not completely occupy the partition allocated to it or because some partitions are too small for user programs to run.

One process in memory

A special case of a circuit with fixed sections– the work of the memory manager of a single-tasking OS. There is one user process in memory. It remains to determine where the user program is located in relation to the OS - in the upper part of the memory, in the lower or in the middle. Moreover, part of the OS may be in ROM (for example, BIOS, device drivers). The main factor influencing this decision is the location of the interrupt vector, which is usually located at the bottom of the memory, so the OS is also located at the bottom. An example of such an organization is the MS-DOS operating system.

Protection address space The OS from the user program can be organized using a single boundary register containing the address of the OS boundary.

Overlay structure

Since the size of the logical address space process can be larger than the size of the partition allocated to it (or larger than the size of the largest partition), sometimes using a technique called overlay or overlapping structure organization. The main idea is to keep in memory only those program instructions that are needed at the moment.

The need for this loading method appears if the logical address space the system is small, for example 1 MB (MS-DOS) or even only 64 KB (PDP-11), and the program is relatively large. On modern 32-bit systems where virtual address space measured in gigabytes, problems with insufficient memory are solved in other ways (see the section "Virtual memory").

Branch codes overlay structure programs reside on disk as absolute memory images and are read by the overlay driver when necessary. For description overlay structure Usually a special simple language is used (overlay description language). The set of files of the executable program is supplemented by a file (usually with the extension .odl) that describes the call tree within the program. For the example shown in Fig. 8.5, the text of this file might look like this:

The syntax of such a file can be recognized by the loader. Link to physical memory occurs at the moment of the next loading of one of the program branches.

Overlays can be implemented entirely at the user level on systems with a simple file structure. The OS only does a few things more operations I/O A typical solution is for the linker to generate special commands that turn on the loader every time a call to one of the overlapping branches of the program is required.

Careful design overlay structure takes a lot of time and requires knowledge of the program structure, its code, data and description language overlay structure. For this reason, the use of overlays is limited to computers with small logical address space. As we will see later, the problem of programmer-controlled overlay segments is no longer a problem with the advent of virtual memory systems.

Note that the possibility of organizing structures with overlaps is largely due to the property of locality, which allows you to store in memory only the information that is needed at a specific moment of computation.

Dynamic distribution. Swaping

Dealing with package systems, you can get by fixed sections and don't use anything more complicated. In time-sharing systems, it is possible that memory cannot contain all user processes. We have to resort to swapping - moving processes from main memory to disk and back entirely. Partial offloading of processes to disk is carried out in systems with paging and will be discussed below.

The dumped process can be returned to the same address space or to another. This limitation is dictated by the binding method. For a run-time binding scheme, you can load the process to a different memory location.

Swaping is not directly related to memory management, but rather is associated with the process scheduling subsystem. Obviously, swapping increases the context switch time. Unloading time can be reduced by organizing a specially allocated disk space (swap partition). Exchange with the disk is carried out in blocks bigger size, that is, faster than through a standard file system. In many versions of Unix, swapping only comes into play when there is a need to reduce system load.

Variable partition scheme

In principle, a swap system can be based on fixed partitions. More efficient, however, seems to be a dynamic allocation scheme or a scheme with variable partitions, which can also be used in cases where all processes fit entirely in memory, that is, in the absence of swapping. In this case, initially all the memory is free and is not partitioned in advance. A newly arriving task is allocated the strictly required amount of memory, no more. After a process is unloaded, memory is temporarily freed. After some time, the memory is a variable number of sections different sizes(Fig. 8.6). Adjacent vacant lots can be combined.

Simulation showed that the share of useful memory in the first two cases is larger, while the first method is slightly faster. In passing, we note that the listed strategies are widely used by other OS components, for example, for placing files on disk.

A typical work cycle of a memory manager consists of analyzing a request to allocate a free area (partition), selecting it among those available in accordance with one of the strategies (first suitable, most suitable and least suitable), loading the process into the selected partition and subsequent changes to the free and busy tables regions. Similar adjustments are necessary after the process is completed. Linking addresses can be carried out at the loading and execution stages.

This method is more flexible compared to the method fixed partitions, however, it is inherent external fragmentation- Availability large number areas of unused memory that are not allocated to any process. Choice placement strategies process between the first fit and the best fit has little effect on the amount of fragmentation. Interestingly, the best-fit method can be the worst method, since it leaves many small unallocated blocks.

Statistical analysis shows that on average 1/3 of memory is lost! This well-known rule 50% (two adjacent free areas, unlike two adjacent processes, can be merged).

One solution to the problem external fragmentation– organize compression, that is, the movement of all occupied (free) areas in the direction of increasing (decreasing) addresses, so that all free memory formed a continuous region. This method is sometimes called a floating partition design. Ideally, there should be no fragmentation after compression. Compression, however, is an expensive procedure, the algorithm for choosing the optimal compression strategy is very difficult, and, as a rule, compression is carried out in combination with uploading and downloading to other addresses.

Electrical control system

Modern electric and mixed systems of remote automatic control, in which commands are transmitted using electrical connections, have an unlimited range of action and an almost instantaneous speed of propagation of an electrical impulse, which allows them to be used for control over short distances.

Electrical systems are performed in two main types:
1. Automatic continuous electric drives.
2. Automatic intermittent electric drives, so-called contact-relay automatic control circuits.

Automation electrical circuits built on non-contact elements are highly reliable, but are more expensive and have not yet been widely used on river vessels. There are remote control systems for engines with one control element. In these circuits, synchronizers of machine telegraphs are used as sensors, and synchros connected to the control handle are used as receivers. The mismatch current is amplified by a semiconductor amplifier and drives an electric motor, which, through a gearbox, sets the handle to the agreed position.

Below is a description of the contact relay tracking system for ship engines NVD -48. Automation of motors of this type comes down to controlling a number of simple “on-off” position control operations. Starting and reversing are carried out using pneumatic means. To control these operations, electromagnetic valves are used, and specially designed electric drive mechanisms are used to drive the reverse and start handles.

Electrical remote automatic engine control system NVD-48

The electrical circuit diagram of the considered DAU system for the NVD -48 engine is shown in Fig. 188. The system operates as follows. Let's assume that the engine needs to be switched from reverse to forward. When the engine telegraph handle is set to the “Full forward” position, the “Reverse - forward”, “Start” and “Fuel supply” circuits are closed to “Full forward”. At the same time, relay coil B receives power and its contacts turn on the electric motor D1 of the reverse handle drive mechanism, which moves the handle to the “Forward” position, after which it is turned off by the 1KB limit switch. At the same time, the limit switch ZKV in the reverse relay circuit PP is closed. The RR relay turns on the electromagnetic valve-pilot for the reverse EMR, through which air enters the reverse valve and opens it. Air flows through the reverse valve and spool into the reversing mechanism, which moves the camshaft to the “Forward” position. In this position, the 5KV limit switch opens the electromagnet circuit through the PP relay. The reverse valve closes and the air from the pipeline is released into the atmosphere. The reverse ends here.

Rice. 1. Electrical diagram of remote automatic engine control NVD-48

If an engine is started that was stopped in the “Forward” position, then reversing when the engine telegraph handle is installed in the “Full forward” position does not occur, but “Start” is immediately performed, which is carried out as follows. Simultaneously with the 5KV starting switch turning off, the 7KV limit switch is turned on in the RP start relay circuit, which opens the main starting valve through the EEMF start solenoid valve. In this case, starting air enters the cylinders and begins to spin the crankshaft.

In NVD -48 engines, before the camshaft begins to move during reversal, the cylinder starting valves open. After repositioning the camshaft, the start valves close. To prevent starting air from being supplied to the cylinders during the period when they are exposed to the atmosphere, and not being released in vain, a start delay mechanism is installed.

To delay the opening of the main starting valve until the cylinder starting valves close after reversing, a pneumatic relay is used, consisting of a container and two non-return valves. During reverse, the tank is filled with air, and during start-up, the air bleed from this tank delays the opening of the main starting valve for the time during which the starting valves are closed.

After the engine speed reaches the required value, the RNV relay, receiving power from the tachogenerator connected to the main engine shaft, opens the PC speed relay circuit. The PC relay opens the P relay circuit. As a result, the starting air supply is stopped and the start handle moves to the “Run” position. In this case, the electric motor D2 of the start handle is turned off by the 11KV limit switch. If the engine does not start, its speed begins to decrease, the RNV relay closes its contacts, and the start is automatically repeated.

When the speed relay PC is activated, relay B is also activated, which turns on the fuel supply electric motor D3. The electric motor turns on the pumps to full fuel supply and is turned off by the PVg limit switch. Simultaneously with turning on and off the electric motor D3, the brake electromagnet TEM is turned on and off, releasing or braking the electric motor D3.

The engine stops when the machine telegraph handle is set to the “Stop” position, after which it is turned off by the 9KV limit switch through relay C. The fuel supply is stopped, the speed relay PC closes the coil circuit M, and the electric motor D3 moves the fuel supply handle to the position corresponding to the fuel supply when start, and is turned off by the PVv starting switch.