MB39C811-EVB-02

AN205406 Dead Time Compensation Implementation In MB9Bxxxx/MB9Axxxx Series Associated Part Family: MB9BFXXXX/ MB9AFXXXX Series This application note describes dead-time compensation implementation in- MB9Bxxxx/MB9Axxxx Series and the algorithm implementation of software and test performance. Contents 1 Introduction ............................................................... 1 1.1 Advantages and disadvantages of using a deadtime compensation function ................................ 1 1.2 How to realize type ............................................. 2 2 Dead-time Compensation Principle .......................... 2 2.1 Six phases inverter IPM Structure ....................... 2 2.2 Motor Control Block Overview............................. 3 2.3 Current aberration and compensation implement .......................................................... 5 1 3 Dead-time compensation Implementation ................ 8 3.1 How to detect current polar correctly .................. 8 3.2 Dead-time compensation Software implementation ................................................. 11 4 Dead-time compensation Function Performance ... 20 4.1 Basic Verification .............................................. 20 5 Conclusion.............................................................. 28 6 Document History ................................................... 29 Introduction This application note describes the algorithm implementation of software and test performance. Error voltage vectors caused by dead-time effects of PWM inverter were given, the vector synthesis method was adapted to reduce amplitude and phase formulas of synthesized voltage vector produced by 3-phase stator windings under dead-time effects, the characteristic of synthesize voltage vector was analyzed with simulations. In order to make practical conduct time equal to ideal given time of switching devices, a dead-time compensation method based on time was proposed, simple arithmetic was obtained with the characteristic of space vector PWM (SVPWM). A dead-time compensation method based on voltage was proposed also to eliminate error voltage vector, compensation formulas were calculated in 3-phase and 2-phase static reference frame respectively corresponding to SPWM and SVPWM. Experimental results show that the proposed method can make motor phase current waveform sinusoidal, and improved the output performance of the inverter. 1.1 Advantages and disadvantages of using a dead-time compensation function Advantages One of most important reasons for dead-time compensation and perfect the sinusoidal wave is harmonious wave reduction. Which in turn , Because the six phase inverter IPM of the upper arm and the lower arm don’t allow open together, so we need add the delay time at the upper arm and the lower arm switching that will abstain up and down IGBT short circuit cause the IPM destroyed. But this modifying cause the efficiency vector voltage changed. So we add the dead-time compensation reduce this modify effecting. Moreover, add the dead-time compensation can reduce the noise and vibration that motor torque change caused. www.cypress.com Document No. 002-05406 Rev. *B 1 Dead Time Compensation implementation in MB9Bxxxx/MB9Axxxx Series Disadvantages During the dead-time compensation function, a modification on the sinusoidal-modulation pattern needs to be made in order to allow current to be real current. This pattern modification could generate some current ripple. If you detect the current positive or negative polar is error. Due to modification of patterns and correction of the same modifications, more CPU is used to implement this algorithm. Current sector define as shown bellows: Figure 1. dead-time compensation sector region 1.2 How to realize type One possible solution to this problem is to ignore current polar detect during these zero cross periods. This is not desirable since some algorithms, including the one used in this application note, require information from all three currents polar in order to add the dead-time compensation to cause the current is sinusoidal. Another solution is to base the estimate position to detect the three phase current polar. This could be one good solution, but this type will have some error at the current D-axis don’t be equal to zero. The third solution is to using the assemble current to detect the three phase current polar. Moreover, to add the filters reduce the current wave. This would real detect the three phase current polar. Moreover, we can use the hall sensor to detect the current polar, but this need add the hardware cost. So the third solution is good type. We will focus on this type to describe the algorithm. 2 Dead-time Compensation Principle 2.1 Six phases inverter IPM Structure 2.1.1 Three phases current module The PM synchronous motor is a rotating electric machine with a classic three-phase stator like that of an induction motor; the rotor has surface-mounted permanent magnets. IPM work in order to change DC voltage to sinusoidal wave. But such as upper arm IGBT Sa+ and lower arm IGBT Sa- at switching need add delay time to prevent the IGBT short circuit. So the real voltage will not the need vector if don’t add the dead-time compensation. The IPM and the motor connect and structure as bellow: www.cypress.com Document No. 002-05406 Rev. *B 2 Dead Time Compensation implementation in MB9Bxxxx/MB9Axxxx Series Figure 2. inverter and motor structure 2.2 Motor Control Block Overview This section describes the PMSM FOC control theory with dead-time compensation. Figure 3 below shows the whole block. www.cypress.com Document No. 002-05406 Rev. *B 3 Dead Time Compensation implementation in MB9Bxxxx/MB9Axxxx Series Figure 3. PMSM FOC Block with Dead-time Compensation Modules explanation: 1. When Ua、Ub、Uc change to the voltage vector, the right switching time will change because the delay time work after adding the dead-time . 2. Base the Id and Iq filter value can obtain the current polar, so the dead-time infection can reduce overpass the dead-time compensation. And ia、ib and ic compare with the Ter base on the dead-time compensation table as shown below. Table 1. three phase current positive or negative polar and dead-time compensation The 3-phase currents are converted to a two axis system. This conversion provides the variables iα and iβ from the measured ia and ib and the calculated ic values. iα and iβ are time-varying quadrature current values as viewed from the perspective of the stator. www.cypress.com Document No. 002-05406 Rev. *B 4 Dead Time Compensation implementation in MB9Bxxxx/MB9Axxxx Series 3. The two axis coordinate system is rotated to align with the rotor flux using a transformation angle calculated at the last iteration of the control loop. This conversion provides the Id and Iq variables from iα and iβ. Id and Iq are the quadrature currents transformed to the rotating coordinate system. For steady state conditions, Id and Iq are constant. We need filter the Id and Iq value to obtain the standard value, using the value can calculate the theta of current. 4. Error signals are formed using Id, Iq and reference values for each. The Id reference controls rotor magnetizing flux. The Iq reference controls the torque output of the motor. The error signals are input to PI controllers. The output of the controllers provides Vd and Vq, which is a voltage vector that will be sent to the motor. 5. A new transformation angle is estimated where vα, vβ, iα and iβ are the inputs. The new angle guides the FOC algorithm as to where to place the next voltage vector. 2.3 Current aberration and compensation implement It is nature to insert a switching delay time in sinusoidal pulse width modulation (PWM) voltage fed inverters to prevent a short circuit in the DC link. This causes well known dead-time effects which distorts the output voltage and current. Many compensation schemes are proposed to overcome the drawbacks. Based on the traditional average dead-time compensation techniques, an improved method was proposed to advance the performance of dead-time compensation. The method is based on SVPWM strategy and it can be implemented with software without any extra hardware. Simulation results demonstrate the validity of the proposed method. The current only across maintain current diode at the dead-time moment. At this moment the current will decrease until zero value whatever the current polar. Such as the Sa phase as the below structure, if we set the current is positive that flow from the inverter to motor. Otherwise, the current will define the negative polar. When Sa >0, the current will has two statement, one is normal work statement that upper arm IGBT VT1 will close and the lower arm IGBT VT4 will open, the current flow from the inverter to the motor cross the VT1. The other statement is dead-time moment. The IGBT VT1 and VT4 will shut together, this moment the current will cross maintain current diode VD4 as the same as upper flow. At this condition, the upper IGBT work time will decrease about the dead-time long. So need to add as equal to the decrease time. When Sa