Energy and Power Engineering, 2013, 5, 713-716
doi:10.4236/epe.2013.54B138 Published Online July 2013 (http://www.scirp.org/journal/epe)
Research and Implementation of the Power Equipment
Inverter Switching Algorithm
Jinquan Wang, Jianke Li, Jingjing Chen, Shuhua Qian, Pengfei Hou
PLA Univ. of Sci. & Tech., College of National Defense, Nanjing, China
Received March, 2013
ABSTRACT
Frequency control technology can achieve the purpose of energy saving of power equipment, but also bring problems of
harmonic loss formula. The relationship between the loss rate and load rate is constituted by formula derivation, and
calculate the load rate when the loss rate is the minimum and the total power of power-consuming devices. Then design
the digital PID controller and research the power-saving optimization feedback algorithms and design the software
process. Finally, carry out the inverter switching algorithm based on ABB ACS510 low voltage inverter.
Keywords: Frequency Conversion; Power Loss; Energy-saving; Load rate
1. Introduction
With the continuing development and application of fre-
quency conversion speed regulator, a large number of
convertors are used to control the fan and pump load in
industrial and civil fields in order to achieve variable-
speed energy-saving operation which bring considerable
economic benefits [1-3]. The inverter is actually a power
electronic conversion apparatus, due to the nonlinear
characteristic of the power electronic switches, causing
the input current waveform distortion when transforming
the power which means that produce harmonics and in-
ject into the grid [4].
The harm of harmonics is quite serious, including re-
ducing the reliability of power supply, decreasing the
effective capacity of the system, affecting the operating
of the devices, making the electromagnetic environment
deteriorative and resulting in the increase of the power
system losses. One of the important research directions
of harmonic and its hazards is that harmonic arouses the
additional loss of power system [5-8].
The George J. Wakileh produces the calculation method
of power equipment heat loss [9]. Zhang Qi conducts the
simulation research that the skin affects wire with har-
monic. The additional loss which generate by harmonic
will increase the total power loss of power supply and
distribution system.
The additional loss of the power system generated by
harmonic counteracts with part energy which saved by
frequency conversion speed regulator. Therefore, the
efficiency of energy fails to achieve the desired effect.
Nowadays, some literatures just research the harmonic
power loss of each device, such as motor and transformer.
However, there is no qualitative and quantitative research
about the problems of frequency conversion energy sav-
ing with considering the harmonic power loss.
2. The Principle of Energy-saving
Taking the control system of airiness frequency conver-
sion for example, hypothesis the total power of system is
P and total loss power is ΔP. PA represents variable loss
power and PB represents constant loss power. β symbols
of load rate and PN symbol of the rating power. The ac-
tual power is PL. That is:
L
PP P

 (1)
A
PP P
B

 (2)
ρ represents the attrition rate which is the ratio of power
loss and input power.
L
PP
PP P



 (3)
Substituting (1) and (2) into (3). And (3) can also be
rewritten as:
2
2
BA
N
BA
PP
PP P



 (4)
where,
L
N
P
P
 , PB and PN are constant.
Derivative with β on both sides of (4),

J. Q. WANG ET AL.
714
22
22
2()()( 2)
()
ANBA BANA
NB A
PPPPPPP P d
dPPP
  

 

(5)
The attrition rate ρ is minimum when (5) equal to zero,
and the load rate is:
0
B
A
P
P
  (6)
According to the definition of load rate, the actual
power PL0 is,
0
B
LN
A
P
PP
P
 (7)
The optimize energy of ventilation system consuming
is achieved by substituting (2) and (2) into (1),
0
B
N
A
A
P
PP PP
P

B
(8)
Through the above analysis, it can be drawn: the
minimum loss rate of the system changes as the load
changes. And the loss power is the smallest when the
system is running in the minimum loss rate, with highest
efficiency. According to the minimum loss rate, in order
to reach the purpose of energy-saving, the optimal oper-
ating range of the equipment can be obtained by calcu-
lating, then making reasonable optimization scheduling
to equipment, such as inverter switching, speed control,
transformer switching.
3. Inverter Power Saving Optimization
Algorithm
Inverter input and resection point is that the loss power
of power equipment running separately and with inverter
operation. That is,
ΔP0=ΔP1 (9)
where, ΔP0——The loss power when transducer doesn’t
work.
ΔP1——The loss power when transducer work.
(9) also can be written as,
2
2.
BAH BAH
NBAH NB AH
PP PP
PPP PP P




 (10)
In order to ensure the running of the fan according to a
predetermined optimal scheduling, a PID controller is
adopted to implement feedback control on fan.
3.1. Design of Digital PID Controller
The core idea of the digital PID control is that the con-
tinuous signal which measured by the sensor converted
to a unified standard signal which pour into PID regula-
tor and a given frequency of transducer is obtained after
operating by regulator. And this can control the speed of
fan. Control process shown in Figure 1.
3.2. Research of Feedback Arithmetic
The control law of PID controller can be described by
formula (11),
 
0
1
1t
PD
de t
utKetetdt T
Tdt


 




 (11)
where, KP—Proportionality coefficient
TI—Integral coefficient
TD—Differential coefficient
The main unit is unable to control objects with con-
tinuous control. The only method is discrete treatment,
then performing PID control by software algorithms. In a
continuous time t, sample k times with sampling cycle T,
after discrete transformation can be obtained,



 

00
1
k
k
k
t
i
j
kk
ut u
et e
etdt Teut
de tee
dt T


 











 (12)

1
1
1
k
D
kpkj kk
j
T T
uKee ee
TT





 




 (13)
where, k=1, 2, 3…

1
11 1
1
1
k
D
kpkj kk
j
T T
uKee ee
TT

 


2







 (14)
where, k= 2, 3,4…
1kkk
uuu


 (15)

1
0
1
1
1
2(1)
PDP
P
I
PDP
I
k
PDP DP
Pk
I
DP
Pk
TKTK
Ke
TT
TKTKek
TT
u
TK TKTK
k
K
ee
TT T
TK
Kek
T



 






 





 




 



(16)
Figure 1. Control process.

J. Q. WANG ET AL. 715
where, Δuk—Increment value of the k times sampling
ek—The deviation value of the k times sampling
time input
In order to prevent integral saturation brought by mo-
tor speed changing largely, integral separation method
can be used to control. Hypothesis emax is the upper limit
of the sampling deviation value, if |ek | <emax , PID con-
trol is applied, and vice versa PD control is applied, il-
lustrating by (18) and (19).

1
0
10
()
PDP
P
I
PDP
kk
I
DP DP
Pk
TKTK
Ke
TT
TKT K
ue
TT
TK TK
Keee
TT







 








max
max
ee
e
(17)
1
max
1
2max
2
()
2
()
DP DP
PkDk
DP
k
k
PDP DP
PkP
I
DP
kk
TK TK
KeK e
TT
TK ee
T
uTK TKTK
k
K
eK e
TT T
TK eee
T



 

 
 

 





 





 


(18)
4. Transducer Power-saving Switching
Realization
Visual Basic 6.0 software (VB6.0), a flexible and easy to
operate, is used to describe the power-saving system of
frequency conversion power equipment, mainly includ-
ing the design of man-machine interface, switching man-
agement on transducer and controlling power equipment,
communicating between the host computer and the digi-
tal variable frequency control cabinet by communication
protocol to complete remote operation.
4.1. The Design and Development of Software
Process
The software process designing of transducer power-
saving consists of closed-loop control process designing
and inverter switching control design.
1) Closed-loop control process designing
The designing of PID algorithm process is shown in
Figure 2, and the designing of the fan closed-loop con-
trol process is shown in Figure 3. The system can control
the fan speed according to the PID algorithm to achieve
the purpose of adjusting the amount of wind.
2) Single wind turbine power saving process designing
Single wind turbine power saving process is shown in
Figure 4. After device initialization, the system operates
based on the real-time data, when the loss of all system is
greater than the electricity savings, the transducer opera-
tion; contrary resection inverter.
Figure 2. PID algorithm.
Figure 3. Motor control software flowchart.
Figure 4. Frequenc y c o nver sion power counter.

J. Q. WANG ET AL.
716
4.2. Hardware Implementation
According to the characteristics of wind turbine equip-
ment, ABB ACS510 low voltage inverter which is a
high-quality motor frequency control devices is taken for
example. It is widely used in the industrial field, espe-
cially suitable for fan and pump drive control, with ad-
vantages of reliable operation, low noise motor, and sim-
ple installation.
Design power supply and control circuit based on the
technical requirements of the ACS510. Figure 6 shows
power counter with transducer.
5. Conclusions
Controlling power equipment, such as fans, pumps, with
transducer can achieve the purpose of energy-saving.
However, in the meantime, also produces a lot of har-
monic powers. Minimum loss rate of system changes as
the load changes. The loss power is at the bottom when
the system runs at the minimum loss rate. If the lowest
loss rate is known, the optimal operating range of
equipment can get by calculating, resulting in reasonably
optimized scheduling, such as transducer switching,
speed control, to reach the aim of energy-saving.
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