GUIDELINES FOR THE PREPARATION OF



Speed Control of Induction Motor by Z-source Indirect Matrix Converter with PSO PI Controller

|Majid salim *, Mohammad sarvi**, and Mohsen rezaei*** |

|*Islamic Azad University Saveh Branch, Ma.salim1986@ |

|**Imam Khomeini International University, Sarvi@ikiu.ac.ir |

|***Third Author Affiliation, Third Author Email |

Abstract: In this paper the results which are produced by simulating the Z-source indirect Matrix converters for induction motor speed control are shown. The method used for this purpose is flux control keeping the V/f ratio and regulating slippage. For achieving to desirable voltage at different frequencies with much or less transmitting voltage ratio, the modulation coefficient at inverter section and the shoot-through at Z-source has been used. Also, for optimizing the PI controller coefficient at proposed system PSO Algorithm and for showing the results of PSO Algorithm and for showing the results of simulation in matlab/simulink, the parameters of an induction motor 5HP has been used. The results show to using the proposed system and indirect z-source matrix converter, appropriate velocity and desirable torque are obtained in a short time. Keywords: Z-source indirect matrix converter, Induction motor, Pso algorithm

1. Introduction

Experts and engineers in power electronic and industrial have always paid interested in how to motor speed control.

Thus; there has always been an attempt to present effective and useful methods for this important matter. To change frequency and AC voltage level, Conventional transformers first convert the input voltage to DC and then transform it to a desired AC level. The operation can result in loss and harmonic in the form of voltage wave and current. On the other hand; this is while we need high capacity elements to store energy. Direct converters such as cyclo-converters are not favourable as they cause harmonic in voltage and current and affect the speed and torque of motor negatively [1,2,13].

Also, only the output frequency can be a less than input frequency [3]. The matrix converter (fig.1) and its controlling method were presented in 1985 by Venturini and because of some problems it could not find a huge application in the industry [4]. Matrix converter besides such advantages as simplicity and integrity, possibility of adjusting output frequency and voltage in a wide range, no need to energy storing parts of high capacity and high coefficient of power[5-8], has also disadvantages such as the low level of voltage transfer ratio (about 0.866). in this article, the model of indirect matrix converter that is made of the direct one having 18 unidirectional switches.

(As shown in fig. 2) so that 12 switches are placed in the rectifier section while 6 switches are placed in the inverter section.

Fig.1: Direct matrix converter

Using the impedance network converter (z-source) [9]in the indirect matrix converter can solve the problem of the voltage transfer ratio in the converter and regulate it at a desirable value. Since in the matrix converter the power conversion can be done directly, there is no need for energy storage requirements.

Fig.2: Indirect matrix converter

Moreover, the converter can accommodate the changes in moment-speed in induction motor in four quarters that proves advantageous compared to other types of converters[10]. The control method of motor speed control here V/F is for the stabilization of flux and maximum torque for all of the speeds in the offered system [11] and for a good response, PI controllers have been optimized by particle swarm optimization( PSO) algorithm[12].

2. Z- source Indirect Matrix Converter (ZSIMC)

As it was mentioned before, one of the disadvantages of matrix converter is the low level of voltage transfer ratio.The problem however could be resolve by juxtaposing an impedance network converter with matrix converter.Fig.3 shows the ZSIMC.

Fig.3:Z-source indirect matrix converter

2.1 Configuration and Operating Principle

As shown in fig.3, converter has been formed of three main sections:

The rectifier section includes 6 bidirectional switches, the impedance network is a joint between rectifier part and inverter which Also carries out the function of increasing the voltage transfer ratio and the inverter section made up of 6 unidirectional switches and the converter's output is for connection to the load. PWM technique has been applied to control the switches in the rectifier section so that at any time, the highest positive or negative three-phase input voltages are put in the rectifier output. The working and switching stages are presented in Fig.4. The impedance network (Z-Source) operates in the two operational modes of Active and Shoot-through. These modes are created by the switches operating in the inverter section. Simple boost control method is applied to control the operational modes of the impedance network alongside inverter. The process is shown in Fig.5[9].

Fig.4:Rectifier stage in Z-source indirect matrix converter

Fig.5:Simple boost control method

2.2 The Calculation of Voltage Transfer Ratio

Let’s assume the three-phase input voltage follows the (1):

((((((((((((((((((((((((((((((( (1)

As a result of using PWM method to control the inverter; the calculation of the average voltage in one stage from fig.4 for example,in first stage includes two sections Vac and Vab whose share in each one of them in first stage can be written as follows:

[pic]((((((((( (2)

[pic]

In accordance to fig.5 the average voltage at first

stage can be calculated as follows:

(3)

For Z-source to take two equivalent circuit at shoot through condition in fig.6(a) and active condition in fig.6(b) into account the voltage transfer ratio can be calculated like this:

(a)

(b)

Fig.6:Z-source operation.(a) shoot-through condition.(b) active condition

At shoot-through condition:

[pic] (4)

At active condition:

[pic] (5)

To take the time of shoot-through condition with[pic] and the time of active condition with[pic]and by considering that the average voltage of inductor in a period is zero, we will have:

(6)

(7)

(8)

(9)

M:modulation index

On the other hand, as a result of using simple boost control method in inverter section the relation between [pic] and M can be written like this:

(10)

By replacing the (10) in (7) and (9) we will have:

(11)

3. The Proposed System

Fig.8 presents the practical circuit of controlling method of closed loop. Velocity error signal will be imposed to PI controller and from that also to the slip regulator.

The speed error signal will be applied to P1controller and subsequently to the slip adjuster. This way the Wsl reference signal will be adjusted. Synchronous speed will

be obtained through addition of Wsl and Wm. The result could be used to determine the operational frequency of the converter and motor. Moreover, by Wms, we can determine the motor’s needed voltage by the flow control block. Given V is lower than the maximum output voltage of the matrix converter, in the absence of impedance network (Z-Source), modulation coefficient (m) in the block 1 will be applied to adjust the output voltage of converter. Otherwise, since the amplitude of the needed voltage is more than the converter’s maximum generated voltage through the block 1, the block 2 (which is accompanied by impedance network or Z-Source) will be used to obtain the needed voltage amplitude. The structure of Block 1 has been obtained from Equation 11, and Block 2, from Equation (12). Considering Equation 12, due to dependency of D0 on the quantity of m, the equation has been written based on m. Use of the proposed system leads into decrease of voltage stress and losses in converter switchers since it doesn’t use the z-source converter and Shoot-through state at low frequencies.

(12)

As:

Where Vcon is control voltage and Vtri is triangular voltage in Sinusoidal Pulse Wide Modulation, Vd is output voltage of the rectifier part and Vac is the first harmonic range and output voltage of the converter.The process is operated by a selector. In the proposed system (Fig.8), three PI controllers have been used. Each has two variables of P and I and six variables are defined for the system totally. In order to achieve improved quantities for the system, a primary population consisting of 10 particles was defined. Each comprises all six variables. Consequently, a matrix of 10 × 6 is defined. After repetition for three times and according to the target function, which is minimization of the velocity and torque error, the improved quantity of controllers has

5. Particle Swarm Optimization (PSO) Algorithm

Pso is a novel population based optimization method that was introduced by kennedy and eberhart in 1995 for simulating bird flock and fish school .it uses a number of particles that constitute a swarm .that swarm continuously updates the knowledge of given searching space.

Each particle in the swarm involves a position array and a velocity array. the position array is a possible solution to the problem. Let x and v denote a particle coordinates and its corresponding flight velocity in a search space, respectively. The particle update their velocities and positions as:

Fig.8:Proposed system

(14)

(15)

(16)

Where k is current iteration.[pic] and [pic] are two positive factors called acceleration coefficients. [pic] and[pic] are two random number in range of [0,1] with uniform distribution.[pic]is the best previous position of particle and [pic]is the best particle among all the particles.[pic]is inertia weight suitable selection of W provides a balance between global and local explorations.

X is constriction factor to ensure convergence is a function of [pic],[pic] as below:

(17)

Where [pic] and [pic]

Fig.9:Motor starting with no load condition

6. Simulation Results

Simulations have been performed to confirm the theoretical concepts of proposed system, parameters belonging to a squirrel cage induction motor of 5Hp, 460v and 4poles were taken into consideration. for simulation studies on computer used matlab program and switching frequency at rectifier side and inverter side are 20KHZ and 10KHZ,respectively.input voltage for matrix converter is balanced three phase:180V,50HZ

Figure 9 shows velocity, electric torque, and current in induction motor and inductor current of the z-source converter part and load torque in startup condition with PSO-PI controller. In this state, at 3.2 seconds, a load of 3N.m is devised on the shaft of the motor.

[pic]

(a)

[pic]

(b)

[pic]

(c)

[pic]

(d)

[pic]

(e)

Fig.9. Start up condition a) velocity curve b) torque curve c) motor current d) Z-source inductor current e) load torque

Figure (10) indicates line voltage, three-phase current, velocity and electric torque of the motor for change in load torque respectively. In this state, first, load torque is 5 [N.m] to the motor and at t=2 [sec], torque is decreased to 2.5 [N.m] and at t=5.1 [Sec], the torque equals to zero and the only load on the shaft of the motor are friction and inertia. During this process, it is found that motor velocity enjoys minor fluctuations and finally, it remains constant at 50 [rad/sec].

[pic]

[pic]

[pic]

[pic]

[pic]

(e)

Fig.10. System parameter response to load torque changes a) line voltage b) three-phase motor current c) motor velocity d) electromagnetic torque e) load torque.

Figure (10) shows Command signal indicates the velocity, induced to the system. Respective results of changes of motor parameters and converter are shown in figure (11).

[pic]

Fig.10. Command signal induced to the system

Figure 11 shows variation in motor parameter compared to command signal changes.

[pic] (a)

[pic]

(b)

[pic]

(c)

[pic]

(d)

[pic]

(e)

Figure 11: changes in motor parameters and converter, compared to command signal changes in resistive- generator breaking state a) velocity b) torque c) three-phase current of the motor d) output voltage of the converter e) output voltage of Z-source converter.

7. Conclusion

in this paper the results simulation of indirect matrix converter with Z-source was exhibited by matlab/ simulink. In order to study the improvement of characteristics, corresponding results have been compared to PI results. Respective characteristics of z-source converter have been used for increase voltage transfer ratio in the matrix converter. With respect to study of various break methods and in consideration of the results obtained in this regard, it has been revealed that innate characteristic of the converter can be used in order to establish various break states and extra circuits can be discarded accordingly. Moreover, use of the offered system has led to increase and decrease of voltage in the converter by Shoot-through coefficient and that of modulation index for various frequencies of management resulting in decrease of voltage stress and losses in the switches of the converter. Considering number of PI controllers in the system, PSO Algorithm has been used for improvement. Corresponding results have shown that this method enjoys more desirable reactions compared to common PI.

References

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