Network Working Group M. Allman Request for Comments: 2414 NASA Lewis/Sterling Software Category: Experimental S. Floyd LBNL C. Partridge BBN Technologies September 1998 Increasing TCP’s Initial Window
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract
This document specifies an increase in the permitted initial window
for TCP from one segment to roughly 4K bytes. This document
discusses the advantages and disadvantages of such a change,
outlining experimental results that indicate the costs and benefits
of such a change to TCP.
Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
1. TCP Modification
This document specifies an increase in the permitted upper bound for TCP’s initial window from one segment to between two and four
segments. In most cases, this change results in an upper bound on
the initial window of roughly 4K bytes (although given a large
segment size, the permitted initial window of two segments could be
significantly larger than 4K bytes). The upper bound for the initial window is given more precisely in (1):
min (4*MSS, max (2*MSS, 4380 bytes)) (1)
Allman, et. al. Experimental [Page 1]
Equivalently, the upper bound for the initial window size is based on the maximum segment size (MSS), as follows:
If (MSS <= 1095 bytes)
then win <= 4 * MSS;
If (1095 bytes < MSS < 2190 bytes)
then win <= 4380;
If (2190 bytes <= MSS)
then win <= 2 * MSS;
This increased initial window is optional: that a TCP MAY start with a larger initial window, not that it SHOULD.
This upper bound for the initial window size represents a change from RFC 2001 [S97], which specifies that the congestion window be
initialized to one segment. If implementation experience proves
successful, then the intent is for this change to be incorporated
into a revision to RFC 2001.
This change applies to the initial window of the connection in the
first round trip time (RTT) of transmission following the TCP three- way handshake. Neither the SYN/ACK nor its acknowledgment (ACK) in
the three-way handshake should increase the initial window size above that outlined in equation (1). If the SYN or SYN/ACK is lost, the
initial window used by a sender after a correctly transmitted SYN
MUST be one segment.
TCP implementations use slow start in as many as three different
ways: (1) to start a new connection (the initial window); (2) to
restart a transmission after a long idle period (the restart window); and (3) to restart after a retransmit timeout (the loss window). The change proposed in this document affects the value of the initial
window. Optionally, a TCP MAY set the restart window to the minimum of the value used for the initial window and the current value of
cwnd (in other words, using a larger value for the restart window
should never increase the size of cwnd). These changes do NOT change the loss window, which must remain 1 segment (to permit the lowest
possible window size in the case of severe congestion).
2. Implementation Issues
When larger initial windows are implemented along with Path MTU
Discovery [MD90], and the MSS being used is found to be too large,
the congestion window ‘cwnd’ SHOULD be reduced to prevent large
bursts of smaller segments. Specifically, ‘cwnd’ SHOULD be reduced
by the ratio of the old segment size to the new segment size.
Allman, et. al. Experimental [Page 2]
When larger initial windows are implemented along with Path MTU
Discovery [MD90], alternatives are to set the "Don’t Fragment" (DF)
bit in all segments in the initial window, or to set the "Don’t
Fragment" (DF) bit in one of the segments. It is an open question
which of these two alternatives is best; we would hope that
implementation experiences will shed light on this. In the first
case of setting the DF bit in all segments, if the initial packets
are too large, then all of the initial packets will be dropped in the network. In the second case of setting the DF bit in only one
segment, if the initial packets are too large, then all but one of
the initial packets will be fragmented in the network. When the
second case is followed, setting the DF bit in the last segment in
the initial window provides the least chance for needless
retransmissions when the initial segment size is found to be too
large, because it minimizes the chances of duplicate ACKs triggering a Fast Retransmit. However, more attention needs to be paid to the
interaction between larger initial windows and Path MTU Discovery.
The larger initial window proposed in this document is not intended
as an encouragement for web browsers to open multiple simultaneous
TCP connections all with large initial windows. When web browsers
open simultaneous TCP connections to the same destination, this works against TCP’s congestion control mechanisms [FF98], regardless of the size of the initial window. Combining this behavior with larger
initial windows further increases the unfairness to other traffic in the network.
3. Advantages of Larger Initial Windows
1. When the initial window is one segment, a receiver employing
delayed ACKs [Bra89] is forced to wait for a timeout before
generating an ACK. With an initial window of at least two
segments, the receiver will generate an ACK after the second data segment arrives. This eliminates the wait on the timeout (often up to 200 msec).
2. For connections transmitting only a small amount of data, a
larger initial window reduces the transmission time (assuming at most moderate segment drop rates). For many email (SMTP [Pos82]) and web page (HTTP [BLFN96, FJGFBL97]) transfers that are less
than 4K bytes, the larger initial window would reduce the data
transfer time to a single RTT.
3. For connections that will be able to use large congestion
windows, this modification eliminates up to three RTTs and a
delayed ACK timeout during the initial slow-start phase. This Allman, et. al. Experimental [Page 3]
would be of particular benefit for high-bandwidth large-
propagation-delay TCP connections, such as those over satellite
links.
4. Disadvantages of Larger Initial Windows for the Individual
Connection
In high-congestion environments, particularly for routers that have a bias against bursty traffic (as in the typical Drop Tail router
queues), a TCP connection can sometimes be better off starting with
an initial window of one segment. There are scenarios where a TCP
connection slow-starting from an initial window of one segment might not have segments dropped, while a TCP connection starting with an
initial window of four segments might experience unnecessary
retransmits due to the inability of the router to handle small
bursts. This could result in an unnecessary retransmit timeout. For a large-window connection that is able to recover without a
retransmit timeout, this could result in an unnecessarily-early
transition from the slow-start to the congestion-avoidance phase of
the window increase algorithm. These premature segment drops are
unlikely to occur in uncongested networks with sufficient buffering
or in moderately-congested networks where the congested router uses
active queue management (such as Random Early Detection [FJ93,
RFC2309]).
Some TCP connections will receive better performance with the higher initial window even if the burstiness of the initial window results
in premature segment drops. This will be true if (1) the TCP
connection recovers from the segment drop without a retransmit
timeout, and (2) the TCP connection is ultimately limited to a small congestion window by either network congestion or by the receiver’s
advertised window.
5. Disadvantages of Larger Initial Windows for the Network
In terms of the potential for congestion collapse, we consider two
separate potential dangers for the network. The first danger would
be a scenario where a large number of segments on congested links
were duplicate segments that had already been received at the
receiver. The second danger would be a scenario where a large number of segments on congested links were segments that would be dropped
later in the network before reaching their final destination.
In terms of the negative effect on other traffic in the network, a
potential disadvantage of larger initial windows would be that they
increase the general packet drop rate in the network. We discuss
these three issues below.
Allman, et. al. Experimental [Page 4]
Duplicate segments:
As described in the previous section, the larger initial window
could occasionally result in a segment dropped from the initial
window, when that segment might not have been dropped if the
sender had slow-started from an initial window of one segment.
However, Appendix A shows that even in this case, the larger
initial window would not result in the transmission of a large
number of duplicate segments.
Segments dropped later in the network:
How much would the larger initial window for TCP increase the
number of segments on congested links that would be dropped
before reaching their final destination? This is a problem that can only occur for connections with multiple congested links,
where some segments might use scarce bandwidth on the first
congested link along the path, only to be dropped later along the path.
First, many of the TCP connections will have only one congested
link along the path. Segments dropped from these connections do not "waste" scarce bandwidth, and do not contribute to congestion collapse.
However, some network paths will have multiple congested links,
and segments dropped from the initial window could use scarce
bandwidth along the earlier congested links before ultimately
being dropped on subsequent congested links. To the extent that the drop rate is independent of the initial window used by TCP
segments, the problem of congested links carrying segments that
will be dropped before reaching their destination will be similar for TCP connections that start by sending four segments or one
segment.
An increased packet drop rate:
For a network with a high segment drop rate, increasing the TCP
initial window could increase the segment drop rate even further. This is in part because routers with Drop Tail queue management
have difficulties with bursty traffic in times of congestion.
However, given uncorrelated arrivals for TCP connections, the
larger TCP initial window should not significantly increase the
segment drop rate. Simulation-based explorations of these issues are discussed in Section 7.2.
Allman, et. al. Experimental [Page 5]
These potential dangers for the network are explored in simulations
and experiments described in the section below. Our judgement would be, while there are dangers of congestion collapse in the current
Internet (see [FF98] for a discussion of the dangers of congestion
collapse from an increased deployment of UDP connections without
end-to-end congestion control), there is no such danger to the
network from increasing the TCP initial window to 4K bytes.
6. Typical Levels of Burstiness for TCP Traffic.
Larger TCP initial windows would not dramatically increase the
burstiness of TCP traffic in the Internet today, because such traffic is already fairly bursty. Bursts of two and three segments are
already typical of TCP [Flo97]; A delayed ACK (covering two
previously unacknowledged segments) received during congestion
avoidance causes the congestion window to slide and two segments to
be sent. The same delayed ACK received during slow start causes the window to slide by two segments and then be incremented by one
segment, resulting in a three-segment burst. While not necessarily
typical, bursts of four and five segments for TCP are not rare.
Assuming delayed ACKs, a single dropped ACK causes the subsequent ACK to cover four previously unacknowledged segments. During congestion avoidance this leads to a four-segment burst and during slow start a five-segment burst is generated.
There are also changes in progress that reduce the performance
problems posed by moderate traffic bursts. One such change is the
deployment of higher-speed links in some parts of the network, where a burst of 4K bytes can represent a small quantity of data. A second change, for routers with sufficient buffering, is the deployment of
queue management mechanisms such as RED, which is designed to be
tolerant of transient traffic bursts.
7. Simulations and Experimental Results
7.1 Studies of TCP Connections using that Larger Initial Window
This section surveys simulations and experiments that have been used to explore the effect of larger initial windows on the TCP connection using that larger window. The first set of experiments explores
performance over satellite links. Larger initial windows have been
shown to improve performance of TCP connections over satellite
channels [All97b]. In this study, an initial window of four segments (512 byte MSS) resulted in throughput improvements of up to 30%
(depending upon transfer size). [KAGT98] shows that the use of
larger initial windows results in a decrease in transfer time in HTTP tests over the ACTS satellite system. A study involving simulations Allman, et. al. Experimental [Page 6]
of a large number of HTTP transactions over hybrid fiber coax (HFC)
indicates that the use of larger initial windows decreases the time
required to load WWW pages [Nic97].
A second set of experiments has explored TCP performance over dialup modem links. In experiments over a 28.8 bps dialup channel [All97a, AHO98], a four-segment initial window decreased the transfer time of a 16K
B file by roughly 10%, with no accompanying increase in the drop rate. A particular area of concern has been TCP performance over low speed tail circuits (e.g., dialup modem links) with routers with
small buffers. A simulation study [SP97] investigated the effects of using a larger initial window on a host connected by a slow modem
link and a router with a 3 packet buffer. The study concluded that
for the scenario investigated, the use of larger initial windows was not harmful to TCP performance. Questions have been raised
concerning the effects of larger initial windows on the transfer time for short transfers in this environment, but these effects have not
been quantified. A question has also been raised concerning the
possible effect on existing TCP connections sharing the link.
7.2 Studies of Networks using Larger Initial Windows
This section surveys simulations and experiments investigating the
impact of the larger window on other TCP connections sharing the
path. Experiments in [All97a, AHO98] show that for 16 KB transfers
to 100 Internet hosts, four-segment initial windows resulted in a
small increase in the drop rate of 0.04 segments/transfer. While the drop rate increased slightly, the transfer time was reduced by
roughly 25% for transfers using the four-segment (512 byte MSS)
initial window when compared to an initial window of one segment.
One scenario of concern is heavily loaded links. For instance, a
couple of years ago, one of the trans-Atlantic links was so heavily
loaded that the correct congestion window size for a connection was
about one segment. In this environment, new connections using larger initial windows would be starting with windows that were four times
too big. What would the effects be? Do connections thrash?
A simulation study in [PN98] explores the impact of a larger initial window on competing network traffic. In this investigation, HTTP and FTP flows share a single congested gateway (where the number of HTTP and FTP flows varies from one simulation set to another). For each
simulation set, the paper examines aggregate link utilization and
packet drop rates, median web page delay, and network power for the
FTP transfers. The larger initial window generally resulted in
increased throughput, slightly-increased packet drop rates, and an
increase in overall network power. With the exception of one
scenario, the larger initial window resulted in an increase in the Allman, et. al. Experimental [Page 7]
drop rate of less than 1% above the loss rate experienced when using a one-segment initial window; in this scenario, the drop rate
increased from 3.5% with one-segment initial windows, to 4.5% with
four-segment initial windows. The overall conclusions were that
increasing the TCP initial window to three packets (or 4380 bytes)
helps to improve perceived performance.
Morris [Mor97] investigated larger initial windows in a very
congested network with transfers of size 20K. The loss rate in
networks where all TCP connections use an initial window of four
segments is shown to be 1-2% greater than in a network where all
connections use an initial window of one segment. This relationship held in scenarios where the loss rates with one-segment initial
windows ranged from 1% to 11%. In addition, in networks where
connections used an initial window of four segments, TCP connections spent more time waiting for the retransmit timer (RTO) to expire to
resend a segment than was spent when using an initial window of one
segment. The time spent waiting for the RTO timer to expire
represents idle time when no useful work was being accomplished for
that connection. These results show that in a very congested
environment, where each connection’s share of the bottleneck
bandwidth is close to one segment, using a larger initial window can cause a perceptible increase in both loss rates and retransmit
timeouts.
8. Security Considerations
This document discusses the initial congestion window permitted for
TCP connections. Changing this value does not raise any known new
security issues with TCP.
9. Conclusion
This document proposes a small change to TCP that may be beneficial
to short-lived TCP connections and those over links with long RTTs
(saving several RTTs during the initial slow-start phase).
10. Acknowledgments
We would like to acknowledge Vern Paxson, Tim Shepard, members of the End-to-End-Interest Mailing List, and members of the IETF TCP
Implementation Working Group for continuing discussions of these
issues for discussions and feedback on this document.
Allman, et. al. Experimental [Page 8]
11. References
[All97a] Mark Allman. An Evaluation of TCP with Larger Initial
Windows. 40th IETF Meeting -- TCP Implementations WG.
December, 1997. Washington, DC.
[AHO98] Mark Allman, Chris Hayes, and Shawn Ostermann, An
Evaluation of TCP with Larger Initial Windows, March
1998. Submitted to ACM Computer Communication Review.
URL: "https://www.doczj.com/doc/3714682804.html,/?mallman/papers/
initwin.ps".
[All97b] Mark Allman. Improving TCP Performance Over Satellite
Channels. Master’s thesis, Ohio University, June 1997.
[BLFN96] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
[Bra89] Braden, R., "Requirements for Internet Hosts --
Communication Layers", STD 3, RFC 1122, October 1989.
[FF96] Fall, K., and Floyd, S., Simulation-based Comparisons of Tahoe, Reno, and SACK TCP. Computer Communication
Review, 26(3), July 1996.
[FF98] Sally Floyd, Kevin Fall. Promoting the Use of End-to-End Congestion Control in the Internet. Submitted to IEEE
Transactions on Networking. URL "http://www-
https://www.doczj.com/doc/3714682804.html,/floyd/end2end-paper.html".
[FJGFBL97] Fielding, R., Mogul, J., Gettys, J., Frystyk, H., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
RFC 2068, January 1997.
[FJ93] Floyd, S., and Jacobson, V., Random Early Detection
gateways for Congestion Avoidance. IEEE/ACM Transactions on Networking, V.1 N.4, August 1993, p. 397-413.
[Flo94] Floyd, S., TCP and Explicit Congestion Notification.
Computer Communication Review, 24(5):10-23, October 1994. [Flo96] Floyd, S., Issues of TCP with SACK. Technical report,
January 1996. Available from http://www-
https://www.doczj.com/doc/3714682804.html,/floyd/.
[Flo97] Floyd, S., Increasing TCP’s Initial Window. Viewgraphs, 40th IETF Meeting - TCP Implementations WG. December,
1997. URL "ftp://https://www.doczj.com/doc/3714682804.html,/talks/sf-tcp-ietf97.ps". Allman, et. al. Experimental [Page 9]
[KAGT98] Hans Kruse, Mark Allman, Jim Griner, Diepchi Tran. HTTP
Page Transfer Rates Over Geo-Stationary Satellite Links.
March 1998. Proceedings of the Sixth International
Conference on Telecommunication Systems. URL
"https://www.doczj.com/doc/3714682804.html,/?mallman/papers/nash98.ps". [MD90] Mogul, J., and S. Deering, "Path MTU Discovery", RFC
1191, November 1990.
[MMFR96] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP
Selective Acknowledgment Options", RFC 2018, October
1996.
[Mor97] Robert Morris. Private communication, 1997. Cited for
acknowledgement purposes only.
[Nic97] Kathleen Nichols. Improving Network Simulation with
Feedback. Com21, Inc. Technical Report. Available from
https://www.doczj.com/doc/3714682804.html,/pages/papers/068.pdf.
[PN98] Poduri, K., and K. Nichols, "Simulation Studies of
Increased Initial TCP Window Size", RFC 2415, September
1998.
[Pos82] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC
821, August 1982.
[RF97] Ramakrishnan, K., and S. Floyd, "A Proposal to Add
Explicit Congestion Notification (ECN) to IPv6 and to
TCP", Work in Progress.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2309] Braden, B., Clark, D., Crowcroft, J., Davie, B., Deering,
S., Estrin, D., Floyd, S., Jacobson, V., Minshall, G.,
Partridge, C., Peterson, L., Ramakrishnan, K., Shenker,
S., Wroclawski, J., and L. Zhang, "Recommendations on
Queue Management and Congestion Avoidance in the
Internet", RFC 2309, April 1998.
[S97] Stevens, W., "TCP Slow Start, Congestion Avoidance, Fast
Retransmit, and Fast Recovery Algorithms", RFC 2001,
January 1997.
[SP97] Shepard, T., and C. Partridge, "When TCP Starts Up With
Four Packets Into Only Three Buffers", RFC 2416,
September 1998.
Allman, et. al. Experimental [Page 10]
12. Author’s Addresses
Mark Allman
NASA Lewis Research Center/Sterling Software
21000 Brookpark Road
MS 54-2
Cleveland, OH 44135
EMail: mallman@https://www.doczj.com/doc/3714682804.html,
https://www.doczj.com/doc/3714682804.html,/?mallman/
Sally Floyd
Lawrence Berkeley National Laboratory
One Cyclotron Road
Berkeley, CA 94720
EMail: floyd@https://www.doczj.com/doc/3714682804.html,
Craig Partridge
BBN Technologies
10 Moulton Street
Cambridge, MA 02138
EMail: craig@https://www.doczj.com/doc/3714682804.html,
Allman, et. al. Experimental [Page 11]
13. Appendix - Duplicate Segments
In the current environment (without Explicit Congestion Notification [Flo94] [RF97]), all TCPs use segment drops as indications from the
network about the limits of available bandwidth. We argue here that the change to a larger initial window should not result in the sender retransmitting a large number of duplicate segments that have already been received at the receiver.
If one segment is dropped from the initial window, there are three
different ways for TCP to recover: (1) Slow-starting from a window of one segment, as is done after a retransmit timeout, or after Fast
Retransmit in Tahoe TCP; (2) Fast Recovery without selective
acknowledgments (SACK), as is done after three duplicate ACKs in Reno TCP; and (3) Fast Recovery with SACK, for TCP where both the sender
and the receiver support the SACK option [MMFR96]. In all three
cases, if a single segment is dropped from the initial window, no
duplicate segments (i.e., segments that have already been received at the receiver) are transmitted. Note that for a TCP sending four
512-byte segments in the initial window, a single segment drop will
not require a retransmit timeout, but can be recovered from using the Fast Retransmit algorithm (unless the retransmit timer expires
prematurely). In addition, a single segment dropped from an initial window of three segments might be repaired using the fast retransmit algorithm, depending on which segment is dropped and whether or not
delayed ACKs are used. For example, dropping the first segment of a three segment initial window will always require waiting for a
timeout. However, dropping the third segment will always allow
recovery via the fast retransmit algorithm, as long as no ACKs are
lost.
Next we consider scenarios where the initial window contains two to
four segments, and at least two of those segments are dropped. If
all segments in the initial window are dropped, then clearly no
duplicate segments are retransmitted, as the receiver has not yet
received any segments. (It is still a possibility that these dropped segments used scarce bandwidth on the way to their drop point; this
issue was discussed in Section 5.)
When two segments are dropped from an initial window of three
segments, the sender will only send a duplicate segment if the first two of the three segments were dropped, and the sender does not
receive a packet with the SACK option acknowledging the third
segment.
When two segments are dropped from an initial window of four
segments, an examination of the six possible scenarios (which we
don’t go through here) shows that, depending on the position of the Allman, et. al. Experimental [Page 12]
dropped packets, in the absence of SACK the sender might send one
duplicate segment. There are no scenarios in which the sender sends two duplicate segments.
When three segments are dropped from an initial window of four
segments, then, in the absence of SACK, it is possible that one
duplicate segment will be sent, depending on the position of the
dropped segments.
The summary is that in the absence of SACK, there are some scenarios with multiple segment drops from the initial window where one
duplicate segment will be transmitted. There are no scenarios where more that one duplicate segment will be transmitted. Our conclusion is that the number of duplicate segments transmitted as a result of a larger initial window should be small.
Allman, et. al. Experimental [Page 13]
14. Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
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Allman, et. al. Experimental [Page 14]
所谓三电平是指逆变器交流侧每相输出电压相对于直流侧有三种取值，正端电压(+Vdc/2)、负端电压(-Vdc/2)、中点零电压(0)。二极管箱位型三电平逆变器主电路结构如图所示。逆变器每一相需要4个IGBT开关管、4个续流二极管、2个箱位二极管;整个三相逆变器直流侧由两个电容C1、C2串联起来来支撑并均衡直流侧电压，C1=C2。通过一定的开关逻辑控制，交流侧产生三种电平的相电压，在输出端合成正弦波。 三电平逆变器的工作原理 以输出电压A相为例，分析三电平逆变器主电路工作原理，并假设器件为理想器件，不计其导通管压降。定义负载电流由逆变器流向电机或其它负载时的方向为正方向。 (l) 当Sa1，、Sa2导通，Sa3、Sa4关断时，若负载电流为正方向，则电源对电容C1充电，电流从正极点流过主开关Sa1、Sa2，该相输出端电位等同于正极点电位，输出电压U=+V dc/2; 若负载电流为负方向，则电流流过与主开关管Sa1、Sa2反并联的续流二极管对电容C1充电，电流注入正极点，该相输出端电位仍然等同于正极点电位，输出电压U=+V dc/2。通常标识为所谓的“1”状态，如图所示。
“1”状态“0”状态 “-1”状态 (2) 当Sa2、Sa3导通，Sa1、Sa4关断时，若负载电流为正方向，则电源对电容C1充电，电流 从O点顺序流过箱位二极管D a1，主开关管Sa2:，该相输出端电位等同与0点电位，输出电压U=O;若负载电流为负方向，则电流顺序流过主开关管Sa3和箱位二极管D a2，电流注入O点，该相输出端电位等同于O点电位，输出电压U=0，电源对电容C2充电。即通常标识的“0”状态，如图所示。
无尘车间规章制度 < ':10 5 0 20:10 0 0 -15;' 1. 无尘车间规章制度 2. 无尘车间管理规章制度 3. 无尘车间管理规章制度 4. 无尘车间管理规章制度 5. 无尘车间工作应遵守的管理规章制度 1、无尘车间规章制度 目的：为了维持良好的生产秩序，提高劳动生产率，保证生产工作的顺利进行特制订以下管理制度。 范围：适应于生产车间全体工作人员。 一、早会制度 1．员工每天上班必须提前5分钟到达车间开早会，不得迟到、早退。 2．员工在开早会时须站立端正，认真听主管或组长的讲话，不得做一些与早会无关的事项。 3．各条线的组长每天上班必须提前10分钟到达车间组织员工准时开早会. 4．各条线的组长在开早会时必须及时向员工传达前天的工作情况以及当天的生产计划，时间应控制在15分钟。5．组长开早会时讲话应宏亮有力,多以激励为主,不得随意批评和责骂员工。 二、请假制度 1．如特殊事情必须亲自处理,应在2小时前用书面的形式请假,经主管与相关领导签字后,才属请假生效,不可代请假或事后请假(如生病无法亲自请假,事后必须交医生证明 方可有效),否则按旷工处理。 2．杜绝非上班时间私下请假或批假。 3．员工每月请假不得超过两次，每天请假不得超过5%。
4．员工请假核准权限：（同厂规一致） (1)一天以内由班长批准;三天以内由车间主管批准; (3)超过三天必须由生产部经理批准; (4)连续请假按照累计天数依上述规定办理。 三、清洁卫生制度 1.员工要保持岗位的清洁干净，物品要按规定位置放置整齐，不得到处乱放,组长要保持办公台的整齐干净。 2.每天下班后值日生打扫卫生，周末须进行大扫除（公司内的门、厕所、窗户、地面、生产线、设备、风扇、饮水机等都须清洁）。 3.卫生工具用完后须清洗干净放在指定的区域，工具由专组专人保管，不得乱丢，倒置、甚至损坏。 4.不得随便在公司内乱丢垃圾、胡乱涂划； 四、车间生产秩序管理制度 1.员工进入车间前须将手部、脸部清洁，须换正确佩带厂牌、上岗证、穿静电拖鞋、穿静电衣、带静电帽、带静电环过淋室后方可进入车间，不得携带任何个人物品，如手机3.手袋.食品等。 2.上班前,物料员须及时将当天所需的物料备到生产线,并严格按照规定的运作流程操作,不得影响工作的顺利进行。 3.上班前须测试静电环，严禁代签 4.员工在作业过程中,必须保持50-80以上的距离,不得挤坐在一起，作业时须按要求做好防静电措施，同时必须自觉做好自检与互检工作,如发现问题并及时向品检与班级长反应,不可擅自使用不良材料以及让不合格品流入下道工序,必须严格按照品质要求作业。 5.每道工序必须接受车间品管检查、监督，不得蒙混过关，虚报数量；除些之外还要配合品检工作，不得顶撞、辱骂。 6.小零配件必须用黑色防静电盒盛放,一个盒子只可装一种零配件,安装过程中发现的 不良品必须用红色防静电盒盛放,所有的物料盒排成一行放于工作台面的左手边。
三电平逆变器的主电路结构及其工作原理 所谓三电平是指逆变器交流侧每相输出电压相对于直流侧有三种取值，正端电压(+Vdc/2)、负端电压(-Vdc/2)、中点零电压(0)。二极管箱位型三电平逆变器主电路结构如图所示。逆变器每一相需要4个IGBT开关管、4个续流二极管、2个箱位二极管;整个三相逆变器直流侧由两个电容C1、C2串联起来来支撑并均衡直流侧电压，C1=C2。通过一定的开关逻辑控制，交流侧产生三种电平的相电压，在输出端合成正弦波。 三电平逆变器的工作原理 以输出电压A相为例，分析三电平逆变器主电路工作原理，并假设器件为理想器件，不计其导通管压降。定义负载电流由逆变器流向电机或其它负载时的方向为正方向。 (l) 当Sa1，、Sa2导通，Sa3、Sa4关断时，若负载电流为正方向，则电源对电容C1充电，电流从正极点流过主开关Sa1、Sa2，该相输出端电位等同于正极点电位，输出电压U=+V dc/2; 若负载电流为负方向，则电流流过与主开关管Sa1、Sa2反并联的续流二极管对电容C1充电，电流注入正极点，该相输出端电位仍然等同于正极点电位，输出电压U=+V dc/2。通常标识为所谓的“1”状态，如图所示。
“1”状态“0”状态 “-1”状态 (2) 当Sa2、Sa3导通，Sa1、Sa4关断时，若负载电流为正方向，则电源对电容C1充电，电流 从O点顺序流过箱位二极管D a1，主开关管Sa2:，该相输出端电位等同与0点电位，输出电压U=O;若负载电流为负方向，则电流顺序流过主开关管Sa3和箱位二极管D a2，电流注入O点，该相输出端电位等同于O点电位，输出电压U=0，电源对电容C2充电。即通常标识的“0”状态，如图所示。 (3) 当Sa3、Sa4导通，Sa1、Sa2关断时，若负载电流为正方向，则电流从负极点流过与主开 关Sa3、Sa4反并联的续流二极管对电容C2进行充电，该相输出端电位等同于负极点电位，输出电压U=-V dc/2;若负载电流为负方向，则电源对电容C2充电，电流流过主开关管Sa3、Sa4注入负极点，该相输出端电位仍然等同于负极点电位，输出电压U=-V dc/2。通常标识为“-1”状态，如图所示。
无尘车间洁净度如何确定详细分析 一、净化车间的规格 净化车间的规格一般适用于美国联邦规格NO.209B。这个规格对净化间的环境要素即空气洁净 度、温湿度、室内压等都进行了规格化规定。但是，伴随着洁净化程度的不断提高，美国联邦规格进行了改版，其内容主要是以洁净度进行分类。最新版已成为NO209E,名称也进行了变更。NO.209E 的级别表示是把0.5um以上的颗粒数为10x个/m3，把X表示成级别，同时加上米制M的意思，表 示成M3.5等等。在表7里表示的是美国联邦规格NO.209B，表8表示的是美国联邦规格NO.209E。 在日本，相应的规格是JIS B9920。JIS9920的级别表示是把O.lum以上的颗粒数规定为10X个，用 Y表示级别。表9、图2表示了JIS B 9920的级别的主要内容。 表8,美国联邦规格NO.209E的洁净度级别分类
*上表中表示的级别上限值仅仅是为了级别分类而定义的，并不表示实际的粒径分布值。**针对中间级别的浓度上限值，用如下的公式进行计算。 粒子直径/m3=10M（0.5/d）2.2，其中，M : SI单位里的级别名称，D :粒径（um） *** 国际单位（Systeme International d 'nites 的缩写） 图1，209E的洁净度级别（图略）图中的?标记表示评价洁净度级别用的对象粒子。 （）内数值是用English unit表示级别。 图2，JIS B 9920的洁净度级别的上限浓度 三、不同用途所要求的洁净度 如前所述，净化间的级别一般分成M3.5（100）、M4.5（1000）、M5.5（10000）、M6.5（100000） 4个级别。但根据各产业领域的作业工序不同，形成必要的级别是不一样的。例如，在半导体制造 工厂等里边，根据作业内容，要求有M1（10）—M5.5（1000）的净化间。而且，在制药工厂里，根据产品的纯度、作业工序，需有从M3.5到M6.5（100，000）范围广泛的级别不等净化间。因此说，各种产业所需要的净化间，其要求的洁净度是不同的。就一般级别而言，表11可以作为参考。 表11,各产业所要求的净化间级别一览
[三电平逆变器的主电路结构及其工作原理]三电平逆变器 工作原理 三电平逆变器的主电路结构及其原理 所谓三电平是指逆变器侧每相输出电压相对于直流侧有三种取值，正端电压(+Vdc/2)、负端电压(-Vdc/2)、中点零电压(0)。二极管箱 位型三电平逆变器主电路结构如图所示。逆变器每一相需要4个IGBT 开关管、4个续流二极管、2个箱位二极管;整个三相逆变器直流侧由两个电容C1、C2串联起来来支撑并均衡直流侧电压，C1=C2。通过一定的开关逻辑控制，交流侧产生三种电平的相电压，在输出端合成正弦波。 三电平逆变器的工作原理 以输出电压A相为例，分析三电平逆变器主电路工作原理，并假 设器件为理想器件，不计其导通管压降。定义负载电流由逆变器流向电机或其它负载时的方向为正方向。 (l) 当Sa1、Sa2导通，Sa3、Sa4关断时，若负载电流为正方向，则电源对电容C1充电，电流从正极点流过主开关Sa1、Sa2，该相输出端电位等同于正极点电位，输出电压U=+Vdc/2;若负载电流为负方向，则电流流过与主开关管Sa1、Sa2反并联的续流二极管对电容C1
充电，电流注入正极点，该相输出端电位仍然等同于正极点电位，输出电压U=+Vdc/2。通常标识为所谓的“1”状态，如图所示。 “1”状态“0”状态 “-1”状态 (2) 当Sa2、Sa3导通，Sa1、Sa4关断时，若负载电流为正方向，则电源对电容C1充电，电流从O点顺序流过箱位二极管Da1，主开关管Sa2:，该相输出端电位等同与0点电位，输出电压U=O;若负载电流为负方向，则电流顺序流过主开关管Sa3和箱位二极管Da2，电流注入O点，该相输出端电位等同于O点电位，输出电压U=0，电源对电容C2充电。即通常标识的“0”状态，如图所示。 (3) 当Sa3、Sa4导通，Sa1、Sa2关断时，若负载电流为正方向，则电流从负极点流过与主开关Sa3、Sa4反并联的续流二极管对电容C2进行充电，该相输出端电位等同于负极点电位，输出电压U=-Vdc/2;若负载电流为负方向，则电源对电容C2充电，电流流过主开关管Sa3、Sa4注入负极点，该相输出端电位仍然等同于负极点电位，输出电压U=-Vdc/2。通常标识为“-1”状态，如图所示。 三电平逆变器工作状态间的转换
净化洁净车间操作规范 一、操作和使用 1、本洁净车间在使用前必须对周围的环境进行全面性清洁工 作，洁净室的一般清扫必须在生产工艺操作结束后进行，如 有必要在生产前清扫，则工艺生产必须在净化系统开机运行 时间达到自净要求后方可开始进行。为了防止交叉污染，清 扫洁净厂房设施的工具均应按产品特点、工序要求、空气洁 净度等级的不同分别专用。洁净室的清扫工具一般采用仪器 固定式或便携移动式真空清扫设备，以确保在定期清扫时能 清除微粒污染；也能有效地适时地清除某些不适合在洁净室 外进行工作所带来的污染。当设置集中固定式真空清扫系统 时，其排风机应安装在洁净室外；洁净室内的连接插座在不 使用时应严密封盖，以免危及洁净室内的压差或气流形式。 当设置便携式真空清扫设备时，应配置有排风过滤器，其过 滤效率应至少与所在洁净环境的等级相同；还应注意在使用 时对洁净室内气流的影响。若洁净室不具备上述清扫条件时， 也可采用不掉纤维的材料如丝光毛巾、尼龙由等进行擦拭， 一般每天1次或数次。当洁净室内产品生产工艺要求不能进 行擦拭时，应采用真空清扫设备进行清扫。 2、物料进出由不锈钢连锁传递窗或货淋室/缓冲间。（传递窗两个 门不能同时打开） 3、本洁净室在开机使用前应先检查各电器线路、设备是否完好，
工作人员在进入洁净室前，应预先开机15分钟，确保工作时 能达到洁净指标。 4、空调净化系统在关机前，应先关工艺设备后，送风机继续开 5-10分钟，方可关闭电源，特别是加热系统应先关闭加热器 20分钟后，才能关闭风机，切断电源。 二、洁净室的管理 1、对洁净室工作人员进入、物料进入、各类设备的搬入以及相 关的设备、管线的维护管理，应做到不得将微粒、微生物带 入洁净室。 2、操作管理人员，对洁净室内人员用洁净工作服的制作、穿着 和清洗；操作人员的移动和动作；室内设备及装修材料的清 扫、灭菌等。尽可能地减少、防止洁净室内尘粒、微生物的 产生、滞留、繁殖等。 3、严格各类设备、设施的维护管理，制定相应的操作规程，保 证各类设备设施按要求正常运转，包括净化空调系统、各类 水气电系统、生产工艺设备和工具等。以确保产品生产工艺 要求和空气洁净度等级。 4、进入洁净室的人员应严格执行人身净化制度、路线和程序， 任何人不得随意更改。在洁净室内必须按规定进行换鞋、更 衣，戴帽，经过缓冲间进入净化间。 5、作业人员在洁净室内工作时，动作要轻，严格按照操作规程， 不允许跑跳、打闹，不作不必要的动作，不作易发尘和大幅
无尘车间等级标准 无尘车间洁净度等级标准ISO14644根据悬浮粒子浓度这个唯一指标来划分洁净室（区）及相关受控环境中空气无尘车间洁净度的等级，并且仅考虑粒径限值（低限）～范围内累计分布的粒子群。根据粒子径，可以划分为常规粒子（～）、超微粒子（＜）和宏粒子（＞）。 空气无尘车间洁净度分级标准：GB/T16292-1996（中国标准） 美国联邦标准（USA Federal Standard） 空气中微粒的洁净等级对照 空气微粒洁净等级（每立方米，每立方英尺）微粒的最大浓度限值
中国药品生产洁净室（区）的空气无尘车间洁净度标准 国家药品监督管理局1999年8月1日发布实施 洁净室及洁净区空气中悬浮粒子无尘车间洁净度等级
国家标准GB50073-2001 无尘室的等级说明 使用者在开无尘室的等级给供货商时，有以下几个小技巧。 首先是等级定义的模式如下： Class X (at Y μm ) 其中X是无尘室的等级，例如100或10000等等，Y是粒径如μm , μm等，可复选。意思就是使用者规定，该无尘室微粒含量，在这些粒径必须满足该等级的限度。这样可以减少纷争，以下是几个例子： Class1 μm, μm , μm) Class 100μm , μm ) Class 100μm, μm , μm ) 在Classes 100 and Greater (Class 100，1000，10000....)，一般看一个粒径即可。在Classes Less than 100 (Class 10，1.... )，一般要看多几个粒径。 第二个技巧是规定无尘室的状态，例如： Class X (at Y μm )，At-rest 供货商就很清楚知道无尘室要在At-rest状态下验收。 第三个技巧是自订微粒浓度上限，一般在As-built时无尘室都很干净，微粒控制能力测试不易，这时可以干脆把验收上限压低，例如： Class 10000 μm <= 10000)，As-built Class 10000 μm <= 1000)，As-built 这样做的目的是确保无尘室在Operational状态时，依然有足够的微粒控制能力。
三电平逆变器的主电路结构 及其工作原理 -标准化文件发布号：（9556-EUATWK-MWUB-WUNN-INNUL-DDQTY-KII
三电平逆变器的主电路结构及其工作原理 所谓三电平是指逆变器交流侧每相输出电压相对于直流侧有三种取值，正端电压 (+Vdc/2)、负端电压(-Vdc/2)、中点零电压(0)。二极管箱位型三电平逆变器主电路结构如图所示。逆变器每一相需要4个IGBT开关管、4个续流二极管、2个箱位二极管;整个三相逆变器直流侧由两个电容C1、C2串联起来来支撑并均衡直流侧电压，C1=C2。通过一定的开关逻辑控制，交流侧产生三种电平的相电压，在输出端合成正弦波。 三电平逆变器的工作原理 以输出电压A相为例，分析三电平逆变器主电路工作原理，并假设器件为理想器件，不计其导通管压降。定义负载电流由逆变器流向电机或其它负载时的方向为正方向。 (l) 当Sa1，、Sa2导通，Sa3、Sa4关断时，若负载电流为正方向，则电源对电容C1充电，电流从正极点流过主开关Sa1、Sa2，该相输出端电位等同于正极点电位，输出电压 U=+V dc/2;若负载电流为负方向，则电流流过与主开关管Sa1、Sa2反并联的续流二极管对电容C1充电，电流注入正极点，该相输出端电位仍然等同于正极点电位，输出电压U=+V dc/2。通常标识为所谓的“1”状态，如图所示。
“1”状态“0”状态 “-1”状态 (2) 当Sa2、Sa3导通，Sa1、Sa4关断时，若负载电流为正方向，则电源对电容C1充电，电流 从O点顺序流过箱位二极管D a1，主开关管Sa2:，该相输出端电位等同与0点电位，输出电压U=O;若负载电流为负方向，则电流顺序流过主开关管Sa3和箱位二极管D a2，电流注入O点，该相输出端电位等同于O点电位，输出电压U=0，电源对电容C2充电。即通常标识的“0”状态，如图所示。 (3) 当Sa3、Sa4导通，Sa1、Sa2关断时，若负载电流为正方向，则电流从负极点流过与主开 关Sa3、Sa4反并联的续流二极管对电容C2进行充电，该相输出端电位等同于负极点电位，输出电压U=-V dc/2;若负载电流为负方向，则电源对电容C2充电，电流流过主开关管Sa3、Sa4注入负极点，该相输出端电位仍然等同于负极点电位，输出电压U=-V dc/2。通常标识为“-1”状态，如图所示。
目的：本规程《药品生产质量管理规范》（2010修订版）规定了洁净厂房清洁标准操作规程。 范围：本规程适用于洁净厂房清洁标准操作。 职责：质量管理部、生产部 内容： 1清洁准备 1.1清洁工具 不脱落擦布、塑料水桶、塑料刷、笤帚（不脱落）、簸箕、拖布（不脱落）。 1.2清洁剂和消毒剂 饮用水、纯化水、84消毒液、新洁尔灭溶液、臭氧。 1.3清洁频次 1.3.1每周末必须对洁净区进行局部清洁、消毒，包括地面、圆弧角、回风罩、直排风口、地漏。 1.3.2 每季度必须对洁净区进行全面清洁、消毒，并做洁净厂房清洁记录。 1.3.3 每周对洁净厂房进行臭氧消毒两次，并做臭氧消毒记录。 1.3.4 洁净区操作室的清洁依据岗位清洁sop进行清洁，并做清场记录。 1.4清洁要求 1.4.1洁净走廊的顶棚、灯罩、墙面、清洁后表面必须光亮。 1.4.2洁净走廊的地面、地漏、圆弧角、直排风口清洁后表面必须见本色。 2清洁方法和程序 2.1顶棚、灯罩、墙面的清洁 2.1.1 用饮用水洗净擦布并挤压去水后将顶棚、灯罩、墙面擦拭至表面见光亮。 2.1.2 用消毒液擦布将顶棚、灯罩、墙面擦拭、消毒。 2.2直排风口的清洁
2.2.1 用塑料刷将直排风口黏附的粉尘刷去。 2.2.2 用纯化水洗净擦布并挤压去水后将直排风口擦拭至表面见本色。 2.3地面、圆弧角的清洁 2.3.1 用饮用水洗净拖布并挤压去水后将地面拖拭至表面见本色。 2.3.2 用消毒液拖布将地面拖拭、消毒。 2.4地漏的清洁、消毒 2.4.1 刷洗地漏盖、地漏凹槽内的杂物，用饮用水冲洗地漏至表面见本色。 2.4.2 在地漏凹槽内加入消毒液，将地漏盖扣住，液封 3消毒液的配制 3.1配制方法依据消毒液的说明书进行配制。 3.2消毒液隔月交替使用。 4洁具的清洁和存放 4.1擦布、拖布、塑料桶、笤帚、塑料刷、簸箕在洁具洗涤间用纯化水清洗至水质清澈。 4.2已清洁洁具拧干或擦干后放于洁具存放间规定的位置，挂“已清洁·待用”状态标识卡。 4.3每周末将洁具洗净后置于消毒液中浸泡30min用纯化水冲洗后晾置。
摘要 三相三电平逆变器具有输出电压谐波小，/ dv dt小，EMI小等优点，是高压大功率逆变器应用领域的研究热点，三相二极管中点箝位型三电平逆变器是三相三电平逆变器的一种主要拓扑，已经得到了广泛的应用。三相T型三电平逆变器，是基于三相二极管中点箝位型三电平逆变器的一种改进拓扑。这种逆变器中，每个桥臂通过反向串联的开关管实现中点箝位功能，是逆变器输出电压有三种电平。该拓扑比三相二极管中点箝位型三电平拓扑结构每相减少了两个箝位二极管，可以降低损耗并且减少逆变器体积，是一种很有发展前景的拓扑。 本设计采用正弦脉宽调制（SPWM），本文介绍了三相T型三电平逆变器的设计，介绍其结构和基本工作原理，及SPWM控制法的原理，并利用SPWM控制的方法对三电平逆变器进行设计与仿真。本设计采用SIMULINK对T型三电平逆变电路建立模型，并进行仿真。 关键词： T型三电平逆变器、正弦脉宽调制、SIMULINK仿真
目录 第一章绪论 (6) 1.1研究背景及意义 .. 1.2三电平逆变器拓扑分类 第一章 T型三电平逆变器工作原理分析 (6) 1.1逆变器的结构 1.2本章小结 第二章正弦脉波调制（SPWM） (7) 3.1 PWM与SPWM的工作原理 3.2三电平逆变电路SPWM的实现 3.3本章小结 第三章电路仿真与参数计算 (10) 4.1逆变器的基本要求 4.2电路图 4.3调制电路 4.4L-C滤波电路 4.5结果分析 第四章课程设计小结 (14) 参考文献 (15)
第一章绪论 1.1 研究背景及意义 近年来，随着经济的飞速发展，人类对能源的需求也大幅度增加，而传统能源面临着枯竭的危机。在这种情况下，我们不得不加速开发新型能源。各国的专家致力于新能源的开发与利用，光伏发电、风力发电、生物发电等各种新型发电技术已经得到了一定的应用，并且正在蓬勃的发展，尤其是光伏发电，因其成本低、稳定性较好，控制简单等优点，在各国得到了广泛的应用。受地区气象条件的影响，太阳能光伏电池板输出的直流电压极不稳定，而且电压幅值低，容量小。为了高效利用太阳能，需要将不稳定的光伏电池串、并联组合，并且经过多级电力电子变换器组合输出恒频交流电压并网运行。而把这些初始能源转化为可用电能的桥梁就是逆变器。随着开关器件的不断发展，逆变器的拓扑、调制方式和控制策略也在不断发展，控制理论在逆变器的控制上得到了很好的应用，这一切都保证了优良的供电质量。在一些高电压、大功率的应用场合，传统的两电平逆变器由于开关器件耐压限制，无法满足需求。在这种情况下，如何将低耐压开关器件应用于高电压大功率场合成为各国专家研究的热点，由此，多电平逆变器技术应运而生。多电平的概念最早是由日本专家南波江章(A.Nabae)等人在 1980 年提出的[1]，通过改变主电路的拓扑结构、增加开关器件的方式，在开关器件关断的时候将直流电压分散到各个器件两端，实现了低耐压开关器件在大功率场合应用。 1.2三电平逆变器拓扑分类 常见的多电平的电路拓扑主要有三种：二极管箝位型逆变器、飞跨电容箝位型逆变器和具有独立直流电源的级联型逆变器。本文研究的 T 型三电平逆变器可以说是中点箝位型逆变器的改进拓扑，其优势主要体现在减少了电流通路中的开关器件数量，减少了传导损耗。而且与二极管箝位型三电平逆变器相比，T 型三电平逆变器的每个桥臂少用了两个箝位二极管，其控制方法和二极管箝位型三电平逆变器类似[2]。T 型三电平逆变器融合了两电平和三电平逆变器的优势，既有两电平逆变器传导损耗低，器件数目少的优点，又有三电平逆变器输出波形好，效率高的优点，是很有发展前景的一种三电平逆变器拓扑。
无尘车间洁净度标准文件编码（GHTU-UITID-GGBKT-POIU-WUUI-8968）
无尘车间洁净度如何确定详细分析一、净化车间的规格 净化车间的规格一般适用于美国联邦规格。这个规格对净化间的环境要素即 空气洁净度、温湿度、室内压等都进行了规格化规定。但是，伴随着洁净化程 度的不断提高，美国联邦规格进行了改版，其内容主要是以洁净度进行分类。 最新版已成为No209E，名称也进行了变更。的级别表示是把以上的颗粒数为10x 个/m3，把X表示成级别，同时加上米制M的意思，表示成等等。在表7里表示 的是美国联邦规格，表8表示的是美国联邦规格。在日本，相应的规格是JIS B9920。JIS9920的级别表示是把以上的颗粒数规定为10X个，用Y表示级别。 表9、图2表示了JIS B 9920的级别的主要内容。 表7 美国联邦规格 表8, 美国联邦规格的洁净度级别分类
级别上限值是各级别名。上限值用指定粒径以上的浓度（单位堆积粒子数）表示。* * 上表中表示的级别上限值仅仅是为了级别分类而定义的，并不表示实际的粒径分布值。 ** 针对中间级别的浓度上限值，用如下的公式进行计算。 粒子直径/m3=10M d)，其中，M : SI单位里的级别名称，D : 粒径（um） ***国际单位（Systeme International d’Unites的缩写） 图1 ，209E的洁净度级别（图略）图中的●标记表示评价洁净度级别用的对象粒子。 （）内数值是用English unit 表示级别。 图2 ，JIS B 9920的洁净度级别的上限浓度
表9，JIS B 9920主要内容 表10，美国航空宇宙局规格主要内容 三、不同用途所要求的洁净度 如前所述，净化间的级别一般分成（100）、（1000）、（10000）、（100000）4个级别。但根据各产业领域的作业工序不同，形成必要的级别是不一样的。例如，在半导体制造工厂等里边，根据作业内容，要求有M1（10）—（1000）的净化间。而且，在制药工厂里，根据产品的纯度、作业工序，需有
洁净厂房清洁、消毒的标准操作规程 1.目的:建立一个洁净厂房清洁、消毒的标准操作规程,指导清洁操作。 2.范围:适用于公司内各洁净级别厂房的清洁操作。 3.职责:洁净区工作人员对本规程的实施负责。 4.内容: 4.1清洁剂:注射用水、纯化水、洗洁净 4.2消毒剂: (10.1%新洁尔灭、0.5~1%84消毒液、3~5%苯酚、0.5%过氧乙酸、0.05%~0.1%杜灭芬(消毒宁,使用的消毒液品种需每半月更换一次。 (2甲醛溶液、乳酸。 4.3清洁工具:不脱落纤维的抹布、胶棉拖把、水桶。 清洁工具应专区专用,不得混用。 4.4清洁原则:先上后下、先内后外、先高级别后低级别。 4.5C级(局部A级区的清洁、消毒: 4.5.1清洁周期: ①每一生产阶段结束后; ②房间(区域虽已清洁合格,但超过48h,准备再次使用前; ③房间(区域内发生了可能影响洁净度的变化时。
4.5.2将上次生产的所有遗留物或不属本区域的物品、器具移出本区域;将需拆卸清洗的管道等物品移至器具清洗室;将室内物品定置归位。 4.5.3从本级别的洁具存放间内取出清洁工具,将本区域台面专用抹布在注射用水中浸润后,拧干,依次擦拭本区域内各操作间内工作台(包括台面、边缘及桌腿、设备外表面(设备表面有油污时,应换用设备专用抹布擦拭、室内用具、塑料凳、传递窗内四壁及本侧门和边框、水池内外、回风窗、门窗(包括门把手、墙壁、固定管路 外表面等。 4.5.4用清洁拖把在纯化水中浸润、拧干后擦拭操作区域的墙壁(包括缓冲走廊。 注:①每15L水所擦拭的面积不得大于25m2,超过此范围,需换水。 ②抹布每擦拭一块区域后应及时清洗,拧干后再用。 4.5.5用地面专用抹布或拖把在注射用水中浸润、拧干后,擦拭地面。 4.5.6改用消毒剂按4.5.3~4.5.5清洁、消毒上述区域。 注:抹布或拖把必须在消毒液中浸泡至少3分钟后再开始使用。 4.5.7在正常生产的情况下,每周的最后一个工作日生产结束后,除按上述程序进行清洁外,还需分别用注射用水和消毒液对本区域的顶棚、灯具及水池下方等进行擦拭清洁、消毒。 4.5.8局部A级区应在每次生产的前一天进行乳酸熏蒸消毒。 4.5.8.1消毒用具的准备:从控制区消毒剂存放间取出消毒用试剂(乳酸、酒精等、不锈钢盘、三脚架、酒精灯等。按《器具、物料进入洁净室的标准操作规程》(SOP-进行清洁消毒后,经脱包室、十万级理瓶室、万级精洗室、传入局部百级区。
无尘车间管理制度 5．1 洁净室人员管理制度 5．1．1 洁净室的人员管理包括：制定专职管理人员的职责、洁净室人员的准入制度、人员培训教育规定、进入洁净室人员的“人净程序”管理和退出管理制度等。5．1．2 人员净化与进入 5.3.2.1在洁净厂房内众多的污染源中，人是主要污染源之一，尤其是工作人员 在洁净环境中的活动，会明显地增加洁净环境的污染程度。 5.3.2.2对于高级别洁净区域，应严格控制进入人员数量，并规范进行二次更衣。 5.3.2.3要获得生产环境所需要的空气洁净度等级或延长空气过滤器的使用寿 命，对进入洁净室的人员、物料进行净化十分必要。 5.3.2.4为保持洁净室空气洁净度，应尽量减少进入洁净室人员带入的污染物。 所有进人洁净室的人员必须严格地按规定程序进行人身净化。 5.3.2.5个人衣服物品全部放到指定的柜子里，去掉化妆，换上指定的服装，按 空气洁净度等级相应的脱衣顺序脱衣，放在规定的衣柜内。 5.3.2.6进入脱衣室，在更衣凳前将皮鞋、拖鞋、帆布鞋等脱下放在鞋柜内，禁 止不脱鞋直接跨越更衣凳而进入更衣室。 5.3.2.7若公司后期发展需要更高洁净级别要求的洁净区域（指高于ISO Class7 级别）进入前，需要设置盟洗室用洗手器洗手（先用洁净洗涤剂洗涤， 再用洁净水冲洗。洗涤后用自动烘手器烘干）。 5.3.2.8凡是交叉污染的媒介，要经常洗涤。不要用手触及高净化产品和高净化 包装材料等。要按规定戴手套和指套。 5．3．3 洁净室工作人员须知
5.3.3.1进入洁净室的人员应严格执行人身净化制度、路线和程序，任何人不得 随意更改。在洁净室内必须按规定着衣、戴帽、换鞋。 5.3.3.2进入洁净级别1万级以及高于万级的洁净区域，必须至少经过二次更衣。 可先从一次更衣室进入，进行更鞋、脱外衣、换洁净服、戴口罩、帽子 （或洁净头套）后，经过走廊进入二次更衣室，进行二次更衣、更鞋、 戴防静电腕带、戴口罩、戴帽子，确认更换完毕后，进入风淋室进行风 淋后，才能进入万级以及高于万级的洁净区域。 5.3.3.3严禁不通过风淋而直接走旁通门进入洁净室。旁通门只允许人员出到洁 净间外以及发生紧急情况时的进出。 5.3.3.3.1风淋室使用须知 A. 风淋室是工作人员进入净化区域前进行人身净化的专用设备，它能将人体表 面吸附着的尘埃用高速气流吹去，使工作人员不带污染源进入净化区域，并 能使净化区域与非净化区域起到气闸作用。 B. 风淋室设定和状态：风淋室在投入使用前必须完成调试和设定，使之保持自 动风淋状态。 C. 风淋室使用 ?使用者无需按任何键即可开门进入风淋室内，人数每次限定三人,把门关好即可自动风淋,风淋时旋转身体360度, 等待风机停止工作以后蜂鸣 响，内门开锁，用户出风淋室。 ?按“照明开”键即可打开室内照明灯。 ?风淋室的微电脑对所做设定有记忆功能,关闭风淋室电源再次打开电源时风淋室处于上次操作的最后设定状态。 ?禁止一线使用者对设备的数值设定进行更改，数据更改必须由专业的管理人员进行。 ?禁止使用者野蛮对风淋室的门（红外电控锁）强行推拉而损坏设备。 ?风淋设备若因使用不当而损坏，使用部门应据实反映损坏原因，并立即报修。 ?一线员工在使用过程中发现状态异常，应立即通知主管部门进行处理； 并停止使用风淋室。 D. 风淋室正常/异常状态的界定：
三电平逆变器基本介绍一、三电平逆变器的基本工作原理 + BUS + 1 2 V DC C 1 D 3 Q 1 Q 2 i L L C + u C D 1 GND + u 负 载 Q 3 + 1 2 V DC C 2 D 4 D 2 Q 4 ? BUS 图1三电平逆变器主电路
图2四个开关管的驱动信号波形
当u>0时，u=S* *1/ 2V DC，且S* =1表示Q1 通Q3 断，S* =0 表示 Q1断Q3通； 当u<0时，u=(S* ?1) *1/ 2V DC，且S* =1表示Q2 通Q4 断，S* =0 表示Q2断Q4通； 由以上可见，S1代表了Q1 通（输出电压的正半周）或Q2 通* = （输出电压的负半周），而由图2 可见，Q1 正半周与Q2 负半周的驱动波形组合起来与原两电平的上管驱动波形完全一致，因此可以直接在原两电平的控制器平台上进行一定的修改，即可得到适合于三电平的控制器。 u = V S *1/ 2V DC = DC 4V t (S1) *1/ 2V ?= DC *v m t V DC 4V 1 4 + V DC 1 ? *v V m DC 4 u u > < 时 时
图3三电平逆变器模型（包括调制部分）
图4三电平逆变器的控制框图二、三电平逆变器的缓冲电路 P1P2 + 1 2 V DC ? G2 G1C DC1 D R1 1 C 1 D 3 Q 1 Q 2 A L i L +u C + u C ? 负 载 + 1 2 V DC ?C DC2 C 2 D R2 2 D 4 Q 3 Q 4 N1N2 图 5 实验中所采用的NPC 缓冲电路
三电平逆变器基本介绍 一、三电平逆变器的基本工作原理 DC V 2 1DC V 21 图1 三电平逆变器主电路 图2 四个开关管的驱动信号波形
当u 时，u ，且表示Q1通Q3断，S 表示 Q1断Q3通； 0>DC V S 2/1**=1*=S 0*= 当u 时，u ，且表示Q2通Q4断，表示Q2断Q4通； 0
图4 三电平逆变器的控制框图 二、三电平逆变器的缓冲电路 DC V 21DC V 21 图5 实验中所采用的NPC 缓冲电路
实验中发现在突加RCD 负载时会在Q2、Q3上产生很大的电压尖峰，经仔细分析，主要有以下两个方面的原因： 第一：在突加RCD 负载时会产生很大的电流尖峰，由于控制板在设计时考虑的状况是当出现过流信号时同时封锁Q1、Q2、Q3、Q4的驱动信号，从而导致A 点电位在封锁Q1、Q2、Q3、Q4驱动瞬间的变化最大幅值可以达到V ，很类似于两电平逆变 器工作时的状态，容易导致开关管上出现电压尖峰。 DC 解决办法：当出现电流尖峰时仅仅封锁Q1、Q4的驱动信号，而Q2、Q3的驱动不封锁，仍然保持原状态不变，如此一来在封锁Q1、Q4驱动瞬间A 点电位的变化最大幅值仅仅为1，因此大大减小了开关管上的电压尖峰。 DC V 2/第二：在突加RCD 负载时输出电压的正负半周会出现误判的状况。 以一个实际的工作状况对此加以说明，假设当前处于桥臂输出电压的正半周，但是由于此时突加RCD 负载因此误判为是在电压的负半周，因此会做以下操作：将原来处于开关状态的Q1改为常断；将原来常通的开关管Q2改为开关状态；将原来处于开关状态的开关管Q3改为常通；将原来常断的开关管Q4改为开关状态，而在此转换过程当中，负载电流很大，很容易在开关管上产生电压尖峰。
无尘车间管理规范 集团文件版本号：（M928-T898-M248-WU2669-I2896-DQ586-M1988）
无尘车间管理规范 核准：审核：编制： 会签 ■生产部■品质部■工程部■市场部■行政部■研发部■资材部PMC■资材部采购■资材部仓管 修订履历 1.0目的 加强无尘车间管理规范，约束员工行为，以提高产品合格率，为产品质量所需生产环境提供保障。 2.0适用范围 公司无尘车间及所有进出无尘车间人员。 3.0职责 3.1生产部 对环境、温湿度及压差进行日常定时监控并记录。 负责对无尘车间之温度、湿度及气压差进行判断及不定期监控； 负责对风速、尘埃进行日常测量、监控、判断与记录； 对环境出现异常状态时，对是否继续生产做出相关决定，并对环境改善效果进 行确认。 3.2异常处理 生产出现异常时，负责对其发生异常原因进行分析，并制定相应之应急措施以及长期改善措施。 3.3各部门 3.4.1凡进入无尘车间的员工必须遵守并执行本规定； 3.4.2必要时，协助品质及工程人员分析并改善环境之异常。 4.0作业程序 4.1人员管理 4.1.1 体质的要求：选取的作业者应该排除以下不适当的体质者从事无尘车间的作业； 各种严重皮肤病，如湿疹、皮肤受重伤等；
对于化学物有过敏的体质者； 对于无尘车间里使用的材料有过敏体质者； 与普通人相比有异常，如皮肤很多脱皮、头屑和头发容易掉者； 化装（特别是擦粉）和擦指甲油者（基础性化装除外）； 4.1.2 精神上的要求：应该选取以下特性的人从事无尘车间的作业； 注意力集中，忍耐性强的人； 对周边能经常整理整顿和打扫者； 对健康状况有经常注意者； 4.1.3 外来人员及我司生产部相关以外人员，需进入无尘车间者需先申请，待批准后 由我方人员陪同在场并按要求穿戴好无尘服，在风淋室门外册子上做好记录并 戴好出入证后，才能进入； 4.1.4除工作环境（例如生产人员、工程技术人员等）在无尘车间的人员外，其他 需进入无尘车间者也需要在风淋室门外册子上做好记录并戴出入证； 4.1.5无尘车间OCA贴合车间静电棚中除里面的工作人员以外，同时进入的人数 （流动人数）不得超过2人。 4.2 物品与资材管理 4.2.1无尘车间内禁止迁入的物品； 4.2.1.1未经过批准的清洁的用具、办公用具、测试夹具等一切物品； 4.2.1.2以下是作业者个人严禁携带的物品； 香烟、火柴、打火机等 饮料、口香糖、食品类 个人装饰品、化装品（金属性、特别是戒指禁止戴） 手机通信物品 手册或其他个人物品 4.2.2 无尘车间材料运输方法 4.2.2.1无尘车间迁入的一切材料，包括物品工具、设备材料等，禁止没有清洁而直 接进入； 4.2.2.2清洁方法、污染物的种类、需清洁物品的状态、构造、材料特性、清洁度的 要求等问题由无尘车间的管理者决定； 4.2.2.3 对于无尘车间迁入的设备等大型物品应从开始的污染区中用吸尘器或通过 吹气达到必要的清洁； 4.2.2.4无尘车间里使用的一切小型物品要用风淋吹干净； 4.2.2.5 无尘车间里面的设备或物品要尽量少搬迁； 4.2.3无尘车间所使用的化学物品必须加贴标示。
242IEEE TRANSACTIONS ON POWER ELECTRONICS,VOL.15,NO.2,MARCH2000 A Comprehensive Study of Neutral-Point V oltage Balancing Problem in Three-Level Neutral-Point-Clamped V oltage Source PWM Inverters Nikola Celanovic,Student Member,IEEE,and Dushan Boroyevich,Member,IEEE Abstract—This paper explores the fundamental limitations of neutral-point voltage balancing problem for different loading con-ditions of three-level voltage source inverters.A new model in DQ coordinate frame utilizing current switching functions is developed as a means to investigate theoretical limitations and to offer a more intuitive insight into the problem.The low-frequency ripple of the neutral point caused by certain loading conditions is reported and quantified. Index Terms—Neutral-point voltage balancing,space vector modulation,three-level converter. I.I NTRODUCTION S INCE it’s introduction in1981[1],the three-level neutral-point-clamped(NPC)voltage source inverter(VSI),Fig.1, has been shown to provide significant advantages over the con-ventional two-level VSI for high-power applications. The main advantages are as follows. 1)V oltage across the switches is only half the dc bus voltage. This feature effectively doubles the power rating of VSI’s for a given power semiconductor device.Moreover,this is achieved without additional,often cumbersome,hard-ware for voltage and current sharing. 2)The first group of voltage harmonics is centered around twice the switching frequency[1],[7].This feature en-ables further reduction in size,weight,and cost of passive components while at the same time improving the quality of output waveforms. On the other hand this topology also has its disadvantages. 1)Three-level VSI’s require a high number of devices. 2)The complexity of the controller is significantly in- creased. 3)The balance of the neutral-point has to be assured. The three-level VSI was first considered with respect to high-capacity high-performance ac drive applications[1].To this day, it remains the area where this topology is most widely used [2]–[4],[7]–[9],[15],and[16].Other interesting applications of Manuscript received March10,1999;revised September22,1999.Recom-mended by Associate Editor,F.Z.Peng. The authors are with the Department of Electrical and Computer Engi-neering,Virginia Polytechnic Institute and State University,Blacksburg,V A, 24061-0111USA. Publisher Item Identifier S 0885-8993(00)02327-9. Fig.1.Circuit schematic of a three-level VSI. this technology include static V AR compensation systems[11], [12],HVDC transmission systems[18],active filtering applica- tions,as well as applications in power conditioning systems for superconductive magnetic energy storage(SMES)[13]. The neutral-point(NP)voltage balancing problem of three-level NPC VSI’s has been widely recognized in litera- ture.Various strategies have been presented,and successful operation has been demonstrated with a dc-link voltage balance maintained.In addition,some of the proposed algorithms avoid the narrow pulse problem[5],[9],minimize losses by not switching the highest current[10],or share the balancing task with front-end converters as in[2]. NP control for the carrier-based PWM has been studied in[15]–[17].In[15],the switching frequency optimal PWM method is introduced.This method controls the NP by,essen- tially,adding the zero sequence voltage to the inverter output. This work was extended in[16],where the authors propose an analytical method for analysis of the NP potential variation, show some limitations of the NP control,and also deal with the dc-link capacitors design issues.In[17],the authors analyze the stability of the NP control based on an insightful dynamic model of the NP control they developed. This paper discusses the issues of NP control from the space vector modulation(SVM)point of view.In addition,the broader range of inverter operating conditions is addressed,and a new mathematical formulation of NP balancing problem is given. Furthermore,low-frequency NP voltage ripple,normalized with the output current and the size of the dc-link capacitors,is given for all operating conditions. 0885-8993/00$10.00?2000IEEE